Revisit to the quasi bi-weekly period oscillation (QBW) in precipitation in the Bangladesh-Himalaya-Tibet region and its role in the whole Asian summer monsoon system

The Asian summer monsoon has intraseasonal variability in precipitation and associated atmospheric circulations with two dominant time scales: one is 30-50 day period, and the other is 10-20 day period or quasi-biweekly (QBW) period. Some recent studies (e.g., Fujinami and Yasunari, 2004, 2009; Fujinami et al., 2010; Murata et al., 2008) have revealed that particularly the QBW oscillation is dominant over and around the Tibet-Himalaya region including the northeast India (the Assam/Meghalaya) and Bangladesh. An interesting and essential issue is that this QBW oscillation plays a dominant role in determining interannual activity of monsoon precipitation over this region (Fujinami et al., 2010). The atmospheric circulation of the QBW oscillation has also proved to involve the modulation of the East Asian monsoon activitiy (Meiyu/Baiu) (Fujinami and Yasunari, 2009). However, why and how the QBW oscillation is so dominant over this particularly region, and the origin and dynamics of the QBW oscillation are still an open question. Our preliminary analysis has suggested that the dynamical and thermo-dynamical effect of the Tibet-Himalayan mountain range may play a key role, including the interaction between tropical and mid-latitude circulation over and around there. This study will report our further analysis on the the dynamics of the QBW oscillation, and its implication to the role of the whole Asian summer monsoon system.