2026-04-09 東京都立大学
図１：太平洋高気圧張り出し熱波パターン時と熱帯低気圧接近熱波パターン時の上空約1,500mでの大気の流れのパターン（矢印: 統計的に有意な場合のみ表示）。等値線は、ジオポテンシャル高度の気候平均からの偏差で、正の値は高気圧性、負の値は低気圧性を示す。左（右）は、ほとんどが正（負）の値で高気圧性（低気圧性）である。
＜関連情報＞
- https://www.tmu.ac.jp/news/topics/38474.html
- https://link.springer.com/article/10.1007/s44394-026-00018-3
西日本における8月の熱波に関連する大気循環パターン：熱帯および中緯度の影響 Atmospheric circulation patterns associated with August heat waves in western Japan: tropical and mid-latitude influences
Hiroshi G. Takahashi,Hirokazu Endo,Yuhei Takaya,Tomoaki Ose,Nozomi Kamizawa & Toshiyuki Nakaegawa
Journal of Meteorological Society of Japan Published:09 April 2026
DOI:https://doi.org/10.1007/s44394-026-00018-3
Abstract
To classify and understand the causes of heat waves in western Japan, this study investigated atmospheric circulation patterns during August from 1992–2021, using reanalysis data. First, we defined heat-wave days using daily surface air temperature and identified 108 days out of 930, each having a spatial scale larger than a few hundred kilometers. We then applied empirical orthogonal function (EOF) analysis to the 850-hPa geopotential height for those 108 heat-wave days. The leading three EOF modes explained over 60% of the total variance. Because positive and negative principal components (score time-series) of the EOF modes can be associated with physically different phenomena, we did composite analyses separately for the EOF1-positive and EOF1-negative cases. Expectedly, westward extension of the subtropical high, considered the major cause of heat waves in western Japan, was observed. Additionally, slightly different patterns, such as a southwestward extension, produce regional differences across East Asia. In contrast, other causes were also observed under retreated-subtropical-high conditions. These other causes include a tropical cyclone approaching along the southern coast of western Japan and a response to convective activity around the Philippines (Pacific–Japan-like teleconnection pattern), accounting for 24% and 12% of events, respectively, indicating that these circulation types are non-negligible contributors to heat waves in the region. Notably, the tropical-cyclone–related categories induce a relatively unique “moist heat wave.” We also examined the long-term frequency variability of each category. Our research shows that exploring the causes of heat waves in climate projections improves understanding of future heat waves.
