| Co-Investigator(Kenkyū-buntansha) |
NITTA Takasi Tokai University, School of Humanity and Culture, Professor, 教養学部, 教授 (30256185)
MIMURA Kazuo Tokai University, School of Humanity and Culture, Associate Professor, 教養学部, 助教授 (70200110)
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| Research Abstract |
The Stratospheric Sudden Warming phenomena is characterized by not only the sudden warming but also the sudden reversal of winter type westerly polar vortex to the summer type easterly polar vortex. And it is well known that the basic scenario is written not thermally but dynamically, by using the propagating Rossby wave packet in the stratoshere. Therfore, it is not wrong that this phenomena is called as "Stratospheric Sudden reversal of Polar Vortex"
In planetary scale atmospheric waves, the "local plane wave approximation", which is a premise in typical "Wave, Mean-flow Interaction" scenario, is not always satisfied. In such strong non-linear interaction, "through how process", "in how much area" and "at how much strength", the polar vortex reversal shall be cause?
In order to answer such questions, the above scenario was much more simplified, and a new type experimental equipment, in which the behavior of hemispheric Rossby waves was simulated, was set up.
In our experiment, the cente
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r and the side of our rotating cylindorical water pool correspond to the north pole and the low latitude region, respectively. By using this equipment, we succeeded to simulate the total process of excitation and horizontal propagation of steady Rossby waves, and further more the reversal of initial westerly polar vortex.
As the result of this laboratory experiment, it was found that the final area and strength of polar vortex reversal are depend upon the strength of initial westerly polar vortex. By the velocity field analysis, the process of the vortex reversal was also found.
Finally, a spherical barotropic numerical model which correspond to this experiment was set up, and the process of the polar vortex reversal was investigated in not only various strength of initial westerly polar vortex, but also various zonal wave numbers and strength of Rossby waves which are excited at low latitudes. As the result of this numerical experiment, it was found that there are some stable wave patterns which is easy to coexist with strong easterly polar vortex. Less
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