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Results

The continuous wavelet transform (CWT) with Morlet wavelet is applied to vertical perturbation profiles of temperature and partial pressure of ozone from September 1992 to December 1997. Statistical distributions of spectral lines deduced from CWT show evidence of dominant modes with vertical wavelengths of 1-7 km from the ground up to 27 km in vertical perturbation profiles of temperature and ozone (Chane-Ming et al., 2000b). Localized multi-scale structures are observed in the troposphere and the stratosphere during Austral summer and winter. Structures with 1-5 km vertical wavelengths have similar characteristics in both ozone and temperature during Austral summer and winter. Therefore these structures are examined through some case studies and a climatology of laminae induced by gravity waves and large scale advection from September 1992 to December 1998.

The CWT is applied to vertical profiles of perturbations of temperature and ozone on January 10, 1995 in Austral summer. Frames of CWT amplitudes so-called scalograms show evidence of a quasi-monochromatic structure of 2 km vertical wavelength in the upper troposphere and the stratosphere on both ozone and temperature profiles (Figure 1). Wavelike structures of 1.2-2.4 km vertical wavelengths are extracted from vertical profiles of ozone and temperature perturbations with the multi-resolution analysis (MRA) (Chane-Ming et al., 2000a) and compared using equation 1 (Figure 2a).

Similar amplitudes and phase are observed at heights of 10-21 km with values of correlation superior to 0.7. This indicates the presence of a gravity wave.

Chane-Ming et al. (2000b) present another case of gravity wave structure observed in the UT/LS in Austral winter with 3-4 km vertical wavelengths.

In other cases, values of correlation are weak and structures are attributed to the horizontal advection. In the case study of June 29, 1993, the amplitude and phase relationships between the normalized perturbations are not verified in the middle and upper troposphere where strong amplitudes and weak values of correlation are observed at heights of 5-15 km (Figure 2b).

Back-trajectories show evidence of a quasi-horizontal motion of air parcels at heights of 14 km (Figure 3).

The nature and the frequency of occurrence of these structures are analyzed to provide some quantitative information about the role of such structures in horizontal and vertical transport processes and in mixing on both sides of the tropopause and the subtropical barrier.

Vertical short-scale structures are automatically extracted and identified using a method based on the MRA and similar values of parameters proposed by Grant et al. (1998).

Laminar structures induced by gravity waves are localized in the UT/LS in Austral summer and in the middle troposphere up to the lower stratosphere in Austral winter with vertical wavelengths of 2.4 km and 2.4-4.8 respectively (Figure 4a, 4b). The frequency of occurrence of gravity waves are 1.3 times more important in winter (refer to Table 2 in Chane-Ming et al. (2000b)).

Structures induced by horizontal advection are 2 times more important in winter and are mostly detected at heights of 13-15 km independently of the season with vertical wavelengths of 2.4-4.8 km (Figure 4c, 4d).