Abstract
The combined effect of the Arctic Oscillation (AO) and Western Pacific (WP) teleconnection pattern on the temperature variation during the winter in the northern hemisphere and East Asia over the last 56 years (1958/1959–2013/2014) was investigated using NCEP/NCAR reanalysis data. The study results revealed that the effect of the AO on winter temperature in East Asia could be changed depending on the phase of the WP pattern in the North Pacific. The negative relationship between the temperature of East Asia (25–45°N, 110–145°E) and the AO increased when the AO and WP were in-phase with each other. Hence, when winter negative (positive) AO was accompanied by negative (positive) WP, negative (positive) temperature anomalies were dominant across the entire East Asia region. Conversely, when the AO and WP were out-of-phase, the winter temperature anomaly in East Asia did not show distinct changes. Furthermore, from the perspective of stationary planetary waves, the zonal wavenumber-2 patterns of sea level pressure and geopotential height at 500 hPa related to the East Asian winter monsoon (EAWM) circulation strengthened when the AO and WP were in-phase but were not significant for the out-of-phase condition. An index considering the effect of both AO and WP on East Asia winter temperature was proposed. The correlation between the index and the East Asia winter temperature was statistically significant at the 99 % confidence level. The index was correlated with synoptic characteristics of the EAWM, including the Siberian High, East Asian trough, East Asian jet stream and surface air temperature.
Highlights
The East Asian winter monsoon (EAWM) is one of the most active climate systems in the northern hemisphere in the boreal winter, and is caused by the thermal contrast between the Eurasian continent and the Indian and Pacific Oceans (Wu and Wang 2002; Wang et al 2010)
The EAWM is characterized by the northwesterly wind over the east coast of Eurasia caused by the pressure gradient between the Siberian High in the Eurasian continent and the Aleutian Low in the North Pacific, the East Asian trough (EAT) in mid-latitude and the polar jet stream near the south of Japan in the upper troposphere (Jhun and Lee 2004; Chen et al 2013)
The Western Pacific (WP) has statistically positive significant temporal correlations with T2m_EA for all winter months with the 99 % confidence level. This implies that the WP is strongly related to T2m_EA, the Arctic Oscillation (AO) still affects the temperature over the region
Summary
The East Asian winter monsoon (EAWM) is one of the most active climate systems in the northern hemisphere in the boreal winter, and is caused by the thermal contrast between the Eurasian continent and the Indian and Pacific Oceans (Wu and Wang 2002; Wang et al 2010). The EAWM is characterized by the northwesterly wind over the east coast of Eurasia caused by the pressure gradient between the Siberian High in the Eurasian continent and the Aleutian Low in the North Pacific, the East Asian trough (EAT) in mid-latitude and the polar jet stream near the south of Japan in the upper troposphere (Jhun and Lee 2004; Chen et al 2013). Variations of these characteristics affect temperature and precipitation during the boreal winter in East Asia.
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