Download Weather and Climate

Physical Landscapes: Weather and Climate
What is Weather?
 Weather is the condition of the air that we find all around us at a point in time
 The weather is made up of elements and when you describe or explain the weather
write about these different elements.
What is climate?
 Climate is the average weather over long periods of time (usually at least 25 years).
 Within a broad climatic region, the climate may vary from place to place –These
areas with their small variations are called microclimates. Towns, valleys, hills,
forests and coastal areas all have their own microclimates.
 Climates are influenced by many factors, such as proximity to the equator or the
poles and proximity to the sea, as well as things like ocean currents, atmospheric
pressure belts and prevailing winds.
 A place's climate influences the types of vegetation and animals that live there. It is
possible to divide the world into a number of climatic zones or biomes, each with
their own characteristic climate, vegetation and wildlife.
The Factors Affecting the Climate of a Place- A L A D O A
A
L
A
Altitude
Latitude
Aspect
D
Distance from the sea
O
Ocean Currents
A
Air Masses/ Prevailing
Winds
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The height of a place above sea level
The distance in degrees a place is from the Equator
The direction a slope faces in relation to the sun
and the prevailing wind
Whether a place has a continental or a maritime
location
A warm or cold ocean current can make the
climate of an area near the sea different from
what is expected at that latitude
A large body of air which brings the weather of its
source region (that is where it originally comes
from)Prevailing winds are the most common
direction
Factors affecting climate
1) Altitude or height above sea level
 Locations at a higher altitude have colder temperatures as the air gets thinner with
height above sea level. Temperature usually decreases by 1°C for every 100
metres in altitude.
2) Latitude or distance from
the equator (in degrees)
 Temperatures decrease the
further an area is from the
Equator due to the
curvature of the earth. In
areas closer to the Poles
the sun’s rays are spread
over a wider surface area
so the energy is less
concentrated and is colder. In the Tropics the rays are more concentrated as the
sun is at a higher angle in the sky (almost overhead) making temperatures warmer.
 In addition, the presence of ice and snow nearer the poles causes a higher albedo,
meaning that more solar energy is reflected, also contributing to the cold.
3) Aspect of a slope.

