Chapter 11 Section 8 What causes local winds? Objective: Describe patterns of local winds.

Key Terms monsoon: wind that changes direction with the seasons

Sea and Land Breezes All winds are produced by temperature differences caused by unequal heating of Earth’s surface. Local winds are simply small-scale winds produced by local changes in air pressure.

Sea and Land Breezes A breeze coming from the sea toward the land is a sea breeze. A breeze going from the land toward the sea is a land breeze. Land and sea breezes are local winds.

Sea and Land Breezes The Sun heats land faster than it does water. As a result, air over the land is warmer and lighter than air over the water. The cooler, heavier air over the ocean moves in toward the land. The warmer, lighter air over the land rises. The result is a sea breeze.

Sea and Land Breezes At night, the land cools faster than the water. The air over the land becomes cooler than the air over the water. The heavier air over the land moves toward the water. The warmer, lighter air over the water rises. The result is a land breeze.

COMPARE: Which cools faster, land or water?

Mountain and Valley Breeze Mountain regions also have local winds. During the day, the air on a mountain slope is warmer than the air in the valleys. Warm air has low pressure. Air in the valley is cooler and has high pressure. Air moves from the high pressure of the valley to the low pressure of the mountain slope. This is a valley breeze. At night, the valleys are warmer than the mountaintops. The heavier mountain air moves downhill toward the valley. This is a mountain breeze.

2. DESCRIBE: In which direction do valley breezes move?

Monsoons Parts of some continents have winds that change direction with the seasons. These winds are called monsoons.

Monsoons In the summer, when the land is warmer than the water, winds move from the ocean toward the land. In the winter, when the land is colder than the water, the winds move from the land toward the ocean. Winds blow toward the ocean all winter. India is famous for its monsoons. The summer monsoon brings warm, moist air with heavy rains. The winter monsoon carried dry air. There is little rain in winter.

3. DEFINE: What are monsoons?

11-8 Classwork A sea breeze blows toward the ___ from the ocean. Land is heated ___ than water. Movement of air from the land toward the ocean is called a ___ breeze. A ___ breeze moves downhill toward a valley. Winds that change direction with the seasons are ___.