Structure and Maintenance of Potential Vorticity in the Midlatitude Atmosphere

本项目涉及地球中纬度大气位涡（PV）平均结构的数值和理论研究。特别令人感兴趣的是(1)非保守过程（摩擦、辐射、潜热等）如何与平流过程相互作用，以维持高度不均匀的PV结构，如在对流层顶和平流层极涡边缘发现的PV结构；(2)如何维持对流层PV的值和梯度。将采用一种新的诊断技术来定义平均PV剖面，该技术基于拉格朗日质量坐标，由首席研究员最近开发。与传统的纬向和时间平均方法截然不同，该方法将等熵输运描述为PV轮廓线之间的质量再分配，而扩散等非保守过程是必不可少的。混沌平流被认为是PV轮廓线的拉伸，影响了微尺度扩散的可用界面。这种拉格朗日诊断似乎比传统方法更好地识别强PV梯度。在此框架内，将根据对流层的质量收支来研究斜压调整和对流层顶高度，同时考虑到平流层-对流层质量交换和地面的质量汇/源（热通量），并考虑到由于斜压涡流调节这些过程而产生的搅拌。利用二维模型，PI将首先模拟斜压大气的统计稳定状态，并研究对流层顶形成和维持的机制。基于GFDL的SKYHI全球环流模式的高分辨率模拟，分析将扩展到三维空间。同样的方法将用于研究平流层极地涡旋边缘的维持，只是破碎的罗斯比波将取代斜压波作为搅拌剂。这些研究的目的是寻找中纬度大气环流各方面的统一理论。* * *

9627040 Nakamura This project involves numerical and theoretical investigations of the mean structure of the potential vorticity (PV) in the earth's midlatitude atmosphere. Of particular interest are (1) how the nonconservative processes (friction, radiation, latent heating, etc.) interact with advective processes to maintain the highly inhomogeneous PV structures such as those found at the tropopause and at the edge of the stratospheric polar vortex and (2) how the values and gradients of the tropospheric PV are maintained. A new diagnostic technique to define the mean PV profile, based on the Lagrangian mass coordinate and recently developed by the principal investigator, will be employed. In a radical departure from the conventional zonal- and time-mean approaches, the method characterizes the isentropic transport as redistribution of mass between PV contours for which nonconservative processes such as diffusion are essential. Chaotic advection is viewed as the stretching of the PV contours, affecting the available interface for microscale diffusion. This Lagrangian diagnostic appears to identify strong PV gradients much better than conventional methods. Within this framework the baroclinic adjustment and the height of the tropopause will be investigated in terms of the mass budget of the troposphere, considering both the stratosphere-troposphere mass exchange and the mass sink/sources (heat fluxes) at the ground, with stirring due to baroclinic eddies regulating these processes. Using a two-dimensional model, the PI will first simulate a statistical steady state of the baroclinic atmosphere and examine the mechanism of tropopause formation and maintenance. The analysis will be extended to three dimensions, based on the high resolution simulations with the GFDL's SKYHI global circulation model. The same approach will be used to investigate the maintenance of the stratospheric polar vortex edge except that breaking Rossby waves will replace baroclinic waves as the stirr ing agent. These studies are directed at finding unifying theories of various aspects of the midlatitude general circulation. ***