Abstract
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 11 m s−1, respectively. The 3.6-day wave has an average vertical wavelength from the three radars of about 42 km. 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 84–94 km 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. Keywords. Electromagnetics (wave propagation) – history of geophysics (atmospheric sciences) – meteorology and atmospheric dynamics (middle atmosphere dynamics)
Highlights
Planetary waves (PWs) are prominent features that appear in the mesosphere and lower thermosphere (MLT) region.The source of these waves is most likely to be excitations with a periodicity of ∼ 2 to 20 days, which have been observed using medium-frequency (MF) radar and meteor radar wind measurements (Williams and Avery, 1992; Tsuda et al, 1988)
It can be seen that before mid-April, zonal winds are mostly westward for all radars, while the flow is eastward for most observation days after this period
According to Venkateswara Rao et al (2012), westward winds are stronger than eastward winds within ±9◦ latitude, whereas at ±22◦ eastward winds are stronger
Summary
Planetary waves (PWs) are prominent features that appear in the mesosphere and lower thermosphere (MLT) region.The source of these waves is most likely to be excitations with a periodicity of ∼ 2 to 20 days, which have been observed using medium-frequency (MF) radar and meteor radar wind measurements (Williams and Avery, 1992; Tsuda et al, 1988). It can be seen that before mid-April, zonal winds are mostly westward for all radars, while the flow is eastward for most observation days after this period.
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