Multiyear Observations of Gravity Wave Momentum Fluxes in the Midlatitude Mesosphere and Lower Thermosphere Region by Meteor Radar

Multiyear high-frequency gravity wave (GW) momentum fluxes and variances in the mesosphere and lower thermosphere region are revealed using four meteor radars along 120 degrees E longitude at Northern Hemisphere midlatitudes for the first time, which are located at Mohe (53.5 degrees N, 122.3 degrees E), Beijing (40.3 degrees N, 116.2 degrees E), Mengcheng (33.3 degrees N, 116.5 degrees E), and Wuhan (30.5 degrees N, 114.2 degrees E), respectively. The seasonal and latitudinal variations of GW momentum fluxes in the midlatitude are discussed. The directions of the monthly mean zonal momentum fluxes are mostly against the background mean zonal winds, which agree well with the selective filtering mechanism. The seasonal variations of meridional momentum fluxes have similar trends over all four stations. The latitudinal variations in the seasonal variation of GW momentum fluxes are mainly due to the latitudinal variations of background winds and GW sources. The unexpected eastward momentum fluxes in winter over Beijing are likely caused by the secondary GWs propagating eastward from the source region over the Tibetan Plateau (25 degrees-40 degrees N, 70-100 degrees E). The GW variances show a V-shaped structure indicating annual and semiannual variations over four stations in zonal component. A quasi-4-month oscillation was observed over Mohe, Mengcheng, and Wuhan in meridional component. The background winds play decisive roles in these GW variance structures.