Validation of Met Office upper stratospheric and mesospheric analyses

The accuracy of Met Office middle atmospheric analyses is investigated via direct validation against observational temperature data from two independent satellite instruments. A climatology of monthly zonal mean temperature biases from January 2005 to December 2010 is presented. For analyses produced before October 2009 there is a consistent cold bias of ∼30–40 K in the polar winter lower mesosphere, suggestive that gravity wave forcing in this region is too weak. Such cold biases are accompanied by smaller-magnitude cold biases in the opposing summer hemisphere, most likely associated with compensating warm biases from an insufficient gravity wave-driven circulation and cold biases resulting from deficiencies in radiative heating due to the operational ozone climatology. For analyses produced after October 2009, where the model lid was raised to include the upper mesosphere, cold biases in the winter lower mesosphere are reduced. However, systematic warm biases of ∼40–60 K in the summer upper mesosphere again suggest that gravity wave forcing within the operational system is underestimated. The absence of cold biases in the winter upper mesosphere also suggests that radiative errors contribute significantly in this region.