Oscillations of GW Activities in the MLT Region over Mid-Low-Latitude Area, Kunming Station (25.6 N, 103.8 E)

Gravity wave (GW) activities play a prominent role in the complex coupling process of wave-wave and wave-background circulation around mid-low-latitude and equatorial areas. The wavelengths are wide, from about 10 m to 100 km, with a period from minutes to hours. However, the oscillations of GW activities are apparently different between the period bands of 0.1 to 1 h (HF) and 1 to 5 h (LF). To further understand the characteristics of GW activities, the neutral winds during 2008-2009 with a resolution of 3 min obtained from a medium-frequency (MF) radar in Kunming (25.6 degrees N, 103.8 degrees E) were analyzed. Using two numerical filters, the HF and LF GWs were estimated. Interestingly, the power spectral density grows larger as the frequency increases. It linearly falls with decreasing frequency when the period is less than 2 h. The seasonal variations in both HF and LF GWs are strongly demonstrated in August-September, November, and February-March with maximum meridional variances of 1100 m2 s-2 and 500 m2 s-2 and maximum zonal variances of 800 m2 s-2 and 350 m2 s-2 in, respectively. The turbulent velocity was also calculated and shows similar oscillations with GW activities. Furthermore, the GW propagation direction exhibits strong seasonal variations, which may be dependent on the location of the motivating source and background wind.