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Next Week: QUIZ

Next Week: QUIZ. One question from each of week: 9 normal lectures + global warming lecture Over main topic of lecture and homework Multiple choice, short answer, matching, map question Powerpoints: http://www.aos.wisc.edu/~ahulme/aos101/. AOS 101. Thickness and Thermal Wind. April 15/17.

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Next Week: QUIZ

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  1. Next Week: QUIZ • One question from each of week: • 9 normal lectures + global warming lecture • Over main topic of lecture and homework • Multiple choice, short answer, matching, map question • Powerpoints: http://www.aos.wisc.edu/~ahulme/aos101/

  2. AOS 101 Thickness and Thermal Wind April 15/17

  3. Thickness • The vertical distance in meters between two pressure levels 500 hPa = 5600 m THICKNESS = 5600 m – 0 m = 5600 m Z 1000 hPa = 0 m

  4. Consider a column… • Cool the average temperature of the column by 20 K • Air becomes more dense, mass stays the same so volume must decrease • Air takes up less space • COLUMN SHRINKS 500 hPa = 5600 m COOL 1000 hPa = 0 m

  5. Consider a column… • Cool the average temperature of the column by 20 K • Air becomes more dense, mass stays the same so volume must decrease • Air takes up less space • COLUMN SHRINKS 500 hPa = 5000 m COOL Z = 5000 m 1000 hPa = 0 m

  6. Consider a column… • Warm the average temperature of the column by 20 K • Air becomes lessdense, mass stays the same so volume must increase • Air takes up more space • COLUMN EXPANDS 500 hPa = 5600 m WARM 1000 hPa = 0 m

  7. Consider a column… 500 hPa = 6200 m • Warm the average temperature of the column by 20 K • Air becomes lessdense, mass stays the same so volume must increase • Air takes up more space • COLUMN EXPANDS Z = 6200 m WARM 1000 hPa = 0 m

  8. Summary • COOL air will result in LOW THICKNESS • WARM air will result in HIGH THICKNESS • Thus, the thickness between two pressure layers is proportional to the average temperature of that layer Z ≈ const xTave

  9. Thermal Wind • Not an actual wind • “Blows” along thickness contours with cold (low thickness) air to the left • Stronger temperature gradients imply stronger thermal wind • Equal to the SHEAR of the wind (i.e. is related to the observed wind)

  10. VT V200 V850

  11. COLD 5540 m VT 5600 m 5660 m WARM

  12. Veering Backing Clockwise turning of winds with height Counterclockwise turning of winds with height VT 300 hPa 850 hPa 300 hPa VT 850 hPa WARM AIR ADVECTION COLD AIR ADVECTION

  13. Midlatitude Weather • Upper-level winds will be much stronger than low-level winds • i.e. thermal wind will be very close to upper-level wind • Consider a front with cold air to the north and warm air to the south.

  14. Geostrophic wind into page Thermal wind into page P = 500 hPa PGF LOW heights HIGH heights P = 700 hPa COOL WARM NORTH

  15. Thermal Wind Balance • Pressure gradient increases with height • Winds increase with height • Thus, areas of strong temperature (thickness) gradient will have strong winds above them.

  16. 700 hPa Temperature 500-850 hPa Thickness

  17. 500 hPa Height 500 hPa Wind Speed

  18. 500-850 hPa Thickness 500 hPa Wind Speed

  19. Cyclone • Symbols: • Point in direction of front movement COLD WARM OCCLUDED STATIONARY

  20. Warm Front WARM COOL

  21. Associated Weather (WF) • Gradual Slope • Stratiform rain • long lasting light rain • occurs on cool side of front • Temperature increases prior to frontal passage • Wind becomes southerly after passage

  22. Cold Front WARM COOL

  23. Associated Weather (CF) • Much Steeper Slope • More intense (convective) rain • Thunderstorms for a shorter period • occurs on warm side of front • Temperature decreases after frontal passage • Wind becomes northerly after passage

  24. COOL AIR L LIGHTER RAIN COLD AIR WARM AIR HEAVIER RAIN

  25. Finding a Front • Temperature (dewpoint) Gradient • Change in wind direction • Converging winds at the front • “Kink” or “trough” in isobars (lower pressure) • Banded precipitation

  26. Upper-level terminology • TROUGH: area of lower heights • RIDGE: area of higher heights L H

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