Ch18_Winds_student
- 1. CH. 18 – AIR PRESSURE & WINDS
- 2. Air PressureWeight of atmosphere above a given placeStandard barometric pressure = 1013.2 millibars (mb)Low pressure <1013.2 mbHigh pressure >1013.2 mb
- 3. WindHorizontal movement of air
- 4. Factors affecting wind speed & direction1) Pressure Gradient Force (PGF)- air at surface always moves from high pressure to low pressure* PGF is only force that generates wind!
- 5. Pressure Gradient Force Caused by the differential heating of Earth’s surface- causes high & low pressure centers to develop
- 7. Pressure Gradient ForceIsobar = line that connects points of equal air pressureIdeally, air flow would be perpendicular to isobars- shortest distance to low pressure
- 8. Pressure Gradient ForceSpacing of isobars indicates gradientGradient = change in pressure over certain distance(similar to “slope” of land)
- 9. Pressure Gradient ForceSteep gradient = isobars spaced closely together = _______ wind speedWeak gradient = widely spaced isobars = _______ winds
- 10. Factors affecting wind speed & direction2) Coriolis Effect- caused by Earth’s rotation on its axis- free-moving objects are deflected from their path of motionEx: wind, water currents
- 11. Coriolis Effect
- 12. Coriolis EffectNorthern Hemisphere – deflected to right of its path of motionSouthern Hemisphere – deflected to left of its path of motion
- 14. Coriolis Effecta) Affects only wind direction, not wind speedb) Is affected by wind speedFaster winds = _______ deflectionSlower winds = ______ deflection
- 15. Coriolis Effectc) Strongest at poles, weakest at equatorHurricanes can’t form between 5oN and 5oS
- 16. Factors affecting wind speed & direction3) FrictionImportant only w/in a few km of Earth's surface- slows wind speed & reduces Coriolis Effect
- 17. FrictionStrongest over land, weakest over waterQUESTION:Which diagram represents air flow over land?
- 18. Surface Circulation PatternsAssociated w/ high & low pressure centersLow pressure center = cycloneAir flow around low pressure = cyclonic air flow
- 19. Surface Circulation PatternsHigh pressure center = anticycloneAir flow around high pressure = anticyclonic air flow
- 21. Weather GeneralizationsLow pressure center- rising air- cloud formation & possible ppt.- converging surface winds
- 22. Weather GeneralizationsHigh pressure center- descending air- clear skies- diverging surface winds
- 23. Surface Circulation PatternsMovement of mid-latitude cyclone w/ changing wind directions- very common occurrence in Midwest
- 24. Barometric TendencyUsed for short-term weather predictions (several hours ahead)1) Falling – approach of low pressure (clouds)
- 25. Barometric Tendency2) Rising – approach of high pressure (clear skies)3) Steady – maintain status quoWeather Proverbs (handout)
- 26. Global Air CirculationGeorge Hadley (1735):On a uniform non-rotating Earth:Heated equatorial air risesUpper-level air cools & sinks at poles
- 28. Global Air CirculationCreates low pressure at equatorCreates high pressure at poles
- 29. Global Air CirculationHowever:Air flow is deflected by Coriolis EffectBreaks circulation pattern into four global pressure zones
- 30. Global Pressure ZonesEquatorial Low (0o)- hot humid air rises & cools adiabaticallyproduces clouds & ppt.Ex: Tropical rain forests (Amazon & Congo)
- 31. Global Pressure ZonesSubtropical High (30oN & 30oS)- air aloft “piles up” from the Coriolis Effectcold air sinks
- 32. produces prevailing trade winds at surfaceSubtropical HighDescending air heats adiabaticallycreates arid environmentsEx: Sahara Desert (N. Africa), Arabian Desert, Australian deserts
- 33. July temp’s
- 34. January temp’s
- 35. Hadley Cell
- 36. Global Pressure Zones(90oN & 90oS)ColPolar High destair aloft sinks towards poles“polar easterlies” winds blow towards lower latitudesGlobal Pressure ZonesSubpolar Low (60oN & 60oS) Cold air from poles meets warm air from subtropical highs- air converges and rises- produces stormy region known as the “polar front”