While a few existing cumulus parameterization schemes explicitly represent the effects of the mesoscale convective organization, observation-based evaluation of those schemes had been difficult because there was no single accepted method of objectively quantifying the degree of convective organization or clustering from observations. Using ground-based radar observations in the tropical Indian Ocean, we successfully quantified the degree to which precipitating cumulus clouds are spatially aggregated at scales larger than the size of individual clouds (Cheng et al. 2018). Our scalar metric of convective aggregation can serve as the basis of future parameterization development. Using the scalar metric, we performed cloud-system resolving model simulations of an observed convective clustering event and conducted a series of intervention experiments in which we intentionally weaken selected interactions/feedbacks (Cheng et al. 2020). One of the key findings from the modeling study is that low-tropospheric vertical wind shear helps organize convection even for non-squall-line type convective systems.

We are currently studying the mechanisms of mesoscale convective organizations in the tropical marine and mid-latitude continental environments. Of particular interest will be to investigate the exact roles of boundary layer cold pools and stratiform clouds in the organization of convection. We also plan on evaluating existing parameterizations of the convective downdraft and boundary layer cold pools using in-situ observations and cloud-system resolving simulations.