High- and mid-latitude quasi-2-day waves observed simultaneouslyby four meteor radars during summer 2000

Abstract

Abstract.Results from the analysis of MLT wind measurements at Dixon (73.5 • N, 80 • E), Esrange (68 • N, 21 • E), Castle Eaton (UK) (53 • N, 2 • W), and Obninsk (55 • N, 37 • E) during summer 2000 are presented in this paper. Using S-transform or wavelet analysis, quasi-two-day waves (QTDWs) are shown to appear simultaneously at high-and mid-latitudes and reveal themselves as several bursts of wave activity. At first this activity is preceded by a 51-53 h wave with S=3 observed mainly at mid-latitudes. After a short recess (or quiet time interval for about 10 days near day 205), we observe a regular sequence of three bursts, the strongest of them corresponding to a QTDW with a period of 47-48 h and S=4 at mid-altitudes.We hypothesize that these three bursts may be the result of constructive and destructive interference between several spectral components: a 47-48 h component with S=4; a 60-h component with S=3; and a 80-h component with S=2. The magnitudes of the lower (higher) zonal wave-number components increase (decrease) with increasing latitude. The S-transform or wavelet analysis indicates when these spectral components create the wave activity bursts and gives a range of zonal wave numbers for observed bursts from about 4 to about 2 for mid-and high-latitudes. The main spectral component at Dixon and Esrange latitudes is the 60-h oscillation with S=3. The zonal wave numbers and frequencies of the observed spectral components hint at the possible occurrence of the nonlinear interaction between the primary QTDWs and other planetary waves. Using a simple 3-D nonlinear numerical model, we attempt to simulate some of the observed features and to explain them as a consequence of the nonlinear interaction between the primary 47-48 h and the 9-10 day waves, and the resulting linear superposition of primary and secondary waves. In addition to the QTDW bursts, we also infer forcing of the 4-day wave with S=2 and the 6-7 day wave with S=1, possibly arising from nonlinear decoupling of the 60-h wave with S=3. The starting mechanism for this decoupling is the Rossby wave instability (e.g.Correspondence to: E. Merzlyakov (eugmer@typhoon.obninsk.org) Baines, 1976). This result is consistent with the day-to-day wind variability during the observed QTDW events. An interesting feature of the final stage of the observed QTDW activity in summer 2000 is the occurrence of strong 4-5 day waves with S=3.

On the nonlinear Rossby-type wave interaction in the upper atmosphere, some numerical results

“…During that summer they also observed long-period 14-17-day wind oscillations of s ¼ 1. A similar observation except for 9-10-day wave instead of the 14-17-day wave was presented by Merzlyakov et al (2004) for summer 2000. These works implicitly or explicitly state the question: which of these waves are primary and which ones are secondary waves, respectively.…”

Climatology of the quasi two-day wave over Saskatoon (52°N, 107°W): 14 Years of MF radar observations

“…The modulation of the Q2DW by other planetary waves with longer periods and/or the interference between several coexisting spectral components (Merzlyakov et al, 2004) could be possible explanations of such behavior. The duration of a burst can vary from 3 to 10 cycles (6-20 days).…”

The two-day wave in the Antarctic and Arctic mesosphere and lower thermosphere

“…Observations of the 2-day wave have revealed that its amplitude maximises at middle to low latitudes in summer (e.g., Wu et al, 1996;Limpasuvan and Wu, 2003;Merzlyakov et al, 2004;Limpasuvan et al, 2005). At middle and low latitudes, the wave is composed primarily of westward-propagating zonal wavenumbers 3 and 4 (hereafter W3 and W4).…”

“…Recent studies made using ground-based radars have investigated the summertime mesospheric polar 2-day wave and have also revealed the existence of strong 2-day wave activity around the winter solstice at high latitudes (Nozawa et al, 2003a, b;Manson et al, 2004;Merzlyakov et al, 2004;Nozawa et al, 2005;Palo et al, 2007;Baumgaertner et al, 2008;Sandford et al, 2008). Nozawa et al (2003a) presented a climatology of the 2-day wave in the Arctic based on three years of observations at heights of 70-91 km made by an MF radar at Tromsø (69.6 • N, 19.2 • E).…”