Abstract
Abstract. This paper presents a study of diurnal tidal winds observed simultaneously by two meteor radars located on each side of the Equator in the equatorial region. The radars were located in Santa Cruz, Costa Rica (10.3∘ N, 85.6∘ W) (hereafter CR) and São João do Cariri, Brazil (7.4∘ S, 36.5∘ W) (hereafter CA). The distance between the sites is 5800 km. Harmonic analysis has been used to obtain amplitudes and phases (hour of peak amplitude) for diurnal, semidiurnal and terdiurnal tides between 82 and 98 km altitude, but in this work we concentrate on the diurnal component. The period of observation was from April 2005 to January 2006. The results were compared to the Global Scale Waves Model (GSWM-09). Magnitudes of zonal and meridional amplitudes from November to January for CR were quite different from the predictions of the model. Concerning phases, the agreement between model and radar meridional tidal phases at each site was good, and a vertical wavelength of 24 km for the diurnal tide was observed practically every month, although on some occasions determination of the vertical wavelength was difficult, especially for the zonal component, due to nonlinear phase variations with height. For the diurnal zonal amplitude, there were notable differences between the two sites. We attribute this site-to-site difference of the diurnal zonal amplitude to the nonmigrating component of the tide and propose that an anomaly was present in the troposphere in the winter (Northern Hemisphere) of 2005–2006 which produced substantial longitudinal variation.
Highlights
Atmospheric tides are driven principally by solar heating, which results in significant day–night differential heating; they are dynamically very dominant at mesospheric and lower thermospheric heights
Interesting results include a peak in amplitude observed in the diurnal zonal amplitude at the Costa Rican site in December, which is not predicted by the model, and a clear antiphase between CR and CA in regard to the diurnal meridional component
Comparing zonal and meridional components observed in CR and CA, we can say that the meridional amplitude seems to be more accurately described by Global Scale Wave Model (GSWM)-09 than the zonal data
Summary
Atmospheric tides are driven principally by solar heating, which results in significant day–night differential heating; they are dynamically very dominant at mesospheric and lower thermospheric heights. The observed meridional diurnal phase in the equatorial region presents a more well-defined behavior as a function of altitude and season than the zonal component (Deepa et al, 2006; Buriti et al, 2008; Davis et al, 2013), which makes the calculation of the meridional vertical wavelength more accurate relative to the zonal component Perhaps this difference occurs because the nonmigrating tides have a relatively more important impact on the zonal wind field at low latitudes. Interesting results include a peak in amplitude observed in the diurnal zonal amplitude at the Costa Rican site in December, which is not predicted by the model, and a clear antiphase between CR and CA in regard to the diurnal meridional component
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