在地球赤道區的平流層中，緯向風場約每兩年會規律性的發生東風與西風交替變換的現象，此為大氣的準雙年振盪（QBO）。自1953至2015年中，QBO規律且持續的發生。但在2015年末至2016年初這段期間，原本應該向下移動的西風帶突然反轉向上移動，和規律而來的東風相遇。這種異常現象持續了近半年，直到 2016年中才恢復為以往正常的東西風交替形態。由於QBO與全球氣候有直接關聯，因此QBO異常現象立即成為學界的重要課題。截至目前為止，研究顯示來自中緯度的西向羅士比波與聖嬰現象是造成異常QBO的可能原因。綜觀目前的研究論文，幾乎都將重心擺放在造成QBO異常現象的西向羅士比波以及修正預報模式上。至於另一個對於QBO有重要貢獻的東向克耳文波目前尚無人詳加討論。因此本計畫利用衛星觀測與大氣再分析資料，分三年期研究克耳文波在此QBO異常時期的傳播特性以及其與背景風場之間的交互作用。此外，本計畫也將關注克耳文波在此QBO異常時期是否影響電離層。本計畫在第一年期與第二年期已經探討克耳文波在平流層到低熱氣層的傳播特性及克耳文波與高空風場半年振盪（SAO）的關係。而此次的第三年期計畫將利用全電子含量和電離層探測儀的觀測資料，探討超快速克耳文波對電離層的影響。計畫的成果將有助於推動大氣層與電離層耦合研究的進展。 ;The Quasi-Biennial Oscillation (QBO) is a regular variation of the zonal wind that blows in the stratosphere above the equator. Strong eastward and westward winds in the region completely change direction alternatively. The full cycle takes roughly 28 months, making it the most regular slow variation in the atmosphere since 1953 when QBO has been constantly documented. Unexpectedly, the evolution of QBO during the Northern hemisphere winter of 2015-2016 shows different features. A band of the westward wind began to form above the eastward wind, as expected, at the end of 2015, but it was cut off by a new band of the eastward wind that appeared below it, keeping the QBO from completing a normal cycle. Propagation of planetary scale Rossby waves from the NH mid-latitudes into the tropical region and the strong 2015-2016 ENSO effects may be the clues to the causes of this QBO anomaly. Because the QBO is forced by the interaction of Kelvin waves and mixed Rossby-gravity waves with the zonal mean flow, we are going to study the propagation characteristics of the atmospheric Kelvin waves during this QBO anomaly. Moreover, propagation features of ultra-fast Kelvin waves that travel to the ionosphere will also be investigated to examine with more ionospheric disturbances. The whole research project contents three phases, and this is the third phase. In the first two phases, we have studied the properties of Kelvin waves and further their propagation in the stratosphere, mesosphere, and lower thermosphere. The interactions between Kelvin waves and the background zonal winds have also been investigated. Therefore, in this 3rd phase, we will use total electron content and ionosonde data to find out the impacts of ultra-fast Kelvin waves on the ionosphere. The results of this project will further promote the study on the atmosphere-ionosphere coupling.
