Analytical studies of low-level internal gravity waves over the Kanto Plain associated with a stationary front

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(-1), and the direction of propagation was toward 50degrees (NE). The profiles from ACARS revealed that the Scorer parameter decreased rapidly with height above 1500 m 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.