The Effect of Increasing C02 Amounts on TOVS Longwave Sounding Channels

Abstract

Radiative transfer models used in processing TIROS-N sounder data via Physical retrieval schemes do not explicitly account for changes in CO2 mixing ratio. However, CO2 mixing ratios have increased by approximately 30 ppmv over the past 17 years. A simulation study has been conducted using a line-by-line radiative transfer model to study the effect of increasing CO2 on the seven HIRS 15-µm channels used for temperature sounding. The mutts show that the brightness temperature differences can he as large as 1 K for a 30-ppmv CO2 increase and that a seasonal variation of a few tenths of a kelvin may exist. These deviations are of the same order as the standard deviations of brightness temperature expected from errors in a 6-h numerical weather prediction forecast in a data assimilation cycle.