A reconstruction of the East Asian summer monsoon index over the half past millennium
- 1Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
- 2CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China
- 3Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute, Université Catholique de Louvain, Louvain-la-Neuve 1348, Belgium
- 4Key Laboratory of Physical Oceanography–Institute for Advanced Ocean Studies, Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266100, China
- 5Department of History/Bolin Centre for Climate Research, Stockholm University, SE-10691 Stockholm, Sweden
- 6CIC-FEMD/ILCEC, Key Laboratory of Meteorological Disaster of Ministry of Education, College of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China
- 7Department of Atmospheric Sciences, University of Hawaii at Mānoa, Honolulu, Hawaii 96822, USA
- 8State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China
- 9University of Chinese Academy of Sciences, Beijing 100049, China
The EASM largely determines variations in summer precipitation in the East Asian monsoon region where approximately one-quarter of the world’s population live. A reliable East Asian summer monsoon (EASM) index covering several centuries is important in order to understand EASM dynamics. The wind-field is frequently used to calculate the EASM index during the instrumental period. However, available climate proxy data rather respond to direct precipitation changes. A gridded extended summer (May–September, MJJAS) precipitation reconstruction for China covering AD 1470–2000 is used to indirectly reconstruct two types of EASM indices (defined by the strength of the 850hPa southwesterly winds and a north-south gradient of the zonal winds), using the negative correlation between the EASM index and summer (June–August, JJA) rainfall in the middle and lower reaches of the Yangtze River of China. The two EASM indices are validated by independent historical documentary data for eastern China. The physical processes ruling the EASM variability are explored, highlighting a baroclinic structure over the middle and lower reaches of the Yangtze River. It includes an anticyclonic circulation accompanied by high pressure anomalies in the lower troposphere and a cyclonic circulation with low pressure anomaly in the upper troposphere. This is associated with a decrease in atmospheric water vapor content (due to divergence), which will decrease summer rainfall in the region, and contribute to the strengthen of the EASM variability. The dominated and inter-annual component of the EASM variation is possibly linked to the ‘ENSO-like’ sea surface temperature according to a data assimilation experiment performed with the Community Earth System Model-Last Millennium Ensemble (CESM-LME) simulation.
How to cite: Shi, F., Goosse, H., Li, J., Ljungqvist, F. C., Zhao, S., Liu, T., Yin, Q., and Guo, Z.: A reconstruction of the East Asian summer monsoon index over the half past millennium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6488, https://doi.org/10.5194/egusphere-egu2020-6488, 2020.
