Download 03-07-2014 Hurricanes, cont`d

Midterm 2:
45 Possible
High Score = 45
Average = 34.4
Approximate Grades
A = 38.0 – 45.0
B = 30.5 – 37.5
C = 20.0 – 30.0
NP < 20
Hurricane Katrina on August 28, 2005
-­‐ Hurricanes consists of many cloud bands -­‐ upward moving air inside clouds -­‐ downward moving air in between clouds and in eye -­‐ Hurricanes consists of many cloud bands -­‐ upward moving air inside clouds -­‐ downward moving air in between clouds and in eye -­‐ Inflow at surface is cyclonic (CCW in NH) -­‐ Ou?low at top is an@cyclonic (CW in NH) -­‐ Hurricanes consists of many cloud bands -­‐ upward moving air inside clouds -­‐ downward moving air in between clouds and in eye -­‐ Inflow at surface is cyclonic (CCW in NH) -­‐ Ou?low at top is an@cyclonic (CW in NH) -­‐ Hurricane is fueled from below (warm moist air) and exhaust is at top. Hurricane Formation
At Surface: Need area of convergence for thunderstorms to develop
Hurricane Formation
At Surface: Need area of convergence for thunderstorms to develop
(1) Along Intertropical Convergence Zone (ITCZ)
- tradewinds converge at surface
Hurricane Formation
At Surface: Need area of convergence for thunderstorms to develop
(1) Along Intertropical Convergence Zone (ITCZ)
- tradewinds converge at surface
(2) Easterly Waves in Tropics
- westward moving areas of low pressure
- converging surface air on back side of wave
convergence at surface level (at surface) (at surface) Hurricane Formation
At Surface: Need area of convergence for thunderstorms to develop
(1) Along Intertropical Convergence Zone (ITCZ)
- tradewinds converge at surface
(2) Easterly Waves in Tropics
- westward moving areas of low pressure
- converging surface air on back side of wave
- often form over Africa and move into tropical Atlantic
Hurricane Formation
At Surface: Need area of convergence for thunderstorms to develop
(1) Along Intertropical Convergence Zone (ITCZ)
- tradewinds converge at surface
(2) Easterly Waves in Tropics
- westward moving areas of low pressure
- converging surface air on back side of wave
- often form over Africa and move into tropical Atlantic
(3) Occasionally, cold fronts extending over warm water
- Gulf of Mexico – very warm water
Clicker Question
Set Frequency to "AD"
Y
X
cool
warm
air
air in
cloud
Air within the cloud is warmer
than the air outside at a given
altitude. At the points labeled "X" and "Y", would you expect
(A) high pressure at X; low pressure at Y's
(B) low pressure at X; high pressure at Y's
(C) same pressure at all points
Y
cool
air
Clicker Question
Set Frequency to "AD"
Y
X
cool
warm
air
air in
cloud
Air within the cloud is warmer
than the air outside at a given
altitude. At the points labeled "X" and "Y", would you expect
(A) high pressure at X; low pressure at Y's
(B) low pressure at X; high pressure at Y's
(C) same pressure at all points
Y
cool
air
Hurricane Formation
As thunderstorms develop:
1. Warm moist air rising
2. Vapor condenses => latent heat released
2
1
Hurricane Formation
As thunderstorms develop:
4
HIGH
3
2
1
1. Warm moist air rising
2. Vapor condenses => latent heat released
3. In upper part of cloud, air warmer than air
outside of cloud
4. High Pressure forms near top of clouds
Hurricane Formation
As thunderstorms develop:
4
HIGH
3
2
1
LOW
6
5
1. Warm moist air rising
2. Vapor condenses => latent heat released
3. In upper part of cloud, air warmer than air
outside of cloud
4. High Pressure forms near top of clouds
5. Air aloft flows away from high
=> divergence aloft
6. Low pressure forms at surface
Hurricane Formation
As thunderstorms develop:
4
1. Warm moist air rising
2. Vapor condenses => latent heat released
3. In upper part of cloud, air warmer than air
outside of cloud
4. High Pressure forms near top of clouds
5. Air aloft flows away from high
=> divergence aloft
6. Low pressure forms at surface
7. Surface air converges towards low
Winds increase
= more evaporation
= more latent heat release
= air in cloud gets even warmer
5
HIGH
3
2
POSITIVE FEEDBACK LOOP
1
LOW
6
7
Conditions for Hurricane Formation
- initial surface convergence
- need warm water to provide enough energy (latent heat)
SST > 26-27°C (~80°F)
- need some Coriolis force for winds to rotate around low
Latitude > 5-10°
- need little or no vertical wind shear (opposite of severe thunderstorm)
Why?
Hurricane Formation
HIGH
LOW
- air inside cloud warmer than outside air ==> creates low pressure at surface
and high pressure aloft
Hurricane Formation
If Vertical Wind Shear:
HIGH
LOW
Vertical wind shear "tilts" the storm clouds
- warm air in clouds and the HIGH pressure aloft no longer
above LOW pressure at surface
- the low pressure weakens => winds weaken => less latent heat released
=> storm weakens
Conditions for Hurricane Formation
- initial surface convergence
- need warm water to provide enough energy (latent heat)
SST > 26-27°C (~80°F)
- need some Coriolis force for winds to rotate around low
Latitude > 5-10°
- need little or no vertical wind shear (opposite of severe thunderstorm)
EXHAUST
OUT
FUEL IN
EXHAUST
OUT
FUEL IN
If exhaust inhibited (strong winds or wind shear aloft)
or
If fuel reduced (cool ocean water or moves over land)
==> Storm Weakens
EXHAUST
OUT
FUEL IN
Main Energy Source:
- energy in warm ocean water transferred
to air aloft via evaporation at surface and
condensation in clouds
Saffir - Simpson Scale
Category
Sustained
Wind Speed
Storm
Surge
1
74-95 mph
4-5 ft
2
96-110 mph
6-8 ft
3
111-130 mph
9-12 ft
4
131-155 mph
13-18 ft
5
155 + mph
18 + ft
Clicker Question
Set Frequency to "AD"
Why do we not observe hurricanes off the coast of California?
(A) not enough Coriolis force at this latitude
(B) too much Coriolis force at this latitude
(C) ocean water temperature too cold
(D) ocean water temperature too warm
Clicker Question
Set Frequency to "AD"
Why do we not observe hurricanes off the coast of California?
(A) not enough Coriolis force at this latitude
(B) too much Coriolis force at this latitude
(C) ocean water temperature too cold
(D) ocean water temperature too warm
Clicker Question
Set Frequency to "AD"
In general, if the ocean water warms would you expect the
average hurricane intensity to:
(A) increase
(B) decrease
(C) stay the same
Clicker Question
Set Frequency to "AD"
In general, if the ocean water warms would you expect the
average hurricane intensity to:
(A) increase
(B) decrease
(C) stay the same
Expect warmer ocean water in future....
However, still not sure about future hurricanes since upper
level winds may change as well
2003
May up to 15Aug
2003
After 15Aug
ODen, most hurricane damage is due to flooding, not wind. Rising water level due to: • High waves • Wind pushing water towards coast • Low pressure of storm center (up to 2 feet alone) Combined effects called “Storm Surge” Dauphin Island, Alabama
Dauphin Island, Alabama
Dauphin Island, Alabama
Waveland, MS
Waveland, MS