30-Year Atmospheric Temperatures Derived from Satellite Microwave Sounding Instruments Using a 1D-Var Approach

In past 30 years, satellite observations of the microwave radiation emitted from the atmosphere have been utilized for deriving the atmospheric temperature profiles. Specifically, the radiance measurements from Microwave Sounding Unit (MSU) on board the early National Oceanic and Atmospheric Administration (NOAA)-6 to NOAA-14 and Advanced Microwave Sounding Unit-A (AMSU-A) on board NOAA-15 to -19 have been reprocessed to form a fundamental climate data record (FCDR). The FCDR were inter-calibrated and the major anomalies related to the instrument calibration were removed. In this study, a climatology temperature profile is used as an initial guess in one-dimensional variation (1D-Var) retrieval to further derive the thematic CDR (TCDR) of atmospheric temperatures that are appropriate for climate change study. The retrieval temperature profiles are collocated with Global Positioning System (GPS) radio occultation (RO) data over global oceans and compared with the GPSRO temperature profiles. It is shown that the assimilation of MSU/AMSU-A four channels into the climatology profiles can produce a reasonably accurate temperature analysis in the troposphere, and the assimilation of AMSU-A 15 channels available since 1998 allows such a TCDR to be extended to the stratosphere and higher. The global climate trend of the atmospheric temperature deduced from the TCDR not only confirms a warming in the troposphere and a cooling in the stratosphere, but also a stronger warming in the upper troposphere than in the low troposphere.