Observations of the ultra-fast Kelvin wave in the tropical mesosphere during equinox

Regular and systematic measurements of mesospheric temperatures have been carried out during March and April 2007 to determine planetary-scale wave activities in the tropical region, utilizing ground-based Rayleigh Light Detection and Ranging (LiDAR) and satellite-based Microwave Limb Sounder (MLS) data from Gadanki, India (13.5° N, 79.2° E) and MLS data over a site in North America (23.5° N, 100° W). A dominant component of the 3–5 day period wave is revealed at four altitudes (80, 70, 60 and 50 km) over the two observation stations. The estimated vertical wavelength (∼40 km), zonal phase speed (∼140 m s⁻¹), longitudinal and latitudinal extensions have suggested the wave to be an ultra-fast Kelvin (UFK) wave with zonal wave number 1. In addition to the UFK wave, a probable quasi 2 day Rossby gravity wave is also found to be present most of the time. Another 5–7 day wave component, observed at some altitudes with significant prominence, is surmised to be a manifestation of a 6.5 day wave.