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

Braesicke, Peter; Hai, Ooi See; Samah, Azizan Abu

doi:10.1002/asl.372

Cited by 13 publications

(9 citation statements)

References 17 publications

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“…Once in the deep tropics, we show that the polluted air masses can be lifted out of the boundary layer into the mid-and upper troposphere. This process may be enhanced by the more vigourous regional convection typically induced by the cold surge circulation, as considered before within the framework of Borneo Vortex events (Braesicke et al, 2012). Our trajectory calculations suggest that, in total, transport from the East Asian boundary layer to the tropical upper troposphere (above 200 hPa) can occur in fewer than 10 days.…”

Section: Summary and Discussionsupporting

confidence: 49%

Rapid transport of East Asian pollution to the deep tropics

et al. 2015

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Abstract. Anthropogenic emissions from East Asia have increased over recent decades. These increases have led to changes in atmospheric composition as far afield as North America under the prevailing westerly winds. Here we show that, during Northern Hemisphere (NH) winter, pollution originating in East Asia also directly affects atmospheric composition in the deep tropics. We present observations of marked intra-seasonal variability in the anthropogenic tracer perchloroethene (C 2 Cl 4 ) collected at two locations in Borneo (117.84 • E, 4.98 • N and 118.00 • E, 4.22 • N) during the NH winter of 2008/2009. We use trajectories calculated with the Numerical Atmospheric-dispersion Modelling Environment to show that the observed enhancements in C 2 Cl 4 mixing ratio are caused by rapid meridional transport, in the form of "cold surges", from the relatively polluted East Asian land mass. In these events air masses can move from ∼35 • N to Borneo in 4 days. We then present data from the Monitoring Atmospheric Composition and Climate reanalysis which suggest that air masses high in C 2 Cl 4 may also contain levels of the pollutants carbon monoxide and ozone that are approximately double the typical "background" levels in Borneo. In addition to strengthening the meridional transport from the north, cold surges can enhance convection in Southeast Asia, and further trajectory calculations indicate that the polluted air masses can subsequently be lifted to the tropical upper troposphere. This suggests a potentially important connection between midlatitude pollution sources and the very low stratosphere.

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Section: Summary and Discussionsupporting

confidence: 49%

Rapid transport of East Asian pollution to the deep tropics

et al. 2015

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“…Moreover, cold surges in the Maritime continent often spin up meso-α-scale cyclonic circulation known as Borneo vortices (e.g. Chen et al, 1986;Lau and Chang, 1987;Johnson and Houze, 1987;Juneng and Tangang, 2010;Braesicke et al, 2012) near the Borneo Island. Chang et al (2005) studied the variability in the Borneo vortex and cold surge using satellite observational and reanalysis data sets.…”

Section: S Koseki Et Al: Borneo Vortex and Mesoscale Convective Raimentioning

confidence: 99%

Borneo vortex and mesoscale convective rainfall

2014

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Abstract.We have investigated how the Borneo vortex develops over the equatorial South China Sea under cold surge conditions in December during the Asian winter monsoon. Composite analysis using reanalysis and satellite data sets has revealed that absolute vorticity and water vapour are transported by strong cold surges from upstream of the South China Sea to around the Equator. Rainfall is correspondingly enhanced over the equatorial South China Sea. A semi-idealized experiment reproduced the Borneo vortex over the equatorial South China Sea during a "perpetual" cold surge. The Borneo vortex is manifested as a meso-α cyclone with a comma-shaped rainband in the northeast sector of the cyclone. Vorticity budget analysis showed that the growth/maintenance of the meso-α cyclone was achieved mainly by the vortex stretching. This vortex stretching is due to the upward motion forced by the latent heat release around the cyclone centre. The comma-shaped rainband consists of clusters of meso-β-scale rainfall cells. The intense rainfall in the comma head (comma tail) is generated by the confluence of the warmer and wetter cyclonic easterly flow (cyclonic southeasterly flow) and the cooler and drier northeasterly surge in the northwestern (northeastern) sector of the cyclone. Intense upward motion and heavy rainfall resulted due to the low-level convergence and the favourable thermodynamic profile at the confluence zone. In particular, the convergence in the northwestern sector is responsible for maintenance of the meso-α cyclone system. At both meso-α and meso-β scales, the convergence is ultimately caused by the deviatoric strain in the confluence wind pattern but is significantly self-enhanced by the nonlinear dynamics.

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“…Once in the deep tropics, we show that the polluted air masses can be lifted out of the boundary layer in to the mid-and upper troposphere. This process may be enhanced by the more vigourous regional convection typically induced by the cold surge circulation, as considered before within the framework of Borneo Vortex events (Braesicke et al, 2012). The tropical upper troposphere is a key gateway to the lower stratosphere (e.g.…”

Section: Summary and Discussionmentioning

confidence: 96%

Rapid transport of East Asian pollution to the deep tropics

Ashfold¹,

Pyle²,

Robinson³

et al. 2014

Preprint

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Abstract. Anthropogenic emissions from East Asia have increased over recent decades, and under the prevailing westerly winds, these increases have led to changes in atmospheric composition as far afield as North America. Here we show that, during Northern Hemisphere (NH) winter, pollution originating in East Asia also directly affects atmospheric composition in the deep tropics. We present observations of marked intra-seasonal variability in the anthropogenic tracer perchloroethene (C2Cl4) collected at two locations in Borneo during the NH winter of 2008/09. We use the NAME trajectory model to show that the observed enhancements in C2Cl4 mixing ratio are caused by rapid meridional transport, in the form of "cold surges", from the relatively polluted East Asian land mass. In these events air masses can move across > 30° of latitude in 4 days. We then present data from the Monitoring Atmospheric Composition and Climate reanalysis which suggests that air masses high in C2Cl4 may also contain levels of the pollutants carbon monoxide and ozone that are approximately double the typical "background" levels in Borneo. Convection in Southeast Asia can be enhanced by cold surges, and further trajectory calculations indicate that the polluted air masses can subsequently be lifted to the tropical upper troposphere. This suggests a potentially important connection between mid-latitude pollution sources and the very low stratosphere.

show abstract

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

Cited by 13 publications

References 17 publications

Rapid transport of East Asian pollution to the deep tropics

Rapid transport of East Asian pollution to the deep tropics

Borneo vortex and mesoscale convective rainfall

Rapid transport of East Asian pollution to the deep tropics

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