Zonal Differences in the Interannual Variability of Baiu Front

The interannual variability of the Baiu frontal activity is examined in this work. In particular, the zonal differences are diagnosed from 1979 to 2002 (24 years), using NCEP/NCAR reanalysis and GPCP data in June. The interannual variability in Baiu precipitation shows significant zonal differences without temporal correlation. The western part is centered near the Tsushima current, while the eastern one appears on the Kuroshio current. We may zonally divide the Baiu phenomenon into two, i.e., the western Baiu (W-Baiu) and the eastern one (E- Baiu). Correlation analysis reveals that the interannual variability in the W-Baiu is associated with circulation in the tropical Pacific, while that in the E-Baiu seems to be related to the mid-latitude circulation over the Eurasian Continent. In fact, when the latter is dominant, the stationary Rossby wave activity is strong in the upper tropospheric westerly jet near 35N over the Eurasian Continent through Japan. The anomalous southward shift of the Asian jet, which is led by the enhancement of anticyclonic circulation in the southeastern part of the Tibetan High, contributes to the establishment of a waveguide for the Rossby wave propagation. At the eastern edge near Japan, the Rossby wave enhances the cyclonic circulation in the upper troposphere, which converges the water vapor for the anomalous precipitation in the E-Baiu. In contrast, the interannual variability in the W-Baiu is controlled by the anomalous meridional circulation in the western Pacific. The anomalous cyclones are located around East China and Southeast Asia, while the anomalous anticyclone is lain on the Philippine Sea between them. This anomalous pattern seems to be related to the so-called Pacific-Japan pattern in the western North Pacific. As such, the detailed inspection detects the differences in physical processes of the interannual Baiu activity.