Characteristics of inertia-gravity waves (IGWs) at high latitude in Antarctica are investigated using radiosondes launched daily at Jang Bogo Station (74°37 0 S, 164°13 0 E), a new Antarctic station that has been operating since 2014, in the troposphere (z = 2-7 km) and lower stratosphere (z = 15-22 km) for 25 months (December 2014 to December 2016). The vertical propagation of IGWs exhibits strong seasonal variations in the stratosphere, with an enhancement (reduction) in downward (upward)-propagating IGWs from May to mid-October. In the troposphere, both upward-and downward-propagating IGWs have similar occurrence rates without seasonal variations. The intrinsic phase velocity of IGWs mostly direct to the west (isotropic), while the ground-relative phase and group velocities are dominant in the east and southeast (northeast), respectively, in the stratosphere (troposphere). The intrinsic frequency, vertical wavelength, and horizontal wavelength of IGWs averaged in the troposphere (stratosphere) are 3.57f (1.93f; where f is the Coriolis parameter), 1.48 (1.48) km, and 63.06 (221.81) km, respectively. The wave energy in the stratosphere has clear seasonal variations with large values in autumn and spring, while that in the troposphere is smaller without obvious seasonal variations. Zonal and meridional momentum fluxes averaged in the stratosphere (troposphere) are À0.008 (À0.0018) and À0.0005 (0.001) m 2 /s 2 , respectively. The momentum flux of downward-propagating IGWs in the stratosphere is mostly positive in both zonal and meridional directions, whereas the directional preference is not obvious in the troposphere. In Part 2, sources of the observed IGWs in the troposphere and stratosphere will be examined.

The role of gravity waves (GWs) in a sudden stratospheric warming (SSW) event that occurred in January 2009 (SSW09) is investigated using the MERRA-2 reanalysis dataset. Nearly 2 weeks prior to the central date (Lag = 0), at which the zonal-mean zonal wind at 10 hPa and 60°N first becomes negative, westward GW drag (GWD) is significantly enhanced in the lower mesosphere and stratosphere. At 5 days before Lag = 0, planetary waves (PWs) of zonal wavenumber (ZWN)-2 in the stratosphere are enhanced, while PWs of ZWN-1 are weakened, which are evident from the amplitudes of the PWs and their Eliassen-Palm flux divergence (EPD). To examine the relationship between PWs and GWs, a nonconservative GWD (NCGWD) source term of the linearized quasi-geostrophic potential vorticity equation is considered. A ZWN-2 pattern of the NCGWD forcing is developed around z = 55–60 km with a secondary peak around z = 40 km just before the PWs of ZWN-2 in the stratosphere began to enhance. A significant positive correlation between the NCGWD forcing in the upper stratosphere and lower mesosphere (USLM; 0.3–0.1 hPa in the present data) and the PWs of ZWN-2 in the stratosphere (5–1 hPa) exists. This result demonstrates that the amplification of the PWs of ZWN-2 in the stratosphere before the onset of SSW09 is likely related to the generation of PWs by GWD in the USLM, which is revealed by the enhanced downward-propagating PWs of ZWN-2 into the stratosphere from above.

Potential sources of inertia‐gravity waves (IGWs) in the lower stratosphere (z = 15–22 km) at Jang Bogo Station, Antarctica (74°37′S, 164°13′E) are investigated using 3‐year (December 2014 to November 2017) radiosonde data, including the 25‐month result (December 2014 to December 2016) analyzed in Yoo et al. (2018, https://doi.org/10.1029/2018JD029164, Part 1). For this investigation, three‐dimensional backward ray tracing calculations are conducted using the Gravity wave Regional Or Global RAy Tracer. Among 248 IGWs, 112, 68, and 68 waves are generated in the troposphere (z < 8 km), tropopause (z = 8–15 km), and lower stratosphere (z = 15–18.5 km), respectively. These waves mainly propagate from the northwestern and southwestern regions of Jang Bogo Station dominated by the prevailing westerlies between the upper troposphere and lower stratosphere. Potential sources of IGWs are categorized into orography, fronts, convection, and the flow imbalance including the upper‐tropospheric jet stream. In the troposphere, relatively large numbers of waves are associated with fronts (37) and orography (35) compared with convection (28). In the tropopause (stratosphere), 36 (42) waves, including 11 cases associated with the upper‐tropospheric jet stream, are excited by the flow imbalance. Waves related to the flow imbalance are characterized by low intrinsic frequency (1–2f), short vertical wavelength (1–2 km), and longer horizontal wavelength (50–1000 km), whereas the waves induced by the tropospheric sources have wider ranges of intrinsic frequency (1–20f) and vertical wavelengths (1–15 km) with relatively shorter horizontal wavelengths (less than 500 km).

Atmospheric gravity waves (GWs) can be generated from various tropospheric sources such as orography, jet stream, and convection, and these waves play a major role in determining the spatiotemporal structure of the middle atmosphere wind and temperature by transferring momentum and energy to high altitudes (Lindzen, 1981). In the mesosphere, GW breaking is frequently observed (Nappo, 2013), and momentum and energy transfer accompanied by GW breaking is essential in accounting for the thermal and wind structure of the mesosphere (

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