A Process-Oriented Analysis of GCOM-C/SGLI for Quantifying the Response of Water Cloud Properties to Aerosols

This study employs satellite-borne multispectral imagers, SGLI onboard the JAXA's GCOM-C satellite, in an attempt to unravel the processes of cloud and precipitation and their response to aerosols. For this purpose, multiple cloud microphysical parameters retrieved are combined in particular manners to construct particular statistics and correlations. An emphasis is placed on a process-oriented analysis of the SGLI-derived cloud properties to quantify the response of water cloud to aerosols through identifying cloud growth stages and their relationships to aerosols. The SGLI is a multispectral imager onboard the JAXA's new satellite GCOM-C launched in the end of 2017 with characteristics similar to MODIS in terms of the spectral channels (19 channels; 380 nm - 12 µm), the swath (250 m - 1 km) and the resolution (> 1000 km). A unique aspect of GCOM-C/SGLI includes polarimetry observation functions for land aerosol retrieval and 763 nm channels for cloud geometric thickness estimation. Using the cloud and aerosol parameters retrieved with these SGLI capabilities, we first quantify the susceptibility of cloud to aerosols by applying the traditional statistical approach but with a particular attention to isolate cloud responses to aerosol from correlations generated by meteorological field by taking conditional correlations among the parameters constrained by meteorological factors. We obtained the susceptibility of cloud to aerosols, d ln(r_e)/d ln(AI) of -0.06 to -2.6 and d ln(LWP) /d (AI) of -0.02 to 0.13 when stratified by meteorological conditions. The results are consistent with previous studies based on MODIS. Secondly, as a more process-oriented approach, we also devise a new approach of investigating spatial variances of imager-derived cloud parameters to identify cloud particle growth processes. Specifically, the relative standard deviations of the cloud droplet number concentration and the liquid water path are compared to characterize whether condensation or coalescence processes are dominating and to investigate how such process characteristics are mapped geographically. These two analysis methods are further combined to explore how the cloud responses to aerosols are interpreted from a process perspective of the cloud growth stage.