Rotating annulus experiments to simulate the air motion in the stratified layer

到目前为止，平流层中的空气运动已经得到了理论和数值模拟的研究。然而，实验室模拟对于研究它们的基本动力学结构也是有用的。本项目的目的是在旋转的流体环空上进行实验，研究斜压气流向上层层流的向上传播，并在平流层产生类似极地涡旋的紧闭涡旋。利用水深13~14 cm的环空，成功地在3 cm以下产生了径向温差作用下的下层斜压气流，并通过加热水面使4 cm以上的上层分层。在本研究项目的前半部分(2001~2002年)，我们在没有引入β效应的情况下，证实了以下两个实验结果。(1)流体向上运动使斜压流按…更多的肉类进入上层。然而，稳定的层结抑制了上升运动，使纬向流体速度随高度呈指数下降，这符合大气动力学中的准地转位涡方程。(2)它们的最大值出现在斜压下层的顶层，径向温度梯度的符号根据热风关系而变化：即上层环空内侧较暖。这种温度分布反映在混合了两层的经向流体环流中，这与真实的大气现象相对应。如果层结足够深，强烈的层结(垂直温度梯度)是斜压下层出现稳定的轴对称或波流所必需的。将这一结果应用于实际大气，发现吸收紫外线并加热空气以形成平流层的臭氧层对中纬度大尺度对流层风是必不可少的。描述结果(1)和(2)的论文已经并将发表在《流体实验》(2003,2005)上。在大气动力学中，众所周知，贝塔效应，即科里奥利力随纬度的变化，导致中纬度大尺度对流层波(如西风)垂直非指数衰减传播，并诱导平流层中的主要波动。在这个研究项目的后半部分，我们演示了在水箱中设置圆锥形底部以产生等效的β效应的旋转流体环状实验。在波数为2的流动中观察到了三个重要的贝塔效应证据：波流垂直传播，其临界水平上升，漂移速度降低。然后，准地转位涡方程在略低于临界层的高度下成功地描述了这一现象，但在临界层附近却失败了。这一结果在提交给《流体中的实验》(2005)的论文中进行了总结。较少

The air motions in the stratosphere have been so far studied theoretically and by numerical simulations. Laboratory simulations are, however, also useful to investigate their basic dynamical structures. The purpose of this project is to conduct experiments on a rotating fluid annulus to study the upward propagations of the baroclinic flows into the upper stratified layer and to produce the tightly closed vortex such as the polar one in the stratosphere. Using the annulus whose water depth is 13〜14 cm, we have succeeded in producing the baroclinic flows in the lower layer imposed the radial temperature difference below 3 cm and making the upper layer above 4 cm stratified by heating the water surface. In the former half of this research project which followed the previous Grant-in-Aid for Scientific Research (2001〜2002), we had confirmed the following two experimental results for the cases without the introduction of the beta-effect. (1)Upward fluid motions make the baroclinic flows per … More meate into the upper layer. The stable stratification, however, suppresses the upward motions so that the zonal fluid velocities decrease exponentially with height, which was shown to follow the quasi-geostrophic potential vorticity equation in the atmospheric dynamics. (2)In fact, their maximum appears at the top level of the baroclinic lower layer and the sign of the radial temperature gradient changes there according to the thermal wind relation: Namely it is warmer on the inner side of the annulus in the upper layer. This temperature profile is reflected in a meridional fluid circulation mixing both layers, which corresponds to real atmospheric phenomena. If the stratified layer is sufficiently deep, strong stratification (vertical temperature gradient) is necessary for steady axisymmetric or wave flows to emerge in the baroclinic lower layer. Applying this result to the real atmosphere, the ozone layer that absorbs the ultraviolet light and warm up the air to make the stratosphere is found essential for the mid-latitude large-scale tropospheric winds. The papers to describe results (1) and (2) was and will be published in Experiments in Fluids (2003, 2005).In atmospheric dynamics, it is well known that the beta-effect, namely the variation of Coriolis force with latitude causes mid-latitude large-scale tropospheric waves such as the westerlies to propagate non-exponentially-decreasingly vertically and induces predominant wave motions in the stratosphere. In the latter half of this research project, we demonstrate rotating fluid annulus experiments setting a conical bottom in a tank to create an equivalent beta-effect. Three dear evidences of the beta-effect were observed in wavenumber-2 flow: the wave flow propagated vertically, its critical level rose, and its drift velocity reduced. Then the quasi-geostrophic potential vorticity equation succeeded in describing this phenomenon below a height a little lower than the critical level, but failed near that level. This result was summarized in the paper submitted to Experiments in Fluids (2005). Less