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Thermodynamic controls of the Western Tibetan Vortex on Tibetan air temperature

Lookup NU author(s): Dr Xiaofeng Li, Professor Hayley Fowler, Dr Jingjing Yu, Dr Nathan Forsythe, Dr Stephen Blenkinsop, Dr David Pritchard

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

The “Western Tibetan Vortex” (WTV)—also termed the Karakoram Vortex—dominates the middle-to-lower troposphere and the near-surface air temperature variability above the western Tibetan Plateau (TP). Here, we explore the thermodynamic mechanisms through which the WTV modulates air temperature over the western TP by diagnosing the three major terms of the thermodynamic energy equation—adiabatic heating, horizontal temperature advection, and diabatic heating—that maintain the atmospheric thermal balance. We composite these major terms to examine the differences between anti-cyclonic and cyclonic WTV events. Our theoretical approach demonstrates that adiabatic sinking-compression (rising-expansion) provides the overwhelming control on both the middle-to-lower tropospheric and lower stratospheric temperature increases (decreases) under anti-cyclonic (cyclonic) WTV conditions over the western TP high mountain area in all four seasons. This also explains the mechanisms behind the anomalous temperature “dipole” found between the mid-lower troposphere and lower stratosphere when the WTV was initially identified. Spatially, adiabatic heating effects are centred on the central western TP in summer and the south slope centring at 70°–80°E of the TP in other seasons. The other two terms, horizontal temperature advection and diabatic heating, have localized importance over the edges of the western TP. In a case study over the Karakoram area, we further demonstrate that adiabatic heating (rising-expanding-cooling/sinking-compressing-warming) is the dominant thermodynamic process controlling Karakoram air temperatures under WTV variability, except for at the very near surface in autumn and winter. Our analysis methods can be applied to investigate the thermodynamic processes of other atmospheric circulation systems or climate variability modes.


Publication metadata

Author(s): Li X-F, Fowler HJ, Yu J, Forsythe N, Blenkinsop S, Pritchard D

Publication type: Article

Publication status: Published

Journal: Climate Dynamics

Year: 2019

Pages: Epub ahead of print

Online publication date: 30/05/2019

Acceptance date: 19/04/2019

Date deposited: 17/05/2019

ISSN (print): 0930-7575

ISSN (electronic): 1432-0894

Publisher: Springer

URL: https://doi.org/10.1007/s00382-019-04785-2

DOI: 10.1007/s00382-019-04785-2


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