Fan, CX; Wang, MH; Rosenfeld, D; Zhu, YN; Liu, JH; Chen, BJ (2020). Strong Precipitation Suppression by Aerosols in Marine Low Clouds. GEOPHYSICAL RESEARCH LETTERS, 47(7), e2019GL086207.

The adjustment of cloud amount to aerosol effects occurs to a large extent in response to the aerosol effect on precipitation. Here the marine boundary layer clouds were studied by analyzing the dependence of rain intensity measured by Global Precipitation Measurement on cloud properties. We showed that detectable rain initiates when the drop effective radius at the cloud top (r(e)) exceeds 14 mu m, and precipitation is strongly suppressed with increasing cloud drop concentration (N-d), which contributes to the strong dependence of cloud amount on aerosols. The rain rate increases sharply with cloud thickness (CGT) and r(e) when r(e) > 14 mu m. The dependence of rain rate on r(e) and CGT presents a simple framework for precipitation susceptibility to aerosols, which explains other previously observed relationships. We showed that sorting data by CGT and using alternative cloud condensation nuclei proxy rather than aerosol optical depth are critical for studying aerosol-cloud-precipitation interactions. Plain Language Summary Aerosol-cloud interaction remains the greatest uncertainty in future climate projection. Precipitation is a key process that mediates how the cloud amount responds to aerosol perturbations. Here we combined precipitation measured by the radar onboard the satellite of Global Precipitation Measurement (GPM) and cloud properties retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua satellite for studying the dependence of rain intensity on cloud properties for marine boundary layer water clouds over the Southern Hemisphere Ocean. Our results showed that rain is sharply intensified when droplets at the cloud top grow larger than 14 mu m, and precipitation decreases with increasing cloud drop number concentration (N-d). A simple framework to explain the relationship between precipitation and aerosols is proposed here by showing the dependence of precipitation on N-d and cloud geometric thickness. We also discussed why using aerosol optical depth (AOD) as CCN proxy in previous studies could lead to great uncertainties and why sorting cloud geometrical thickness is necessary.