Fluid Mechanics in Typhoon


Takeo R.M. Nakagawa and Ai Nakagawa

It is found that the spiral wind velocity profile of Typhoon can be modeled by the exact non-steady solution of the Navier-Stokes equation. Typhoon Hagibis was not just a blustery storm: The areal extent with winds in excess of 15m/s was as large as 1,400 km in diameter and the minimum pressure at the eye was 915 hPa, accompanying significant rainfall and risk of coastal flooding. There are six main requirements for tropical cyclogenesis, viz. 1. Sufficiently warm sea surface temperature above 26.5 , 2. Atmospheric instability, 3. High humidity in the lower to middle levels of troposphere, 4. Enough Coriolis force to develop a low pressure center, 5. Pre-existing low pressure focus or seed, and 6. Low vertical wind shear smaller than 10m/s.  It is realized that there are always regions, called anticyclones of high pressure, which are tightly connected with the Typhoon.   In fact, the flow is usually circulating from the Typhoon to anticyclone, and vice versa, until it decays.   It is inferred that such a flow circulation plays a vital role in sustaining the life of Typhoon.   The Pacific Ocean high pressure is developed at the region covering the middle latitude of the Northern Hemisphere owing to the global circulation of atmosphere air mass surrounding the earth.   During the Typhoon moves over the Pacific Ocean, air mass circulation between the Typhoon and the high pressure is sustained as if the toy horse turns around the center column of a revolving machine.


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