QBWO of Asian Monsoon Rainfall in Late Summer and Autumn: Different Types of Structure and Propagation

This study contrasts two types of quasi-biweekly oscillation (QBWO) in late summer and autumn (from August to October). QBWO is one of the major components of the intraseasonal oscillation (ISO), which is paid less attention to than the 30-60-day oscillation. Using tracking method, we calculated the frequency of QBWO events over Asian monsoon region. Results suggest that there are two types of QBWO. One originates from 110°-140°E, and influences the southern China westward. The other with initiation locations from 160°E to the date line, has less effect on the mainland. The condition of moisture fluxes determine whether the oscillation could spread across 120°E and affect the precipitation in southern China. The analyses suggest that stronger South Asian high and weaker West Pacific subtropical high would accelerate the generation of different types of QBWO. The high correlation between QBWO and ENSO indicates that the western Pacific SST anomalies may be the main trigger of QBWO.