COOPERATIVE INSTITUTE FOR MESOSCALE METEOROLOGICAL STUDIES
THE UNIVERSITY OF OKLAHOMA

Annual Report
FY 1997 Progress/FY 1998 Plans

Peter J. Lamb, Director
Randy A. Peppler, Associate Director

INTRODUCTION

The University of Oklahoma (OU) and NOAA established the Cooperative Institute for Mesoscale Meteorological Studies (CIMMS) in 1978. Through mid-1995, CIMMS promoted cooperation and collaboration on problems of mutual interest among research scientists in the NOAA Environmental Research Laboratories (ERL) National Severe Storms Laboratory (NSSL), and faculty, postdoctoral scientists, and students in the School of Meteorology and other academic departments at OU.

The Memorandum of Agreement (MOA) between OU and NOAA that established CIMMS was updated in 1995 to include the National Weather Service (NWS). This expanded the formal OU/NOAA collaboration to the Operational Support Facility (OSF) for the WSR-88D (NEXRAD) Program, the NCEP (National Centers for Environmental Prediction) Storm Prediction Center (SPC), and the NWS Forecast Office, all located on the OU campus in Norman, Oklahoma.

Through CIMMS, OU faculty and NOAA ERL/NWS scientists collaborate on research supported by NOAA programs and laboratories as well as other agencies such as the National Science Foundation (NSF), the U.S. Department of Energy (DOE), the Federal Aviation Administration (FAA), and the National Aeronautics and Space Administration (NASA).

The current 5-year cooperative agreement between OU and NOAA for CIMMS funding took effect on July 1, 1996. Under this agreement, CIMMS concentrates its efforts and resources on the following five principal research themes, the fifth of which is new under the current plan: (1) basic convective and mesoscale research, (2) forecast improvements, (3) climate effects of/controls on mesoscale processes, (4) socioeconomic impacts of mesoscale weather systems and regional-scale climate variations, and (5) Doppler weather radar research and development.

This document describes research progress at CIMMS during fiscal year 1997 (July 1, 1996 through June 30, 1997) and gives research plans for fiscal year 1998 (July 1, 1997 through June 30, 1998).

BASIC CONVECTIVE AND MESOSCALE RESEARCH

Progress - FY 97

• For the last several years, Drs. Don MacGorman and Dave Rust, both of whom are CIMMS Fellows and employees of the National Severe Storms Laboratory, have been writing The Electrical Nature of Storms, a graduate textbook to be published by Oxford University Press. To aid this effort, CIMMS has provided an office and other resources to Dr. MacGorman as its Resident Fellow. Editing the book was completed in early 1997. Proof reading the typeset book began in June 1997 and was completed that summer. Oxford University Press expects to release the book for sale in February 1998.

• In collaboration with scientists from Institute of Atmospheric Optics in Russia, we initiated a study of radiative transfer in an inhomogeneous cloud medium. It combines a 3-D Monte-Carlo model with the CIMMS 3-D Large Eddy Simulation (LES) XMP model. The Monte-Carlo approach allows for the most accurate calculation of the 3-D fields of radiative fluxes, and can be applied to any irregular cloud geometry. It also accounts for spatial inhomogeneity of liquid water, water vapor, and atmospheric gases. The model employs a computationally efficient maximal cross-section method that allows efficient simulations of 60-160 million photons scattering and absorption events on the rather modest power DEC ALPHA 150 MHz workstation. The results from simulations of radiative transfer in solid and broken stratiform clouds showed an important role of cloud vertical inhomogeneity and its implications for radiative parameterization development.

• The effect of cloud inhomogeneity on the two commonly used parameterizations of the cloud optical depth have been studied by contrasting them with the exact definition of optical depth, through the cloud drop distribution function. The results showed that the parameterization which takes into account the vertical stratification of liquid water content and cloud drop effective radius can significantly overestimate the true value of cloud optical depth. Another conclusion from the study is that determination of the value of the cloud drop effective radius averaged in both the horizontal and vertical is much more important than simply accounting for vertical inhomogeneity.

• A drizzle parameterization applicable for cloud-scale LES models has been developed. The cloud parameterization (which constitutes the major part of a Dissertation by an OU Ph.D. student in meteorology) was successfully tested using both field observations and simulations with the CIMMS LES explicit microphysics model. Another Ph.D. Dissertation focused on the aerosol processing by marine boundary layer cloud layers using a model with an aerosol tracking option. The major production experiment has been completed and the analysis of the data is now underway. The results of this research will contribute to the refinement of drizzle parameterizations used in bulk cloud scale models.

• Data from the April 1997 Intensive Observing Period on cloud-aerosol interactions over the ARM site were selected for analysis and preparation for modeling studies. The data include in-situ measurements of cloud microphysical parameters of liquid (April 2) and mixed phase (April 7) stratocumulus clouds, as well as cloud radar reflectivity time series. Analyses have been completed and LES simulations of the experimental cases are underway. The goal of the study will be to extend cloud radar retrieval schemes to mixed phase clouds, as well as to validate cloud radiative transfer parameterizations.

• The objective of an ongoing U.S. Department of Defense/Office of Naval Research ASSERT grant is to provide an opportunity for U.S. citizens to learn about aerosol-cloud-radiation interactions with an emphasis on cloud microphysics, drizzle formation, boundary layer dynamics, and turbulence. A case study will be based on the July 16, 1993, flight during the SOCEX field program. During this case of a well-mixed marine boundary layer with abundant drizzle, two aircraft "stacks" were flown (west of Cape Grim, Tasmania) to make thermodynamic, radiation, wind, microphysical, and aerosol measurements over a two-hour period. The microphysical spectra near the surface, at cloud base, and in-cloud have now been processed. The aircraft data set is supplemented by estimates of back trajectories and mean subsidence, standard synoptic observations, and AVHRR data.

• Balanced and unbalanced dynamics were studied for three-dimensional substructures embedded in balanced nonlinear symmetric circulations. Four types of unstable modes were identified. The Type I mode was characterized by horizontally tilted bands, similar to the tilted primary mode obtained previously by other investigators. The remaining three modes were highly three-dimensional and emerged consecutively as the base-state Richardson number decreased significantly below the critical value. These modes resembled many observed three-dimensional substructures embedded in frontal rainbands.

• Balanced dynamics were also studied relating to cold fronts passing over a three-dimensional mesoscale mountain ridge. A hyperbolic differential equation was derived for the movement of the surface cold front. This equation was shown to be useful for understanding the topographic effects on the evolution of fronts.

• An idealized two-fluid model of density current in constant shear previously used was extended and tested with ARPS (Advanced Regional Prediction System) model simulations. The numerical results agreed closely with the theoretical analyses. The simulated flow features could be described in terms of locally (small-scale) balanced and unbalanced dynamics.

• The classic adjoint theory derived for differentiable systems of equations has been found not applicable to systems with parameterized discontinuities. To overcome this, the classic theory was recently generalized. During this past year, the generalized adjoint formulations were further developed to deal with various complex situations in numerical models.

• A least squares method has been upgraded to include background wind fields from OLAPS (Oklahoma Local Analysis and Prediction System). The upgraded method was applied to single-Doppler data collected by the Twin Lakes, Oklahoma, WSR-88D radar on May 7, 1995, during VORTEX. The retrieved winds were used together with Oklahoma Mesonet surface data to improve the initial conditions for the ARPS model's short-term prediction. Early results have been encouraging.

• To overcome the drawbacks of the conventional Bowen ratio energy balance technique and the profile method, a variational method was developed to compute surface fluxes of sensible and latent heat, using data from the Surface Energy and Radiation Balance Systems (SERBS). This method makes better and more complete use of the data and constraints provided by the surface energy balance equation and the similarity profile equations.

• A comprehensive review of historical observations related to tornadogenesis was completed. This study will allow comparison of new results on tornadogenesis to past ones in terms of their consistency. This work has produced a new conceptual model of tornadogenesis, which, it is believed, is consistent with historical observations and some of the VORTEX data sets. VORTEX data are being used to refute or refine this hypothesis.

• Analyses of VORTEX field data included an intensive study of the June 2, 1995, Dimmitt, Texas, tornadic storm. The focus to date has been on a complete four-dimensional analysis, including airborne Doppler radar from the NOAA P-3 aircraft, the NCAR ELDORA, and the Doppler on Wheels (DOW) radar. Additional data analyzed include those from "Mobile Mesonet" vehicles. Analyses were completed on several time periods prior to tornadogenesis, during the tornado, and the during the tornado dissipation stage. It was found that a mesoscale boundary was fundamentally important in leading to marked low-level changes in supercell mesocyclone strength and tornadogenesis. The character of this boundary, and its role in tornadogenesis, was examined.

