モンゴルにおける寒冬および暖冬下の多雪 Cold- and warm-deep-snow winters in Mongolia

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Abstract

ユーラシアの春の積雪面積は,温暖化に伴い過去数十年で減少傾向が見られる。しかし冬の積雪状態については,データ不足のため未だあまり解明されていない地域も残る。本研究では特に温暖化の著しいモンゴルの冬季(11月~2月)に着目し,積雪深,気温,及び降水量とそれらに関連する大気循環について解析を行った。標準化した冬季における降水量,平均積雪深,及び平均気温を,モンゴル全域に分布する代表観測点で平均して指数化し,各指数の1961年から2007年の経年変動を明らかにした。解析期間前半に発生した多雪冬は著しく寒い冬と一致していたが,1990年代以降,温暖な冬にも多雪冬が現れた。平年より寒冷,及び温暖な多雪冬それぞれの合成の総観解析を行った。寒冷な多雪冬には,平年モンゴルの東に位置する上層のトラフがより西側に張り出しており,モンゴルへより強い寒気の流入があった。一方,温暖な多雪冬には,モンゴルの東のトラフの張り出しは弱く,西からモンゴルへのより強い水蒸気輸送があった。過去数十年にわたり気温が上昇するなか,冬季積雪深は減少しておらず,その背景に温暖多雪冬の存在が示唆される。今後頻度が増すと考えられる暖冬においても,モンゴルでは強まった水蒸気輸送により,依然大量の積雪に見舞われ得る可能性が示唆された。

Eurasian snow cover in spring has followed a decreasing trend since the mid-1960s, but winter conditions remain unknown because of a lack of data. To address this issue with a regional focus on the eastern part of Eurasia, we conducted an observational study of winter temperature, precipitation, and snow depth in Mongolia and the associated atmospheric circulation. We used the meteorological data at 21 representative Mongolian weather stations for four winter months (November to February) from 1960 through 2007. Time series analysis was applied to three indices: standardized deviations from the mean for this 4-month period averaged over the 21 stations in Mongolia for snow depth, precipitation, and temperature. This analysis revealed a significant multi-decadal trend in temperature, but not in snow depth.<br>During the 1960s and 1970s deep-snow winters coincided with extreme cold. However, beginning in the winter of 1992-1993, a new type of deep-snow winter with warmer conditions has occurred in some years. Moreover, a synoptic analysis demonstrated that a trough at the 500-hPa level that is usually climatologically located east of Mongolia extended westward to Mongolia during the cold-deep-snow winters. This indicates that enhanced cold surges from the north to Mongolia led to the historically typical deep snow conditions. On the other hand, the warm-deep-snow winters were characterized by a weakened trough, weakened cold surges, and concurrently intensified moisture transport from the west into Mongolia. The new circulation pattern observed here shows that warm winters, which may become more frequent in the future, still have the potential to cause deep snow in Mongolia.

Journal

  • Journal of Agricultural Meteorology

    Journal of Agricultural Meteorology 66(2), 103-110, 2010

    The Society of Agricultural Meteorology of Japan

Cited by:  1

Codes

  • NII Article ID (NAID)
    130004878262
  • NII NACSIS-CAT ID (NCID)
    AA11530034
  • Text Lang
    ENG
  • Article Type
    Journal Article
  • ISSN
    0021-8588
  • NDL Article ID
    10739766
  • NDL Call No.
    Z18-388
  • Data Source
    CJPref  NDL  J-STAGE  JASI 
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