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

迄今为止，人们对平流层中的空气运动进行了理论和数值模拟研究。然而，实验室模拟对于研究它们的基本动力学结构也很有用。本项目的目的是在旋转的流体环上进行实验，研究斜压流向上传播进入上层层，并在平流层中产生类似极地涡的紧密闭合涡。利用水深为13 ~ 14 cm的环空，通过加热水面，成功地产生了下层斜压流，施加了3 cm以下径向温差，使上层4 cm以上分层。在该研究项目的前半部分（2001 ~ 2002年）中，我们在没有引入beta效应的情况下确认了以下两个实验结果。(1)向上的流体运动使斜压流动…更多的肉进入上层。稳定的分层抑制了上升运动，纬向流体速度随高度呈指数递减，符合大气动力学中的准地转位涡方程。(2)实际上，它们的最大值出现在斜压低层的顶层，径向温度梯度的标志根据热风关系发生变化，即在上层环空的内侧更温暖。这一温度分布反映在两层混合的经向流体环流中，与实际大气现象相对应。如果分层层足够深，强分层（垂直温度梯度）对于在斜压下层出现稳定的轴对称流或波流是必要的。将这一结果应用到实际大气中，发现吸收紫外线并使空气变暖以形成平流层的臭氧层对中纬度大规模对流层风至关重要。描述结果(1)和(2)的论文已经并将发表在《流体实验》（2003年、2005年）上。在大气动力学中，众所周知，β效应，即科里奥利力随纬度的变化，会导致中纬度大尺度对流层波，如西风带，在垂直方向上以非指数递减的方式传播，并在平流层中诱发主要波运动。在本研究项目的后半部分，我们演示了旋转流体环空实验，在水箱中设置锥形底部以产生等效的β效应。在波数为2的流动中观察到三个重要的β效应证据：波流垂直传播，波流临界水平上升，波流漂移速度减小。准地转位涡方程在略低于临界高度处可以成功地描述这一现象，但在接近临界高度处则不能。这一结果被总结在提交给《流体实验》（2005）的论文中。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