Effects of Eccentricity and Horizontal Electric Field on the Characteristics and Outcomes of Binary Collisions of Water Drops.

Effects of eccentricity and horizontal electric field (EH) on the binary‐collision outcomes of water drops are examined using numerically calculated collision characteristics from previous studies and results of simulation experiment conducted by the authors. For a fixed collision kinetic energy (CKE), filament breakups can occur at all values of eccentricity but events of coalescence decrease, and that of sheet breakup increase with increasing eccentricity in absence of EH. However, as EH increases to ∼300 kVm−1 it opposes the variability of the coalescence and sheet breakup events with eccentricity. When EH exceeds ∼300 kVm−1 the collision outcomes might be determined only by the CKE and EH. The calculated value of coalescence efficiency and total number of fragments after a binary collision decreases with an increase in EH. It is argued that an electric field can significantly modify drop size distribution in thunderclouds and needs to be considered for development of precipitation. Plain Language Summary: Growth of water drops in clouds is mostly governed by the drop size distribution in them. When two drops collide with each other, they can either coalesce to form a single larger drop, or disintegrate into many smaller drops, or bounce back. These different outcomes after their collisions are mostly determined by whether the collisions are centric where the eccentricity of the collision is zero or grazing where the eccentricity is one or somewhere in between the two extremes. The present study shows that if the collisions occur in presence of a horizontal electric field, it opposes the effect of eccentricity on the outcomes of the collisions. In this study, simultaneous effects of eccentricity and horizontal electric field are examined from numerically calculated collision characteristics from previous studies and utilizing the results of a simulation experiment recently conducted by the authors. Simultaneous effects of eccentricity and electric field on coalescence efficiency and total and spectral size distribution of fragments generated after the collision have also been evaluated. The results suggest that the electric field can significantly modify drop size distribution in thunderclouds and need to be considered for the development of precipitation. Key Points: Horizontal electric field opposes the variability of coalescence/sheet breakup of water drops with eccentricity in binary collisionsNumber of fragments close to small (large) parent drop size decreases (increases) after collisions in the higher horizontal electric fieldBinary collisions in horizontal electric fields can substantially modify drop size distribution in thunderclouds [ABSTRACT FROM AUTHOR]