Miaoni Gao^1,2, Bin Wang^3,4, Jing Yang^5,*, Wenjie Dong⁶

¹Key Laboratory of Environmental Change and Natural Disaster, Ministry of Education, Beijing Normal University, Beijing, China

² School of Systems Science, Beijing Normal University, Beijing, China

³ Department of Atmospheric Sciences, and International Pacific Research Center, University of Hawai‘i at Manoa, Honolulu, Hawaii

⁴ Earth System Modeling Center, Nanjing University of Information Science and Technology, Nanjing, China

⁵ State Key Laboratory of Earth Surface Processes and Resource Ecology, and Academy of Disaster

Reduction and Emergency Management, Faculty of Geographical Science, Beijing Normal University, Beijing, China

⁶ School of Atmospheric Sciences, Sun Yat-sen University, Guangdong, China

 

*Corresponding author: J. Yang, yangjing@bnu.edu.cn

 

Abstract: The Yangtze–Huaihe River basin (YHRB) is the core region of sultry heat wave occurrence over China during peak summer [July and August (JA)]. The extremely hot and muggy weather is locally controlled by a descending high pressure anomaly connected to the western Pacific subtropical high. During 1961–2015, the heat wave days (HWDs) in JA over the YHRB exhibit large year-to-year and decadal variations. Prediction of the total number of HWDs in JA is of great societal and scientific importance. The summer HWDs are preceded by a zonal dipole SST tendency pattern in the tropical Pacific and a meridional tripole SST anomaly pattern over the North Atlantic. The former signifies a rapid transition from a decaying central Pacific El Niño in early spring to a developing eastern Pacific La Niña in summer, which enhances the western Pacific subtropical high and increases pressure over the YHRB by altering the Walker circulation. The North Atlantic tripole SST anomalies persist from the preceding winter to JA and excite a circumglobal teleconnection pattern placing a high pressure anomaly over the YHRB. To predict the JA HWDs, a 1-month lead prediction model is established with the above two predictors. The forward-rolling hindcast achieves a significant correlation skill of 0.66 for 1981–2015, and the independent forecast skill made for 1996–2015 reaches 0.73. These results indicate the source of predictability of summer HWDs and provide an estimate for the potential predictability, suggesting about 55% of the total variance may be potentially predictable. This study also reveals greater possibilities for dynamical models to improve their prediction skills.

 

Published in Journal of Climate, 2018, DOI: 10.1175/JCLI-D-17-0342.1.

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0342.1