Toshiaki Imai

Finescale Doppler Radar Observation of a Tornado and Low-Level Misocyclones within a Winter Storm in the Japan Sea Coastal Region

Abstract Life histories of low-level misocyclones, one of which corresponded to a tornado vortex within a winter storm in the Japan Sea coastal region on 1 December 2007, were observed from close range by X-band Doppler radar of the East Japan Railway Company. Continuous plan position indicator (PPI) observations at 30-s intervals at the low-elevation angle revealed at least four cyclonic misocyclones within the head of the comma-shaped echo of the vortical disturbance under winter monsoon conditions. The meso-β-scale vortical disturbance developed within the weak frontal zone at the leading edge of cold-air outbreaks. High-resolution observation of misocyclones revealed the detailed structures of these misocyclones and their temporal evolution. As the parent storm evolved, a low-level convergence line was observed at the edge of the easternmost misocyclone. This convergence line was considered to be important for the initiation and development of the misocyclones and the tornado through vortex stretching...

New train regulation method based on wind direction and velocity of natural wind against strong winds

Abstract Since there have been some railway accidents caused by strong winds in recent years in Japan, it is necessary to establish effective measures to prevent wind-induced accidents and ensure safety of train operation under strong winds. On February 22, 1994, a derailment accident was caused by strong winds on the Nemuro line of Hokkaido Railway Company. Railway Technical Research Institute carried out researches on investigation of the accident and measures at this section. As countermeasures, wind barriers were installed and a new train regulation method based on not only a natural wind velocity but also a natural wind direction was applied to the section. As a result, the railway company has had much less chances of slowdown and suspending of train operation than before and never experienced cancellation of train operation.

Evaluation of the Influence of Anemometer Position around Railway Structures on Wind Observation Data

Anemometers are used to detect wind speed for operation control of trains. Since these anemometers usually are installed close to railway structures along sections of railway line, the wind velocity data readings may be affected by the structures. This study uses wind-tunnel tests and field wind observations to investigate the influence of the anemometer position on the wind velocity readings. Three types of railway structure were considered: a single-track bridge, a double-track viaduct and a single-track embankment. The results showed that the maximum instantaneous wind-velocities at the anemometer position on the leeward side of the railway structure were higher than those at the reference point as the wind direction against the railway track approached 90 degrees. The height of the measurement point and the size of the wind-direction angle in relation to the location of the railroad truck had an effect on the maximum instantaneous wind-velocity ratios regardless of the kind of railroad structure and location (leeward or windward) of the measurement point.