Could the North Pacific Oscillation be modified by the initiation of the East Asian winter monsoon?

Abstract

This study investigates the modulation of North Pacific Oscillation (NPO) variability upon initiation of the East Asian winter monsoon (EAWM). The data show that the initiation of EAWM in the Philippine Sea strongly connects to the southern lobe variability of the NPO in January followed by a basin-scale oceanic Victoria mode pattern. No apparent connection was found for the northern lobe of the NPO when the ENSO signals are removed. The strengthening of the EAWM in November interacts with the Kuroshio front and generates a low-level heating source in the Philippine Sea. Significant Rossby wave sources are then formed in the lower to midtroposphere. Wave ray tracing analyses confirm the atmospheric teleconnection established by the Rossby wave propagation in the mid- to upper troposphere. Analyses of the origin of wave trajectories from the Philippine Sea show a clear eastward propagating pathway that affects the southern lobe of the NPO from the southern lobe of the western Pacific pattern at 500 hPa and above on the time scale of 20 days. No ray trajectories from the lower troposphere can propagate eastward to influence the central-eastern subtropical Pacific. The wave propagation process is further supported by the coupled model experiments.