On the evolution of mesoscale convective systems during DYNAMO

The deployment of the dual-polarimetric S-PolKa radar during DYNAMO provided a rare opportunity to investigate the microphysical properties of precipitating oceanic tropical convection. While this data is being used, as part of the larger DYNAMO radar network, to describe the evolution of the entire cloud population, this study focuses, in particular, on the evolution of mesoscale convective systems, which dominated the rainfall accumulations during the active phases of the MJO. In an environment of deep directional wind shear, embedded convective lines collapsed to maintain widespread stratiform echo, which was rapidly advected by the upper-level winds in the opposite direction as the low-level flow. Under different conditions, especially later in the project, deep, strong westerlies extending throughout much of the troposphere led to fast-moving squall lines with a much smaller stratiform fraction. The dual-polarimetric radar data from these events provides an opportunity to describe the microphysical evolution of MCSs as they transition from convective to stratiform in these differing scenarios. This is crucial for understanding the feedback on the environment through tropospheric moistening and heating and radiative feedbacks, as well as providing a guide for numerical simulations and forecasts of the MJO.