Global distribution of maritime low clouds with an emphasis on different aerosol types and meteorological parameters inferred from multi-satellite and reanalysis data during 2007-2016

The present study investigates the comparison of spatiotemporal distributions of maritime cloud top height (CTH) and aerosol optical depth (AOD) based on level 3 products of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Moderate-resolution Imaging Spectroradiometer (MODIS) sensors. Besides, the latest cloud and aerosol products from CALIPSO and Modern Era Retrospective-Analysis for Research (MERRA-2) reanalysis meteorology variables, the response of marine low cloud amount (LCA) as the function of occurrence frequencies of different aerosols (AOF), including clean marine (CM), Desert Dust (DD), and Dusty Marine (DM, the mixed type of CM and DD) are explored for the period 2007-2016. The study suggests, on an annual mean, the total agreement between CALIPSO and MODIS is 72.2%/69.5% during the daytime/nighttime for MLC (marine low cloud) and NMLC (not marine low cloud). It is revealed that the CALIPSO captures 11.4%/15.3% of MLC and 88.6%/84.7% of NMLC. While the MODIS captures 20.4% MLC and 79.6% NMLC during both day and nighttimes, partly due to the misidentification of MLC as aerosols by MODIS. Meanwhile, the discrepancy of AOD between MODIS and CALIPSO is approximately 0.053 on the annual scale, which is likely caused by detection sensitivity and surface reflectance models. Further, we have noticed that the aerosol effects on MLC are dependent on their types. It is evident that the CM tends to invigorate MLC and promote more LCA, and DD inclines to inhibit MLC and contribute to less LCA. However, DM shows the net significant aerosol effect on MLC possibly due to the contrasting aerosol effect of CM and DD. We also found that these aerosol invigoration or suppression effects on MLC present the non-monotonic mode under the condition of heavy aerosol loading.

Automated summary

The study explores the comparison of spatiotemporal distributions of maritime cloud top height (CTH) and aerosol optical depth (AOD) between CALIPSO and MODIS, revealing discrepancies in the identification of marine low clouds and the influence of different types of aerosols on these clouds. The annual total agreement between CALIPSO and MODIS is around 72.2%/69.5% during the daytime/nighttime for marine low clouds (MLC) and not marine low clouds (NMLC). Furthermore, different aerosol types have varying effects on MLC, with clean marine aerosols tending to invigorate MLC, desert dust aerosols inhibiting MLC, and mixed aerosols showing significant effects possibly due to the contrasting effects of clean marine and desert dust aerosols.