1. AOS 101 Discussion Sections 302 and 303
Cyclones
AOS 101 Discussion Sections 302 and 303

2. Cyclones
A cyclone is: An area of low pressure around which the winds flow counter-clockwise in the northern hemisphere, and clockwise in the southern hemisphere
Hurricane (tropical cyclone)
Mid-latitude cyclone

3. Ridge Trough Ridge

4. Cyclones L

5. Fronts and Advection

6. Locate a Cyclone L

7. Norwegian Cyclone Model (NCM)

8. Polar Front
The wave cyclone (often called a frontal wave) develops along the polar front
When a large temperature gradient exists across the polar front - the atmosphere contains a large amount of Available Potential Energy

9. Incipient Stage
Northward moving warm air and southward moving cold air are forced around each other, forming a bend in the temperature gradient (b). This forms the warm front and the cold front. Now with a counter-clockwise spin, winds converge at the newly formed low pressure minimum at the center of rotation.

10. Mature Stage
A fully-developed cyclone is seen hours It consists of:
a warm front moving to the northeast
a cold front moving to the southeast
region between warm and cold fronts is the "warm sector"
central low
wide-spread precip. ahead of the warm front
narrow band of precip. along the cold front
Wind speeds continue to get stronger as the low deepens

11. Occluded Stage
As the cold front moves swiftly eastward, the systems starts to occlude.
Storm is most intense at this stage
have an occluded front trailing out from the surface low
triple point/occlusion - is where the cold, warm, and occluded fronts all intersect

12. Occluded Fronts
A region where a faster moving cold front has caught up to a slower moving warm front.
Generally occurs near the end of the life of a cyclone
Drawn with a purple line with alternating semicircles and triangles

13. Cold and Warm Occlusion

14. Diminishing Cyclone
The warm sector diminishes in size as the systems further occludes.
The storm has used most all of its energy and dissipates
cloud/precip production has diminished
The warm sector air has been lifted upward
The cold air is at the surface - stable situation.

15. Cyclone on Radar

16. Tropical Storms Low pressure cyclones over tropical waters
Between 30° N and 30° S
Develop in areas with no horizontal temperature gradient
Season (Atlantic)
June 30 – November 30

17. Conditions for a Tropical Storm

18. 3 4 2 1

19. Tropical Depressions Cyclonic rotation Low pressure system No eye
Not very organized
Low pressure system
No eye
Winds up to 38 mph
Not named yet

20. Tropical Storm Now named More organized Usually no eye
Winds up to 73 mph

21. Tropical Cyclones Names Western Pacific: Typhoon
Hurricane
Names
Western Pacific: Typhoon
Indian Ocean: Tropical Cyclone
Atlantic/Eastern Pacific Oceans: Hurricanes

22. Tropical Cyclone Names NOAA Rotate six lists Greek names
Alternate male and female names
Retire certain names after particularly damaging hurricanes
Ex. Andrew (1992), Katrina (2005), Rita (2005), Ike, (2008), Igor (2010)
Greek names
Used for when there are more than 21 cyclones in a year

23. Cyclone Structure

24. Eye Center of the cyclone Calmest part of the storm
Due to downdraft at the very middle
Often clear skies, but sometimes have haze instead
Center of extremely low pressure

25. Eyewall Ring of thunderstorms Eyewall replacement Produce heavy rains
Usually produce the strongest winds
Clouds also are the highest in the storm here
Eyewall replacement
When inner wall weakens, outer wall replaces it
A new outer wall can be made

26. RAINBAND
EYEWALL
EYE
HURRICANE KATRINA