Avila and Pereyra 2000 Review Adam W Clayton

Avila and Pereyra 2000 Review Adam W. Clayton 26 March 2019 Adam W. Clayton 3/26/19

Overview • Numerous studies have found sign of charge on graupel depends on: • Effective Liquid Water Content • Temperature • Jayarante and Saunders [1985], Avila [1998, 1999], and Pereyra [2000] found the sign of graupel charge depends also on drop size distribution • This study focuses on a narrow DSD and a broad DSD and its effects on the charge of graupel • Utilizes experiment and results from Pereyra [2000] Adam W. Clayton 3/26/19

Pereyra [2000] Experiment • Adam W. Clayton 3/26/19

Drop Size Distribution 190 mm nozzle • 15 mm nozzle Adam W. Clayton 3/26/19

Graupel Charge Sign depends on drop size • Gray – positive charge Black – negative charge Adam W. Clayton 3/26/19

Takahashi 1978 Adam W. Clayton 3/26/19

Saunders 1991 Adam W. Clayton 3/26/19

Saunders and Peck 1998 - Convert RAR to EW Typical graupel fall speed 4 -8 m/s Below 1 g m-3 Cumulonimbus: 1 -4 g m-3 0. 67 g m-3 Adam W. Clayton 3/26/19

Discussion: Charge Structure Normal Tripole Thunderstorm Anomalous Thunderstorm • Low LCLs • High LCLs • Large Warm Cloud Depth • Small Warm Cloud Depth • Collision-Coalescences robs mixed phase of supercooled liquid water • Collision-Coalescence not efficient • C-C also promotes larger drops • More supercooled liquid water in the mixed phase region • Graupel more likely to charge negatively • Drops are smaller • Graupel more likely to charge positively Adam W. Clayton 3/26/19