Strongly Negative Correlation between Monthly Mean Temperatures in April and August since 1998 in Northern Japan

Journal of the Meteorological Society of Japan. Ser. II

Hiromitsu KANNO¹ 

[1]NARO Tohoku Agricultural Research Center, Morioka, Japan

关键词: northern Japan;    climatic shift;    temperature;    ENSO;    AO;   

DOI  :  10.2151/jmsj.2013-308

学科分类：大气科学

来源: Meteorological Society of Japan

【 摘 要 】

 Monthly mean temperatures for April and August have been strongly and negatively correlated from 1998 to 2011 in northern Japan. When monthly mean temperatures in April were either significantly below or significantly above normal, the temperatures in the following August had the opposite anomalies. We attribute this seasonal behavior of temperatures to a displacement of the core of upper-level westerly winds. When monthly mean temperature was higher than normal in August, the subtropical jet stream had been strengthened in April and a continental polar air mass affected northern Japan in April. In August of that year, if a jet located north of Japan moved further north, Japan was covered by a maritime tropical air mass, and a maritime polar air mass rarely affected summer weather in northern Japan. In the opposite case, when temperatures were cool in August and warm in April, we inferred that the jet had been weak and the continental polar air mass did not move south and affect northern Japan in April; thus, in August the jet shifted southward and the maritime polar air mass could affect summer weather. An empirical orthogonal function analysis of the 200-hPa height field revealed that two principal component modes were associated with the anomalous temperatures in these two months. On the basis of these results, we identify these modes as the cause of upper level westerly wind variations on the northern hemispheric scale. Based on a singular value decomposition analysis of the 200-hPa height field and the sea surface temperature, the year 1998 marked one of the several pronounced climatic shifts of the last century.

【 授权许可】

Unknown