著者

羽生 寿郎 山田 幸兵衛

出版者

日本農業気象学会

雑誌

農業気象 (ISSN:00218588)

巻号頁・発行日

vol.9, no.2, pp.45-48, 1954

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In Aomori prefecture the prevailing north-easterlies have been named &ldquo;Yamase-winds&rdquo;. In warm period they accompany the cold and bad weather, and so great concern has been given them from the standpoint of agriculture.<br>The authors classified the wind directions of 10.00 JST observed at Hachinohe Weather Station for the five months from April to September, for the period of 1937-1951 and made some statistical study.<br>A. The range of wind direction and climatic characters of Yamase winds from May to August are as follows:<br>(1) The wind direction ranges from NNW to SE including E.<br>(2) The principal winds of Yamase (NE, ENE, E) are about 5&deg;C lower that of prevailing westerlies (SW, WSW, W) and about 18% wetter in relative humidity.<br>(3) Yemase-winds are more frequent than the westerlies in all kinds of weather, but the percentage of occurrence of low cloud overcast, rainy and foggy days for the Yamase-winds is greater than that for the westerlies and vice versa for the percentage of occurrence of fine and high and middle cloud overcast days.<br>(4) The duration of sunshine is generally shorter for Yamase than the westerlies, but in NE and ENE winds, sunshine is more abundant in Yamase. This may be because of the direction of the sea breezes being included in the range of Yamase-winds.<br>B. The relation between notable low temperatures and Yamase-wands. The monthly mean air tempertures corrected by the deviation of wind direction are obtained from the formula (1) (&Delta;&theta;_d, <i>n</i>_d are mean air temperature departures and number of days for each direction. <i>n</i> is number of days a month.) and shown by the broken lines in Fig. 5. In the year of bad harvest the actual air temperature departures (full line) are 2-3&deg;C lower than the former. It is considered that these differences are due to the kind of air mass or bad weather.<br>In order to see the effect of bad weather the wind directions are classified into two groups, the Yamase winds (NNW-SE) and other winds including calm, and the kinds of weather are classified into five groups, clear, fine, high and middle cloud overcasts, low cloud overcast and rain including fog. Then the monthly mean temperature departures corrected according to weathar and wind direction are obtained by the formula (2) (&Delta;&theta;_w, <i>n</i>_w are mean temperature departures and number of days for each kind of weather for each wind direction) and are shown by the dotted lines in Fig. 5. During the summers of 1941 and 1945, the monthly mean temperatures are much lower than these values. Therefore, it is considered that these notable low temperatures are due to the cold air mass.

著者

今 久 羽生 寿郎

出版者

千葉大学

雑誌

千葉大学園芸学部学術報告 (ISSN:00693227)

巻号頁・発行日

vol.39, pp.17-22, 1987-03-30

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1985年4月24日関東地方の広い範囲でひょうが降った.被害は約5億円に達したが,季節的に早かったせいもあり,規模の割には少なかったといえる.しかし,降ひょうの規模が大きかったので,降ひょう予測という点に注目しながら解析を行なった.その結果,次のような知見が得られた.1.進行速度は日本海上で少し遅くなるが,500mbの寒気の大陸上の移動速度を使って外挿することでおおむね予想できた.2.降ひょう日には対流不安定が地上から3000mまで達し,下層は南よりの風で湿度が高く,上層は北よりの風が卓越していた.3.ショワルターの安定指数を用いた降ひょう子測では850mbより900mbの気塊を用いた方がうまく予報できた.4.クラスターの南側と東側では風向・風速・気温降下の間に異なる関係が見られた.5.風向が変化した時から降ひょうと風速ピークが生ずるまでの時間は,平均的に見ると30から40分程度であった.6.降雨域と気温降下域にずれがあったが,最大の気温降下量は温度の時間変化の軌跡から,連続した複数の積乱雲による下降気流によってもたらされたと判断された.