SECTION 2 Air Masses And Fronts - Southwest Middle School
Name CHAPTER 16 Class Date Understanding Weather SECTION 2 Air Masses and Fronts National Science Education Standards BEFORE YOU READ After you read this section, you should be able to answer these questions: ES 1j How is an air mass different from a front? How do fronts affect weather? What Are Air Masses? Have you ever been caught outside when it suddenly started to rain? What causes such an abrupt change in the weather? Changes in weather are caused by the movement of bodies of air called air masses. An air mass is a very large volume of air that has a certain temperature and moisture content. There are many types of air masses. Scientists classify air masses by the water content and temperature of the air. These features depend on where the air mass forms. The area over which an air mass forms is called a source region. One source region is the Gulf of Mexico. Air masses that form over this source region are wet and warm. Each type of air mass forms over a certain source region. On maps, meteorologists use two-letter symbols to represent different air masses. The first letter indicates the water content of the air mass. The second letter indicates its temperature. The figure below shows the main air masses that affect North America. M0 C0 READING CHECK 1. Identify How do scientists classify air masses? M0 TAKE A LOOK C4 M4 STUDY TIP Summarize As you read, make a chart comparing the four kinds of fronts. In your chart, describe how each kind of front forms and what kind of weather it can cause. M4 MARITIME M FORMS OVER WATER WET POLAR 0 FORMS OVER THE POLAR REGIONS COLD CONTINENTAL C FORMS OVER LAND DRY TROPICAL 4 FORMS OVER THE 4ROPICS WARM 2. Apply Concepts Describe the temperature and moisture content of a cT air mass. Copyright by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 309 Understanding Weather
Name SECTION 2 Class Date Air Masses and Fronts continued COLD AIR MASSES READING CHECK 3. Identify What is the source region for cP air masses? Most of the cold winter weather in the United States comes from three polar air masses. Continental polar (cP) air masses form over northern Canada. They bring extremely cold winter weather. In the summer, cP air masses can bring cool, dry weather. Maritime polar (mP) air masses form over the North Pacific Ocean. They are cool and very wet. They bring rain and snow to the Pacific Coast in winter. They bring fog in the summer. Maritime polar air masses also form over the North Atlantic Ocean. They bring cool, cloudy weather and precipitation to New England. WARM AIR MASSES Critical Thinking 4. Infer Why don’t warm air masses form over the North Atlantic or Pacific oceans? Four warm air masses influence the weather in the United States. Maritime tropical (mT) air masses form over warm areas in the Pacific Ocean, the Gulf of Mexico, and the Atlantic Ocean. They move across the East Coast and into the Midwest. In summer they bring heat, humidity, hurricanes, and thunderstorms to these areas. Continental tropical air masses (cT) form over deserts and move northward. They bring clear, dry, hot weather in the summer. Air mass How it affects weather cP from northern Canada mP from the North Pacific Ocean mT from the Gulf of Mexico TAKE A LOOK 5. Identify Fill in the blank spaces in the table. cT from the deserts What Are Fronts? READING CHECK 6. Define What is a front? The place where two or more air masses meet is called a front. When air masses meet, the less dense air mass rises over the denser air mass. Warm air is less dense than cold air. Therefore, a warm air mass will generally rise above a cold air mass. There are four main kinds of fronts: cold fronts, warm fronts, occluded fronts, and stationary fronts. Copyright by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 310 Understanding Weather
Name Class SECTION 2 Date Air Masses and Fronts continued COLD FRONTS A cold front forms when a cold air mass moves under a warm air mass. The cold air pushes the warm air mass up. The cold air mass replaces the warm air mass. Cold fronts can move quickly and bring heavy precipitation. When a cold front has passed, the weather is usually cooler. This is because a cold, dry air mass moves in behind the cold front. #OLD FRONT 7ARM AIR MASS #OLD AIR MASS TAKE A LOOK 7. Describe What happens to the warm air mass at a cold front? A cold front forms when a cold air mass pushes a warmer air mass away. The front moves in the direction that the cold air mass is moving. -OVEMENT OF FRONT WARM FRONTS A warm front forms when a warm air mass moves in over a cold air mass that is leaving an area. The warm air replaces the cold air as the cold air moves away. Warm fronts can bring light rain. They are followed by clear, warm weather. Warm front READING CHECK 8. Define What is a warm front? Warm air mass Cold air mass Movement of front A warm front forms when a warm air mass moves in and replaces a cold air mass. The front moves in the direction the warm air mass is moving. Copyright by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 311 Understanding Weather
