Role of the quasi‐biweekly oscillation in the onset of convection over the Indochina Peninsula

Abstract

ABSTRACT:The characteristics of convection onset over the Indochina Peninsula and its possible mechanism are investigated using the reanalysis of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and the black-body temperature at the top of the cloud (T BB ). Results show that the convection onset occurs before the systemic northward progression of the tropical convection and is earlier than the onset of the summer monsoon over this region. The prominent difference between the onset of convection and that of the summer monsoon appears in the westmost part of the western Pacific subtropical high. When the convection bursts, the Indochina Peninsula is under the control of the western Pacific subtropical high. However, the summer monsoon onset follows the splitting of the subtropical high belt and the eastward retreat of the western Pacific subtropical high out of the Indochina Peninsula.The climatological features of T BB over the Indochina Peninsula indicate that the convective activities have a close relationship with the quasi-biweekly oscillation (QBWO). Based on the onset dates determined by the T BB data, casestudies and composite analyses are implemented on exploring the possible mechanism of the convection onset. It is found that the onset of convection is mainly influenced by factors as follows. The wet phase of QBWO of the tropical convection propagates northward from Sumatra to the Indochina Peninsula. Over the southern Indochina Peninsula, anomalous southerlies (the Rossby wave response to the tropical convective QBWO) are beneficial to both the northward progression of the convective disturbances and the convergence of the low-level moisture flux. Furthermore, the Indochina Peninsula is easily affected by any cold surge invading southwards from higher latitudes, which intensifies the convective activities when merging with the wet/warm current.

Structure and Origin of the Quasi-Biweekly Oscillation over the Tropical Indian Ocean in Boreal Spring

“…The study of the QBWO in boreal spring is useful because it may significantly impact the Asian monsoon onset (Zhang et al 2002;Wen and Zhang 2007). The generation mechanism for QBWO in boreal spring might be different from that in other seasons.…”

Impact of the quasi‐biweekly oscillation over the western North Pacific on East Asian subtropical monsoon during early summer

“…Intraseasonal oscillation is one of the most important components of the tropical atmospheric variation. It generally involves two major modes: the well‐known Madden‐Julian Oscillation (MJO) with a characteristic period of 30–60 days [ Madden and Julian , , ] and the quasi‐biweekly oscillation (QBWO) with a typical time band of 10–20 days [ Krishnamurti and Ardanuy , ; Chen and Chen , , ; Fukutomi and Yasunari , , ; Wen and Zhang , , ; Jiang and Lau , ; Kikuchi and Wang , ; Wen et al ., ].…”

“…Observational facts of MJO have been documented by abundant studies [e.g., Li and Wu , ; Li and Zhou , ; Salby and Hendon , ; Jones and Weare , ; Maloney and Hartmann , ; Woolnough et al ., ; Fu et al ., ; Sperber , ; Jiang et al ., , ; Zhang , ; Li et al ., ] and many investigations have been conducted on its impacts on global weather and climate [ Higgins and Shi , ; Lawrence and Webster , ; Wheeler and McBride , ; Donald et al ., ; Jeong et al ., ; Wheeler et al ., ; Zhang et al ., ; Tong et al ., ; Jia et al ., ; Li et al ., ]. Compared to the MJO, less effort has been devoted to understanding the QBWO, and most previous studies of QBWO have focused on the tropical Asian monsoon region and the western North Pacific (WNP) including the South China Sea (SCS) [ Krishnamurti and Ardanuy , ; Chen and Chen , , ; Fukutomi and Yasunari , , ; Chen et al ., ; Chan et al ., ; Mao and Chan , ; Zhou and Chan , ; Wen and Zhang , ; Chen and Sui , ; Park et al ., ]. Atmospheric oscillation of 10–20 days was earliest reported in the Indian monsoon [ Krishnamurti and Ardanuy , ; Chen and Chen , ].…”

A Numerical Study of the Interaction between the Large-Scale Monsoon Circulation and Orographic Precipitation over South and Southeast Asia

“…The commencement of convection, however, occurred in April before monsoon onset. Wen and Zhang (2007) suggested that premonsoon precipitation and monsoon onset are associated with different background circulations and mechanisms. The premonsoon convection may be triggered by the tropical quasi-biweekly oscillation propagating from the south and cold surges invading from the north.…”