An Intercomparison of Temperature and Moisture Fields Derived from TIROS Operational Vertical Sounder Data by Different Retrieval Techniques. Part I: Basic Statistics

Abstract

Fields of temperature, thickness and precipitable water, derived from common sets of Tiros Operational Vertical Sounder (TOVS) radiance data have been intercompared. These fields were produced by a variety of institutions using different retrieval techniques. The fields have been derived over three regions; the Alpine Experiment (ALPEX) in 1982, the Tasman Sea, and the United States. Basic statistics have been produced by comparing these derived fields to analyses produced by the European Centre for Medium Range Weather Forecasts (ECMWF), and with collocated radiosonde (RAOB) data. In most cases it appeared, for both physical and statistical retrieval techniques, that in the midtroposphere (700 to 400 mb) the satellite temperature soundings exhibited rms temperature differences of near 2 K when compared to ECMWF analysis or collocated radiosonde data. These figures include significant contributions due to radiosonde error, collocation differences, analysis error and other factors. Diferent vertical resolutions among the compared fields contributed to the larger differences which were evident near the tropopause and the surface. Near the surface the differences appeared to be more a function of the use of ancillary data or constraints, rather than the retrieval scheme. Basic statistics for thickness and moisture fields have also been presented in this study.