Variations in Cloudiness, Temperature and Satellite-Derived Outgoing Longwave Radiation for Alaska,
ALASKA UNIV FAIRBANKS GEOPHYSICAL INST
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Monthly values of outgoing longwave radiation OLR from 1974 to 1990 were obtained from NOAA satellites. Seasonal variations in the OLR were related to cloudiness and surface temperature data for Alaska. It was found that higher amounts of cloudiness increase the OLR in winter for most of Alaska, but decrease it in summer. For one particular location, Barter Island, trends in cloudiness, temperature, and OLR will be discussed and the seasonal sensitivity of OLR to changes in cloud amount will be examined. For Barter Island, a decrease of less than 7 in the amount of cloudiness was found to decrease the OLR by 5 W m-2 during the spring months, a season in which cloudiness and OLR are positively correlated. During the summer, however, OLR and cloudiness are anti-correlated owing to the relatively cold radiative temperatures at cloud-top height compared to the surface temperature in the absence of strong surface temperature inversions, which persist for most of the rest of the year. Hence relatively small changes in the amount of cloudiness may have a large effect on the radiation balance in the Arctic, even more so than changes expected due to increasing concentration of C02 and other radiatively active gases. As parameterization of sky cover in GCMs is not well advanced, studies like this should help in a better quantitative understanding of sky cover and OLR.
- Atmospheric Physics