A Bore-like Disturbance Observed in the Kanto Plain Area

Shortly before midnight of 28 November 1991, the Tokyo (Haneda) airport was hit by two wind bursts in short succession. These gusty winds were responsible for some aviation hazards the airport suffered from. This paper investigates the nature and cause(s) of this event, mainly through the analysis of autographic records from the meteorological observatories and AMeDAS (Automated Meteorological Data Acquisition System) data. It is found that abrupt changes in wind direction and speed occurred at the airport, when an isolated, mesoscale migrating disturbance impinged into a strong low-level southwesterly flow associated with an extratropical cyclone. It is further revealed that the disturbance traveled across the central part of the Kanto Plain toward the east or southeast with the phase speed of 13-16 ms-1. Its horizontal dimension was roughly 30 km, and the disturbance was accompanied by not only abrupt changes in wind, but also abrupt increases in pressure and temperature at the passage time of the disturbance. All these characteristics are common in the Morning-Glory-like bore, which is known to develop when a stable layer underlying a neutral layer is disturbed by an external disturbance. Thus, it is concluded that the disturbance detected in this case is a type of the internal bore. Its generating mechanism remains unclear, however. To the best knowledge of the authors, this is the first paper that documents a bore-like disturbance observed in Japan.