IMPACT OF CONVECTION OVER THE SOUTH CHINA SEA ON TROPICAL CYCLONE MOTION OVER THE WESTERN NORTH PACIFIC DURING SUMMER MONSOON

Abstract:

The intraseasonal oscillation (ISO) of the South China Sea (SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific (WNP) tropical cyclones (TCs) were explored, based on the daily average of NCEP/NCAR reanalysis data, the OLR data and the western North Pacific tropical cyclone best-track data from 1979 to 2008. The mechanism of the influences of ISO on TC movement and the corresponding large-scale circulation were discussed by a trajectory model. It was found as follows. (1) During the SCS summer monsoon, the SCS convection exhibits the ISO features with active phases alternating with inactive phases. The monsoon circulation patterns are significantly different during these two phases. When the SCS convection is active (inactive), the SCS-WNP monsoon trough stretches eastward (retreats westward) due to the activity (inactivity) of SCS monsoon, and the WNP subtropical high retreats eastward (stretches westward), which enhances (suppresses) the monsoon circulation. (2) The amount of TC genesis in the active phase is much more than that in the inactive phase. A majority of TCs form west of 135 °E during the active phases but east of 135 °E in the inactive phases. (3) The TCs entering the area west of 135 °E and south of 25 °N would move straight into the SCS in the active phase, or recurve northward in the inactive phase. (4) Simulation results show that the steering flow associated with the active (inactive) phases is in favor of straight-moving (recurving) TCs. Meanwhile, the impacts of the locations of TC genesis on the characteristics of TC track cannot be ignored. TCs that occurred father westward are more likely to move straight into the SCS region.