ATM OCN 100

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ATM OCN 100 Summer 2004LECTURE 2B

• ATMOSPHERIC PRESSURE
• A Fundamental Weather Element (cont.)
• A. Practical Problem
• B. Basic Concepts
• C. Barometry
• D. Climatology of Atmospheric Pressure
• E. Altimetry

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MADISONS CURRENT WEATHER
Madison Weather at Madison Weather at 1000 AM
CDT MON 23 JUN 2003 Temperature 25.6C (78F)
Dewpoint 15.0C (59F) RH  52 Pressure
(altimeter) 29.93 inches Hg (1013.6 mb)Sea-leve
l 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 with Isobars (iso
equal bar weight), Fronts Radar
Isobars
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Observations for MADISON DANE RGNL, WI
(MSN) 1453Z 18 Jun 2003 to 1353Z 19 Jun 2003
                                                  
                              

• http//weather.uwyo.edu/surface/meteogram/
• http//weather.uwyo.edu/cgi-bin/wyowx.fcgi?TYPEsf
  gramDATEcurrentHOURcurrentUNITSASTATIONMSN
  

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Deadly Tornado in Nebraska
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Current Surface Weather Map with Isobars (iso
equal bar weight), Fronts Radar
Isobars
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Current Surface Winds with Streamlines
Isotachs (iso equal tach speed)
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Streamlines
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Current Surface Winds with Streamlines
Isotachs (iso equal tach speed)
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Streamlines
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L
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Clouds
Current Visible Satellite Image
Current Visible Satellite Image
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Current Temperatures (F) Isotherms(iso
equal therm temperature)
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Tomorrow AM Forecast Map
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The Summer Solstice was Saturday _at_ 210 PM CDT
See Fig. 3.10 Moran (2002)
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ATM OCN 100 Summer 2004LECTURE 2B

• ATMOSPHERIC PRESSURE
• A Fundamental Weather Element (cont.)
• A. Practical Problem
• B. Basic Concepts
• C. Barometry
• D. Climatology of Atmospheric Pressure

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LATEST RADAR
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MADISONS CURRENT WEATHER
Madison Weather at 1000 AM CDT MON 24 JUN 2002
Updated twice an hour at 05 and 25

Sky/Weather SUNNY
Temperature 81 F (27 C) Dew
Point 64 F (17 C) Relative
Humidity 56 Wind SW6 MPH
Barometer 30.11F (1019.6 mb)
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Current Surface Weather Map with Isobars (iso
equal bar weight), Fronts and Radar
Isobars
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Rule of Thumb

• The tighter the packing of the isobars, the
  stronger the winds!

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Current Surface Winds with Streamlines
Isotachs (iso equal tach speed)
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H
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H
L
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Current Surface Weather Map with Isobars (iso
equal bar weight), Fronts and Radar
Isobars
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Current Temperatures (F) Isotherms(iso
equal therm temperature)
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Current Surface Weather Map with Isobars (iso
equal bar weight), Fronts and Radar
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GABRIELLE
CURRENT IR
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Tomorrow AM Forecast Map
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Happy Summer SolsticeToday at (238 AM CDT) See
Fig. 2.10 Moran Morgan (1997)
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Announcements

• Homework 1
• Get from our webpage
• http//www.aos.wisc.edu/hopkins/aos100/homework/
  
• Due Thursday 26June 2003

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Current Surface Weather Map with Isobars (iso
equal bar weight), Fronts Radar
Isobars
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Did You know that Sunday is summer solstice
(757 PM CDT)? See Fig. 3.10 Moran (2002)
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ATM OCN 100 Summer 2004LECTURE 2B

• ATMOSPHERIC PRESSURE
• A Fundamental Weather Element
• A. PRACTICAL PROBLEM
• The pump problem Why cant water be lifted more
  than 30 ft?

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B. BASIC CONCEPTSATMOSPHERIC PRESSURE
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B. BASIC CONCEPTSATMOSPHERIC PRESSURE

• Fundamental concepts
• Importance of air pressure

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B. BASIC CONCEPTSATMOSPHERIC PRESSURE
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Current Surface Weather Map with Isobars (iso
equal bar weight), Fronts Radar
Isobars
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Explaining Differences in Air Pressure

• Low Pressure

• High Pressure

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H
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Isobars -- lines of equal barometric pressure-
use sea level corrected pressure
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Display of Pressure Differences on a Weather Map
- Isobars
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Announcement

• Homework 1 is due 1 week from today (Thurs. 28
  June 2001)

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C. BAROMETRY

• The Science of Barometry
• How is air pressure measured?
• Types of Barometers
• Mercury Barometers
• Aneroid Barometers
• where ...

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MERCURY BAROMETERS

• Torricelli invention in 1643
• A self-supported column of mercury
• A balance between weight of atmosphere weight
  of mercury in tube.

