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
Air Masses April 28th 2014 Air Masses Definition: Air mass - a large dome of air which has similar horizontal temperature and moisture characteristics throughout. Continental Arctic (cA): • • • • Frigid – record low temperatures Dry - very low dew points Dense - very high barometric pressure Usually originate north of the Arctic Circle Siberian Express • Usually once or twice a winter • very rarely form during the summer because the sun warms the Arctic. Continental polar (cP): • • • • Cold and dry Usually originates in NW Territory of Canada Influences mainly the northern USA Responsible for clear and pleasant weather during the summer • Usually in winter • Lake effect snow in Great Lakes areas Maritime polar (mP): • Cool and moist • Originate over N. Atlantic and N. Pacific • Main Influence - the Pacific Northwest and the Northeast. • can form any time of the year • Generally not as cold as cP air masses Maritime tropical (mT): • Warm and very moist • Originate in the Gulf of Mexico and the Southern Atlantic Ocean • Influences the eastern USA • Usually in the summer • Responsible for hot, humid summer days across the South and the East. Continental Tropical (cT): • Very Hot and very dry • Originates in Desert Southwest and northern Mexico • Occurs in the summer, rarely in winter • Usually keeps the Desert Southwest scorching above 100oF during summer • Generally clear skies, hot, low humidity Source Regions Work Time Activity Reasoning for Tornadoes Orographic Perfection Meeting of • Moist - mT • Hot - cT • Cool – cP Tornado Alley http://www.britannica.com/thunderstorms_tornadoes/video/ocli wea124v4.mov Fujita Scale (NationalAtlas.com) Fronts and their symbols Fronts: Boundary between two air masses Characterized by shift in weather Cold Warm Stationary Occluded 5 Characteristics of a Front Sharp temperature changes over a relatively short distance. Changes in air moisture content Shifts in wind direction Pressure changes Clouds and precipitation Cold Fronts • Temperature – drops rapidly • Pressure – rises steadily • Clouds – Vertical building • Precipitation – Heavy along front • Winds – Strong and shifting • Typically move faster than warm front Cold Front Cold Front (Fozzy) Cold Front In the summer, cold fronts can trigger: thunderstorms large hail dangerous winds tornadoes Graphic Depiction! Warm Fronts • Temperature – rises slowly • Pressure – slight rise, then fall • Clouds – strato- and cirro• Precipitation – long, steady • Winds – variable and light • Typically will have affect for days Warm Front Warm Front Warm Front Effects of warm fronts Slow-moving warm front can mean days of wet weather before warm air Sometimes water vapor in warm fronts condense to produce rain snow sleet freezing rain Stationary Front Stationary Fronts • Temperature – stagnent • Pressure – slightly fluctuates • Clouds – altocumulus • Precipitation – none • Winds – variable and light • Can last for days weeks Occluded Front Occluded Fronts • Temperature – • Warm – gets milder • Cold – gets colder • Pressure – • Warm - slight drop • Cold – slight rise • Clouds – cumulus • Precipitation – steady and light • Winds – variable and light Occluded Front Different Temperatures Different Pressures Less Dense Cool Air Less Pressure Denser Warm Air More Pressure Pressure and Air Movement Pressure Gradient Force Difference in pressure over a given distance---between isobars Close together = step pressure gradient STRONG winds Far apart = gentle pressure gradient Light winds • Just like contour lines Pressure Gradient Force Isobaric Maps Coriolis Effect Apparent force due to the rotation of the Earth (Think Merry-go-round) N. Hemisphere wind turns right S. Hemisphere wind turns left Strength depends on latitude and wind speed Coriolis Effect Coriolis Effect Centripetal Force In-ward directed force Allows an object to remain in circular motion Winds moving around high and low pressure areas Clockwise around Highs. Counter-clockwise around Lows. Friction (What a Drag) The resistance to movement Surface winds are affected by friction Why? Ground resistance: trees, mountains, houses, buildings, etc. This drag causes winds to blow across pressure gradient at the surface. Pressures All Together General Planetary Circulation Winds Horizontal surface movements at from WHERE it came from…not where it is going!!! Names Around Pressure Cells Pressure Cells High – In and Up Converge at surface Ascend in center Diverge Aloft Low – Down and Out Converge aloft Descend in center Diverge at surface X-section of Planetary Circulation January Global Pressure Map January July Global Pressure Map July Summer Highs Quiz Questions: 1. 2. 3. 4. Where would you expect there to be the strongest winds? Why? Where would you expect there to be the calmest winds? Where would you expect clear, cool skies? Where would you expect cloudy skies with the greatest potential for precipitation? Work Cited (Incomplete) http://www.usatoday.com/weather/tg/wamsorce/wamsorce.htm seen 1/03/06 http://www.srh.weather.gov/srh/jetstream/synoptic/airmass.htm