Extension of HIRS Derived Upper Tropospheric Humidity Record with IASI Measurement

Operational routine satellite infrared sounder measurements of upper tropospheric humidity (UTH) started with the High-resolution Infrared Radiation Sounder (HIRS) instrument on board Television InfraRed Observation Satellite N (TIROS-N), which was launched in 1978. Since then, the UTH measurement has been continuously produced from the National Oceanic and Atmospheric Administration (NOAA) and Meteorological Operational satellite (Metop) polar-orbiting satellites. The UTH is derived from one of the HIRS channels, channel 12. A HIRS UTH climate data record was developed at the National Centers for Environmental Information (NCEI) and has been maintained for more than a decade. This dataset has supported numerous studies on the UTH variability and its relationship with large-scale atmospheric circulations. However, with the aging and failure of present HIRS instruments, there is a need to use new satellite measurements to extend and continue the UTH time series. We are using the Infrared Atmospheric Sounding Interferometer (IASI) to produce HIRS-like longwave channel brightness temperatures. Inter-instrument and inter-satellite calibrations are further performed to homogenize IASI simulated HIRS (IHIRS), specifically channel 12. The new version of the infrared sounder UTH dataset, which includes HIRS and IASI measurements, is now produced operationally.