Impact of Convective Invigoration due to Aerosol on Shallow Couds during Shallow Meridional Circulation.

Abstract:

Past work suggests deep convective clouds will deepen and/or ascend faster as a result of increasing aerosol concentrations, an effect called “convective invigoration”. While a number of model and observational studies have looked at this effect, the possible interaction between aerosol-invigorated deep cloud and shallow clouds remains uninvestigated. One objective of this work is to understand the remote responses of shallow and/or deep clouds to convective invigoration due to changes in synoptic scale motions. The large scale motion chosen for this study is the Hadley Circulation associated with the Eastern Pacific Inter-Tropical Convective Zone, which has been found in a number of studies to exhibit a shallow meridional circulation (SMC). In this study we use the Weather Research and Forecasting (WRF 3.5.1) model and set up an idealised case in order to reproduce the circulation. SMC remains robust to the different resolutions of 20 km and 2 km (where cumulus schemes are used at 20 km but not at 2 km).

We investigate the potential affect of aerosols in two ways: by adding a proxy effect of aerosols in the form of localised heating perturbations that mimic latent heating effects, and by directly increasing the CCN concentration from 100 to 800 per cc. Four simulations are performed. The first simulation is considered as a control in which there is no added heating perturbation. The next two are perturbed cases in which localised heating perturbations are added - to latent heating in the cumulus and microphysics schemes at 20km and 2km resolutions respectively. The final simulation increases the cloud condensation nuclei (CCN) concentration to a high value. Results from both proxy heating and high CCN 2km resolution simulations show invigoration of deep convective clouds with no effect on shallow clouds. Proxy heating experiment at 20 km resolution show similar invigoration of deep convective clouds followed by suppression of shallow clouds. Cloud changes with respect to aerosol from two different methodology will be presented and throughly discussed.