Quantification of the contribution of equatorial Kelvin waves to the QBO wind reversal in the stratosphere

Abstract

Both global scale waves (e.g., Kelvin, equatorial Rossby, or Rossby-gravity waves) and mesoscale gravity waves contribute to the wind reversals of the quasi biennial oscillation (QBO). The relative contributions of the different wave types are highly uncertain. In our work we quantify the contribution of equatorial Kelvin waves to the reversal from stratospheric easterlies to westerlies averaged over two QBO cycles in the period 2002-2006. Our analysis is based on longitude-time spectra of temperatures measured by the SABER satellite instrument, as well as temperatures from ECMWF operational analyses. Kelvin waves of zonal wavenumber 1-6 and periods longer than 2.5 days are covered. It is found that the contribution of Kelvin waves is about 30-50% of the observed wind reversal and only 20-35% of the expected total wave forcing. The larger part of the wave forcing therefore has to be contributed by other waves, likely mesoscale gravity waves. Copyright 2009 by the American Geophysical Union.