Variations of the East Asian Jet Stream and Asian–Pacific–American Winter Climate Anomalies

Variations of the surface temperature in Hong Kong during the last century

“…During the cold winters (Figure 6(a)), the northeasterly monsoon flow is strong over East Asia and a well-defined cyclonic pattern appears over the North Pacific. These are the typical features that occur when the East Asian jet stream is strong (see Figure 8 of Yang et al (2002)). During the hot summers (Figure 6(b)), anomalous northerly winds blow from China to the SCS.…”

“…Figure 3 shows the patterns of anomalous atmospheric circulation at 850 hPa for 30 August 1992 and February 1968, which correspond to the times when the extremes of daily maximum and monthly minimum temperatures appeared, as shown in Table I. (Note that, because of the potential problem in the NCEP-NCAR reanalysis for Asia during the early period (see Yang et al (2002)), only the data since 1968 are analysed in this study.) The large-scale features of the atmospheric circulation associated with the extremely high HK temperature on 30 August 1992 (Figure 3(a)) include the anomalously strong Asian summer monsoon flow over the tropical oceans like the Arabian Sea, the Bay of Bengal, and the SCS.…”

Multidecadal and interannual changes of stationary Rossby waves

“…Yang et al (2002) found that the EAJS does not strongly link to the tropical central-eastern Pacific SST, but a strong EAJS is significantly associated with a decrease in the extratropical western North Pacific SST. Since, during warm PDO regimes, the western and central North Pacific Ocean typically exhibits low surface temperature anomalies, while the eastern tropical Pacific exhibits above-average temperatures (Zhang et al, 1997a), there is an indication that the increase in the EAJS and the enhancement and eastward extension of the Aleutian low observed for the period 1979-2000 are associated with a major regime shift in the Pacific climate, from a cold to warm PDO phase, which occurred after late 1970s.…”

“…Previously, an EAJS strengthening (Figure 1(c)), which could be associated with the PDO warm phase, was noted in the latter period. Yang et al (2002) noted that a strong EAJS is clearly associated with an intensification of many atmospheric circulation systems, including the Asian continent high, east Asian trough, Aleutian low and the ridge over western North America, and related to a strong east-southeastward propagation of stationary wave activity. Thus an intensified EAJS is followed by an adjustment of the large-scale circulation systems that favour a stronger wave train pattern across Asia, the Pacific and North America.…”

“…At the same time, warmer and drier conditions appear in the western USA but a colder and drier climate is seen in the eastern part (Yang et al, 2002). Since one of the fundamental mechanisms that drive the monsoon circulation is the land-sea thermal contrast, the monsoon can be interpreted as thermally forced SRW.…”