Radiosonde observations of equatorial atmosphere dynamics over Indonesia: 2. Characteristics of gravity waves

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<jats:p>This paper discusses the characteristics of gravity waves in the equatorial region revealed by analyzing radiosonde measurements of wind velocity and temperature fluctuations at 0–35 km, with a height resolution of 150 m, made every 5–7 hours between February 27 and March 22, 1990, in East Java, Indonesia. We conducted hodograph analysis to delineate vertical and horizontal propagation characteristics and found that most gravity waves were generated in the middle of the troposphere and that they propagated upward into the stratosphere. The amplitudes of wind velocity and temperature fluctuations due to gravity waves were larger in the stratosphere than in the troposphere. The direction of horizontal propagation of gravity waves was rather uniformly distributed in the troposphere, but it became eastward in the lower stratosphere, being opposite to that of the mean winds because of quasi‐biennial oscillation. The vertical wavenumber spectra of wind velocity were described fairly well by a saturated model spectrum, although their amplitudes were smaller in the stratosphere. A typical vertical wavelength was 2–2.5 km, while the horizontal phase velocities were 5–7 and 12 m/s in the troposphere and stratosphere, respectively. The amplitudes of small‐scale gravity waves were significantly larger in the equatorial stratosphere than at middle latitudes. Time‐height variation of the wind velocity variance due to gravity waves showed a clear correlation with that for high relative humidity, which implies that cloud convection is an important mechanism of gravity wave generation in the equatorial region.</jats:p>

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