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

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.

Gravity Waves excited during a Minor Sudden Stratospheric Warming

“…In agreement with previous observational studies (e.g., Whiteway et al, 1997, Yoshiki et al, 2004, significant stratospheric wave activity could be detected in the high-resolution IFS data at times when the PNJ was situated over Kiruna (cf. Figures 2a and 7a, b), i.e.…”

“…As in the studies by Yoshiki and Sato (2000) and Yoshiki et al (2004), most of the published gravity wave analysis relies on operational radiosondes launched once or twice a day. At high latitudes, only few of these radiosondes reach altitudes higher than 30 km in winter as the conventional 300 … 500 g rubber balloons burst in the cold stratosphere.…”

“…Most of the existing studies concentrate on statistical aspects derived from high-vertical resolution radiosondes (e.g., Yoshiki and Sato, 2000;Yoshiki et al, 2004), from ground-based (e.g., Whiteway et al, 1997, Whiteway and Duck, 1999, Khaykin et al, 2015 and space-borne (e.g., Waters, 1996, Hindley et al, 2015) remote-sensing observations. The observations of Whiteway 15 at Eureka, Nunavut, Canada (80°N) during four Arctic winters showed an increase of stratospheric gravity wave energy in the vicinity of the PNJ.…”

“…Yoshiki and Sato (2000) speculated that one source candidate is likely to be the PNJ. Yoshiki et al (2004) investigated the 25 temporal variation of the gravity wave energy in the lower stratosphere with respect to the position of the polar vortex by using the equivalent latitude coordinate for the Antarctic station Syowa (69°S, 40°E). In agreement with the results of Whiteway et al (1997), gravity wave energy is enhanced when the edge of the polar vortex approaches Syowa Station.…”

Global distribution of vertical wavenumber spectra in the lower stratosphere observed using high-vertical-resolution temperature profiles from COSMIC GPS radio occultation

“…Orographic generation of GWs has previously been observed with balloon soundings and satellite measurements over the Andes (Alexander et al, 2008a) and Antarctica (Baumgaertner and McDonald, 2007;Sato and Yoshiki, 2008). Effects of the polar night jet and sudden stratospheric warming events on GW excitation have also been studied (Yoshiki et al, 2004;Hei et al, 2008).…”