On the occurrence and variability of the terdiurnal tide in the equatorial mesosphere and lower thermosphere and a comparison with the Kyushu-GCM

Abstract

[1] We studied the occurrence characteristics and variability of the terdiurnal tide (8 hour period) in the equatorial mesosphere and lower thermosphere (MLT), using a meteor radar at Koto Tabang (0.2°S, 100.3°E) and MF radars at Tirunelveli (8.7°N, 77.8°E) and Pameungpeuk (7.4°S, 107.4°E). These locations, one being located right over the equator and the other two at conjugate points around the equator within ±10°, form a unique experimental setup to study equatorial MLT dynamics. The terdiurnal tide exists as a distinct wave signature at all three locations. While the daily amplitudes can be as large as 15 m s −1 , the monthly mean amplitudes lie between 1 and 10 m s −1 . The amplitude of the terdiurnal tide at Pameungpeuk is generally smaller than that observed at Tirunelveli and Koto Tabang. The seasonal variation in amplitude shows both annual and semiannual oscillations of ∼1 m s −1 at all three locations. The present observations combined with previous reports indicate that the timing of the primary maximum of the terdiurnal tide amplitude shifts from autumn to late spring and early summer as one moves from high latitudes to the equator (all with respect to the Northern Hemisphere). The amplitudes and seasonal variation in the present observations show good comparison with that simulated by the General Circulation Model (GCM) developed by Kyushu University, Japan. This study supports the occurrence of nonlinear interaction between diurnal and semidiurnal tides and shows that gravity waves play an important role in the generation of the terdiurnal tide.Citation: Venkateswara Rao, N., T. Tsuda, S. Gurubaran, Y. Miyoshi, and H. Fujiwara (2011), On the occurrence and variability of the terdiurnal tide in the equatorial mesosphere and lower thermosphere and a comparison with the Kyushu-GCM,

Observations of OI 557.7 nm nightglow at Kolhapur (17° N), India

“…An analysis of the entire OI 557.7 nm intensity and OH temperature database indicates that the long period temporal variations are probably driven by a terdiurnal tide on most occasions, and OI 557.7 nm intensity variation leads that of OH temperature variation by less than an hour. These observations of terdiurnal tides from Kolhapur (16.8 • N) are consistent with the recent report of terdiurnal tides in the meteor wind data from Tirunelveli (8.7 • N) by Rao et al (2011). On a few occasions, similar waves (having periodicity in the range of 2-3 h) were noted in OI 557.7 nm intensity and OH temperature series.…”

“…This is the first report of terdiurnal tides observed in the nightglow measurements over the Indian subcontinent. Many previous works have reported the observations of 8 h tide in the MLT region (for example, Glass and Fellons, 1975;Teitelbaum et al, 1989;Oznovich et al, 1995Oznovich et al, , 1997Thayaparan, 1997;Taylor et al, 1999;Smith, 2000;Younger et al, 2002;Taori et al, 2005;Wu et al, 2005;Beldon et al, 2006;Jiang et al, 2009;Rao et al, 2011). Glass and Fellons (1975) and Teitelbaum et al (1989) suggested that this wave can be interpreted both as the solar driven terdiurnal tide and as the result of nonlinear interaction between diurnal and semi-diurnal tides.…”

“…Smith (2000) reported the latitudinal structure and seasonal variation of the terdiurnal tides using the wind observations of HRDI instrument on-board UARS. Younger et al (2002) investigated the 8 h tidal phenomena Rao et al (2011) have reported the occurrence and variability of terdiurnal tides in the MLT region over Tiruneveli (8.7 • N, 77.8 • E), Koto Tabang (0.2 • S, 100.3 • E), and Pameungpeuk (7.4 • S, 107.4 • E) using meteor wind radar measurements. It is worthy to mention here that Tirunelveli is an equatorial station located within a distance of 9 • from Kolhapur -the site of current study.…”

A case study of mesospheric planetary waves observed over a three-radar network using empirical mode decomposition

“…The yield of mesospheric wind data depends on the occurrence of echoes, the electron densities, and the strength of the scatters (Gregory et al, 1982). The Kototabang radar is an all-Sky interferometric meteor radar (SKiYMET), the details of which are well described by Venkateswara Rao et al (2011). Briefly, the radar operates at a frequency of 37.7 MHz with an output power of 12 kW, installed at the ERA (equatorial atmosphere radar) site.…”

A remarkable correlation between short period gravity waves and semiannual oscillation of the zonal wind in the equatorial mesopause region

“…Short data gaps in the 10 min time series were linearly interpolated. From this dataset, contributions from diurnal, semi-, ter-, and quarter-diurnal tides are removed (Venkateswara Rao et al, 2011b). Then, GW variance is calculated for three bands of periods (20-120 min, 2-10 h, 10-20 h).…”