Nimbus-7 observations of the effect of clouds on the earth's radiation budget
Date
1990-08
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Journal ISSN
Volume Title
Abstract
Outgoing longwave (LW) flux and shortwave (SW) albedo data obtained from narrow field-of-view scanner measurements aboard the Nimbus-7 satellite are used along with coincident cloudiness data to estimate the effect of clouds on the earth's radiation budget (ERB). A simple technique is described to obtain clear sky albedos and LW fluxes using daily Nimbus-7 ERB and total cloud amount data. The analysis is done for the following four seasons: June-August 1979, September-November 1979, December-February 1980, and March-May 1980. When compared with the recent results from the Earth Radiation Budget Experiment (ERBE) the Nimbus-7 derived clear sky LW and SW fluxes are about 5-6 Wm-2 too low and 3-4 Wm-2 too high, respectively, most likely resulting from cloud contamination. The concept of cloud radiative forcing, referred to in this study as cloud effect, can provide a quantitative measure of the impact of clouds on the ERB. It is defined as the difference between the clear sky flux and the cloudy sky flux at the top of the atmosphere. The SW cloud effect is shown to be negative over most of the earth and is greatest in the midlatitudes in areas of stratus clouds and storm tracks. The LW cloud effect, on the other hand, is primarily positive and most significant in the tropics. The net cloud effect is found to be negative over most of the earth, with a near cancellation of the SW and LW effects in the tropics and a significant negative effect in the midlatitudes. Moreover, it is shown that the net cloud effect, when globally averaged, is negative and varies with season. A comparison of the Nimbus-7 derived LW and SW cloud effects to those obtained from ERBE shows, on average, a 5-6 Wm-2 bias resulting from cloud contamination of the Nimbus-7 clear sky fluxes.
Description
August 1990.
Rights Access
Subject
Nimbus (Artificial satellite)
Nimbus Project (U.S.)
Meteorological satellites
Clouds -- Observations