Equatorial waves in temperature in the altitude range 4 to 70 km

Abstract

SUMMARYUsing altitude pro les of temperature in the range 4 to 70 km derived from Mesosphere-StratosphereTroposphere radar and lidar observations at Gadanki (13.5 ± N, 79.2 ± E) from 18 January 1999 to 5 March 1999, characteristics of equatorial waves are studied. Two-dimensional Fourier-transform analysis of the temperature pro les is carried out to identify the periodicities and their vertical wave numbers. From the characteristics obtained, equatorial slow Kelvin waves with periodicities 15.7 d, 9.4 d, 7.8 d and 6.7 d are identi ed in the troposphere and stratosphere regions and among these 7.8 d and 6.7 d periodicities are found to penetrate into the mesosphere. Equatorial waves with smaller periodicities in the range 5.2 d to 3.6 d are also observed. The vertical ux of horizontal momentum (zonal) of the identi ed slow Kelvin-wave periodicities in the altitude region 4-25 km is estimated. It is found that equatorial waves modulate tropical tropopause temperature and altitude.

A study of tropical tropopause using MST radar

“…In the summer seasons there were a couple of days with cloudy skies (during the observation period) which were not included in the analysis. It may be noted here that the method of Revathy et al (1996) has been successfully used for the studies on the diurnal variation of troposphere temperatures and equatorial waves (Revathy et al, 2001;Krishna Murthy et al, 2002). The temperature profiles thus obtained and the vertical wind profiles (from MST radar) form the basic data for obtaining the tropopause altitude (and temperature), according to its definitions given above.…”

Study of equatorial Kelvin waves using the MST radar and radiosonde observations

“…They reported increased Kelvin-wave variance accompanying the descent of the westerly phase of the QBO, with the largest amplitudes occurring in the westerly shear zone. Equatorial wave characteristics have been reported in several studies (Salby et al, 1984;Dhaka et al, 1995;Krishna Murthy et al, 2002;Fujiwara et al, 2003) using temperature observations. Tsuda et al (1994a,b) conducted an observational campaign for 24 days in Watukosek, Indonesia (7.6 • S, 112.7 • E).…”

“…These waves showed downward phase progression with an average vertical wavelength of 10 km. More recently, Krishna Murthy et al (2002), using radar and Lidar data, identified equatorial slow Kelvin waves with different periodicities from 6-16 days in the troposphere and stratosphere regions. They found that equatorial waves modulate tropical tropopause temperature and altitude.…”

Rayleigh lidar observations of planetary waves in the middle atmosphere over Gadanki (13.5°N, 79.2°E)

“…More recently, two unique campaigns of coordinated measurements have been conducted for studies on equatorial waves with emphasis on estimation of momentum fluxes. The first one involved 45 days of simultaneous measurements by co-located Rayleigh lidar and Indian MST radar (Krishna Murthy et al, 2000) and the second one employing lidar, MST radar and rockets (Krishna Murthy et al, 2002).…”