Download Depressions

Weather systems in midlatitudes 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)
Pm
Tm
Stage 2 : Mature Depression
-increased amplitude of wave
-pressure continues to fall as warms
sector 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 & shorter
duration 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 to
form an occlusion or occluded front
-No warm sector left at ground level
-Less uplift – less condensation – less
latent 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 – cumulus
Low 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