Characteristics of Mesoscale Convective Organization in the Australian Tropics

Organized mesoscale convective systems (MCSs) have a variety of archetypes that are ultimately related to aspects of the background environment, including its stability (e.g., CAPE) and profiles of wind shear. Such archetypes range from the canonical front-fed, upshear tilted and downshear propagating model, which is common for long-lived and linear systems, through to a large set of combinations of mesoscale tilts and propagation directions relative to the mean flow and shear. Previous studies have characterised the occurrence and longevity of the range of archetypes over the midlatitudes (e.g., in the USA). Here we develop an objective identification algorithm, which analyses radar archives, to determine the characteristics of Australian MCSs with particular focus on the tropics. This algorithm is combined with other data (i.e., radiosonde and reanalysis data) to determine the propagation and mesoscale tilt characteristics with respect to the mean wind and shear.

In this presentation we summarise three related studies. The first characterises the MCS archetypes over Darwin, Australia over 15 wet seasons, using the objective identification algorithm. This analysis quantifies the relative frequency of different modes of mesoscale organisation, and identifies the dominance of the canonical model, followed by parallel stratiform archetypes. The second study uses the algorithm to evaluate an operational convection-permitting forecasting system, identifying key systematic biases in the occurrence and organizational characteristics of the forecast convection. The third study examines the entire Australian radar archive, comparing the characteristics of tropical and midlatitude organized systems, and relates these differences to aspects of the large-scale flow.