Using model analysis and satellite data to assess cloud and precipitation in midlatitude cyclones

Midlatitude cyclones taken from 18 months of global operational Met Office Unified Model analysis archives were combined to form three-dimensional composite cyclones. Given an accurate dynamical and thermodynamical representation of the atmosphere from 4D-Var analysis, this study attributes differences between observations and the model cloud/precipitation to potential shortcomings in the physical parametrizations that control cloud/precipitation. Coincident (+/- 6 h) data from CloudSat radar, AMSR-E microwave, and ISCCP flux products were collected into composites for comparison. Only cyclones over the ocean were analysed here. Considering all of the observations in a single composite shows that horizontal slices through the composite display qualitative agreement between the mean reflectivity structures seen in the UM and CloudSat data. Splitting the composite cyclone into quadrants reveals that the UM underpredicts fractions of reflectivities greater than -20 dBZ and +10 dBZ at heights above 2 km in the poleward quadrants. This lack of cloud is manifested in smaller short-wave top-of-atmosphere fluxes from the UM composite cyclone than from the observations. Comparison of UM precipitation rates with CloudSat shows agreement to within the assumed potential bias of the observations. Copyright (C) 2011 British Crown copyright, the Met Office. Published by John Wiley & Sons Ltd.