Seasonal variation of air transport in the Antarctic and Atmospheric Circulation in 1997

To better understand how present and past climates at Syowa Station, Antarctica relate to climate elsewhere, we analyzed the tropospheric air transport to Syowa Station for the year 1997 using a dataset from the European Centre for Medium Range Weather Forecasts(ECMWF). The five-day trajectories of the air parcels were estimated and analyzed. In the middle troposphere in winter, air parcels were usually from the lower troposphere over the Atlantic. However, in January, most of the air parcels came from latitudes higher than 60°S . The trajectories had little vertical motion and were associated with a low pressure system that forms along the coastal region of Antarctica only in summer. In the lower troposphere, trajectories could be classified as originating in one of three regions: the Southern Ocean, the continental interior, and the east coast. In contrast to the middle troposphere, air parcels from the Southern Ocean had the lowest frequency, irrespective of the time of year. This is partially due to a low pressure system that blocks air parcels from outside the continent. Most trajectories are affected by the drainage flow. An amplified quasi-stationary planetary wave for September to November and a blocking circulation in June make trajectories pass over Antarctica

Addressing our planetary crisis: Consensus statement from the presenters and International Advisory Committee of the Regional Action on Climate Change (RACC) Symposium held in conjunction with the Kyoto-based Science and Technology in Society (STS) Forum, 1 October 2021.

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ジャワ島周辺における月降水量の時空間変動の解析

この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました。ジャワ島およびその周辺地域における23年間(1951-1973)の月降水量変動を解析した結果, 変動度(variability)は, 乾期(東風卓越期)に大きく, 雨期(西風卓越期)には比較的小さいこと, 地域的には, インド洋側がジャワ海側より大きいことが明らかとなった。経年変動の時間的空間的特性を, 平年偏差値についての経験的直交函数解析を用いて調べた。その結果, 準2年周期振動(QBO)がもっとも卓越する成分(総分散の29.4%)として現われ, この振動は, ジャワ島のみならず, 少なくともスマトラ, ボルネオ, スラウェシ各島の南半部にまで拡がる地域で, ほぼ同位相を持って卓越していることが明らかとなった。乾期における大きな変動度は, このQBOが大きく寄与しており, 乾期(雨期)の伸縮, 時期的なずれ, 乾期降水量の増減を決める因子として重要なモードと推測される。第2成分(総分散の6.2%)は, 雨期最盛期(1,2月)の降水量変動を説明しており, 数年(以上)の長周期変動として現われている。空間パターンは, 島の北側平野部と南側山岳部が逆の位相で変動していることを示している。上記ふたつの卓越成分に関連した大気循環パターンを, グローバルな地上気圧資料を用いて調べた結果, 第1成分は, オーストラリア周辺から南太平洋東部域を中心とする南半球中緯度の気圧のQBOに対応したものであり, 第2成分は, 北半球冬期のモンスーン循環系(シベリア高気圧-アリューシャン低気圧)の南北方向の偏位に関連していることが確認された。これらふたつの変動モードと, いわゆる"southern oscillation"との関連についても, 若干の考察を試みた。The analysis of the long-term fluctuation of monthly rainfall (1951-1973) revealed that the year-to-year variability of the rainfall in and around Java is large in the "east monsoon" (dry) season and relatively small in the "west monsoon" (rainy) season. The empirical orthogonal function analysis of the anomaly rainfall showed that the quasi-biennial oscillation (QBO) is dominant over the whole of Java with the large variance (29.4% of the total variance), and that a large variability in the "east monsoon" season is mostly explained by this component. The second component (6.2% of the total variance) represents the variation in the "west monsoon" season with a contrastive spatial pattern between the Java Sea side and the Indian Ocean side of the island. It was also confirmed that the first component (the QBO mode) in the anomaly rainfall is closely connected with the QBO in the surface pressure field over Australasia through the eastern south Pacific and the second component is associated with the north- (or south-) ward shift of the winter monsoon circulation system in the Northern Hemisphere. In addition, the relations between these two modes and the "southern oscillation" are briefly discussed