Comparison of gravity wave propagation directions observed by mesospheric airglow imaging at three different latitudes using the M-transform
<p>We developed user-friendly software based on Matsuda et al.'s (2014) 3D-FFT method (Matsuda-transform, M-transform) for airglow imaging data analysis as a function of Interactive Data Language (IDL). Users can customize the range of wave parameters to process when executing the program...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-11-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/36/1597/2018/angeo-36-1597-2018.pdf |
| Summary: | <p>We developed user-friendly software based on Matsuda et al.'s (2014) 3D-FFT
method (Matsuda-transform, M-transform) for airglow imaging data analysis as
a function of Interactive Data Language (IDL). Users can customize the range
of wave parameters to process when executing the program. The input for this
function is a 3-D array of a time series of a 2-D airglow image in
geographical coordinates. We applied this new function to mesospheric airglow
imaging data with slightly different observation parameters obtained for the
period of April–May at three different latitudes: Syowa Station, the
Antarctic (69<span class="inline-formula"><sup>∘</sup></span> S, 40<span class="inline-formula"><sup>∘</sup></span> E); Shigaraki, Japan (35<span class="inline-formula"><sup>∘</sup></span> N,
136<span class="inline-formula"><sup>∘</sup></span> E); and Tomohon, Indonesia (1<span class="inline-formula"><sup>∘</sup></span> N, 122<span class="inline-formula"><sup>∘</sup></span> E).
The day-to-day variation of the phase velocity spectrum at the Syowa Station
is smaller and the propagation direction is mainly westward. In Shigaraki,
the day-to-day variation of the horizontal propagation direction is larger
than that at the Syowa Station; the variation in Tomohon is even larger. In
Tomohon, the variation of the nightly power spectrum magnitude is remarkable,
which indicates the intermittency of atmospheric gravity waves (AGWs). The
average nightly spectrum obtained from April–May shows that the dominant
propagation is westward with a phase speed <span class="inline-formula"><50</span> m s<span class="inline-formula"><sup>−1</sup></span> at the Syowa Station and
east-southeastward with a phase speed of up to <span class="inline-formula">∼80</span> m s<span class="inline-formula"><sup>−1</sup></span> in
Shigaraki. The day-to-day variation in Tomohon is too strong to discuss
average characteristics; however, a phase speed of up to <span class="inline-formula">∼100</span> m s<span class="inline-formula"><sup>−1</sup></span> and faster is observed. The corresponding background wind
profiles derived from MERRA-2 indicate that wind filtering plays a
significant role in filtering out waves that propagate eastward at the Syowa
Station. On the other hand, the background wind is not strong enough to
filter out relatively high-speed AGWs in Shigaraki and Tomohon and the
dominant propagation direction is likely related to the
distribution and characteristics of the source region, at least in April and May.</p> |
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| ISSN: | 0992-7689 1432-0576 |