Terdiurnal tides in the MLT region over Cachoeira Paulista (22.7ºS; 45ºW)

Abstract

Five years of winds measurements obtained by a SkiYmet meteor radar at Cachoeira Paulista (22.7 • S, 45.0 • W) are used to investigate the terdiurnal tide. This type of tide is frequently observed in the meteor region but the mechanisms responsible for its production are not yet completely explained. Among the possible causes are solar direct forcing and nonlinear interactions between the diurnal and semidiurnal tides. Nonlinear interaction between diurnal and semidiurnal tides can generate two secondary waves: a diurnal tide and a terdiurnal tide. The origin and seasonal distribution of the terdiurnal tide may indicate the presence of a secondary diurnal tide as a cause of variability in the primary diurnal tide. In this work we analyze the winds data in search of evidence for these mechanisms.

The 8-h tide in the mesosphere and lower thermosphere over Maui (20.75° N, 156.43° W)

“…The meridional component of Maui 8-h tide exhibits semiannual variations similar to those observed at Cachoeira Paulista (22.7 • S, 45 • W), a low-latitude station in the Southern Hemisphere (Tokumoto et al, 2007). The 8-h tides at both sites peak near the equinoxes and at higher altitudes.…”

“…The vertical wavelength reported by the previous studies was found to vary widely, over a range from 12 to more than 1000 km. At high-latitude, 68 • N, the vertical wavelength was from 31 km to 91 km (Younger et al, 2002); at mid-latitudes, ∼43-52 • N, the vertical wavelength varied in a large range from 22 to ≥1000 km (Thayaparan, 1997;Namboothiri et al, 2004); and at the low latitude of 22 • S shorter vertical wavelengths ∼12-32 km in the meridional wind were reported by Tokumoto et al (2007).…”

“…But, at the low latitude site in the Southern Hemisphere, Cachoeira Paulista (22.7 • S, 45 • W), the vertical wavelength of the 8-h tide in equinoxes is observed to be ∼12-20 km (Tokumoto et al, 2007). Furthermore, the vertical wavelengths observed at different stations are very different, and range from 12 km to more than 1000 km (Thayaparan, 1997;Namboothiri et al, 2004;Tokumoto et al, 2007). At present, the number of reported studies of the 8-h tide in the MLT region is insufficient for us to clearly understand the temporal and spatial patterns of this wave.…”

“…Moreover, the phase variation with Smith and Ortland (2001). But, at the low latitude site in the Southern Hemisphere, Cachoeira Paulista (22.7 • S, 45 • W), the vertical wavelength of the 8-h tide in equinoxes is observed to be ∼12-20 km (Tokumoto et al, 2007). Furthermore, the vertical wavelengths observed at different stations are very different, and range from 12 km to more than 1000 km (Thayaparan, 1997;Namboothiri et al, 2004;Tokumoto et al, 2007).…”

“…The features and seasonal variabilities of the diurnal tide and semidiurnal tide in the mesosphere and lower thermosphere (MLT) have been quite well investigated through observations and model simulations (Manson and Meek, 1986;Teitelbaum et al, 1989;Thayaparan, 1997;Pendleton et al, 2000;Smith, 2000;Smith and Ortland, 2001;Akmaev, 2001;Younger et al, 2002;Batista et al, 2004;Namboothiri et Correspondence to: G. Jiang (gyjiang@spaceweather.ac.cn) al., 2004;Taori et al, 2005;Zhao et al, 2005;Beldon et al, 2006;Tokumoto et al, 2007). Nevertheless, the 8-h tide, as a distinct wave signature in the MLT region, is not well understood, especially compared to the diurnal tide and semidiurnal tide.…”