• A climatology of supercell spectrum was completed. It was found that anvil-level storm relative flow is the largest identifiable environmental influence on supercell type. This work is being followed by a numerical modeling study using a next-generation cloud model.

• An examination was conducted of all 1992 soundings that had non-zero CAPE. Soundings were classified as supercells producing significant tornadoes, supercells not producing significant tornadoes, or non-supercells. SELS log and lightning strike data were used to identify events.

• A collaborative study of the utility of the tornadic vortex signature (TVS) in very short-term tornado prediction was undertaken. Nearly all TVSs are associated with tornadoes, yet for a variety of reasons, most tornado warnings appear to be based instead on the appearance of a mesocyclone and other features observed by Doppler radar. The premise this work is that a tornado warning based on a TVS can have adequate tornadogenesis lead-time as well as predictive skill. Based on a relatively large sample of tornadoes observed by WSR-88D radars across the country, such utility depends on TVS behavior and also the deleterious effects of radar sampling on TVS representativeness. Thus, this strategy should be appropriate only for a certain percentage of tornado events. Behavior was linked to the way in which the tornado develops -- (1) formation aloft and then gradual descent to the ground, or (2) rapid formation either uniformly over a several kilometer vertical depth or very near the ground. Results to date support earlier findings that both modes of tornado formation/TVS behavior are equally likely.

• In recent years, considerable progress has been made in adapting numerical meteorological models to the input requirements of air-quality models. Despite this progress, however, serious limitations remain. One of the most significant sources of error affecting air-quality studies using meteorological models is the absence of an adequate representation of shallow convective clouds. These clouds are usually of secondary importance meteorologically, but they can be dominant in terms of air chemistry, providing a vehicle for the vertical transport of pollutants and creating an aqueous reaction chamber in an otherwise dry environment. Our research has been directed toward the development and evaluation of a shallow convection parameterization for mesoscale meteorological models, which will greatly enhance the capability of these models to provide a realistic representation of the processes that are important components of atmospheric chemistry, namely turbulence, vertical mixing, and cloud. This has included testing, refinement, and evaluation in 1-D and 3-D model frameworks. Performance evaluation and parameter estimation are based on comparisons with numerous data sources, including several field programs. To allow the broadest possible application, we are also maintaining modularity, portability and computational efficiency. By meeting these goals, we have provided air-quality models with explicit and self-consistent mesoscale meteorological information representing the critical physical processes associated with shallow convection. Thus, we provide the means to enable these models to more realistically simulate the evolution and transport of ozone, particulates, and other pollutants than is currently possible. We anticipate that this development will considerably enhance the overall skill of the air-quality models. Work during this time period focused on providing a mechanism for well-resolved scales in a numerical model to allow for the accumulation and fractional coverage of inactive (i.e., decaying) subgrid-scale clouds. In particular, working with a 1-D (vertical column) version of the Penn State/NCAR mesoscale model (MM5), we formulated equations to allow cloudy air mass from (parameterized) active, buoyancy-driven cumulus clouds to accumulate and undergo realistic decay processes within individual model grid elements. This parameterization of the passive phase of shallow clouds included formation and regeneration as a product of active updrafts, as well as dissipation of both liquid water content and fractional area as a function of lateral mixing, cloud-top-entrainment instability, and microphysical effects. This aspect of the shallow convection process is absent in most existing parameterizations, but decaying clouds can have a significant impact on numerical weather prediction (NWP) because they often cover a fraction of the sky that is an order of magnitude or so larger than the fractional area occupied by active updrafts. Moreover, they are critically important for atmospheric chemistry processes.

• Some climatologies were developed. A climatological data set was developed to examine various climatological distributions of static stability across the U.S. A freezing rain climatology was developed from U.S. surface data obtained from the National Climatic Data Center (NCDC). The various NCDC data formats were combined into a more usable format for this study.

• A close-out of the CIMMS Doppler Weather Radar Level II data archive was completed in March 1997, with all original Level II Exabyte tapes shipped back to the NCDC for permanent archive. Up to that point, archive activities took place at CIMMS. In all, over 18,000 such tapes were archived, and several hundred requests for tape copies were processed.

Plans - FY 98

• Continuing the study of cloud radiative effects, simulations of radiative transfer for different cloud types and conditions will continue. The long-term goal of such work will be the development of an algorithm to account for cloud inhomogeneities in radiative transfer parameterizations.

• Further work on the ASSERT grant (aerosol-cloud-radiation interactions) will involve numerical simulations using the 3-D model with explicit (spectral) formulation of aerosol and cloud drop size-resolving microphysics, as well as observational analysis of data from the Southern Ocean Cloud Experiment (SOCEX). The objective of this work will be to determine the accuracy of the measurement of the mean boundary layer state, which is required to obtain a targeted accuracy in the microphysical measurements.

• A project to simulate the electrification of storms with 3-D numerical cloud models will be undertaken. Parameterizations of electrification processes and lightning have been added to a model developed at OU and studies are underway to test the sensitivities of the parameterizations and to begin electrification studies. Journal papers describing these parameterizations and initial results will be prepared this year. A graduate student in physics is adding these parameterizations to the ARPS regional prediction model for his doctoral research and will incorporate numerical modeling in a study of severe storms that produce positive cloud-to-ground lightning.

• The field program for Mesoscale Electrification and Polarimetric Radar Studies (MEaPRS) is planned for May 15 - June 15 1998. One goal of the program is to provide extensive observations of individual mesoscale convective systems, capable of revealing the distribution of charge and electric fields from the convective line back through the stratiform region. Instrumentation planned for the field program includes electric field sensors, particle charge sensors, and X-ray detectors carried by balloons and microphysical probes, along with a Doppler radar mounted on the NOAA P-3 aircraft, the NSSL polarimetric Doppler radar, and a 3-D lightning mapper from the New Mexico Institute of Mining and Technology.

• Balanced and unbalanced dynamics associated with mesoscale fronts and frontal rainbands continue to be examined. In particular, potential applications of these dynamics in mesoscale data assimilation will be explored.

• Further improvements to the simple adjoint and least squares methods will be attempted for single-Doppler wind retrievals, with the goal of incorporating these improvements into an existing mesoscale data assimilation system. Further development of the generalized adjoint theory will need to be made toward its practical application.

• Additional VORTEX case study work is planned. This work includes a focus on additional tornadic supercells to confirm or refute the findings of the Dimmitt, Texas, case. Also, nontornadic supercells will be analyzed to compare and contrast with tornadic supercells. Work has just begun on the nontornadic supercell that occurred near Elmwood, Oklahoma, on June 8, 1995. Other case studies just underway or planned involve the Friona (tornadic), Allison (tornadic), Shamrock (nontornadic) and Hanston (tornadic) storms observed in May-June 1995.

• During VORTEX, nearly every tornado observed was associated with an echo-weak hole in airborne radar data. A theory has been developed for their existence that involves a lateral drag force/centrifugal force balance. This balance would lead to "accumulation zones" of hydrometeors around a weak echo, or echo-free hole. It can be shown that Doppler divergence estimates contain serious errors near these holes. The observational evidence of this study is being developed.

• The causes of variability in storm-relative helicity (SRH) within VORTEX data sets will be further examined. Initial studies have seen large variability in SRH on all resolved scales in four 0000 UTC analyses that have been done. There is reason to believe that this variability is on the scale of kilometers or at most tens of kilometers. Analysis of the equations governing the generation of horizontal vorticity shows that it is generated through baroclinic effects (horizontal buoyancy gradients), increased/decreased through reorientation and/or horizontal stretching, and dissipated through turbulence effects. In some instances, we can show inconclusive evidence that boundaries cause significant increases in horizontal vorticity and SRH. In the few tornadic supercells investigated to date, tremendous increases in SRH through stretching in the inflow were shown. Climatological analyses have shown clearly that SRH is much higher in soundings associated with significant tornadoes than in other thunderstorm soundings. These analyses have also shown a very high false alarm rate. Based on this, it is hypothesized that on days with significant tornadoes, SRH is higher than normal across large regions in an average sense. However, due to its large natural variability, most storms do not "see" sufficient SRH to become tornadic. It appears that only a few storms that happen onto very local circumstances with SRH greatly enhanced over the high areal mean value eventually become tornadic. Finally, the variability observed in SRH is much larger than depicted in any mesoscale prediction models. Further answers to these topics will be sought over the next year.

• A new-generation cloud model is being developed. As part of this work, a new method for representing Lagrangian cloud processes in an Eulerian model has been developed. Initial tests of the new model suggest that it can simulate the supercell spectrum. Storms have been simulated using composite wind profiles developed during the observational part of this study. The model shows much promise for investigating all aspects of supercells that depend strongly on microphysical processes. Work is ongoing.

• A multi-year climatology of sounding thunderstorm parameters is planned. This work would examine the interannual variability of supercell-associated parameters, and their geographical and interseasonal variations.

