Abstract
The middle-tropospheric East Asian trough (EAT) is one important component of the East Asian monsoon system. Previous studies have focused on the variability of the EAT in winter and have highlighted its crucial role in the climate over East Asia and beyond; however, little attention has been given to the EAT in summer. This study investigates interannual variability of the summer EAT using the European Centre for Medium-Range Weather Forecast (ECMWF) Reanalysis version 5 (ERA5) dataset for 1979–2019 and reveals its impact on rainfall and the underlying dynamic mechanisms. The results show that the interannual variability of the EAT is characterized by intensity variation. Related to an enhanced EAT, rainfall increases significantly within the East Asian subtropical rainy belt extending from the Yangtze-Huaihe River valley to western and central Japan and decreases in North China. The rainfall anomalies are triggered by the anomalous ascending motion due to warm advection in the east of the EAT and descending motion due to cold advection in the west. The interannual variation in the EAT intensity is significantly modulated by the extratropical Arctic Oscillation. In addition, it is also affected by tropical rainfall anomalies in South Asia and the western North Pacific, through a zonally-oriented circumglobal teleconnection and a meridional East Asia–Pacific teleconnection, respectively. Moreover, the EAT intensity is significantly connected with summer sea surface temperature (SST) anomalies in the tropical eastern Pacific, bridged by the SST-induced rainfall anomalies in South Asia. The summer SST anomalies can be traced back to the preceding spring, implying potential predictability of the summer EAT intensity. Finally, the difference between the EAT and northern East Asian low in the lower troposphere is discussed.
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Data availability
The ERA5 reanalysis data (https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5) are provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). The GPCP precipitation data (https://psl.noaa.gov/data/gridded/data.gpcp.html) are available from the National Oceanic and Atmospheric Administration (NOAA) and the HadISST SST data (https://www.metoffice.gov.uk/hadobs/hadisst/) from the Met Office Hadley Centre.
Code availability
The code data that support the findings of this study are available upon reasonable request from the authors.
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Acknowledgements
The authors thank three anonymous reviewers for their value comments. The authors also thank Prof. Chongyin Li for his valuable comment on discussion of the relationship between the NEAL and EAT, Dr. Ping Huang on SST relationship, and Dr. Jingbei Peng for region selection of the EAT. This study was supported by the National Natural Science Foundation of China (Grant Nos. 41775062, 41630424, and 42175074) and the Youth Innovation Promotion Association, CAS (Grant No. 2017105).
Funding
This work is supported by NSFC #41775062, 41630424, 42175074 and YIPA # 2017105.
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ZL and CB designed the study. ZL carried the analysis and wrote the first draft. Both authors contributed to interpreting and discussing the results, and writing and revising the manuscript.
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Lin, Z., Bueh, C. Interannual variability of the East Asian trough in summer. Clim Dyn 59, 2293–2309 (2022). https://doi.org/10.1007/s00382-022-06210-7
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DOI: https://doi.org/10.1007/s00382-022-06210-7