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The sensitivity of long‐wave radiation fields and the response of a GCM to water‐vapour continuum absorption
Author(s) -
Haigh Joanna D.
Publication year - 1999
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.1999.49712555614
Subject(s) - emissivity , radiation , infrared window , environmental science , water vapor , atmospheric sciences , latitude , computational physics , sky , infrared , climatology , meteorology , physics , materials science , optics , geology , astronomy
A wide‐band radiation model has been used to assess the impact of various models of the water‐vapour continuum on the infrared radiation fields of a three‐dimensional clear‐sky climatology and also on the climate of a general‐circulation model with fixed sea surface temperatures. The radiation model uses the emissivity method based on narrow‐band model and line‐by‐line transmittance calculations with four different continuum models: (a) a mainly window region, based on empirical fitting and ‘dimer’ method, (b) an implementation of the line‐wings method CKD‐0, (c) an implementation of the updated CKD version 2.2 and (d) CKD‐2.2 with a stronger temperature dependence in the window region based on aircraft and satellite measurements. The CKD methods decrease outgoing long‐wave radiation by about 5 W m ‐2 and increase downward radiation at the surface by about 3.5 W m ‐2 in the clear‐sky climatology. The difference between the CKD versions is less than 0.5 W m ‐2 in both fields. The stronger temperature dependence causes only a small further decrease in outgoing long‐wave radiation but a further 2.5 W m ‐2 in downward radiation at the surface. The spectral composition of all these changes, and its impact on the latitude‐height heating‐rate structure, is discussed. The changes in the radiation fields of the GCM are consistent with those shown in the clear‐sky climatology but the decrease in static stability, caused by the heating‐rate changes, results in modifications to the strength of the Hadley cells, mid‐latitude eddy heat transport, relative humidity and surface sensible and latent‐heat fluxes.