Interannual variabilty of the earth's radiation budget: some regional studies

Abstract

A detailed study is presented of the interannual variability of the Earth's radiation budget (ERB) at the top of the atmosphere in three equatorial regions: the western Pacific over Indonesia, the eastern Pacific off the west coast of South America and the eastern Atlantic off the west coast of Africa. The objective is to try and understand the cloud, surface and ERB interactions that occur in these areas, each of which shows a large interannual signal in the net radiation balance. The period studied extends from March 1979 through to April 1985, for which coincident ERB and cloud data are available from the Nimbus-7 ERB and Cloud Climatology data sets. This period encompasses the exceptional 1982–1983 ENSO as well as the 1984 Atlantic warming event. Additionally, sea-surface temperature data from the Global Ocean Surface Temperature Atlas (GOSTA) data set are used in combination with the ERB data to partition the outgoing longwave radiation into surface emission and greenhouse-effect components. The methodology involves examination of the time series of anomalies in all of these quantities together with the formulation of statistical relationships amongst them. These methods firstly allow the shortwave (SW) and longwave (LW) components of the ERB anomalies to be identified. The SW and LW anomalies are themselves seen to be made up of different components and, much like the net balance, are often the residuals of two competing effects. This is exemplified in the eastern Pacific and Atlantic regions, which both experienced periods of anomalously high SSTs. In such areas the SW anomaly can arise due to an imbalance between the cooling effect of increased high cloudiness and warming due to reduction of low level cloud, whilst the LW anomaly is composed of warming due to the increase in high cloud amount and cooling due to increased surface emission. The result is that anomalies in the net balance term, which is ultimately the most important with regard to climate variability, are seen to arise as a result of complex interactions between the atmosphere, cloudiness and surface. © 1997 the Royal Meteorologcal Society.