• A lightning flash/sounding climatology is also planned. Preliminary work has been done relating total cloud-to-ground flash counts to sounding parameters. This work indicates that a climatology of such a relationship would be useful.

• Plans are being made to continue tornadogenesis field observations during spring 1998 (Sub-VORTEX). The primary goal of this field work is to capture the entire genesis stage in a supercell, from prior to the first appearance of a significant low-level rotation to tornado formation, using dual-DOW radars and Mobile Mesonets.

• The study of the utility of TVSs in very short-term tornado forecasting will be continued. This work will involve additional analyses of archived data sets to increase the sample size and therefore the robustness of the results. There has been some suggestion of a correlation between certain storm types and the mode of TVS behavior. This will be explored further. Finally, we will pursue the best ways of disseminating our results to the operational community. Current plans are to produce training materials that will be available to forecasters via the World Wide Web.

• A demonstration project is planned for the fall 1998 hurricane season using DOW radars to document the nature of severe local wind phenomena that occur in conjunction with hurricane landfall.

• To adapt numerical meteorological models to the input requirements of air-quality models, the 1-D version of the shallow convective scheme has been tested and optimized in a variety of convective environments. The scheme has been incorporated in the fully 3-D version of MM5 model and is fully functional. Testing is currently underway to evaluate its behavior within this framework and its impact on meteorological parameters. A framework for the implementation of the scheme in a coupled meteorological/air chemistry model is already in place. In collaboration with other scientists, evaluation of the new scheme in the fully coupled model will begin in the second half of this fiscal year.

• Analyses of the climatology of static stability have been submitted for publication. Additionally, at least three storm outbreak cases will be identified to examine the evolution of static stability during these events. Since an observational data set of mesoscale variables is not available for most of these cases, they will be modeled with the NCAR/PSU MM4 model. Using the model results and a static stability tendency equation, the stability trends during these events will be examined to determine the important processes that affect these trends.

• Climatologies using rawinsonde data will be created for freezing rain events to develop an understanding of the conditions that are present during these events and the amount of variability associated with these conditions.

FORECAST IMPROVEMENTS

Progress - FY 97

• Improving quantitative precipitation forecasting (QPF) for the 1-2 day forecast period is listed as one of the top priorities of the United States Weather Research Program (USWRP). Achieving this goal depends heavily on providing operational forecasters with better numerical guidance than is currently available. Thus, a considerable amount of effort was applied toward improving operational NWP models, with an emphasis on precipitation parameterizations. During this time period, the U.S. Environmental Modeling Center's (EMC's) operational MesoEta forecast model was ported to NSSL. With assistance from EMC scientists, this model was configured to run on the SGI Power Challenge workstation, marking the first time this model had been run successfully outside of EMC's computing environment. Preliminary testing, which focused on the replacement of the operational convective parameterization scheme (CPS) with the Kain-Fritsch CPS, showed considerable promise for improving numerical QPF.

• A study has been completed that compares maximum ground flash rates with radar-derived characteristics (relative isolation of cells, maximum reflectivity, VIL, and thickness of regions with ³ 30-dBZ at temperatures £ 0°C) of storm cells identified by the real-time Warning Decision Support System (WDSS), developed by the NSSL. It was found that low ground flash rates were produced by many of the cells having almost any combination of radar characteristics. However, the proportion of cells with higher ground flash rates and the maximum ground flash rates produced by cells within a particular category of radar characteristics tended to increase as some radar-derived parameters increased. The strongest relationship was found with the degree of cell isolation. Maximum ground flash rates increased considerably as the storm-cell embedded reflectivity increased and as cells occurred closer together. There also was a fairly strong tendency for a cell’s maximum ground flash rate to increase as the 30-dBZ thickness of the cell increased. Maximum ground flash rates depended less on VIL and maximum reflectivity. Storm cells with large ground flash rates had larger values of 30-dBZ thickness and almost all were either embedded in larger reflectivities or were close to other cells identified by the WDSS algorithms.

• CIMMS scientists in the Mesoscale Applications Group (MAG) at NSSL spent time working with forecasters at the SPC, in an effort to promote mutually beneficial organized interactions and collaborations on scientific problems. From January through March 1997, CIMMS scientists worked with the SPC to develop, refine, and test a new winter weather forecast product. CIMMS scientists also worked side-by-side with SPC forecasters during daily simulated operational forecast shifts and issued experimental forecasts for the occurrence of hazardous winter weather within the 48 contiguous states.

• A detection algorithm for bounded weak echo regions (BWER) was developed. It was tested on five storm cases. The algorithm uses image processing and fuzzy logic techniques to find candidate regions in WSR-88D reflectivity images to classify a region as being a BWER. The algorithm was also tested at two locations as part of NSSL's WDSS.

• A project examining storm longevity prediction using NEXRAD storm cell parameters was undertaken. The FAA needs storm evolution forecasts to aid Air Traffic Control (ATC) decision-making relating to flight departures and arrivals. In 1997 the value of NEXRAD storm characteristics was investigated for storm longevity forecasts. Sixteen characteristics determined by the Storm Cell Identification and Tracking (SCIT) algorithm and the Hail Detection Algorithm (HDA), and storm longevity, were determined using univariate and multiple linear regression analyses. The study included 879 storms (4,990 volume scans) that formed over the Memphis, Tennessee, vicinity on late spring and summer days. The purpose of this study was to determine if any of these relationships were strong enough to warrant the inclusion of one or more storm characteristics in the development of storm longevity forecasts. Both the univariate and multivariate linear regression analyses of all storm characteristics and remaining storm lifetime showed that remaining lifetime discrimination based on these storm characteristics is relatively poor. The storm maximum reflectivity was most strongly related to remaining lifetime, and the combined storm characteristics were slightly more related to remaining lifetime.

• Ensemble forecasting of convective weather events using a mesoscale model was conducted. Numerical simulations of the various ensemble members for two events were created using the NCAR/PSU MM5 (Version 2) model. In preparing for this, significant development work and testing was put into coding the adjoint formulation within the Mesoscale Adjoint Modeling System (MAMS) for various parameters that are used to create the ensemble member initial conditions. While a little more effort in the development of this code is required, most of the pieces needed to create all of the ensemble members were completed. The two cases chosen for study are the June 10-11, 1985, PRE-STORM squall line that has been well documented in the literature, and the May 27-28, 1985, PRE-STORM MCS that was the longest-lived MCS during PRE-STORM. Results from the May MCS case illustrated the very different outcomes one can realize by changing the model physical parameterization schemes. For this event, the MCSs initiated in the High Plains from South Dakota to Colorado and propagated into Iowa, Missouri, Kansas, Nebraska, or Arkansas over the next 36 hours. The various model runs produced three main tracks, and the longevity of the MCS varied from 12 to 30 hours. The simulation that best approximated the observed track and lifetime of the MCS was from the Grell convective scheme using the Blackadar planetary boundary layer (PBL) scheme. However, when the Grell scheme was used with the Burk-Thompson PBL scheme, the simulation was substantially different, with the MCS propagating more slowly and dissipating earlier. Thus, changes in just one model physical parameterization scheme can lead to large differences in the numerical prediction. Similar differences were seen in the June MCS case, even though the large-scale forcing for this event was much stronger than for the May case. Several dominant tracks again were found, with some MCSs moving southeastward across Oklahoma into northeast Texas, while others propagated southward across western Oklahoma into western Texas during the same time period.

• Development and testing work was undertaken for algorithms to determine storm severity based on cloud top temperature, height, and/or growth. Analyses of several supercell thunderstorms supported previous research showing correlations between cloud top temperature characteristics and storm severity. Tested and rejected code from a visiting scientist to NWS/TDL identified cold cloud aspects in infrared imagery. Computer code for tropical mesoscale convective systems was also under development. An algorithm will ultimately be developed that detects and computes trends in temperature and the areal expansion of thunderstorm anvils for the SCAN (System for Convection Analysis and Nowcasting) project, which will be part of AWIPS.

• Significant progress was made on a USWRP project to investigate the utility of satellite, radar, lightning, and other data in determining the onset and demise of mid-latitude mesoscale convective systems. Data sets were collected and analyses of individual sensors were completed. Significant work included use of the latest wind and divergence algorithms from CIMSS at the University of Wisconsin as applied to water vapor data, and the co-analyses of data from adjacent WSR-88D sites to build a larger picture of the evolution of the MCS. This work should be finished early in 1998.

• NSSL staff participated in the SWAMP (SouthWest Area Monsoon Project) during 1997, which included the launching of sondes and the daily analysis of the large-scale weather setting over the southwestern U.S., including the issuance of storm guidance.

