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Lookup NU author(s): Dr Xiaofeng Li, Professor Hayley Fowler, Dr Jingjing Yu, Dr Nathan ForsytheORCiD, Dr Stephen Blenkinsop, Dr David Pritchard
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
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.
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
Volume: 53
Pages: 4267–4290
Print publication date: 01/10/2019
Online publication date: 03/05/2019
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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