SHORT-PERIOD DISTURBANCES IN THE EQUATORIAL LOWER STRATOSPHERE

Temperature and horizontal wind fluctuations with periods shorter than 3 days in the equatorial lower stratosphere are examined by using dat a from routine rawinsonde observations at Singapore (1N, 104E) during 1978-1993. Internal wave-like structures having a period of about 2 da ys and a short vertical wavelength of 5 km are occasionally observed b oth in temperature and wind fluctuations. The result of power spectral analysis indicates that short-period fluctuations have significant en ergy, separated from Kelvin waves and mixed Rossby-gravity waves. Long -term variations of the spectral characteristics are investigated in r elation to the quasi-biennial oscillation (QBO). Zonal wind and temper ature variances due to the short-period fluctuations are generally lar ge and particularly enhanced in the QBO phase when the direction of me an wind changes from easterly to westerly. Co-spectra of temperature a nd zonal wind fluctuations at short periods are significantly larger t han the quadrature spectra, and the sign of co-spectra changes accordi ng to the phases of the QBO. These results indicate strong connection of the short-period disturbances with the QBO.