Evaluating Precipitation, Latent Heat Release and Potential Vorticity in Extratropical Cyclones in a High Resolution Climate Model using Reanalysis and Remote Sensing Data

Abstract:

Climate models must be capable of adequately simulating the processes that drive extratropical cyclones if they are to realistically represent their evolution and propagation. One such process which models need to capture is the magnitude and location of latent heat release within cyclones. Precipitation is closely related to column integrated latent heating, but both the magnitude and the (horizontal and vertical) location of the latent heat release in the context of the relative vorticity structure in a cyclone is important as the potential vorticity generation is determined by both of these factors. Here, an evaluation of precipitation and latent heat release in a climate model (HiGEM) is presented. The model is evaluated against a range of remote sensing data and global reanalyses (ERA-Interim) using an innovative storm compositing technique. Many studies compare models to reanalysis, but at the scale of individual weather systems, the latent heat release in global reanalyses may not be strongly constrained by the observations. Remote sensing data that measures processes associated with latent heat release is therefore employed to extend this work. Forward modelled radiances from the model and reanalysis are created using an offline simulator (COSP: CFMIP Offline Simulator Package) to provide fields that can be directly compared to remote sensing data from ISCCP (International Satellite Cloud Climatology Project) and CloudSat, in addition to direct comparison of the model and reanalysis data to the GPCP (Global Precipitation Climatology Project) dataset. The potential vorticity structure and evolution of composite extratropical cyclones is then compared in HiGEM and ERA-Interim, with starkly divergent results, which are related to differences in latent heating.