Abstract
The Global atmospheric Electric Circuit (GEC) is a fundamental coupling network of the climate system connecting electrically disturbed weather regions with fair weather regions across the planet. The GEC sustains the fair weather electric field (or potential gradient, PG) which is present globally and can be measured routinely at the surface using durable instrumentation such as modern electric field mills, which are now widely deployed internationally. In contrast to lightning or magnetic fields, fair weather PG cannot be measured remotely. Despite the existence of many PG datasets (both contemporary and historical), few attempts have been made to coordinate and integrate these fragmented surface measurements within a global framework. Such a synthesis is important in order to fully study major influences on the GEC such as climate variations and space weather effects, as well as more local atmospheric electrical processes such as cloud electrification, lightning initiation, and dust and aerosol charging.The GloCAEM (Global Coordination of Atmospheric Electricity Measurements) project has brought together experts in atmospheric electricity to make the first steps towards an effective global network for atmospheric electricity monitoring, which will provide data in near real time. Data from all sites are available in identically-formatted files, at both 1 s and 1 min temporal resolution, along with meteorological data (wherever available) for ease of interpretation of electrical measurements. This work describes the details of the GloCAEM database and presents what is likely to be the largest single analysis of PG data performed from multiple datasets at geographically distinct locations. Analysis of the diurnal variation in PG from all 17 GloCAEM sites demonstrates that the majority of sites show two daily maxima, characteristic of local influences on the PG, such as the sunrise effect. Data analysis methods to minimise such effects are presented and recommendations provided on the most suitable GloCAEM sites for the study of various scientific phenomena. The use of the dataset for further understanding of the GEC is also demonstrated, in particular for more detailed characterization of day-to-day global circuit variability. Such coordinated effort enables deeper insight into PG phenomenology which goes beyond single-location PG measurements, providing a simple measurement of global thunderstorm variability on a day-to-day timescale. The creation of the GloCAEM database is likely to enable much more effective study of atmospheric electricity variables than has ever been possible before, which will improve our understanding of the role of atmospheric electricity in the complex processes underlying weather and climate.
Highlights
Earth's electrical environment has been studied since the 1750s, but its more recently-appreciated connections to clouds (Tinsley et al, 2007; Nicoll and Harrison, 2016) and climate (Price, 1993; Rycroft et al, 2000; Williams, 1992, 2005) have highlighted some incompleteness in understanding of atmospheric electricity in the climate system
Measurements of PG can contribute to our understanding of how thunderstorms and the global atmospheric electrical system may be varying within our changing climate, which are difficult to assess by global lightning networks because they are not stable with time
PG measurements are useful in understanding some of the fundamental processes occurring inside thunderstorms which are only just starting to be understood such as high energy particle emissions related to thunderstorm ground enhancements (TGEs) and terrestrial gamma ray flashes (TGFs) (e.g. Chilingarian et al, 2015; Chilingarian, 2018)
Summary
Earth's electrical environment has been studied since the 1750s, but its more recently-appreciated connections to clouds (Tinsley et al, 2007; Nicoll and Harrison, 2016) and climate (Price, 1993; Rycroft et al, 2000; Williams, 1992, 2005) have highlighted some incompleteness in understanding of atmospheric electricity in the climate system. In order that truly global signals are considered in understanding the processes within the global circuit, many validating measurements must be made simultaneously at different locations around the world Beyond thunderstorms, another area of current research in atmospheric electricity is the role that atmospheric electricity plays in modulating cloud properties and its indirect effects through clouds on the Earth's radiative balance. This paper describes the properties of the GloCAEM database, as well as presents a summary of some of the initial analysis performed with the dataset This focuses on the application of the data to Global Electric Circuit research, and provides advice on choice of the best GloCAEM sites at which to study a variety of different atmospheric and geophysical processes related to atmospheric electricity
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