Variational bias correction in ERA-Interim

TitleVariational bias correction in ERA-Interim
Publication TypeMiscellaneous
Year of Publication2008
AuthorsDee, DP, Uppala, S
Secondary TitleTechnical Memorandum

This paper describes the performance of the variational bias correction system for satellite radiance data in ERA-Interim, and considers implications for the representation of climate signals in reanalysis. We briefly review the variational formulation of the method and its ability to automatically develop bias estimates when newly available radiance measurements are first introduced. We then present several results obtained from the first 16 years (1989-2004) of ERA-Interim. These include the identification of MSU instrument calibration errors, the response of the system to the Pinatubo eruption in 1991, some difficulties in constraining model errors in the upper stratosphere, and the detection of a long-term drift in biases of tropospheric AMSU-A data. We find that our results support the notion that global reanalysis provides an appropriate framework for climate monitoring and climate change assessment.