Nonlinearity of the combined warm ENSO and QBO effects on the Northern Hemisphere polar vortex in MAECHAM5 simulations



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Calvo Fernández, Natalia and Giorgetta, Marco A. and García Herrera, Ricardo and Manzini, Elisa (2009) Nonlinearity of the combined warm ENSO and QBO effects on the Northern Hemisphere polar vortex in MAECHAM5 simulations. Journal of geophysical research-atmospheres, 114 . ISSN 2169-897X

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The influence of the quasi-biennial oscillation (QBO) on the Northern Hemisphere (NH) polar vortex response to warm El Nino-Southern Oscillation (ENSO) events and the impact of the warm ENSO events on the QBO signal in the NH polar stratosphere have been analyzed using the Middle Atmosphere ECHAM5 model. The experiment setup was designed to include simulations of extended NH winter seasons for either strong easterly or strong westerly phases of the tropical QBO, forced with either sea surface temperatures (SSTs) from the strong ENSO event that occurred in 1997/1998 or with climatological SSTs. It has been found that the weakening and warming of the polar vortex associated with a warm ENSO are intensified at the end of the winter during both QBO phases. In addition, the westerly QBO phase delays the onset of the warm ENSO signal, while the easterly QBO phase advances it. Warm ENSO events also impact the extratropical signal of the QBO by intensifying ( weakening) the QBO effects in early ( late) winter. Therefore, it appears that during warm ENSO events the duration of QBO signal in the northern extratropics is shortened while its downward propagation accelerated. Our dynamical analysis has revealed that these results are due to changes in the background flow caused by the QBO combined with changes in the anomalous propagation and dissipation of extratropical waves generated by warm ENSO. In both cases, a nonlinear behavior in the response of the polar vortex is observed when both warm ENSO and the easterly phase of the QBO operate together. These results suggest that the Arctic polar vortex response to combined forcing factors, in our case warm ENSO and the QBO phenomena, is expected to be nonlinear also for other coexistent forcing factors able to affect the variability of the vortex in the stratosphere.

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© 2009 by the American Geophysical Union.
N. Calvo was supported by the visitor program of the Max Planck Institute for Meteorology in Hamburg, the Spanish Ministry of Education and Science, and the Fulbright Commission in Spain. The simulations described here were carried out on the NEC-SX6 computer at the German Climate Computing Center (DKRZ). We thank Rolando R. García and Daniel Marsh for their helpful comments and suggestions.

Uncontrolled Keywords:Quasi-biennial oscillation; Interannual variability; Solar-cycle; Stratosphere; Circulation; Model; Atmosphere
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
ID Code:34499
Deposited On:26 Nov 2015 16:45
Last Modified:10 Dec 2018 15:05

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