Earth’s Oceans and Weather Systems Weather Factors

Think of a sunny summer day Think of a sunny summer day. When you get up in the morning, the sun is low in the sky and the air is cool. As the sun rises, the temperature increases. By noon it is quite hot. As you will see in this chapter, heat is a major factor in the weather. The movement of heat in the atmosphere causes temperatures to change, winds to blow, and rain to fall.

Even though you may not feel them, you are being showered by electromagnetic waves.

Energy from the Sun Electromagnetic waves are a form of energy that can travel through space. Electromagnetic waves are classified according to wavelength. The direct transfer of energy by electromagnetic waves is called radiation.

In what form does energy from the sun travel to Earth? Visible light Infrared radiation Small amount of ultraviolet radiation

Visible Light Most of the energy from the sun reaches Earth in the form of visible light and infrared radiation, and a small amount of ultraviolet radiation

Transverse Wave

Electromagnetic Spectrum

Most of the energy that keeps Earth warm comes from the sun Most of the energy that keeps Earth warm comes from the sun. Some of this energy is reflected or absorbed in the atmosphere. The rest of the energy reached Earth’s surface, where it is reflected or absorbed.

Warming Earth Sunlight travels through the atmosphere to Earth’s surface. Earth’s surface then gives off infrared radiation. Much of this energy is held by the atmosphere, warming it.

What happens to energy from the sun when it reaches Earth? Whenever the energy reaches Earth’s surface is heated, it radiates some of the energy back into the atmosphere as infrared radiation.

14-1 Energy in the Atmosphere

Heat Transfer Thermal Energy and Temperature The lemonade is cold, so the molecules move slowly. The herbal tea is hot, so the molecules move faster than the molecules in the lemonade. Inferring Which liquid has a higher temperature?

Temperature How is temperature measured? Air temperature is usually measured with a thermometer. A thermometer is a thin glass tube with a bulb on one end that contains a liquid, usually colored alcohol.

Temperature Temperature units are degrees. Two most common scales: Scientists use the Celsius scale. Freezing point of pure water is 0°C Boiling point of pure water is 100°C. Weather reports in the United States use the Fahrenheit scale. Fahrenheit scale: Freezing point of water is 32°F Boiling point is 212°F.

Measuring According to this thermometer, what is the air temperature in degrees Celsius?

How Heat Is Transferred Radiation: electromagnetic waves Conduction: direct contact of molecules Convection: movement of a fluid

Heat Transfer in the Troposphere

Heat 14-2

Winds Horizontal movement of air from an area of high pressure to an area of lower pressure. All winds are caused by differences in air pressure.

Anemometer Measures Wind Speed An anemometer has three or four cups mounted at the ends of spokes that spin on an axle. The increased cooling that a wind can cause is called the wind-chill factor.

Local winds Local winds are winds that blow over short distances Caused by unequal heating of Earth’s surface Sea Breeze: wind that blows from an ocean or lake onto land Land Breeze: flow of air from land to a body of water

Monsoons Sea and land breezes over a large region that change direction with the seasons

Global Winds

Coriolis Effect: Earth’s rotation makes winds curve It is named for the French mathematician who studied and explained it in 1835.

Longitude and Latitude

Northern Hemisphere, All global winds gradually turn toward the right A wind blowing toward the north gradually turns toward the northeast.

Southern Hemisphere Winds curve toward the left. A south wind becomes an southeast wind, and a north wind becomes a northwest wind.

Coriolis Effect As Earth rotates on its axis, the Coriolis effect turns winds in the Northern Hemisphere toward the right. Interpreting Diagrams Which way do winds turn in the Southern Hemisphere?

Global Wind Belts Doldrums: Near the equator, the sun heats the surface strongly Warm air rises steadily, creating an area of low pressure Regions near the equator with little or no wind

Global Wind Belts Horse Latitudes: Warm air that rises at the equator divides and flows both north and south. At about 30° north and south latitudes, the air stops moving toward the poles and sinks.

