Mechanisms of Mesoscale Convective Clustering in a Maritime Two-Day Rain Event (AMIE/DYNAMO) and in a Continental Afternoon Precipitation Event (MC3E)

Description

The spatial organization of mesoscale convection can significantly impact Earth’s climate. However, organized mesoscale convection is missing in most contemporary GCMs, mainly due to our lack of understanding of the convective clustering processes. This study presents a thorough examination of the key mechanisms of the mesoscale convective clustering in two distinct environments: a maritime two-day rain event and a continental afternoon precipitation event. The two-day rain event is selected from the Atmospheric Radiation Measurement Madden-Julian Oscillation Investigation Experiment (AMIE)/Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign. Our recent study (Cheng et al. 2018) identified two distinct phases of convective clustering with different spatial evolutions. A series of mechanism-denial experiments is performed to examine the key mechanisms for each phase’s convective clustering. The mechanism-denial experiments highlight three key processes during Phase 1 clustering: i) the cold pool-updraft interaction that helps trigger new convection near existing ones, ii) moist patches in the lower troposphere that localize convection within them, and iii) the lower-tropospheric wind shear which suppresses convection in dry regions via increased entrainment. During Phase 2 clustering, stratiform clouds form and the associated mesoscale circulation develops, constraining convection to form within a localized region and maintaining the relatively aggregated convection from dissipation. In this phase, the relatively dry anomalies under the stratiform clouds that control the strength of the mesoscale circulation are shown to be a key factor for convective clustering. The convective clustering processes over land are investigated with an afternoon precipitation event (23 May 2011) during the Midlatitude Continental Convective Clouds Experiment (MC3E). The ARM observations collected during MC3E and the mechanism-denial simulations are used to study the mechanisms of convective clustering in this continental environment. A comparison of the mechanisms of mesoscale convective clustering between the two cases and its implication on parameterizing the organized mesoscale convection in the global models will be discussed. Cheng, W.-Y., D. Kim, A. Rowe, 2018: Objective Quantification of Convective Clustering Observed During the AMIE/DYNAMO Two-Day Rain Episodes. J. Geophys. Res. Atmos., 123, 10361-10378.