The Influence of the QBO and Solar Variability on the North Annular Mode.

Details The Influence of the QBO and Solar Variability on the North Annular Mode. The Influence of the QBO and Solar Variability on the North Annular Mode.

May 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.a14a..05r&link_type=abstract

American Geophysical Union, Spring Meeting 2004, abstract #A14A-05

Physics

1610 Atmosphere (0315, 0325), 1620 Climate Dynamics (3309), 1650 Solar Variability, 3362 Stratosphere/Troposphere Interactions

Scientific paper

The Quasi-Biennial Oscillations (QBO) and solar variability are two natural stratospheric forcings affecting atmospheric dynamics and possibly climate. We study how these forcings affect the major mode of the wintertime atmospheric variability in the Northern Hemisphere, the North Annular Mode (NAM). This mode extends from the top of the stratosphere through the troposphere to sea level accounting for 22% of the variance in geopotential heights at sea level and more in the stratosphere (Thompson and Wallace, 1998; Baldwin and Dunkerton, 1999). It has been found (Ruzmaikin and Feynman, 2002) that the NAM of the coupled troposphere-stratosphere is influenced by decadal solar variability. But the influence depends on the phase of the QBO and phase of the winter season. Thus, in early (late) winter for the West (East) QBO, the NAM is more positive for low UV than for high UV fluxes. The effect was shown to be statistically significant. Here we present the results of our search for a physical mechanism by which the QBO and solar variability combined with seasonality affect the NAM. Because the NAM is excited in the interplay between the planetary waves and mean zonal wind (see for example Limpasuvan and Hartmann, 2000), we investigate the latitudinal, vertical and time distributions of the wave (EP) fluxes employing the NCEP Reanalysis Data and the ECMWF Data. We also investigate the possible effect of the QBO associated circulation on the NAM. References: Baldwin, M. P. and T. J. Dunkerton, J. Geophys. Res. 104, 30,937, 1999; Limpasuvan, V., and D. L. Hartmann, J. of Climate, 4414, 2000; Ruzmaikin, A., J, Feynman, J. Geophys. Res., 107, D14, 10.1029/2001JD001239, 2002; Thompson, D. W. J. and J. M. Wallace, Geophys. Res. Lett., 25, 1297, 1998.

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