BOX 4.3

Response of Earth’s Radiation Budget to a Volcanic Eruption

The response of the radiation balance to the eruption of Mount Pinatubo was directly measured with broadband radiation instruments on Earth-orbiting satellites. This allowed not only a direct confirmation of the effect of stratospheric volcanic aerosols in reducing the energy balance but also verification of the model-predicted surface cooling in response to the eruption, giving additional confidence in our ability to model climate variability and change (Hansen et al. 1992, Minnis et al. 1993, Soden et al. 2002; Figure 4.9). The stratospheric aerosols resulting from the eruption were independently measured from Advanced Very High Resolution Radiometer (AVHRR) data and Stratospheric Aerosol and Gas Experiment SAGE data (McCormick et al. 1995). This is a prime example of how the length and continuity of a given data record yields additional scientific benefits beyond the initial research results of the mission and beyond the monitoring implications for operaitonal agencies.

FIGURE 4.9 Comparison of the observed anomalies in absorbed shortwave (top panel) and emitted longwave (bottom panel) radiative fluxes at the top of the atmosphere from ERBE satellite observations (black) and three ensembles of Global Climate Model (GCM) simulations (red). The observed anomalies are expressed relative to a 1984-1990 base climatology, and the linear trend is removed. The GCM anomalies are computed as the difference between the control and Mount Pinatubo simulations for each ensemble member (the Mount Pinatubo eruption of May 1991 is marked on the bottom panel). The results are expressed relative to the preeruption (January to May 1991) value of the anomaly and smoothed with a 7-month running mean (thick line). Both the model and the observed global averages are from 60° N to 60° S due to the restriction of observed data to these latitudes. SOURCE: Soden et al. (2002). Reprinted with permission from AAAS, copyright 2002.

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