1. Chapter 19.3
Regional Wind Systems

2. Local Winds
In the middle latitudes (where we live) the wind circulation is complex.
Local winds are small-scale winds produced by locally generated pressure gradients.
They are caused by topographic effects or by variation in surface composition (land and water) in the immediate area.

3. Land and Sea Breezes
At costal areas the land will heat up more during the water. That makes the air above the land heat up, expand, and rise making an area of low pressure.
A sea breeze will happen because cooler air over the water (that is at a higher pressure) moves toward the warmer land and low pressure air.
A sea breeze will usually start around noon and blow at the greatest intensity mid- to late afternoon.

4. At night the opposite may take place, the land cools off faster than the water. The cooler air (high pressure) over the land will move to the sea, where the air is warmer (lower pressure).
Large lakes can also simulate these conditions.

5. Valley and Mountain Breezes
During the day, the air along the slopes of the mountains is heated more than the air at the same elevation on the valley floor. Because of this warmer air on the mountain is less dense, it move up along the slope and makes a valley breeze.

6. Again after sunset the reverse may happen
Again after sunset the reverse may happen. The rapid cooling of the air along the mountain slope produces cooler air next to the ground, this air is dense so it will move downslope into the valley. This is called a mountain breeze.

7. How Wind is Measured 2 basic wind measurements – direction and speed.
Winds are labeled based on the direction from which they blow. So a northern wind blows from the north to the south.
A wind vane will help determine which way the wind is blowing.

8. Wind Direction
Wind will constantly blow more often from one direction – this is called a prevailing wind.
In the United States, the westerlies consistently move weather from the west to the east across the continent.

9. Wind Speed
An anemometer is used to measure wind speed.

10. El Nino and La Nina
There is a cold ocean current that moves toward the equator along the coast of Ecuador and Peru. Near the end of the year, a warm current that flows southward along the coasts of Ecuador and Peru replaces the cold current. During this time the local residents named this warm current El Nino.
These warm currents only usually last a few weeks. Then the cold current comes back.

11. El Nino
Every 3 to 7 years, the warm current become unusually strong and replace the cold offshore waters with warm waters.
El Nino is these periods of time where the ocean warming affects the eastern tropical Pacific.
This brings about abnormal weather patterns. They will receive an abnormal amount of rain. The warm water will move the jet streams. This brings different weather conditions, mostly more rain in areas that normally don’t get a lot of rain.

12. La Nina
This is when surface temperatures in the eastern Pacific are colder than average. This also gives a unique weather pattern.
Cold air will blow over the Pacific Northwest and the northern Great Plains. The rest of the United States will be warm. The Northwest will also get more precipitation.
La Nina can cause more severe hurricanes.

13. Global Distribution of Precipitation
Tropical areas get the most rain. This is the area where we will find rain forests.
Subtropical areas contain deserts.