Journal
ATMOSPHERIC RESEARCH
Volume 258, Issue -, Pages -Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.atmosres.2021.105611
Keywords
East Asian westerly jet; Spring rainfall in northern China and Yangtze-Huaihe River Valley; External forcings; Blocking effect of the Tibetan Plateau; Tropical SSTA; Barotropic quasi-stationary waves
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Funding
- National Natural Science Foundation of China [41805052, 42030605]
- Second Tibetan Plateau Scientific Expedition and Research Program (STEP) [2019QZKK0103]
- Innovation and Entrepreneurship Training Plan for College Students [201810300003z]
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The study investigates the association of East Asian westerly jet (EAWJ) variations with spring rainfall anomalies in Northern China and Yangtze-Huaihe River Valley (NC-YHV) and the dynamics using reanalysis datasets. Anomalous intensification of EAWJ leads to negative rainfall anomalies in NC-YHV, with quasi-barotropic Pacific-Japan-like (PJ) teleconnection observed along coastal China. Tibet Plateau plays a role in reducing anomalous southwesterly momentum and turning westerly anomalies into northwesterly anomalies, affecting moisture transport and inducing reduced rainfall anomalies in NC-YHV.
The present study investigates the association of East Asian westerly jet (EAWJ) variations with spring rainfall anomalies in Northern China and Yangtze-Huaihe River Valley (NC-YHV) and the dynamics using reanalysis datasets. Based on the climatology and interannual variation in 200-hPa zonal winds, the index EAWJI is defined as the average 200-hPa zonal wind velocity over a zonal 10-degree-width belt centered around the seasonal-mean jet axis between 105 degrees E and 145 degrees E. Associated with anomalously strengthened EAWJ, significant negative rainfall anomalies are observed over NC-YHV. The dynamics are as follows. When the EAWJ is anomalously intensified, a quasi-barotropic Pacific-Japan-like (PJ) teleconnection along coastal China and an associated anomalous westerly flow over NC-YHV are observed. In middle-lower troposphere, Tibetan Plateau (TP) drastically reduces the anomalous southwesterly momentum transported into NC-YHV, turning the westerly anomalies into northwesterly anomalies. The anomalous northwesterly winds over NC-YHV advect cold and dry air southeastward toward NC-YHV, which induce downward motion (diabatic heating feedback is weak) and negative moisture anomalies, respectively, and thus cause reduced rainfall anomalies over NC-YHV. Anomalous winter SSTAs in western Pacific and tropical Indian Ocean associated with ENSO are sustained until spring, inducing barotropic waves that propagate northwards to cause EAWJ-associated circulation anomalies and thus bring about spring rainfall anomalies in NC-YHV. The quasi-barotropic features of the EAWJ-associated circulation anomalies and their association with the northward propagation of tropical SSTA-induced barotropic waves together suggest that EAWJ-associated circulation variations are at least partly among the external forcings responsible for spring rainfall anomalies in NC-YHV.
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