Inertia-gravity waves in Antarctica: A case study using simultaneous lidar and radar measurements at McMurdo/Scott Base (77.8°S, 166.7°E)

This study presents the first coincident observation of inertia-gravity waves (IGWs) by lidar and radar in the Antarctic mesopause region. This is also the first known observation of two simultaneous IGWs at the same location. An Fe Boltzmann lidar at Arrival Heights (77.8 degrees S, 166.7 degrees E) provides high-resolution temperature data, and a co-located MF radar provides wind data. On 29 June 2011, coherent wave structures are observed in both the Fe lidar temperature and MF radar winds. Two dominant waves are determined from the temperature data with apparent periods of 7.7 +/- 0.2 and 5.0 +/- 0.1 h and vertical wavelengths of 22 +/- 2 and 23 +/- 2 km, respectively. The simultaneous measurements of temperature and wind allow the intrinsic wave properties to be derived from hodograph analyses unambiguously. The analysis shows that the longer-period wave propagates northward with an azimuth of =11 degrees +/- 5 degrees clockwise from north. This wave has a horizontal wavelength of h=2.2 +/- 0.2x103 km and an intrinsic period of I=7.9 +/- 0.3 h. The intrinsic horizontal phase speed (CIh) for this wave is 80 +/- 4 m/s, while the horizontal and vertical group velocities (Cgh and Cgz) are 48 +/- 3 m/s and 0.5 +/- 0.1 m/s, respectively. The shorter-period wave has I=4.5 +/- 0.3 h and =100 degrees +/- 4 degrees with h=1.1 +/- 0.1x103 km and CIh=68 +/- 5 m/s. Its group velocities are Cgh=58 +/- 5 m/s and Cgz=1.1 +/- 0.1 m/s. Therefore, both waves propagate with very shallow elevation angles from the horizon (phi=0.6 degrees +/- 0.1 degrees and phi=1.1 degrees +/- 0.1 degrees for the longer- and shorter-period waves, respectively) but originate from different sources. Our analysis suggests that the longer-period IGW most likely originates from the stratosphere in a region of unbalanced flow.