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Local Winds

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Local Winds

How can they stand up?

When you try to walk against a 20 mile an hour wind it's not easy. Just standing up is like walking really fast!

Local Winds

Local winds result from air moving between small low and high pressure systems. High and low pressure cells are created by a variety of conditions. Some local winds have very important effects on the weather and climate of some regions.

Land and Sea Breezes

Since water has a very high specific heat, it maintains its temperature well. So water heats and cools more slowly than land. If there is a large temperature difference between the surface of the sea (or a large lake) and the land next to it, high and low pressure regions form. This creates local winds.

  • Sea breezes blow from the cooler ocean over the warmer land in summer. Where is the high pressure zone and where is the low pressure zone? ( Figure below ). Sea breezes blow at about 10 to 20 km (6 to 12 miles) per hour and lower air temperature much as 5 to 10 o C (9 to 18 o F).
  • Land breezes blow from the land to the sea in winter. Where is the high pressure zone and where is the low pressure zone? Some warmer air from the ocean rises and then sinks on land, causing the temperature over the land to become warmer.

How do sea and land breezes moderate coastal climates?

Land and sea breezes create the pleasant climate for which Southern California is known. The effect of land and sea breezes are felt only about 50 to 100 km (30 to 60 miles) inland. This same cooling and warming effect occurs to a smaller degree during day and night, because land warms and cools faster than the ocean.

Monsoon Winds

Monsoon winds are larger scale versions of land and sea breezes; they blow from the sea onto the land in summer and from the land onto the sea in winter. Monsoon winds occur where very hot summer lands are next to the sea. Thunderstorms are common during monsoons ( Figure below ).

In the southwestern United States relatively cool moist air sucked in from the Gulf of Mexico and the Gulf of California meets air that has been heated by scorching desert temperatures.

The most important monsoon in the world occurs each year over the Indian subcontinent. More than two billion residents of India and southeastern Asia depend on monsoon rains for their drinking and irrigation water. Back in the days of sailing ships, seasonal shifts in the monsoon winds carried goods back and forth between India and Africa.

Mountain and Valley Breezes

Temperature differences between mountains and valleys create mountain and valley breezes. During the day, air on mountain slopes is heated more than air at the same elevation over an adjacent valley. As the day progresses, warm air rises and draws the cool air up from the valley, creating a valley breeze . At night the mountain slopes cool more quickly than the nearby valley, which causes a mountain breeze to flow downhill.

Vocabulary

  • sea breeze : A  breeze blowing toward the land from the sea, especially during the day owing to the relative warmth of the land.
  • land breeze : A  breeze blowing toward the sea from the land, especially at night, owing to the relative warmth of the sea.
  • monsoon winds : Winds caused by  a seasonal reversing  wind  accompanied by corresponding changes in  precipitation.
  • valley breeze A gentle wind blowing up a  valley  or mountain slope during the day, caused by the warming of the mountainside.
  • mountain breeze A breeze that blows down a mountain slope at night due to the gravitational flow of cooled air.

Summary

  • Water has high specific heat, so its temperature changes very slowly relative to the temperature of the land. This is the reason for sea and land breezes and monsoon winds.
  • The cause of all of these winds is the differential heating of Earth's surface, whether it's due to the difference in water and land, the difference with altitude, or something else.
  • Winds blow up and down slope, on and off land and sea, through deserts or over mountain passes.

Practice

Use these resources to answer the questions that follow.

1. What are Chinook winds?

2. Where do Chinook winds occur?

3. Explain how Chinook winds work.

4. What are the Santa Ana winds?

5. Where do the Santa Ana winds occur?

6. What causes the Santa Ana winds?

7. Explain how the Santa Ana winds affects the weather.

8. What can be caused by the Santa Ana winds?

Review

1. How does the high specific heat of water result in the formation of sea and land breezes?

2. Describe the conditions that lead to Santa Ana winds.

3. How do Chinook winds lead to rainshadow effect?

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