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Estimation of outgoing longwave radiation from meteorological variables accessible from numerical models
Author(s) -
Jensenius John S.,
Cahir John J.,
Panofsky Hans A.
Publication year - 1978
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.49710443909
Subject(s) - outgoing longwave radiation , environmental science , cloud cover , radiant flux , atmospheric sciences , meteorology , dew point , climatology , statistics , mathematics , physics , convection , geology , cloud computing , quantum mechanics , computer science , operating system
A regression equation was developed and tested for directly estimating infrared flux density at the top of the atmosphere from variables available in numerical forecast models. The relation was developed in a stepwise procedure which used observed radiant flux density from the NOAA‐3 satellite in the 10.5 to 12.5 μ window as the predictand and predictors derived from the US National Meteorological Center's Limited Fine Meshm model which are believed to have associations with cloudiness and with temperature. The equation was developed from continental data for the winter of 1974/5 and tested on data for February 1976, for which the weather regime was significantly different. By far the best predictor was the Planck function calculated from a temperature which approaches the boundary layer temperature when the 500mb dewpoint depression is large, and an upper tropospheric temperature when it is small. This variable alone accounted for almost 61% of the variance of the predictand in the initial sample. Four additional predictors increased the explained variance to over 67%. The corresponding variance explained in the test sample increased to over 71%. The distribution of mean fluxes at each gridpoint was especially well described. The mean field estimated by the equation explained over 97% of the variance of the mean observed field in the initial sample and almost 95% in the test sample. On a daily basis, predicted fields of radiant flux density appeared to be somewhat smoother than the observed fields, but the regression equation rather accurately predicted the location of relative radiant flux density minima caused by clouds having cold tops. When combined with a similar relation for reflected shortwave radiation, this equation offers a method of estimating the radiation balance at the top of a numerical model atmosphere which allows for cloudiness change without explicit prediction of cloudiness. The present paper illustrates the method for the restricted case of longwave radiation over a continent in winter.