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In this paper, we examine how clouds over snow and ice affect ozoneabsorption and how these effects may be accounted for in satelliteretrieval algorithms. Over snow and ice, the Aura Ozone MonitoringInstrument (OMI) Raman cloud pressure algorithm derives an effectivescene pressure. When this scene pressure differs appreciably from thesurface pressure, the difference is assumed to be caused by a cloudthat is shielding atmospheric absorption and scattering belowcloud-top from satellite view. A pressure difference of 100 hPa isused as a crude threshold for the detection of clouds thatsignificantly shield tropospheric ozone absorption. Combining the OMIeffective scene pressure and the Aqua MODerate-resolution ImagingSpectroradiometer (MODIS) cloud top pressure, we can distinguishbetween shielding and non-shielding clouds.  To evaluate this approach, we performed radiative transfer simulationsunder various observing conditions. Using cloud vertical extinctionprofiles from the CloudSat Cloud Profiling Radar (CPR), we find thatclouds over a bright surface can produce significant shielding (i.e.,a reduction in the sensitivity of the top-of-the-atmosphere radianceto ozone absorption below the clouds). The amount of shieldingprovided by clouds depends upon the geometry (solar and satellitezenith angles) and the surface albedo as well as cloud opticalthickness. We also use CloudSat observations to qualitativelyevaluate our approach. The CloudSat, Aqua, and Aura satellites fly inan afternoon polar orbit constellation with ground overpass timeswithin 15 min of each other.  The current Total Ozone Mapping Spectrometer (TOMS) total column ozonealgorithm (that has also been applied to the OMI) assumes no cloudsover snow and ice. This assumption leads to errors in the retrievedozone column. We show that the use of OMI effective scene pressuresover snow and ice reduces these errors and leads to a more homogeneousspatial distribution of the retrieved total ozone

What do satellite backscatter ultraviolet and visible spectrometers see over snow and ice? A study of clouds and ozone using the A-train