Qualifying Contributions of Teleconnection Patterns to Extremely Hot Summers in Japan

• Published in: Journal of the Meteorological Society of Japan Vol. 100; no. 3; pp. 509 - 522
• Main Authors: MOGI, Atsushi, WATANABE, Masahiro
• Format: Journal Article
• Language: English
• Published: Meteorological Society of Japan 2022
• Subjects: circumglobal teleconnection; Japan summer temperature; Pacific-Japan pattern; Siberian pattern; statistical model
• ISSN: 0026-1165; 2186-9057
• DOI: 10.2151/jmsj.2022-025

Extremely hot days in Japan are known to persist for a week or more, and they are measured by the temperature anomaly at 850 hPa averaged over Japan derived from the JRA-55 reanalysis data, denoted as T850JP. Severe high-temperature anomalies are often accompanied by multiple teleconnection patterns that affect the weather in Japan, but their relative contribution to individual heat wave events has not yet been quantified. In this study, we examined the effects of three major teleconnection patterns, namely, the Pacific-Japan (PJ), circumglobal teleconnection (CGT), and Siberian patterns, on T850JP in July and August from 1958–2019 using daily low-pass-filtered anomalies with 8 days cutoff timescale derived from the reanalysis.A linear regression analysis demonstrated that T850JP tended to show a large positive anomaly one or two days after the peak of these patterns. On the basis of this relationship, we reconstructed a daily T850JP time series using a multivariate statistical model wherein the parameters were estimated using regression analyses between T850JP and the indices of the three teleconnection patterns. The reconstructed T850JP showed that the three teleconnection patterns together accounted for 50 % of the total variance of T850JP for extremely hot summers, to which each of the three teleconnection patterns were found to have a similar degree of contribution. The statistical model reproduces the interannual variability along with the long-term T850JP trend. The PJ pattern has the largest effect on the interannual variability of T850JP, probably due to the PJ teleconnection occurring over a longer timescale compared with the other two patterns. The reconstructed T850JP also displays a warming trend associated with an increasing trend in the CGT index, which may be a factor, along with the direct thermodynamic effects due to global warming, to explain the long-term increase in the heat wave frequency in Japan.