Energy enhancements of gravity waves in the Antarctic lower stratosphere associated with variations in the polar vortex and tropospheric disturbances

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Abstract

[1] Gravity waves in the Antarctic lower stratosphere are examined using original operational radiosonde data obtained at Syowa Station (69.0°S, 39.6°E) with fine vertical resolution. In the lower stratosphere the temporal variation in gravity wave energy depends on height. In the height region of 13–15 km, just above the tropopause, the seasonal variation in gravity wave energy is not evident. The wave energy is rather enhanced when the absolute value of potential vorticity in the upper troposphere becomes small over Syowa Station. This fact implies that tropospheric disturbances affect the dynamical processes of gravity waves there. However, the gravity wave energy in the height region of 15–25 km shows clear seasonal variation having a maximum in spring. The time variation in gravity wave energy is examined in detail in terms of the polar vortex by using the equivalent latitude coordinate. Energy enhancements occur when the edge of the polar vortex approaches Syowa Station, and the enhancements are especially large when the polar vortex breaks down in spring. These results suggest that height variation in the background atmosphere leads to the difference of wave characteristics between the two height regions. The enhancements of wave energy are partly explained as modification of the wave structure by the background wind speed and the static stability, but it is also likely that enhancements of wave activity contribute to the energy enhancement at the edge of the polar vortex in spring.

Ancillary