Mean winds, tides, and gravity waves during the westward phase of the mesopause semiannual oscillation (MSAO)

Abstract

Abstract. MF radar observations of mean winds, tides, and gravity waves (in the period range 30-120 min) over Tirunelveli (8.7øN, 77.8øE) during April 1993, when the mesopause semiannual oscillation (MSAO) was in the westward phase, are presented in this work. The focus herein is on the observed relationship between these dynamical parameters, which is explained in the context of the current understanding of the behavior of MSAO winds, tidal dissipation, and gravity wave-tide interactions. The observed diurnal tide amplitude and phase variations with height indicate (1,1) wave damping and subsequent westward momentum deposition. The gravity wave variances are shown to be modulated by the diurnal tide. Though the analysis does not lead to an estimation of gravity wave contributions to the time-mean zonal flow and its shears, the observations do suggest that the short-term tidal variability contributes, either directly, or indirectly through the gravity wave-tidal interactions, to the variation of the strength of the time-mean westward flow associated with the MSAO.

On the variability of the seasonal scale oscillations over Cachoeira Paulista (22.7°S, 45°W), Brazil

“…Wu et al (2008) concluded a possible relationship of weak gravity wave filtering and strong migrating diurnal tide filtering associated to westerly phase of the SQBO. Gurubaran and Rajaram (2001) inferred the possible role of interaction between the gravity waves and diurnal tide to alter the strength of the easterly phase of the MSAO. Unfortunately, in the present study, we are unable to verify the role of gravity waves with the present low temporal resolution wind data.…”

Observation of semiannual and annual oscillation in equatorial middle atmospheric long term temperature pattern

“…variation of solar zenith angle with the season and incident solar flux change throughout the year. Tides and gravity waves and their mutual interaction can be an important factor for modification of such seasonal scale variability (Gurubaran and Rajaram, 2001). Kelvin waves can be an important contributor for the generation of the stratospheric SAO as suggested by Hirota (1978).…”

Spatial and frequency characteristics of equatorial enhancement of geomagnetic field variations

“…In recent years, in situ measurements of neutral winds by MF radar at equatorial station Tirunelvelli (dip lat. 0:18 • N) have conÿrmed the presence of gravity waves in the period range of 30 -120 min (Gurubaran and Rajaram, 2001). However, the precise nature of the link between these gravity waves with electric and related magnetic ÿelds is yet to be established conclusively.…”