2WeatherWeather is the term used to describe the conditions that exist in a certain place for a short time.
3The Force Behind Weather The Sun provides the energy that forms weather.Solar energy heats the equator more than the poles.
4The Force Behind Weather As land or the ocean warms, it heats the air next to it and this air begins rising. As the heated air rises, air from elsewhere flows in to replace it.What is this type of heat transfer called?
5Convection causes pressure changes Low pressurecaused by rising aircounterclockwise rotationassociated with stormsHigh pressurecaused by sinking airclockwise rotationassociated with sunny days and calm weather
6What causes winds?Wind is a horizontal movement of air from an area of high pressure to an area of low pressureIt is this difference in pressure that makes the air move=windWinds are measured by direction and speedWind speed is measured with an anemometer.
7Local Winds Winds that blow over short distances Caused by unequal heating of Earth’s surface over a small areaOften occurs near a large body of water because land heats and cools faster than water
8Sea Breeze Land warms up faster than water. The air over the land becomes warmer than the air over the water.The warmer air rises and cooler air blows inland from the water.
9Land Breeze Land cools faster than water. The air over the land becomes cooler than the air over the water.The warmer air rises and cooler air blows towards the water.
11MonsoonsSea and land breezes over a large region that change direction with the seasonsIn the summer in South and Southeast Asia, the land gradually gets warmer than the ocean.A large “sea breeze” blows steadily inland from the ocean all summer, even at night.In the winter, the land cools and becomes colder than the ocean.A “land breeze” blows steadily from the land to the ocean.
12Global WindsWinds that blow steadily from specific directions over long distancescreated by convection currents in the atmosphere
13Coriolis EffectBecause Earth is rotating, global winds do not follow a straight path.As the winds move, Earth rotates from west to east underneath them, making it seem as if the winds have curved. This is called the Coriolis effect.Northern Hemisphere- winds turn toward right.Southern Hemisphere, winds curve toward left.
14Global Wind Belts Doldrums Regions near the equator with little or no wind.Horse Latitudes belt of calm air at about 30° north and south latitudes where the air stops moving toward the poles and sinksThe Coriolis effect and other factors combine to produce a pattern of calm areas and wind belts around Earth
15Global Wind Belts Trade Winds Prevailing Westerlies Polar Easterlies steady easterly windsFrom the equator to 30° north latitude and 30° south latitudePrevailing Westerlies blow generally from the southwest between 30° and 60° north latitudes and from the northwest between 30° and 60° south latitudes.play an important part in the weather of the United States.Polar Easterlies meet the prevailing westerlies at about 60° north and 60° south latitudes, along a region called the polar front.has a major effect on weather changes in the United States.
17Air Masseshuge body of air that has similar temperature, humidity, and air pressure throughout ithas the same characteristics of the surface over which it developsClassified byHumidity—Continental (dry) or Maritime (humid)Temperature—Tropical (warm, low pressure) or Polar (cold, high pressure)generally move west to east in N. America
19Fronts the boundary between air masses Caused when air masses collide Four types—warmcoldstationaryoccluded
20Warm Frontwarm air slides over departing cold air- large bands of precipitation formThis is the symbol on a map for a warm front
21Cold FrontsCold air pushes under a warm air mass. Warm air rises quickly=narrow bands of violent storms formThis is the symbol for a cold front
22Occluded Front2 cold air masses merge and force warm air between them to rise quickly. Strong winds and heavy precipitation will occurThis is the weather map symbol for an occluded front
23Stationary FrontWarm or cold front stops moving. Light wind and precipitation may occur across the front boundaryThis is the weather map symbol for a stationary front
24Currents Also Affect Weather streams of water within the oceans that move in regular patternsWarm currents carry warm water from tropics toward the poles.Cold currents bring cold water from polar zones toward the equator.The surface of the water warms or cools the air above it. The warmed or cooled air then moves over the nearby land.