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ATM OCN 100 - Fall 2001LECTURE 4

• ATMOSPHERIC PRESSURE
• A Fundamental Weather Element (cont.)
• A. Practical Problem
• B. Basic Concepts
• C. Barometry

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Principles of a Mercury Barometer See Fig 5.1,
Moran (2002)
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MERCURY BAROMETERS (cont.)
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ANEROID BAROMETERS

• Perfected in 1840s
• An evacuated canister
• A balance between force of atmosphere force of
  spring inside canister.

See Fig 5.2 A, Moran (2002)
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Aneroid BarometerSee Fig 5.2 B, Moran (2002)
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BAROGRAPH See Fig 5.3, Moran (2002)
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A pressure trace from a barographSee Fig. 5.6,
Moran (2002)
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C. BAROMETRY (cont.)

• Placement of Barometers
• Pressure Units
• Inches or millimeters of mercury
• Pounds per square inch or millibars.
• The Millibar
• Traditional meteorological pressure unit (a
  metric unit of force per unit area)
• Sea level pressure ??1000 millibars
  (or 1 bar).

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C. BAROMETRY (cont.)

• Placement of Barometers
• Pressure Units
• Inches or millimeters of mercury
• Pounds per square inch or millibars.
• The Millibar
• Traditional meteorological pressure unit (a
  metric unit of force per unit area)
• Sea level pressure ??1000 millibars
  (or 1 bar).

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D. CLIMATOLOGY ofATMOSPHERIC PRESSURE

• Spatial variation in Sea-level air pressure
• Typical range 900 mb to 1060 mb.
• Temporal variation of Sea-level air
  pressure
• Typically less than 1 mb per 3 hours.

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D. CLIMATOLOGY ofATMOSPHERIC PRESSURE

• Spatial variation in Sea-level air pressure
• Extremes
• Typical range 980 mb to 1040 mb
• such as

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Average Sea Level Air Pressure Atmospheric
Circulation
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D. CLIMATOLOGY ofATMOSPHERIC PRESSURE (cont.)

• Temporal variation of Sea-level air
  pressure
• Typically less than 1 mb per 3 hours, but

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A pressure trace from a barographSee Fig. 5.6,
Moran (2002)
5-6 mb in 3 hrs
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D. CLIMATOLOGY ofATMOSPHERIC PRESSURE (cont.)

• Why Do Variations occur in Air Pressure?
• Piling On or taking offby
• Local Heating (convection)
• Dynamic Effects

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AIR PRESSURE CLIMATOLOGY (cont.)

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Vertical Cross-Section of Air Converging Aloft
See Fig. 8.20, Moran (2002)
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Map View of Flow around High Pressure Fig. 1.3A,
Moran (2002)
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Vertical Cross-Section of Air Diverging Aloft
Fig. 8.21, Moran (2002)
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Map View of Flow around Low Pressure Fig. 1.3B,
Moran (2002)
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D. CLIMATOLOGY ofATMOSPHERIC PRESSURE (cont.)

• Vertical Variations in air pressure
• The higher up, the lower the pressure.
• Why?

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AIR PRESSURE CLIMATOLOGY (cont.)Vertical
Variation

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Pressure falls
Pressure _at_ top of building 5-6 mb less than _at_
street level So how tall is the building?
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AIR PRESSURE CLIMATOLOGY (cont.) See Fig. 5.4,
Moran (2002)
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AIR PRESSURE CLIMATOLOGY (cont.) See Fig. 5.4
Moran (2002)
50 of surface
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AIR PRESSURE CLIMATOLOGY (cont)

• Variation of air pressure with height
• Lower atmosphere 1mb per 10 m height rise
• or

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E. ALTIMETRY

• Background
• Pressure Altimeters Aneroid Barometers that
  indicate altitude rather than pressure
• Computation

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AIR PRESSURE CLIMATOLOGY (cont.) See Fig. 5.4,
Moran (2002)
1 mb drop for 10 meter height rise
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ALTIMETRY (cont.)

• Sources of error
• Standard or model atmosphere does not always
  apply!

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ALTIMETRY

• Background
• Pressure Altimeters Aneroid Barometers that
  indicate altitude rather than pressure
• Computation
• Sources of error
• Standard or model atmosphere does not always
  apply!

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Altimetry Air Temperature(see Figure, pg. 107,
Moran (2002))
Warm
Cold
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Flying with a pressure altimeterSee Fig, pg.
107, Moran (2002)
Warm
Cold
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Sea-Level Pressure Reduction

• Desire
• To view only horizontal pressure variations on
  weather map
• Need
• To eliminate effects of topography from station
  pressure.

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Sea-Level Pressure Reduction (cont.)

• Result
• Assume that pressure increases at fixed rate down
  to sea level.

Station Pressure
Station Pressure
1 mb per 10 m
1 mb per 10 m
Sea level Pressure readings
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Isobars -- lines of equal barometric pressure-
use sea level corrected pressure
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Current Surface weather map 24 June 2003
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Current Surface Weather Map with Isobars (iso
equal bar weight), Fronts Radar
Isobars
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Atmosphere in Perspective (UCAR)