(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 51, No. 8, pp. 567-581, 2004
Between 1996 and 2001, three hailstorms with downbursts occurred over the Kanto Plain, on 15 July 1996, 24 May 2000, and on 11 May 2001. These storms were analyzed with data from Doppler weather radars, conventional weather radars, radiosondes, surface observations, and damage investigations, revealing the following:
(1) The supercells were isolated with a single-cell structure, a BWER (bounded weak-echo region) and a mesocyclone at midlevels with an overhanging vault above. The stability of the atmospheric stratification, the vertical wind shear, and the structure of surface wind convergence strongly influenced the disturbance characteristics, including temporal and spatial scales and severity.
(2) The three storms had similar lifecycles. Initially, the southwestern part of a multicellular storm developed into a hailstorm, the radar echo of which had a clump pattern. This occurred when the storm was located in the convergence between warm moist southerly winds from Tokyo Bay and dry northerly winds from a colder air mass. After hail had fallen, the system gradually developed again and produced a hail core (a domain with radar reflectivity exceeding 60 dBZ) and a WER. This new system then developed a BWER as it moved into a region of northeasterly winds from Kashima Bay (the formation stage). The storm then entered the developing stage, growing upward rapidly and producing prominent downbursts. The mature stage was marked by expansion of the hail area in the upper part of the storm and continuous hail damage. The subsequent decaying stage was accompanied by downbursts. During these stages, the hail core moved up and down with a period of 18 to 24 minutes.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 51, No. 9, pp. 655-665, 2004
The largest flood in the 19th century within the Shinano River Basin occurred in July 20-22, 1896. The present report analyzed the meteorological condition which caused the large precipitation, by using the surface observation data. Result of the analysis indicates that the passage of a very weak tropical depression along the North Pacific subtropical anticyclone that stayed east of Japan, and the successive passage of an extratropical depression in the northern latitude caused a large precipitation over the whole basin of Shinano River and its branches.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 51, No. 9, pp. 667-678, 2004
As a possible indicator of the terrestrial evaporation trend, pan evaporation measured over the past 34 years at 13 stations operated by Japan Meteorological Agency were analyzed in terms of its long term trends. It was clearly shown that, except some stations under strong influences of the local urbanization, the past records of the pan evaporation measurements contain a clear decreasing trend all over the Japan for all seasons. Detailed analyses show that the decreasing pan evaporations were accompanied with the increasing vapor pressure deficit that is the indication of increasing terrestrial evaporation. In the northern regions, however, increasing cloudiness, i. e., decreasing solar radiation, was also found to have an influence on the decreasing pan evaporation trend. A correlation/regression analysis also indicates that there is distinction in the controlling factors of pan evaporation between the northern and the southern region of Japan.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 51, No. 11, pp. 805-816, 2004
The trend in the frequency of heavy rainfall events, which are defined by six time scales (1-, 3-, 6-, 12-, 24-hour precipitations and accumulated precipitation) and three threshold values (2, 5, and 10 years probability precipitations), was analyzed by using hourly precipitation data at 18 meteorological observatories in Japan from 1950 to 2003. In the warm season (from May to October), on the whole, the frequency of heavy rainfall events was high from 1950 to the early 1960's and low from the late 1960's to the 1980's, and was highest after 1990. However, the frequency of 3- and 6-hour precipitation events above the 2 years probability is high only after 1990. The increasing trend in the frequency of heavy rainfall events during the latter half of these 54 years is significant at the 5% level for most of the time scales and threshold values of heavy rainfall, although the decreasing trend during the early half is statistically significant for only limited time scales or threshold values. The high frequency of heavy precipitation events above the 2 years probability after 1990 is found both for the Baiu season (from May to July) and the typhoon season (from August to October), apart from some differences according to the time scale of heavy rainfall.
(Tenki is the bulletin journal of the Meteorological Society of Japan in Japanese.)
TENKI, Vol. 51, No. 12, pp. 881-894, 2004
Intensive observations including double theodolite pilot balloon observations have been carried out for investigating the characteristics of the local strong easterly wind, Kiyokawa-dashi, which blows at the exit of the narrow valley in the Shonai region. Two types of Kiyokawa-dashi have been observed:blowing locally (Obs-1) and widely (Obs-2 and 3). Double theodolite pilot balloon observations have been conducted at the exit of the valley. Vertical cross sections reveal that the height of the easterly wind was different in each case, and the low level jet (Kiyokawa-dashi jet) appeared 200-400 m above the ground. A strong vertical wind speed of more than 1 m/s appeared above the Kiyokawa-dashi jet. A simple gap wind equation based on the pressure difference along the axis of the valley is quite capable of creating the observed magnitudes of wind speed at the exit of the valley, except for Obs-1. A remarkable inversion layer was observed in all the cases by analyzing the aerological observation data obtained at Sendai and Akita. Especially in Obs-1, the inversion layer of Sendai, which lies in the upstream region of the valley, was lowest near the crest around Kiyokawa, and the Froude number was small being approximately 0.11. In this case, hydraulic jump is favored near the exit of the valley. Therefore, the strong wind field would be limited at the exit of the valley. On the other hand, in Obs-2 and 3, the inversion layer of Sendai was higher than the crest, and the Froude number was relatively higher being approximately 0.58. Therefore, the strong wind would blow widely downstream of the valley in these cases. The mechanisms of the strong wind will differ in each synoptic situation.