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Challenge of the
Weather and Climate
Weather Vs Climate
Weather is the day to day interaction of
the atmosphere.
Climate is the weather over a period of
years, often 30 year periods.
Factors affecting climate
Latitude or distance from the
equator
Temperatures drop the further an area is from the
equator. Due to the curvature of the earth. In areas
closer to the poles, sunlight has a larger area of
atmosphere to pass through and the sun is at a
lower angle in the sky. As a result, more energy is
lost and temperatures are cooler.
In addition, the presence of ice and snow nearer the
poles causes a higher albedo. This means that more
solar energy is reflected, also contributing to the
cold.
Air Masses
Different Air Mass =
different weather
The main air masses that affect Britain are
those that form over the Mid-Atlantic but
there are several other air masses that bring
particular weather conditions.
The air masses are defined according to where
they originated and their course of travel.
For example air from Arctic regions is
classified as Arctic maritime as it originates in
the Arctic and travels across the North Sea.
Another example is Tropical maritime air
which originates near the Gulf of Mexico and
travels across the warm Atlantic Ocean
before arriving in Britain.
Other air masses include the Polar maritime,
Polar continental and Tropical continental.
Ocean Currents
A warm ocean current called the North
Atlantic drift is a major driving force,
especially in the winter giving us milder
temperatures than places with the same
latitude eg. Moscow.
North Atlantic Drift
Prevailing Winds
The prevailing wind is the most frequent wind
direction a location experiences.
In Britain the prevailing wind is from the
southwest, which brings warm, moist air from
the Atlantic Ocean.
This contributes to the frequent rainfall. When
prevailing winds blow over land areas, it can
contribute to creating desert climates.
Maritime Influence
 Britain has a maritime climate. A warm ocean
current called the North Atlantic Drift keeps
Britain warmer and wetter than places in
continental Europe.
 The sea affects the Uk climate. We live on an
island, so the air above us tends to be humid
(with water). This explains the mainly cloudy
weather with large amounts of rainfall.
Continentality (distance
from the sea)
 Oceans heat up and cool down much more
slowly than land.
 This means that coastal locations tend to be
cooler in summer and warmer in winter than
places inland at the same latitude and altitude.
 Derry, for example, is at a similar latitude to
Moscow, but is much milder.
Altitude
Locations at a higher altitude have colder
temperatures. Temperature usually decreases
by 1° C for every 100m in altitude.
If it is 20 degrees at the bottom of the
mountain, with the mountain 1000m high, then
it will be 10 degrees at the top.
Air is forced to rise up over upland areas giving
them higher amounts of precipitation.
Types of Rainfall
There are 3 types:
1. Convectional
2. Relief
3. Frontal (Depressions)
Stage 1.
The sun heats the ground and warm air rises.
Stage 2
As the air rises it cools and water vapour condenses to
form clouds.
Stage 3.
When the condensation point is reached large
cumulonimbus clouds are formed.
Stage 4.
Heavy rain storms occur. These usually include thunder
and lightening due to the electrical charge created by
unstable conditions.
Stage 1.
Warm wet air is forced to rise over high land.
Stage 2.
As the air rises it cools and condenses. Clouds
form and precipitation occurs.
Stage 3.
The drier air descends and warms.
Stage 4.
Any moisure in the air (e.g. cloud) evaporates.
Stage 1.
An area of warm air meets and area of cold air.
Stage 2.
The warm air is forced over the cold air.
Stage 3.
Where the air meets the warm air is cooled and
water vapour condenses.
Stage 4.
Clouds form and precipitation occurs.
What is pressure?
Pressure is the weight of air pressing
down on the earth's surface. Pressure
varies from place to place and results in
pressure systems.
Isobars and fronts
Isobars are lines on a weather map
joining together places of equal
atmospheric pressure.
On the map the isobar marked 1004
represents an area of high pressure,
while the isobar marked 976 represents
an area of low pressure.
Note that:
 The numbers measure the atmospheric pressure in millibars.
 Usually isobars are drawn at intervals of two or four
millibars (one thousandth of a bar).
 The closer the isobars are together the windier it is.
 If the lowest number is in the middle circle this is a low
pressure or depression. Often low pressures mean wet and
windy weather.
 If the highest number is in the middle circle, this is a high
pressure or anticyclone. Often high pressures mean dry,
sunny weather.
 Air pressure tends to range from 890mb (a hurricane) to
1060mb (an anticyclone).
Synoptic charts
3 types of front

Note the three different kinds of front shown on the map - a cold front, a
warm front and an occluded front.

