Cross Correlations between the Radiation and Atmospheric Variables in a General Circulation Model and in Satellite Data

Abstract

The classical picture of the influence of midlatitude troughs on cloud patterns is investigated in a general circulation model (GCM) and in satellite and National Meteorological Centre (NMC) data by comparing the cross correlation of the poleward component of the wind and the outgoing longwave radiation (OLR). The GCM stimulation is found to compare quite well with data for the bandpass (2.5- to 6-day) waves over the midlatitudes. Over the storm tracks, a significant portion of the variance of the OLR is explained by a correlation with the poleward component of the horizontal wind; this is forced, as expected, by stronger correlations with the vertical velocity through the cloud and humidity fields. The correlation of broadband OLR and tropospheric temperature is generally small over short time scales and more significant over land than over water. The GCM wind-OLR correlation is a maximum for bandpass waves of synoptic (spherical harmonic wavenumber 8?15) dimension, but it shows only a small variation with the temporal or spatial scale or with the height of the wind. Stratiform clouds are found to have a dominant impact on the model OLR fluctuations, even over much of the tropics.