Radar observations of the 3.5-day ultra-fast Kelvin wave in the low-latitude mesopause region

Abstract

The medium frequency (MF) radar observations of the 3.5-day ultra-fast Kelvin (UFK) wave in the mesopause region (84–) over Tirunelveli (), India for a period of nearly 3 years are reported in the present work. The UFK wave reveals semi-annual variability at heights () where the mesopause semi-annual oscillation (MSAO) in the mean wind peaks. Large-amplitude wave events preferentially occur during the westward flow regimes of the background wind. Mean eastward winds and their shears are qualitatively shown to be associated with bursts of waves with moderate amplitudes. Vertical wavelength estimates agree with earlier estimates based on satellite temperature retrievals for a wavenumber 1 ultra-fast Kelvin wave.