The quality of layer-mean temperatures and humidities retrieved with the improved initialization inversion (3I) (version 2) algorithm from measurements of the TIROS operational vertical sounder (TOVS) radiometer has been studied for two summer periods in 1987 and 1990 in the Weddell Sea region (Antarctica) by means of collocations with radiosoundings, European Centre for Medium-Range Weather Forecasts (ECMWF) analyses and special sensor microwave/imager (SSM/I) retrievals. Appropriate corrections of the atmospheric transmission functions have been used for the two periods. A significant influence on the accuracy of the retrievals has been observed. Collocation statistics with radiosoundings for layer-mean temperatures based on 160 cases show very satisfying results.

The standard deviation is very close to the deviations expected from collocation errors alone, but an overall negative bias of the retrieved temperatures is observed. Considerably smaller biases in clear conditions sugget that the frequent cloudy situations are one reason. The atmospheric stability index derived from the retrievals corresponds well to the observations. However, surface inversions and inversions capping the boundary layer (being characteristics of the polar environment) cannot be resolved by the TOVS. Layer-mean humidities and integrated water vapor content are calculated by the 3I algorithm with a good absolute accuracy and errors are comparable to those occurring at lower latitudes. But problems have been found in the ability to correctly retrieve varying water vapor contents in different situations which is caused by weak signals in the very dry Antarctic conditions. Comparisons of the total water vapor content to results based on SSM/I measurements show a good agreement between the two different instruments and retrieval methods. Comparisons of temperature and humidity retrievals to ECMWF analyses show a better correspondence between retrievals and analyses or 1990, related probably to model and assimilation system changes. The ECMWF analyses show deviations from radiosoundings comparable to those of the retrievals emphasizing the value of TOVS retrievals as an important source of information in this data-sparse region. ¿ American Geophysical Union 1995