Lightning evolution related to radar-derived microphysics in the 21 July 1998 EULINOX supercell storm

Results of a combined analysis of data from a C-band polarimetric Doppler r adar and a 3D VWF interferometric lightning mapping system, as obtained dur ing the European Lightning Nitrogen Oxides project (EULINOX) field campaign , are presented. For 21 July 1998, the lightning data from a supercell thun derstorm weakly indicate a tendency for a bi-level vertical distribution of lightning VHF emissions around the - 15 degreesC and - 30 degreesC tempera ture levels. Also, in some parts of the clouds, evidence is found for the p resence of a lower positive charge center near the freezing level. However, where strong vertical motions prevail, VHF emissions are not organized in horizontal layers but in oblique or vertical regions. Correlation of VHF si gnals with radar quantities shows that in the growing storm, peak VHF activ ity is low and related to reflectivity factors around 30 dBZ, while after t he mature stage, the peak VHF activity is about three times larger. The hig hest density of VHF signals is now found near reflectivity factors of 45 dB Z. A polarimetric hydrometeor classification indicates that during storm de velopment, most lightning activity occurs where graupel and, secondarily, s now and sm,all dry hail are present. In the decaying phase of the supercell hailstorm, however, most lightning VHF emissions stem from the region with hail and heavy rain. Furthermore, while the VHF signal frequency per cubic kilometer in the graupel and min regions remains nearly constant throughou t the supercell life cycle, the signal frequency in the hail region rises d uring storm decay. (C) 2001 Elsevier Science B.V. All rights reserved.