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

涡旋（如与中纬度天气系统相关的涡旋）和平均气流（特别是中纬度急流）之间的相互作用是大气环流中一个长期存在的课题。 很明显，急流和涡流强烈地相互作用，但传统的理论来解释它们的相互作用是有限的，因为，出于数学原因，他们假设涡流是平均流的小振幅扰动。 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。 新的理论将被应用于1）评估气候状态的非保守驱动（辐射强迫，摩擦，混合等）。通过仔细记录和分析缓慢变化的参考状态; 2）量化斜压涡旋的稳定作用（“斜压平差”），比较观测到的纬向平均时均状态的线性稳定性和由理论导出的无涡参考状态的线性稳定性; 3）将环形模态变率表征为纬向平均纬向风和波浪活动密度的共变，（4）归纳了Rossby波破裂的判据，并用数值模拟和气象再分析对理论预报进行了检验; 5）进一步推广了纬向变化平均流的波浪破碎准则，其更广泛的影响是，涡均流理论及其衍生的诊断工具可以应用于更广泛的流类，包括平流层，对流层，和海洋。 此外，该项目将支持和培训两名研究生，从而发展这一领域的科学工作者队伍。 研究结果也将纳入PI在其流体动力学实验室进行的演示中，供研究生，本科生和高中生观众使用。

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.