Abstract
This study reveals an intensified impact of winter (November–February mean) Arctic Oscillation (AO) on simultaneous precipitation over the mid–high latitudes of Asia (MHA) since the early 2000s. The unstable relationship may be related to the changes in the tropospheric AO mode and the subtropical jet. Further analyses suggest that their changes may be attributable to the interdecadal changes in the stratospheric polar vortex. During 2002–2017, the anomalously weak stratospheric polar vortex is accompanied by intensified upward-propagating tropospheric planetary-scale waves anomalies. Subsequently, the stratospheric geopotential height anomalies over the North Atlantic high-latitudes propagate downward strongly, causing the changes in the tropospheric AO mode, that is, the positive height anomalies over the North Atlantic high-latitudes are stronger and extend southward, corresponding to the stronger and eastward extension of negative height anomalies over the North Atlantic mid-latitudes. Thus, the Rossby wave source anomalies over Baffin Bay and the Black Sea are strong, and correspondingly so too are their subsequently excited the Rossby waves anomalies. Meanwhile, the planetary-scale waves anomalies propagate weakly along the low-latitude waveguide, causing the intensified and southward shift of the subtropical jet. Therefore, the strong Rossby waves anomalies propagate eastward to the MHA. By contrast, during 1979–1999, the strong stratospheric polar vortex anomaly is accompanied by weak upward-propagating planetary-scale waves anomalies, resulting in weaker height anomalies over the North Atlantic mid–high latitudes. Consequently, the anomalous Rossby waves are weak. In addition, the subtropical jet weakens and shifts northward, which causes the Rossby waves anomalies to dominate over the North Atlantic, and thereby the impact of winter AO on simultaneous precipitation over the MHA is weak.
Highlights
As Arctic Oscillation (AO) is an important mode of atmospheric circulation in the Northern Hemisphere (NH) extratropics, previous studies have shown that AO has a significant impact on the tropospheric climate variability over the mid–high latitudes of Asia (MHA) in winter, including East Asia winter monsoon (EAWM) (Gong et al, 2001; Wu and Wang, 2002a, 2002b; Chen et al, 2005), Siberian high (Gong et al, 2001; Wu and Wang, 2002; Huang et al, 2016), surface air temperature (SAT) (Thompson and Wallace, 1998; Thompson and Wallace, 2000; He and Wang, 2013; Yu et al, 2015; He and Wang, 2016; He et al, 2019) and precipitation (Thompson and Wallace, 2001; Gong and Wang, 2003; Yang and Li, 2008; He et al, 2017)
The stronger and southward extension of positive anomalies over the North Atlantic high-latitudes are accompanied by stronger and eastward-extended negative anomalies over the North Atlantic mid-latitudes—that is, AO/ North Atlantic Oscillation (NAO) mode changes. These results reveal that the differences in the strength of downward propagation and the range of southward extension of the −AO index (AOI)-related stratospheric polar vortex anomaly over North Atlantic high-latitudes in the two periods are consistent with their differences of climatic anomalies (Figures 9A, 9B, 10A,B,D,E), indicating that the differences in the climatic anomalies of the stratospheric polar vortex over the North Atlantic high-latitudes in the two periods may be part of the reason for the differences in −AOI-related stratospheric polar vortex anomaly over the region in the corresponding period
This study reveals an intensified impact of winter AO on simultaneous precipitation over the MHA since the early 2000s
Summary
Studies on winter climate variability over the mid–high latitudes of Asia (MHA) focused mostly on cold waves (Tao, 1957; Ding, 1999; Li and Sun, 2003; Wang and Ding, 2006), surface air temperature (SAT) (Li, 1989; Chen et al, 2000; Wang L. et al, 2009), and the underlying physical mechanisms (Wu and Huang, 1999; Gong et al, 2001; Wu and Wang, 2002a), but few on precipitation. As AO is an important mode of atmospheric circulation in the Northern Hemisphere (NH) extratropics, previous studies have shown that AO has a significant impact on the tropospheric climate variability over the MHA in winter, including EAWM (Gong et al, 2001; Wu and Wang, 2002a, 2002b; Chen et al, 2005), Siberian high (Gong et al, 2001; Wu and Wang, 2002; Huang et al, 2016), SAT (Thompson and Wallace, 1998; Thompson and Wallace, 2000; He and Wang, 2013; Yu et al, 2015; He and Wang, 2016; He et al, 2019) and precipitation (Thompson and Wallace, 2001; Gong and Wang, 2003; Yang and Li, 2008; He et al, 2017).
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