Monday, 10 February 2003
Intraseasonal and Synoptic Variations of Radiation Budget
The Clouds and Earth Radiant Energy System instruments aboard the Terra spacecraft has provided measurements of outgoing longwave radiation (OLR) and reflected solar radiation (RSW) over the Earth for more than 2 years. The time histories of OLR and RSR are Fourier-analyzed for each 2.5 degree region of the globe. From these results the temporal spectra are computed for each region. Maps of spectral power of variations in the 20-60 day range are formed. At the Equator these variations are due to the Madden-Julian Oscillation and the OLR and RSW are quantified. Variations also occur at 20 degrees North and are shown to propagate from east to west. The peak centres of spectral power in the 20-60 day range are over the Equatorial Indian Ocean and the South China Sea. The Southwest Pacific Convergence Zone vacillates north and south on an intraseasonal time scale.
A map of spectral density for a 2-day period shows strongest variations at 10 degrees north and at 45 degrees north and south. The spectral density is assumed to have a power law distribution for the 2 to 20 days, and the exponent is found to have a low value (0.8 or less) in the 45 degree latitude zones over ocean and much higher elsewhere. The subsidence zones of the equatorial Pacific Ocean just west of South America, of the Atlantic Ocean between 10 and 20 degrees south and of the eastern Sahara Desert have very little variation at all time scales.