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Transcript of ATM OCN 100 Summer 2003 1 ATM OCN 100 – Summer 2004 LECTURE 2B ATMOSPHERIC PRESSURE: A Fundamental...
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MADISON’S CURRENT WEATHERMADISON’S CURRENT WEATHERMadison Weather at Madison Weather at 1000 AM CDT MON 23 JUN 2003 Temperature: 25.6°C (78°F) Dewpoint: 15.0°C (59°F) [RH = 52%] Pressure (altimeter): 29.93 inches Hg (1013.6 mb)[Sea-level pressure: 1012.9 mb] Winds: from the S (170 degrees)
at 13 MPH (11 knots; 5.7 m/s) Visibility: 10 or more miles (16+ km) Ceiling: at least 12,000 feet AGL Clouds: sky clear below 12,000 feet AGL Present Weather: no significant weather observed
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Current Surface Weather Map Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radarwith Isobars (“iso” = equal & “bar” = weight), Fronts & Radar
Isobars
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Deadly Tornado in NebraskaDeadly Tornado in Nebraska
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Current Surface Weather Map Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radarwith Isobars (“iso” = equal & “bar” = weight), Fronts & Radar
Isobars
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Clouds
Current Visible Satellite ImageCurrent Visible Satellite ImageCurrent Visible Satellite ImageCurrent Visible Satellite Image
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Tomorrow AM Forecast MapTomorrow AM Forecast Map
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The Summer SolsticeThe Summer Solstice was Saturday @ 2:10 PM CDTwas Saturday @ 2:10 PM CDT
See Fig. 3.10 Moran (2002)See Fig. 3.10 Moran (2002)
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Rule of Thumb Rule of Thumb
The tighter the packing of the The tighter the packing of the isobars, the stronger the winds!isobars, the stronger the winds!
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AnnouncementsAnnouncements
Homework 1 Homework 1 – Get from our webpageGet from our webpage
http://www.aos.wisc.edu/~hopkins/aos100/homework/ http://www.aos.wisc.edu/~hopkins/aos100/homework/
– Due Thursday 26June 2003Due Thursday 26June 2003
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Current Surface Weather Map Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radarwith Isobars (“iso” = equal & “bar” = weight), Fronts & Radar
Isobars
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Did You know that –Did You know that –Sunday is summer solstice (7:57 PM CDT)?Sunday is summer solstice (7:57 PM CDT)?
See Fig. 3.10 Moran (2002)See Fig. 3.10 Moran (2002)
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ATM OCN 100 – Summer 2004ATM OCN 100 – Summer 2004LECTURE 2BLECTURE 2B
ATMOSPHERIC PRESSURE:ATMOSPHERIC PRESSURE:A Fundamental Weather ElementA Fundamental Weather Element
A. PRACTICAL PROBLEMA. PRACTICAL PROBLEM– The pump problem: Why can’t The pump problem: Why can’t
water be lifted more than 30 ft?water be lifted more than 30 ft?
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B. BASIC CONCEPTS:B. BASIC CONCEPTS:ATMOSPHERIC PRESSUREATMOSPHERIC PRESSURE
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B. BASIC CONCEPTS:B. BASIC CONCEPTS:ATMOSPHERIC PRESSUREATMOSPHERIC PRESSURE
Fundamental conceptsFundamental concepts
Importance of air pressureImportance of air pressure
Pressure Weight ( Force)Area
Weight = Mass gravity
or
where
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 3333
B. BASIC CONCEPTS:B. BASIC CONCEPTS:ATMOSPHERIC PRESSUREATMOSPHERIC PRESSURE
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Current Surface Weather Map Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radarwith Isobars (“iso” = equal & “bar” = weight), Fronts & Radar
Isobars
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Explaining Differences inExplaining Differences in Air Pressure Air Pressure
Low PressureLow Pressure High PressureHigh Pressure
LL HH
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 3636
Isobars -Isobars -- - lines of equal barometric pressurelines of equal barometric pressure- use sea level corrected pressure- use sea level corrected pressure
HHHH
LL
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Display of Pressure Differences on a Display of Pressure Differences on a Weather Map - IsobarsWeather Map - Isobars
HH LL
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 3939
C. BAROMETRYC. BAROMETRY
The Science of BarometryThe Science of Barometry– How is air pressure measured?How is air pressure measured?
Types of BarometersTypes of Barometers– Mercury BarometersMercury Barometers– Aneroid BarometersAneroid Barometers where ...where ...
