ALBERT

Description: Despite considerable efforts aimed at studying X-ray and gamma radiation arising from lightning discharges, the detailed characteristics, generation conditions, and mechanisms of such radiation remain poorly understood. This problem continues to be one of the most pressing problems in lightning physics and its applications. It is directly related to the study of various processes that determine the dynamics of electrical discharges in the Earth's atmosphere and their effects, including the processes of initiation and development of streamers and leaders. The use of satellite monitoring of high-energy emissions during thunderstorms provides a general picture of the prevalence of this phenomenon, however, to elucidate the mechanisms of their generation, it is necessary to use other methods, such as laboratory and numerical simulation of electric discharges. The joint use of various methods for observing and modeling high-energy radiation associated with thunderstorm activity seems to be one of the most promising areas of modern geophysics.

Description: The ionospheric potential (IP), being the sum of contributions from thunderstorms and electrified shower clouds all over the globe, is arguably the most fundamental characteristic of the direct current global electric circuit (GEC) intensity. The IP variation on different timescales reflects global changes in the distribution of electrified clouds, which, in turn, are closely associated with the dynamics of deep convection. This motivates the search for patterns in the GEC variation which would reflect various modes of climate variability (especially those affecting the tropics, where convection is strongest).Here we report our recent findings in this direction, focusing on two important modes of climate variability which affect tropical convection, namely the El Niño—Southern Oscillation (ENSO) and Madden–Julian Oscillation (MJO). Using the results of long-term IP simulations involving the Weather Research and Forecasting model (WRF) and the results of long-term surface potential gradient (PG) measurements at the Vostok station in Antarctica, we compare the data for El Niño and La Niña years and for the eight traditionally distinguished phases of the MJO. This reveals clear and statistically significant effects of both the ENSO and MJO on the main parameters of the GEC.Our findings agree with other observations published in the literature, but simulations also allowed us to identify the mechanisms behind the observed effects, clearly demonstrating how changes in global convection patterns eventually result in the patterns observed in the simulated IP and in the PG measured in Antarctica and other locations.

Description: Based on the analysis of the average characteristics of the radio emission of a thundercloud, namely, the rms value (intensity) and the kurtosis coefficient, calculated over short time intervals (100 microseconds), specific events were detected, probably corresponding to cloud-to-ground lightning discharges. These events begin suddenly with a series of fairly rare submicrosecond bipolar pulses of large amplitude, which manifests itself in a moderate intensity level and high values of the kurtosis coefficient. This stage of the event can last from a few to several hundred milliseconds and can be called the preparatory stage of a lightning discharge. The next stage is characterized by a successive decrease in the kurtosis coefficient with a slight change in both the amplitude and intensity of the radiation, and a decrease in the level of intensity fluctuations and the kurtosis coefficient, which indicates an increase in the frequency and a decrease in the amplitude of the pulses, as well as the possible appearance of a noticeable quasi-continuous (noise) component in the lightning radiation clouds. This stage may be associated with the development of a stepped lightning leader. Finally, the event ends with a sharp peak in intensity and a drop in the kurtosis coefficient to the background level, which corresponds to a return lightning strike. Observation of the short-wavelength radio emission of a thundercloud can make it possible to predict the time of a lightning strike (in a few tens of milliseconds), and, in combination with interferometry, its location.