A Statistical Investigation of Inertia Gravity Wave Activity Based on MST Radar Observations at Xianghe (116.9°E, 39.8°N), China

Abstract

AbstractUsing three‐dimensional wind observations from a Mesosphere‐Stratosphere‐Troposphere radar at Xianghe for two years from September 2011 to August 2013, we study inertia gravity wave (IGW) activity in the two height segments of 3–10 and 15–25 km to reveal the characteristics of waves in the source region at midlatitude. Case investigation indicates that three‐dimensional wind fluctuations are usually dominated by a strong IGW. Statistics on 15,617 IGWs extracted show that most waves have typical horizontal scales of tens to thousands of kilometers, the vertical scale of a few kilometers, intrinsic frequencies in 1–4 times the inertial frequency, and amplitudes of 1–4 ms−1 in horizontal winds but less than 0.3 ms−1 in the vertical wind. In the lower region, occurrence possibilities of upward and downward propagating waves are almost the same throughout the year. Whereas in the upper region, IGWs display a predominant upward propagation with a maximum of 85.3% in February but a minimum of 63.6% in July, and a preferential propagation in the zonal direction relative to the meridional direction. Meanwhile, wave energy has a prominent seasonal cycle with the maximum in winter and the minimum in summer. Subtropical jet, as wave source and propagation condition, plays an important role in these different features between the two regions. The annual average of momentum flux indicates that the IGWs in the lower stratosphere can apply a persistent eastward drag on the background flow at higher altitudes through momentum transported by these waves.