NEWTON:Wind at Altitude
 
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Name: TheMistokles
Status: other
Grade: other
Country: Greece
Date: Summer 2013


Question:
Is there a constant air velocity always present at certain heights above sea level. For example, at more than 1/2 mile altitude (or on top of mountains), is there always a breeze or wind of say, a few kilometers per hour?


Replies:
Hi TheMistokles,

Thanks for the question. Yes, the air does move in the upper atmosphere. The air flow is not the same: sometimes it blows one way and sometimes another. However, there is the jet stream in the upper atmosphere for which the motion is known. For instance, the jet stream can carry a balloon from Japan to Oregon. And this happened during World War II. If you are looking for detailed wind velocity as a function of altitude, I would suggest you consult aviation web sites as this information is necessary for the aircraft navigation.

I hope this helps. Thanks Jeff Grell


No, there is not a constant air velocity always present at certain heights above sea level. The winds are variable at all altitudes.

To provide information to aircraft on winds at different altitudes, the weather service provides charts at: FL 25 (2,500 ft) FL 50 (5,000 ft) FL 75 (7,500 ft) FL 100 (10,000 feet) And so on.

Please see this URL for a complete list of winds aloft charts provided to aviators.

http://www.wunderground.com/Aviation_Maps/Winds_Aloft/FL100-12.html

Sincere regards, Mike Stewart


Above the PBL (Planetary Boundary Layer) the air moves at approximately the speed of movement of weather systems. This speed is called the geostrophic wind speed and is nearly parallel to the isobars (lines of constant pressure).

The PBL can be as shallow as 200 m at night and can grow with heating of the Earth's surface during the daytime to as large as 1500 m. The wind speed in the PBL itself is reduced by friction with the Earth's surface.

Above the PBL, in the so-called "free atmosphere", the wind will exhibit the geostrophic wind speed.

However, there can still be calm or nearly calm periods in the free atmosphere near the center of a strong high pressure system.

So there is no certain height at which you can always say that there is a wind speed, although typically there is a wind speed above the PBL.

David R. Cook Meteorologist Atmospheric and Climate Research Program Environmental Science Division Argonne National Laboratory


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