Simulation of Mt. Pinatubo Volcanic Aerosol with the Hamburg Climate Model ECHAM4 |
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| Authors: | C Timmreck H-F Graf J Feichter |
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| Institution: | (1) Max-Planck Institut für Meteorologie, Hamburg, Germany, DE |
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| Abstract: | Summary We study the three-dimensional transport of Mt. Pinatubo volcanic cloud with the climate model ECHAM4. In order to obtain
model results comparable with observations a Newtonian relaxation technique was applied, which forces prognostic model variables
towards the observations. A comparison of the simulated aerosol distribution with satellite data reveals good agreement for
the first months after the eruption. The model, however, is unable to simulate the tropical aerosol maximum in 1992 and also
overestimates the vertical downward and northward transport of aerosols. Substantial improvement was achieved with the introduction
of reduced advective vertical transport through the 380 K isentropic layer. Heating rates and top of the atmosphere fluxes,
which were calculated online for the first half year after the eruption, are in the observed range. A comparison of Pinatubo
simulations between three different vertical ECHAM4 versions (ECHAM4 L19, ECHAM4 L39, MA/ECHAM4) indicates that a vertical
resolution of ≈ 700 m in the tropopause region is sufficient to realistically reduce the vertical transport through the tropopause.
Consideration of the upper branch of the Brewer Dobson circulation in the MA/ECHAM4 model improves the geographical distribution
of the volcanic cloud. The application of a relaxation technique can further reduce major shortcomings of stratospheric simulations
with the standard climate model. There remain, however some critical points in the global transport characteristics in all
three models which are not fully understood.
Received December 19, 1997 Revised July 22, 1998 |
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