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Unstable relationship between the Arctic Oscillation and East Asian Jet Stream in winter and possible mechanisms Print


【Introduction】

   Based on long-term reanalysis datasets, this study revealed that the relationship between the Arctic Oscillation (AO) and the East Asian jet stream (EAJS) is significant negative during 1925-1945 and 1985-2005 (significant periods; hereafter SPs) whereas insignificant during 1900-1920 and 1955-1975 (insignificant periods; ISPs). The unstable AO-EAJS relationship might be related to the interdecadal change of AO’s spatial structure. During SPs winters, anomalous positive AO events are characterized by atmospheric negative anomalies in the Arctic with two anomalous positive centers located in the extratropical Atlantic and Pacific, exhibiting a quasi-barotropic structure. By contrast, the anomalous center in the North Pacific is barely observed during ISPs winters. Further analysis indicated that such interdecadal change might be attributed to change of troposphere-stratosphere coupling and the North Pacific air-sea interaction. On one hand, anomalous AO at surface is closely related to obvious planetary waves downward from the stratosphere during SPs, which favors the subtropics-Arctic teleconnection. On the other hand, the Inter-decadal Pacific Oscillation (IPO) shows warm phase during SPs, which induces larger variance of the Aleutian Low and more intensive divergence anomalies at upper level troposphere. Due to the advection of vorticity induced by stronger divergence is favorable for stronger Rossby wave source, the Rossby wave activity is much stronger and could further propagate eastward to the North Atlantic during SPs, resulting in the Pacific-Atlantic teleconnection. Such a mechanism is supported by the numerical simulations from two individual models that are perturbed by warm/cold IPO sea surface temperature anomalies.


【Citation】

Liu Y, He SP, Li F, Wang HJ, and Zhu YL (2017), Unstable relationship between the Arctic Oscillation and East Asian jet stream in winter and possible mechanisms. Theoretical and Applied Climatology, 1-15. https://doi.org/10.1007/s00704-017-2354-8.



【Link】


https://link.springer.com/article/10.1007/s00704-017-2354-8


【Key figure】




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Fig. 1 The winter mean AO index (bars) and EAJS index (line) based on the (a) ERA-20C and (b) NOAA-20C reanalysis datasets together with time series of the (c) 21-year sliding correlation coefficients between AO index and EAJS index for winter during 1900-2009 (curve: solid one for ERA-20C and dashed one for NOAA-20C) and IPO index (bar). The long and short dashed lines indicate the results are significant at 95% and 90% confidence level, respectively; estimated by Student’s t-test.



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Fig. 2 Differences of winter zonally averaged zonal wind (blue contours, interval 1 m s-1), cross sections of E-P flux (vector, units: 108 m2 s-2) and its divergence (red contours, units: m s-1 day-1) during (a) significant periods and (b) insignificant periods between high and low AO index. Shaded regions indicate the zonal wind anomalies significant at 95% confidence level from a two-tailed Student’s t test. Vectors only display those significant at 95% confidence level.



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Fig. 3 Differences of winter 500-hPa streamfunction (contours; interval 106 m2 s-1), and WAF (vectors; m2 s-2) during (a) significant periods and (b) insignificant periods between high and low AO index. Light and dark shaded regions indicate the streamfunction anomalies significant at 90%, 95% confidence level from a two-tailed Student’s t test. 






 

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