Eastward-propagating planetary waves in the polar middle atmosphere
<p>According to Modern-Era Retrospective Research Analysis for Research and Applications (MERRA-2) temperature and wind datasets in 2019, this study presents the global variations in the eastward-propagating wavenumber 1 (E1), 2 (E2), 3 (E3) and 4 (E4) planetary waves (PWs) and their diagnosti...
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| Autores principales: | , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/6210ae12c5d74e7f96975d43dc25cfb4 |
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| Sumario: | <p>According to Modern-Era Retrospective Research Analysis for Research and
Applications (MERRA-2) temperature and wind datasets in 2019, this
study presents the global variations in the eastward-propagating wavenumber
1 (E1), 2 (E2), 3 (E3) and 4 (E4) planetary waves (PWs) and their diagnostic
results in the polar middle atmosphere. We clearly demonstrate the eastward
wave modes exist during winter periods with westward background wind in both
hemispheres. The maximum wave amplitudes in the Southern Hemisphere (SH) are
slightly larger and lie lower than those in the Northern Hemisphere (NH).
Moreover, the wave perturbations peak at lower latitudes with smaller
amplitudes as the wavenumber increases. The period of the E1 mode varies between 3–5 d in both hemispheres, while the period of the E2 mode is slightly longer in
the NH (<span class="inline-formula">∼</span> 48 h) than in the SH (<span class="inline-formula">∼</span> 40 h). The
periods of the E3 are <span class="inline-formula">∼</span> 30 h in both the SH and the NH, and the period
of E4 is <span class="inline-formula">∼</span> 24 h. Despite the shortening of wave periods with
the increase in wavenumber, their mean phase speeds are relatively stable, <span class="inline-formula">∼</span> 53, <span class="inline-formula">∼</span> 58, <span class="inline-formula">∼</span> 55 and <span class="inline-formula">∼</span> 52 m/s at 70<span class="inline-formula"><sup>∘</sup></span> latitudes for E1, E2, E3 and
E4, respectively. The eastward PWs occur earlier with increasing zonal
wavenumber, which agrees well with the seasonal variations in the critical
layers generated by the background wind. Our diagnostic analysis also
indicates that the mean flow instability in the upper stratosphere and upper
mesosphere might contribute to the amplification of the eastward PWs.</p> |
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