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  • Author or Editor: K. Strabala x
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W. P. Menzel, D. P. Wylie, and K. I. Strabala

Abstract

GOES VAS multispectral observations in the carbon dioxide absorption band at 15 μm have been used to compile cloud-cover statistics over the continental United States for the past 4 years. The CO2 technique calculates both cloud-top pressures and effective emissivities and reliably distinguishes semitransparent cirrus from opaque clouds. The frequency of semitransparent cirrus clouds exhibits small seasonal variation; they are generally present 25%–30% of the time in all seasons. Diurnal variations of semitransparent cirrus are found only in the summer months and correspond to diurnal variations in convection in the Rocky Mountains and southeastern United States, increases of 20% in cirrus are noted subsequent to the convective cloud activity. In the winter months, no diurnal change in semitransparent cirrus is detected. Attempts to correlate cirrus with some common atmospheric features reveal that a majority of cirrus occurred where dynamic parameters indicate rising vertical motion but that considerable cirrus were also found where the dynamics was weak. Intercomparison with ground reports of cloud cover reveals that the satellite observations are corroborating or complementary 80% of the time; many of the disagreements come from the satellite identifying cold ground as low cloud or ground observations missing high thin clouds.

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S. A. Ackerman, A. S. Bachmeier, K. Strabala, and M. Gunshor

Abstract

A cold, dry arctic air mass occupied southeastern Canada and the northeastern United States on 13–14 January 2004. This air mass was quite dry—total column precipitable water values at Pickle Lake, Ontario, Canada, and The Pas, Manitoba, Canada, were as low as 0.02 in. (0.5 mm)—allowing significant amounts of radiation originating from the surface to be detected using Geostationary Operational Environmental Satellite (GOES) 6.5-μm “water vapor channel” imagery. On this day the strong thermal gradient between the very cold snow-covered land surface in southern Canada and the warmer, unfrozen, cloud-free water along the northern portion of the Great Lakes was quite evident in GOES-12 imager water vapor channel data. Several hours later, as the cold dry air mass moved eastward, the coast of Maine, Cape Cod, and the Saint Lawrence River were also apparent in the water vapor channel imagery.

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