• Maintenance and operation of the Oklahoma Mesonetwork continued at the Oklahoma Climatological Survey. Reliable data services included greater than 98% real-time data availability and over 99.9% availability of research-quality archived data. NWS data users during FY1996 included Weather Forecast Offices in Norman, Tulsa, Amarillo, Dodge City, Wichita, and Shreveport, the Storm Prediction Center, and the Arkansas-Red River Basin River Forecast Center in Tulsa. Mesonet data were used frequently in short term nowcasts as evidenced by numerous references to the Mesonet in various "State Forecast Discussions". In addition, case studies using the data served as important training tools on which to improve NWS operations. The data will continue to impact the NWS as it continues its modernization program, especially in the areas of hydrometeorology and radar rainfall calibrations.

• Activities involving the hydrologic modeling group in the aforementioned Mesonet grant concluded during 1997. Activities included providing training sessions to the Tulsa River Forecast Center, setting up hydrologic databases for the Tahlequah basin of the Illinois River, and developing infiltration parameters for the entire Arkansas-Red River Basin. Activities involving the radar/raingauge calibration group included researching the impact of calibrated radar estimates of rainfall on Quantitative Precipitation Forecasts (QPFs), studying the effect those estimates have on the stream-flow hydrograph produced by hydrologic models, writing a tutorial to document the software that supports this hydrometeorological analysis and forecast system, calibrating WSR-88D precipitation data using raingauge observations from the Oklahoma Mesonet, and working to determine the biases of the WSR-88D radar rainfall estimates. Several manuscripts for peer-reviewed journals were submitted.

• The validation of hydrologic models that will be developed for GCIP (GEWEX Continental International Project; GEWEX = Global Energy and Water Cycle Experiment of the World Climate Research Programme) will depend, to a significant degree, on the accuracy of precipitation data, since precipitation is the largest component of the water cycle. Two means of measuring precipitation are raingauges and radar, and both are susceptible to errors in observation. A three-year study was undertaken to assess the accuracy (bias and error variance) of hourly rainfall as estimated by WSR-88D NEXRAD radars. The reference data sets for determining this accuracy are from a network of raingauges in Oklahoma. An important goal of the research is to determine the effect of wind on undercatch for raingauges used in building the reference data set and the effect of sampling error on the validation process. A raingauge testbed was constructed to investigate the undercatch problem. Part of the effort to facilitate this research included establishment of the Environmental Verification and Analysis Center (EVAC), which collaborates closely with GCIP in developing and applying statistical averaging techniques designed to minimize the error arising from incomplete spatial sampling and field inhomogeneities. EVAC has allowed scientists the opportunity to obtain assessments of quality concerning the accuracy of remotely sensed variables and model output. It has also allowed for two-way data exchange to enhance the quality of the GCIP database and access to data by research scientists.

• The OK-FIRST Project (OKlahoma's First-response Information Resource System using Telecommunications) is at its halfway point. It is an initiative by the Oklahoma Climatological Survey to improve access to and the use of weather and environmental information by public safety agencies. More environmental information is generated now than ever before, but public safety agencies such as emergency management, fire, and police have had inadequate telecommunication infrastructures to fully access and exploit such information to make informed environmental-based decisions. Sufficient training on how to use such information has also been lacking. OK-FIRST is supported partially by the U.S. Department of Commerce to provide these services to such agencies, and it has been a collaborative project. A first step in the project included an OCS partnership with Unisys Weather Information Services to allow cost-effective redistribution of WSR-88D data. The State of Oklahoma became involved as an Internet provider through its new "OneNet" system. To date, two training sessions totaling 44 public safety agency participants have been held at OU.

Plans - FY 98

• Building upon the strong working relationship and scientific foundation established between EMC and NSSL scientists during FY 1997, more extensive testing of modified versions of the MesoEta model were to be carried out during the first half of FY98. The MesoEta code was to be optimized and modified to allow it to take of advantage of the parallel-processing capabilities of NSSL's SGI workstation. Furthermore, the interactions between the new convective parameterization and other physical parameterizations within the model were to be studied intensively to identify potential incompatibilities. The modified version of the MesoEta model was run in simulated operational mode at NSSL. During this testing period, the model produced automated daily forecasts in parallel with the operational run at EMC, beginning with the same 03Z initial conditions as the operational run and running for the same forecast period and domain. Precipitation totals for the final 24h period of these parallel runs (i.e., 12Z to 12Z) were compared to each other and to observations in a graphic displayed on the World Wide Web. Common measures of QPF skill compiled for this test period suggested that Kain-Fritsch (KF) runs had marginally better skill in predicting the locations of lighter precipitation amounts, but did not perform as well as the operational runs in predicting the magnitude and location of heavy precipitation amounts. These daily model runs provided a good database for a preliminary evaluation of the KF scheme in the MesoEta model. A number of systematic biases and physically inconsistent interactions between the KF tendencies and other physical parameterizations in the model were identified. Current work, which will continue into the second half of FY98, includes the optimization of these interactions and an evaluation of the performance of the modified code during the upcoming severe weather season.

• During the months of August and September, CIMMS scientists in the MAG were paired with SPC forecasters in order to develop and implement an intensive training program for winter weather forecasting at the SPC. Each pair was assigned a topic related to winter weather forecasting and then tasked with educating their colleagues on this topic and training them on techniques for utilizing the acquired knowledge in the operational forecasting arena. This training procedure involved researching scientific issues and designing formal training procedures, in addition to recruiting external experts to visit and participate in the training program. Currently, plans are underway to conduct a forecast experiment involving SPC, NSSL, and EMC scientists during the spring of 1998. This experiment will evaluate the efficacy of EMC's mesoscale-resolution models to predict the initiation, intensity, propagation, and evolution of deep convection and organized convective systems. This experiment will involve a new version of the mesoscale Eta model and parallel model runs at NSSL using both the operational convective parameterization and the experimental KF scheme.

• Work is focusing on improvements to the algorithm that handles all types of BWERs. The current BWER detection algorithm was found to perform well on small BWERs, but not for broad ones.

• Data sets are being compiled for phase II of the storm longevity prediction project, which focuses on rotating storms. The Mesocyclone Detection Algorithm (MDA) and SCIT are run on numerous NEXRAD level II data sets containing mesocyclones. A number of parameters that indicate whether a storm is a mesocyclone will be examined to determine if that knowledge will help show if the storm will have a longer lifetime than other storms. In addition, storm duration probabilistic forecasts based on storm rotation strength measures will be determined. Output from the SCIT algorithm and the MDA will be combined to determine their relationship to storm longevity. Parameters strongly related to storm longevity will be used in the development of a prototype storm longevity forecast.

• Ensemble forecasting of convective weather using MM5 (Version 2) continues, as production runs with the adjoint-modified initial conditions are slated for later in 1998. This year, we anticipate finishing all model simulations needed to create the ensemble members, likely totaling around 80 simulations (40 for each case). We believe that the results from this work already have very interesting and important implications for operational forecasting of MCSs.

• Improvements in NWP have been hindered by deficiencies in the availability and quality of land cover data. Capabilities to inventory and map land cover conditions and to monitor land surface changes at higher spatial and temporal resolution are needed. To address these issues, a collaborative study was proposed to improve the simulation of surface heat and moisture fluxes in mesoscale NWP models. This proposal focuses upon weather events that are not forecast well by present operational NWP models, such as extreme high and low temperature events, where the incorporation of improved land cover data is likely to have the greatest impact. Four specific objectives were defined: 1) evaluate the ability to improve upon the daily coarse-resolution (1 km) satellite data by blending in very high-resolution satellite data, 2) evaluate the improvements from using a detailed land surface parameterization scheme in mesoscale model simulation by comparing modeled fluxes to the unique flux observations available over Oklahoma, 3) document the improvements in simulating several extreme temperature events that have occurred over the U.S. by comparing mesoscale model simulations with and without the detailed land cover data, and 4) incorporate the improved land surface parameterization scheme into the ARPS model for use in operational NWP efforts. The knowledge gained from this study will provide the information necessary to improve the forecasts of extreme weather events, particularly extreme high and low temperature forecasts, that are a significant economic concern. It is expected that improved forecasts of temperatures would be of great use to insurance companies, electric power utilities, agriculture, and the aviation industry.

• Plans for SCAN have taken on a broader scope beyond that of local storm development. The first phase of this algorithm is now planned to comprise the first satellite algorithm in AWIPS. Initial modification of the tropical MCS algorithm will be used to determine temperature and areal expansion trends for thunderstorm anvils and will be tested in the spring/summer of 1998 in the NWS SCAN at both Ft. Collins, Colorado (NESDIS/CIRA), and Sterling, Virginia (NWSFO). Parallel development will include testing of new algorithms to identify and track individual storm top signatures relevant to storm severity (i.e., warm wake/enhanced-V signatures in infrared imagery).

