Damaging Downburst Prediction and Detection Algorithm (DDPDA)

Algorithm Components

Radial Velocity Data Processing

Convergence and rotation are calculated for each cell component by the following method (Elmore et al 1994?):

Radial velocity data are passed through a median filter
Calculation of convergence and rotation values by least-squares method
Area around each SCIT 2D feature is searched for:

Maximum convergence (divergence)
Maximum convergent (divergent) velocity difference (original method)

Note: delta-V calculations are required to meet a minimum shear threshold

Area of convergence (divergence) meeting some theshold
Other possibilities:

Median of shear values in 2D SCIT component area
Mode of shear values in 2D SCIT component area
Average of top 5% of shear values in 2D SCIT component area

For each complete SCIT-identified cell, the following are calculated:

Maximum convergent velocity difference from 2-8 km AGL
Maximum convergence from 2-8 km AGL

Known problems:

Not enough testing yet to determine usefulness of conv/div calculations and which are the best parameters to use
Area around SCIT components should be based on the cell boundaries (presently it is an arbitrary 5 km by 5 km box)
Some bugs need to be shaken out of new code

Recent fixes:

The problem of large convergent (divergent) areas being attached to only one cell (perhaps the wrong cell) has been addressed
Convergence calculations are now made for every tilt of every detected cell, regardless of strength

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