Eddy-Jet Interaction and Climate

在气候变化的背景下，探测大气环流和全球示踪剂运输中的长期调制是重要的，但由于信噪比低，这一点变得困难。中村博士将通过在涡流和背景流以及它们之间的相互作用之间引入一种新的分隔来缓解这个问题。利用这一新方法获得了初步结果，揭示了2001-2005年期间涡旋和急流的全球多年放大。使用传统方法无法检测到这种扩增。这种方法将应用于气象分析和全球变暖情景下的长期气候模式模拟，以测量大气环流调制的频率和强度。理想化模式(浅水和两层模式)将被用来探索这种调制背后的动力学。喷流及其调制对全球混合性质的影响将使用受观测到的大尺度气流和小尺度扩散系数平流影响的被动示踪剂来研究。示踪剂变化的衰减率是全球混合的一种度量，急流区对衰减率的贡献将用新的诊断方法来量化。所提出的活动将为对流层大气环流和输送提供一个新的诊断平台，适用于探测气候状况的长期变化。拉格朗日平均方法绕过了传统意义上的涡旋-平均流相互作用的复杂性，并允许对非保守过程进行更简单的解释。这一活动的更广泛的影响是，诊断框架可以应用于更广泛的流动类别，包括平流层、对流层，可能还有海洋和数值模拟。将资助两名研究生。

In the context of climate change, detecting long-term modulations in the general circulation and in the global transport of tracers is important, but it is made difficult by the low signal-to-noise ratio. Dr. Nakamura will alleviate this problem by introducing a new partition between the eddies and the background flow and their interaction. Preliminary results using this novel method have been obtained, and a global, multi-year amplification of the eddies and jets, over the period 2001-5 is revealed. This amplification is not detected using traditional methods. This method will be applied to meteorological analyses and to long-term climate-model simulations under global warming scenarios, to measure the frequency and intensity of modulations of the general circulation. Idealized models (shallow water and two-level models) will be employed to explore the dynamics that underlies such modulations.The effects of jets and their modulations on global mixing properties will be studied using a passive tracer subject to advection by the observed large-scale flow together with small-scale diffusivity. The decay rate of the variance of the tracer is a metric of global mixing, and contributions from the jet regions to the decay rate will be quantified with a new diagnostic.The proposed activity will provide a new diagnostic platform for the tropospheric general circulation and transport, suitable for the detection of long-term shifts in the climatic regime. The Lagrangian-mean approach bypasses the complication of eddy-mean flow interaction in the traditional sense, and it allows simpler interpretations in terms of nonconservative processes.The broader impacts of this activity are that the diagnostic framework can be applied to a wide class of flows, including the stratosphere, troposphere, possibly the oceans, and numerical simulations. Two graduate students will be supported.