Stratospheric and tropospheric SSU/MSU temperature trends and compared to reanalyses and IPCC CMIP5 simulations in 1979–2005

Abstract. Using the satellite temperature measurements from the Stratospheric Sounding Units (SSU) and Microwave Sounding Units (MSU including the advanced microwave sounding unit, AMSU) since 1979, the trends and uncertainties in the fifth Coupled Model Intercomparison Project (CMIP5) model simulations from the middle troposphere to the upper stratosphere (5–50 km) have been explored. The temperature trend discrepancies between the new generation reanalyses are investigated. Both the temporal character of the global mean temperature and the regional spatial pattern of the temperature trends are discussed. The results show that the CMIP5 model simulations reproduced common stratospheric cooling and tropospheric warming features although a significant discrepancy among the selected models was observed.

For the temporal variation of the global mean temperature, the CMIP5 simulations reproduce the volcanic signal and were highly consistent with the SSU measurements in the upper stratosphere. In contrast, the CFSR and MERRA reanalyses (excluding ERA-I) exhibit a different result from the CMIP5 simulations. For the spatial variation of the temperature trends, the CMIP5 simulations displayed a different latitudinal-longitudinal pattern from SSU/MSU measurements in all six layers from the middle troposphere to the upper stratosphere. The CFSR reanalysis shows a good spatial correlation with satellite observations in the troposphere but poor spatial correlation in the stratosphere. The ERA-I and MERRA reanalyses have good spatial correlation in the upper stratosphere and an even better spatial correlation in the troposphere.

Generally, the CMIP5 simulations significantly underestimated the stratospheric cooling in the tropics and substantially overestimated the cooling over the Antarctic in the MSU observations. The largest trend spread among the seven CMIP5 simulations is seen in both the south- and north-polar regions in the stratosphere and troposphere. The tropospheric spread values are generally smaller than the stratospheric spread values.