罗斯比波在极地天气和气候中的作用

T. Woollings, Camille Li, M. Drouard, E. Dunn‐Sigouin, Karim A. Elmestekawy, Momme C. Hell, B. Hoskins, C. Mbengue, M. Patterson, T. Spengler
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引用次数: 7

摘要

摘要最近的北极变暖引发了人们对极地天气和气候的兴趣,以及它们如何与低纬度地区相互作用。一些关于极中纬度联系的有趣理论认为罗斯比波的传播是一个关键过程,尽管对这些波至关重要的行星涡度的经向梯度在高纬度地区很弱。在这里,我们回顾了一些基本理论,并提出罗斯比波确实可以解释极地变化的一些特征,特别是当相对涡度梯度存在时。我们认为,大尺度的极地流可以被概念化为地转湍流和罗斯比波传播的混合,就像在中纬度地区一样,但这种平衡进一步倾向于湍流。因此,孤立的漩涡往往占主导地位,但一些波状特征仍然存在。例如,观测数据的统计分析中出现了准平稳或弱向西传播的亚极异常,这与波传播的某种作用是一致的。极地气旋和反气旋的持续存在部分归因于波频散效应的减弱,波频散是导致中纬度下游发展异常衰减的机制。我们还提出,涡旋主导的极地动力学性质促使在热带外环流主成分分析中出现环状模态结构。最后,我们考虑如何从高纬度触发罗斯比波。已知的用于平衡低纬度地区局部加热的线性机制在极地地区的效率较低。相反,我们认为对海冰损失的直接响应通常表现为热量低,辐射冷却与加热平衡。如果相对涡度梯度是有利的,这确实有可能触发罗斯比波响应,尽管与低纬度地区的波相比,这通常会很弱。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
The role of Rossby waves in polar weather and climate
Abstract. Recent Arctic warming has fuelled interest in the weather and climate of the polar regions and how this interacts with lower latitudes. Several interesting theories of polar-midlatitude linkages involve Rossby wave propagation as a key process even though the meridional gradient in planetary vorticity, crucial for these waves, is weak at high latitudes. Here we review some basic theory and suggest that Rossby waves can indeed explain some features of polar variability, especially when relative vorticity gradients are present. We suggest that large-scale polar flow can be conceptualised as a mix of geostrophic turbulence and Rossby wave propagation, as in the midlatitudes, but with the balance tipped further in favour of turbulent flow. Hence, isolated vortices often dominate but some wavelike features remain. As an example, quasi-stationary or weakly westward-propagating subpolar anomalies emerge from statistical analysis of observed data, and these are consistent with some role for wave propagation. The noted persistence of polar cyclones and anticyclones is attributed in part to the weakened effects of wave dispersion, the mechanism responsible for the decay of midlatitude anomalies in downstream development. We also suggest that the vortex-dominated nature of polar dynamics encourages the emergence of annular mode structures in principal component analyses of extratropical circulation. Finally, we consider how Rossby waves may be triggered from high latitudes. The linear mechanisms known to balance localised heating at lower latitudes are shown to be less efficient in the polar regions. Instead, we suggest the direct response to sea ice loss often manifests as a heat low, with radiative cooling balancing the heating. If the relative vorticity gradient is favourable this does have the potential to trigger a Rossby wave response, although this will often be weak compared to waves forced from lower latitudes.
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