Gravity waves observed in temperature, wind and ozone data over Macquarie Island

Abstract

Characteristics of inertia-gravity waves are analysed in high-resolution vertical profiles of temperature, winds and ozone collected at Macquarie Island (54°S, 159°E) during the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) observation programme in 1994. Two particular techniques are outlined to identify gravity-wave modes. The first is based on the continuous wavelet transform and seeks altitudes where the atmospheric fluctuations satisfy the gravity-wave polarisation relations in the temperature and wind soundings. The second analyses the phase and amplitude relationship of small-scale wavelike signatures seen in temperature and ozone profiles. The wavelet method identified gravity-wave modes with vertical wavelengths of 1-10 km, horizontal wavelengths of 50-1000 km and intrinsic frequencies of 1-2 f. Both methods reveal the presence of dominant modes with vertical wavelength <4 km in the upper troposphere and lower stratosphere over Macquarie Island. The energy activity of observed modes agrees well with the seasonal cycle of the upper level jet at 10 km height. These techniques together with classical spectral methods are applied to the case study of 25 October 1994 for which three quasi-monochromatic coherent modes with upwardly propagating wave energy are detected in the lower stratosphere.