Worldwide microphysical thunderstorm variability in different climatic regions: a three-dimensional cloud modeling study

Thunderstorms occur worldwide daily within many dissimilar climatic regimes. With this well-known fact in mind, this study investigates the case-to-case dynamical and microphysical variability of thunderstorms at various times of the year in different climatic zones as well as within a given climate zone.

In the above context, we analyze 105 storm cases across several climatic regimes around the world, using the Wisconsin Dynamical/Microphysical Model (WISCDYMM), a quasi-compressible nonhydrostatic three-dimensional cloud model equipped with bulk microphysics for cloud water, rain and three classes of ice (cloud ice, snow, graupel/hail). The cases are compared with regard to the partitioning of total hydrometeor mass among all five individual components, and between total ice and liquid masses, each integrated over the model domain and time-averaged over a significant portion of the storms' mature stages. Via linear regression, we evaluate to what extent these bulk microphysical storm properties are modulated by pre-storm environmental indices relevant to severe local storm prediction including ground-relative melting level, convective available potential energy (CAPE) and Total Totals.

The model results show many microphysical and dynamical similarities and differences among storms, within each climate regime as well as between regimes. Among several interesting conclusions: (1) The similarities stem from the association of a given climate zone with a typical air mass type; (2) at least outside of the deep tropics, the differences are in part modulated by time of year (seasonality); (3) thunderstorms originating in dissimilar air masses can exhibit similar structural or morphological properties but highly contrasting microphysical properties; (4) the type of air mass visiting a climate zone on a storm day is comparably important to which climate zone it visits; (5) versus the melting level, both the total and cloud (non-precipitating) ice fractions have fair correlations and the rain fraction a somewhat stronger correlation; (6) versus the melting level and CAPE jointly, the correlations are considerably higher; (7) versus Total Totals, the correlations are stronger yet for each of the aforementioned hydrometeor mass fractions.