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Electric field measurements at Vostok station in Antarctica reveal that the El Niño—Southern Oscillation (ENSO) has a statistically significant effect on the global electric circuit, as earlier predicted by simulations. Analysis of 10 October‐February periods during 2006–2016 indicates that the shape of the diurnal variation of the surface electric field is significantly different for El Niño and La Niña years, with an especially pronounced deviation during the super El Niño of 2015/16. During strong El Niños the potential gradient relative to the diurnal mean is generally higher than usual around 8:00–14:00 UTC and lower than usual around 16:00–0:00 UTC; La Niñas are characterized by the opposite behavior. Simulations with the Weather Research and Forecasting model imply that the observed patterns are the result of changes in the global distribution of electrified clouds over the Pacific Ocean, Maritime Continent, and South America during ENSO events. Plain Language Summary: The El Niño—Southern Oscillation (ENSO) is one of the most remarkable modes of climate variability on Earth. Being made up of irregularly alternating warm (El Niño) and cold (La Niña) phases, the ENSO affects atmospheric circulation, global temperature and rainfall patterns, agriculture, and economic output. Recent simulations have suggested that changes in global convection patterns due to ENSO should also affect surface atmospheric electric fields and currents in remote regions of the planet. Here, we present electric field measurements performed during 2006–2016 at Vostok station in the Antarctic that reveal clear patterns related to ENSO as earlier predicted by simulations. Measurements show that the shape of the diurnal variation of the surface electric field is significantly different for El Niño and La Niña years (with an especially pronounced effect during the super El Niño of 2015/16), which, according to simulations, is the result of changes in the global distribution of electrified clouds over the Pacific Ocean, Maritime Continent, and South America during ENSO events. This provides further evidence of the influence of climate fluctuations on the Earth's global electromagnetic environment. Key Points: Electric field measurements in Antarctica show that strong El Niños and La Niñas consistently impact the atmospheric global circuitFor the super El Niño event of 2015/16, the anomalies in the global electric circuit are especially pronouncedSimulations show that the observed effect is due to changes in deep convection over the Pacific Ocean, Maritime Continent, and South America [ABSTRACT FROM AUTHOR]

The diurnal variation of the global electric circuit (GEC) is simulated using the Weather Research and Forecasting model by estimating contributions of grid columns to the ionospheric potential (IP). A parameterization based on cutting off the grid columns with shallow convection and estimating the area covered by GEC generators (electrified clouds) in each column from the amount of precipitation yields the IP variation of the same shape as the classical Carnegie curve with a correlation coefficient of 0.97, although with a smaller peak‐to‐peak amplitude (18% against 34% of the mean) and maxima and minima shifted by 1–2 hr. It is shown that omission in the IP parameterization of either convective activity or the area covered by electrified clouds (estimated using the calculated precipitation) would result in poor similarity between the modeled IP variation and the classical Carnegie curve. The results of simulation show the best agreement with the Carnegie data during Northern Hemisphere winters; the shape of the simulated diurnal variation of the IP substantially changes throughout the year owing to the decrease of South America's contribution and the increase of Southern Asia's contribution in summer. The discrepancies between the results of modeling and the results of observations are probably caused by the limited ability of large‐scale models to differentiate between electrified and nonelectrified clouds. Further improvement of the parameterization of the IP in models of atmospheric dynamics requires using finer grids, which should allow computing microphysical characteristics of clouds and estimating source currents more accurately. Key Points: Large‐scale models of atmospheric dynamics can reproduce the shape of the global circuit diurnal variation but underestimate its amplitudeIt is important to take into account both convective activity and the area covered by electrified clouds (estimated from precipitation)Simulations better agree with measurements in Northern Hemisphere winters; South America and Southern Asia determine annual variation [ABSTRACT FROM AUTHOR]

Contributions of different land and ocean regions to the diurnal variation of the global electric circuit are simulated using the Weather Research and Forecasting model by estimating the ionospheric potential produced by thunderstorms and electrified shower clouds in each grid column. The model predicts that contributions from land regions have maxima at about 14:00–18:00 local time (LT), whereas contributions from oceans have maxima at about 2:00–6:00 LT, and different ocean regions show nearly the same relative diurnal variation. It is remarkable that contributions from ocean regions with many islands (Maritime Continent and Middle America) have maxima at both 14:00–18:00 and 2:00–6:00 LT. Key Points: Diurnal variation of the global electric circuit is simulated with the WRF model using a new parameterization of the ionospheric potentialModel predicts maximum contributions to the global electric circuit at 14:00–18:00 LT for continents and at 2:00–6:00 LT for oceansContributions from ocean regions with many islands (Maritime Continent and Middle America) have maxima at both 14:00–18:00 and 2:00–6:00 LT [ABSTRACT FROM AUTHOR]

Abstract: The statistical distribution of peak currents in cloud‐to‐ground lightning strokes is analyzed and discussed both in the context of the existing experimental data and from a theoretical viewpoint. The distributions of peak currents directly measured at instrumented towers are compared to those of peak currents reported by the U.S. National Lightning Detection Network and peak currents measured in rocket‐triggered lightning experiments; all those appear to be lognormal. To explain the observed peak current distributions, a simple model based on the large‐scale electric field evolution prior to lightning flashes is developed. Based only on the most general assumptions concerning the probability of occurrence of lightning discharge, it is shown that the distribution of the pre‐first‐stroke large‐scale electric field is close to lognormal in a certain range. With the introduction of structure factors relating the leader or cloud electric potential to this field, semiempirical relationships between the potential and the peak current in negative first and subsequent strokes imply that the peak current and pre‐first‐stroke large‐scale electric field obey distributions of the same type. It is demonstrated that with a suitable choice of parameters, the model‐predicted distributions are close to those obtained from direct measurements, and statistical tests show that their agreement with the data is at least as good as that seen for lognormal approximations. [ABSTRACT FROM AUTHOR]

Theoretical estimation of the influence of large-scale conductivity inhomogeneities on the global electric circuit and, in particular, on the ionospheric potential is considered. A well-posed formulation of this problem is presented, on the basis of which an approximate method is developed so as to take account of large-scale conductivity inhomogeneities. Under certain restrictions imposed on the distributions of the conductivity and the external current density, explicit approximate formulas for the ionospheric potential are derived. The approximation developed is shown to be equivalent to that of classical models of atmospheric electricity in which the atmosphere is divided into two or more columns and is replaced by a simple equivalent electric circuit. The effect of conductivity inhomogeneities located inside and outside thunderclouds is discussed and, in particular, it is demonstrated that taking account of the conductivity reduction inside thunderclouds leads to a substantial increase in the ionospheric potential. The results following from the approximate theory are compared with those obtained from direct numerical simulations. It is found that the suggested approximation qualitatively accounts for the dependence of the ionospheric potential on the parameters of the conductivity distribution, although the relative error may be significant, especially in the case of a substantial reduction in the conductivity inside thunderclouds. [ABSTRACT FROM AUTHOR]