نکته های کلیدی در آب و هواشناسی سینوپتیک
خدایا! کمکم کن؛ پیمانی را که در طوفان با تو بستم در آرامش فراموش نکنم
از این ناراحتم كه روزی بسیاری از درهای علوم را بر روی خود بگشاییم و هنوز شناختمان از تو تنها در همین حد باشد.
مدیر وبلاگ : mehdi doostkamian
The Coriolis force is an apparent force resulting from the fact that the earth is constantly rotating. The Coriolis force acts at a 90 degree angle to the right of the motion of a parcel of air (in the northern hemisphere and 90 degrees to the left in the southern hemisphere). This means that a northbound parcel (wind from the south) would have a coriolis force acting toward the east.
So why does the Earth's rotation matter?
Angular Momentum(اندازه حرکت زاویه ای) = Vradial + Vrelative
AM is conserved if the northbound parcel moves eastward or if a southbound parcel moves westward. The magnitude of the coriolis force is proportional to the speed of the wind. Coriolis force acts on all parcels that are in motion that are not at the equator. If you have a slow moving parcel you will have a small AM, VRelative will be small so AM will be small and the latitude displacement will not greatly effect your parcel.
The magnitude of the coriolis force is also dependent on the cosine of the latitude. Generally, the farther way from the equator you go, the stronger the coriolis force is.
So now we know about two important atmsopheric
forces, the pressure gradien force and the Coriolis force. As it turns out, the
magnitude of the PGF and Coriolis force are very similar. In fact, these two
force commonly balance each other:
This figure is in the X-Y plane, along the 500mb surface.
Remember that the Coriolis force acts 90° to the left of the wind in the northern hemisphere.
The example above is looking at the 500 mb
heights. How do we interpret the pressure gradient based on heights?
The frictional force is dependent on the roughness of the surface, the height above the surface, and the speed of the wind.
The roughness of the surface plays a large role in friction. For example, the friction over the ocean will be less than the friction over the mountains.
As you go heigher in the atmosphere, friction has less of an effect. The surface (and therefore friction) only effects the lower levels of the atmosphere
The speed of the wind also determines how large or small the frictional force will be. Large winds - large effect from friction, small winds - small effect from friction
Friction is in the direction exactly opposit the direction of the wind.
At the surface, the effects of friction are
very important. Friction destroys geostrophic balance. As the speed of the wind
increases from zero, friction begins to do it's work.
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