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MERCURY BAROMETERSMERCURY BAROMETERS
Torricelli invention in Torricelli invention in 1643;1643;
A self-supported A self-supported column of mercury;column of mercury;
A balance between A balance between weight of atmosphere weight of atmosphere & weight of mercury & weight of mercury in tube.in tube.
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 4242
Principles of a Mercury BarometerPrinciples of a Mercury Barometer See Fig 5.1, Moran (2002)See Fig 5.1, Moran (2002)
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MERCURY BAROMETERS MERCURY BAROMETERS (con’t.)(con’t.)
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 4444
ANEROID BAROMETERSANEROID BAROMETERS
Perfected in Perfected in 1840’s;1840’s;
An evacuated An evacuated canister;canister;
A balance between A balance between force of force of atmosphere & atmosphere & force of spring force of spring inside canister.inside canister.
See Fig 5.2 A, Moran (2002)See Fig 5.2 A, Moran (2002)
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 4545
Aneroid BarometerAneroid BarometerSee Fig 5.2 B, Moran (2002)See Fig 5.2 B, Moran (2002)
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 4646
BAROGRAPHBAROGRAPH See Fig 5.3, Moran (2002)See Fig 5.3, Moran (2002)
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 4747
A pressure trace from a barographA pressure trace from a barographSee Fig. 5.6, Moran (2002)See Fig. 5.6, Moran (2002)
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C. BAROMETRY C. BAROMETRY (con’t.)(con’t.) Placement of BarometersPlacement of Barometers Pressure UnitsPressure Units
– Inches Inches oror millimeters of mercury; millimeters of mercury;– Pounds per square inchPounds per square inch oror millibars.millibars.
The MillibarThe Millibar– Traditional meteorological pressure unitTraditional meteorological pressure unit
(a metric unit of force per unit area); (a metric unit of force per unit area);– Sea level pressure Sea level pressure 1000 millibars 1000 millibars
( (oror 1 bar). 1 bar).
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 4949
C. BAROMETRY C. BAROMETRY (con’t.)(con’t.) Placement of BarometersPlacement of Barometers Pressure UnitsPressure Units
– Inches Inches oror millimeters of mercury; millimeters of mercury;– Pounds per square inchPounds per square inch oror millibars.millibars.
The MillibarThe Millibar– Traditional meteorological pressure unitTraditional meteorological pressure unit
(a metric unit of force per unit area); (a metric unit of force per unit area);– Sea level pressure Sea level pressure 1000 millibars 1000 millibars
( (oror 1 bar). 1 bar).
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D. CLIMATOLOGY ofD. CLIMATOLOGY ofATMOSPHERIC PRESSUREATMOSPHERIC PRESSURE
Spatial variation in Spatial variation in Sea-level air pressure Sea-level air pressure– Extremes Extremes – Typical range: 980 mb to 1040 mbTypical range: 980 mb to 1040 mb such as … such as …
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 5252
Average Sea Level Air Pressure & Average Sea Level Air Pressure & Atmospheric CirculationAtmospheric Circulation
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 5353
D. CLIMATOLOGY ofD. CLIMATOLOGY ofATMOSPHERIC PRESSURE ATMOSPHERIC PRESSURE (con’t.)(con’t.)
Temporal variation of Temporal variation of Sea-level air pressure Sea-level air pressure– Typically less than 1 mb per 3 hours,Typically less than 1 mb per 3 hours,
but… but…
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 5454
A pressure trace from a barographA pressure trace from a barographSee Fig. 5.6, Moran (2002)See Fig. 5.6, Moran (2002)
5-6 mb in 3 hrs5-6 mb in 3 hrs
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 5555
D. CLIMATOLOGY ofD. CLIMATOLOGY ofATMOSPHERIC PRESSURE ATMOSPHERIC PRESSURE (con’t.)(con’t.)
Why Do Variations occur in Air Why Do Variations occur in Air Pressure?Pressure?
Piling On Piling On oror taking off taking offby:by:– Local Heating (convection)Local Heating (convection)– Dynamic EffectsDynamic Effects
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 5757
Vertical Cross-Section of Vertical Cross-Section of Air Converging AloftAir Converging Aloft See Fig. 8.20, Moran (2002)See Fig. 8.20, Moran (2002)
HH
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 5858
Map View of Flow around High Pressure Map View of Flow around High Pressure Fig. 1.3A, Moran (2002)Fig. 1.3A, Moran (2002)
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 5959
Vertical Cross-Section of Vertical Cross-Section of Air Diverging AloftAir Diverging Aloft Fig. 8.21, Moran (2002)Fig. 8.21, Moran (2002)
LL
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 6060
Map View of Flow around Low Pressure Map View of Flow around Low Pressure Fig. 1.3B, Moran (2002)Fig. 1.3B, Moran (2002)
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D. CLIMATOLOGY ofD. CLIMATOLOGY ofATMOSPHERIC PRESSURE ATMOSPHERIC PRESSURE (con’t.)(con’t.)
