Coordinated radar observations of atmospheric diurnal tides in equatorial regions

Abstract

The long-term behavior of atmospheric tides in the mesosphere and lower thermosphere has been observed with the meteor wind radar (MWR) in Jakarta, Indonesia (6• S, 107• E) from November 1992 to August 1997. The amplitudes and phases of the diurnal tides show systematic seasonal variations, particularly distinct in the meridional component. In addition, substantial interannual variability is evident, characterized by a biennial periodicity of tidal parameters, and considerably small tidal amplitudes exclusively seen in 1996. The MWR results are compared with the Global Scale Wave Model (GSWM) as well as MF radar data collected in two equatorial sites in Pontianak (0.03• N, 109• E) and Christmas Island (2 • N, 158• W) for November 1995-July 1997 and January 1996-October 1997, respectively. Comparison studies of these radar data have revealed the detailed latitudinal structure of the diurnal tide near the equator. The GSWM has successfully described the general characteristics of the radar results, although some discrepancies are recognized. In 1996 when radar data are available at all the three sites, the monthly mean values of tidal amplitudes at 90 km agreed very well between Jakarta and Pontianak, while significant discrepancy was found for Christmas Island, suggesting the existence of geographical effects such as non-migrating tides.

The diurnal and semidiurnal tides over Ascension Island (° S, 14° W) and their interaction with the stratospheric quasi-biennial oscillation: studies with meteor radar, eCMAM and WACCM

“…It is interesting to note that other ground-based studies have also observed tidal phase which increases with height at heights near 80 km (e.g. Tsuda et al, 1999;Buriti et al, 2008;Vincent et al, 1998). Considering the meridional wavelengths presented in Table 1, it can be seen that both observations and eCMAM indicate vertical wavelengths to be between 17 and 30 km for all months.…”

“…The results from this location are particularly interesting because it is at a similar latitude to Ascension Island but displaced by approximately 22 • westwards. Tsuda et al (1999) compared diurnal tide radar results between three equatorial sites and found good agreement between Jakarta (6 • S, 107 • E) and Pontianak (0 • N, 109 • W) but significant discrepancies with Christmas Island (2 • N, 158 • W). Friedman et al (2009) A number of studies have reported strong interannual variability of tidal amplitudes (e.g.…”

Vertical propagation characteristics and seasonal variability of tidal wind oscillations in the MLT region over Trivandrum (8.5° N, 77° E): first results from SKiYMET Meteor Radar

“…The GSWM02 model values also show that over this latitude the diurnal tidal amplitudes of the meridional wind are larger than that of zonal winds. The observations over other low latitude stations, such as Tirnelveli (8.7 • N) (Gurubaran and Rajaram, 1999) and Christmas Island (2 • N), (Chang and Avery, 1997;Manson et al, 1999;Tsuda et al, 1999), also reported that the amplitude of the meridional diurnal tide is greater than that of zonal diurnal component. The amplitude of meridional winds increases up to 90 km and then decreases during June, April and May.…”

“…It is also known that they are excited by soCorrespondence to: G. Ramkumar (geetha ramkumar@vssc.gov.in) lar heating of water vapor in the troposphere and ozone in the stratosphere. By realizing the importance of tidal activity, extensive wind observations in the MLT region have been carried out across the globe to explore its structure and dynamics (Tetenbaum et al, 1986;Avery et al, 1989;Manson et al, 1988;Portnyagin et al, 1992;Fraser et al, 1995;Tsuda et al, 1999;Zhang et al, 2004). Extensive studies have been carried out on tidal oscillations in the middle and high latitudes, whereas studies from the low-latitude MLT region are very limited (Reddi et al, 1993;Reddi and Ramkumar, 1997;Chang and Avery, 1997;Gurubaran and Rajaram, 1999).…”

Evidence for tropospheric wind shear excitation of high-phase-speed gravity waves reaching the mesosphere using the ray-tracing technique

“…As mentioned earlier, though tidal amplitudes are considered in the HWM-07 model, their day-to-day variability is not taken into account in the model. Amplitudes of the tides may reach values as high as 20 m s −1 over equatorial latitudes (Tsuda et al, 1999). As already mentioned, we have included day-to-day variability of tidal amplitudes into temperature and winds.…”