Local Air Movements Science 1206

Objectives investigate localized air movements (thermals, sea breezes, and land breezes) and its effect on regional weather

Local Air Movements In this lesson you will focus your study on what is known as regional or local weather patterns known as thermals, sea breezes and land breezes.

Local Weather keep in mind that local weather patterns all result from the instability caused by alternating warming and cooling that occurs on a diurnal and nocturnal basis (day and night) as a result of the Earth's rotation about its axis.

Thermals: Thermals are caused by the heating of the land by the sun. Land does not have as high a specific heat capacity as does water so the air above the land becomes heated.

Thermals

Rising convection air currents (sometimes called an updraft) form above the land We know, rising air currents form a local low pressure region. Air from surrounding areas tend to move toward the low pressure region so that by mid day, the local area can develop moderate winds.

Question Why do winds tend to be more calm in the morning and evening? In the evening, when the intensity of sunlight diminishes, the thermal updraft begins to lose its source of driving energy and the local winds die down. This explains why winds tend to be more calm in the early morning and early evening. You should recognize that it is the energy from the sun that drives these local winds.

Sea Breezes: During the day, land tends to heat up much faster than a large body of water nearby, creating a low pressure area. The sea air therefore tends to move in since the air pressure over the sea is higher than over the land. m?chapter_no=visualization

Land Breezes: At night the cool air over the land becomes more dense and forms a high pressure region.

Land Breezes Air above the water tends to be relatively warmer then the cooler air over the land, air begins to move from the land toward the body of water forming a relatively mild land or off-shore breeze.

In-class Read 14.4 "Regional Weather" on pages Answer questions from "Understanding Concepts" on page 555.

1. You are vacationing at a cottage on a lake. A flagpole on the deck overlooking the shore tends to blow in an inland direction during the daytime but toward the lake at night. Which statement best explains the morning onshore wind? a. Land heats up faster than water, resulting in an onshore sea breeze. b. Land heats up faster than water, resulting in an offshore land breeze. c. Water heats up faster than land, resulting in an onshore sea breeze. d. Water heats up faster than land, resulting in an offshore land breeze.

2. Which best describes a thermal? a. wind rising up the side of a mountain b. solar energy heats the land causing the air above to rise c. after sun set, land cools more rapidly than water creating a convection cell d. warm air is generally more dense than cold air

3. Why does air become less dense as it is heated? a. air expands when heated so there are fewer particles of matter in the same volume b. air contracts when heated so there are fewer particles of matter in the same volume c. warmer air holds less moisture, less water means lower density d. warmer air holds more moisture, more water means lower density

4. Which statement is true about local winds? a. sea breezes are generally stronger than land breezes b. land breezes are generally stronger than sea breezes c. thermals normally occur after sunset d. sea breezes blow from land toward the water

6. Which explains why people living near the shore of a large body of water tend to be cooler in summer? a. thermals carry heat away from the land b. sea breezes bring cooler air c. land breezes bring cooler air d. water is always cooler than the land

7. Which is the main factor in causing local winds? a. land has a higher heat capacity than water b. water has a high latent heat of evaporation c. water has a low latent heat of evaporation d. water has a higher heat capacity than land