Appendix

A.1 Definition of the Thomson index

Thomson index = (K-index) - (4-layer best lifted index)

The "best lifted index" or "4-layer lifted index" is a variation of the lifted index. Initially the lifted index is determined for a few levels between the surface and 1600 m. The best (most unstable) lifted index value is then retained. This is helpful when the surface lifted index may misrepresent the actual instability (e.g. morning soundings).

http://www.teachingboxes.org/avc/content/Severe_Weather_Indices.htm

 

A.2 Definition of the Supercell Composite Parameter

This is a multiple-ingredient composite index that includes effective storm-relative helicity (ESRH, Right Supercell Motion by Bunkers et al., 2000), most unstable parcel CAPE (muCAPE), and effective bulk wind difference (EBWD). Each ingredient is normalized to supercell "threshold" values, and larger values of SCP denote greater "overlap" in the three supercell ingredients. Only positive values of SCP are displayed, which correspond to environments favoring right-moving (cyclonic) supercells.

This index is formulated as follows:
SCP = (muCAPE / 1000 J kg-1) * (ESRH / 50 m2 s-2) * (EBWD / 20 m s-1)

EBWD is divided by 20 m s-1 in the range of 10-20 m s-1. EBWD less than 10 m s-1 is set to zero, and EBWD greater than 20 m s-1 is set to one.

 

A.3 Data used to classify the intensity of the convective events analyzed in Section 6

To classify the storms or storm systems according to their intensity, the following data were collected about the mature phases of the convective events:

  • Severe storm reports published in the news, or in the European Severe Weather database (ESWD);
  • 10-min surface measurements (in Hungary): maximum wind gust and maximum rain amount;
  • Radar data covering the Carpathian Basin, measured by the Hungarian radar system: rain rate (calculated from column maximum reflectivity), cloud top height (ETOPS), probability of hail, vertical integrated liquid (VIL) value (the higher the VIL the higher the hail size) and the VIL/ETOPS ratio;
  • Minimum brightness temperature in the SEVIRI 10.8 µm channel;
  • Radar features where present; e.g. comma echo, bow echo, weak echo region (WER) or bounded weak echo region (BWER) in vertical cross sections;
  • Satellite features where present; e.g. long-lived cold rings or ice plumes, and
  • Forecasters’ assessment.