REMINDERS: UPCOMING REVIEW SESSIONS: - Thursday, Feb 28, 6:30-8:00pm in CSB 002

Transcription

1 REMINDERS: Midterm 2: Friday, March 1 - Lecture material covering chapters 6, 7, and 15 (since first midterm and through Wed lecture) - Multiple Choice, a few Short Answers, a few Definitions - Practice midterm and Study Guide on course website - Closed-book, no notes, no calculator. - No scantron necessary UPCOMING REVIEW SESSIONS: - Thursday, Feb 28, 6:30-8:00pm in CSB 002

2 3-CELL MODEL Polar Cell NP 60 Ferrel Cell 30 Hadley Cell EQ Hadley Cell Ferrel Cell SP Polar Cell

3 Tradewinds - Northeasterly in N.Hem - Southeasterly in S. Hem NP Polar Cell 60 Ferrel Cell 30 Hadley Cell EQ Hadley Cell Ferrel Cell SP Polar Cell

4 Island of Hawai'i NE Tradewinds Most rainfall on east side of island

5 Satellite Image

6 Surface HIGHS where air is SINKING SINKING AIR NP H Polar Cell 60 L L L Ferrel Cell SINKING AIR 30 H H H Hadley Cell EQ L L L 30 H H H Hadley Cell SINKING AIR 60 L L L Ferrel Cell SINKING AIR H SP Polar Cell

7 Semi-permanent Subtropical Highs Pacific High - Pacific High is an important factor for California's climate Bermuda High

8 U.S. West vs. East Coast Weather/Precipitation 34 N 34 N

9 U.S. West vs. East Coast Weather/Precipitation Why so little precipitation during summer in So Cal? 34 N 34 N

10 Clicker Question Set Frequency to "BB" When are the semi-permanent high pressure systems known as the "Pacific High" and "Bermuda High" at their maximum intensity? (A) Summer (B) Winter (C) Equal at all times of the year

11 Clicker Question Set Frequency to "BB" When are the semi-permanent high pressure systems known as the "Pacific High" and "Bermuda High" at their maximum intensity? (A) Summer (B) Winter (C) Equal at all times of the year

12 West US: Prevailing wind is from the Northwest bringing cool and moist air onto land. Because air is cool, still not much actual water vapor in air, so over land RH is low. => inhibits thunderstorm development East US: Prevailing wind is from the Southeast bringing warm and moist air onto land. Because air is warm there is large amount of water vapor in air, so over land RH is high. => good for thunderstorm development

13 West US: Prevailing wind is from the Northwest bringing cool and moist air onto land. Because air is cool, still not much actual water vapor in air, so over land RH is low. => inhibits thunderstorm development East US: Prevailing wind is from the Southeast bringing warm and moist air onto land. Because air is warm there is large amount of water vapor in air, so over land RH is high. => good for thunderstorm development Also important: in summer ocean water off West coast (50-70 F) much colder than water off East coast (70-85 F)

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16 Polar Front

17 Polar Front 300 mb 300 mb COLD AIR WARM AIR N.Pole ~60 N ~30 N

18 Polar Front PGF 300 mb 300 mb COLD AIR WARM AIR N.Pole ~60 N ~30 N

19 Polar Front JET JT Coriolis Deflects air to the right => Polar Jet (into the screen = westerly) => Maximum speed near top of troposphere PGF 300 mb 300 mb COLD AIR WARM AIR N.Pole ~60 N ~30 N

20 Clicker Question Set Frequency to "BB" When do you think the Polar Jet Stream would be strongest? (A) Equal at all times of the year (B) Winter: When temperature contrast across front is largest (C) Summer: When temperature contrast across front is smallest

21 Clicker Question Set Frequency to "BB" When do you think the Polar Jet Stream would be strongest? (A) Equal at all times of the year (B) Winter: When temperature contrast across front is largest (C) Summer: When temperature contrast across front is smallest

22 Polar Front PGF Stronger Temperature Difference: ==> Stronger PGF ==> Stronger Coriolis needed to balance ==> Stronger Winds 300 mb 300 mb COLD AIR WARM AIR N.Pole ~60 N ~30 N

23 Polar Jet Stream meanders in a wave-like pattern...

24 Also a "Subtropical Jet Stream" Jet Streams at Maximum Intensity near Tropopause

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26 Polar Jet (aka Midlatitude Jet) Subtropical Jet

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29 Now, back to the Surface Winds... Polar Easterlies Polar Front Mid-Latitude Westerlies Horizontal Shear Zone - wind changes direction and/or speed - will induce air to rotate

