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Atmosphere 2
- 1. 1 ATMOSPHERE 2: Weather ppt. by Robin D. Seamon
- 2. 2 How do we measure Weather?
- 3. 3 MEASURING AIR PRESSURE Air pressure: weight of air; exerted in all directions • Mercury Barometer- • Inverted tube in a bath of Mercury; • Air pressure pushes down on the Mercury bath, causing the Mercury to go up the tube
- 4. 4 • Aneroid Barometer- portable • Metal chamber partially emptied of air (vacuum) with elastic top • As air pressure changes, the chamber compresses or expands • Pointer indicates level of change
- 5. 5 • Electric Barometer- portable 1. Calibrate device: set barometer to local air pressure setting (altitude) since factory settings are at sea level 2. Place barometer- (Avoid AC rooms, sunlight, drafty rooms) 3. Reference device: Set manual hand to current reading 4. Check device for change in pressure Daily changes: 0.02 – 0.10 inch
- 6. 6 5. Forecasting Weather • Pressure falls: indicates storms & rain • Pressure rises: fair weather • Pressure steady: more of the same
- 7. 7 WIND Wind: horizontal differences in air pressure; air moves from areas of high pressure to areas of low pressure • pressure gradient- spacing of isobars show amount of pressure change over a distance • Isobars- closer spaced isobars = steep pressure gradient/high winds
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- 9. 9 WIND : 1. Pressure difference: Solar radiation unevenly heating atmosphere 2. Coriolis effect: Earth’s rotation affects movement of objects; deflects objects to the right in N Hemisphere 3. Friction: slows air masses near the surface
- 10. 10 Pressure difference: Solar radiation unevenly heating atmosphere
- 11. 11 Coriolis effect: Earth’s rotation affects movement of objects; deflects objects to the right in N Hemisphere Actual Movement Direction of Movement
- 12. 12 Friction: • Friction Layer: landforms slow air masses near the surface • Jet stream: high, fast moving air above the friction layer; West to East direction
- 13. 13 HIGHS and LOWS Highs- Anticyclones • Areas of high pressure • Pressure increases from outer isobars towards center
- 14. 14 •Big Blue H •EXAMPLE: warm air mass stays low to the ground, pushing on the ground.) •At ground: swirling cool, dry air •Fair weather •Clockwise swirl in N Hemisphere “Hi! How are you?” arms HIGH PRESSURE SYSTEMS H
- 15. 15 HIGHS and LOWS Lows- Cyclones • Areas of low pressure • Pressure decreases from outer isobars toward center
- 16. 16 •Big Red L •EXAMPLE: warm air mass lifts and moves vertically, causing less pressure on the ground.) •At ground: warm, moist air, strong winds •Severe weather/ thunderstorms •Counter clockwise swirl in N Hemisphere Feeling “low” running away arms LOW PRESSURE SYSTEMS L L
- 17. 17 GLOBAL WINDS Because of uneven heating of Earth, the atmosphere acts as a giant heat-transfer system to maintain balance Non-rotating Earth Model Rotating Earth Model 2 cell-convection Multi-cell convection
- 18. 18 LOW pressure LOW pressure LOW pressure HIGH pressure HIGH pressure
- 19. 19 LOW pressure LOW pressure LOW pressure HIGH pressure HIGH pressure Polar Air Circulation Ferrel Air Circulation Hadley Air Circulation
- 20. 20 LOW pressure LOW pressure LOW pressure HIGH pressure HIGH pressure Polar Air Circulation Ferrel Air Circulation Hadley Air Circulation Polar Easterlies Westerlies NE Trade winds SE Trade winds
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- 23. 23 MEASURING WIND Wind speed: anemometer- measures wind speed
- 24. 24 Wind Direction Prevailing winds in the US: • from West to East
- 25. El Nino- part of GLOBAL WEATHER • Cold Peruvian current flows toward equator, allowing upwelling & good fishing • In December, warm waters replace the current, lasting for a few weeks, upsetting weather patterns; blocking upwelling; inland areas get more rain than usual 25
- 27. 27 Patterns
- 28. 28 Air Masses m Maritime: origins over the ocean c Continental: origins over continents P Polar: low humidity T Tropical: high humidity
- 29. 29 Air Masses
- 31. 31 cool, rainy weather LAKES: make Snowy weather warm, wet weather warm, dry weatherwarm, wet weather cool, snowy weather cool, dry weather mP cP mP cT mT mT
- 32. 32 Front: boundary between two air masses
- 33. 33 WARM FRONT • Warm air moves into an area formerly covered by cooler air • Hard to move the cooler & denser air, so it slowly rides on top of it… Creates HEAVY (High) pressure • Associated with stable, fair weather, possible light rain if front remains for a few days
- 34. 34 Half circles… SMOOTH & SLOW Half circles on the side the front is moving
- 35. 35 COLD FRONT • Cold, dense air moves into a region occupied by warmer air • Forceful lifting of warm, wet air causes instability; thunderstorms & strong wind • Faster front because it’s denser
- 36. 36 Faster b/c denser Triangles on the side the front is moving Triangles… SHARP CUT & FAST
- 37. 37 STATIONARY FRONT • When air flow on either side is neither toward cold mass or warm mass • Stable • Sometimes, gentle precipitation
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- 39. 39 OCCLUDED FRONT • When an active cold front moves fast & overtakes a warm front • Wedges the warm air upwards causing heavy rain • Front moves slowly, so rains for several days
- 40. 40 OCCLUDED FRONT When a cold front overtakes a warm front that was moving ahead of it.
- 41. 41 Middle Latitude Cyclones Large centers of low pressure, moving West to East, causing stormy weather • between 30° and 60° latitude US WEATHER REMEMBER:
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- 44. 44 STORMS Thunderstorm- storm generating lightening &b thunder • 2,000 thunderstorms happening at any given time; highest number in the tropics (warm, humid) • Southeast US • Warm, humid air rises in an unstable environment
- 45. 45 TORNADO Tornado- violent windstorms, rotating column of air called a vortex • US: 770 tornadoes each year • Form in updraft of a thunderstorms
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- 49. 49 Tri-State Tornado: March 18, 1925 • killed 695, injured 2,027 • 300 miles • Missouri • Illinois • Indiana
- 50. 50 Tornado Warning System • Issued by National Weather Service Watch: conditions are favorable for a tornado Warning: a tornado has been spotted; seek shelter immediately
- 51. 51 TORNADO SAFETY • Go to low ground: basement, ditch • Avoid windows • Leave mobile home • At school: follow the drill- interior hallway, cover head • Leave vehicle, find a low ditch, cover head AFTER: • Do NOT touch downed power lines or sharp objects • Stay out of heavily damaged buildings
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- 53. 53 HURRICANE Hurricane- whirling tropical cyclones producing winds of at least 74 mph • Name is regional: • Hurricane • Typhoon • Cyclone • Tropical cyclone • Associated with storm surges and flooding • Occurrences seem to be increasing with global warming
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- 59. 59 Hurricane Katrina August 2005 • Extremely destructive and deadly Category 5 hurricane • 1,800 deaths • Struck Gulf of Mexico • Damage from central Florida to Eastern Texas • New Orleans: sits below sea level & was catastrophically flooded VIDEO Katrina (5 min)
- 61. 61 HURRICANE SAFETY • Easily predicted, so pay attention to weather forecasts • Prepare: food, water, flashlight, first aid kit • Stay indoors during hurricanes • Heed local warnings; if an evacuation is called, LEAVE before the hurricane • Know evacuation routes
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