• OK-FIRST progress has been faster than expected. All feedback from public safety participants and funding agencies has been extremely positive. Work will continue through at least September 30, 1998.

• The NWS has issued requirements for new integrated-remote-sensor applications and training for its new AWIPS workstations. The OSF's Operations Training Branch (OTB) is helping to meet the requirement with Focus on Integrated Remote Sensing Technologies Training (FIRSTT). Work on the development and implementation of radar and satellite remote sensing applications continues. These applications are used to construct distance-learning training modules, which are used to instruct the entire NWS workforce on the new applications.

• The one-year SPaRCE pilot study is being enhanced into a full project. SPaRCE is a cooperative rainfall climatology field project involving high school and college level teachers and students from various Pacific Ocean Island and atoll nations. The goals of the project are both research and education oriented. SPaRCE provides participants with videotaped lectures describing various topics relating to rainfall and climate, instrumentation, and instrument siting. Standard raingauges are distributed to the various sites (two per site). Students are responsible for properly siting the raingauges and maintaining a continuous daily rainfall record at their site. Interactive sessions with the participants follow the distribution of each videotaped lecture using the PEACESAT satellite radio communication system. Efforts are being made to seek funding to include schools from Oklahoma and Hawaii. SPaRCE itself is being incorporated into the EVAC, as EVAC now facilitates the storage, analysis, and data dissemination of the SPaRCE data.

• Work is underway on a project to develop flash flood prediction capabilities using the NSSL WDSS.

CLIMATIC EFFECTS OF/CONTROLS ON MESOSCALE PROCESSES

Progress - FY 97

• Most investigations of relationships between tropical Pacific sea surface temperature anomaly (SSTA) events and regional climate patterns have assumed the teleconnections to be linear, whereby the climate patterns associated with cold SSTA events are considered to be similar in structure and morphology but opposite in sign to those linked to warm SSTA events. In contrast, and motivated by early evidence of nonlinearity in the above regard, this study identified characteristic (i.e., composite) calendar monthly central and eastern North American precipitation patterns separately for warm and cold SSTA events in different regions of the tropical Pacific (central, eastern, west-central "horseshoe", far western) identified through principal component analysis. The precipitation anomaly patterns were computed from an approximately 1°-latitude/longitude set of monthly station data for 1950-92. Their robustness and nonlinearity were established using local, regional, and field statistical tests and a variance analysis. This combination of unique SSTA analyses, the composite selection that followed, and characteristic precipitation anomaly determination from a fine resolution data set increased our understanding of tropical Pacific-North American precipitation teleconnections in several respects. First, significant linkages to the two SSTA modes related to traditional warm and cold events (central and eastern tropical Pacific) were identified for all months except September and October, with all exhibiting some nonlinear characteristics. Conversely, several regions/seasons were confirmed to have essentially linear associations with traditional warm and cold events. However, only nonlinear precipitation teleconnections were associated with SSTAs in tropical Pacific regions largely unrelated to ENSO. The results also demonstrated the sensitivity of central and eastern North American precipitation teleconnections to the location and extent of tropical Pacific SSTAs.

• Land-atmosphere interactions are central to the natural environment, involving and affecting individual weather systems, regional climate, the hydrological cycle, soil and vegetation status, and agricultural production. This importance is manifest in several long-term, international, biological and geophysical programs, including GEWEX. The first major GEWEX activity, GCIP, is focusing on the land-atmosphere interactions of the greater Mississippi River basin during the second half of this decade. A land-atmosphere interaction suite of pervasive environmental importance involves the classical issue of the relative contributions to regional precipitation of locally evapotranspired (i.e., recycled) moisture versus externally advected atmospheric water vapor. Using a new but simple formulation, we obtained the first comprehensive estimation of the intraseasonal and interannual variability of those moisture sources for the growing season precipitation of arguably the World's most productive, largely unirrigated, agricultural region -- the Corn Belt and surrounding areas of the Midwestern United States -- which also occupies ~35% of the GCIP domain. Consistent with its GCIP co-location, this region is considered representative of the mid-latitude, mid-continent, land-atmosphere interactions that are vital for global water resources and hence food production. For four highly contrasting growing seasons, we found the contribution of the locally evapotranspired moisture to this precipitation to be relatively small and remarkably consistent (largely 19-24%) on a monthly and seasonal mean basis, despite large precipitation and crop yield variations, and to decrease markedly (from a 28% to 15% average) with increasing precipitation on a daily basis. Our approach and results yielded considerable physical insight into the complex land-atmosphere interactions involved, including into plant behavior and the apparent paradox between the above monthly/seasonal and daily time-scale results. The moisture budget components and related parameters were evaluated for a large area (about 106 km²) in the Midwestern United States for all 24-hour (12-12 UT) periods during the highly (contrasting) May-August periods of 1975, 1976, 1979, and 1988. Relationships among the budget components were obtained by first stratifying them in different ways, and then by using linear correlation and cross-spectral analysis. The results showed that the calculation of evaporation as a residual of the moisture budget equation yielded values close to the (few) existing observations, especially for periods on the order of one month or longer. The evaporation showed a clear bimodal distribution with respect to precipitation, with high evaporation associated with low and high precipitation amounts, and with a minimum of 3.1 mm/d for a precipitation rate of about 4-5 mm/d. The interannual and intraseasonal variation in precipitation was mostly accounted for by the fluctuations of the moisture flux divergence (and chiefly by its velocity divergence component). An extremely high negative correlation (in the 24-hour moisture budget) was found between the horizontal moisture advection and the time change of precipitable water. A high correlation was also found between rainfall and the vertically integrated vertical moist advection. Rainfall and total precipitable water were also positively correlated. In addition there is a low, but significant positive correlation between precipitation and horizontal advection and a negative correlation between precipitation and the time change of precipitable water. Precipitation was found to be correlated with evaporation on a monthly time scale (but not on shorter time scales) indicating a possible feedback between the two variables on that time scale. Power spectrum analysis of the 12-hour moisture budget components revealed peaks in three major frequency bands, located at 2-4, 5-6, and 8-12 days. Several pairs of budget terms exhibited a high coherence squared with a nearly constant phase difference within a broad frequency band in all four summers. The most outstanding results were that maximum precipitation follows the maximum horizontal convergence term by 15 degrees and the moist advection maximum by 120 degrees. Another finding was that the time change of precipitable water and moist advection have a very high coherence squared, and are in-phase over a wide frequency band. Finally, the maximum in precipitation follows maximum precipitable water by about 20 degrees and the maximum time change of precipitable water by 110 degrees.

• In an ongoing collaborative effort with the Kingdom of Morocco, a project has been underway to increase our understanding of the interannual to decadal variability of Moroccan winter semester (November-April) precipitation, and to use this knowledge to develop a seasonal precipitation prediction capability. This project was motivated by the predominance of extremely poor Moroccan winter precipitation seasons since the late 1970s. During FY 1997, three Experimental Prediction Statements were issued to the Moroccan government for their 1996-97 precipitation season. The primary focus of these Prediction Statements was the likelihood of extreme NAO (North Atlantic Oscillation) values and associated precipitation in the heart of the November-April rainy season. This was made possible by our newly discovered August-November-January NAO variation for years with extreme January values. An historical analog analysis was also done with years that had a similar NAO evolution to the 1996-97 season. The secondary focus of these Prediction Statements was based on our research that found an association of late winter Moroccan precipitation with midwinter tropical Pacific SSTs.

• The goal of the ARM/GCIP measurements of soil moisture and temperature profiles (SWATS) at the ARM Southern Great Plains Site effort is to deploy a rugged, automated, and affordable soil water sensor at the surface flux stations of the ARM Southern Great Plains Site. This was also done in an attempt to meet the soil water data needs of ARM and GCIP investigators. Various factors required that a different approach from traditional efforts within the soil science or hydrologic communities be devised, requiring choosing the best currently available sensor given logistical and fiscal constraints, implementing a plan, and seeing if it worked. The implementation of this network was completed during this fiscal year. Data analysis, including data quality assessment, is underway.

• ARM data are being used to improve empirical estimates of downward longwave radiation using Brutsaert's formulation as the basis. A clearness index was developed and is used to estimate cloud attenuation and monthly profiles of moisture from the ARM Central Facility data collection site.

• A field deployment of radiometers at OU was used to collect, archive, and analyze solar radiation data. The aim of this work was to develop a long time-series of daily albedo values from these data. The study used ARM data to further analyze spatial broadband and narrow band albedos.

• A project to study climate variations and trends associated with tropical variability is underway. Notable milestones have included enhanced documentation of the tropical-wide height mode at numerous geopotential height levels in both the NCEP reanalysis data and the ECHAM4 GCM. The GCM work has enabled documentation of how a small change in SST in the central tropical Pacific Ocean, co-located where observed SST has increased over the past 40 years, generates a height rise through the equatorial zone around the globe with a spatial structure similar to that observed. Moreover, the GCM runs have enabled us to test hypotheses on the generation and maintenance of the height rise.

