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Ch 24-Weather Objectives Explain how air mass forms

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1 Ch 24-Weather Objectives Explain how air mass forms
Main types of air masses Describe how air masses affect the weather of N America Weather patterns of cold and warm fronts Describe how midlatitude cyclone forms Development of hurricanes, thunderstorms, tornadoes Instruments that measure lower atmospheric weather conditions Describe how scientists measure conditions in the upper atmosphere Explain how computers help scientists understand weather

2 Explain how weather stations communicate weather data
Explain how a weather map is created Explain how computer models help meteorologists forecast weather Types of weather that meteorologists have attempted to control





7 Air Masses How does air move? Formation of air masses
Air pressure differences are small=air is stationary Stationary air takes on characteristic temp and humidity of that region Air mass-large body of air throughout which temp and moisture content are similar Frozen polar regions=very cold and dry Tropical=warm and moist

8 Types of Air Masses Classified according to source regions-determines temp and humidity of air mass Maritime-air masses that form over ocean Humidity higher than continental Maritime polar-moist and cold Tropical-warm and dry Continental-air masses that form over land, dry Form over large landmasses. N Canada, N Asia, SW U.S. Humidity is low, dry weather conditions Polar-cold and dry

9 N American Air Masses Continental tropical-form over desert, hot dry weather in summer, no winter Maritime tropical-form over warm water of tropical Atlantic, mild cloudy weather to E U.S. in winter, hot humid weather in summer Form over Pacific, never reach coast Winter, maritime tropical air masses bring moderate precipitation to coast and SW deserts

10 Polar Air Masses Continental polar Canadian- Continental air masses form over ice and snow covered land, move into U.S. and can reach Gulf Coast Summer, cool and dry weather Winter, very cold weather to N U.S. Maritime Polar Pacific-Very moist during winter on P coast, cool and foggy in summer Maritime Polar Pacific- Cold, cloudy and snow to New England and E Canada. Summer produces cool weather w/ low clouds and fog

11 Air Masses Of N America Air Mass Source Location Movement Weather cP
Polar regions in Canada South-southeast Cold and dry mP Polar pacific; polar Atlantic Southeast; southwest-south Cold and moist cT U.S. southwest North-northeast Warm and dry mT Tropical Pacific; tropical Atlantic Northeast; north-northwest Warm and moist

12 Sec 2-Fronts Front-boundary between air masses. Cool air mass is dense, does not mix w/ less dense air of warm air mass Do not exist in tropics. Why? Types of fronts Cold fronts-front edge of moving mass of cold air pushes beneath warmer air mass like a wedge Cumulus and Cumulonimbus Storms short lived, violent Squall Warm-front edge of advancing warm air mass replaces colder air w/ warmer air Precipitation over large area, violent weather Stationary front Occluded front Fronts

13 Midlatitude Cyclone Polar front-cold polar air meets tropical air mass of middle latitudes, over ocean Wave-bend that forms in cold front or stationary front Wave cyclones-low pressure storm centers when waves are the beginnings Mid latitude cyclones-areas of low pressure, characterized by rotating wind that moves toward the rising air of central low pressure region Strongly influence weather patterns in middle latitudes

14 Stages of Mid latitude cyclone
Lasts several days, 45 km/h in easterly direction, spin counterclock wise in N America Move from P coast to A coast, loose moisture and energy over mts Anticyclones-sinks and flows outward from a center of high pressure Circulation is clockwise. Why? Bring dry weather, sinking air does not promote cloud formation Air pollution. Why? May cause droughts. Why?

15 Thunderstorms Usually brief, heavy storm that consists of rain, strong winds, lightning, and thunder 3 stages 1st water vapor condenses to form cumulus clouds Mature stage-Cumulonimbus clouds form, heavy rain and hailstones may fall Dissipating stage- thunderstorm dissipates, lightning and thunder heat the air

16 Hurricanes Develops over tropical oceans, winds more than 120 km/h, spiral in toward the intensely low pressure storm center Thick cumulonimbus clouds, spiral upward toward center of storm Eye of storm=calmest Saffir-Simpson scale-central pressure, wind speed, storm surge, 5 categories






22 Tornadoes Smallest, most violent and shortest lived storm
Destructive, rotating column of air, very high wind speeds, visible as funnel shaped cloud Forms when thunderstorms meet high altitude, horizontal winds cause rising air in thunderstorm to rotate Narrow, funnel shaped extension may touch ground, may not Tornado Alley What causes main destructive power? Winds-400 km/h




26 Sec 3-Weather Instruments
Measuring weather conditions Air temp-thermometer uses mercury or alcohol, electrical thermometer, thermistor Air pressure-barometers Wind speed-anemometer Wind direction-wind vane Temp, dew pt, wind velocity-radiosone Velocity and location of objects-radar Weather satellites

27 Computers Help solve mathematical equations and describe behavior of atmosphere Can store weather data from around world Helpful in forecasting weather changes, store weather records for quick retrieval

28 Sec 4-Forecasting the Weather
When do you think predicting weather forecasts came about? 1844 by telegraph National Weather Service Shares info about weather conditions Exchanges weather data w/ other nations Global Weather Monitoring How do weather stations communicate weather data? Reported hourly by recording barometric pressure, speed and direction of surface wind, precipitation, temp, and humidity World Weather Watch Exchanges weather info in developing countries Helps establish or improve meteorological services

29 Weather Maps Use data collected by weather stations and transfer to weather maps Use symbols and colors Cloud cover, wind speed, wind direction, precipitation, storm activities, air temp, dew pt, atmospheric pressure Plot temp and pressure by using isotherms which are lines that connect pts of equal temp. Isobars=atmospheric pressure Fronts=sharp changes in wind speed and direction, temp or humidity Precipitation=colors or symbols

30 Weather Forecasts Plot intensity and path of weather systems on maps
Weather data-computer models show possible weather conditions for several days Temp, wind direction, wind speed, cloudiness and precipitation-accurately Types of forecasts Nowcasts Daily forecasts Extended forecasts Medium forecasts Long range Watch-issued when conditions are ideal for severe weather Warning-severe weather has been spotted or is expected w/in 24 hrs

31 Controlling the Weather
Cloud seeding Most researched method for producing rain How does this work? Hurricane control Seed w/ freezing nuclei in effort to reduce intensity of storm Not attainable w/ existing technology Lightning control Seed potential lightning storms w/ silver iodide nuclei No conclusive results

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