On the variability of the quarter-diurnal tide in the MLT over Brazilian low-latitude stations

Abstract

The characteristic features of the quarterdiurnal tide (QDT) in the mesosphere and lower thermosphere (MLT) are investigated using meteor radar observations from three low-latitude southern hemispheric stations, Sao Joao do Cariri (7.4°S, 36.5°W), Cachoeira Paulista (22.7°S, 45°W) and Santa Maria (29.7°S, 53.7°W) in 2005. The QDT shows consistent appearance with a weak enhancement during late summer and fall interval. The QDT amplitudes are found to be much smaller (< 3 m/s) than the longer period tidal components most of the times of the year consistent with the previous investigations carried out from various locations over the globe. The vertical wavelength is found to reach up to 80 km in the MLT maximizing in winter although most of the times it remains within 20 km. Therefore, based on the observed characteristics of the QDT, it is surmised that both the migrating and nonmigrating components are involved in manifestation of the QDT at present locations. Further detailed investigations are sought in connection with the important issues pertained to the actual excitation mechanisms and existing dominant QDT modes in the low-latitude MLT.

Quarterdiurnal signature in sporadic E occurrence rates and comparison with neutral wind shear

“…This can be utilized to obtain information about the ionosphere and the neutral atmosphere. More detailed information on the principles of the RO technique is given by Hajj et al (2002) and Kursinski et al (1997).…”

“…The SNR is very sensitive to vertical variations of the electron density, and these occur within an Es layer. These vertically localized electron density variations lead to phase fluctuations of the GPS signal, which can be observed as changes in the received signal strength (Hajj et al, 2002). In order to avoid influences from the different basic signal power values on the further data analysis, every SNR profile is normalized first.…”

Forcing mechanisms of the migrating quarterdiurnal tide

“…They mainly found maxima during early and late winter at middle latitudes, which coincided with modeled vertical shear QDT maxima of the zonal wind. The QDT has also been observed in radar wind measurements in the MLT region (e.g., Sivjee and Walterscheid, 1994;Smith et al, 2004;Jacobi et al, 2017b;Guharay et al, 2018). Guharay et al (2018) analyzed the variability of the QDT in the MLT over Brazilian low-latitude stations and found QDT wind amplitudes that reach 2 ms −1 with a maximum during late summer and fall.…”

“…The QDT has also been observed in radar wind measurements in the MLT region (e.g., Sivjee and Walterscheid, 1994;Smith et al, 2004;Jacobi et al, 2017b;Guharay et al, 2018). Guharay et al (2018) analyzed the variability of the QDT in the MLT over Brazilian low-latitude stations and found QDT wind amplitudes that reach 2 ms −1 with a maximum during late summer and fall. Jacobi et al (2017b) analyzed MLT (80-100 km) radar data from Collm (51 • N, 13 • E) and Obninsk (55 • N, 37 • E).…”

“…The dynamics of the upper mesosphere and lower thermosphere (MLT) are strongly influenced by atmospheric waves, especially solar tides (Forbes, 1982a, b;Forbes et al, 1994;Manson et al, 1989;Hagan et al, 1995;Jacobi et al, 1999;Pancheva et al, 2002;Yigit and Medvedev, 2015). Tides are global-scale oscillations with periods of a solar day (24 h) and its harmonics (12, 8 and 6 h), which mainly result from the absorption of solar radiation by water vapor in the troposphere and ozone in the stratosphere (Chapman and S., 1970;Andrews et al, 1987;Xu et al, 2012).…”