Atmospheric environmets of convectively generated wind gusts in Southern Brazil

This study investigates convective wind gusts measured by National Meteorological Institute (INMET, in Portuguese) operational automated surface weather stations network in southern Brazil from 2005 to 2015. Only events unequivocally associated with deep convective storms were selected, as evaluated with a set of criteria that include the employment of geostationary satellite data. Wind gusts exceeding 25 ms ^-1 are categorized as severe, while non-severe gusts with moderate intensity range from 15 ms ^-1 to 24.9 ms ^-1, and weaker gusts from 10 ms ^-1 to 14.9 ms ^-1.

Convective parameters computed from the Fifth Generation of the European Centre for Medium-Range Weather Forecasts Reanalysis (ERA5) are used to investigate the atmospheric conditions conducive to severe wind gusts. Emphasis is placed on assessing the ability of convective parameters to discriminate between severe and sub-severe wind gust environments. The results indicate that the mean wind computed from the surface to the 6 km layer was the only parameter that showed some discriminatory ability. Overall, convective parameters alone are unable to distinguish environments conducive to the formation of storms capable of generating intense winds from those generating weak wind gusts. This result aligns with ingredient-based analysis, as individual parameters alone do not encompass all the necessary ingredients required for the development of these storms.

Therefore, we evaluate the combined product of ERA5-based convective available potential energy (CAPE) and bulk wind difference in the 0-6 km layer (BWD). The results indicate that as the gust intensity increase, the high CAPE high shear space gradually becomes more preferable. In other words, there is a tendency for more severe storms to cluster in the sector of the diagram where both CAPE and BWD values are moderate to high.