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.

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).

Squeal is a noise phenomenon occurring in the last stage of automobile braking with a high-frequency sound. It is very difficult to express the phenomenon using a mathematical model, since the origin of squeal noise is physically complex. However, the possibility of squeal generation can be predicted by solving the vibration equation of the self-excited system using the complex eigenvalue analysis method. The results of the method are expressed as the magnitude of the unstable mode, and the generation of squeal noise can be prevented by reducing the magnitude of the unstable mode of the brake system. The objective of this research is to determine the optimal design process focused on the calliper housing shape to suppress squeal noise generation by reducing the system instability. The objective function is set to minimize the real part of the complex eigenvalue, i.e. the instability index. In the optimization design process, the design variable for topology optimization is established by focusing on the finger part of the calliper housing, which transmits the braking pressure to the pad lining. To supplement the complex shape generated by the topology optimization process, parametric design variables are selected for the subsequent process. Parameters are set to adjust the housing finger stiffness and are defined by considering the topology optimization result. Finally, the asymmetric shape of the calliper housing is obtained to reduce squeal noise generation.

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