Finite-amplitude Eddy-mean Flow Interaction in the Extratropical Atmosphere

温带大气中的有限振幅涡均流相互作用

• 批准号: 1151790
• 负责人: Noboru Nakamura
• 金额: $ 56.78万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-02-01 至 2016-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1151790&HistoricalAwards=false
• 关键词: Finite; amplitude; Eddy; mean; Flow

The mutual interaction between eddies (such as those associated with midlatitude weather systems) and the mean flow (midlatitude jet streams, in particular) is a longstanding topic in atmospheric general circulation. It is clear that jet streams and eddies interact strongly, but traditional theories to account for their interaction are limited because, for mathematical reasons, they assume that the eddies are small-amplitude perturbations of the mean flow. The Principal Investigator (PI) has developed a theory of eddy-mean flow interaction which works for large-amplitude eddies, and work conducted under the award seeks to explore the implications of this new theory. The new theory will be applied to 1) evaluate nonconservative driving of the climate state (radiative forcing, friction, mixing, etc.) by carefully documenting and analyzing the slowly varying reference state; 2) quantify the stabilizing effects of baroclinic eddies ("baroclinic adjustment") by comparing the linear stability of the observed zonal-mean time-mean state and that of an eddy-free reference state derived from the theory; 3) characterize annular mode variability as co-variation of the zonal-mean zonal-wind and wave activity density, and in turn associate it with the variation in the zonal phase speed and energy of the eddies; 4) generalize the criterion for the onset of Rossby wave breaking and testing this theoretical prediction with numerical simulation and meteorological reanalysis; and 5) further generalize the wave breaking criterion for zonally varying mean flows.The broader impacts of this activity are that the eddy-mean flow theory and the diagonstic tools derived from it can be applied to a wide class of flows, including the stratosphere, troposphere, and the oceans. In addition, the project will support and train two graduate students, thereby developing the scientific workforce in this area. Results of the research will also be incorporated into demonstrations performed by the PI in his fluid dynamics laboratory, for audiences at the graduate, undergraduate, and high school levels.

涡流（例如与中纬度天气系统相关的涡流）和平均流（特别是中纬度急流）之间的相互作用是大气环流中长期存在的话题。 很明显，急流和涡流相互作用强烈，但解释它们相互作用的传统理论是有限的，因为出于数学原因，它们假设涡流是平均流的小幅度扰动。 首席研究员（PI）开发了一种适用于大振幅涡流的涡流-平均流相互作用理论，该奖项下进行的工作旨在探索这一新理论的含义。 新理论将应用于：1）通过仔细记录和分析缓慢变化的参考状态来评估气候状态的非保守驱动（辐射强迫、摩擦、混合等）； 2) 通过比较观测到的纬向平均时间平均状态的线性稳定性和从理论推导的无涡流参考状态的线性稳定性，量化斜压涡流的稳定效应（“斜压调整”）； 3) 将环模变异性描述为纬向平均纬向风和波浪活动密度的共同变化，并进而将其与涡流的纬向相速度和能量的变化相关联； 4）推广罗斯贝波破碎发生的标准，并通过数值模拟和气象再分析检验这一理论预测； 5) 进一步推广纬向变化平均流的破波准则。这项活动更广泛的影响是涡流平均流理论和从中导出的对角工具可以应用于广泛的流类，包括平流层、对流层和海洋。 此外，该项目还将支持和培训两名研究生，从而培养该领域的科学人才。 研究结果还将被纳入 PI 在其流体动力学实验室为研究生、本科生和高中水平的观众进行的演示中。