CLIMATE PARAMETERS FROM SATELLITE SPECTRAL MEASUREMENTS .1. COLLOCATED AVHRR AND HIRS 2 OBSERVATIONS OF SPECTRAL GREENHOUSE PARAMETER/

An automated method of monitoring various climate parameters using col located Advanced Very High Resolution Radiometer (AVHRR) and High-Reso lution Infrared Sounder-2 (HIRS/2) observations has been developed. Th e method, referred to as CHAPS (collocated HIRS/2 and AVHRR products) was implemented during the months of July 1993 and January and July 19 94. This paper presents the oceanic cloud screening method and analysi s of the spectral greenhouse parameter (g(lambda)) for July 1993 and J anuary 1994. In addition, the CHAPS derived clear-sky parameters are c ompared to the NESDIS historical dataset. There is agreement between N ESDIS and CHAPS for the g(6.7) and g(7.3). The NESDIS 8.2-mu m data ap pears to be cloud contaminated. Through comparison with CHAPS, it is s uggested that the mode, rather than the mean, provides the better esti mate of the central tendency of the NESDIS clear-sky 8.2-mu m radiance distribution, particularly for regions with extensive low-level cloud cover. It is shown that the spectral greenhouse parameter at waveleng ths sensitive to middle and upper atmospheric water vapor content is d ependent on SST via its connection to large-scale atmospheric circulat ion patterns. It is also shown that the variability of the spectral gr eenhouse parameter is strongly a function of latitude at these wavelen gths, as well as in spectral regions sensitive to lower-level water va por. Standard deviations are largest in the Tropics and generally decr ease poleward. In contrast, variability in the spectral regions sensit ive to upper-tropospheric temperature peaks in the middle latitudes an d has its minimum in tropical latitudes. Variability in the relationsh ip between g(lambda) and SST shows only a weak dependence on season fo r channels sensitive to water vapor content. A strong seasonal depende nce is found in the g(14.2) for the middle-latitude regions associated with changes in the temperature structure of the upper troposphere. T he relationship between the spectral greenhouse parameter and the broa dband greenhouse parameter is presented and discussed. It is found tha t the range in broadband g for warm tropical SSTs is driven by spectra l changes at wavelengths sensitive to upper-tropospheric water vapor. For cooler SSTs associated with the middle latitudes, the range in g i s a function of the spectral greenhouse parameter sensitive to the tem perature structure of the upper troposphere.