Name SECTION 2 Class Date Air Masses and Fronts continued OCCLUDED FRONTS An occluded front forms when a warm air mass is caught between two cold air masses. Occluded fronts bring cool temperatures and large amounts of rain and snow. Warm air mass Warm air mass Occluded front Occluded front TAKE A LOOK 9. Describe What happens to the warm air mass in an occluded front? Cold air mass An occluded front forms when a warm air mass is trapped between two cold air masses. The cold air masses move together and push the warm air out of the way. Cold air mass Movement of front STATIONARY FRONT A stationary front forms when a cold air mass and a warm air mass move toward each other. Neither air mass has enough energy to push the other out of the way. Therefore, the two air masses remain in the same place. Stationary fronts cause many days of cloudy, wet weather. TAKE A LOOK 10. Infer What do you think is the reason that stationary fronts bring many days of the same weather? 3TATIONARY FRONT #OLD AIR MASS 7ARM AIR MASS A stationary front forms when air masses stay in one place. Copyright by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 312 Understanding Weather
Name SECTION 2 Class Date Air Masses and Fronts continued How Does Air Pressure Affect Weather? Remember that air produces pressure. However, air pressure is not always the same everywhere. Areas with different pressures can cause changes in the weather. These areas may have lower or higher air pressure than their surroundings. A cyclone is an area of the atmosphere that has lower pressure than the surrounding air. The air in the cyclone rises. As the air rises, it cools. Clouds can form and may cause rainy or stormy weather. An anticyclone is an area of the atmosphere that has higher pressure than the surrounding air. Air in anticyclones sinks and gets warmer. Its relative humidity decreases. This warm, sinking air can bring dry, clear weather. Cyclones and anticyclones can affect each other. Air moving out from the center of an anticyclone moves toward areas of low pressure. This movement can form a cyclone. The figure below shows how cyclones and anticyclones can affect each other. (IGH PRESSURE Anticyclone ,OW PRESSURE Critical Thinking 11. Compare Give two differences between cyclones and anticyclones. TAKE A LOOK 12. Identify In which direction does air move: from a cyclone to an anticyclone, or from an anticyclone to a cyclone? Cyclone Copyright by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 313 Understanding Weather
Name Class Date Section 2 Review NSES NSES ES 1j SECTION VOCABULARY air mass a large body of air throughout which temperature and moisture content are similar anticyclone the rotation of air around a high pressure center in the direction opposite to Earth’s rotation. cyclone an area in the atmosphere that has lower pressure than the surrounding areas and has winds that spiral toward the center front the boundary between air masses of different densities and usually different temperatures 1. Identify Relationships How are fronts and air masses related? 2. Compare Fill in the table to describe cyclones and anticyclones. Name Compared to surrounding air pressure, the pressure in the middle is. cyclone .lower than surrounding pressure. anticyclone What does the air inside it do? What kind of weather does it cause? sinks and warms 3. List What are four kinds of fronts? 4. Identify What are the source regions for the mT air masses that affect weather in the United States? 5. Describe What kind of air mass causes hot, clear, dry summer weather in the United States? Copyright by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 314 Understanding Weather
Earth Science Answer Key continued 4. about 30 g/cm3 5. 10 g/m3 23 g/m3 0.43 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 5. 0.43 100 43% relative humidity Humidity is the absolute amount of water vapor in the air. Relative humidity is a measure of how saturated with water vapor the air is. wet-bulb and dry-bulb thermometers about 87% Water vapor condenses into liquid water. The glasses are as cold as the air outside. They absorb heat from the air inside. As a result, the air inside cools below its dew point. Water condenses on the glasses. water vapor in the air by shape and by altitude A nimbostratus cloud is producing precipitation. water that falls to Earth from clouds They get bigger. several ice crystals joined together when it is too heavy to be carried by updrafts How it affects weather cP from northern Canada very cold winter weather and cool, dry summer weather mP from the North Pacific Ocean rain and snow in the Pacific in the winter, fog in the summer mT from the Gulf of Mexico heat, humidity, hurricanes, thunderstorms in East Coast and Midwest cT from the deserts clear, dry, hot weather in the summer 6. a place where two or more air masses meet 7. It rises because the cold air pushes it up. 8. a place where a warm air mass moves over a 9. 