Abstract
Abstract. There have been comparatively few studies reported of the 2-day planetary wave in the middle atmosphere at polar latitudes. Here we report on a study made using high-latitude meteor radars at Rothera in the Antarctic (68° S, 68° W) and Esrange in Arctic Sweden (68° N, 21° E). Observations from 2005–2008 are used for Rothera and from 1999–2008 for Esrange. Measurements were made of horizontal winds at heights of 80–100 km. The radar data revealed distinct summertime and wintertime 2-day waves. The Antarctic summertime wave occurs with significant amplitudes in January – February at heights between about 88–100 km. Horizontal wind monthly variances associated with the wave exceed 160 m2 s−2 and the zonal component has larger amplitudes than the meridional. In contrast, the Arctic summertime wave occurs for a longer duration, June–August and has meridional amplitudes larger than the zonal amplitudes. The Arctic summertime wave is weaker than that in the Antarctic and maximum monthly variances are typically 60 m2 s−2. In both hemispheres the summertime wave reaches largest amplitudes in the strongly sheared eastward zonal flow above the zero-wind line and is largely absent in the westward flow below. The observed differences in the summertime wave are probably due to the differences in the background zonal winds in the two hemispheres. The Antarctic and Arctic wintertime 2-day waves have very similar behaviour. The Antarctic wave has significant amplitudes in May–August and the Arctic wave in November–February. Both are evident across the full height range observed.
Highlights
The quasi-2-day, or 2-day, wave is a prominent feature of the mesosphere and lower thermosphere (MLT) region
The occurrence of 2-day waves in the MLT region observed icantly weaker around the equinoxes
A Morlet wavelet was used with 6 cycles of the wave contained within a Gaussian envelope. This wavelet was chosen because it has a similar morphology to the episodes of planetary-wave activity often reported in the MLT
Summary
The quasi-2-day, or 2-day, wave is a prominent feature of the mesosphere and lower thermosphere (MLT) region. It is observed each year around summer solstice. Satellite observations have been used to investigate the global-scale structure of the wave (e.g., Rodgers and Prata, 1981; Wu et al, 1993; Ward et al, 1996; Lieberman, 1999; Limpasuvan and Wu, 2003; Smith, 2003; Riggin et al, 2004; Sandford et al, 2008). Theoretical studies have investigated the excitation of the wave, its global-scale structure and its interaction with other waves and tides (e.g., Norton and Thuburn, 1996; Palo et al, 1999; Jacobi et al, 2006; Salby and Callaghan, 2008)
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