Shuji Yamakawa

Atmospheric Conditions of the Northern Hemisphere in Spring Followed by Unusual Cool Summers Focusing on Stratospheric Ozone Depletion and Cold Vortexes

In this study, atmospheric conditions of the Northern Hemisphere in spring followed by unusual cool summers are discussed focusing mainly on stratospheric ozone depletion and cold vortexes (CVs). The distribution patterns where an AV (Arctic vortex) and CVs tend to form frequently are examined. The relationship between the Arctic Oscillation (AO) and total ozone volume is investigated. In a negative AO year, 1L (Icelandic low) seldom appears from March through May, while the appearance of AL (Alutian low) is conspicuous; moreover, CVs tend to form over Siberia in spring and summer. The atmospheric conditions had an influence on the movement of CVs from Siberia toward Japan, which made extraordinary the frontal activities including the Baiu front in spring and summer. According to the 30 hPa height anomaly analyses, from spring through summer negative areas were prevailing in 1993 in and around the Arctic Circle while positive areas were prevailing in 2003 when two sudden warmings occurred in both mid-January and early February. The most remarkable feature underlying conditions of 1993 was the developing Arctic cold air mass due to aerosol which originated from the Pinatubo great eruption (DVI:1000) on 15 June 1991. On the contrary, in 2003 the positive height areas covered the Arctic Circle in the lower stratosphere owing to the sudden warming, therefore in the troposphere the positive areas led to blocking highs, particularly Okhotsk highs. As for the summer cool damage in 1993 as well as in 2003, not only the Yamase type (the first type) but also the CV type (the second type) were complicated. However, the pressure systems of these cool summers differ considerably. The Okhotsk highs in the summer of 1993 and 2003 stem from different sources.