Utility of AIRS Retrievals for Climate Studies

摘要

Satellites provide an ideal platform to study the Earth-atmosphere system on practically all spatial and temporal scales. Thus, one may expect that their rapidly growing datasets could provide crucial insights not only for short-term weather processes/predictions but into ongoing and future climate change processes as well. Though Earth-observing satellites have been around for decades, extracting climatically reliable information from their widely varying datasets faces rather formidable challenges. AIRS/AMSU is a state of the art infrared/microwave sounding system that was launched on the EOS Aqua platform on May 4, 2002, and has been providing operational quality measurements since September 2002. In addition to temperature and atmospheric constituent profiles, outgoing longwave radiation [OLR] and basic cloud parameters are also derived from the AIRS/AMSU observations. However, so far the AIRS products have not been rigorously evaluated/validated on a large scale. Here we present preliminary assessments of climatically important "Level3" (monthly and 8-day means, 1° × 1° gridded) AIRS "Version 4.0" retrieved products (available to the public through the DAAC at NASA/GSFC) to assess their utility for climate studies. Though the current AIRS climatology covers only ～4.5 years, it will hopefully extend much further into the future. First we present "consistency checks" by evaluating the ～4.5-yr long time series of global and tropical means, as well as grid-scale variability and "anomalies" (relative to the first full years worth of AIRS "climate statistics" of several climatically important retrieved parameters). Finally, we also present preliminary results regarding interrelationships of some of these geophysical variables, to assess to what extent they are consistent with the known physics of climate variability/change. In particular, we find at least one observed relationship which contradicts current general circulation climate (GCM) model results: the global water vapor climate feedback which is expected to be strongly positive is deduced to be slightly negative (shades of the "Lindzen effect"?).