MADISONS CURRENT WEATHER Madison Weather at 1000 AM

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MADISON’S CURRENT WEATHER Madison Weather at 1000 AM CDT MON 24 JUN 2002 Updated

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: SW 6 MPH Barometer: 30. 11 F (1019. 6 mb)

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar Isobars ATM OCN 100 Summer 2002 5

Rule of Thumb u The tighter the packing of the isobars, the stronger the

Rule of Thumb u The tighter the packing of the isobars, the stronger the winds! ATM OCN 100 Summer 2002 6

Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed)

Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) H L ATM OCN 100 Summer 2002 L H 7

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar Isobars ATM OCN 100 Summer 2002 8

Current Temperatures (°F) & Isotherms (“iso” = equal +”therm” = temperature) ATM OCN 100

Current Temperatures (°F) & Isotherms (“iso” = equal +”therm” = temperature) ATM OCN 100 Summer 2002 9

Tomorrow AM Forecast Map ATM OCN 100 Summer 2002 12

Tomorrow AM Forecast Map ATM OCN 100 Summer 2002 12

Announcements u Homework 1 – Get from our webpage F http: //www. aos. wisc.

Announcements u Homework 1 – Get from our webpage F http: //www. aos. wisc. edu/~hopkins/aos 100/ho mework/ – Due this Thursday 27 June 2002 ATM OCN 100 Summer 2002 15

ATM OCN 100 – Summer 2002 LECTURE 4 ATMOSPHERIC PRESSURE: A Fundamental Weather Element

ATM OCN 100 – Summer 2002 LECTURE 4 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 2002 16

B. BASIC CONCEPTS: ATMOSPHERIC PRESSURE ATM OCN 100 Summer 2002 17

B. BASIC CONCEPTS: ATMOSPHERIC PRESSURE ATM OCN 100 Summer 2002 17

B. BASIC CONCEPTS: ATMOSPHERIC PRESSURE u Fundamental u Importance ATM OCN 100 Summer 2002

B. BASIC CONCEPTS: ATMOSPHERIC PRESSURE u Fundamental u Importance ATM OCN 100 Summer 2002 concepts of air pressure 18

B. BASIC CONCEPTS: ATMOSPHERIC PRESSURE ATM OCN 100 Summer 2002 19

B. BASIC CONCEPTS: ATMOSPHERIC PRESSURE ATM OCN 100 Summer 2002 19

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar Isobars ATM OCN 100 Summer 2002 20

Explaining Differences in Air Pressure u Low Pressure L ATM OCN 100 Summer 2002

Explaining Differences in Air Pressure u Low Pressure L ATM OCN 100 Summer 2002 u High Pressure H 21

Isobars - lines of equal barometric pressure - use sea level corrected pressure L

Isobars - lines of equal barometric pressure - use sea level corrected pressure L H H ATM OCN 100 Summer 2002 22

Display of Pressure Differences on a Weather Map - Isobars H ATM OCN 100

Display of Pressure Differences on a Weather Map - Isobars H ATM OCN 100 Summer 2002 L 23

C. BAROMETRY u The Science of Barometry – How is air pressure measured? u

C. BAROMETRY u The Science of Barometry – How is air pressure measured? u Types of Barometers – Mercury Barometers – Aneroid Barometers where. . . ATM OCN 100 Summer 2002 25

MERCURY BAROMETERS u Torricelli invention in 1643; u A self-supported column of mercury; u

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 2002 26

Principles of a Mercury Barometer ATM OCN 100 Summer 2002 28

Principles of a Mercury Barometer ATM OCN 100 Summer 2002 28

MERCURY BAROMETERS (con’t. ) ATM OCN 100 Summer 2002 29

MERCURY BAROMETERS (con’t. ) ATM OCN 100 Summer 2002 29

ANEROID BAROMETERS u Perfected in 1840’s; u An evacuated canister; u A balance between

ANEROID BAROMETERS u Perfected in 1840’s; u An evacuated canister; u A balance between force of atmosphere & force of spring inside canister. ATM OCN 100 Summer 2002 30

Aneroid Barometer ATM OCN 100 Summer 2002 31

Aneroid Barometer ATM OCN 100 Summer 2002 31

BAROGRAPH ATM OCN 100 Summer 2002 32

BAROGRAPH ATM OCN 100 Summer 2002 32

A pressure trace from a barograph See Fig. 5. 5, Moran & Morgan (1997)

A pressure trace from a barograph See Fig. 5. 5, Moran & Morgan (1997) ATM OCN 100 Summer 2002 33

C. BAROMETRY (con’t. ) Placement of Barometers u Pressure Units u – – u

C. BAROMETRY (con’t. ) Placement of Barometers u Pressure Units u – – u 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). ATM OCN 100 Summer 2002 34

