THE ATMOSPHERE IN MOTION

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THE ATMOSPHERE IN MOTION

• CHAPTER 19

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AIR PRESSURE AND WIND

• AIR CONSTANTLY MOVES ACROSS THE SURFACE OF THE
  EARTH
• THIS DOES THREE THINGS
• 1. MODERATES SURFACE TEMPS
• 2. DISTRIBUTES MOISTURE
• 3. CLEANS THE ATMOSPHERE
• DIFFERENCES IN AIR PRESSURE SETS THE AIR IN MOTION

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WHAT IS AIR PRESSURE?

• THE WEIGHT OF THE ATMOSPHERE AS IT PUSHES DOWN
  UPON EARTHS SURFACE
• EXERTS A FORCE PER UNIT OF AIR
• EXERTED IN ALL DIRECTIONS
• A COLUMN OF AIR FROM THE TOP OF THE ATMOSPHERE TO
  SEA LEVEL WEIGHS 14.7 LBS PER SQ. INCH

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AIR PRESSURE

• AIR PRESSURE DECREASES AS ALTITUDE INCREASES
• CRITICAL TO THE BALANCE OF ALL LIVING THINGS
• EACH SPECIES HAS EVOLVED TO LIVE IN A PARTICULAR
  AIR PRESSURE ADAPTATION
• IF THAT CHANGES THE ORGANISM COULD DIE

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AIR PRESSURE

• AIR PRESSURE IS MOST NOTICEABLE WHEN IT CHANGES
• AS YOU RIDE UP AN ELEVATOR
• FLY IN AN AIRPLANE
• DRIVE UP MOUNTAINS
• GREATEST AT SEA LEVEL AND LEAST ON TOP OF
  MOUNTAINS OR EVEN HIGHER

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MEASURE AIR PRESSURE

• MERCURY BAROMETER
• USES MERCURY MUCH LIKE A THERMOMETER
• ANEROID BAROMETER
• USES A THIN METAL WIRE THAT EXPANDS AND CONTRACTS

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MERCURY BAROMETER

• MEASURES THE AIR PRESSURE IN INCHES OF MERCURY
• AT SEA LEVEL THE LEVEL IS AROUND 30 INCHES OF
  MERCURY
• IF AIR PRESSURE INCREASES THE COLUMN RISES

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ANEROID BAROMETER

• METAL CAPSULE REGISTERS CHANGES IN PRESSURE
• CAUSES THE SPRING TO MOVE
• RECORDS THE MOVEMENTS ON A BAROGRAPH

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AIR PRESSURE MEASUREMENT

• STANDARD AIR PRESSURE AT SEA LEVEL
• 1013MB OR 29.92 INCHES OF MERCURY
• PRESSURES ARE ADJUSTED AS IF ALL REPORTING
  STATIONS ARE AT SEA LEVEL TO BE ABLE TO COMPARE
  PRESSURES

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WHY DOES AIR PRESSURE CHANGE?

• 1. CHANGES IN ELEVATION
• 2. TEMPERATURES
• AIR PRESSURE AT SEA LEVEL DECREASES AS TEMPS
  INCREASE
• 3. HUMIDITY LEVELS
• AIR PRESSURE DECREASES AS HUMIDITY LEVELS
  INCREASE

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FORECASTING THE WEATHER

• DECREASE IN AIR PRESSURE (LOW) USUALLY BRINGS
  WARMER, MORE HUMID AIR WITH RAIN OR SNOW
• LOW PRESSURE SYSTEMS MOVE INWARD AND UP
• INCREASE IN AIR PRESSURE (HIGH) OFTEN BRINGS
  COOLER, DRIER, FAIR WEATHER
• HIGH PRESSURE SYSTEMS MOVE DOWN AND OUTWARD

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FORECASTING

• ISOBARS ARE USED TO ANALYZE PRESSURE PATTERNS ON
  WEATHER MAPS
• THE CLOSER THE ISOBARS ARE TOGETHER THE STRONGER
  THE WINDS WILL BLOW
• CALLED PRESSURE GRADIENTS
• WINDS MOVE FROM HIGH TO LOW PRESSURE

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WHY DOES THE WIND BLOW?

• UNEQUAL HEATING OF THE EARTHS SURFACE
• CAUSES DIFFERENCES IN AIR PRESSURES
• CAUSES PRESSURE GRADIENTS TO FORM WHICH THE WINDS
  RIDE ON
• WINDS MOVE FROM HIGH TO LOW PRESSURE AREAS
• THE GREATER THE DIFFERENCE IN THE TEMPS THE
  STRONGER THE WINDS WILL BE

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MEASURING WIND SPEED AND DIRECTION

• DIRECTION WIND VANE, WEATHER VANE
• SPEED ANEMOMETER
• WINDS ARE NAMED FROM THEIR PLACE OF ORIGIN
• A WIND THAT BLOWS FROM THE WEST TO THE EAST IS A
  WEST WIND OR WESTERLY

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FACTORS AFFECTING THE WIND

• THE ROTATION OF THE EARTH THE CORIOLIS EFFECT
• FRICTION OF THE EARTHS SURFACE
• JET STREAM
• UNEVEN HEATING PATTERNS ON THE EARTH

