Marine Cirrus Properties from Satellite Remote Sensing over the South China Sea: Spatiotemporal Variations and a Case Study

Cirrus clouds play a crucial role in the energy balance of the Earth–atmosphere system. We investigated the spatiotemporal variations of cirrus over the South China Sea (SCS) using satellite data (MOD08, MYD08, CALIPSO) and reanalysis data (MERRA-2) from March 2007 to February 2015 (eight years).The horizontal distribution reveals lower cirrus fraction values in the northern SCS and higher values in the southern region, with minima observed in March and April and maxima sequentially occurring in August (northern SCS, NSCS), September (middle SCS, MSCS), and December (southern SCS, SSCS). Vertically, the cirrus fraction peaks in summer and reaches its lowest levels in spring. Opaque cirrus dominates during summer in the NSCS and MSCS, comprising 53.6% and 55.9%, respectively, while the SSCS exhibits a higher frequency of opaque cirrus relative to other cloud types. Subvisible cirrus clouds have the lowest frequency year-round, whereas thin cirrus is most prominent in winter in the NSCS (46.3%) and in spring in the MSCS (45.3%). A case study from September 2021 further explores the influence of ice crystal habits on brightness temperature (BT) over the SCS. Simulations utilizing five ice crystal shapes from the ARTS DDA (Atmospheric Radiative Transfer Simulator Discrete Dipole Approximation) database and the RTTOV 12.4 radiative transfer model reveal that the 8-column-aggregate shape best represents BT in the NSCS and SSCS, while the large-block-aggregate shape performs better in the SSCS.