Seasonal variation of gravity waves with various temporal and horizontal scales in the MLT region observed with radar and airglow imaging Original Research Article

Seasonal variations of activity and horizontal propagation direction of gravity waves in the MLT region at mid-latitude over Shigaraki, Japan (35 N) are investigated for various time and spatial scales using the MU radar observations and recent airglow imaging observations. Semiannual variation with solsticial maxima and equinoctial minima are generally observed for short period (< 5 hours) gravity waves. Eastward preference in summer and westward in winter for horizontal propagation direction is generally observed except for small scale (horizontal wavelength < about 15 km) gravity waves. Meridional preference such as northward in summer and southward in winter is also found in airglow imaging and some of the radar results. The preferential propagation direction between northward and eastward in summer is more commonly observed at various horizontal and time scales.