The quasi 2‐day wave observed in the polar mesosphere: Comparison of the characteristics observed at Tromsø and Poker Flat

Abstract

A comparison of the quasi 2‐day wave (Q2DW) observed at Tromsø (69.6°N, 19.2°E) and Poker Flat (65.2°, 147.6°W) is presented at four heights of 70, 76, 82, and 88 km using wind data taken for ∼4 years, from 1 November 1998 to 7 November 2002. The characteristics of the Q2DW such as seasonal variation, occurrence of period of maximum amplitude, ratio of meridional to zonal amplitudes, shape of altitude profile of phase, and modulation of amplitude at a 4–10 days rate found at Poker Flat are very similar to those found at Tromsø reported by Nozawa et al. [2003]. The activity of the Q2DW is higher in winter than in summer for meridional and zonal components at the two sites. Long‐term variation (i.e., seasonal variation) of the Q2DW is found to be similar between the two sites, while short‐term variations (i.e., over several days) do not synchronize well with each other. The ratio of amplitudes of the Q2DW between the two sites varies mainly between 0.5 and 2, and there is no significant preference toward either site. Phase differences of Q2DWs between the two sites are examined, and it is found that in‐phase‐like events are more frequently seen than out‐of‐phase‐like events at 76, 82, and 88 km in winter and at 88 km in summer. This can be interpreted to mean that the zonal wave number of the Q2DW appears to be 2 or 4 more often than 3 in the polar upper mesosphere. These results suggest that observed Q2DWs have features consistent with the Rossby gravity wave mode, but the amplitude and phase of the Q2DW are affected significantly by local sources. A possibility that the observed Q2DW is an eastward moving wave is also discussed.