The quasi 2‐day wave observed in the polar mesosphere

Abstract

Using MF radar data obtained at Tromsø (69.6°N, 19.2°E) for ∼37 months between 1 November 1998 and 8 December 2001, we have examined characteristics of the quasi 2‐day wave (Q2DW) in the polar mesosphere in the height range from 70 to 91 km. The activity of the Q2DW is higher in winter months (November–February) than in summer months (May–August) over this height region. The maximum values of the amplitude are ∼25 m s−1 in winter and ∼15 m s−1 in summer. Between 70 and 82 km, the amplitude appears to maximize near winter solstice over the 3 years. The average ratio of meridional to zonal amplitudes is ∼1.1–1.2 over the height region. Thus, there is no significant preference towards either components. The variations of the periods of maximum amplitude are also examined, and periods with 45.2 and 54.9 hours occur more frequently than those with 48.0 and 51.2 hours. However, no clear seasonal trend of the variation of the period is found. In addition, the amplitude is modulated at 4–10 day rate. With simultaneous observational data from the MF radar and the EISCAT UHF radar colocated in Tromsø, we have examined whether or not the Q2DW was able to penetrate to the lower thermosphere for the period of 1–9 July 1999. It is found that the amplitude of the Q2DW with period of 51.2 hours maximized at 95 km height with values of ∼25 m s−1 in both meridional and zonal components. The Q2DW was attenuated above 95 km, but it appears to survive up to 108 km height in the meridional component. Between 85 and 95 km for the meridional component during this 8‐day interval, the Q2DW and semidiurnal tide were the strongest among the periodic components.