Mid-Latitude Cyclones

Question 1

Another name for mid-latitude cyclones

Answer 1

Frontal depressions
Extratropical cyclones
Temperate cyclones

Question 2

Origin

Answer 2

Form 60 N and S at polar fronts

Warm air from subtropics meets cold air from poles.

Question 3

Circulation

Answer 3

Southern hemisphere: air rotates clockwise around the centre of the low pressure system.
Air converges and rises.

Question 4

Diameter

Answer 4

From 1000km to 4000km wide

Question 5

Movement

Answer 5

Rossby waves from west to east within westerly wind belt (30 to 60 latitude)

Speeds of 60 to 90 km/h

Question 6

Season

Answer 6

All year round
Most influence our weather in winter when cold fronts bring rain to SW Cape.
In summer they migrate south with the shifting of the sun’s rays and have little effect on SAs weather.

Question 7

When mid latitude cyclones follow closely after one another

Answer 7

A family of fronts

Question 8

Worst weather?

Answer 8

Closest to centre of the low pressure

Question 9

Duration

Answer 9

Last 2 to 5 days - up to 14

Question 10

Stages? (4)

Answer 10

Initial
Mature
Occluded
Dissipating

Question 11

Initial stage

Answer 11

Forms at polar front: warm, moist tropical air meets cold, dry polar air.

Two air masses move in opposite directions.

Disturbance due to rotary movement causes low pressure to form at the wave point.

Question 12

Mature stage

Answer 12

Cold and warm fronts develop

Air circulates clockwise (SH), is drawn into the low pressure centre and rises.

Warm front: warm air rises gradually over cold air ahead of it.

Cold front: cold air wedges in under warm air, forcing it to rise sharply.

Question 13

Occluded stage

Answer 13

Cold front moves faster than warm front and catches up with it.
Causes warm sector air to rise.

Warm air is now isolated from the ground and the low pressure centre is completely surrounded by cold air.

Produces an occluded front.

Question 14

Dissipating stage

Answer 14

Separation of the cyclones from the warm air eventually leads to the storm’s decay.
As only cold air remains on surface.

Question 15

Temperature (Cold front)

Answer 15

Decreases rapidly
Move from warm to cold sector

Question 16

Wind direction (Cold front)

Answer 16

Backs from NW to colder SW/W winds
Clockwise rotation of air in southern hemisphere.

Question 17

Wind speed (Cold front)

Answer 17

Increase; gusty
Strong uplift as cold air forces warm air to rise.

Question 18

Air pressure (Cold front)

Answer 18

Decreases
Closer to centre of low pressure system

Question 19

Relative humidity (Cold front)

Answer 19

Decreases, then increases when it rains.
Increases as colder temperature means saturation point is reached sooner.

Question 20

Cloud cover (Cold front)

Answer 20

Increases to 8/8, mostly cumulonimbus clouds.

The cold air forces the warm air to rise sharply, so condensation occurs to greater heights.

Question 21

Precipitation (Cold front)

Answer 21

Heavy rain
Cumulonimbus clouds cause heavy rain, thunderstorms (hail if an active cold front)
Rain can occur along entire line of front (500-600km), known as a line squall

Soft, penetrating drizzle of cold front not too steep and warm sector is stable.

Question 22

Temperature (warm front)

Answer 22

Increases gradually as warm sector approaches

Question 23

Wind (warm front)

Answer 23

Backs from NE to NW and N

Question 24

Cloud cover, type and precipitation (warm front)

Answer 24

Increases from cirrus to cirrostratus and altostratus, then nimbostratus which brings soft, soaking rain.

Question 25

Dew point temperature (warm front)

Answer 25

Increases as warm sector approaches

Question 26

Air pressure (warm front)

Answer 26

Decreases rapidly before onset of the warm front

Question 27

Impact of mid latitude cyclones

Answer 27

Trees uprooted Buildings damaged Roofs ripped off homes Powerlines down (no electricity) Flooding Displaced people Evacuations Motor vehicle accidents (poor visibility)