Wind & Climate

1. Wind & Climate Wind – the horizontal movement of air. Low pressure – warm air rising. High pressure – cold air falling. Winds always blow from highpressure to low pressure. Winds are named for where they come from: Easterly winds come from the east; Southerly winds come from the south; Sea breezes come from the sea. Prevailing Wind—Regular, predictable, normal wind direction for an area.

3. Sea Breeze In the day time the land heats faster than the water. The rising warm air over the land creates a low pressure. Low Pressure High Pressure 120C 200C The water is cooler, the falling cool air creates a high pressure. Sea Breeze – winds blow from the sea (high) to the land (low).

4. Sea Breeze • Day time • Cool Breeze • From the Ocean

5. Land Breeze In the night time the land loses heat much faster than the water. The falling air over the land creates a high pressure. High Pressure Low Pressure 11oC 90 C The water is warmer, the rising warm air creates a low pressure. Land Breeze – winds blow from the land (high) to the water (low).

6. Land Breeze • Night time • Cool Breeze • From the Land

7. Winds and Pressure Belts Look at Figure 4.10 on page 63.

8. Global convection cells are created because of the differential heating of the earth's surface. • Warm air at the equator rises creating a low pressure. • Cold air at the poles falls creating a high pressure. • Alternating high and low pressure systems develop between these. • Prevailing winds then develop as winds blow from high to low. • 0 0 to 30 0 – Trade winds. • 30 0 – 60 0 – Westerlies. • 60 0 – 90 0 – Polar easterlies.

9. Coriolis Effect • Objects in motion (winds) in the northern hemisphere are deflected to the right while in the southern hemisphere they are deflected to the left. This is caused by the rotation of the earth.

10. Wind & Temperature

11. Some prevailing winds bring warm air from the south. Some winds bring cold air from the north. The affect on temperature varies with seasons as well. Wind off the land in summer is usually warm. (Land heats up faster) However, in the winter wind off the landis usually cold. (Land cools off faster)

12. Types of Rain Orographic Rainfall • Moisture laden air blows off the sea; • It is forced up by mountains ; • Air cools at higher altitudes and holds less moisture; • Clouds condense (vapor turns to liquid) and rain falls. • Often occurs in mountainous areas close to water.

13. Frontal Rainfall • Warm moist air meets cold air; • Warm air is less dense & is forced up over the cold air; • The warm air cools; • The clouds condense and rain falls. • Often occurs close to coastlines where warm and cool air meet.

14. Convectional Rainfall • Usually occurs in hot areas like tropics or inland during summer; • Sun heats the earth which heats the air above it; • Warm moist air rises and cools at higher altitude; • Clouds condense and rain falls.

15. Wind & Precipitation Winds from the ocean are often moist and usually bring more rain. Winds from the land are often dry and usually bring less rain.