Monday, 14 January 2002: 4:00 PM
Temporal spectra of Earth radiation budget components
The Clouds and Earth Radiant Energy System (CERES) instrument flew aboard the Terra spacecraft in December 1999. It has since provided broadband measurements of outgoing longwave radiation (OLR) and of reflected solar radiation (RSR). from the Earth for over a year. When daily global maps of these parameters are viewed in sequence as a movie, variations of OLR and RSR at a wide range of temporal and spatial scales are seen. These variations are of special interest when weekly means are first computed so as to eliminate synoptic variations. The yearly cycles are quite pronounced. Intraseasonal variations are seen, especially in the Tropics, with effects propagating to higher latitudes. These intraseasonal variations are due to weather patterns which persist well beyond the traditional concept of predictability and require research to understand. Due to the duration of the patterns, there is ample time for radiation to interact with dynamics in their development.
In order to study these variations of OLR and RSR, the time history is Fourier-analyzed for each 2.5 degree region of the globe. From these results the temporal spectra are computed for each region. The question then arises: how does one examine the temporal spectrum for a map? The approach here is to form a movie in which the temporal frequencies are viewed in sequence, i.e one exchanges the time domain for the Fourier domain. Another approach is to integrate the spectra over selected frequency domains, e.g. corresponding to 20 to 60 days, and form maps of these partial variances.
The time history can also be reassembled from the Fourier description using any desired set of frequencies so as to separate seasonal, intraseasonal and synoptic effects and hopefully simplify the variations to permit the development of insight into the physics of these variations.