Aerosol Impacts on Convective Updraft Core Characteristics: A Modeling Study

In this study, we explore the indirect effects of Aerosol serving as Cloud Condensation Nuclei (CCN) on tropical convection. The case study is during the Tropical Warm Pool – International Cloud Experiment (TWP-ICE) field campaign in 2006. A convective system during the active Monsoon period between 00 UTC, Jan. 22 and 00 UTC, Jan. 24, 2006 is simulated using the Goddard Cumulus Ensemble (GCE) model. In order to realistically simulate the aerosol impacts on deep tropical convection, we use the Hebrew University Cloud Model (HUCM) spectral bin microphysical scheme that explicitly simulates size distributions of various hydrometeor types, as well as aerosols serving as CCN. Three sensitivity tests are carried out. The control experiment uses the observed mean aerosol profile during TWP-ICE. The two sensitivity tests use half (low case) and 10x (high case) of the observed aerosol concentration.

Since the cloud-resolving model simulations are forced by the observed large-scale forcing, the total energy budget of the model domain is tightly constrained. The total surface rainfall is identical for the 3 sensitivity studies. The simulated radar reflectivity compares well with the surface C-band radar observations in terms of the storm structure and evolution. However, model simulations underestimate stratiform rainfall portion, as shown by many similar studies, mainly due to constraints in model domain configurations. There are interesting sensitivities shown in the updraft core statistics, in that the high case has much stronger convective updrafts compared with the control and low case, especially in deep/undiluted cores. Nevertheless, all simulations significantly overestimate updraft speed compared with the dual Doppler radar retrievals. In this study we will present detailed analyses of model simulations to understand mechanisms of aerosol affecting updraft core statistics and its ramifications in tropical convection in general.