ATM OCN 100 Summer ATM OCN 100 Summer 2002 LECTURE 4 ATMOSPHERIC PRESSURE: A Fundamental Weather Element (cont.) 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 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 ( 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 14 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 FDue this Thursday 27 June 2002 ATM OCN 100 Summer ATM OCN 100 Summer 2002 LECTURE 4 ATMOSPHERIC PRESSURE: A Fundamental Weather Element u A. PRACTICAL PROBLEM The pump problem: Why cant 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 and 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 (cont.) u A. Practical Problem u B. Basic Concepts u C. Barometry ATM OCN 100 Summer Principles of a Mercury Barometer ATM OCN 100 Summer MERCURY BAROMETERS (cont.) ATM OCN 100 Summer ANEROID BAROMETERS u Perfected in 1840s; u An evacuated canister; u A balance between force of atmosphere & force of spring inside canister. ATM OCN 100 Summer Aneroid Barometer ATM OCN 100 Summer BAROGRAPH 33 A pressure trace from a barograph See Fig. 5.5, Moran & Morgan (1997) ATM OCN 100 Summer C. BAROMETRY (cont.) 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 Average Sea Level Air Pressure & Atmospheric Circulation ATM OCN 100 Summer D. CLIMATOLOGY of ATMOSPHERIC PRESSURE u Why Do Variations occur in Pressure? u Temporal variation of Sea-level air pressure Typically less than 1 mb per 3 hours. ATM OCN 100 Summer A pressure trace from a barograph See Fig. 5.5, Moran & Morgan (1997) ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (cont.) ATM OCN 100 Summer Vertical Cross-Section of Air Converging Aloft Fig Moran & Morgan (1997) ATM OCN 100 Summer Map View of Flow around High Pressure Fig Moran & Morgan (1997) ATM OCN 100 Summer Vertical Cross-Section of Air Diverging Aloft Fig Moran & Morgan (1997) ATM OCN 100 Summer Map View of Flow around Low Pressure Fig Moran & Morgan (1997) ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (cont.) Vertical Variation ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (cont.) See Fig. 5.4 Moran & Morgan (1997) ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (cont.) See Fig. 5.4 Moran & Morgan (1997) 50% of surface ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (cont) AIR PRESSURE CLIMATOLOGY (cont) u Variation of air pressure with height Lower atmosphere: 1mb per 10 m height rise ; or ATM OCN 100 Summer ALTIMETRY u Background Pressure Altimeters Aneroid Barometers that indicate altitude rather than pressure u Computation ATM OCN 100 Summer AIR PRESSURE CLIMATOLOGY (cont.) See Fig. 5.4 Moran & Morgan (1997) 1 mb drop for 10 meter height rise ATM OCN 100 Summer ALTIMETRY (cont.) u Sources of error Standard or model atmosphere does not always apply! ATM OCN 100 Summer Altimetry & Air Temperature (see Fig. 1 on pg. 113 Moran & Morgan, 1997) ATM OCN 100 Summer Flying with a pressure altimeter See Fig. 1, pg. 113, Moran & Morgan (1997) 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 (cont.) u Result Assume that pressure increases at fixed rate down to sea level. ATM OCN 100 Summer Isobars - - lines of equal barometric pressure - use sea level corrected pressure H H L ATM OCN 100 Summer Surface weather map June 2002 ATM OCN 100 Summer Current Surface Weather Map with Isobars (iso = equal & bar = weight), Fronts and Radar Isobars
