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ABSTRACT
An observational analysis of the low-level internal gravity waves over the Kanto Plain in Japan on 17 October 1998 was performed. The data from the Doppler Radar for Airport Weather (DRAW), as well as Aircraft Communications Addressing and Reporting System (ACARS) data of wind and temperature, provided unique observations with high spatial and temporal resolutions and were used to analyze detailed wave structures and environmental conditions, especially the wave-trapping mechanism.
According to the data analysis, the horizontal wavelength was approximately 7 km, the ground-relative phase speed of the waves was approximately 1 m s^sup -1^, and the direction of propagation was toward 50 deg (NE). The profiles from ACARS revealed that the Scorer parameter decreased rapidly with height above 1500 rn AGL and became less than the horizontal wavenumber near 2600 m AGL. These results indicate that the atmosphere acts as a duct and the waves were trapped vertically and reflected downward.
The observed horizontal wavelength, profile of horizontal velocity amplitudes, and surface pressure perturbations are in agreement with estimates presented herein derived from a linear theory on neutral modes. The frequency and the phase of surface pressure perturbations are consistent with theoretical relations with internal gravity waves, suggesting that they were caused by the passage of the internal gravity waves.
1. Introduction
Internal gravity waves in the lower troposphere have been studied by many authors. Early case studies have typically analyzed barograph data. Several authors have used routine barograph traces of the National Weather Service in the United States to be digitized and subjected to digital bandpass filtering and cross-spectral analysis (e.g., Uccellini 1975; Stobie et al. 1983; Koch and Dorian 1988). On the other hand, Curry and Murty (1974), Keliher (1975), Balachandran (1980), and Monserrat and Thorpe (1992) detected gravity wave events from temporal records of microbarograph arrays. At Halley Base (Antarctica), Rees and Mobbs (1988) used time series of wind speed and direction with three meteorological masts of 8 m. These observational studies have been confined to surface observations with little or no direct information concerning the vertical structure. In more recent studies, some remote sensing instruments were used to examine gravity wave vertical structures. King et al. (1987) performed temperature measurements from a 30-m mast and a sodar....