This is the direction a slope faces. A south facing slope will receive more direct
sunlight making it warmer. A north facing slope is sheltered from the sunny making
it colder. In Britain west facing slopes can be wetter than east facing ones as they
face the Atlantic and the prevailing winds.
4) Distance from the sea
 Oceans heat up and cool down much more slowly than land. This means that
Maritime locations (near the coast) tend to be cooler in summer and warmer in
winter than places inland at the same latitude. Glasgow, for example, is at similar
latitude to Moscow, but is much milder in winter because it is nearer to the coast
than Moscow. Continental locations are hotter in summer and colder in winter.
5) Ocean currents
 Britain has a maritime climate. A warm ocean current called the North Atlantic
Drift keeps Britain warmer and wetter than places in continental Europe or at
similar latitude in eastern Canada where the cold Labrador Current lowers
temperatures to create a Tundra environment.
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6) Air Masses/Prevailing wind
 The prevailing wind is the most frequent wind direction a location experiences. In
Britain the prevailing wind is from the south west, which brings warm, moist air from
the Atlantic Ocean. This contributes to the frequent rainfall. When prevailing winds
blow from land areas, it can contribute to creating desert climates.
Weather and Climate in Britain
Britain’s Climate is:
 Variable - it changes from day to day
 Temperate – there are never extremes e.g. it is never too hot or too cold
 Maritime- proximity to ocean affects our weather
Britain is renowned for cool summers and mild winters.
Different parts of Britain experience slightly different regional climates. These can be
summarised as:
 north west - cool summers, mild winters, heavy rain all year
 north east - cool summers, cold winters, steady rain all year
 south east - warm summers, mild winters, light rain all year, especially summer
 south west - warm summers, mild winters, heavy rain all year, especially winter
Air Masses
 An Air Mass is a large volume of air which travels from one area to another. The
weather an air mass brings is determined by the region it has come from and the
type of surface it has moved over.
 They can be damp or dry, warm
or cold, depending on where they
came from and over what type of
surface they have travelled.
 For example, an air mass that has
travelled over the sea will
increase its moisture content and
be more likely to produce rainy
weather. One from the Sahara
Desert brings hot dry weather in
the summer.
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Air Masses Affecting Britain and Ireland
Britain’s Air Masses
The five air masses which affect Britain’s weather are shown above and in the table below.
The most common to affect Britain are Tropical Maritime and Polar Maritime. These two air
masses meet off the coast of North America and travel towards us across the Atlantic.
The 5 Air Masses affecting Britain and Western Europe
Name
Source Area
Weather
Characteristics
Tropical Maritime – all year
Tropical Continental –
mainly summer
Polar Maritime- all year
Polar Continental – mainly
winter
Arctic Maritime – mainly
winter
Atlantic Ocean
Southern Europe and North
Africa
North Atlantic
Northern Europe
Warm and wet
Warm and dry
Arctic Ocean
Very cold – not always wet
due to low humidity.
Cold and wet
Cold and dry
Weather Elements
When describing or explaining weather in an exam answer mention different elements
which make up the weather to gain more marks. These are listed below: Precipitation: Shower, Down pour, Sleet, Snow, Hail, Rain, Drizzle
 Sunshine: Dull, Sunny
 Wind speed: Breeze, Windy , Gale, Calm
 Wind Direction: N, S, E, W, NE, SW
 Visibility: Clear, Misty, Fog
 Temperature: Freezing, Hot, Cool, Warm, Cold
 Cloud Cover: Dull, Clear
 Air Pressure: Low, High
Element
Description
Units of measurement
Precipitation
Moisture from the sky e.g. rain, snow etc.
Millimetres (mm.)
Temperature How hot or cold the air is
Degrees Celsius ( c)
Wind Speed
How fast the wind is blowing
Knots, or by the Beaufort Scale
Wind
Direction
Where the wind is blowing from
Points of the compass (north,
north-west etc),
Humidity
The amount of water vapour in the air
Relative Humidity (% of water
vapour in the air at the actual
temperature)
Air Pressure
The "weight" of the air pushing on the
surface of the Earth
Millibars
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Element
Description
Cloud Cover The amount of cloud in the sky
Units of measurement
Oktas - eighths of the sky
Visibility
How far you can see
Kilometres
Sunshine
The hours of sunshine
Hours and minutes
Weather Station Circles






A circle which represents the location of the weather station
A line leading TO the circle, which represents the direction FROM WHICH THE
WIND IS COMING
‘feathers’ on the line which indicate the SPEED OF THE WIND (each feather
represents 10 knots, half a half feather represents 5 knots)
A number beside the station which indicates TEMPERATURE
Shading within the circle showing the amount of cloud cover in eighths
A ‘general weather’ symbol indicating the type of precipitation (if any) or mist or
fog.
In an exam you may be asked to match a
weather station circle to locations on the
weather map.
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Air Pressure is an element we are not generally aware of BUT it is important for weather
forecasting
There are two types of weather systems WHICH YOU NEED TO KNOW ABOUT.

Low pressure systems OR Depressions which bring changeable wet and windier
weather.

High pressure systems OR Anticyclones which bring stable dry, sunny weather.
These systems affect the weather we receive from day to day.
Synoptic Charts

