Tenki, Vol. 54, No. 1

(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)

TENKI, Vol. 54, No. 1, pp. 53-64, 2007

Tornado Disaster in Yokosuka on October 7, 2002
--Strong Wind Disasters from October 6 through 7, 2002--

Fumiaki KOBAYASHI*1, Hiroyuki FUJITA*1, Takashi NOMURA*2,
Yukio TAMURA*3, Masahiro MATSUI*3, Tadashi YAMADA*4
and Shuichi TSUCHIYA*4

*1 Department of Geoscience, National Defense Academy.
*2 Department of Civil Engineering, Nihon University.
*3 Wind Engineering Research Center, Tokyo Polytechnic University.
*4 Department of Civil Engineering, Chuo University.

(Received 15 March 2006;Accepted 20 November 2006)


As an extratropical cyclone developed on October 6, 2002 and moved east, extensive wind disasters occurred in various places in Japan. Areas presently known to be damaged areas are Kaseda-city in Kagoshima, Kagoshima-city, Minamichita-cho in Aichi, Hamamatsu-city in Shizuoka, Ohshima-cho in Tokyo, Miura-city and Yokosuka-city in Kanagawa, Tateyama-city in Chiba. In Yokosuka-city at approximately 03:50 JST on October 7, 2002 a gust with thunderstorm occurred and caused damage in Morisaki, Kugo-cho and Miharu-cho. We were able to assess the features of damage in a densely built-up area where ground level can vary by 20-30 m. The maximum wind speed cannot be fully determined because of the lack of structures appropriate for speed estimation. However, judging by the damage of the traffic sign, we can deduce that the damage scale of the tornado was F1 and locally F2. The tornado was rated F2-P1-P1 on the Fujita-Pearson scale.
There are three reasons why the gust in the area was a tornado as follows.
1) The damaged area lies in a narrow line.
2) Indication of rotatory (cyclonic) wind was observed.
3) Two signs of suction vortices were found.
Damage to over 100 residential buildings was observed and the damage area extends over a line of about 2.5 km by 150 m. Looking in detail at the damage map, we can see that the damaged area is discontinuous and meandering. The discontinuity is probably due to the repetitive touchdown (the so-called 'tornado jump') affected by the rugged landscape. The damaged area, which extends mostly near Kugo elementary school, indicates the complicated tornado's path in the mature stage. The features of the parent cloud were as follows:
4) The damage area was located at southwestern edge of the strong echo.
5) The vortex with 7 km in diameter (mesocyclone) was observed by a Doppler radar.
6) Pressure drop of 1 hPa was recorded below the mesocyclone.
The wind disaster in Yokosuka was caused by one of the tornadoes, which formed in the tapering cloud developed in the warm sector of a synoptic low.

Tenki, Vol. 54, No. 2

(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)

TENKI, Vol. 54, No. 2, pp. 169-174, 2007

The Amplitudes and the Phases of Terdiurnal (eight-hourly)
Pressure Oscillations at the Stations of Low Latitude Islands,
Higher Mountain and Some Central Area of Japan

Kunimoto IWAI*

* Faculty of Education, Shinshu University, 6-ro Nishinagano, Nagano, 380-8544, Japan.

(Received 9 May 2006;Accepted 11 December 2006)


Monthly mean terdiurnal oscillations in atmospheric surface pressure (S3) of the stations of low latitude islands, mountain and central area of Japan were determined by the harmonic analyses of 11 or 12 years time series of hourly barometric data. Annual variations of the amplitudes and the phases of S3 at each station are very regular, that is, maximum amplitudes of S3 of about 0.3 hPa and about 0.12 hPa occur respectively on December or January and on June or July and their minima occur on April and September. The phases of S3 from October to March and May to August remain constant respectively. Their phases, however, are out of phase. From the analyses of the phase of S3 at four low latitude stations in the Pacific Ocean, S3 can be interpreted that the tidal wave of zonal wave number three propagates westward at the phase speed of 15 degree longitude per hour.
The amplitudes and the phases of S3 at high altitude such as the summit of Mt. Fuji (3773 m above sea level) etc. were also determined. S3 amplitudes at altitude higher than 1,000 m above sea level are slightly smaller than those of near at the sea level. S3 phases of them are the same as those of low level altitude.