Abstract
AbstractIn winter, the western Pacific jet stream (WPJS) is located at the downstream of East Asian subtropical jet (EASJ) and East Asian polar front jet (EAPJ). It can be affected by sea surface temperature (SST) and has great impact on precipitation along the North American coast. Synergistic effects of midlatitude atmospheric upstream disturbances and oceanic subtropical front intensity variability on WPJS in winter are investigated in both observation and model experiments. It reveals that the strength and location of WPJS are determined by the configuration of atmospheric upstream disturbances and subtropical frontal zone (STFZ) intensity variability that exist concurrently. During the strong atmospheric upstream disturbances years, the WPJS is anchored at about 25–45°N, and its strength is enhanced (abated) by the intensified (weakened) STFZ. However, when the atmospheric upstream disturbances are weak, the intensity of STFZ changes the location of WPJS. An intensified (weakened) STFZ makes WPJS move southward (northward). Further studies show that strong atmospheric disturbances induce a wide and deep atmospheric baroclinicity anomaly zone, which makes the lower atmosphere obtain baroclinic energy from STFZ. Accordingly, the WPJS is anchored just the north of STFZ. At this time, the intensified (weakened) STFZ just increases (decreases) the upward baroclinic energy at the same position and thus the WPJS. However, with the weakened atmospheric upstream disturbances, the intensified (weakened) STFZ corresponds to an overhead narrow atmospheric baroclinicity anomaly zone, thus leading to the southward (northward) movements of upward baroclinic energy and the WPJS.
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