A synoptic chart is a map which summarises atmospheric conditions such as
temperature, precipitation and wind speed.
Isobars are lines on a weather map that join-up places of equal atmospheric pressure.
The closer together isobars are, the windier it is.
Depressions (low Pressure)
What happens to the weather when the air masses meet?
•
Low pressure systems (known as Depressions) form when a cold air mass meets
a warm air mass.
•
Where two different air masses are called a front. A front is associated with a
change in the weather.
What are Fronts?
Weather fronts are where two airstreams meet. The warmer air, being lighter, rises up over
the cooler air. The warm air expands and cools as it rises. Colder air can hold on to less
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water vapour. The water condenses out of the atmosphere, forms clouds and eventually
rain.
A warm front means that warm air is coming.
At a warm front, warm air is rising over cold air.
This usually produces clouds and rain.
It is shown as a curved line with semi circles
A cold front means that cold air is coming.
At a cold front, cold air pushes under the warm air.
This produces strong winds and heavy rain.
It is shown as a curved line with triangles.
Occluded fronts happen at the point where a cold front joins up with a warm front.
Occluded fronts bring changeable weather with rain. This is also often the start of a period
of torrential rain.
A low pressure system (depression)
Depressions are areas of low atmospheric pressure, which produce cloudy, rainy and
windy weather.
The isobars in a low pressure system are normally close together – meaning strong winds.
In a low pressure system winds blow anticlockwise, parallel to the isobars.
Depressions or Low pressure bring the following conditions:

Windy weather

Cloudy conditions

Periods of rain, and in winter, snow

Unsettled, changeable weather
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It is easy to identify depressions on synoptic charts (weather maps):

The ISOBARS, (lines joining places with equal air pressure) are close together

The air pressure gets lower as you move into the centre of the low

Frequently they have WEATHER FRONTS
To be able to ‘read’ a depression on a weather map, it is important to remember the
following points;

Winds blow (more or less) parallel to the isobars

The closer the isobars the faster the wind

In the Northern Hemisphere winds blow ANTICLOCKWISE around the centre of the
low

Fronts mean RAIN – WARM FRONTS bring a long period of STEADY RAIN,
COLD AND OCCLUDED FRONTS bring a shorter spell of HEAVY RAIN

The temperature between the warm and cold fronts is higher than outside them –
this warmer, drier area is called the WARM SECTOR

Usually depressions move West to East over Britain.
The Passing of a Depression
It can be helpful to split a depression into five parts and consider the weather each part
brings. The following list is in the order it passes over Britain.
1. In ‘front of’ (east of) the warm front. The wind is increasing, the temperature is
relatively cool, clouds are high and thin and it is dry.
2. At the warm front. The wind is stronger, cloud cover is lower and thicker, the
temperature is warmer and it is raining.
WEST
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EAST
3. In the Warm Sector (between the fronts). As the name suggests this is the
warmest part of a depression. It has broken cloud and occasional showers.
4. At the cold Front. Thick cloud, heavy rain and hail, and a sudden drop in
temperature. Wind direction continues to veer, and the wind picks up speed.
5. Behind (west of) the cold front. Cold with clearing showers. Wind speed drops
off.
High Pressure Systems (Anticyclones)
 High pressure systems are also known as anticyclones
 Anticyclones are the opposite of depressions - they are an area of high atmospheric
pressure where the air is sinking.
 An anticyclone brings settled weather
 An anticyclone has no fronts – therefore no rain
 The isobars are far apart – showing it is not windy
 In high pressure winds blow clock-wise
 High pressure systems tend to stay around longer than low pressure systems and
this means that the weather can be unchanged for a week or more.
 The only real difference in the weather they bring is with summer and winter
anticyclones.
HIGH
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SUMMER ANTICYCLONES
WINTER ANTICYCLONES
 DRY
 DRY
 CLEAR SKY – FEW CLOUDS
 CLEAR SKY – FEW CLOUDS
 SUNNY
 SUNNY (but fewer hours due to a
 CALM
 WARM / HOT
shorter amount of daylight
 CALM
 COLD TO VERY COLD
 FROSTY MORNINGS
 FOG
Weather Forecasting



Weather forecasting is based on knowledge of patterns of air pressure as recorded
on synoptic charts.
Many different sectors of society require weather information, which can have a big
impact on people’s work and day-to-day making. For example, transport networks
and workers, pilots of aircraft and ships, construction workers, tourists, farmers and
many other rely on weather forecasts.
Weather maps are often published in newspapers or used on television news
programmes to describe and predict the weather.
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