Fronts occur where two different air masses meet.

Occluded fronts occur at the point where a cold front takes over a
warm front or vice versa. If a cold front undercuts a warm front it is
known as a cold occlusion and if the cold front rises over the warm
front it is called a warm occlusion. Occluded fronts bring
changeable weather conditions.
On a synoptic chart occluded fronts are represented by semi-circles
and triangles positioned next to each other. The triangles are in blue
and the semicircles are in red, or both are purple (mixing both red
and blue colours together).

Warm Front
Warm fronts are formed when warm air rises over a
mass of cold air. As the air lifts into regions of
lower pressure, it expands, cools and condenses
the water vapour as wide, flat sheets of cloud.
Warm fronts are shown on synoptic charts by a
solid line with semicircles pointing towards the
colder air and in the direction of movement. On
coloured weather maps, a warm front is drawn with
a solid red line with red semicircles.
Cold Front
Cold fronts are usually associated with
depressions.
A cold front is the transition zone where a
cold air mass is replacing the warmer air
mass.
The cold air is following the warm air and
gradually moves underneath the warmer air.
When the warm air is pushed upwards it will
rain heavily.
Weather with a cold front
passing over
Often more rain will fall in the few
minutes the cold front passes than it
will during the whole passage of a
warm front. As the cold front passes,
the clouds roll by and the air
temperature is cooler.
Cold fronts are shown on synoptic
charts by a solid line with triangles
along the front pointing towards the
warmer air and in the direction of
movement. On coloured weather
maps, a cold front is drawn with a
solid blue line with blue triangles.
Occluded Fronts
 Occluded fronts occur at the point
where a cold front takes over a warm
front or vice versa. If a cold front
undercuts a warm front it is known as
a cold occlusion and if the cold front
rises over the warm front it is called a
warm occlusion. Occluded fronts
bring changeable weather conditions.
 On a synoptic chart occluded fronts
are represented by semi-circles and
triangles positioned next to each
other. The triangles are in blue and the
semicircles are in red, or both are
purple (mixing both red and blue
colours together).
Depressions
 http://www.echalk.co.uk/Geography/geog
raphyContent.htm
 http://www.interactiveteachingresources.c
om/tag/weather
Depressions are areas of low
atmospheric pressure which produce
cloudy, rainy and windy weather.
These low-pressure systems often begin
in the Atlantic, moving eastwards towards
the UK. They are responsible for the UK's
changeable weather.
Warm Front
At the Warm Front
 At the warm front, lighter, warmer air from
the south (tropical maritime air) meets
cooler air from the north (polar maritime air)
and rises gradually over it.
 As the warm air slowly rises it cools, its
water content condenses and clouds form
(nimbostratus then altostratus). The result
is steady rain, later giving way to drizzle
and finally clearer skies with high cirrus
clouds.
In the Warm sector
 Behind the warm front is an area of
warm, rising air and low pressure - the
centre of the low-pressure system. As
this part of the depression passes
over, there may be a short period of
clear, dry weather
Cold Front
At the Cold Front
 However, at the trailing cold front, heavier, cooler
air meets the warm air at the centre of the
depression, undercutting it and forcing it steeply
upwards. Quickly moving air masses produce high
winds and cooler temperatures...
 As the rapidly rising warm air cools, its water
condenses and clouds form (cumulonimbus, then
cumulus). The result is heavy rain or
thunderstorms, giving way to showers and finally
to clear skies as the cold front moves away
eastwards.
Occluded Front - Depression
Anticyclones
Anticyclones are the opposite of depressions
– they are an area of high atmospheric
pressure where the air is sinking.
As the air is sinking, not rising, no clouds or
rain are formed. This is because as the air
sinks it warms - meaning it can hold more
water.
Anticyclones
What type of weather do
Anticyclones bring?
The absence of fronts means winds
may be very light.
Consequently, high-pressure areas are
often associated with settled, dry and
bright conditions.
Summer Vs Winter
In summer, anticyclones bring dry, hot
weather. In winter, clear skies may
bring cold nights and frost.
In cold conditions, anticyclones may
also bring fog and mist. This is because
the cold forces moisture in the air to
condense at low altitudes.