Observational Studies of Gravity Waves Associated with Convection

Abstract

Using twice-daily radiosonde data from Singapore taken over a 10 year timespan, equatorial short-period (1–3 day) waves are examined in terms of the quasi-biennial oscillation (QBO). Power spectra of temperature (T) and zonal wind (u) fluctuations have year-to-year variation synchronized with the QBO. In both QBO phases, the short-period waves have large variance, comparable to that of long-period (5–20 day) Kelvin waves in westerly shear. Synchronization with the QBO is also clear for cross spectra of T and u and particularly for the co-spectra. A new method is considered to estimate positive and negative momentum fluxes associated with oppositely propagating gravity and equatorial waves, separately. This method uses both quadrature and co-spectra of T and u. Results of an analysis of the Singapore data suggest that positive and negative momentum fluxes associated with short-period waves are largely cancelled and the summation of absolute values of the momentum flux are 3–10 times larger than that associated with long-period Kelvin waves. The importance of gravity waves with periods shorter than 1 day is also discussed.