| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 2004: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2003: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
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
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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
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