Long-term HIRS-based temperature and humidity profiles

Temperature and humidity profiles for climate applications are derived based on NOAA polar orbiting satellites' High-resolution Infrared Radiation Sounder (HIRS) observations. Global HIRS observations from more than a dozen satellites during the 1979-2017 time period are inter-calibrated to a base satellite to form a temporally homogeneous time series. A retrieval scheme is designed using a neural network technique to derive temperature profiles at standard pressure levels from the surface to lower stratosphere and humidity profiles from the surface to upper troposphere. The retrieval algorithm includes a two-tiered cloud screening method and calibration using radiosonde and Global Positioning System Radio Occultation (GPS RO) measurements. As atmospheric profiles over high surface elevations can differ significantly from those over low elevations, different neural networks are developed for several classifications of surface elevations. The significant impact from the increase of carbon dioxide in the last several decades on HIRS temperature sounding channel measurements is accounted for in the retrieval scheme. The cloud screening method incorporates Advanced Very High Resolution Radiometer (AVHRR) observations to assess the likelihood of cloudiness in HIRS pixels. Calibrating the retrievals with radiosonde and GPS RO reduces biases in retrieved temperature and humidity. Comparisons with independent observations will be presented.