Meteorological Parameters of Thunderstorm Ground Enhancements
<p>Thunderstorm&#160;ground enhancements (TGEs) are events of energetic particle flux increases, discovered and observed at&#160;the&#160;Aragats Research Station (Armenia). Energetic particles are accelerated and multiplied in the electric field of clouds, and may be registered by ground-based detectors. Analysis of the structure of thunderclouds producing TGEs is crucial for clarifying the&#160;mechanism of particle acceleration.</p><p>In the present study the hydrometeor dynamics are analysed on the basis of&#160;the state of&#160;the&#160;atmosphere modeling&#160;by means of&#160;Weather Research and Forecasting Model.&#160;Meteorological characteristics typical of TGE occurrence in the mountainous region of Aragats are discovered. A&#160;technique has been developed for estimation of the charge distribution in a cloud on the basis of&#160;comparison of the simulations and experimental data. The retrieved cloud electrical structure is used to estimate the dependence of the electrification process on the temperature and liquid water content.</p><p>An unusually low concentration of ice particles leads to&#160;the great importance of snow particles in&#160;the process of charge separation. A typical charge distribution in a TGE-producing cloud is found to be well approximated by a two-layered charge structure with a lower positive charge region formed by graupel particles and an upper negative region formed by snow particles. Characteristic charge density is 0.01 C/km^3 for graupel cluster and 0.02 C/km^3 for snow cluster. A vertical distance of about 1-2 km between the lower positive and upper negative layers is sufficient for the development of an energetic particle avalanche.</p><p>The obtained estimation of the hydrometeor content and the electrical structure of a TGE-producing cloud provides new evidence on particle acceleration mechanisms in the atmosphere and processes of charge distribution in mountainous conditions.</p>