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METEOROLOGY WEATHER – SHORT TERM VARIATIONS IN ATMOSPHERIC CONDITIONS WHAT CAUSES WEATHER? • The main cause of all weather is the imbalanced heating of the Earth’s surface. • As the various areas of Earth are heated differently, the air interacts in various ways which we will study in this section. AIR MASS- LARGE VOLUME OF AIR THAT HAS CHARACTERISTICS OF THE AREA OVER WHICH IT FORMS. A (Arctic)- Extremely cold and dry, forms over northern Canada. cP (Continental Polar) dry and cold, forms over central Canada. mP (Maritime Polar) Cold and wet, forms over northern Pacific and Atlantic oceans. mT (Maritime Tropical) warm and wet, forms over southern Pacific and Atlantic Oceans. cT (Continental Tropical) Warm and dry, forms over Mexico in the SUMMER ONLY. • Types of Air Masses EXAMPLES OF AREAS THAT HAVE SPECIFIC AIR MASSES cP- Central Canada, North Dakota, Siberia mP- Maine, Northern Canadian Coast, Washington and Alaska mT- Florida, Rainforests, Northern Australian Coast cT- Texas, Mexico, Los Vegas, Arizona A- Northern Siberia, Arctic Circle, Northern Canada and Alaska and Greenland cP mP mT mT cT A The global winds discussed in our last unit are one of the forces that carry air masses across the globe The Coriolis Effect causes global winds and ocean currents to curve. This is due to the Earth’s rotation. **In the northern hemisphere, winds and currents rotate clockwise. **In the southern hemisphere, winds and currents rotate counter-clockwise. How come an airplane you are travelling on never travels in a straight line? The other force that moves these air masses is the jet stream. It is a narrow band of wind that occurs in the stratosphere above large temperature contrasts. Jet stream As the land and sea are heated up or cooled down, the air above them rises or sinks, causing a circulation. During the day, the breeze comes from the sea (sea breeze) because the land heats up so quickly that the air above it begins to rise and is replaced by air from the ocean.. At night, the breeze comes from the land (land breeze) because the land cools down very quickly and air above it sinks and moves out to sea. Fronts- The boundary at the front of an air mass The front created depends on the characteristics of the air mass.. Cold Front – Cold air moves in, forcing warm air up. Intense precipitation and storms are common with cold fronts. Warm Front – Warm air moves in, displacing the cold air. The warm air rises gradually causing widespread light precip. Stationary Front – When 2 air masses meet but neither advances. They are usually similar in temperature. Causes cloudy weather with light winds and occasional precipitation. Occluded Front – When a cold front catches up to and takes over a warm front. Warm air is forced up violently. Typically causes strong winds and heavy precipitation. http://www.physicalgeography.net/fundamentals/7r.html LOW/HIGH PRESSURE SYSTEMS Rising air (makes clouds/precipitation) Sinking air (no rising air means no clouds) ISOTHERMS AND ISOBARS Isotherms – Lines on a weather map of equal temperature. Isobars – Lines on a weather map of equal pressure. Both can be useful in predicting and analyzing weather SUPERCELLS AND DOWNBURSTS Downbursts are violent downward drafts of wind with speeds over 100 mph. These winds can cause as much damage as tornadoes. A supercell in Montana. Supercells are intense rotating storms in which updrafts can take 10-20 minutes to reach the top of the clouds. Cumulonimbus Clouds- these are the dangerous thunderstorm clouds, they are also called thunderheads. These clouds usually form on a hot and humid day when the warm air rises quickly Lightning- is a sudden spark or discharge released from energy within a cumulonimbus cloud. Lightning can be up to 30,000°C. Thunder- is the sound of the explosion. Since light travels so much faster than sound, you always see the lightning first, than HEAR there explosion within seconds of the lightning. Tornadoes- is a rapidly whirling, funnel-shaped cloud that reaches from the cloud to the Earth’s surface. Tornadoes usually last less than 15 minutes but within that time, tornadoes can have winds speeds up to 320 miles per hour and be up to half a mile wide! TORNADO FORMATION TV Warning vs WatchThunderstorm or tornado Warning means that there IS A STORM or funnel cloud and it is heading your way! Watch means that there is a very good chance that the thunderstorm and tornado COULD FORM. Tornado Safety- safest places are a strong cement basement or bath tub with a mattress over your body. If in a car, get out! Get to a bridge overpass or lie in a ditch with your hands over your head away from any objects that could become projectile. CAUSE FOR TORNADO ALLEY: 1. CP AIR MASS FROM THE NORTH MIXES WITH THE MT FROM THE SOUTH. THE LARGE TEMPERATURE CONTRASTS CAUSE THE FORMATION OF SUPERCELLS (EXTREMELY POWERFUL THUNDERSTORMS). THE ROTATION BEGINS WITHIN THE THUNDERSTORM CLOUDS AND THE UPDRAFTS CREATE A COLUMN WHICH INCREASES ROTATION. THE AIR PRESSURE LOWERS IN THE CENTER CAUSES A VIOLENT INCREASE IN WIND SPEED. The Fujita Scale Rates Tornadoes : F0-F1 (last 1-10 minutes and winds up to 45-120 mph) F2-F3 (last 20 minutes, winds up to120-220mph) F4- F5 (Last up to 1 hour, winds are up to 220-340mph) What is the most violent season for tornadoes? Location of Tornado Alley Hurricane Irene HURRICANES: Sandy Prezi Hurricane Formation: 1. Warm air absorbs moisture from the ocean. 2. Water Vapor is lifted into the atmosphere. 3. As the water vapor rises, the cooler upper air condenses it into liquid droplets. 4. Condensation releases latent heat into the atmosphere, making the air less dense. 5. As the lighter air rises, moist air from the ocean takes its places creating a wind current. 6. Moving air begin the rotate due the Coriolis Effect (the process curving large wind and water systems due to the very fast rotation of the Earth) 7. Tropical Depression- Some thunderstorms and winds are 25-40 mph 8. Tropical Storm- thunderstorm wall becomes more solid, winds 42-78mph 9. Hurricane or Cyclone- distinguished eye with a surrounding eyewall (layers of thunderstorms that surrounds the eye) and winds are more than 78 mph. HURRICANE FORMATION Hurricane Katrina STORM SURGE A wall of water created as hurricane-force winds force ocean water toward land.