Vertical Variations in air pressureVertical Variations in air pressure The higher up, the lower the The higher up, the lower the
pressure.pressure.– Why?Why?
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AIR PRESSURE CLIMATOLOGY AIR PRESSURE CLIMATOLOGY (con’t.)(con’t.)Vertical VariationVertical Variation
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Pressure fallsPressure falls
Pressure @ top of building Pressure @ top of building ~ 5-6 mb less than ~ 5-6 mb less than
@ street level@ street level
So how tall is the building?So how tall is the building?
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VERTICAL PRESSURE PROFILEUS STANDARD ATMOSPHERE, 1976
01020304050
0 200 400 600 800 1000
AIR PRESSURE [millibars]
ALTI
TUDE
[km
]AIR PRESSURE CLIMATOLOGY AIR PRESSURE CLIMATOLOGY (con’t.)(con’t.)
See Fig. 5.4 Moran (2002)See Fig. 5.4 Moran (2002)
50% of surface
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AIR PRESSURE CLIMATOLOGY AIR PRESSURE CLIMATOLOGY (con’t)(con’t)
Variation of air pressure with heightVariation of air pressure with height
– Lower atmosphere: Lower atmosphere: 1mb per 10 m height rise1mb per 10 m height rise;;
– ororSea Level 1000 mb
5,500 meters 500 mb11,000 meters 250 mb
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E. ALTIMETRYE. ALTIMETRY
BackgroundBackground– Pressure Altimeters Pressure Altimeters
Aneroid Barometers that indicate Aneroid Barometers that indicate altitude rather than pressurealtitude rather than pressure
ComputationComputation
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VERTICAL PRESSURE PROFILEUS STANDARD ATMOSPHERE, 1976
012345
500 600 700 800 900 1000
AIR PRESSURE [millibars]
ALTI
TUDE
[km
]AIR PRESSURE CLIMATOLOGY AIR PRESSURE CLIMATOLOGY (con’t.)(con’t.)
See Fig. 5.4, Moran (2002)See Fig. 5.4, Moran (2002)
1 mb drop for 10 meter height rise
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ALTIMETRY ALTIMETRY (con’t.)(con’t.)
Sources of errorSources of error– Standard or model atmosphere Standard or model atmosphere
does notdoes not always apply! always apply!
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 7171
Altimetry & Air TemperatureAltimetry & Air Temperature(see Figure, pg. 107, Moran (2002))(see Figure, pg. 107, Moran (2002))
ColdColdWarmWarm
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 7272
Flying with a pressure altimeterFlying with a pressure altimeterSee Fig, pg. 107, Moran (2002)See Fig, pg. 107, Moran (2002)
ColdColdWarmWarm
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 7373
Sea-Level Pressure ReductionSea-Level Pressure Reduction
Desire –Desire –– To view only horizontal pressure To view only horizontal pressure
variations on weather map;variations on weather map; Need –Need –
– To eliminate effects of topography from To eliminate effects of topography from station pressure.station pressure.
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 7474
Sea-Level Pressure Reduction Sea-Level Pressure Reduction (con’t.)(con’t.)
ResultResult– Assume that pressure increases at fixed Assume that pressure increases at fixed
rate down to sea level.rate down to sea level.
Station PressureStation Pressure
Station PressureStation Pressure
Sea level Pressure readingsSea level Pressure readings
≈ ≈ 1 mb per 10 m1 mb per 10 m≈ ≈ 1 mb per 10 1 mb per 10 mm
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 7575
Isobars -Isobars -- - lines of equal barometric pressurelines of equal barometric pressure- use sea level corrected pressure- use sea level corrected pressure
HHHH
LL
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 7676
Current Surface weather map 24 June 2003Current Surface weather map 24 June 2003
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 7777
Current Surface Weather Map Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radarwith Isobars (“iso” = equal & “bar” = weight), Fronts & Radar
Isobars
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ATM OCN 100 Summer 2003ATM OCN 100 Summer 2003 7878
Atmosphere in Perspective Atmosphere in Perspective (UCAR)(UCAR)