Abstract:
A Numerical Perspective on Storm Electrification
Decades of field and laboratory research have identified ice hydrometeors as the primary drivers of storm electrification, so two main issues for modeling are 1. Microphysics (representation of hydrometeor processes) and 2. Electrification (charge separation). The dependence of charge separation on the precise mix of ice and liquid hydrometeors places high expectations on microphysical schemes to reproduce the (largely unknown) conditions inside storms. Laboratory results show that graupel can gain either negative or positive charge from rebounding ice collisions. Those same results have had significant disagreements with each other, however, and can produce dramatically differenct outcomes when parameterized in models, including a complete reversal of storm polarity. Furthermore, it is uncertain how well laboratory experiments replicate turbulent storm conditions and how important that may be.
So far, no one particular set of model parameters (microphysical and electrical) has been able to reproduce the wide range of observed storm electrical behavior. One the one hand, each laboratory-based charge separation parameterization tends to generate a particular charge structure regardless of storm type. On the other hand, precipitation processes are highly parameterized in bulk models and may not be flexible enough to generate a sufficient range of phase space that exists in real storms. This talk will look at recent modeling results and give an overview of what the models can and cannot currently do for us.
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