Characteristics of inertia-gravity waves revealed in rawinsondes at Jang Bogo Station (JBS), Antarctica (74.374S, 164.137E)

Abstract

High-resolution radiosonde data obtained at Jang Bogo Station (74˚37’S, 164˚13’E) are used to investigate characteristics and sources of inertia-gravity waves (IGWs) in the troposphere (z = 27 km) and the lower stratosphere (z = 1522 km) for 25 months (Dec. 2014Dec. 2016). In the stratosphere, most of IGWs propagate upward, while from May to October, down-going IGWs increase with reduction of up-going IGWs. In the troposphere, 60 (40) % of IGWs propagate upward (downward) without seasonal variations. Most of the observed IGWs in the stratosphere propagate eastward significantly, while this feature is less evident in the troposphere. The average intrinsic frequency, vertical wavelength, and horizontal wavelength of IGWs in the troposphere (stratosphere) are 3.48f (1.94f) (where f is the Coriolis parameter), 1.48 km (1.48 km), and 67.17 km (222.94 km), respectively. Intrinsic frequency and vertical wavelength in the stratosphere show clear seasonal variations with an increase (decrease) from autumn to winter (spring to summer), resulting corresponding horizontal wavelength increasing (decreasing) from spring to summer (autumn to winter), while the variations are not shown in the troposphere. Wave energy in the stratosphere has clear seasonal variations with the maximum in August (6.2 J kg-1) and minimum in January (2.5 kg-1), while tropospheric ones have much smaller energy without seasonal variations. The momentum flux (MF) of up-going IGWs in the stratosphere is more negative (positive) in zonal (meridional) direction, while that of down-going IGWs is mostly positive for both directions. Potential sources of the observed IGWs are examined. First, several mountains located on the west of JBS can generate up-going IGWs with small ground-based phase speed when the critical level filtering does not occur. Second, synoptic-scale disturbance near the tropopause is likely to generate the down-going (up-going) GWs in the troposphere (stratosphere). Third, the polar-night jet in the stratosphere, which locates at 50˚S70˚S can be an important source inducing down-going GWs. Considering that the observed IGWs can propagate significantly in horizontal direction, tropical convection can also be a possible source. The possibility will be assessed by gravity-wave MF by convection shown in Kang et al. (2017). These sources will be identified using 3-dimensional ray-tracing model of GWs.