A case study of mesospheric planetary waves observed over a three-radar network using empirical mode decomposition

Abstract

In this paper an attempt is made to study equatorial Kelvin waves using a network of three radars: Kototabang (0.204°S, 100.320°E) meteor radar, Pameungpeuk (7.646°S, 107.688°E) medium-frequency radar, and Pontianak (0.003°S, 109.367°E) medium-frequency radar. We have used the continuous data gathered from the three radars during April-May 2010. Empirical mode decomposition (EMD), Lomb-Scargle periodogram (LSP) analysis, and wavelet techniques are used to study the temporal and altitude structures of planetary waves. Here, we used a novel technique called EMD to extract the planetary waves from wind data. The planetary waves of ∼ 6.5 and ∼ 3.6 days periodicity are observed in all three radar stations with peak amplitudes of about 12 and 11ms-1, respectively. The 3.6-day wave has an average vertical wavelength from the three radars of about 42km. The 3.6- and 6.5-day planetary waves are particularly strong in the zonal wind component. We find that the two waves are present at the 84-94km height region. The observed features of the 3.6- and 6.5-day waves at the three tropical-latitude stations show some correspondence with the results reported for the equatorial-latitude stations.