Middle Atmosphere Climatologies from the Troposphere–Stratosphere Configuration of the UKMO’s Unified Model

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Abstract
A climatology of the middle atmosphere is determined from 11-yr integrations of the U.K. Meteorological Office Unified Model and compared with 18 years of satellite observations and 5 years of data assimilation fields. The model has an upper boundary at 0.1 mb, and above 20 mb uses Rayleigh friction as a substitute for gravity wave drag. Many of the results are, however, found to be relatively insensitive to enhancing the damping above 0.3 mb. As with most general circulation models, the polar night jet in both hemispheres is too strong and does not have the observed equatorward slope with height. The model suffers from the common “cold pole” problem and, apart from a local warm pool centered just below 100 mb in northern high latitudes in January, and another at about 30 mb at 70°S in July, has a cold bias throughout the stratosphere. At the level where polar stratospheric clouds occur, the temperature bias is about −4 K in the Northern Hemisphere and up to +6 K in the Southern Hemisphere. For t... Abstract A climatology of the middle atmosphere is determined from 11-yr integrations of the U.K. Meteorological Office Unified Model and compared with 18 years of satellite observations and 5 years of data assimilation fields. The model has an upper boundary at 0.1 mb, and above 20 mb uses Rayleigh friction as a substitute for gravity wave drag. Many of the results are, however, found to be relatively insensitive to enhancing the damping above 0.3 mb. As with most general circulation models, the polar night jet in both hemispheres is too strong and does not have the observed equatorward slope with height. The model suffers from the common “cold pole” problem and, apart from a local warm pool centered just below 100 mb in northern high latitudes in January, and another at about 30 mb at 70°S in July, has a cold bias throughout the stratosphere. At the level where polar stratospheric clouds occur, the temperature bias is about −4 K in the Northern Hemisphere and up to +6 K in the Southern Hemisphere. For t...

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