west to east. In the middle of the jet stream, you'll see the jet streak where wind speeds are as high as two hundred knots.
LOCAL WIND SYSTEMS We have already talked about many local wind systems, such as sea breezes, land breezes and katabatic breezes. Most of these have a diurnal pattern passing just a few hours a day and many affect a small area on the earth's surface. We have not, however, talked about all of these kinds of local wind systems. Let's review them: •
Anabatic winds – these come from slopes that are heated by the sun, expanding the air upward. Cool air is down below in the valleys. This causes a slight breeze up a slope. These of course happened in the daytime.
•
Katabatic winds – these are downslope winds that occur when the air on the slopes cools. This air becomes dense and slides down the slopes, leading to nighttime winds that head down the mountainside. Neither of these winds is very strong, usually only 3 to 4 meters per second.
•
Sea breezes – these are cool winds that come in from the sea after the lowpressure system develops just inland over warmer air. This brings in cool and moist air from the ocean. The speed of these breezes depends on the temperature differential exerted by the sun and other forces. These breezes occur during the daytime.
•
Land breezes – these of course come from the land and spread out to the sea, occurring mainly at nighttime or in the early morning hours before the sun warms. They occur at night because the air cools more over land that it does over the sea.
There are many of these breezes that are named according to the region. Here are some examples: •
The Bise – this is seen in the mountains of France and Switzerland in the wintertime.
67
