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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. | en_US |