Dynamical mechanism for the increase in tropical upwelling in the lowermost tropical stratosphere during warm ENSO events

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The Brewer-Dobson circulation strengthens in the lowermost tropical stratosphere during warm El Nino-Southern Oscillation (ENSO) events. Dynamical analyses using the most recent version of the Whole Atmosphere Community Climate Model show that this is due mainly to anomalous forcing by orographic gravity waves, which maximizes in the Northern Hemisphere subtropics between 18 and 22 km, especially during the strongest warm ENSO episodes. Anomalies in the meridional gradient of temperature in the upper troposphere and lower stratosphere (UTLS) are produced during warm ENSO events, accompanied by anomalies in the location and intensity of the subtropical jets. This anomalous wind pattern alters the propagation and dissipation of the parameterized gravity waves, which ultimately force increases in tropical upwelling in the lowermost stratosphere. During cold ENSO events a similar signal, but of opposite sign, is present in the model simulations. The signals in ozone and water vapor produced by ENSO events in the UTLS are also investigated.
© 2010 American Meteorological Society. The National Center for Atmospheric Research is sponsored by the National Science Foundation. N. Calvo was supported by the Spanish Ministry of Education and Science, the Fulbright Commission in Spain, and the visitors' program of the Atmospheric Chemistry Division at the National Center for Atmospheric Research (NCAR). She was also partially supported by the Spanish Ministry of Education and Sciences under Contract CGL2007-65891-C05-02/CLI (TRODIM project). WACCM calculations presented in this paper were carried out at NCAR; at the NASA Advanced Supercomputing Division, Ames Research Center; and at the Oak Ridge Leadership Computing Facility of the U. S. Department of Energy.
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