In-Situ observation of energetic electron fluxes inside thunderclouds using Balloon-borne instruments

Abstract:

In this presentation we will report on our first observations of energetic electron flux from inside thunderclouds. Energetic electrons can produce high-energy radiation. High-energy radiation is routinely produced by thunderclouds and lightning. This radiation is in the form of x-rays and gamma-rays with timescales ranging from sub-microsecond (x-rays associated with lightning leaders), to sub-millisecond (Terrestrial Gamma ray Flashes), to minute long glows (Gamma-ray Glows from thunderclouds seen on the ground and in or near the cloud by aircrafts and balloons). It is generally accepted that these emissions originate from bremsstrahlung interactions of relativistic runaway electrons with air, which can be accelerated in the thundercloud/lightning electric fields and gain up to multi-MeV energies. However, the exact physical details of the mechanism that produces these runaway electrons are still unknown.

Our balloon-borne campaign at Florida Tech is intended to directly measure the flux of energetic electrons inside thunderclouds. Each balloon carries two Geiger counters to record the energetic particles. Geiger counters are well suited for directly measuring energetic electrons and positrons and have the advantage of being lightweight and dependable. Data from our payloads are saved onboard and also get transmitted in real time to our ground station at a transmission rate of 115.2 kb/s. This would provide us a high resolution radiation profile over a relatively large distance.

This work was supported in part by the NASA grant NNX12A002H and by DARPA grant HR0011-1-10-1-0061.