Betz, Hans-Dieter

Höller, Hartmut

Schmidt, Kersten

English

Institute of Transport Research:Publications

MODELING THE OPTICAL EMISSIONS OF LIGHTNING TO BE OBSERVED FROM MTG-LIHartmut Höller1, Hans-Dieter Betz2, Kersten Schmidt1(1) Institut für Physik der Atmosphäre, DLR-Oberpfaffenhofen, (2) Physics Department, University of MunichABSTRACTFuture geostationary satellite systems will  offer a variety of  improved observing capabilities which will  be extremely useful for many applications like numerical weather forecasting, nowcasting of severe weather, climate  research  or  hydrology.  The  planning  for  MTG  (Meteosat  Third  Generation)  includes  an  optical  lightning imager (LI) as part of the payload. This study investigates the future data streams by developing a statistical  model of  RF (radio frequency) -based  prediction  of  lightning  optical  emissions  resulting  from  a  comparison  of  ground  based  lightning  measurements from LINET (Lightning Location Network) in the VLF/LF radio frequency (RF) range and the optical lightning imaging sensor (LIS) aboard the TRMM satellite. As LINET had been operated in a series of  field  campaigns  in  the  tropics  (TROCCINOX,  SCOUT-03  and  AMMA)  statistical  analyses  of  a  large  number  of  TRMM overpasses (up  to  90  sec  local  observing  time)  could  be performed.  It  was found that  often a direct temporal coincidence of RF signals (LINET strokes) and optical pulses (LIS groups) exists. Due to  the  complex  flash  structures  and  scattering  processes  of  light  within  a  thunderstorm stroke  peak  current and optical radiance were only poorly correlated to each other. The same conclusion holds for peak current and the size of the optical  footprint observed at cloud top. Besides the directly corresponding RF and optical counterparts there are a series of inter-stroke optical pulses to be observed within the duration of  a  flash.  But  also  cases  were  observed  consisting  of  a  series  of  strokes  having  no  obvious  optical  correspondence. In addition to this flash specific behaviour there are also non-coincident events in space and time. The flash comparisons described above are used for modelling the time series of  optical  emissions from thunderstorms  as  expected  to  be  seen  by  MTG-LI  from  geostationary  orbit.  In  addition  to  lightning  time  series from African tropical storms another focus of the present study is on thunderstorms occurring over Europe.  In  a  comparative  study  using  LINET  in  four  different  continents  it  was  found  that  lightning  in  mid-latitude storms was as intense as in extreme cases from the tropics. Continuous LINET observations over  Europe  are  available  now  for  several  years.  Based  on  some  typical  European  case  studies  we  investigate  the  stream of  optical  data  to  be  expected  during  such  convective  periods.  The  output  of  this  study will be used for the development of the MTG-LI lightning data processor.

Modelling the optical emissions of lightning to be observed from MTG-LI

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