Interannual variations of surface radiation budget

The NASA/GEWEX Surface Radiation Budget (SRB) data set covers the 22-year period from July 1983 through June 2005. The interannual variations of shortwave downward flux (SWD), longwave upward flux (LWU) and longwave downward flux (LWD) at the surface are computed using the monthly means. Variations of SWD are due to variations of cloud, whereas variations of LWU are due to variations of surface temperature. Variations of LWD can be due to variations in fraction of coverage and altitude of clouds and to variations of atmospheric temperature and humidity. Whereas the diurnal and annual cycles of radiation components are due to cycles of insolation, interannual variations are due to free variations of the coupled cryosphere-ocean-atmosphere-land system.

The root-mean-squares of the interannual variations are 14.9 W m^-2 for SWD, 6.8 W m^-2 for LWU, and 7.3 W m^-2 for LWD. A principal component analysis was performed on each component. The eigenvalues for the principal components decrease quite slowly with order. For SWD, the largest principal component describes the El Nino. The next term shows a definite trend of increasing SWD over the data period. Artifacts of the data set appear in higher order principal components. Current research is examining the relation of the principal components to interannual variations of other processes.