Decadal Variability in Tropical Broadband Radiation Budget

Top-of-atmosphere (TOA) broadband reflected shortwave (SW: 0.2 to 5.0 microns) and broadband outgoing Longwave (LW: 5.0 to 50.0 microns) radiation observations collected from the NASA Earth Radiation Budget Experiment (ERBE) nonscanner instruments on the Earth Radiation Budget Satellite (ERBS) between January 1985 to September 1999 are used to examine the long term climate variability of the TOA tropical radiative energy budget. This dataset indicates a rise in the TOA tropical outgoing LW radiation with a corresponding fall in TOA tropical reflected SW radiation over the span of the 15-year period. These observed decadal features in TOA tropical radiative energy budget are validated against observations taken from three totally independent broadband radiation data sources; the ERBE/ERBS Scanner dataset (1985 to 89), the Scanner for Radiation Budget (ScaRAB) dataset (1994 to 95), and the Clouds the Earth's Radiant Energy System (CERES/TRMM) dataset (1998). Specifically, remarkable agreements are found between the scanner and the nonscanner datasets when the various scanner datasets are overlaid onto the nonscanner long term time series. While the exact cause of this observed decadal variability in tropical radiative energy budget is currently under investigation, it is clear from this study that a continuous, long term observation of TOA broadband SW and LW radiation is necessary for detecting and understanding long time scale climate variability and climate change.