Experimental measurements of charge separation under wet growth conditions

Abstract

In this work we present the results of experimental measurements of the charge transferred to simulated graupel under wet growth conditions. The range of temperature was between −7 and −18 °C. The speeds of collision employed in the measurements were between 8 and 13 m/s with the goal of representing graupel of different initial densities. The aim of this study was to corroborate the existence of charge transfer under wet growth. The results show the presence of positive charge when graupel reaches partial wet growth, and the magnitude of this charge is comparable to the charge transferred under dry growth conditions. On the other hand, when total wet growth is reached no charge transfer is registered. This leads to the conclusion that the non‐inductive mechanism could be working under partial wet growth conditions when the ice crystals collide with the dry regions of the graupel surface and then bounce off.

Charge Separation in Collisions Between Ice Crystals and a Spherical Simulated Graupel of Centimeter Size

“…Recently, Jayaratne and Saunders () found substantial positive CC when ice crystals impacted with a rod of 4 mm in diameter under wet growth conditions. Luque et al () corroborated the results from Jayaratne and Saunders () by working with a spherical simulated graupel of 1 cm in diameter.…”

“…They used two size distributions A (larger droplets) and B (smaller droplets) to make their point and found that larger droplets promote a predominance of negative CC on the target. In the current work, the laboratory setup used to generate the cloud droplets was the same as those used by Ávila and Pereyra () to generate the larger size distribution (Spectrum A), as well as the droplet size distribution subsequently used by Pereyra et al (), Bürgesser et al (), Ávila et al (), Luque et al (), and Luque et al ().…”

Surface temperature distribution on a spherical ice particle growing by accretion in wet growth regime

“…Luque et al . () reported that the ice particle that had grown by accretion under wet growth conditions exhibited transparent and opaque surface areas. Ice transparent regions were located around the stagnation point, while opaque ice areas extended near the equator (Figure ).…”

“…From this, it is possible to think that inhomogeneous surface temperature observed by Jayaratne and Saunders () and by Luque et al . () could disappear if the ice particle is put into rotation. However, List et al .…”

“…In particular, we compare the experimental results provided by Luque et al . () with the numerical results obtained using as environmental conditions for the calculations the same ones reported by the authors mentioned. However, given that these experimental measurements were conducted using a fixed target, a situation not entirely representative of the conditions observed in thunderclouds, the results found here cannot be directly applied to natural thunderstorms.…”