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Weather Lecture
 

Weather Lecture

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    Weather Lecture Weather Lecture Presentation Transcript

    • Weather Chapters 12 &13
    • Air Masses
      • Large body of air that takes on the charateristics of the area where it was formed (over land masses are drier)
      • Classifying air masses
        • Temperature
          • Polar (P), Tropical (T)
        • Location
          • Continental (c), Maritime (m), Arctic (a)
    •  
    • Wind Systems
      • Coriolis Effect- Earth’s rotation causes wind patterns
        • N. Hemisphere  wind to right
        • S. Hemisphere  wind to the left
      • Polar Easterlies (Westerlies)- 60 °- poles- NE in N Hemis.; SW in S Hemis.
      • Prevailing Westerlies- 30-60°- westward winds
      • Trade winds- 30-0° - Easterlies
      • Intertropical Convergence Zone- “doldrums”- rising air causes frequent rain  rain forests (near equator)
      • Jet streams- high altitude winds, move weather patterns
    •  
    • Fronts
      • Narrow region separating 2 air masses of different densities (temperatures)
      • Cold front
        • Cold dense air, displaces (pushes) warn air up along STEEP front; as warm air rises it condenses  showers, clouds
        • Larger temperature differences  more “powerful” cold front
    • Fronts- Cont’d
      • Warm Front-
        • Warm air pushes cold air (slowly) upwards  gradual slope
        • Very cloudy, precipitation
    • Fronts-Cont’d
      • Stationary- two air masses meet and neither forces the other out (temperature (density) difference between them is very small)  cloudy
      • Weather doesn't change until another front comes through
    • Pressure Systems
      • High Pressure- air sinks (few clouds) and spreads out; circulates in RIGHT in N Hemis.
      • Low pressure- air rises  replaced  in and upward motion (LEFT in N hemis.)
    • Cyclone (Nor'easter)
      • Develops along a stationary front  imbalance (temp, pressure, density) causing part of the front to move south as Warm front moves North  upper and lower level winds must be favorable fro a low pressure cyclone to form
    • Measuring Weather
      • Thermometer- measures temperature
      • Barometer- measures air pressure
      • Anemometer- measures wind speed
      • Hygrometer measures humidity
      • Radar
      • Infrared- temperature sensitive assists with measuring cumulonimbus clouds
    • Thunderstorms
      • Formation
        • 1. Need abundant source of moisture in lower atmosphere
        • 2. Air lifting  allows for condensation
        • 3. unstable atmosphere
      • Limitations
        • 1. Rising air meets stable air
        • 2. Rate of condensation not able to keep cloud warmer than air (limits cumulonimbus to 18,000 m)
    • Types of Thunderstorms
      • Air Mass- caused by unequal heating (late afternoon thunderstorms)
        • Mountain T-storms- orographic lifting
        • Sea-breeze T-storms- extreme temp differences at shore
      • Frontal- mostly advancing cold fronts- rapid upward flow  line of T-storms at leading edge
    • Development
      • 1. Cumulus- air rises vertically  creating updrafts- moisture at the top of cloud
      • 2. Mature- precipitation forces air under cloud to cool  creates downdraft
      • 3. Dissipation– downdrafts cool surrounding air  no steady, warm moist air
    •  
    • Severe T-storms
      • Super cells- cold front powers updrafts
      • 10 % of all T-storms
      • Hail- frozen layered precipitation
    • Lightning
      • Caused by friction between updrafts and downdrafts
        • Positive and negative ions form
        • Stepped leader[-] (invisible) extends towards ground
        • Return stroke [+] reaches up to meet stepped leader
        • When they meet channel forms lightning bolt
      • Thunder- sound caused by rapid expansion/contracting of air
    •  
    • Tornadoes
      • Violent, whirling wind column of air with contact to ground
        • Often associated with Super cells
        • Caused by a sudden change in wind speed/direction  wind shear
        • Causes horizontal swirling winds near ground
        • Interaction with updrafts force tornado upright
        • More likely in Spring and late afternoon/evening
          • Spring b/c of clash of polar and maritime air over Great Plains
    • Hurricanes
      • Tropical cyclone- large, rotating low pressure system
        • Form b/c large amount of energy and moisture join with a tropical disturbance
        • Pressure decreases at center causing circulation (low pressure)
      • Needs:
        • 1. Abundance of very warm water
        • 2. Disturbance to lift warm air
    • Stages
      • 1. traveling tropical disturbance
      • 2. Circulation
      • 3. Winds of 65 km/hr  tropical storm
      • 4. Winds of 120 km/hr  hurricane
        • Eye development
        • Eye wall- highest winds
      • 5. decline- after landfall  no water supply
    •  
    • Hurricane Hazards
      • Storm surge- hurricane force winds drive ocean waters inwards sometimes 6 m higher than usual
      • Flooding
      • Wind
      • Rain