Observed Covariations of Aerosol Optical Depth and Cloud Cover in Extratropical Cyclones

Using NASA Moderate Resolution Imaging Spectroradiometer aerosol optical depth and total cloud cover retrievals, CloudSat-CALIPSO cloud profiles, and a database of extratropical cyclones and frontal boundary locations, relationships between changes in aerosol optical depth and cloud cover in extratropical cyclones occurring over Northern Hemisphere oceans are examined. A reanalysis data set is used to constrain column water vapor and ascent strength in the cyclones in an attempt to distinguish their impact on cloud cover from the effect of changes in aerosol loading. The results suggest that high aerosol optical depth cyclones exhibit larger middleand high-level cloud cover than their low aerosol optical depth counterparts. However, the opposite behavior is found for low-level cloud cover. These relationships are found to depend on the large-scale environment, in particular the column water vapor and vertical motion. Despite the inability of the observations to provide a causal physical link between aerosol load and cloud cover, these results can help to constrain and evaluate model simulations.