Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
What Influences Weather? What is weather? • Weather is the short-term state of the atmosphere, including temperature, humidity, air pressure, wind and visibility. How does the water cycle affect weather? • Liquid water from the oceans evaporates into water vapor which enters the atmosphere affecting humidity levels. • Clouds and fog form as a result of condensation of water vapor. Fog limits visibility. • Precipitation occurs when rain, snow, sleet or hail falls from the clouds to the Earth’s surface. How do air masses affect weather? • An air mass forms when the air over a large region of the Earth’s surface stays in place for many days. • The air gradually takes on the temperature and humidity of the land or water below it. • The weather changes when a new air mass moves into your area as the one that was there moves out. Air Masses • A huge body of air with similar characteristics: Humidity Temperature Air Pressure • Classified according to two characteristics: Temperature: Where did the air mass form? Humidity: Did the air mass form over water or land? Maritime Air Masses • Maritime air masses form over oceans. • Water evaporates from the ocean creating a humid air mass. Tropical Air Masses • Warm air masses form in the tropics as a result of direct rays from the sun. These air masses have low air pressure. Polar Air Masses • • Cold air masses form north of 50°N latitude and south of 50°S latitude. Polar air masses have high air pressure. Continental Air Masses • • Form over land, in the middle of continents. Continental air masses have very dry air. Air Masses Continental Polar Maritime Polar Maritime Polar Maritime Tropical Continental Tropical Maritime Tropical Maritime Tropical • mT- originates over a warm tropical ocean. • Warm and Moist (humid air) • Causes high heat and humidity in the Midwest and Eastern US. • Thunderstorms form due to the moist air and heat available, or heavy rain or snow in the winter. Air Masses Maritime Polar • mP- Originates over the ocean in a polar region. • Cold, Damp (humid) air. • Not as cold as cP • If cooled to the dew point, precipitation occurs, bring fog, rain and cool temps. Air Masses Continental Tropical • cT- Originates over a desert region. • The air mass is hot and dry air. • Produces tremendous heat waves. • Produces drought like conditions. Air Masses Continental Polar • cP- Originates over Alaska and Canada. (Those that affect North America) • The air mass is cold and dry air. • Can create precipitation by picking up moisture over the Great Lakes. Air Masses How do air masses move? • • • • Global winds bring air masses of different temperatures and moisture content to a region. The Prevailing Westerlies (a major global wind belt) generally push air masses from west to east across the United States. Jet streams are long-distance winds that travel above global winds for thousands of kilometers. Jet streams can affect temperatures in the United States by pulling cold air masses down from Canada or by pulling warm air masses up from the tropics. Where do weather fronts form? • When two air masses meet, density differences caused by temperature differences prevent the air masses from mixing. • A boundary, called a front, forms between the air masses. • Fronts result in a change in the weather, usually bringing unsettled weather conditions as they pass. • Unsettled weather conditions mean changeable or stormy. Fronts • There are four different types of weather fronts. • They are determined by the characteristics of the air masses and how they are moving. Warm Fronts • • • A moving warm air mass collides with a slower moving cold air mass. The warm air moves over top of the cold air. (warm air is less dense) Types of weather produced: – – – – Clouds, storms and rain. If the rising air is humid, light rain forms. If the rising air is dry, scattered clouds form. After the front passes, it is likely to be warmer and more humid. A Warm Front Cold Fronts • • • • • Cold air is very dense and tends to sink. Warm (less dense) air is pushed up. As it rises it cools and forms clouds which may bring heavy rain or snow. These fronts move very quickly, and can cause abrupt weather changes including violent thunderstorms. After the front moves through, cool, dry air creates clear skies and cooler temps. A Cold Front Stationary Fronts • • • Stationary fronts occur when cold and warm air masses meet, but neither can force the other to move. Water vapor in the warm air condenses into rain, snow, fog or clouds. If the front stalls over an area, it can bring these conditions for several days. Stationary Fronts Occluded Fronts • • An occluded front is a complex situation that occurs when a cold front catches up to a warm front. Occluded fronts bring rainy or snowy weather. Occluded Fronts What are pressure systems and how do they interact? • Areas of different air pressure cause changes in weather. • In a high pressure system, the air sinks and warms bringing clear skies and calm air or gentle breezes. • In a low pressure system, the air rises and cools bringing overcast skies and stormy weather. How do ocean currents affect weather? • The same global winds that blow across the surface of the Earth also push water across the oceans, causing ocean currents. • Ocean currents carry warm water or cold water. • The air above these currents becomes warm or cold depending on the temperature of the current. • The air over ocean currents can change local temperatures, humidity levels, and affect local weather and climate. The North Atlantic Current • In areas where warm ocean currents flow, coastal cities have warmer winter temperatures than inland cities at similar latitudes. The California Current • The California Current is a coldwater current that keeps the average summer high temperature cooler than inland cities at similar latitudes. It’s time for a formative Assessment. Grab a white board, marker and eraser. It is 98°F and humid outside. A front is approaching and the sky begins to darken. Heavy rain and hail fall during a severe thunder and lightning storm. After the passing of the front, the temperature was 87°F and the air was less humid. Which type of weather front passed through the area? A. Warm Front B. Cold Front C. Stationary Front D. Occluded Front An air mass moves into your area bringing hot, dry conditions that last for several days. You learn from the news that you are not allowed to wash your car or water your lawn. Which type of air mass moved into your area? A. Maritime Tropical B. Maritime Polar C. Continental Tropical D. Continental Polar An air mass forming over the Gulf of Mexico moves northwest toward the central part of the United States. It collides with a continental polar air mass moving down from Canada resulting in the formation of a tornado. Which type of air mass moved northwest from the Gulf of Mexico? A. Maritime Tropical B. Maritime Polar C. Continental Tropical D. Continental Polar Two air masses collide over your town. They push against each other without moving. Rain falls for several days. Which type of weather front formed over your area? A. Warm Front B. Cold Front C. Occluded Front D. Stationary Front A maritime polar air mass is pushed from over the northern Pacific Ocean into the west coast of the United States. Which global wind system is responsible for the movement of this air mass? A. The Polar Easterlies B. The Prevailing Westerlies C. The Trade Winds According to the weather map, there are two pressure systems affecting the weather over the United States. The western and central U.S. are experiencing clear skies, and gentle breezes. The northeastern U.S. is experiencing rain, ice and snowfall. Which type of pressure system is affecting the weather over the northeastern part of the United States? ? ? A. A Sprinkler Pressure System B. A High Pressure System C. A Compact Pressure System D. A Low Pressure System