Gerstell, M. F. and Crisp, Joy and Crisp, David (1995) Radiative Forcing of the Stratosphere by SO_2 Gas, Silicate Ash, and H_2SO_4 Aerosols Shortly after the 1982 Eruptions of El Chichón. Journal of Climate, 8 (5). pp. 1060-1070. ISSN 0894-8755 http://resolver.caltech.edu/CaltechAUTHORS:20120712-081103844
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The 1982 eruptions of the El Chichón volcano injected large quantities of sulfur dioxide gas and silicate ash into the stratosphere. Several studies have shown that the long-lived sulfuric acid aerosols derived from these volcanic effluents produced measurable changes in the radiative heating rates and the global circulation. The radiative and dynamical perturbations associated with the short-lived but more strongly absorbing sulfur dioxide and ash clouds have received much 1ess attention. The authors therefore used an atmospheric radiative transfer model and observations collected by satellites, aircraft, and ground-based observers to estimate the amplitudes of the stratospheric radiative heating rate perturbations produced by each of these components during the first few weeks after the El Chichón eruption. One week after the 4 April 1982 eruption, net radiative heating rate perturbations exceeding 20 K per day were found at altitudes near 26 km. The absorption of sunlight by the silicate ash accounts for the majority of this heating. The sulfur dioxide gas and sulfuric acid aerosols each produced net heating perturbations that never exceeded 3 K per day. In spite of the intense heating by the ash, observations indicate that stratospheric temperatures never increased by more than a few degrees Kelvin. The authors therefore concluded that this radiative heating was largely balanced by upwelling and adiabatic cooling. The amplitude and spatial extent of this upwelling was estimated with a diagnostic, two-dimensional dynamical model. The ash heating rates may have been balanced by a global enhancement in the stratospheric meridional circulation, with zonally averaged upward velocities of about 1 cm sec^(−1) near the latitude of the plume. This enhanced stratospheric circulation persisted only for a few weeks but it may have played a major role in the vertical and horizontal dispersal of the plume. The vertical transport needed to balance the heating by sulfur dioxide gas was only 5%–10% as large, but this perturbation may have produced a 2-km increase in the altitude of the plume. These results suggest that the radiative forcing by the ash and the sulfur dioxide gas should be included in more comprehensive models of the plume evolution. They also suggest that particle size distributions inferred from ash fallout rates could be wrong if the upwelling associated with this radiative heating is not considered.
|Additional Information:||© 1995 American Meteorological Society. Manuscript received 15 March 1994, in final form 14 September 1994. We thank Ian Sprod and Arlin Krueger for providing TOMS sulfur dioxide data. We thank Frank Eparvier for providing a preprint of his SME aerosol columns. We acknowledge use of the ISCCP-C2 database for 1984-86. We are grateful for the detailed comments of two anonymous referees. Support for this study was provided by the NASA Global Change Research Program, the NASA Volcano- Climate Interactions Program, and the NASA Upper Atmosphere Research Program. The work by J. Crisp and D. Crisp was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contracts with the National Aeronautics and Space Administration. The work by M. Gerstell was carried out at the California Institute of Technology in partial fulfillment of the requirements for a Ph.D. degree in the Division of Geological and Planetary Sciences, under a contract with the National Aeronautics and Space Administration.|
|Official Citation:||Gerstell, M. F., Joy Crisp, David Crisp, 1995: Radiative Forcing of the Stratosphere by SO2 Gas, Silicate Ash, and H2SO4 Aerosols Shortly after the 1982 Eruptions of El Chichón. J. Climate, 8, 1060–1070. doi: http://dx.doi.org/10.1175/1520-0442(1995)008<1060:RFOTSB>2.0.CO;2|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||13 Jul 2012 17:27|
|Last Modified:||26 Dec 2012 15:30|
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