ATM OCN 100 Summer ATM OCN 100 – Summer 2004 LECTURE 2B ATMOSPHERIC PRESSURE: A Fundamental Weather Element (con’t.) u A. Practical Problem u B. Basic Concepts u C. Barometry u D. Climatology of Atmospheric Pressure u E. Altimetry
ATM OCN 100 Summer MADISON’S CURRENT WEATHER Madison 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): inches Hg ( mb) [Sea-level pressure: 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
ATM OCN 100 Summer Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radar Isobars
ATM OCN 100 Summer Observations for MADISON DANE RGNL, WI (MSN) 1453Z 18 Jun 2003 to 1353Z 19 Jun 2003 u eogram/ eogram/ eogram/ u bin/wyowx.fcgi?TYPE=sfgram&DATE =current&HOUR=current&UNITS=A& STATION=MSN bin/wyowx.fcgi?TYPE=sfgram&DATE =current&HOUR=current&UNITS=A& STATION=MSN bin/wyowx.fcgi?TYPE=sfgram&DATE =current&HOUR=current&UNITS=A& STATION=MSN
ATM OCN 100 Summer Deadly Tornado in Nebraska
ATM OCN 100 Summer Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radar Isobars
ATM OCN 100 Summer Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) H H L Streamlines
ATM OCN 100 Summer Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) H Streamlines H L L H L
ATM OCN 100 Summer Clouds Current Visible Satellite Image
ATM OCN 100 Summer Current Temperatures ( ° F) & Isotherms (“iso” = equal +”therm” = temperature)
ATM OCN 100 Summer Tomorrow AM Forecast Map
ATM OCN 100 Summer The Summer Solstice was 2:10 PM CDT See Fig Moran (2002)
ATM OCN 100 Summer ATM OCN 100 – Summer 2004 LECTURE 2B ATMOSPHERIC PRESSURE: A Fundamental Weather Element (con’t.) u A. Practical Problem u B. Basic Concepts u C. Barometry u D. Climatology of Atmospheric Pressure
ATM OCN 100 Summer LATEST RADAR
ATM OCN 100 Summer
MADISON’S 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 ( mb)
ATM OCN 100 Summer Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar Isobars
ATM OCN 100 Summer Rule of Thumb u The tighter the packing of the isobars, the stronger the winds!
ATM OCN 100 Summer Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) H L L H L H
ATM OCN 100 Summer Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar Isobars
ATM OCN 100 Summer Current Temperatures ( ° F) & Isotherms (“iso” = equal +”therm” = temperature)
ATM OCN 100 Summer Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar
ATM OCN 100 Summer CURRENT IR GABRIELLE
ATM OCN 100 Summer Tomorrow AM Forecast Map
ATM OCN 100 Summer
26 Happy Summer Solstice Today at (2:38 AM CDT) See Fig Moran & Morgan (1997)
ATM OCN 100 Summer Announcements u Homework 1 –Get from our webpage F –Due Thursday 26June 2003
ATM OCN 100 Summer Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radar Isobars
ATM OCN 100 Summer Did You know that – Sunday is summer solstice (7:57 PM CDT)? See Fig Moran (2002)
ATM OCN 100 Summer ATM OCN 100 – Summer 2004 LECTURE 2B ATMOSPHERIC PRESSURE: A Fundamental Weather Element u A. PRACTICAL PROBLEM – The pump problem: Why can’t water be lifted more than 30 ft?
ATM OCN 100 Summer B. BASIC CONCEPTS: ATMOSPHERIC PRESSURE
ATM OCN 100 Summer B. BASIC CONCEPTS: ATMOSPHERIC PRESSURE u Fundamental concepts u Importance of air pressure
ATM OCN 100 Summer B. BASIC CONCEPTS: ATMOSPHERIC PRESSURE
ATM OCN 100 Summer Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radar Isobars
ATM OCN 100 Summer Explaining Differences in Air Pressure u Low Pressure u High Pressure LH
ATM OCN 100 Summer Isobars - - lines of equal barometric pressure - use sea level corrected pressure H H L
ATM OCN 100 Summer Display of Pressure Differences on a Weather Map - Isobars HL
ATM OCN 100 Summer Announcement u Homework 1 is due 1 week from today (Thurs. 28 June 2001)
ATM OCN 100 Summer C. BAROMETRY u The Science of Barometry – How is air pressure measured? u Types of Barometers – Mercury Barometers – Aneroid Barometers where... where...
ATM OCN 100 Summer MERCURY BAROMETERS u Torricelli invention in 1643; u A self-supported column of mercury; u A balance between weight of atmosphere & weight of mercury in tube.
ATM OCN 100 Summer ATM OCN Fall 2001 LECTURE 4 ATMOSPHERIC PRESSURE: A Fundamental Weather Element (con’t.) u A. Practical Problem u B. Basic Concepts u C. Barometry
ATM OCN 100 Summer Principles of a Mercury Barometer See Fig 5.1, Moran (2002)
ATM OCN 100 Summer MERCURY BAROMETERS (con’t.)
