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Understanding Convection and Lightning Activity from Ground-based and Multi-satellite Observations for Hydrology Applications

Defer Eric

Defer E., /LERMA, Paris, France/
Molinié G., /LTHE, Grenoble, France/
Betz H. D., /Munchen University, Germany/

The cloud microphysical structure is of primary importance concerning rainfall studies either from numerical simulations, space-borned passive microwave or ground-based radar measurements. Observational tools (polarimetric radar, satellite radiometry,...) can be used to assess cloud microphysical structures but they are not continuously available everywhere in Europe or over the Mediterranean Sea. For example polarimetric radars are not routinely operated while geostationnary infra-red/visible radiometry scans only the upper layer of the clouds and sensors onboard low-orbit satellites suffer of a poor temporal sampling of storms.
In thunderclouds, lightning flashes occur in highly electrified areas.
Microphysical processes responsible for the cloud electrification occur in specific environnements. Basically, cloud-water and ice mixing ratios as well as updraft control the electrification rate and implicitely the occurence of lightning flashes. Thus, in many cases, the lightning flash activity in terms of rate and flash density can be compared to the convection intensity.
Our goals are:
- to gain further insight in the understanding of the interactions between cloud microphysics, cloud dynamics, cloud electrification and occurence of lightning flashes in continental and maritime storms;
- to assess the potential improvement of rainfall retrieval gained in using lightning flash measurements in conjunction with more classical observations/products for operational applications in weather and hydrological nowcasting.
As an introduction to our work over the South-East of France, we will show comparisons between satellite brightness temperatures at different wavelengths (Visible, IR and passive microwaves) with the lightning flash activity of the 8-9 September, 2002 and the 7-9 September, 2005 flash flood events.
The newly-operational Lightning Network (LINET) [1] monitors continuously the total (intracloud and cloud-to-ground) lightning activity and provides a three dimensional mapping of the lightning flashes both at high temporal and spatial resolutions. Data are available over western Europe since May 2006. The capabilities of LINET network will be illustrated.
Our middle-term perspective is to compare the lightning flash activity as sensed by LINET to the simulated one using mesocale electrified thundercloud simulations along with passive microwaves observations. Both lightning flash and electrification schemes will be discussed.
[1] Betz, H D, W. P. Oettinger, K. Schmidt, and E. Defer, LINET : A New Lightning Detection Network in Central Europe, Eos Trans. AGU, 87(52), Fall Meet. Suppl., Abstract AE42A-08, 2006.