10. 11. 12. Review 1. Possible answer: Water can condense from cold air mass The cold air masses push it out of the way. Stationary fronts do not move, so the weather they bring stays in one place. Cyclones have lower pressures than surrounding areas, but anticyclones have higher pressures. Cyclones bring rainy or stormy weather, but anticyclones bring dry, clear weather. anticyclone to cyclone Review 1. A front is a place where two air masses meet. 2. First row, from left to right: rises and cools; air that is below its dew point. 2. the sun 3. Air rises and cools. When it cools below its dew point, water vapor condenses to form liquid water droplets or ice crystals. These droplets or ice crystals form a cloud. 4. Sleet forms when liquid water freezes in clouds and falls to the ground as ice. Snow forms when water vapor turns directly into a solid. 5. Name Altitude Shape Precipitation? cloudy, rainy, and stormy Second row, from left to right: . higher than surrounding pressure; dry and clear 3. cold, warm, occluded, stationary 4. Pacific Ocean, Atlantic Ocean, Gulf of Mexico 5. cT SECTION 3 SEVERE WEATHER Cirro-stratus high layered no 1. It must contain enough water vapor to form Altocumulus middle puffy no Nimbostratus low layered yes Cumulonimbus low to middle puffy yes clouds. Electricity travels between an area with a positive charge and an area with a negative charge. sound produced by vibrations in expanding air that was superheated by lightning The center of the tornado has low pressure. when it touches the ground 74 mph to 112 mph Ocean water is too cold there. the Coriolis effect the center of the hurricane that contains warm, fairly calm air with low pressure 2. 3. 4. 5. 6. 7. 8. 9. SECTION 2 AIR MASSES AND FRONTS 1. 2. 3. 4. Air mass by water content and temperature of the air dry, warm northern Canada Warm air masses form over warm water or land, and the North Atlantic and Pacific are cold. Copyright by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook Answer Key 56 Earth Science
Occluded fronts bring cool temperatures and large amounts of rain and snow. Warm air mass Cold air mass Cold air mass Warm air mass Movement of front Occluded front Occluded front An occluded front forms when a warm air mass is trapped between two cold air masses. The cold air masses move together and push the warm air out of the way .
Air masses that form near the equator are called tropical air masses. Those air masses that form in cold regions are called polar air masses. Air masses that form near the poles are called arctic and antarctic air masses. Visual Check 2. Classify Where does continental polar air come fro
air masses as they form is important to resulting weather conditions when air masses move. Fronts As these air masses move and collide with each other, fronts form at the boundaries between the air masses. Depending upon the air masses involved, a warm front, cold front, st
Continental Polar Air- air masses over northern land and ice and are cold and dry. Maritime Tropical Air- air masses over oceans around 20-30oN and are warm and moist. Continental Tropical Air -air masses that are warm and dry. These air masses affect t
Occluded fronts bring cool temperatures and large amounts of rain and snow. Warm air mass Cold air mass Cold air mass Warm air mass Movement of front Occluded front Occluded front An occluded front forms when a warm air mass is trapped between two cold air masses. The cold air masses move together and push the warm air out of the way .
Front Cold Front Warm Front Stationary Front Occluded Front A huge body of air that has smilier temperature, humidity and air pressure The boundary where unlike air masses meet but do not mix Fast moving cold air mass runs into slow moving warm air mass Warm air mass runs into slow moving cold air mass Warm Cold Cold and arm air masses meet,
Air masses Are huge bodies of air, are formed over water or land in tropical or polar regions. Air masses move. When they form, the temperature or humidity in them results in different weather conditions. Fronts the boundary between 2 air masses when they collide Depending upon the air masses
Characteristics of Air Masses & Fronts Polar air masses are colder in winter, and milder in summer Tropical air masses have less seasonal variation, due to nearly uniform sunlight duration and intensity Air masses modify as they move away from source region – Starts taking on the characteristics of the
AWJM, the abrasive particles are allowed to entrain in water jet to form abrasive water jet with significant velocity of 800 m/s. Such high velocity abrasive jet can machine almost any material. Fig. 1 shows the photographic view of a commercial CNC water jet machining system along with close-up view of the cutting head.
