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Balloon-borne observations of short vertical wavelength gravity waves and interaction with QBO winds
  • Robert A. Vincent,
  • M. Joan Alexander
Robert A. Vincent
University of Adelaide, University of Adelaide
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M. Joan Alexander
NorthWest Research Associates, CoRA Office, NorthWest Research Associates, CoRA Office

Corresponding Author:[email protected]

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The quasi-biennial oscillation (QBO), a ubiquitous feature of the zonal mean zonal winds in the equatorial lower stratosphere, is forced by selective dissipation of atmospheric waves that range in periods from days to hours. However, QBO circulations in numerical models tend to be weak compared with observations, probably because of limited vertical resolution that cannot adequately resolve gravity waves and the height range over which they dissipate. Observations are required to help quantify wave effects. The passage of a superpressure balloon (SPB) near a radiosonde launch site in the equatorial Western Pacific during the transition from the eastward to westward phase of the QBO at 20 km permits a coordinated study of the intrinsic frequencies and vertical structures of two inertia-gravity wave packets with periods near 1-day and 3 days, respectively. Both waves have large horizontal wavelengths of about 970 and 5500 km. The complementary nature of the observations provided information on their momentum fluxes and the evolution of the waves in the vertical. The near 1-day westward propagating wave has a critical level near 20 km, while the eastward propagating 3-day wave is able to propagate through to heights near 30 km before dissipation. Estimates of the forcing provided by the momentum flux convergence, taking into account the duration and scale of the forcing, suggests zonal force of about 0.3-0.4 m/s/day for the 1-day wave and about 0.4-0.6 m/s/day for the 3-day wave, which acts for several days.