engleski

Analysis of atmospheric instability indices based on radio sounding and ALADIN data, weather types and lightning detection

A use of the instability indices of the atmosphere has a long tradition in the forecasts of deep convection by displaying a convective activity through a single number. A calculation of the instability indices can be done either from radiosoundings, numerical atmospheric models or on the basis of satellite data. Here we have used radiosounding data for 7 stations (Zagreb, Zadar, Vienna, Budapest, Szeged, Udine and San Pietro Capofiume) in a 7- year period (1st January 2007 – 31st December 2013), trying to estimate instability indices thresholds (by stations, season and time of day) and correlate them with measured lightning. The instability thresholds (for LI, CAPE, CIN, KI, TT, SI, SWEAT, BRN, TPW) are found using the frequency distribution method. We have found acceptable probabilities for successful convection prediction using noon sounding data (e.g., for LI < 1°C, KI > 27°C, TT > 46°C, SI < 3°C). The most typical weather regimes associated with lightning are the precipitation regime and almost non-gradient pressure field (NG). Regimes which include high pressure formations are relatively rarely associated with convection. The most common flow type for days with lightning is the SW wind associated with large SWEAT index (> 161). While the largest average values of CAPE, LI, KI and TPW indices occur within NG, the greatest average values of the SWEAT index have been found during the precipitation regime. An additional comparison between radiosonde and ALADIN model for increased set of indices showed that the ALADIN model has been successfully predicted indices that are mainly derived from temperature and wind at significant levels. Weaker results were obtained for the indices that are dependent on the specific levels, e.g., the level of condensation.

atmospheric instability indices; total lightning; weather types; wind regimes; ALADIN numerical model; Adriatic; Pannonian Plain

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