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arXiv 1905.00515physics.ao-phmath.OCstat.CO
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用action最小化最大化模拟热带气旋强度

Maximizing simulated tropical cyclone intensity with action minimization

David A. Plotkin, Robert J. Webber, Morgan E O'Neill, Jonathan Weare, Dorian S. Abbot

摘要:

在天气模式中对强热带气旋的直接计算机模拟受到计算费用的限制。强烈的TC是罕见的,并且具有小规模的结构,因此很难在高分辨率下产生大的风暴集合。此外,模型往往无法捕捉到快速强化的过程,这是许多强烈TC的一个显著特征。在全球变暖的背景下,理解快速强化尤其重要,这可能会增加强烈TC的频率。为了更好地利用计算资源的快速集约化的研究,我们介绍了一个行动最小化算法应用于WRF和WRFPLUS模型。行动最小化推动模型形成更强烈的TC比它否则会;它这样做是通过极大似然路径的随机制定的模型,从而允许有针对性的研究强化机制。我们将动作最小化应用于6 km分辨率的飓风Danny(2015)和Fred(2009)的模拟,以证明该算法始终通过物理上合理的路径增强TC。我们显示了大约十倍的计算节省使用行动最小化研究的TC强度分布的尾部。此外,对于飓风丹尼和弗雷德,行动最小化产生的扰动,优先减少低层切变相比,上层切变,至少在大约$4 \mathrm{\ m \ s^{-1}}$的阈值以上。我们还表明,不对称的,随时间变化的加热模式可以导致显着的TC强化超出对称,方位平均加热,并找到一个制度的非线性响应不对称加热,在以前的工作中没有得到广泛的研究。

英文摘要:

Direct computer simulation of intense tropical cyclones (TCs) in weather models is limited by computational expense. Intense TCs are rare and have small-scale structures, making it difficult to produce large ensembles of storms at high resolution. Further, models often fail to capture the process of rapid intensification, which is a distinguishing feature of many intense TCs. Understanding rapid intensification is especially important in the context of global warming, which may increase the frequency of intense TCs. To better leverage computational resources for the study of rapid intensification, we introduce an action minimization algorithm applied to the WRF and WRFPLUS models. Action minimization nudges the model into forming more intense TCs than it otherwise would; it does so via the maximum likelihood path in a stochastic formulation of the model, thereby allowing targeted study of intensification mechanisms. We apply action minimization to simulations of Hurricanes Danny (2015) and Fred (2009) at 6 km resolution to demonstrate that the algorithm consistently intensifies TCs via physically plausible pathways. We show an approximately ten-fold computational savings using action minimization to study the tail of the TC intensification distribution. Further, for Hurricanes Danny and Fred, action minimization produces perturbations that preferentially reduce low-level shear as compared to upper-level shear, at least above a threshold of approximately $4 \mathrm{\ m \ s^{-1}}$. We also demonstrate that asymmetric, time-dependent patterns of heating can cause significant TC intensification beyond symmetric, azimuthally-averaged heating and find a regime of non-linear response to asymmetric heating that has not been extensively studied in previous work.

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