Large-scale Changes in Marine Fog in a Warmer Climate

Abstract:

Marine fog especially over the mid-latitude ocean is an important target in climate simulation because it affects maritime traffic in human lives and the sky obscuring marine fog is a contributor to the earth radiation budget due to its significant coverage. The purpose of the present study is to reveal global-scale changes in marine fog in a warmer climate.

The changes in marine fog with climate change are investigated using AMIP, AMIP4K (where a uniform +4 K SST is added to the AMIP SSTs), and AMIPfuture (where a patterned SST perturbation is added to the AMIP SSTs) experiment data simulated by the MRI-CGCM3 (Yukimoto et al. 2012), which was used for CMIP5 runs. First, the representation of the fog in the model was examined using ship observation data and cloud mask data retrieved from CALIPSO satellite data (Kawai et al. 2015). The comparison showed that the MRI-CGCM3 can represent the climatological global distribution of marine fog relatively well. Basically marine fog represented by the model is warm air advection fog, and it was found that the change in the horizontal temperature advection near the surface mostly determines the changes in marine fog in a warmer climate. Therefore, the changes in marine fog can be almost explained by the large-scale circulation changes. On the other hand, in-cloud LWC (liquid water content) of the fog is consistently increased in a warmer climate for the same horizontal surface temperature advection. The changes in mid-latitude marine fog in both the northern and southern hemispheres and for both summer and winter seasons are discussed in connection with the large-scale circulation changes.