A case study of the Borneo Vortex genesis and its interactions with the global circulation

Abstract

During the East Asian winter or the northeast monsoon (November–March), cold surges associated with cold air outbreaks from the Siberian high propagate equatorward and interact with the near‐equatorial trough in the southern South China Sea. Usually, in the later phase of the monsoon, the so‐called Borneo vortex develops over the sea and is the main driver for the formation of deep convection and heavy rainfall in East Malaysia. We present a case study of a cold‐surge‐induced event during January 2010. We diagnose a substantial export of potential energy from the Borneo vortex strengthening the subtropical jet. At 200 hPa, the velocity potential maximum related to the established Hadley circulation is shifted eastward from 140°E toward the dateline from presurge to postsurge periods. This modifies the general circulation patterns in the Southern Hemisphere with possible consequences for trace gas distributions. In addition, we explore implications for vertical transport by deep convection occurring in association with the Borneo vortex by diagnosing potential vorticity changes in the vicinity of the vortex.

Properties of strong off‐shore Borneo vortices: a composite analysis of flow pattern and composition as captured by ERA‐Interim

“…Note that the regional climatological mean of geopotential is already below our threshold value, which is considered to avoid artefacts. The chosen PV threshold value provides a good detection of the BV event studied by Ooi et al (2011), see their Figure 13 showing PV profiles. The occurrences are mapped and counted for each grid box.…”

“…This composite BV is further to the north-east and exceeds in relative vorticity magnitude the December 1978 case discussed by Mower et al (1984) by around a factor of two (this BV: ∼50 × 10 −6 s −1 ). The composite includes the case discussed by Ooi et al (2011). A large area of lower than average temperatures (blue shading) is located to the north-west, with a cold tongue extending towards Borneo.…”

“…A similar configuration is shown in Chang et al (2003) using data from 1951 to 2002 and discovering the unique case of a weak drifting BV playing a role in the formation of a tropical cyclone in December 2001, the first observed typhoon development within ± 1.5 • from the equator. Focusing on extreme weather in Malaysia, Juneng et al (2007) studied a BV event in December 2004 that caused extreme precipitation over the east coast of Peninsular Malaysia and Ooi et al (2011) discussed a case in January 2010 that resulted in heavy rainfall over most of Sarawak and Sabah (Borneo). Notably, the strong BV event described in Ooi et al (2011) stayed north of the climatological occurrence frequency maximum described by Chang et al (2003).…”

“…Focusing on extreme weather in Malaysia, Juneng et al (2007) studied a BV event in December 2004 that caused extreme precipitation over the east coast of Peninsular Malaysia and Ooi et al (2011) discussed a case in January 2010 that resulted in heavy rainfall over most of Sarawak and Sabah (Borneo). Notably, the strong BV event described in Ooi et al (2011) stayed north of the climatological occurrence frequency maximum described by Chang et al (2003).…”

Primary productivity and its variability in the equatorial South China Sea during the northeast monsoon

“…The availability of source gases and the efficiency of transport from the tropo-10 spheric boundary layer into the lowermost stratosphere determine the overall impact on the stratospheric ozone budget (Pyle et al, 2011). With respect to the efficiency of transport, a case study of a cold surge-induced Borneo vortex event in January 2010 (Ooi et al, 2011 andBraesicke et al, 2012) shows that the equatorward (i.e. south of the near-equatorial trough) convective clusters related to the vortex are potentially 15 efficient/fast transport routes to the lowermost stratosphere.…”