Winds Air Masses Fronts


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Winds Air Masses Fronts

  1. 1. Winds
  2. 2. What makes the wind blow? <ul><li>uneven heating of the atmosphere </li></ul><ul><li>warm air rises (forming low pressure) </li></ul><ul><li>cool air sinks ( high pressure) to replace the warm air </li></ul><ul><li>movement from high to low pressure is what generates wind </li></ul><ul><ul><li>steep pressure gradient=high winds </li></ul></ul><ul><ul><li>lower pressure gradient=slower wind </li></ul></ul>
  3. 3. The Coriolis Effect <ul><li>The deflective effect of the earth's rotation on all free-moving objects, including the atmosphere and oceans. </li></ul>Gaspard-Gustave de Coriolis, 1835
  4. 4. coriolis effect <ul><li>A plane flying from Anchorage, Alaska directly toward Miami, Florida would miss its target due to the Coriolis effect. The target location where the plane was headed when it took off has moved with Earth's rotation, so the plane would end up to the right of its original target. </li></ul>coriolis (n.hemisphere) coriolis demo
  5. 5. Coriolis Effect (Southern Hemisphere) (Southern Hemisphere) A plane flying from Tierra del Fuego, Argentina directly toward Rio de Janeiro, Argentina would miss its target due to the Coriolis effect. The target location where the plane was headed when it took off has moved with Earth's rotation, so the plane would end up to the left of its original target. In reality, pilots take the Coriolis effect into account so they do not miss their targets coriolis (s. hemisphere) coriolis demo
  6. 6. Surface Winds <ul><li>Winds between pressure zones are named for the direction that they come from : </li></ul><ul><li>Three main wind systems: </li></ul><ul><ul><li>trade winds : blow from 30˚ towards the equator; warm and steady in both direction and speed; provided regular trade routes for sailing ships </li></ul></ul><ul><ul><li>Prevailing westerlies : blow from 30˚ to 60˚; change direction and speed frequently; speed increases with latitude & is faster over ocean than land </li></ul></ul><ul><ul><li>Polar easterlies : blow from poles towards 60˚; cold and stormy </li></ul></ul>
  7. 7. Wind Belts
  8. 8. view wind belts animation global IR imagery
  9. 9. High Altitude Winds <ul><li>Jet Stream : narrow stream of air in the upper troposphere which moves eastward at high speed-usually in middle latitudes </li></ul><ul><ul><li>height range: 6,000-12,000 meters, speed: 150-300 knots </li></ul></ul><ul><ul><li>dips account for cold polar air in US during winter </li></ul></ul><ul><ul><li>related to strong thunderstorms in spring & summer </li></ul></ul><ul><ul><li>used by planes to assist with eastbound flights </li></ul></ul>
  10. 10. Daily winds <ul><li>during day, land heats faster than water, and generates a sea breeze : cool breeze blowing from the ocean to replace the rising warm air from land </li></ul><ul><li>at night, land cools faster than water and generates a land breeze (opposite of above) </li></ul>
  11. 11. land and sea breezes
  12. 12. Monsoons <ul><li>seasonal change in wind direction </li></ul><ul><ul><li>in summer (from water to land) </li></ul></ul><ul><ul><li>in winter (from land to water) </li></ul></ul><ul><li>are similar to effects of land vs sea breezes but on a much grander scale </li></ul><ul><li>most famous from over India, SE Asia & Indian Ocean-winds turn completely around between winter and summer </li></ul>
  13. 13. Air Masses <ul><li>air mass : huge section of the lower troposphere that has the same kind of weather throughout </li></ul><ul><li>air that stays in one area for a long time takes on the weather of that area </li></ul><ul><li>Originate in parts of the world where winds are light (polar and subtropical high pressure belts) </li></ul><ul><li>interaction of air masses is what causes weather events (storms, etc) </li></ul>
  14. 14. kinds of air masses <ul><li>air masses are named for their source regions </li></ul><ul><li>maritime tropical ( mT ): warm & humid from tropical seas </li></ul><ul><li>continental tropical ( cT ): hot & dry from tropical land areas </li></ul><ul><li>maritime polar ( mP ): cold & humid from cold ocean waters </li></ul><ul><li>continental polar ( cP ): cold and dry from land areas in high latitudes </li></ul><ul><li>continental arctic ( cA ): cold and dry from ice covered Arctic </li></ul>
  15. 15. weather in an air mass <ul><li>weather of a given place will resemble the weather of the region where the air mass originated </li></ul><ul><li>examples: </li></ul><ul><ul><li>cP in Florida during summer=cool spell </li></ul></ul><ul><ul><li>cT in NJ during summer=very hot & dry </li></ul></ul><ul><li>the faster an air mass moves, the more dramatic change in weather </li></ul>
  16. 16. Skies in an air mass <ul><li>conditions depend on temperature of surface versus temp of air mass </li></ul><ul><li>if ground surface is colder: </li></ul><ul><ul><li>bottom layer is stable, inversions form, smog, condensation, light rain, poor visibility </li></ul></ul><ul><li>if ground surface is warmer: </li></ul><ul><ul><li>bottom layer is unstable, convection forms cumulus clouds, good visibility; dry air=fair, humid air=showers </li></ul></ul>
  17. 18. What is a Front? <ul><li>front : the boundary between any two air masses </li></ul><ul><li>an approaching front means a change in temperature and humidity </li></ul><ul><li>greater change in air masses=greater change in weather </li></ul><ul><li>will usually bring precipitation (warm air is forced to rise along the frontal wedge) </li></ul>
  18. 19. kind of fronts <ul><li>Four types of fronts: </li></ul><ul><ul><li>cold : cold air is advancing and displacing warmer air up a steep slope </li></ul></ul><ul><ul><li>warm : warm air is pushing ahead and displacing cold air over a more gentle slope </li></ul></ul><ul><ul><li>stationary : neither air mass is being displaced </li></ul></ul><ul><ul><li>occluded : when a cold front overtakes a warm front </li></ul></ul>
  19. 20. cold front
  20. 21. warm front
  21. 22. view cold/warm front animation
  22. 23. Stationary front
  23. 24. occluded front
  24. 25. front symbols
  25. 26. surface maps
  26. 28. last Sunday’s forecast