On the relationships of large to small scales in a convecting atmosphere in the real world and a CRM

Description

Our previous research has elucidated relationships between large and small scales in tropical convection using data at the ARM Darwin site. In particular, we have shown that convective activity is more directly related to convergence—and hence the dynamical state of the tropical atmosphere—than to CAPE, and hence the thermodynamic state of the atmosphere. We also showed that the relationship to convergence is to first order one that controls the area that is convectively active, rather than the intensity of the convection.

Here, we first refine our observational knowledge by extending our analysis to include the depth of the convective cells and investigating its relationship to the large-scale conditions with the aim to test the hypothesis that dry mid-tropospheric states lead to shallower clouds. C-POL radar data at Darwin are used to identify the depth of convective cells and form the backbone of this investigation. First attempts at using the radar data to retrieve vertical velocity in convective cells will also be shown.

Following on from this we investigate how well a cloud-resolving model (CRM) can reproduce both the observed convective structures and their relationship to the state of the large-scale atmosphere. For this purpose the System for Atmospheric Modelling (SAM) CRM is run using forcing data derived from three wet seasons at the Darwin site. Model results are compared to the observed relationships derived from the C-POL observations.