ATM OCN 100 Summer ANEROID BAROMETERS u Perfected in 1840’s; u An evacuated canister; u A balance between force of atmosphere & force of spring inside canister. See Fig 5.2 A, Moran (2002)
ATM OCN 100 Summer Aneroid Barometer See Fig 5.2 B, Moran (2002)
ATM OCN 100 Summer BAROGRAPH See Fig 5.3, Moran (2002)
ATM OCN 100 Summer A pressure trace from a barograph See Fig. 5.6, Moran (2002)
ATM OCN 100 Summer C. BAROMETRY (con’t.) u Placement of Barometers u Pressure Units – Inches or millimeters of mercury; – Pounds per square inch or millibars. u The Millibar – Traditional meteorological pressure unit (a metric unit of force per unit area); – Sea level pressure 1000 millibars (or 1 bar).
ATM OCN 100 Summer C. BAROMETRY (con’t.) u Placement of Barometers u Pressure Units – Inches or millimeters of mercury; – Pounds per square inch or millibars. u The Millibar – Traditional meteorological pressure unit (a metric unit of force per unit area); – Sea level pressure 1000 millibars (or 1 bar).
ATM OCN 100 Summer D. CLIMATOLOGY of ATMOSPHERIC PRESSURE u Spatial variation in Sea-level air pressure – Typical range: 900 mb to 1060 mb. u Temporal variation of Sea-level air pressure – Typically less than 1 mb per 3 hours.
ATM OCN 100 Summer D. CLIMATOLOGY of ATMOSPHERIC PRESSURE u Spatial variation in Sea-level air pressure – Extremes – Typical range: 980 mb to 1040 mb such as … such as …
ATM OCN 100 Summer Average Sea Level Air Pressure & Atmospheric Circulation
ATM OCN 100 Summer D. CLIMATOLOGY of ATMOSPHERIC PRESSURE (con’t.) u Temporal variation of Sea-level air pressure – Typically less than 1 mb per 3 hours, but…
ATM OCN 100 Summer A pressure trace from a barograph See Fig. 5.6, Moran (2002) 5-6 mb in 3 hrs
ATM OCN 100 Summer D. CLIMATOLOGY of ATMOSPHERIC PRESSURE (con’t.) u Why Do Variations occur in Air Pressure? u Piling On or taking off by: – Local Heating (convection) – Dynamic Effects
ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (con’t.)
ATM OCN 100 Summer Vertical Cross-Section of Air Converging Aloft See Fig. 8.20, Moran (2002) H
ATM OCN 100 Summer Map View of Flow around High Pressure Fig. 1.3A, Moran (2002)
ATM OCN 100 Summer Vertical Cross-Section of Air Diverging Aloft Fig. 8.21, Moran (2002) L
ATM OCN 100 Summer Map View of Flow around Low Pressure Fig. 1.3B, Moran (2002)
ATM OCN 100 Summer D. CLIMATOLOGY of ATMOSPHERIC PRESSURE (con’t.) u Vertical Variations in air pressure u The higher up, the lower the pressure. – Why?
ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (con’t.) Vertical Variation
ATM OCN 100 Summer Pressure falls top of building ~ 5-6 mb less street level So how tall is the building?
ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (con’t.) See Fig. 5.4, Moran (2002)
ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (con’t.) See Fig. 5.4 Moran (2002) 50% of surface
ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (con’t) AIR PRESSURE CLIMATOLOGY (con’t) u Variation of air pressure with height – Lower atmosphere: 1mb per 10 m height rise ; – or
ATM OCN 100 Summer E. ALTIMETRY u Background – Pressure Altimeters Aneroid Barometers that indicate altitude rather than pressure u Computation
ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (con’t.) See Fig. 5.4, Moran (2002) 1 mb drop for 10 meter height rise
ATM OCN 100 Summer ALTIMETRY (con’t.) u Sources of error –Standard or model atmosphere does not always apply!
ATM OCN 100 Summer ALTIMETRY u Background – Pressure Altimeters Aneroid Barometers that indicate altitude rather than pressure u Computation u Sources of error –Standard or model atmosphere does not always apply!
ATM OCN 100 Summer Altimetry & Air Temperature (see Figure, pg. 107, Moran (2002)) Cold Warm
ATM OCN 100 Summer Flying with a pressure altimeter See Fig, pg. 107, Moran (2002) Cold Warm
ATM OCN 100 Summer Sea-Level Pressure Reduction u Desire – –To view only horizontal pressure variations on weather map; u Need – –To eliminate effects of topography from station pressure.
ATM OCN 100 Summer Sea-Level Pressure Reduction (con’t.) u Result –Assume that pressure increases at fixed rate down to sea level. Station Pressure Sea level Pressure readings ≈ 1 mb per 10 m
ATM OCN 100 Summer Isobars - - lines of equal barometric pressure - use sea level corrected pressure H H L
ATM OCN 100 Summer Current Surface weather map 24 June 2003
ATM OCN 100 Summer Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts & Radar Isobars
ATM OCN 100 Summer Atmosphere in Perspective (UCAR)