Equatorial mesoscale wind and temperature fluctuations in the lower atmosphere

Abstract

We present spectrally analyzed high‐resolution balloon measurements of vertical temperature and horizontal wind in the troposphere and lower stratosphere in French Guyana (≈5°N, 52°W) made in 1996/1997. The paper is principally concerned with spectra at vertical scales from a few kilometers down to 100 m. A special balloon has been developed to solve scales below 500 m. For the first time, the equatorial region has been studied extensively at this resolution. We have found wind and temperature spectra following the canonical shape in the logarithmic representation with a slope of ≈−3 for wavenumbers ≧10−3 cycle/m with day‐to‐day significant amplitude variations but a mean spectrum constant with the seasons. We have found isotropic wave horizontal direction of propagation for the troposphere and anticorrelated with the quasi‐biennial oscillation in the stratosphere. The vertical propagation of wave has been found symmetric in the troposphere but highly asymmetric in the stratosphere with dominant upward propagation. We were not able to find any correlation between deep moist convection and wave activity. The ratio kinetic to potential energy spectra, which is the ratio of velocity spectra to temperature spectra multiplied by N2T¯2b/g2 for the troposphere and stratosphere, is constant versus the vertical wavenumber and in good agreement with a model intrinsic frequency spectrum varying as ω−p with 5/3 ≤ p ≤ 2 and without necessity of energy enhancement near the inertial frequency which is close to zero at the latitude measurements.