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CORIOLIS EFFECT

• THE TENDENCY OF AN OBJECT MOVING FREELY OVER THE
  EARTHS SURFACE TO CURVE AWAY FROM ITS PATH OF
  TRAVEL
• NORTHERN HEMISPHERE CURVE TO THE RIGHT
• SOUTHERN HEMISPHERE CURVE TO THE LEFT

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CORIOLIS EFFECT
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CORIOLIS EFFECT

• WINDS IN THE NORTHERN HEMISPHERE TEND TO BLOW
  CLOCKWISE OUT OF HIGH PRESSURE SYSTEMS
• BLOW COUNTERCLOCKWISE OUT OF LOW PRESSURE SYSTEMS
• PATTERN IS REVERSED IN THE SOUTHERN HEMISPHERE

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WINDS

• FRICTION ON THE SURFACE OF THE EARTH SLOWS DOWN
  WIND SPEEDS
• HIGHER ELEVATION THE LESS THE WINDS ARE AFFECTED
  BY FRICTION
• TOP OF THE TROPOSPHERE THE WINDS ARE 120 TO 240
  KM/HR

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JET STREAM

• BANDS OF SWIFTLY MOVING WINDS NEAR THE TOP OF THE
  TROPOSPHERE
• MOVING AT 75 TO 150 MPH
• TYPICALLY THOUSANDS OF METERS LONG AND HUNDREDS
  OF KILOMETERS WIDE AND ONE KM THICK
• OCCASIONALLY WILL WRAP AROUND THE ENTIRE EARTH

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POLAR FRONT JET STREAM

• COOL AIR FROM POLAR REGIONS JOINS WITH WARMER AIR
  TO THE SOUTH
• AFFECTS THE WEATHER IN THE U.S.
• CAN REACH AS FAR SOUTH AS FLORIDA IN THE WINTER
  BUT USUALLY STAYS NORTH IN THE SUMMER

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GLOBAL WIND PATTERNS
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WIND PATTERNS
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WINDS ON A NON-ROTATING EARTH

• AIR AT THE POLES SINKS FALLS DOWN TO THE EQUATOR
• AIR AT THE EQUATOR RISES AND LIFTS UP TO THE
  POLES

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CONTINENTAL AND LOCAL WINDS

• AS EARTHS SURFACE TEMPS CHANGE WITH THE SEASONS
  SO DO GLOBAL WINDS
• WINDS ARE AFFECTED BY LARGE SCALE SHIFTS IN TEMPS
  AND THE POSITION OF THE CONTINENTS

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SUMMER

• IN SUMMER CONTINENTS BECOME HOTTER THAN
  SURROUNDING OCEANS
• CONTINENTS ABSORB RADIANT HEAT QUICKER THAN WATER
• AVERAGE AIR PRESSURE OVER CONTINENTS BECOMES
  LOWER
• AIR PRESSURE OVER WATER BECOMES HIGHER

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PREVAILING WINDS

• IN THE NORTHERN HEMISPHERE SUMMERS, AN ATLANTIC
  HIGH BRINGS PREVAILING SOUTHERLY WINDS TO THE
  EASTERN U.S.
• THE WINTER BRINGS PREVAILING NORTHERLY WINDS

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MONSOON SEASON

• WINDS THAT CHANGE DIRECTION SEASONALLY
• MOST DRAMATIC IS IN SOUTHERN ASIA
• CAUSES COMPLETE WIND REVERSALS

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MONSOON SEASON

• IN WINTER, COLD SINKING AIR ON THE CONTINENT
  FLOWS TOWARD THE SEA
• THE COLD DRY WINDS ARE THE WINTER MONSOONS
• IN SUMMER, HUMID AIR FROM THE OCEANS FLOWS ONTO
  THE LAND
• THE WARM MOIST AIR CAUSES HEAVY RAINFALLS

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LOCAL WINDS

• WINDS CAUSED MAINLY BY TEMP DIFFERENCES
• EXTENDS FOR A DISTANCE OF 100KM OR LESS
• LAND/SEA BREEZES ON THE COAST
• MOUNTAIN/VALLEY BREEZES IN THE MOUNTAINS

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WIND AND PRESSURE BELTS
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ITCZ

• INTERTROPICAL CONVERGENCE ZONE
• THE AIR IS HOT AND HUMID
• LITTLE OR NO WIND
• RAIN IS COMMON
• SURFACE WINDS FROM THE TWO HEMISPHERES COME
  TOGETHER
• CALLED THE DOLDRUMS
• NO WIND, SAILING VESSELS OFTEN GOT STUCK HERE

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HORSE LATITUDES

• BETWEEN 20 AND 30 DEGREES
• AIR GENERALLY SINKS
• FORMS SUBTROPICAL HIGHS
• VERY LITTLE PRECIPITATION
• THESE REGIONS CONTAIN MANY OF THE WORLDS DESERTS

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TRADE WINDS

• BETWEEN THE HORSE LATITUDES AND THE DOLDRUMS
• EASTERLY TRADE WINDS
• WARM AND STEADY
• MERCHANT SHIPS USED THESE WINDS FOR TRADE ROUTES

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PREVAILING WINDS

• WINDS THAT USUALLY BLOW FROM THE SAME DIRECTION
• SUCH AS THE TRADE WINDS AND POLAR EASTERLIES