Download HIGH

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
3-CELL MODEL
Polar Cell
NP
Ferrel Cell
60
30
Hadley Cell
EQ
Hadley Cell
30
Ferrel Cell
60
SP
Polar Cell
Tradewinds
Polar Cell
- Northeasterly in N.Hem
- Southeasterly in S. Hem
NP
Ferrel Cell
60
30
Hadley Cell
EQ
Hadley Cell
30
Ferrel Cell
60
SP
Polar Cell
Island of Hawai'i
NE Tradewinds
Most rainfall on
east side of island
Satellite Image
SINKING AIR
Surface HIGHS where
air is SINKING
NP
H
L
60
Polar Cell
L
Ferrel Cell
L
SINKING AIR
H
30
H
H
Hadley Cell
L
L
EQ
L
Hadley Cell
H
30
H
H
SINKING AIR
60
L
L
Ferrel Cell
L
H
SINKING AIR
SP
Polar Cell
Semi-permanent Subtropical Highs
Pacific High
- Pacific High is an important factor
for California's climate
Bermuda High
U.S. West vs. East Coast Weather/Precipitation
34°N
34°N
U.S. West vs. East Coast Weather/Precipitation
Why so little
precipitation
during summer
in So Cal?
34°N
34°N
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
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
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
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)
Polar Front
Polar Front
300 mb
300 mb
COLD AIR
N.Pole
WARM AIR
~60°N
~30°N
Polar Front
PGF
300 mb
300 mb
COLD AIR
N.Pole
WARM AIR
~60°N
~30°N
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
N.Pole
WARM AIR
~60°N
~30°N
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
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
Polar Front
Stronger Temperature Difference:
==> Stronger PGF
==> Stronger Coriolis needed to balance
==> Stronger Winds
PGF
300 mb
300 mb
COLD AIR
N.Pole
WARM AIR
~60°N
~30°N
Polar Jet Stream meanders in a wave-like pattern....
Also a "Subtropical Jet Stream"
Jet Streams at Maximum Intensity near Tropopause
Polar Jet (aka Midlatitude Jet)
Subtropical Jet
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
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)
Mid-Latitude
Westerlies
(B) Anti-Cyclonically
(CW in N. Hem)
(C) Will vary back and forth
Polar
Easterlies
Horizontal
Shear Zone
Polar Front
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)
Mid-Latitude
Westerlies
(B) Anti-Cyclonically
(CW in N. Hem)
(C) Will vary back and forth
Polar
Easterlies
Horizontal
Shear Zone
Polar Front
Anti-Cyclonic Flow
clockwise in N. Hem
Cyclonic Flow
counter clockwise in N. Hem
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
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
Waves in Jet Stream
high above surface (roughly 300 mb height)
assume equal isobar spacing and Northern Hemisphere
isobars
V1
HIGH
V2
V4
LOW
V3
Waves in Jet Stream
high above surface (roughly 300 mb height)
assume equal isobar spacing and Northern Hemisphere
isobars
V1
HIGH
CW Flow
CF = PGF + V2/R
V2
CF = PGF - V2/R
CCW Flow
V4
LOW
V3
Since Coriolis Force (CF) is proportional to velocity, flow around HIGH is faster
than flow around LOW for the same isobar spacing (PGF=constant).
Waves in Jet Stream
high above surface (roughly 300 mb height)
assume equal isobar spacing and Northern Hemisphere
isobars
V1
HIGH
V2
CF = PGF - V2/R
CCW Flow
LOW
CW Flow
CF = PGF + V2/R
V4
A
V3
Since Coriolis Force (CF) is proportional to velocity, flow around HIGH is faster
than flow around LOW for the same isobar spacing (PGF=constant).
V2 > V3 and air in region A is converging (more entering than leaving)
==> Causes surface pressure to increase
Waves in Jet Stream
high above surface (roughly 300 mb height)
assume equal isobar spacing and Northern Hemisphere
isobars
V1
HIGH
V2
CF = PGF - V2/R
CCW Flow
LOW
CW Flow
CF = PGF + V2/R
V4
A
B
V3
Since Coriolis Force (CF) is proportional to velocity, flow around HIGH is faster
than flow around LOW for the same isobar spacing (PGF=constant).
V2 > V3 and air in region A is converging (more entering than leaving)
==> Causes surface pressure to increase
V3 < V4 and air in region B is diverging (more leaving than entering)
==> Causes surface pressure to decrease => surface low forms
JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM
Jet Streaks
JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM
Largest ∆T => Largest PGF => Smallest Isobar Spacing => Fastest Winds
JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM
Largest ∆T => Largest PGF => Smallest Isobar Spacing => Fastest Winds
isobars
LOW
isobars
HIGH
JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM
Largest ∆T => Largest PGF => Smallest Isobar Spacing => Fastest Winds
LOW
isobars
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)
JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM
Largest ∆T => Largest PGF => Smallest Isobar Spacing => Fastest Winds
LOW
isobars
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)
JET STREAKS = REGIONS OF FASTEST WINDS IN JET STREAM
Largest ∆T => Largest PGF => Smallest Isobar Spacing => Fastest Winds
LOW
isobars
Strong
Divergence
Region
Strong
Convergence
Region
A
isobars
B
Weak
Divergence
Region
Weak
Convergence
Region
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)
Divergence aloft
– creates/enhances low pressure at surface
– leads to rising air
Today's winds at 300 mb (roughly Jet Stream level)
base of trough
jet streak (minor)
Intensifying Mid-latitude Storm