Global Observations of Upper-Tropospheric Water Vapor Derived from TOVS Radiance Data

Abstract

Abstract This paper describes a physically based method for the retrieval of upper-tropospheric humidity (UTH) and upper-tropospheric column water vapor (UTCWV) based an the use of radiance data collected by the TIROS Operational Vertical Sounder (TOVS), principally channels 4 (14.2 μm), 6 (13.7 μm), and 12 (6.7 μm) of High-Resolution Infrared Radiation Sounder. This paper demonstrates how TOVS radiance data, particularly that of the upper-tropospheric water vapor channel 12, can be modeled usefully using a single band Malkmus model with parameters tuned to a particular sensor on a particular satellite. A significant uncertainty arises from the treatment of continuum absorption, even in regions where line absorption is dominant. This uncertainty can introduce a bias as large as 2 K, which in turn leads to an uncertainty of approximately 15%–20% in the retrieved UTH and UTCWV. The research described in this paper points to the critical need for high-accuracy measurements of upper-tropospheric water vapor t...