• A long-term project examining the low-level jet (LLJ) over the ARM site concluded during this period. Thirty days of LLJ activity were examined, using both ARM and NWS observations and model simulations using the NCAR/PSU mesoscale model, and twelve cases were identified for intensive study. Of the twelve cases, six involved strong LLJs and six involved weak LLJs. Results indicated that the model simulations of the strong LLJs were more accurate than those of the weaker LLJs. Yet, importantly, observations indicated that weak LLJs form more often over the southern Great Plains, indicating model simulations of the northward flux of water vapor in low-levels may underpredict the true flux amounts.

• A case of enhanced LLJs owing to the development and evolution of a persistent region of mesoscale convection also was explored. Over a two and half day period, 15 MCSs developed and moved eastward across a moist axis located over the southern Great Plains of the U.S. While the 6-18 hour lifetimes of each of these individual MCSs was not sufficiently long to influence the large-scale environment greatly, it is possible that the cumulative effects of the entire group of MCSs produced significant changes in the large-scale flow patterns. This hypothesis was investigated using output from two runs of a sophisticated mesoscale model. One run included the effects of convection, and the other did not. Results indicated that in low levels, the inflow of warm, moist air into the convective region increased when convection was allowed in the model, enhancing the likelihood that convection will continue and thereby act as a positive feedback mechanism. In upper levels, the convection acted as a Rossby wave source region and produced significant upper-level perturbations that covered at least a 50f-longitude spread. Convective effects also influenced cyclogenesis, as the MCSs strengthened the low-level baroclinicity and modified the phase relationship between pressure and thermal waves in mid levels. Thus, it is clear that the effects of a persistent, mesoscale region of convection on the large-scale environment are substantial.

• A review article on the importance of LLJs to climate was published in the Journal of Climate during July 1996. This work summarizes many studies showing that LLJs occur frequently in many parts of the world. These low-level wind speed maxima are important for both the horizontal and vertical fluxes of temperature and moisture, and have been found to be associated with the development and evolution of deep convection. Since deep convective activity produces a significant amount of upper-level cloudiness and is responsible for a large fraction of the warm season rainfall in the U.S., the relationship between LLJs and deep convection suggests that LLJs are important contributors to regional climate. Results from a number of past studies are reviewed, and the potential for data from the ARM Program to augment our understanding of LLJs is discussed.

• An exploratory study on the ability to simulate nocturnal planetary boundary layers, important to the simulations of LLJs, was undertaken using a simple one-dimensional boundary layer model. Results from both one- and three-dimensional numerical simulations indicated that the nocturnal boundary layer often is too shallow when compared with observations from the ARM Central Facility. Since many complex interactions occur within the nocturnal boundary layer (e.g., gravity waves, drainage flows, mechanically induced turbulence), a procedure to use a statistical mixing approach was developed. In this approach, the amount of mixing that occurs at a given grid point is related to the wind shear in the layer. The greater the wind shear, the more often stronger mixing occurs in the model simulation. This statistical approach replicates the behavior seen in observations of nocturnal boundary layers, and results from 20 cases showed that the depth of the nocturnal boundary layer was better simulated with the statistical intermittent mixing model than with the Blackadar implicit K-theory scheme used in the NCAR/PSU mesoscale model. Initial three-dimensional testing of this approach indicated that while the depth of the nocturnal planetary boundary layer was improved by using the intermittent mixing model, the model simulations of wind speed were slightly less accurate. This suggests refinements in the intermittent mixing approach are needed before further testing is warranted.

• Work was done to combine laboratory intercomparisons/calibrations with field tests of ARM surface meteorological water vapor measurements before and after an intense three-week study of water vapor in September 1996 in northern Oklahoma. Laboratory work was performed in the calibration facility of the Oklahoma Mesonet. This work was instrumental in producing high quality and consistent water vapor measurements during the field study.

• Temperature and relative humidity errors that result from large temperature fluctuations were analyzed. These errors occur because of the filter that is required in the typical probes that measure relative humidity. A new system was designed and used during the September 1996 ARM intensive study of water vapor to remove these errors. In general, these errors are small and are not a large problem. However, if one-minute data are obtained from these probes, then the errors can be significant when air temperature is changing rapidly.

• Research was performed to compare state-of-the-art chilled mirror hygrometers with standard Vaisala relative humidity probes to assess the accuracy of the standard probes and the feasibility of using the chilled mirror sensors for a long period of time in a field situation. It was found that the standard relative humidity probe performed remarkably similar to the chilled mirror standard during a follow-up intensive study of water vapor conducted at the ARM site in September 1997. In fact, it was recommended that the Vaisala probes are sufficient for such purposes, and that the chilled mirrors can be reserved for special field projects. The assessment of the durability of the chilled mirror hygrometers for long-term deployment is still underway.

• Radiosonde calibrations were performed in the Oklahoma Mesonet laboratory and compared to the results provided by the sonde manufacturer (Vaisala). Analysis of results is ongoing. This experiment was designed partly in response to work done at the University of Wisconsin for the ARM Program that involved scaling the radiosonde output to a single humidity measurement on a 60-m tower in order to improve the estimate of the sonde's integrated water vapor. Thus, in order to determine if a single point comparison can increase sonde accuracy, several radiosondes were recalibrated in the laboratory. If the calibration results showed that a significant portion of the error is because of an offset, then comparison of sondes with an accurate moisture measurement prior to sonde launch could lead to improvements in the accuracy of the moisture profiles obtained by the sondes.

• A simple and computationally efficient method that allows a multitude of sensitivity tests for evaluation of the indirect effect of anthropogenic sulfate aerosols was developed. The tests performed focused on the effects of marine stratiform cloud types and amounts, as well as on the seasonality of the indirect forcing. Indirect forcing was found to be -1.1 Wm^-2, with a hemispheric difference of 0.4 Wm^-2. Hemispheric forcing had a strong seasonal cycle, with Northern Hemisphere (NH) forcing exceeding that of the Southern Hemisphere (SH) during the NH spring and summer and the SH forcing prevailing during the SH spring and summer. The contribution to the forcing by different cloud types was also estimated. The estimate of indirect forcing depends on the climatological mean value of transmittance for different cloud types. The transmittance of the clouds, however, may vary widely, resulting in large regional and seasonal variability of the aerosol indirect forcing.

• The bulk cloud parameterization developed for LES models was modified for use in mesoscale NWP models like ARPS and the U.S. Navy mesoscale prediction model COAMPS. A five-moment cloud scale parameterization was designed and tested using both observations from field experiments like ASTEX, as well as simulations with the CIMMS LES explicit microphysics (XMP) model. The five-moment bulk scheme showed excellent agreement with the XMP model. Simulations using various environments showed the significant effect of the ambient aerosol pollution level on the prediction of cloud properties.

Plans - FY 98

• The ongoing collaborative effort with the Kingdom of Morocco will include issuance of three additional Prediction Statements for the 1997-98 precipitation season, using a more refined version of last season's procedure. In addition, research will begin to focus on the origin and predictability of the fraction of Moroccan precipitation variance that is not explained by the NAO. A clearer understanding is needed of eastern North Atlantic low-pressure systems and the spatial/temporal patterns of Moroccan precipitation.

• Future work on a project to validate satellite-based rainfall algorithms over the tropical Pacific includes participation in the 3rd Precipitation Intercomparison Project, which aims to generate areal averaged rainfall estimates over the Pacific Ocean. The signal-to-noise ratio will be utilized as a criterion for incorporation into this data set. Several solar-powered weather stations will be designed for set up on the Woleai atoll in the Micronesia. This work will represent a feasibility study to determine if an atoll makes an adequate platform for open ocean rainfall measurements. Finally, maintenance and quality control of the Comprehensive Pacific Rainfall Data Base (CPRDB) through EVAC will be pursued.

• Research on the diagnostics of climate variations in the extratropical North Atlantic sector will focus on the patterns, causes, and consequences of variations in the NAO, particularly as they characterize the hitherto relatively neglected eastern half of the ocean basin. This work will analyze long-term marine, continental, and satellite data to investigate alternative methods of statistically characterizing the NAO, the variability of the season-to-season progression of this mass oscillation, its relation to the weather systems and rainfall patterns over the eastern North Atlantic and adjacent continental margin (especially the sensitive 30° -50° N zone, which includes Morocco), and the NAO's air-sea interaction involvement on time-scales ranging from interannual to multidecadal. Investigation of the roles of the above NAO variations within the Atlantic climate system will also involve analyses of the results of both previous and new dedicated GCM experiments.

