2017年夏季に出現・停滞したオホーツク海高気圧に関する総観気候学的解析

• Main Authors: 宮本, 大輔, 山川, 修治
• Format: Report
• Language: Japanese
• Published: 日本大学文理学部自然科学研究所 2019
• Subjects: Okhotsk high (OHH); synoptic climatology; quasi-stationary Rossby wave; climatic variation; global warming; Arctic; Okhotsk; Global warming; okhotsk sea
• Online Access: https://repository.nihon-u.ac.jp/xmlui/handle/11263/2362; https://doi.org/10.15006/chs20201054012

In August 2017, temperature was cooler than normal during a few weeks in North and East Japan because of the sta-tionary Okhotsk High (OHH). This study analyzed and discussed the mechanism of the stagnant OHH and its related cli-matic variations from a viewpoint of synoptic climatology. OHH appeared in the five-day mean of the 45 pentad (09 Aug. -13 Aug.) and the 46 pentad (14 Aug. -18 Aug.), so it was indicated that OHH stayed in a few weeks. In the 43 pentad and 44 pentad (30 July -08 Aug.) the temperature at 500 hPa in the Eurasian Continent was high, whereas it was low in the Arctic region. The meridional difference of temperature increased and the polar front jet stream was strong. In the back-ground the AO (Arctic oscillation) was in a positive phase. In the 45 pentad and the 46 pentad, the quasi-stationary Ross-by wave propagated from East Europe to the Far East, which led to the large persistent meandering of the polar frontal jet, which resulted in stationary OHH during a few weeks. In the meanwhile, although positive SST anomalies were found in the Philippine Sea, convective activity revealed a negative anomaly. Convective activity areas shifted towards near Indo-nesia due to stronger northeast winds in the transition from the super El Niño in 2015-2016 to the La Niña. Around the Okhotsk Sea, a positive anomalies were detected in July and August based on 10-year (2008-2017) average of 500 hPa height anomaly. Therefore, OHH has formed more frequently than before. The results of the composite analyses about the difference in meridional temperature gradients in the Eurasian Continent indicated that a ridge developed around the Okhotsk Sea, while a trough was located west off Japan in August. It is pointed out in this case that the atmospheric cir-culation was affected by climatic variations such as AO and ENSO, in August 2017. It is likely that OHH will tend to appear and stay in the coming future. An increase in the number of hot days was predicted with progressing global warm-ing. Nevertheless, there is ...