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Final Report Summary - EGATEC (Engineering model of the global atmospheric electric circuit)

A novel, high-resolution model of the global atmospheric electric circuit, EGATEC, has been created. Thunderstorm and non-thunderstorm cloud current generators, driving the circuit, have been constructed on the basis of satellite measurements of the surface area covered by various types of clouds, available from the International Satellite Cloud Climatology project data, and model current densities of cloud generators, derived from observations of the electric activity of such clouds, in particular using the satellite optical transient detector/lightning detection sensor lightning flash rates.

The areas of the globe where the electric current is generated as well as current source-free areas can be estimated with the spatial resolution of several degrees in latitude and longitude and three-hour time resolution. The resistance load of the atmosphere is calculated using the atmospheric conductivity model by Tinsley and Zhou (Journal Geophysical Research, 2006) which is also spatially dependent and sensitive to the level of solar activity. In addition, representations of the global distributions of aerosol in the summer and winter, available in the conductivity model, allow studies of the seasonal changes of the model global circuit due to the aerosol-related changes of the atmospheric conductivity. The cloud current sources and resistance of the cloud generators and resistance of the cloud-free area associated with a latitude and longitude in a model grid create circuit branches connected in an electrical network representing the global atmospheric electric circuit. This electric network can be solved numerically according to standard circuit theory or simulated by engineering software.

As a result the global distribution and diurnal variation of the air-Earth electric current density due to lower atmosphere current generators and vertical electric field can be obtained from the calculations, with the spatial and time resolution used for the input data. The circuit can be constructed assuming the ionosphere to be either an equipotential or non-equipotential surface, and the ground assumed to be an ideally conducting surface. First model runs performed for a few days in July and December of 2001 and of 2005 showed some seasonal differences in the diurnal variation but confirmed the global atmospheric electric activity peak at ∼21 UT and a minimum at ∼3-6 UT, observed experimentally. Furthermore, according to the model, the current driven by thunderstorm convective clouds is four times the current generated by mid-level rain clouds, and the total current maximises in the northern hemisphere winter.

The model results on seasonal changes of the GEC have been compared qualitatively to the values observed at various observing stations over the globe. The diurnal variation of the vertical electric field and the air-Earth current density, measured at the mid-latitude station Swider, Poland, have been compared with the model predictions, both during the period of fair and foul weather at Swider, and the results of this comparison are satisfactory. These initial results by EGATEC have been submitted for publication in Journal of Geophysical Research.

Developments to the model to include the coupling of the lower atmosphere electric circuit to the ionospheric and magnetospheric current system started in the second phase of the project. These involve using data from the SuperDARN radar network to provide input on the change of the ionospheric potential and currents over polar regions due to the interaction of the Earth's magnetosphere with the solar wind.

Documentation related to the model and the model website is still under preparation and more news on the model will be submitted to the newsletter of the International Commission on Atmospheric Electricity. EGATEC can be relevant to atmospheric scientists, meteorologists and climatologists concerned with the atmospheric electricity, atmospheric circulation and climate modelling.

Reported by

POLISH ACADEMY OF SCIENCES
01-452 WARSAW
Poland
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