Evolution of Negative Ion Composition near Hydrometeors in a Thundercloud

Abstract

Recently, a new mechanism of the lightning discharge initiation in a thundercloud has been discussed. It is based on a noise-induced kinetic transition, which consists of an increase in the concentration of atmospheric ions in the intracloud environment under the impact of the stochastic electric field of charged and polarized hydrometeors (drops, snowflakes, graupel, hail). The source of noise is electric field bursts that occur during collisions or near collisions of hydrometeors and are accompanied by the streamerless corona discharge ignition. The key point in this scenario is the relay process, in which new ionization centers, when the corona discharge is ignited, arise against the background of spots of negative ion charge remaining from the spreading old centers. This leads to a gradual increase in the concentration of negative ions, which could serve as a source of free electrons with a new increase in the electric field. In this work, we theoretically study the possibility of electron detachment from negative ions formed in a streamerless negative corona near hydrometeors under thundercloud conditions. It is shown that in this case the dominant negative ions near corona hydrometeors are \({\text{O}}_{2}^{ - }{{({{{\text{H}}}_{2}}{\text{O}})}_{k}}\) and \({\text{O}}_{4}^{ - }\) cluster ions. It follows from the calculations that when a high electric field is applied, electrons are released not via direct detachment from cluster ions, but in multi-steps in a sequence reverse to that observed without a field during the formation of cluster ions. As a result, to detach electrons from ions like \({\text{O}}_{2}^{ - }{{({{{\text{H}}}_{2}}{\text{O}})}_{k}}\), fairly moderate pre-breakdown reduced electric fields are required at a level of 65 Td.