A study of the character of mesospheric gravity waves observed with MF radar at Poker Flat, and Tromsø

The interaction between gravity waves and tidal waves has been studied by using observations, although the phase relation between them was not fully understood. The neutral wind velocity data from mesosphere to lower thermosphere observed by MF radars at Poker Flat in Alaska and at Tromso in Norway has been observed since the late 1990s. The long-term wind velocity data at Poker Flat and Tromso was analyzed for 10 years of 1999~2008 to show daily and seasonal behaviors of mesospheric gravity waves and horizontal wind of the 12 and 24 hour components. Observed wind velocities having the 1~4 hour period components are analyzed as short-period gravity waves and those having harmonic components with periods of 48, 24, 12, and 8 hours are calculated every 30 minutes. The phase relation between 12 hour components of zonal wind and kinetic energy of gravity waves (GW-KE) shows that their phases are locked for more than 10 days. Such phase lock events are found in several years at both observation sites. We confirmed a phase lock phenomena at both Tromso and Poker Flat continued for about 20 days from November to December in 2000. However, between Tromso and Poker Flat, the phases of 12 hour component of GW-KE differed by 180 degrees. We plan to discuss more detail of underlying physical processes, focusing on gravity wave drags and background state of horizontal wind velocities at both sites.