Strong Precipitation Suppression by Aerosols in Marine Low Clouds. Issue 7 (1st April 2020)

• Record Type: Journal Article
• Authors: Fan, Chongxing; Wang, Minghuai; Rosenfeld, Daniel; Zhu, Yannian; Liu, Jihu; Chen, Baojun
• Is Part Of: Geophysical research letters. Volume 47:Issue 7(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-04-01
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL086207
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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 (re ) exceeds 14 μm, and precipitation is strongly suppressed with increasing cloud drop concentration (Nd ), which contributes to the strong dependence of cloud amount on aerosols. The rain rate increases sharply with cloud thickness (CGT) and re when re > 14 μm. The dependence of rain rate on re 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 μm, and precipitation decreases with increasing cloud drop number concentration (Nd ). A simple framework to explain the relationship between precipitation and aerosols is proposed here by showing the dependence of precipitation on Nd 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. Key Points: Precipitation is strongly suppressed with increasing cloud drop concentration Sorting data by cloud thickness and using alternative CCN proxy rather than AOD are critical for studying aerosol‐cloud interactions Detectable rain initiates when the drop effective radius at the cloud top exceeds 14 μm