Analysis of gravity waves in the tropical middle atmosphere over La Reunion Island (21 degrees S, 55 degrees E) with lidar using wavelet techniques

The capabilities of the continuous wavelet transform (CWT) and the multires olution analysis (MRA) are presented in this work to measure vertical gravi ty wave characteristics. Wave properties are extracted from the first data set of Rayleigh lidar obtained between heights of 30 km and 60 km over La R eunion Island (21 degrees S, 55 degrees E) during the Austral winter in 199 4 under subtropical conditions. The altitude-wavelength representations ded uced from these methods provide information on the time and spatial evoluti on of the wave parameters of the observed dominant modes in vertical profil es such as the vertical wavelengths, the vertical phase speeds, the amplitu des of temperature perturbations and the distribution of wave energy. The s pectra derived from measurements show the presence of localized quasi-monoc hromatic structures with vertical wavelengths < 10 km, Three methods based on the wavelet techniques show evidence of a downward phase progression. A first climatology of the dominant modes observed during the Austral winter period reveals a dominant night activity of 2 or 3 quasi-monochromatic stru ctures with vertical wavelengths between 1-2 km from the stratopause, 3-4 k m and 6-10 km observed between heights of 30 km and 60 km. In addition, it reveals a dominant activity of modes with a vertical phase speed of -0.3 m/ s and observed periods peaking at 3-4 h and 9 h. The characteristics of ave raged vertical wavelengths appear to be similar to those observed during wi nter in the southern equatorial region and in the Northern Hemisphere at mi d-latitudes.