30 Clicker Question Set Frequency to "AB" The horizontal shear along the polar front will induce the air near the surface to rotate. Which direction will it rotate? (A) Cyclonically (CCW in N. Hem) Horizontal Shear Zone Polar Easterlies Polar Front (B) Anti-Cyclonically (CW in N. Hem) Mid-Latitude Westerlies (C) Will vary back and forth

31 Clicker Question Set Frequency to "AB" The horizontal shear along the polar front will induce the air near the surface to rotate. Which direction will it rotate? (A) Cyclonically (CCW in N. Hem) Horizontal Shear Zone Polar Easterlies Polar Front (B) Anti-Cyclonically (CW in N. Hem) Mid-Latitude Westerlies (C) Will vary back and forth

32 Anti-Cyclonic Flow clockwise in N. Hem Cyclonic Flow counter clockwise in N. Hem

33 Now, back to the Surface Winds... Polar Easterlies Polar Front Mid-Latitude Westerlies Horizontal Shear Zone - wind changes direction and/or speed - will induce air to rotate => Cyclonic Flow is induced here => Mid-latitude storms (low pressure) may form if conditions are right

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35 Divergence aloft can lead to low pressure forming/intensifying at surface and possible storm formation. When does divergence aloft occur?? 1) Waves in Jet Stream 2) Jet Streaks

36 Waves in Jet Stream high above surface (roughly 300 mb height) assume equal isobar spacing and Northern Hemisphere isobars V 1 HIGH V 2 LOW V 4 V 3

37 Waves in Jet Stream high above surface (roughly 300 mb height) assume equal isobar spacing and Northern Hemisphere isobars V 1 HIGH CW Flow V 2 CF = PGF - V 2 /R CCW Flow LOW V 4 CF = PGF + V 2 /R V 3 Since Coriolis Force (CF) is proportional to velocity, flow around HIGH is faster than flow around LOW for the same isobar spacing (PGF=constant).

38 Waves in Jet Stream high above surface (roughly 300 mb height) assume equal isobar spacing and Northern Hemisphere isobars V 1 HIGH CW Flow V 2 CF = PGF - V 2 /R CCW Flow LOW V 4 CF = PGF + V 2 /R A V 3 Since Coriolis Force (CF) is proportional to velocity, flow around HIGH is faster than flow around LOW for the same isobar spacing (PGF=constant). V 2 > V 3 and air in region A is converging (more entering than leaving) ==> Causes surface pressure to increase

39 Waves in Jet Stream high above surface (roughly 300 mb height) assume equal isobar spacing and Northern Hemisphere isobars V 1 HIGH CW Flow V 2 CF = PGF - V 2 /R CCW Flow LOW V 4 CF = PGF + V 2 /R A V 3 B Since Coriolis Force (CF) is proportional to velocity, flow around HIGH is faster than flow around LOW for the same isobar spacing (PGF=constant). V 2 > V 3 and air in region A is converging (more entering than leaving) ==> Causes surface pressure to increase V 3 < V 4 and air in region B is diverging (more leaving than entering) ==> Causes surface pressure to decrease => surface low forms

40 JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM Jet Streaks

41 JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM Largest T => Largest PGF => Smallest Isobar Spacing => Fastest Winds

42 JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM Largest T => Largest PGF => Smallest Isobar Spacing => Fastest Winds isobars LOW isobars HIGH

43 JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM Largest T => Largest PGF => Smallest Isobar Spacing => Fastest Winds isobars LOW A isobars HIGH At A: winds increase quickly => Coriolis takes time to adjust => Forces temporarily out of balance (too little Coriolis and wind veers to left)

44 JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM Largest T => Largest PGF => Smallest Isobar Spacing => Fastest Winds isobars LOW A B isobars HIGH At A: winds increase quickly => Coriolis takes time to adjust => Forces temporarily out of balance (too little Coriolis and wind veers to left) At B: winds decrease quickly => Coriolis takes time to adjust => Forces temporarily out of balance (too much Coriolis and wind veers to right)

45 JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM Largest T => Largest PGF => Smallest Isobar Spacing => Fastest Winds isobars Strong Convergence Region LOW Strong Divergence Region A B isobars Weak Divergence Region HIGH Weak Convergence Region At A: winds increase quickly => Coriolis takes time to adjust => Forces temporarily out of balance (too little Coriolis and wind veers to left) At B: winds decrease quickly => Coriolis takes time to adjust => Forces temporarily out of balance (too much Coriolis and wind veers to right)

46 Divergence aloft creates/enhances low pressure at surface leads to rising air

47 Today's winds at 300 mb (roughly Jet Stream level) base of trough jet streak (minor)

48 Intensifying Mid-latitude Storm