Eastward-propagating planetary waves in the polar middle atmosphere

Abstract

Abstract. 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 (∼ 48 h) than in the SH (∼ 40 h). The periods of the E3 are ∼ 30 h in both the SH and the NH, and the period of E4 is ∼ 24 h. Despite the shortening of wave periods with the increase in wavenumber, their mean phase speeds are relatively stable, ∼ 53, ∼ 58, ∼ 55 and ∼ 52 m/s at 70∘ 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.

The Characteristics of Traveling Planetary Waves in the Troposphere and Mesosphere on Mars

“…In addition, Tang et al. (2021) found that strong instability with weak background wind can promote the propagation and amplification of EP flux. The meridional and vertical components of EP flux refer to the flow of wave energy density and the EP flux gives details about the net effect on TPWs of eddy and momentum fluxes.…”

“…Generally, regions with a negative meridional gradient of the quasi-geostrophic potential vorticity (QGPV) indicate a higher probability of barotropic/baroclinic instabilities for generating PWs (Ma et al, 2022;Qin et al, 2021;Yamazaki & Matthias, 2019). In addition, Tang et al (2021) found that strong instability with weak background wind 5), and B on the right of A refers to the periods after the solstice (second half of B in Equation 5). can promote the propagation and amplification of EP flux.…”

On the Quasi-2-Day Planetary Waves in the Middle Atmosphere During Different QBO Phases

“…In addition, they found that the wave periods of W3 and W4 rise during the late summer in the Northern Hemisphere. Tang et al (2021) found the eastward wave in winter periods and westward background wind in both hemispheres. In addition, they observed that the mean phase speeds of zonal wavenumbers -1 (E1), -2 (E2), -3 (E3), and -4 (E4) were relatively stable, which are ~53 m/s, ~58 m/s, ~55 m/s, and ~52 m/s, respectively, at 70˚ latitude.…”

“…In addition, the short-term variation of migrating diurnal tides may be caused by the nonlinear interaction between tidal waves and Q2DWs (Chang et al, 2011). Gu et al (2021) found that W3 and W4 occurred more frequently around 48 h, while W2 tended to be short-period events. In addition, they found that the wave periods of W3 and W4 rise during the late summer in the Northern Hemisphere.…”

“…Quasi-2-day waves (Q2DWs) play an important role in planetary wave observation because of their shorter period and stronger amplitude (Iimura et al, 2021;Gu et al, 2021;Gu et al, 2019;Pancheva et al, 2018;Kumar et al, 2018;Ma et al, 2017;Pancheva et al, 2016).…”