Mechanisms of convective clustering during the AMIE/DYNAMO 2-day rain episodes
Abstract
Previous analysis of the AMIE/DYNAMO field campaign data revealed two distinct stages of convective clustering (CC) during 2-day rain episodes. The Phase 1 (2) CC corresponds to the developing (decaying) period with increasing (decreasing) number of convective entities. The Phase 1 CC is characterized by the tendency of new convective cells forming near the existing ones. In the Phase 2,convective entities tend to form within the edge of the long-lasting stratiform clouds region, maintaining the relatively aggregated state. However, the driving force for CC in the two phases remains unexplored.
In this study, we seek to understand the key physical mechanisms contributing to the observed CC during the AMIE/DYNAMO 2-day rain episodes. Using a cloud-system resolving model (WRF), we perform a series of mechanism-denial experiments to examine the roles of selected processes. For example, to examine the role of the cold pool-updraft interaction, boundary layer temperature is nudged toward its domain mean value at each time step. Similar simulations targeting the moisture-convection feedback, longwave cloud-radiative feedback, and role of vertical wind shear are conducted by homogenizing free-tropospheric moisture, longwave radiative heating rate, and vertical shear, respectively. Process-oriented diagnosis of the mechanism-denial simulations show that homogenizing boundary layer temperature and free-tropospheric moisture both weakens the Phase 1 CC, emphasizing the role of the cold pool-updraft interaction and moisture-convection feedback. Homogenizing free-tropospheric moisture also reduces the Phase 2 CC, presumably because the mesoscale circulation that confines the new convection in the convective region is weakened, due to the homogeneous convective heating as a result of homogenizing free-troposphere moisture. Our results also show that suppressing the mid-troposphere wind shear encourages horizontally small convection, highlighting the role of mid-troposphere wind shear on organizing convection.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A32C..05C
- Keywords:
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- 3310 Clouds and cloud feedbacks;
- ATMOSPHERIC PROCESSESDE: 3314 Convective processes;
- ATMOSPHERIC PROCESSESDE: 3329 Mesoscale meteorology;
- ATMOSPHERIC PROCESSESDE: 3354 Precipitation;
- ATMOSPHERIC PROCESSES