Trade Winds   Cold air over the horse latitudes sinks, it produces a region of high pressure. This high pressure causes surface winds to blow both toward the equator and away from it.

Prevailing Westerlies In the mid-latitudes, winds that blow toward the poles are turned toward the east by the Coriolis effect

Polar Easterlies   Cold air near the poles sinks and flows back toward lower latitudes.

Jet Streams Bands of high-speed winds Jet streams blow from west to east at speeds of 200 to 400 kilometers per hour. As jet streams travel around Earth, they wander north and south along a wavy path.

14-3 Concept Map

Humidity Humidity: Measure of the amount of water vapor in the air Relative Humidity: Percentage of water vapor in the air compared to the maximum amount the air could hold

Measuring Relative Humidity Relative humidity can be measured with a psychrometer. A psychrometer has two thermometers, a wet-bulb thermometer and a dry-bulb thermometer.

Relative Humidity For example, at 10°C, 1 cubic meter of air can hold a maximum of 8 grams of water vapor. If there actually were 8 grams of water vapor in the air, then the relative humidity of the air would be 100 percent. If the air held 4 grams of water vapor, the relative humidity would be half, or 50 percent. The amount of water vapor that the air can hold depends on its temperature. Warm air can hold more water vapor than cool air.

Interpreting Data At lunchtime you use a psychrometer and get readings of 26°C on the dry-bulb thermometer and 21°C on the wet-bulb thermometer. Use the table to the left to find the relative humidity.

Interpreting Data Later in the day you use the psychrometer again and this time get readings of 20°C on the dry-bulb thermometer and 19°C on the wet-bulb thermometer. Find the new relative humidity. Is the relative humidity increasing or decreasing?

How Clouds Form Clouds form when water vapor in the air becomes liquid water or ice crystals. The process by which molecules of water vapor in the air become liquid water is called Condensation How does water condense? As you know, cold air can hold less water vapor than warm air. As air cools, the amount of water vapor it can hold decreases. Some of the water vapor in the air condenses to form droplets of liquid water.

Dew Point The temperature at which condensation begins is called the Dew Point. If the dew point is below the freezing point, the water vapor may change directly into ice crystals. When you look at a cloud, you are seeing millions of tiny ice crystals or water droplets.

Cloud Formation Humid air cools as it is blown up the side of a mountain. Predicting What happens when water vapor condenses out of the air?

Classifying Clouds Meteorologists classify clouds into three main types: Cumulus Stratus Cirrus Clouds are also classified by their altitude. Each type of cloud is associated with a different type of weather

Cumulus Clouds that look like fluffy, rounded piles of cotton Cumulus means “heap” or “mass.” Form less than 2 kilometers above the ground, but may grow in size and height until they extend upward as much as 18 kilometers. Indicate fair weather

Stratus Clouds that form in flat layers are called stratus clouds. Strato means “spread out.” Stratus clouds usually cover all or most of the sky. As stratus clouds thicken, they may produce drizzle, rain, or snow. They are then called nimbostratus clouds.

Cirrus Wispy, feathery clouds are called cirrus clouds. Feathery “hooked” ends are sometimes called mare’s tails. Cirrus clouds form only at high levels, above about 6 kilometers, where temperatures are very low. As a result, cirrus clouds are made of ice crystals.

14-4 Concept Map

Precipitation This water eventually returns to the surface as precipitation. Precipitation is any form of water that falls from clouds and reaches Earth’s surface.

Measuring Precipitation Meteorologists measure rainfall with a rain gauge open-ended can or tube that collects rainfall. The amount of rainfall is measured by dipping a ruler into the water or by reading a marked scale.

Rain Gauge A rain gauge measures the depth of rain that falls Rain Gauge A rain gauge measures the depth of rain that falls. Observing How much rain was collected in the measuring tube of this rain gauge?

Controlling Precipitation In some regions, there may be periods that are much drier than usual. Long periods of unusually low precipitation are called droughts. Droughts can cause great hardship. In the farming regions of the Midwest, for example, droughts may cause entire crops to fail.