Combined effect of the East Atlantic/West Russia and Western Pacific teleconnections on the East Asian winter monsoon

This study investigates the individual effects of the East Atlantic/West Russia (EATL/WRUS) and Western Pacific (WP) teleconnection patterns and their combined effect on the East Asian winter monsoon (EAWM). The contributions of the respective EATL/WRUS and WP teleconnection patterns to the EAWM are revealed by removing the dependence on the Arctic Oscillation (AO) and the El Nio-Southern Oscillation (ENSO) using a linear regression, which are named as N_EATL/WRUS and N_WP, respectively. This is because the EATL/WRUS (WP) is closely linked to the Arctic (tropics) region. A significant increase (decrease) in temperature over East Asia (EA) corresponding to a weak (strong) EAWM is associated with the N_EATL/WRUS and N_WP teleconnection patterns during the positive (negative) phases. In order to examine impacts of these two teleconnections on the EAWM, three types of effects are reconstructed on the basis of +/- 0.5 standard deviation: 1) Combined effect, 2) N_EATL/WRUS effect, and 3) N_WP effect. The positive N_EATL/WRUS teleconnection induces to a weakened Siberian High and a shallow EA trough at the mid-troposphere through wave propagation, leading to the weak EAWM. During the positive N_WP pattern, warm air from the tropics flows toward the EA along western flank of an anomalous anticyclone over the North Pacific that is relevant to the meridional shift of the Aleutian Low. When the two mid-latitude teleconnections have the in-phase combination, the increase in temperature over EA appears to be more pronounced than the individual effects by transporting warm air from tropics via strong southeasterly wind anomalies induced by anomalous zonal pressure gradient between the Siberian High and Aleutian Low. Therefore, the impact of the mid-latitude teleconnections on the EAWM becomes robust and linearly superimposed, unlike a nonlinear in-phase combined effect of the AO and ENSO.