夏季夜間に東京のヒートアイランド現象が局地風系に及ぼす影響 Influence of the Urban Heat Island Phenomenon in Tokyo on the Local Wind System at Nighttime in Summer

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Abstract

 本研究は,2003年と2004年の2年間の夏季の観測データをもとに,東京のヒートアイランド(UHI)現象が局地風系に及ぼす影響を解析した。本研究では,東京の高密度観測システム(METROS)のデータを基本的に使用した。本研究は,夜間のUHIに大きな影響があると考えられる,夜間の局地風系にとくに焦点を当てた。本研究では,最初に昼夜の局地風系の交替が起こった日で事例解析を行った。次に,2年間の夏季のデータで合成図解析を行った。本研究の結果は以下のようにまとめられる。<br> 局地風系の挙動が,東京の気温分布と密接に関連していることがわかった。沿岸部での夜間の北寄りの風の風速と継続時間は,北部や都心部と比べてずっと弱く短かった。気温勾配と南北風速との関係から,夜間に気温勾配が小さい東京のUHIの中心付近に,静穏域の存在が予想された。静穏域の存在は事例解析で確認された。静穏域の形成は,UHIによる風の収束に起因すると考えられる。<br> 事例解析でみられた静穏域は,11日間の昼夜の局地風系の交替が起こった日の合成図解析でも深夜から早朝にみられた。さらに,静穏域は夜間の風速が小さい47日間の弱風日(2年間の7月と8月の38%)の合成図解析でもみられ,夏季に東京で一般的に存在する現象であることが示唆された。

 The present study analyzed the influence of the urban heat island (UHI) phenomenon on the local wind system in Tokyo based on observational data acquired during two summers in 2003 and 2004. Data from Tokyo's high density observation system, the Metropolitan Environmental Temperature and Rainfall Observation System (METROS), was used. This study focused on the local wind system at nighttime, which is considered to greatly influence the nocturnal UHI. We first carried out some case studies on days that showed typical diurnal variations of the local wind system. A composite analysis was then conducted based on the full two-summer dataset.<br> The behavior of the local nocturnal wind system was found to be closely related to the temperature distribution in Tokyo. In the coastal area, the northerly wind was much weaker and lasted for a shorter time than in the northern and central areas of Tokyo. From the relationship between the temperature gradient and the north-south wind speed, a calm zone was predicted around the center of the Tokyo UHI where the nocturnal temperature gradient was small. The existence of this calm zone was confirmed by the case study, and its formation is thought to be caused by wind convergence due to the UHI.<br> The calm zone was also evident from nighttime to early morning from a composite analysis of eleven days on which typical diurnal wind variations were observed. It also appeared during a composite analysis of 47 weak-wind days (38% of days in July and August over two years) when wind speeds at nighttime were low, suggesting that it is a common summer phenomenon in Tokyo.

Journal

  • Journal of Geography (Chigaku Zasshi)

    Journal of Geography (Chigaku Zasshi) 120(2), 341-358, 2011-04-25

    Tokyo Geographical Society

References:  31

Cited by:  3

Codes

  • NII Article ID (NAID)
    10030372516
  • NII NACSIS-CAT ID (NCID)
    AN00322536
  • Text Lang
    ENG
  • Article Type
    Journal Article
  • ISSN
    0022135X
  • NDL Article ID
    11123502
  • NDL Source Classification
    ZM41(科学技術--地球科学)
  • NDL Call No.
    Z15-169
  • Data Source
    CJP  CJPref  NDL  J-STAGE 
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