• Diagnosis of West African monsoon variability will focus on the 1951-90 downtrend of monsoon rainfall in the West African Sahel, including some aspects of the interannual variability within that multidecadal trend. The variability of the distinctive West African tropospheric structure (low-level southwesterly monsoon flow, mid-tropospheric easterly wind maximum, upper tropospheric Tropical Easterly Jet) that supports the rain-producing monsoon disturbances will be investigated for the 1951-90 period using unique sets of individual rawinsonde observations, and for other decadal-scale periods using the results of GCM simulations that have already been performed (e.g., Atmospheric Modeling Intercomparison Project runs for 1979-88; decadal 1 x CO2 control runs). These findings will be related to the resulting smaller-scale monsoon disturbance characteristics (as revealed by daily rainfall data for 1951-90), the underlying larger-scale African-Atlantic basin atmospheric-oceanic-land surface conditions (e.g., meridional SST and tropospheric temperature gradients; tropical and extratropical Atlantic atmospheric circulation patterns, including the North Atlantic Oscillation, NAO; African rainfall anomaly patterns; Sahelian vegetation status) and the more global state of the climate system (e.g., tropical Atlantic versus tropical Pacific SST anomaly patterns).

• Diagnostic and predictability studies of precipitation variations in central and eastern North America will continue to focus on three major goals -- the documentation of all aspects of the intraseasonal and interannual variability of the precipitation through the advanced statistical analysis of a fine resolution set of daily precipitation data for 1949-present; the quantification of the relative importance for precipitation amount of a range of tropospheric processes that occur over the study region, especially during growing season months; and the relation of the distribution, timing, and amount of precipitation to larger climate system controls, such as tropical Pacific sea surface temperature anomaly patterns. During the coming year, this effort will begin to "nest" a weather-system-resolving regional model within a global climate model, in an attempt to obtain maximum physical insight into the crucial links in the teleconnection chain.

• Plans for the remainder of the funding period for investigations of climate variations and trends associated with tropical variability include further ECHAM4 GCM model runs, and linking the height mode to Ward's tropical wide precipitation mode and the Asian monsoon.

• Further testing of the drizzle parameterization will continue in the ARPS mesoscale prediction model. A test will be made of the ability of the parameterization to predict evolution of a polluted air mass over the ocean during the course of 12-24 hour simulation. Limitations of the turbulent mixing formulation in the mesoscale NWP models related to the use of a very large ratio of horizontal to vertical grid size will be explored and possible solutions to the problem suggested.

SOCIOECONOMIC IMPACTS OF MESOSCALE WEATHER SYSTEMS AND REGIONAL-SCALE CLIMATE VARIATIONS

Progress - FY 97

• A whole-farm level decision model was used to examine the impact of the type of decisions producers make on the value of seasonal climate forecasts for east central Texas. Results suggested precipitation forecasts directed toward crop mix and applied nitrogen level decisions would have the largest economic value. Further, the results showed that the economic value of climate forecasts could not be obtained by examining only a small set of decision types. Rather, all decision types must be modeled to correctly value seasonal precipitation forecasts. This occurs because, in response to seasonal climate forecasts, changes in one type of decision may override the need to change other decision types. Finally, forecasts of precipitation during the crop tasseling and grain filling stages may be more valuable than precipitation forecasts for earlier crop growth periods.

• Economic decision models incorporating biophysical simulation models were used to examine the impact of the use of Southern Oscillation (SO) information on sorghum production in Texas. Production for 18 sites was aggregated to examine the impact of the use of SO information on the aggregate supply curve and other economic variables. Two information scenarios were examined. The first scenario assumed producers do not use SO information in making their production decisions. This scenario was contrasted to a scenario in which producers use information concerning the SO in making their production decisions. For all expected prices, the use of SO information increased producers' net returns. The expected Texas aggregate sorghum supply curve using SO information shifted both left and right of the "without information" supply curve depending on the price. Changes in nitrogen use based on the SO information were a major factor causing the shift in the supply curves. Further, the use of SO information decreased aggregate expected costs of production. Changes associated with the use of SO information can be summarized as follows -- the use of SO information provides producers a method to use inputs more efficiently. This more efficient use has implications for both the environment and for the agricultural sector.

• Time series models were used to examine the impact of Southern Oscillation (SO) extreme events in estimating and forecasting Texas sorghum and winter wheat yields. Results were both crop and period specific. Including SO events in forecasting yields decreases the forecast mean square error for winter wheat but had no significant impact on sorghum forecasts. Further, it was shown that a significant correlation between SO events and yields does not necessarily translate into better yield forecasts.

• Continuing progress was made on an investigation of the occurrence of freezing temperatures in the southeastern U.S. and their relationship with insurance claims and losses due to pipe bursting, which began in May 1995. The arrival of a proprietary set of insurance claim data in May 1996 initiated the study of claim occurrence in relation to earlier ongoing analyses of the freezing temperature variability in the Southeast. This work initially culminated in a Master’s Thesis by Brian Skinner. It included results of each of the following: 1) analysis of the climatology of freeze occurrence in the southeastern United States -- mean occurrence, standard deviations, linear and parabolic trends in occurrence, and analysis of spatial variability; 2) analysis of the spatial and temporal variability of pipe-bursting-related insurance claims; 3) daily analysis and comparison of two catastrophic pipe-freezing events; 4) derivation of alert indicator temperature thresholds for pipe-freezing for distinct multi-county regions; and 5) application of the indicator temperature thresholds in economic analyses, a study of the climatology of severe-freezing temperatures, and the development of a loss-prediction method based on predicted monthly temperatures. Beginning in May 1997, the above research results were formulated into a set of reports to the Institute for Business and Home Safety (IBHS). New data were received in May 1997, which were added to the existing results, and an ongoing revision process was initiated based on comments from IBHS and insurance-industry representatives.

Plans - FY 98

• During the next year, a significant enhancement of a carefully structured dialogue between the meteorological and the insurance communities will be undertaken in partnership with the IBHS. This dialogue will focus on how the capabilities of modern meteorology can be used to reduce the toll on life and property resulting from severe weather and climate change, and enhance the competitive positions of proactive primary insurance companies. It will explore how the insurance industry can better use weather and climate information in strategic planning, in anticipating and mitigating losses of insured property, and in operational decisions responding to weather-related catastrophes.

• Revisions to the final report on the investigation of freezing temperatures and their relationship with insurance claims and losses due to pipe bursting for IBHS have continued. A near-final version of the finished report was submitted in September 1997, and additional revisions are now being completed based on reviewer comments received in November 1997. Indications are that the completed report will be submitted to IBHS in January or February 1998.

• In cooperation with the IBHS, a "white paper" on the subject of El Niño and its possible effects on the property insurance industry was prepared. The paper addressed long-term relationships with El Niño of occurrence of floods, wildfires, hurricanes, severe weather, and nor'easters. For each weather phenomenon, the known relationships with El Niño were examined, examples of previous insurance losses were listed, confidence levels in the year-to-year occurrence of the El Niño-related anomalies were discussed, and current predictions were outlined. A one-day workshop on the same topic was to held in Washington, D.C., on November 3, 1997, for approximately 80 top executives from various components of the insurance industry. Presentations were scheduled to be made by Dr. Peter J. Lamb (CIMMS), Dr. Michael B. Richman (University of Oklahoma), Dr. Thomas R. Karl (NCDC), Dr. James D. Laver (CPC), and Dr. Roger S. Pulwarty (CIRES).

• The long-term competitiveness of United States agriculture centers on its adoption of technological advances. Recent developments in the science of meteorology are providing the means to more accurately predict seasonal climatic conditions. Improved forecasts will alter producers' selection of inputs and expectations of output price. Such changes would affect cropping patterns and the use of production inputs that subsequently alter regional and national supply curves. These changes will impact the competitiveness of the United States in international markets. Currently, Australia has improved seasonal climate forecasts that are being made available to the private sector decision-makers. To our knowledge, no study has focused on how these improved climate forecasts affect international competitiveness. The main objective of this proposed study is to address this void by evaluating the role of enhanced climate forecasting ability on international competitiveness in the world grain market. This work is being performed in collaboration with agricultural economists at Texas A & M University.

DOPPLER WEATHER RADAR RESEARCH AND DEVELOPMENT

Progress - FY 97

• NSSL was tasked by the NWS to perform the software development for "re-hosting" the WSR-88D Radar Product Generator (RPG) to an open systems environment. The NWS and ERL signed a Memorandum of Understanding in August 1995 for undertaking this task. Work began shortly thereafter, which included gaining an understanding of the current RPG, initiating the design and development of the Open Systems RPG (ORPG) software infrastructure, determining the best techniques and developing the support software to port the legacy RPG algorithms and product generators to the ORPG environment, and the development of a new Graphical User Interface (GUI) Unit Control Position (UCP). This work continues.

