Weather systems in mid-latitudes and their interaction

with human environments

i) Frontal depressions and associated weather

Polar Front: occurs when Tm meets Pm, it is along this front that depressions form

Life Cycle of a Depression• Stage 1 : Embryo Depression- Waves form due to friction

between 2 air masses- Warm air bulges into cold air- As air rises it spirals

anticlockwise- The greater the diff bet the

warm & cold air masses, the stronger a depression develops

- Move NE due to upper westerlies (PFJS)

Tm

Pm

Stage 2 : Mature Depression

-increased amplitude of wave-pressure continues to fall as warmssector is forced to rise-pressure gradient steepens-wind strength increases-rising air cools to dew point, large amount of latent heat released-clouds form, precipitation falls

Warm front – band of rain up to 150km wide

Cold front – greater intensity & shorterduration of rain (band only 10-50km wide) – Max wind strength due to greater temp difference

Stage 3 : Decay Depression

-Cold front catches up the warm front toform an occlusion or occluded front

-No warm sector left at ground level

-Less uplift – less condensation – lesslatent heat – less ppt – less cloud – pressure rises – winds decrease

-Colder air replaces the uplifted air and ‘infills’ the depression

High clouds : Ci – cirrus, Cc – cirrocumulus, Cs – Cirrostratus, Cb – Cumulo-nimbus

Middle clouds : Ac – altocumulus, As – altostratus, Cu – cumulusLow cloud : St – stratus, Ns – nimbostratus, Sc - stratocumulus

CLOUD ASSOCIATED WITH A DEPRESSION

WEATHER ASSOCIATED WITH A DEPRESSION

Bird’s eye view & cross section of depression

Synoptic Chart & Satellite Image

Synoptic Chart & Satellite Image

Describe weather conditions at O & S.Explain why the weather is like this, think about - time, air pressure.

• Explain how and why weather conditions have changed.

• Why is O now 5 degrees warmer?

• How would weather conditions have affected activities on the ground over these tow days?

‘The Great Storm’ 16 Oct 1987, read page 232-233 of text book plus handout materials. Make a list of the causes of the storm and the effects of the storm.

Complete the noting activities on the second page of handout.

Complete Q,15, 16, 17, 18 on page 258 of your text book. Make sure you have enough detail to

cover the marks allocated.

Tasks on depressions:• 1. Complete Q,15, 16, 17, 18 on page 258 of your text book. Make

sure you have enough detail to cover the marks allocated.

• 2. This task is very important, it looks at the effect that depressions have on peoples lives:

• ‘The Great Storm’ 16 Oct 1987, read page 232-233 of text book plus handout materials. Make a list of the causes of the storm and the effects of the storm. Complete the noting activities on the second page of handout.

• 3. Make a list of all the ways that a typical depression could affect people’s lives