Coordinated radar observations of atmospheric diurnal tides in equatorial regions

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.