• Under the heading of OSF/OTB radar technology transfer project, CIMMS scientists at OSF worked to determine the appropriate WSR-88D Z-R relationship to use from environmental soundings. Using the thermodynamic information contained within GOES satellite sounder data, the atmosphere around a WSR-88D site was quantified. From this information, a more representative Z-R relationship can be used to produce accurate Quantitative Precipitation Estimates (QPE). A technique was also developed to combine profiler and WSR-88D wind data with GOES satellite sounder thermodynamic data. The final products of this technique are measurements of elevated moisture convergence and advection. Tests are underway to determine whether these products help forecast convective initiation and growth/decay.

• A web-based archive calendar of severe weather reports and forecast parameters was developed at OSF/OTB. Following the May 27, 1997, Jarrell, TX, tornado event, a WSR-88D performance review was authored for the NWS Disaster Survey Team. From this review grew an algorithm improvement study involving the combination of radar and satellite data to analyze updraft evolution in this unique tornado event.

• Software was developed at OSF/OTB to provide access to the raw radar data that will be available on AWIPS. This software development represents the infrastructure needed for the manipulation and testing of completely new radar products designed to solve specific field problems. A project also was initiated to move the data from the NWS PUP (Principle User Processor) to the UNIX environment.

• The Multiple Pulse Repetition Frequency Dealiasing Algorithm (MPDA) project involves the mitigation of range and velocity ambiguities inherent in the collection of Doppler radar velocity data. MPDA is a scanning strategy and processing package that collects and merges data at different Nyquist velocities. This is done to create a better representation of the final velocity field than is possible by collecting data at only a single Nyquist velocity. During spring 1997, NSSL successfully tested the package in real-time at the Norman WFO. Fault mitigation continued through the remainder of 1997, and the final code will be delivered to the OSF in the first part of 1998.

• One drawback of the current WSR-88D system is that all algorithm processing is done after the completion of each volume scan. Thus, vital algorithm information such as circulation position updates or detections that may exist at the lower radar elevation angles are not available until after the radar finishes scanning through the higher elevation angles. The lag time encountered can be several minutes. During this fiscal year, NSSL began enhancing existing algorithms to add the capability of making available processed WSR-88D information as it is collected. This is known as "rapid update" software. A given display system can be configured to use this information to alert forecasters to rapidly changing weather conditions.

• Work has been completed documenting how hail and cell detection algorithms in the WSR-88D perform over Arizona. Suggestions have been developed on how these algorithms might be improved.

• During 1997, the Severe Weather Warning Applications and Technology Transfer (SWAT) Team at NSSL continued its primary mission of developing severe weather applications, primarily for the WSR-88D, and transferring technology and knowledge to the NWS and FAA. The team is comprised of two sub-teams - one devoted to the development of tornado warning applications and the other to severe storm warning applications. The SWAT Team's Severe Storms Analysis Package (SSAP) includes the following meteorological algorithms that have been tested off-line and in real-time at WFOs: tornado warning applications (Mesoscale Detection Algorithm - MDA; Tornado Detection Algorithm - TDA; Vortex Detection and Diagnosis Algorithm - VDDA); severe storm warning applications (Storm Cell Identification and Tracking - SCIT - algorithm; Hail Detection Algorithm - HDA; Damaging Downburst Prediction and Detection Algorithm - DDPDA); and applications related to both sets of applications (Near-Storm Environmental - NSE - algorithm). Accomplishments related to each algorithm include:
  • Mesoscale Detection Algorithm (MDA): The MDA allows for the detection of storm-scale vortices of various sizes and strengths and classifies them into a number of different vortex types. Each vortex is also diagnosed using a Neural Network (NN) to determine the probability of tornadoes or severe weather associated with each detection. Testing was done on an expanding database consisting of a variety of tornadic and non-tornadic supercell cases. Enhancements included addition of several diagnostic parameters such as line-integrated divergence and rotation. The MDA has also been amended to include rapid update of mesocyclone location after the first low-altitude radar elevation. Statistics from the output of the MDA/NN were used to determine whether new NWS tornado warning guidance was needed for the 1998 severe weather season (this decision was delayed until 1999).
  • Tornado Detection Algorithm (TDA): The TDA underwent extensive WSR-88D implementation during 1997 and has been recoded to comply with current WSR-88D computing architecture. New techniques added to the TDA this year included the computation of azimuthal and radial shear using a linear least-squares method. The TDA has been amended to include a rapid update of TVS locations after the first low-altitude elevation. This algorithm continues to be used by WFOs and continues to be favored over the current WSR-88D TVS algorithm.
  • Vortex Detection and Diagnosis Algorithm (VDDA): The VDDA represents a merging of the MDA and TDA into a single algorithm, with some new techniques added. This combined algorithm was needed for several reasons. First, from the analysis of many past supercell cases, it was discovered that there are a variety of storm-scale vortices that can be tornadic in supercells, and they range in size from TVS-like to mesocyclones. Second, it is important to share the analysis techniques of the MDA and TDA, such as the vertical and time association techniques. Also, the integration of data from other radar-based algorithms and other sensors will provide a more thorough analysis of the vortices. A new technique that will be featured in the VDDA is an integrated method for diagnosing rotation and divergence within detected vortices.
  • Neural Networking (NN): Two NNs have been developed to examine circulations detected by the MDA, two have been developed to examine circulations detected by the TDA, and two more have been developed to diagnose circulations detected by both. These provide posterior probabilities for the respective phenomena.
  • Tornado Warning Guidance: Scientists at NSSL and OSF worked together in 1997 to generate new, supplemental tornado warning guidance for the NWS based on the latest ideas about and understanding of tornado prediction. Tornado probability diagrams based on numerous radar-based parameters were generated. Work on these statistical analyses continues and should be ready for the 1999 convective season in the form of a warning guidance document.
  • Storm Cell Identification and Tracking (SCIT): The SCIT algorithm has been amended to include a rapid update of storm cell locations after the first low-altitude elevation. Storm cell detections from the previous volume scan are associated with two-dimensional detections from the lowest elevation in the current volume scan, and the position of the old detection is updated.
  • Hail Detection Algorithm (HDA): The HDA was analyzed this year in response to the perception of users that the algorithm was over-warning in summertime storm situations. A total of 78 storm days (hail and non-hail) from locations in Florida, Texas, Virginia, and Illinois were analyzed to determine the bias. The analysis concluded that the over-warning perception could be improved by altering the Probability of Severe Hail (POSH) parameter.
  • Damaging Downburst Prediction and Detection Algorithm (DDPDA): This algorithm is under development to provide the capability to both predict and detect damaging wind events using Doppler radar reflectivity and velocity data. The DDPDA will scan through radar data to locate downburst precursors - events detectable in the middle and upper levels of a storm that may precede the onset of strong winds at the surface. Early versions of the algorithm have focused mostly on predicting damaging wind events from short-lived "pulse" thunderstorms. A prediction equation was developed by analyzing approximately 50 convective cells that produced outflows of varying strengths.
  • Near-Storm Environment (NSE) Algorithm: The goal of the NSE algorithm is to provide the NSSL WSR-88D algorithms input concerning the environment of each storm cell, such as shear and stability parameters. NSE currently uses output from the Rapid Update Cycle (RUC) model to help determine the environment of storm cells. The capability for incorporating surface observations has been recently added.
  • Multiple-Radar Algorithm Comparison Study: A study was conducted to determine the amount of variation in severe storm detection algorithm output that occurs when a storm is viewed simultaneously by more than one WSR-88D radar. This work was part of an initial effort to expand the WDSS to integrate information from multiple WSR-88Ds. Two storms were analyzed. Primary conclusions indicated that large differences were found between algorithm output from the two radars. Also, for ranges less than 130 km, storm-top divergence observations were sensitive to the Volume Coverage Pattern (VCP) being used and can be highly degraded when the radar is scanning in VCP21. In supercells, velocity dealiasing errors occurred more frequently in VCP11 than in VCP21, thus producing more errors in the output of velocity-based algorithms. Finally, integration of the algorithm output from multiple WSR-88Ds into the WDSS will require accurate "error filtering" to avoid propagating incorrect guidance information.
  • WSR-88D Database: The SWAT Team continued to acquire WSR-88D base data (Level II) for development and testing of the above SSAP algorithms. Currently, NSSL has Level II data associated with over 1,500 tornadoes, as well as tens of thousands of severe weather reports.
  • Verification Project: NSSL has initiated a data collection effort aimed at severe thunderstorm ground-truthing. This project emphasizes quality over quantity for the observations it is trying to collect. While Storm Data provides a large, nationwide set of ground-truth data, many instances remain when NSSL needs more detailed and precise information. The Verification Project sets out