Midlatitude Cyclones

Question 1

Polar Front Theory

Answer 1

describes the formation, development, and dissipation of midlatitude cyclones

Question 2

Stationary Polar Front

Answer 2

continental polar air mass meets maritime polar air mass in the sub polar low pressure region
-anticyclonic, clockwise rotation
-air flows parallel to the front

Question 3

Frontal Wave (Cyclogenesis)

Answer 3

-a frontal wave forms a minor kink along the front, giving rise to a cold and warm front
-low pressure center begins to form at the junction between the two fronts
-area of precipitation begins to develop because center of low pressure and convergence starts to incur because of spiraling inwards due to friction

Question 4

Open Wave

Answer 4

-an open wave forms around the low pressure center and wind spirals inwards and towards the low
-precipitation along both frontal boundaries

Question 5

Mature Cyclone

Answer 5

-low pressure deepens at center
-entire system moves towards the east-northeast
-cold front moves faster than warm front, reducing the size of the warm sector

Question 6

Occlusion

Answer 6

beginning of occlusion marks peak in cyclone intensity and wind speeds
fronts begin to occlude and cyclone intensity starts to decrease
-convergence at the surface causes lifting and lots of precipitation

Question 7

Cut off cyclone

Answer 7

-original front disappears
-new stationary front forms, leaving a cut off weakened low pressure center
-low starts to decline in intensity because friction at the surface

Question 8

Steps of a midlatitude cyclone

Answer 8

1. Stationary polar front
2. Frontal wave
3. Open wave
4. Mature cyclone
5. Occlusion
6. Cut off cyclone

Question 9

Precipitation in the mature phase

Answer 9

heaviest precipitation near the low pressure center

Question 10

Vorticity

Answer 10

the spinning motion of air parcels
-the amount of rotation in the wind

Question 11

Planetary vorticity

Answer 11

vorticity due to the rotation of the planet
-planetary vorticity is not constant – it depends on where you’re oriented with the axis
- maximum vorticity at the poles, no vorticity at the equator

Question 12

relative vorticity

Answer 12

vorticity associated with the wind motions

Question 13

What is the vorticity and rotation of low pressure?

Answer 13

positive vorticity and counterclockwise rotation

Question 14

What the the vorticity and rotation of high pressure?

Answer 14

negative vorticity and clockwise rotation

Question 15

What is vorticity like at the trough axis?

Answer 15

it has the largest and positive vorticity

Question 16

What is vorticity like at the ridge axis?

Answer 16

it is at a minimum and has negative vorticity

Question 17

Is vorticity constant?

Answer 17

No, it changes as an air parcel moves along the jet stream

Question 18

How do air parcels increase vorticity?

Answer 18

They contract horizontally to spin faster
-so at the trough axis, air parcels contract and at the ridge axis the expand

Question 19

How is the parcel able to expand and contact?

Answer 19

Convergence and divergence at the surface and aloft in the jet region

Question 20

Where does convergence and divergence occur in the trough axis? What rotation and pressure is associated with this?

Answer 20

Convergence at upper air levels causes contraction of air parcels and results in sinking where they diverge at the surface
-high pressure at surface, clockwise rotation

Question 21

Where does convergence and divergence occur at the ridge axis? What pressure and rotation is associated with this?

Answer 21

Convergence at the surface pushes air upward where it diverges in the upper atmosphere; the divergence cause horizontal expansion and reduces spin (and thus vorticity)
-low pressure, counterclockwise rotation

Question 22

What happens when there is divergence aloft?

Answer 22

the low pressure will deepen, causing the winds to become stronger

Question 23

Effects of zonal height patterns

Answer 23

-prevents development of intense cyclones
-usually mild atmospheric conditions at the surface with mild, clear weather

Question 24

Effects of meridional height patterns

Answer 24

-support cyclone development as vorticity changes between troughs and ridges
-creates cyclones, fronts, and storms

Question 25

In what direction do surface systems move?

Answer 25

in the same direction as the 500 mb flow
-to know where the storm will be, look at what direction the wind is blowing at 500 mb

Question 26

Convergence and divergence is less common in the…

Answer 26

summer

Question 27

Oscillation is more common in the…

Answer 27

winter

Question 28

What are the common midlatitude cyclone paths across North America and what are their characteristics?

Answer 28

Alberta clippers: zonal flow and light precipitation
Colorado Lows: stronger storms and heavy precipitation, from east of the Rocky Mountains and move northeast where they dump a lot of snow

Question 29

Cyclone lifetime

Answer 29

a few days

Question 30

What happens as the low pressure moves along the jet stream?

Answer 30

it becomes weaker until it dissipates

Question 31

Where in the Rossby wave does precipitation occur?

Answer 31

When it approaches the upper level ridge

Question 32

What weather is associated with anticyclones?

Answer 32

clear skies and clam conditions
-if anticyclones linger over a region for a long time, this can lead to drought

Question 33

Cyclogenesis

Answer 33

beginning of cyclone formation

Question 34

Where do midlatitude cyclones usually form? What are some locations?

Answer 34

-appear in low pressure systems
-common near zones of thermal contrast (e.g. coastal regions or boundaries between warm and cold currents)
–common where topographic features, such as mountains, disrupt the normal flow

-may approach West coast after forming off coast of Japan, downwind of the Rockies, Gulf of Mexico

Question 35

Upper level divergence effect on midlatitude cyclones

Answer 35

causes formation and intensification

Question 36

Two causes of divergence or convergence

Answer 36

1. Increase or decrease in speed of air
2. Stretching out or pinching inward of air

Question 37

When are upper level winds stronger and why?

Answer 37

In the winter because there is a stronger temp gradient. This results in a greater PGF and thus greater wind speeds.

Question 38

Are winds in a trough subgeostrophic or supergeostrophic? In a ridge?

Answer 38

Subgeostrophic in a trough
Supergeostrophic in a ridge

Question 39

What happens when divergence aloft is stronger than convergence at the surface?

Answer 39

The low will deepen and intensify the storm