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Q. J. R. Mereorul. Soc. (1999). 125, pp. 2103-2126 The dependence of clear-sky outgoing long-wave radiation on surface
 

Summary: Q. J. R. Mereorul. Soc. (1999). 125, pp. 2103-2126
The dependence of clear-sky outgoing long-wave radiation on surface
temperature and relative humidity
By R. P. ALLAN'*,K. P. SHINE', A. SLINGO' and J. A. PAMMENT2
`Universiy of Reading, UK
Hadley Cenrre,forClimate Prediction and Research, Meteorological OfJlce. UK
(Received 16 January 1998;revised 10 August 1998)
SUMMARY
A simulation of the earth's clear-sky long-wave radiation budget is used to examine the dependence of clear-
sky outgoing long-wave radiation (OLR) on surface temperature and relative humidity. The simulation uses the
European Centre for Medium-Range Weather Forecasts global reanalysed fields to calculate clear-sky OLR over
the period from January 1979 to December 1993, thus allowing the seasonal and interannual time-scales to be
resolved. The clear-sky OLR is shown to be primarily dependent on temperature changes at high latitudes and on
changes in relative humidity at lower latitudes. Regions exhibiting a `super-greenhouse' effect are identified and
are explained by considering the changes in the convectiveregime associated with the Hadley circulation over the
seasonal cycle, and with the Walker circulation over the interannual time-scale. The sensitivity of clear-sky OLR
to changes in relative humidity diminishes with increasing relative humidity. This is explained by the increasing
saturation of the water-vapourabsorption bands with increased moisture. By allowing the relative humidity to vary
in specified vertical slabs of the troposphere over an interannual time-scale it is shown that changes in humidity
in the mid troposphere (400to 700 hPa) are of most importance in explaining clear-sky OLR variations. Relative

  

Source: Allan, Richard P. - Department of Meteorology, University of Reading

 

Collections: Geosciences