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Abstract

The present study investigates possible links between East Asian Winter Monsoon (EAWM) and North American surface air temperature (Ts) anomalies (NA) during ENSO and neutral ENSO winters. During the neutral ENSO winters, two Rossby wave-packets appear over the Eurasia-western Pacific (upstream) and North Pacific-NA (downstream) regions associated with a strong EAWM. Further analysis suggests that the downstream wave-packet is caused by reflection of the upstream wave-packet over the subtropical western Pacific and amplified over North Pacific. The East Asian subtropical westerly jet stream (EAJS) is intensified in the central and downstream North Pacific, too. Hence, increased barotropic kinetic energy conversion and the interaction between transient eddies and the EAJS tend to maintain the circulation anomaly over North Pacific. Therefore, a strong EAWM tends to results in warm Ts anomalies in northwestern NA via the downstream wave-packet emanating from the central North Pacific toward NA. A weak EAWM has opposite effects but with a smaller magnitude. During ENSO winter, anomalous EAJS is mainly confined over East Asia and does not extend into the central North Pacific. The results confirm that the EAWM has an indirect impact on the Ts anomalies in NA via a modulation of the tropical convection anomalies associated with ENSO. Our results indicate that, for seasonal prediction of Ts anomalies in NA, the influence of the EAWM should be taken into account. It produces different responses in neutral ENSO and in ENSO years.