Using MODIS atmospheric profile data to monitor regional atmospheric instability in Greece: two case studies

This study aims at investigating the potential of using atmospheric instability indices, derived by the MODIS/AQUA and TERRA atmospheric profiles, in local weather forecasting. The MODIS Level 2 Atmospheric Profile product consists of several parameters, including temperature and moisture profiles for twenty isobaric level and three atmospheric stability indices: the Total Totals (TT), the Lifted Index (LI), and the K index (K). All of these parameters are produced day and night at 5x5 km pixel resolution at cloud free conditions. The good spatial resolution of the MODIS instrument and of the derived parameters gives a good potential for the identification of pre-convective conditions.
   Two cases of thermal induced convection over Greece on 17 and 20/6/2010 were examined. The first date is a typical case of an early afternoon thermal convection development over continental Greece supported by an advancing upper-level trough. The second case is characterized by the evolution of large storms during evening over Thessaloniki and north-eastern Greece associated with very high lightning activity. These storms were the result of a short wave upper-trough passage northern of Greece which triggered convection over the warm ground surface.
   First, a comparison between the indices derived by MODIS and temporal matched collocated radiosonde data was performed to assess the quality of the derived parameters. From the above analysis it seems that the three satellite derived instability indices are well correlated with those derived from radiosondes.
   Then maps with the spatial distribution of the atmospheric instability based on MODIS satellite data were constructed for the morning satellite passes (9:50 and 8:45 UTC, respectively), a few hours before the convection initiation, and were qualitatively compared to Meteosat Second Generation (MSG) satellite imagery and lightning data to investigate the relation between satellite derived air instability indices and storm occurrence. Among the three instability measures, the Lifted Index and K Index performed best in showing the potential of instability in this region several hours before the initiation of cloud formation.
   These results show that MODIS remotely sensed data can be quite helpful in the short term storm prediction. More precisely, it is possible to derive air instability indices of satisfactory quality using MODIS satellite data. This allows us to have this kind of information with unprecedented spatial resolution in areas with no available radiosonde data. In addition, these satellite derived data can be used to visually enhance the areas of high likelihood of strong convection and of cloud growth in Greece at summertime.
   From the operational point of view MODIS data are not timely since they are available only twice per day. Morning overpasses in Greece occur sometimes too late. Quite often convection has already started producing cumuliform clouds, which in turn prevent the atmospheric profile retrieval. The Global Instability Index (GII) product derived by the 15min time resolution geostationary MSG imagery could be used in the fast recognition and successful prediction of summer convective cloudiness and precipitation, despite its low spatial resolution (50 km).