Objectives
• Be able to describe the formation of a depression weather system.
• Be able to describe the air movement within a depression weather system.
• Be able to identify the features of a depression upon a satellite image.
• Be able to identify the features of a depression upon a synoptic weather chart.
Depressions form at the boundary
between cold artic/polar air in the
North and tropical air in the South.
Cold artic or
polar air
Somewhere
over the
Atlantic…
Polar Front
Tropical air
The cold air is pushing south and the
warm air is pushing north, this creates
a bulge along the polar front.
Cold artic or
polar air
Tropical air
Can you identify the bulge along
the polar front signifying the start
of a depression?
Due to the Coriolis Effect, caused by the
rotation of the Earth, the air moves
around an area of low pressure in an
anti-clockwise direction.
Cold artic or
polar air
Tropical air
We can now see three fronts within the
depression.
Occluded front
Cold artic or
polar air
Warm Front
Cold Front
Tropical air
Identifying a depression on a synoptic chart. Can you identify?
Areas of low
pressure
Isobars tightly
packed
Characteristic
fronts, warm,
cold and
occluded
Like humans, depressions are both born and mature over time…
In order to be
sustained, depressions
need a source of warm
moist air. This is
provided by the warm
conveyor.
This rises rapidly over the cold air in
front of it.
As it does, the moisture within it cools
and condenses to form a characteristic
area of clouds.
The cloud edge is sharp along the cold
front.
Warm conveyor
Can you identify the warm
conveyor on this satellite image?
A ‘cold conveyor’ bring cold air in along
the warm front, which rapidly rises in
the centre of the system.
This forms a characteristic band of cloud
and precipitation as air rises towards the
centre of the depression. This is called
the emerging cloud head.
cold conveyor
Behind the cold front, cold air descends
from the upper atmosphere and spreads
out along the cold front.
This encourages the warm air along the
warm conveyor to rise.
Can you identify the emerging
cloud head on this satellite image?
Over time the depression
begins to decay, the cold
air cuts off the supply of
warm moist air- leaving
the emerging head cloud
along the cold conveyor.
Can you identify the cloud
associated with the decaying
depression on this satellite image?
Movement of depression Klaus…
http://www.youtube.com/watch?v=K_9ciOB8Ot0
Depression or not?…
Which of the following would you associate with a depression?
Statement
Depressions begin when two types of
cold air meet.
Depressions are associated with low
pressure.
The air moves in a clockwise direction
within a depression.
Depressions usually bring rainfall.
In a depression we could expect to
see isobars packed closely together.
There is usually no wind in a
depression.
True
False