Possible Mechanism of the South-Born-South-Persisting West Pacific Subtropical High double Ridges Process

摘要

Analysis based on remote sensing data and NCEP/NCAR reanalysis datasets finds that, on the basis of composing the most typical 'South-Born-South-Persisting' WPSH double ridges processes, anomaly 500 hPa stream field shows that the northern ridge vanishment is climatology, while there is a anomaly anticyclone in the south ridge, making its development and persistence and leading to the WPSH locate much southward than usual after the double ridges process ends. Further studies by the use of vorticity equation indicate that 150 hPa a anomaly anticyclone to the east of the WPSH south ridge region move westward, strengthening the minus vorticty advection of the south ridge region and changing the vertical motion over WPSH region. It not only changes the meridional wind distribution, leading to geostrophic vorticity advection intensify and the anomaly anticyclone develop, but also brings the diabatic heating distribute vertically asymmetrically, inducing a anomaly cyclone between the two ridges and a anomaly anticyclone above the south ridge. Conclusively, the general circulation on the upper level plays an important role in the double ridges process persistence.