The contributions of the equatorial waves to the quasi-biennial oscillation (QBO) are investigated using Hadley Centre Global Environment Model version 2 (HadGEM2). A gravity wave parameterization that couples its source spectrum to the convection is used. The equatorial wave modes are identified in the spectral domain, based on their distinct characteristics associated with momentum and heat fluxes. The Kelvin waves and parameterized gravity waves (PGWs) transport westerly momentum into the equatorial stratosphere by ~0.35 and 0.8 mPa, respectively, while easterly momentum is carried primarily by the PGWs (~0.75 mPa). The resolved inertio-gravity (IG) waves transport both easterly and westerly momentum by ~0.2 mPa. In the lowermost stratosphere, gradual dissipation of the Kelvin waves occurs, and the remaining waves induce eastward forcing in the westerly shear layer by 3-5 m s-1 month-1. The PGWs primarily dissipate within the sheared layer and provide large easterly and westerly forcing in the middle stratosphere (~17 m s-1 month-1), while the forcing in the lower stratosphere is comparable to the Kelvin wave forcing. The IG wave forcing is small because of the small wave dissipation rate. The Rossby and mixed Rossby-gravity (MRG) waves contribute to the westerly-to-easterly QBO transition by ~2 m s-1 month-1. The magnitudes of the simulated Kelvin and Rossby wave forcings are comparable with the Modern-Era Retrospective Analysis for Research and Applications, whereas the MRG and IG wave forcings are underestimated in the lower stratosphere. Differences between the simulation and reanalysis and the uncertainties in both are discussed.
Bibliographical noteFunding Information:
This work was supported by the Korea Meteorological Administration (KMA) Research and Development Program under grant CATER 2012-3054. The use of HadGEM2 was licensed by the MOU between the KMA and the UK Met Office. For the simulation output or the source code of the CGW parameterization, please contact the corresponding author of this article. The MERRA data are available at the public website of the Global Modeling and Assimilation Office (http://gmao.gsfc.nasa.gov/).
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All Science Journal Classification (ASJC) codes
- Aquatic Science
- Water Science and Technology
- Soil Science
- Geochemistry and Petrology
- Earth-Surface Processes
- Atmospheric Science
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science