Variation mechanism and predictability of tropospheric annular mode

2018 Fiscal Year Final Research Report

• Project/Area Number: 26287115
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Partial Multi-year Fund
• Section: 一般
• Research Field: Meteorology/Physical oceanography/Hydrology
• Research Institution: Kyoto University
• Principal Investigator: Mukougawa Hitoshi 京都大学, 理学研究科, 教授 (20261349)
• Co-Investigator(Renkei-kenkyūsha): KURODA YUHJI 気象研究所, 気候研究部, 研究官 (80343888)
• Project Period (FY): 2014-04-01 – 2019-03-31
• Keywords: 環状モード / 対流圏 / 成層圏 / 予測可能性 / 惑星規模波 / 下方伝播

Outline of Final Research Achievements

We investigate the maintenance mechanism of the annular mode, which is the most prevailing variation mode in the extratropical troposphere, using a reanalysis dataset. It is found that the quasi-stationary planetary waves and transient synoptic waves play the most important role in driving the annular mode in the northern hemisphere and southern hemisphere, respectively. It is also revealed that the vertical propagation property of planetary waves in the recovery phase of stratospheric sudden warming events is intimately related to the subsequent formation of annular mode. Moreover, several aspects of the predictability variation of the stratospheric circulation, which are closely related with the tropospheric annular mode, are clarified through the analyses on ensemble reforecast experiments conducted by the MRI (Meteorological Research Institute) ensemble prediction system which is constructed in this study.

Free Research Field

気象学

Academic Significance and Societal Importance of the Research Achievements

対流圏中高緯度大気で最も卓越する変動成分である対流圏環状モード変動を駆動する波動を明らかにすることができた。また、成層圏突然昇温現象の終了時における惑星規模波の鉛直伝播特性が環状モードの形成と関連していることが明らかになった。さらに、これまで力学的には比較的安定と考えられていた成層圏循環は、成層圏突然昇温の生起時などには力学的に極度に不安定となり、成層圏循環自体に予測障壁が存在することが初めて明らかになった。