On the connection between SST, surface convergence and precipitation in the Extratropics

This presentation examines the linkages between Extratropical sea surface temperature (SST), near-surface convergence, surface moisture flux and precipitation in a variety of datasets. A major aim is to assess how well the SST-precipitation relationship is represented in CESM, focusing on the convective parameterization part. It will include some discussion of the sensitivity to time and space scales, and the role of synoptic systems and fronts. The datasets used include CESM1 (high resolution), ERA5, TRMM, IMERG/GPM, J-OFURO, OAFLUX, CCMP. One of the results is that the convective part in CESM1 responds more strongly to SST than in ERA5, and that overall the CESM response is stronger than in the satellite IMERG dataset. Another result is that the near-surface convergence responds to gradients of SST as predicted by boundary layer theory, but is only notable for time scales greater than ~10 days and short space scales (e.g. < 500km). Discussion points of this talk include whether the results would change for later versions of CESM, or for km-scale resolutions.