D. CLIMATOLOGY of ATMOSPHERIC PRESSURE u Spatial variation in Sea-level air pressure – Typical

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 2002 35

Average Sea Level Air Pressure & Atmospheric Circulation ATM OCN 100 Summer 2002 36

Average Sea Level Air Pressure & Atmospheric Circulation ATM OCN 100 Summer 2002 36

D. CLIMATOLOGY of ATMOSPHERIC PRESSURE u Why Do Variations occur in Pressure? u Temporal

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 2002 37

A pressure trace from a barograph See Fig. 5. 5, Moran & Morgan (1997)

A pressure trace from a barograph See Fig. 5. 5, Moran & Morgan (1997) ATM OCN 100 Summer 2002 38

Vertical Cross-Section of Air Converging Aloft Fig. 9. 20 Moran & Morgan (1997) ATM

Vertical Cross-Section of Air Converging Aloft Fig. 9. 20 Moran & Morgan (1997) ATM OCN 100 Summer 2002 40

Map View of Flow around High Pressure Fig. 9. 17 Moran & Morgan (1997)

Map View of Flow around High Pressure Fig. 9. 17 Moran & Morgan (1997) ATM OCN 100 Summer 2002 41

Vertical Cross-Section of Air Diverging Aloft Fig. 9. 21 Moran & Morgan (1997) ATM

Vertical Cross-Section of Air Diverging Aloft Fig. 9. 21 Moran & Morgan (1997) ATM OCN 100 Summer 2002 42

Map View of Flow around Low Pressure Fig. 9. 18 Moran & Morgan (1997)

Map View of Flow around Low Pressure Fig. 9. 18 Moran & Morgan (1997) ATM OCN 100 Summer 2002 43

AIR PRESSURE CLIMATOLOGY (con’t. ) Vertical Variation ATM OCN 100 Summer 2002 44

AIR PRESSURE CLIMATOLOGY (con’t. ) Vertical Variation ATM OCN 100 Summer 2002 44

AIR PRESSURE CLIMATOLOGY (con’t. ) See Fig. 5. 4 Moran & Morgan (1997) 50%

AIR PRESSURE CLIMATOLOGY (con’t. ) See Fig. 5. 4 Moran & Morgan (1997) 50% of surface ATM OCN 100 Summer 2002 46

AIR PRESSURE CLIMATOLOGY (con’t) u Variation of air pressure with height Lower atmosphere: 1

AIR PRESSURE CLIMATOLOGY (con’t) u Variation of air pressure with height Lower atmosphere: 1 mb per 10 m height rise; – or – ATM OCN 100 Summer 2002 47

ALTIMETRY u Background Pressure Altimeters Aneroid Barometers that indicate altitude rather than pressure u

ALTIMETRY u Background Pressure Altimeters Aneroid Barometers that indicate altitude rather than pressure u Computation – ATM OCN 100 Summer 2002 48

AIR PRESSURE CLIMATOLOGY (con’t. ) See Fig. 5. 4 Moran & Morgan (1997) 1

AIR PRESSURE CLIMATOLOGY (con’t. ) See Fig. 5. 4 Moran & Morgan (1997) 1 mb drop for 10 meter height rise ATM OCN 100 Summer 2002 49

ALTIMETRY (con’t. ) u Sources of error – Standard or model atmosphere does not

ALTIMETRY (con’t. ) u Sources of error – Standard or model atmosphere does not always apply! ATM OCN 100 Summer 2002 50

Altimetry & Air Temperature (see Fig. 1 on pg. 113 Moran & Morgan, 1997)

Altimetry & Air Temperature (see Fig. 1 on pg. 113 Moran & Morgan, 1997) ATM OCN 100 Summer 2002 51

Flying with a pressure altimeter See Fig. 1, pg. 113, Moran & Morgan (1997)

Flying with a pressure altimeter See Fig. 1, pg. 113, Moran & Morgan (1997) ATM OCN 100 Summer 2002 52

Sea-Level Pressure Reduction u Desire – – To view only horizontal pressure variations on

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 2002 53

Sea-Level Pressure Reduction (con’t. ) u Result – Assume that pressure increases at fixed

Sea-Level Pressure Reduction (con’t. ) u Result – Assume that pressure increases at fixed rate down to sea level. ATM OCN 100 Summer 2002 54

Isobars - lines of equal barometric pressure - use sea level corrected pressure L

Isobars - lines of equal barometric pressure - use sea level corrected pressure L H H ATM OCN 100 Summer 2002 55

Surface weather map June 2002 ATM OCN 100 Summer 2002 56

Surface weather map June 2002 ATM OCN 100 Summer 2002 56

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar Isobars ATM OCN 100 Summer 2002 57