Modeling Study for the Impacts of Aerosol and Its Embedded Environmental Conditions on Maritime/Continental Deep Convective Systems

We conducted systematic model simulations using the Weather Research and Forecasting (WRF) model coupled with spectral-bin cloud microphysics (SBM) for model intercomparison study. These sensitivity simulations were designed to investigate how atmospheric instability and aerosol concentrations acting cloud condensation nuclei (CCN) may impact deep convective systems in maritime and continental conditions. The spectral-bin microphysical formulation was employed to provide more detailed microphysical simulations, particularly representing effects of different ambient aerosol loading on the cloud microphysical characteristics. We selected one cases of the tropical maritime (derived from the Tropical Warm Pool – International Cloud Experiment, TWP-ICE field campaign) and the mid-latitude continental (derived from the Midlatitude Continental Convective Clouds Experiment, MC3E field campaign) conditions. Modeled aerosol concentrations were dynamically downscaled from the NASAModern-Era Retrospective analysis for Research and Applications (MERRA) Aerosol Reanalysis to arrive at CCN concentration inputs for the WRF-SBM model. Representative CCN concentrations (supersaturation = 1 %) at the ground level for the control simulations were approximately 100 cm^-3in the tropical maritime (TWP-ICE) case and 1500 cm^-3for the mid-latitude continental (MC3E) case.

CCN sensitivity tests were conducted by interchanging the maritime and continental CCN concentrations, feeding the TWP-ICE case with the mid-latitude continental CCN profile and vice versa. For the TWP-ICE case, i.e., real-case simulations based on the maritime thermodynamics through the initial and lateral boundary conditions, a 10% increase in the areal-averaged convective precipitation rate was found when CCN concentrations were interchanged with the mid-latitude values. Increased graupel and hail contents contributed the increase of convective precipitation rate, which is consistent with previous studies on convective invigoration by increased CCN. In contrast, convective precipitation rates were substantially reduced in the MC3E counterpart simulation when the maritime CCN profiles were used instead. Application of our developed polarimetric radar retrieval and instrument simulator (POLARRIS) clarified the change in the microphysical characteristics in these sensitivity tests through comparing polarimetric variable and hydrometeor identification (HID) fields. The HID analysis highlighted the transition of HID from graupel to hail in mixed-phase parts of the deep convective systems. Additionally, we will present sensitivity simulation results in response to simultaneously modifying atmospheric instability and CCN.