Severe convection-related winds in Australia and their associated environments

Abstract

Severe surface wind gusts produced by thunderstorms have the potential to damage infrastructure and are a major hazard for society. Wind gust data are examined from 35 observing stations around Australia, with lightning observations used to indicate the occurrence of deep convective processes in the vicinity of the observed wind gusts. A collation of severe thunderstorm reports is also used to complement the station wind gust data. Atmospheric reanalysis data are used to systematically examine large-scale environmental measures associated with severe convective winds. We find that methods based on environmental measures provide a better indication of the observed severe convective winds than the simulated model wind gusts from the reanalysis data, noting that the spatial scales on which these events occur are typically smaller than the reanalysis grid cells. Consistent with previous studies in other regions and idealised modelling, the majority of severe convective wind events are found to occur in environments with steep mid-level tropospheric lapse rates, moderate convective instability and strong background wind speeds. A large proportion of events from measured station data occur with relatively dry environmental air at low levels, although it is unknown to what extent this type of environment is representative of other severe wind-producing convective modes in Australia. The occurrence of severe convective winds is found to be well represented by a number of indices used previously for forecasting applications, such as the weighted product of convective available potential energy (CAPE) and vertical wind shear, the derecho composite parameter and the total totals index, as well as by logistic regression methods applied to environmental variables. Based on the systematic approach used in this study, our findings provide new insight on spatio-temporal variations in the risk of damaging winds occurring, including the environmental factors associated with their occurrence.