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

Abstract

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.

Equatorial Inertia-Gravity Waves in the Lower Stratosphere Revealed by TOGA-COARE TOP Data

“…Both wave periods and vertical wavelengths are similar to wave structures analyzed by previous observational studies in the equatorial area (Sato et al, 1994), and in the southern area (Tsuda et. al., 1994).…”

“…Cadet and Teitelbaum (1979) analyzed the data of soundings launched from a research vessel during the GATE (GARP [Global Atmospheric Research Programme] Atlantic Tropical Experiment) and showed the inertia-gravity waves propagate westward in the easterly shear background flow. Tsuda et al (1994) discussed the characteristics of gravity waves in the equatorial region by analyzing rawinsonde measurements of wind velocity and temperature fluctuations from February 27 to March 22, 1990 in east Java, Indonesia (7.6oS, 112.7oE). They showed that the typical vertical wavelengths of the waves are 2-2.5km and that most of them propagate eastward in the westerly shear background flow.…”

A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

“…Gravity waves are triggered by a variety of sources. The most prominent sources are orography (Smith, 1985;Durran and Klemp, 1987;Nastrom and Fritts, 1992) and convection (Pfister et al, 1986;Tsuda et al, 1994;Alexander and Pfister, 1995). Other sources include the adjustment of unbalanced flows near jet streams and frontal systems (Fritts and Alexander, 2003;Wu and Zhang, 2004).…”

Studies on atmospheric gravity wave activity in the troposphere and lower stratosphere over a tropical station at Gadanki

“…Before applying the PSD the time series data of wind fluctuation were detrended and then a high pass filter has been used for the data to eliminate low frequency components. Tsuda et al (1994b), the periods ranging from 5 min to 2 h are mainly due to the large wind shears, which are mainly observed during jet streams. The observed periods near the jet streams in the present study (around 16-17 km) lie within the periods, as reported by Tsuda et al (1994).…”