Comparison of the two modes of the Western Pacific subtropical high between early and late summer

Abstract

AbstractIn this work, the first two leading modes of the western Pacific subtropical high (WPSH) between early and late summer are compared. Results show that the first mode of both June and August is featured by an anomalous anticyclonic circulation in the western North Pacific region. The second mode of June (August) is featured by an east–west (south–north) dipole over the North Pacific. Then, the association between the WPSH leading modes and El Niño‐Southern Oscillation (ENSO) is examined. Results show that all PC1s are connected with ENSO developing phase. The connection between June–July–August (JJA) PC2 and ENSO decaying can only be seen in July. In June and August, the connection with ENSO is relatively weak. Finally, the PCs‐related precipitation anomaly is explored. The regressed precipitation anomaly patterns have close connection with the 850‐hPa wind field anomaly. The PC1‐related precipitation shows negative anomaly in the western equatorial Pacific and positive anomaly in the maritime continent. In June a PC1‐related positive rain band is located south to Japan along 30°N, which is absent in August. The PC2‐related positive anomaly in equatorial central Pacific in JJA is mainly attributed to August, while the positive anomaly along the east coast of East Asia is in June and July rather than August. The reasons for the differences between early and late summer are also discussed.