Air Pockets and Eddies

• The Bora – this is a strong and cold wind located in the mountains along the coastline of Croatia.

• The Foehn - these are warm and dry winds seen on the lee side of mountaintops.

They can be very strong and can occur suddenly. These are the same thing as

Chinook winds except they are located elsewhere, such as in New Zealand or in the Alps.

• The Khamsin winds – these are dusty winds seen in Egypt in the springtime.

• The mistral winds – these are extremely strong winds in the Rhône Valley of southern France, usually seen in the wintertime.

You do not need to memorize all of these winds unless they exist in your area. You can expect them to occur at various times of the year and cause a varying degree of damage to property.

AIR POCKETS AND EDDIES

If you've ever traveled by air, you know about air pockets. These can be scary times for airline travelers and represent situations where to bodies of air moving and greatly different speeds and meet together. Airline pilots and meteorologists call this CAT, which stands for clear air turbulence. What this means is that you cannot see anything in the air itself to let you know is coming.

Air pockets tend to be seen at about 7000 to 12,000 meters above the earth's surface and upper troposphere area. You might also see them at the tops of certain mountain ranges. If you see cirrus clouds, it could indicate a higher probability of having an air pocket. Most air pockets are just uncomfortable, but a few can be dangerous.

It is very difficult to detect where an actual air pocket is located, even if you have conventional radar equipment. The best ways to detect these are remotely, using a scintillometer, Doppler radar, laser-based radar, and what is called an N slit inferometer. These techniques will all measure turbulence.

There are certain areas where you can predict a higher chance of having an air pocket. These include near the jet streams, especially if there is horizontal wind shear in the

area. Anytime there is a large temperature gradient between two air masses, you may also see air pockets. Remember that you can have vertical temperature gradients as well as horizontal temperature gradients in the upper atmosphere.

What is wind shear? Windshear is when there is a strong difference in the speed of two air masses next to one another. These will produce circular vortices, where the wind is not moving in a predictable direction. Air density and viscosity will change dramatically in a short period of time, leading to areas of slow and rapid air movement that just cannot be predicted.

Another feature associated with air pockets or CAT is a mountain wave. As you can imagine, mountain waves are undulating waves of air that go up the mountain and back down the other side. Air pockets are seen when there are long mountain ranges, strong winds running perpendicular with respect to the mountain range. There should also be a temperature inversion near the top of the range and the maintenance of wind direction across the altitudes. If you meet these requirements, you have a higher wind shear chance.

Wind shear and clear air turbulence can also be affected by gravity wave windshear. This occurs at the tropopause, where the wind beneath it is cold and moves faster. The wind above it is warmer and move slower. You can imagine this rapid change in wind speed could cause turbulence in this area.

It will not affect the weather on earth, but it will affect aircraft travel because airplanes do not work as well when the air density is not consistent or stable. You will see instability and turbulence as an airplane leaves the jet stream, which is unavoidable. Any changes in course will also affect the chances of being exposed turbulence. Airplanes also fly at constant altitude to avoid turbulence.

On several occasions, clear air turbulence has been dangerous. There have been situations where passengers have been injured because of this. In nineteen sixty-six a Boeing 707 broke up because of turbulence, with all lives lost on board.

The phenomenon of thermals in the air results from areas of local heating. There will be vertical convection and currents of air caused by this. You will see these usually over areas of sand or bare rock, such as over sand dunes. You can imagine that these are very