"清川ダシ"吹走時に観測された強風域および風の鉛直構造の特徴 Observation Evidence of the Spatial Distribution of Wind Speed and the Vertical Structure of the Local Easterly Strong Wind "Kiyokawa-dashi" on the Shonai Plain, Yamagata

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山形県庄内地方に発生する清川ダシの集中気象観測を行い,峡谷出口に強風域が局限される事例(Obs-1)と,全域で強風の事例(Obs-2,3)を観測した.峡谷出口でのパイバル2点観測の結果,東風成分の高度は事例によって異なり,Obs-2では下層200~400mに最強風帯が,その上空付近には1m/s以上の強い上昇流が発生していた.峡谷出口の風速は,峡谷内の気圧傾度によって加速された,地峡風の風速と同様の傾向であったが,Obs-1ではばらつきが大きかった.付近の高層データから,全ての事例で逆転層が認められた.Obs-1では上流である仙台の逆転層が清川周辺の山脈と同程度と低く,フルード数は0.11であり,峡谷出口付近でHydraulic jumpが発生していた可能性がある.一方,Obs-2,3では仙台の逆転層が高く,フルード数は最高0.58で,強風が平野全域に現れやすい状況であったと考えられる.

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.

収録刊行物

  • 天気

    天気 51(12), 881-894, 2004-12-31

    日本気象学会

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各種コード

  • NII論文ID(NAID)
    110001818526
  • NII書誌ID(NCID)
    AN00151568
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    05460921
  • NDL 記事登録ID
    7198010
  • NDL 雑誌分類
    ZM43(科学技術--地球科学--気象)
  • NDL 請求記号
    Z15-35
  • データ提供元
    CJP書誌  CJP引用  NDL  NII-ELS  NDL-Digital 
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