Charge Separation in Severe Storm Conditions

PEREYRA, RODOLFO GUILLERMO; BÜRGESSER, RODRIGO EXEQUIEL; AVILA, ELDO EDGARDO

Trieste

Conferencia; 4Th Eropean Conference on Severe Storms; 2007

Researchers often classify thunderstorms in three categories: stratiform and winter storm, ordinary thunderstorm, and severe storms or super hailstorm, distinguished on the basis of lightning flash rate, updraft speed, liquid water content (LWC), predominant electrical polarity of the cloud, etc. Stratiform and winter storm are shallow with low updrafts, low LWC, and, in general, with conditions for slow particle growth. Ordinary thunderstorms have a more important vertical development with higherLWCs and updrafts leading to the formation of graupel pellets. The severe storms have large LWCs and updraft speed which can produce big hailstones and have tendency to produce copious +CG lightning. Laboratory studies have shown that the magnitude and sign of the charge transfer to riming graupel particles during interactions with ice crystals depend on the cloud temperature, liquid water concentration, cloud droplet size distribution, ice crystal size and impact velocity [Reynoldset al., 1957; Takahashi 1978, Jayaratne et al., 1983; Saunders et al., 1991; Pereyra et al., 2000; Avila and Pereyra, 2000; Bürgesser et al., 2006]. Measurements of charge transfer in ice-ice collisions at high liquid water content are complex due to the difficulty of dissipating thelarge amount of latent heat released during the vapour condensation.