DOI: 10.1007/s00382-014-2359-2
Scopus记录号: 2-s2.0-84925541023
论文题名: The stratospheric wintertime response to applied extratropical torques and its relationship with the annular mode
作者: Watson P.A.G. ; Gray L.J.
刊名: Climate Dynamics
ISSN: 9307575
出版年: 2015
卷: 44, 期: 2017-09-10 起始页码: 2513
结束页码: 2537
语种: 英语
英文关键词: Extratropics
; Gravity wave drag
; Northern annular mode
; Polar vortex
; Stratosphere
; Torque
英文摘要: The response of the wintertime Northern Hemisphere (NH) stratosphere to applied extratropical zonally symmetric zonal torques, simulated by a primitive equation model of the middle atmosphere, is presented. This is relevant to understanding the effect of gravity wave drag (GWD) in models and the influence of natural forcings such as the quasi-biennial oscillation (QBO), El Ninõ-Southern Oscillation (ENSO), solar cycle and volcanic eruptions on the polar vortex. There is a strong feedback due to planetary waves, which approximately cancels the direct effect of the torque on the zonal acceleration in the steady state and leads to an EP flux convergence response above the torque’s location. The residual circulation response is very different to that predicted assuming wave feedbacks are negligible. The results are consistent with the predictions of ray theory, with applied westerly torques increasing the meridional potential vorticity gradient, thus encouraging greater upward planetary wave propagation into the stratosphere. The steady state circulation response to torques applied at high latitudes closely resembles the Northern annular mode (NAM) in perpetual January simulations. This behaviour is analogous to that shown by the Lorenz system and tropospheric models. Imposed westerly high-latitude torques lead counter-intuitively to an easterly zonal mean zonal wind (Formula Presented.) response at high latitudes, due to the wave feedbacks. However, in simulations with a seasonal cycle, the feedbacks are qualitatively similar but weaker, and the long-term response is less NAM-like and no longer easterly at high latitudes. This is consistent with ray theory and differences in climatological (Formula Presented.) between the two types of simulations. The response to a tropospheric wave forcing perturbation is also NAM-like. These results suggest that dynamical feedbacks tend to make the long-term NH extratropical stratospheric response to arbitrary external forcings NAM-like, but only if the feedbacks are sufficiently strong. This may explain why the observed polar vortex responses to natural forcings such as the QBO and ENSO are NAM-like. The results imply that wave feedbacks must be understood and accurately modelled in order to understand and predict the influence of GWD and other external forcings on the polar vortex, and that biases in a model’s climatology will cause biases in these feedbacks. © 2014, The Author(s). 资助项目: NERC, Natural Environment Research Council
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资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/54204
Appears in Collections: 过去全球变化的重建
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作者单位: Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, United Kingdom; National Centre for Atmospheric Science, Oxford, United Kingdom
Recommended Citation:
Watson P.A.G.,Gray L.J.. The stratospheric wintertime response to applied extratropical torques and its relationship with the annular mode[J]. Climate Dynamics,2015-01-01,44(2017-09-10)