Global and Local Weather Patterns

The Earth is heated by the energy from the sun. Radiation – the transfer of energy as electromagnetic waves. (The sun’s energy travels through space.) Conduction – the transfer of thermal energy by direct contact. (Walking barefoot on a hot sidewalk.) Convection – transfer of thermal energy by the circulation or movement of a liquid of gas. (Hot air rises and cool air sinks.)

The GREENHOUSE EFFECT is the Earth’s heating process in which gases in the atmosphere trap thermal energy and heat up the atmosphere. This is a normal occurrence and we could not survive without it. An increase of the greenhouse gas, carbon dioxide may be causing an increase in the greenhouse effect. This rise in average global temperatures is called GLOBAL WARMING.

The RADIATION BALANCE explains the balance between incoming energy and outgoing energy. If greenhouse gases continue to increase the radiation may be affected. If this balance is not maintained, the ability of Earth to support life may also be affected. One way to compensate for the increase of carbon dioxide is to plant trees. Plants absorb the harmful carbon dioxide in their food making process.

Atmospheric Pressure and Winds WIND is moving air and is created by the difference in air pressure. The greater the pressure difference, the faster the wind blows. The difference in air pressure is generally caused by the unequal heating of the Earth. Warm air is less dense and rises. (Low pressure) Cold air is more dense and sinks. (High pressure) Air generally move from areas of high pressure to areas of low pressure. Winds generally move from the poles towards the equator.

Pressure Belts – areas of pressure created by the movement of air. These are caused by the uneven heating of the Earth. These belts occur at about every 30 degrees of latitude.

The Coriolis Effect – the curving of moving objects such as wind by the Earth’s rotation. The winds in the Northern Hemisphere curve to the right. The winds in the Southern Hemisphere curve to the left. There are two main types of winds: local winds and global winds. They are both caused by the uneven heating of the Earth’s surface. Local winds generally move short distances and can blow from any direction. Global winds are part of air circulation that moves across the Earth. They travel longer distances and only in a specific direction.

Global Winds 1. The DOLDRUMS are an area of low pressure around the equator. This is where the trade winds of the Northern and Southern Hemispheres meet. Very little wind because of the warm, rising air. An Old English word meaning “foolish” because sailors were considered foolish to get stuck there. 2. The HORSE LATITUDES are at about 30° north and 30° south latitude. Sinking air creates an area of high pressure with weak winds. Named because sailors stuck in this area would throw horses overboard to conserve water.

The POLAR EASTERLIES are wind belts that extend from the poles to 60° latitude in both hemispheres. Formed from cold, sinking air from the poles. The JET STREAMS are narrow belts of high-speed winds that blow in the upper troposphere and the lower stratosphere. Do not follow regular paths around the Earth. The jet streams controls the movement of storms.

TRADE WINDS are winds that blow from 30° north and south latitude to the equator. The Coriolis Effect causes these winds to curve. Used by early traders to sail from Europe to the Americas. 6. The WESTERLIES are wind belts found in both the Northern and Southern Hemispheres between 30° and 60° latitude. Used by early traders to return to Europe.

(Water holds its temperature MUCH Local Winds Local winds are influenced by the geography of an area. SEA BREEZES are created when warm air over the land rises creating an area of low pressure. Air from over the water moves toward the land creating a sea breeze. LAND BREEZES are created when air over land cools and creates an area of high pressure. The cool air moves toward the water producing a land breeze. (Water holds its temperature MUCH better than land does.)

VALLEY BREEZES are created when the sun heats the valley floor and warms the air above it. The warm air moves upslope creating a valley breeze. 4. MOUNTAIN BREEZES are created when the cold air from the mountains sinks down into the valley. This is caused by the mountains cooling faster than the valleys.

Air Masses and Fronts Changes in weather are caused by the movement and interaction of air masses. AIR MASSES are large bodies of air that have similar temperature and moisture throughout. Air masses get their moisture and temperature characteristics from the area it forms over. The characteristics of these air masses are represented on maps with a two-letter symbol. The first letter indicates the moisture characteristics. The second letter indicates the temperature characteristics.

Symbol Meanings: Examples: cP = mP = mT = cT = M – maritime – forms over water – wet air mass. C – continental – forms over land – dry air mass P – polar – forms over polar regions – cold air mass T – tropical – forms over the Tropics – warm air mass Examples: cP = mP = mT = cT =

Fronts are the boundaries between air masses. Weather at a front is usually cloudy and stormy. There are 4 types of fronts: Cold front – cold air mass meets and displaces a warm air mass. The cold air moves under the warm air pushing it up. Move fast producing thunderstorms, heavy rain, or snow. Cooler weather usually follow a cold front. Warm front – warm air mass meets and overrides a cold air mass. The warm air moves over the cold air and gradually replaces it. Generally bring drizzly precipitation. After the front has passed, weather conditions are warm and clear.

Occluded front – faster moving cold air overtakes a slower moving warm air mass and forces the warm air mass up. The cold air mass then moves on until it meets another cold air mass that is warmer than it is. The cold air mass then forces this air mass to rise. Has cool temperatures and large amounts of precipitation. Stationary front – cold air mass meets a warm air mass and little horizontal movement occurs. Similar weather as that produced by a warm front.

Make sure you know each of the symbols associated with the 4 types of weather fronts!!!!!

Severe Weather SEVERE WEATHER is weather that can cause property damage and even death. There are several different types of severe weather: Thunderstorms – small, intense weather systems that produce strong winds, heavy rain, lightning and thunder. Occur when warm, moist air rises rapidly in an unstable atmosphere. Lightning is a large electrical discharge that occurs between two oppositely charged surfaces. Thunder is the sound that results from a lightning strike. Severe thunderstorms may produce high winds, hail, flash floods, and tornadoes.

Tornadoes – a small, rotating column of air that has high wind speeds and low central pressure and that touches the ground. Starts out as a funnel cloud that pokes through the bottom of a cumulonimbus cloud and hangs in the air. It is only called a tornado when it makes contact with the Earth’s surface. Cause a lot of damage due to their strong spinning winds.

Hurricanes – large, rotating tropical weather systems with wind speeds of at least 119 km/h. Called typhoons in the Pacific Ocean. Called cyclones in the Indian Ocean. Generally form in the area between 5° and 20° north or south of the equator over warm, tropical oceans. Get their energy from the condensation of water vapor. They are fueled by contact with the warm ocean water. Eye wall – group of cumulonimbus clouds that produce heavy rains and winds. Eye – core of warm, relatively calm air. Rain bands – circle the center of the hurricane.