Evaluation of Aerosol-Cloud Interactions on Autoconversion and Accretion using WRF-Chem over Northeast Asia

Abstract:

Autoconversion (Au) and accretion (Ac) are main two factors in determining the complicated aerosol effects on warm-cloud and precipitation process through their interaction mechanism. However, numerical estimates of these aerosol-cloud interactions remain highly uncertain and are poorly understood. In this study, WRF-Chem model was employed, and various sensitivity studies on Au and Ac parameterizations were carried out and compared the modeling results against observations and satellite measurements: the CLAVR-x satellite products. Our modeling-observation intercomparison results showed that modeling with default parameterization (BASE) explored severe discrepancies between model and observation in some cases, which includes the contribution of microphysical process rates according to LWP, N_d versus precipitation rate (R) relation particularly at low LWP condition, and the ratio of accretion to autoconversion (Ac/Au ratio). Therefore, we further carried out various sensitivity tests to reduce these discrepancies, particularly focusing on improving the relationship between N_d and R according to LWP and the Ac/Au ratio through the repeated amendment-and-adjustment process based on both observation and modeling results. Our repeated amendment-and-adjustment approaches suggested five categories from the classification of Au and Ac over Northeast Asia: 1) different accretion rate with autoconverted liquid water, 2) scaled autoconversion rate, 3) susceptibility fitting factor of power law, 4) subgrid variability, and 5) other parameterizations, and discussed some possible improvements for each of the five classified categories.