Global Electric Circuit: Thunderstorm and Electrified Shower Cloud Areas from Lightning and Precipitation

Abstract:

The Carnegie curve describes the diurnal variation of the global electrical circuit, showing that the fair-weather vertical electric field, when averaged over multiple days, has maxima at thunderstorm peak occurrence times in three main regions: Americas, Africa, and Maritime Continent. To quantify the contribution of storm systems to the global circuit, we develop a method that combines lightning and precipitation data to estimate global cloud area of thunderstorms and/or electrified showers every 30 minutes. The cloud area, as defined in this study, is calculated from 0.5° x 0.5° cells that present either lightning rates, precipitation rates, or both above previously tested thresholds. We compare these cloud areas with two fair-weather vertical dc electric field datasets: Vostok, Antarctica (78° S, 107° E) 5-12 Feb. 2015, and Barrow, Alaska (71°N, 156°W) 1-5 Oct. Lightning data are from the World Wide Lightning Location Network (WWLLN), and the precipitation data product is the Integrated Multi-satellitE Retrievals for GPM (IMERG) version v06. We find a high Pearson correlation (r > 0.94) between cloud areas and the two electric field datasets when data are day-averaged over multiple days. Cloud areas and electric fields for individual days, when not day-averaged, have correlation coefficients ranging from r=0.753 to r=0.942 and do not always have trends consistent with the Carnegie curve. Importantly, our results are similar for the Vostok and Barrow electric field datasets, which indicates that our method is neither dependent on electric field measurement location, nor season/year. We have also developed an interactive prototype that generates 3D maps. This tool provides a global view of cloud area, lightning, and precipitation, along with electric field time series data, to identify global circuit variations on time scales of hours to days. The prototype has a public, online version with real-time visualizations that is also useful for weather and climate studies. We plan to use our technique with electric field datasets from additional days and locations, and a multiday time series of fair-weather vertical current density measurements in the stratosphere from a 2021 balloon campaign.