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Stratospheric zonal wind and temperature oscillations observed in a 30 day time series of four times per day radiosonde data taken as part of Nauru99 show a strong negative quadrature relationship at periods of 9.5 days and 5 days. The 9.5‐day waves have vertical wavelength of about 4.5 km, and are deduced to be Kelvin waves of zonal wave number 2; the 5‐day waves have vertical wavelengths in the range of 3–4.5 km, and are deduced to be Kelvin waves of zonal wavenumber 4. Vertical momentum fluxes associated with the 9.5‐ and 5‐day modes are estimated to be 1×10 −4 m 2 s −2 and 2×10 −4 m 2 s −2 , respectively, in the 20–25 km altitude range where the mean zonal flow is characteristic of the westerly phase of the quasi‐biennial oscillation (QBO). These are an order of magnitude smaller than momentum fluxes associated with traditional wavenumber 1 Kelvin waves analyzed in the easterly phase of the QBO.
Holton et al. (Sat,) studied this question.