Intersatellite Calibration of HIRS Upper Tropospheric Water Vapor

Intersatellite calibration is carried out for the upper tropospheric water vapor (UTWV) data from clear-sky HIRS channel 12 measurement. As the intersatellite biases are scene brightness temperature dependent, an algorithm is developed to account for the varying biases with respect to brightness temperature. The bias correction data are derived from overlaps of monthly means of each 10-degree latitude belt. For the colder temperature range, data from the simultaneous nadir overpass observations are incorporated. The HIRS measurements from the NOAA series of polar orbiting satellites are calibrated to a baseline satellite. The time series of the intersatellite calibrated HIRS UTWV data from late 1970s to present is constructed and anomaly data are computed. The anomaly time series is used to track tropical waves and variability. The HIRS UTWV anomaly data are particularly useful in monitoring the Madden-Julian oscillation and various equatorial waves.