個案分析結果顯示夏、冬季之發生機制不同，東亞地區冬季時由於大陸高壓系統向南推移，使副熱帶噴流較靠近台灣，由對流層頂褶皺之位置可發現平流層侵入現象；夏季時由於大陸高壓與噴流系統減弱，導致平流層侵入現象之主因為颱風。鹿林山測站之高度介於中低自由對流層與邊界層之上，且不易受地面都市污染物影響，而其位置鄰近冬季副熱帶噴流南緣、夏季時為東亞地區受颱風侵襲第一線，透過本篇研究之結果證明鹿林山確實可做為東亞副熱帶地區平流層侵入之觀測點。 ;Abstract Stratospheric intrusion (SI) often brings ozone rich air with low humidity from the stratosphere rapidly deep into the troposphere. Tropopause folds, frontal passages, surface high-pressure systems, and cutoff lows mainly counted for the occurrence of SI. In this study we present 5 years of ozone data measured at Lulin Atmospheric Background Station (LABS, 23.47°N, 120.87°E, 2862 m a.s.l.) to investigate the characteristics of SI events occurred in the subtropical East Asia during the period of April 2006 to March 2011.
A fast-screening algorithm was proposed to sift the SI events at the LABS. The ozone was increased approximately 13.5±6.1 ppb on average during the 54 detected SI events, whereas the mean ozone mixing ratio was 32.8±15.2 ppb over the 5 years. By using the Modern Era Retrospective Analysis - 2 (MERRA-2) assimilated data provided by NASA/GSFC, three types of SI events were classified as follows - (1) SI occurred around Taiwan Island, (2) SI occurred in central China and then transported to Taiwan surrounding area, and (3) SI occurred in Northwest Pacific and then transported to Taiwan surrounding area.
From the results of case studies observed at the LABS, the subtropical jet stream was dragged to Taiwan surrounding area due to the Siberian high moving southward. As a result, SI event was occurred at tropospheric folds induced by the subtropical jet in winter. By contrast, the SI was triggered by typhoon or tropical cyclone in summer.
