Infrared retrievals of dust using AIRS: Comparisons of optical depths and heights derived for a North African dust storm to other collocated EOS A‐Train and surface observations

Abstract

AIRS thermal infrared radiance data are used with a fast infrared scattering radiative transfer model to physically retrieve the dust column amount and dust height over both ocean and land. The retrieved optical depths are compared against those retrieved using visible and ultraviolet instruments on the A‐Train, while dust layer heights are evaluated against lidar data. The synergistic use of AIRS data is explored by using dust layer heights constrained by CALIPSO retrievals and coarse mode particle sizes over ocean from PARASOL. Optical depths from AIRS correlate well with those from other instruments over ocean (R ≥ 0.9) and are lower over land when compared to MODIS Deep Blue and OMI retrievals (R ≤ 0.8). AIRS‐derived dust top heights compare favorably with CALIPSO data and can be used to improve OMI optical depth retrievals over a much larger area than CALIPSO can provide. AIRS data can also provide estimates of dust longwave radiative forcing. For the examples examined here, the forcings are estimated to be about +1.5 and +4.5 W/m2 per unit visible optical depth over ocean and land, respectively, compared to a shortwave forcing estimate of −50 W/m2 over ocean. AIRS dust retrievals are possible day or night, can provide dust column amount information over land or ocean, and are unaffected by areas of the oceans covered by sun glint.