Potential-Vorticity Dynamics of Troughs and Ridges within Rossby Wave Packets during a 40-year reanalysis period
Potential-Vorticity Dynamics of Troughs and Ridges within Rossby Wave Packets during a 40-year reanalysis period
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40 年再分析期间罗斯贝波包内波谷和波脊的位涡动力学
DOI：
10.5194/wcd-2020-52
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发表时间：
2020
影响因子：
--
通讯作者：
M. Riemer
中科院分区：
文献类型：
--
作者：
F. Teubler;M. Riemer
罗斯比波包（RWPs）是中纬度动力学的基础，从单个生命周期到气候分布都控制着天气系统。对rwp作为高影响天气事件的前兆和在大气可预测性的背景下重新产生的兴趣促使本研究重新审视rwp的动力学。采用了定量位涡（PV）框架。基于中纬度动力学的PV思想，控制RWP振幅演变的过程包括rosby波的群传播、斜压相互作用、对流层上层辐散流的影响以及非保守过程对PV的直接非绝热修正。PV框架的一个优点是，湿过程的影响比RWP动力学的替代框架更直接地被诊断出来。本文利用ERA5数据分析了1979-2017年6000多个RWP的平均动态，并补充了2008-2010年热带对流年的非保守趋势。</p><p> </p><p>证实了RWP动力学的已有模型，RWP内部的群体传播符合线性正压理论，斜压和辐散放大在RWP成熟阶段最为突出，而不是在RWP的后缘。对已有模型进行改进，发现辐散放大的最大值出现在最大斜压增长之前，斜压相互作用倾向于向前缘减弱RWP振幅。“下游斜压发展”被证实为夏季和冬季的RWP动态提供了有效的描述，尽管夏季的斜压增长要小得多（约50%）。长波辐射冷却对脊槽振幅有一级贡献。然而，这种巨大的影响仅与其他控制过程弱耦合，因此被解释为气候背景过程。其他非保守趋势的直接影响，包括潜热释放，比长波辐射冷却小一个数量级。可以说，潜热释放仍然通过增强对流层上层辐散对rwp产生实质性影响。发散气流放大了脊，减弱了槽。这种影响是领先级的，比斜压增长的影响更大。在一定程度上，辐散与下面的潜热释放有关，我们认为，湿润过程导致了众所周知的槽和脊空间尺度上的不对称。对于脊，辐散放大与斜压生长和潜热释放增强密切相关。因此，我们认为山脊的生命周期最好描述为：下游<em>湿润</em>-斜压发展’；最后，我们的研究结果表明，辐散脊的放大不仅取决于潜热释放的大小，还取决于它与急流的相对位置（,phasing’）
<p>Rossby wave packets (RWPs) are fundamental to midlatitude dynamics and govern weather systems from their individual life cycles to their climatological distributions. Renewed interest in RWPs as precursors to high-impact weather events and in the context of atmospheric predictability motivates this study to revisit the dynamics of RWPs. A quantitative potential vorticity (PV) framework is employed. Based on the well established PV-thinking of midlatitude dynamics, the processes governing RWP amplitude evolution comprise group propagation of Rossby waves, baroclinic interaction, the impact of upper-tropospheric divergent flow, and direct diabatic PV modification by nonconservative processes. An advantage of the PV framework is that the impact of moist processes is more directly diagnosed than in alternative, established frameworks for RWP dynamics. The mean dynamics of more than 6000 RWPs from 1979-2017 are presented using ERA5 data, complemented with nonconservative tendencies from the ‚Year of tropical convection‘ data (available 2008-2010).</p><p> </p><p>Confirming a pre-existing model of RWP dynamics, group propagation within RWPs is consistent with linear barotropic theory, and baroclinic and divergent amplification occur most prominently during the mature stage and rather towards the trailing edge of RWPs. Refining the pre-existing model, the maximum of divergent amplification occurs in advance of maximum baroclinic growth and baroclinic interaction tends to weaken RWP amplitude towards the leading edge. ,Downstream baroclinic development' is confirmed to provide a valid description of RWP dynamics in both, summer and winter, although baroclinic growth is substantially smaller (about 50%) in summer. Longwave radiative cooling makes a first-order contribution to ridge and trough amplitude. This large impact, however, is only weakly coupled to other governing processes and is thus interpreted as a climatological background process. The direct impact of other nonconservative tendencies, including latent heat release, is an order of magnitude smaller than longwave radiative cooling. Arguably, latent heat release still has a substantial impact on RWPs by invigorating upper-troposhperic divergence. The divergent flow amplifies ridges and weakens troughs. This impact is of leading order and larger than that of baroclinic growth. To the extent that divergence is associated with latent heat release below, we argue that moist processes contribute to the well-known asymmetry in the spatial scale of troughs and ridges. For ridges, divergent amplification is strongly coupled to baroclinic growth and enhanced latent heat release. We thus propose that the life cycle of ridges is best described in terms of ,downstream <em>moist</em>-baroclinic development’. Finally, our results demonstrate that divergent ridge amplification does not only depend on the magnitude of latent heat release but also on its relative location to the jet (,phasing’).</p>
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影响因子：
8.9
作者：
C. Grams;H. Wernli;M. Böttcher;J. Čampa;U. Corsmeier;S. Jones;J. Keller;C. Lenz;L. Wiegand-
通讯作者：
C. Grams;H. Wernli;M. Böttcher;J. Čampa;U. Corsmeier;S. Jones;J. Keller;C. Lenz;L. Wiegand-
影响因子：
8.9
作者：
J. Chagnon;S. Gray;J. Methven
通讯作者：
J. Chagnon;S. Gray;J. Methven
使用罗斯贝波分量解释具有水分参数化效应的斜斜波
影响因子：
3.1
作者：
Frame T
通讯作者：
Frame T
罗斯贝波结构的系统模型预报误差
影响因子：
5.2
作者：
Gray S
通讯作者：
Gray S
斜压初值问题的解释：具有非零内部 PV 梯度的简单基本状态的结果
影响因子：
3.1
作者：
Frame T
通讯作者：
Frame T