5: Extratropical Cyclones

Question 1

Direction of cyclones in Northern hemisphere. Where does it develop?

Answer 1

• Surface winds blow counterclockwise and go inwards towards the low pressure center
• Develops in mid to high latitudes from warm and cold front working together

Question 2

What is the Cyclone Life Cycle (Just brief, main purpose). Image

Answer 2

1. Incipient cyclone: intensification of horizontal pressure gradient
2. Wave cyclone: comma cloud formation
3. Beginning occlusion: pressure drops
4. Bent back occlusion: cyclone slowly dies as pressure drops

Image 1

Question 3

Term for the birth of a cyclone

Answer 3

Cyclogenesis

Question 4

Incipient Cyclone

Answer 4

• first step in cyclone life cycle
• Strong horizontal divergence develops east of an upper level trough which leads to the intensification of surface low
• Intensification of horizontal pressure gradient at the lower troposphere results in cyclonic circulation
• HIgh and low pressure and fast and slow wind speed alternate
• 1a

Question 5

Wave Cyclone

Answer 5

• second step of cyclone life cycle
• front bends and form a wave like pattern
• upper level trough (low pressure) deepens
• central low pressur ~990mb
• Comma cloud formation
• 1b

Question 6

Comma cloud

Answer 6

• formed in wave cyclone step
• Comma head: surface low
• Comma tail: surface cold front
• Dry slot behind tell: descending cold air
• image 2

Question 7

Beginning Occlusion

Answer 7

• third step of cyclone life cycle
• Comma cloud will intensify
• Pressure drops to ~985mb
• Cold front catches warm front and occlusion begins
• Closed circulation above the surface low and descending dry air behind the cold front
• 1c

Question 8

Bent Back occlusion

Answer 8

• last step of cyclone life cycle
• Cikd front will eventually overtake warm front and cyclone will die
• Central low pressure drops to ~980mb
• North Atlanta and North Pacific Occeans origin of intense cyclones
• 1d

Question 9

Airflow in Cyclone Model

Answer 9

• Called conveyor belt model
• Warm moist air stream is ascending
• Dry air stream is descending
• Cold moist air stream is ascending
• image 3

Question 10

wind direction in northern hemisphere

Answer 10

always west to east

Question 11

Cyclone Characteristics like wind, temperatue, clouds and precipitation, and pressure

Answer 11

• image 4
• Wind: 4a, know it. counterclockwise and inwards
• temperature: 4b. Warm front is to the right of low pressure center and cold front is south of it. Behind the cold front and in front of the warm front is cold air mass. The warm air mass is between the cold and warm air mass, in front of the cold front an dbehind the warm front.
• Clouds and precipitation: know 4c. right in front of warm front is fog and drizzle, and as you go up is rain. The snow is more NW of th low pressure center. Ahead of the cold front are thunderstorms
• Pressure: 3d. Rising presure behind the cold front and falling pressure in front of the warm front

Question 12

Principal Cyclone Tracks in Canada

Answer 12

• Storm travels eastwards and as it goes through water bodies it will carry lots of moisture –> results in huge amount of precipitation in the east coast (cyclones end in the Canadian Maritimes: Newfoundland)
• East Gulf Cyclone track is most common with most intense cyclones
• Many cyclones start in the lee of the Rocky Mountains

Question 13

Lee Cyclogenesis for Alberta winter storms

Answer 13

• Cyclonic spin weakens as air ascends the western slopes of Rockies (horizontal divergence)
• Cyclonic spin strengthens as air descends the leeward slopes of Rockies –> smaller radius so faster (horizontal convergence)
• Conservation of angular momentum
• image 5

Question 14

What is conservation of angular momentum

Answer 14

• smaller radius means faster
• Formula given: radius x velocity = new velocity

Question 15

What is a Cyclone Bomb and other type of Bomb

Answer 15

Cyclone Bomb: cyclone whose central pressure falls by ≥ 24mb/24hrs rapidly

ERICA: Experiment on Rapidly Intensifying Cyclone over the Atlantic
* ERICA bomb: cyclose whose central pressure falls by ≥10 mb/6hrs

Question 16

1. If the surface wind backs from northeast to north, Halifax (Nova
   Scotia) usually experiences
   a. cold air advection.
   b. warm air advection.
   c. snow changing to rain.
   d. falling air pressure.
   e. hail

Answer 16

a
* Initially wind coming from north east and is changed from north wind –> north air mass usually cold so will result in cold air

Question 17

2. If the surface wind veers from east to southeast to south, Halifax (Nova Scotia usually
   experiences
   a. cold air advection.
   b. warm air advection.
   c. rain changing to snow.
   d. rising air pressure.
   e. falling temperatures.

Answer 17

b
* South wind air mass usually warm so will result in warm air

Question 18

3. In a mature extratropical cyclone, fog and drizzle are most likely to develop
   a. to the northwest of the low center.
   b. in the warm air behind the warm front.
   c. in the cold air just ahead of the surface warm front.
   d. in the warm air just ahead of the surface cold front.
   e. None of the above is correct.

Answer 18

c

Question 19

4 . If a weather station reports a wind shift from northeast to north and then northwest and a
steady rain turning to snow flurries, the low center is most likely moving

a. from west to east, north of the station.
b. from northeast to southwest, north of the station.
c. from southwest to northeast, east of the station.
d. from southwest to northeast, north of the station.
e. None of the above is correct

Answer 19

c

Question 20

5. Precipitation tends to be steady and persistent in the sector of a mature extratropical cyclone

a. northeast
b. northwest
c. southeast
d. southwest

Answer 20

a

Question 21

6. The coldest sector of a mature extratropical cyclone is usually __________ of the cyclone
   center.

a. northeast
b. northwest
c. southeast
d. southwest

Answer 21

b

Question 22

The warmest sector of a mature extratropical cyclone is usually __________ of the cyclone
center.
a. northeast
b. northwest
c. southeast
d. southwest

Answer 22

c

Question 23

The warmest air associated with a mature extratropical cyclone is usually located
a. at the low center.
b. southwest of the low center.
c. northwest of the low center.
d. southeast of the low center.
e. None of the above is correct.

Answer 23

d

Question 24

9. What is the surface wind direction in the northwest sector of a mature extratropical cyclone?
   a. southeast
   b. east
   c. south
   d. northwest
   e. southwest

Answer 24

d

Question 25

10. Viewed from above, the surface wind circulation about an Alberta-type cyclone is
    a. clockwise and outward.
    b. clockwise and inward.
    c. counterclockwise and outward.
    d. counterclockwise and inward.
    e. None of the above is correct

Answer 25

d