What is Weather + Climate

Weather is the hour-by-hour, day-by-day conditions of the

atmosphere.

Climate is the the average weather conditions over a long

period of time.

Factors affecting Weather

Temperature

Precipitation

Air pressure

Wind speed and direction

Sunshine

Humidity

Cloud Cover

Temperature

Temperature is measured in

degrees centigrade by a

maximum and minimum

thermometer. During the

day, the mercury or alcohol

expands and in the night the

mercury or alcohol

contracts.

Precipitation

Rainfall (a type of precipitation) is

measured in mm by a rain gauge.

The water collected can be poured

into a measuring cylinder and then

can be recorded.

Air Pressure

Air pressure is measured in

millibars (mb) on a barometer.

As the pressure changes the

cylinder rises causing the

lever to move and the pen to

draw on the rotating drum.

Wind Speed

Wind speed is measured in

miles per hour or knots and is

measured using an

anemometer. A wind meter can

also be used.

Wind Direction

Wind direction is measured by

a wind vane which turns in the

direction the wind is coming

from. Most of Britain’s winds

come from the south-west.

These are called prevailing

winds.

Sunshine

Sunshine is measured

using a Campbell Stokes’

sunshine recorder. A note

is made of how much

sunshine there is everyday.

Humidity

Humidity is measured by a

hygrometer in milliliters per cubic

centimeters. However some

hygrometers measure humidity in

percentages.

Cloud Cover

Cloud cover is measured in

oktas. Each okta represents

one-eighth of the sky

covered by cloud.

Stevenson Screen

A Stevenson Screen is a store

where weather instruments are

kept. It is white to reflect sunlight

and slatted to allow air to

circulate. It is placed on grass

away from buildings and trees.

Types of Clouds

Cumulus, Stratus and Stratocumulus

Altocumulus and Altostratus

Cirrocumulus, Cirrus, Cirrostratus and Cumulonimbus

The lowest clouds

The lowest clouds in the atmosphere are stratus, cumulus

and stratocumulus. These clouds are around 6,000 feet

high. Stratus clouds are horizontal layers and cumulus

clouds are cotton-like in appearance. Stratocumulus is a

cross between them.

Mid-Level Clouds

Mid-level clouds include altocumulus and altostratus.

Theses clouds range from 6,000 feet to 20,000 feet.

Altocumulus clouds are dark individual segments.

Altostratus clouds are thin sheets from which the sun can

be seen through.

The Highest Clouds

The highest clouds are cirrus, cirrocumulus, cirrostratus

and cumulonimbus. They are around 20,000 feet high.

Cirrus clouds look like thin wispy stripes, cirrocumulus

clouds look like fish scales, cirrostratus clouds look like

white veils and cumulonimbus clouds are very tall, large

clouds.

The Water Cycle

1. The sun causes water to form water vapour and rise up into the atmosphere. i.e. evaporation.

2. At the same time transpiration (the transfer of water from trees into the atmosphere) occurs.

3. As water vapour rises it begins to cool. The temperature falls by 1ºC for every 100m you ascend. At the dew pointthe water vapour cools to form clouds.

4. Soon the water droplets become heavy and fall as precipitation.

The Water Cycle Diagram

Britain’s Air Masses

How do They Affect Us?

Britain receives a lot of rainfall the prevailing winds blow

from the southwest, bringing the tropical maritime air

mass. When the wind blows from the south we receive

the tropical continental air mass, which is dry and comes

from Northern Africa. A northerly or easterly wind in

winter results in snowy conditions generated by the artic

and polar continental air masses. Winds from the north-

west bring the cold weather of the polar maritime air

mass.

Factors Affecting UK’s Climate

Latitude

The Gulf Stream

South-westerly Prevailing Winds

Altitude

Distance from the Sea

Latitude

The higher the latitude, the colder it will be as the

Sun’s rays have to travel further through the

atmosphere to reach areas of higher latitude like

Britain.

The Gulf Stream

The Gulf Stream (North Atlantic Drift) is a water current

from the Gulf of Mexico that brings moist warm air

across the Atlantic Ocean to the west of the British

Isles.

SW Prevailing Winds

The south-westerly prevailing winds are the UK’s most

common winds which travel across the Atlantic Ocean

picking up lots of moisture which then gets dropped on

the first land mass it meets - Britain.

Altitude

The higher the altitude, the colder it is. Higher areas

like Lake District receive more rainfall because air is

forced to rise upwards and the water vapour condenses

to form clouds.

Distance to 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 which are at the same latitudes and altitudes.

Microclimates

Shelter

Surface

Aspect

Natural Physical Features

Buildings

Shelter

Buildings, walls, hills and valleys can provide shelter. It

will feel a degree or two warmer on the sheltered side

than the side facing the wind.

This side of the

hedge is warmer. This side is colder as

it is facing the wind.

Surface

Dark surfaces absorb heat and are therefore warmer

than light shiny surfaces. Light surfaces reflect heat and

are therefore cooler.

Light surface

reflects heat

Dark surfaces absorb

heat

Aspect

As the sun moves through the sky, it warm slopes that

face it. In Britain, south-facing slopes receive more

sunlight than north-facing slopes as the sun moves

through the south during the day.

This slope is

warmer

Buildings

During the day, dark buildings absorb heat and release

it in the night. Buildings also break up the wind

depending on the direction they are facing and the

prevailing wind direction.

Buildings absorb

heat.

Natural Physical Features

Rain is caught in the canopy of a forest, reducing

precipitation. In winter, it feels warmer in a sheltered

forest as the trees provide protection from the cooling

wind. In summer it feels cooler as the trees block out

the sun.

Warmer in winter and

colder in summer

Pressure Systems

Anticyclones

Depressions

Anticyclones

Anticyclones

Process Cool air sinking

Air Masses One air mass at time.

Isobars on Map Isobars dispersed

Weather Still or very light winds

Seasonal Variation Very cold in winter; hot in

summer

Pressure High Pressure

Depressions

Depression

Process Warm air rising

Air Masses Two air masses

Isobars on Map Isobars tightly packed

Weather Wind, cloudy skies

Seasonal Variation Wet, mild and windy

throughout the year.

Pressure Low pressure

Types of Rainfall

Relief Rainfall

Convectional Rainfall

Frontal Rainfall.

Relief Rainfall

1. Prevailing winds bring moist air to Britain.

2. Air is forced to rise over high areas.

3. Air cools and condenses

4. Clouds form and it starts to rain.

5. Air descends on the other side of the mountain.

6. It warms up and dries over an area to the east of the

mountains known as the rain shadow.

Relief Rainfall Diagram

Convectional Rainfall

1. The sun heats the earth.

2. The earth heats the air above it.

3. Hot air rises because it is less dense.

4. The water vapour cools at the dew point and condenses into water droplets.

5. These water droplets join together and then fall as rain.

Convectional Rainfall Diagram

Frontal Rainfall

1. When a warm and cold air mass meet they don’t mix.

2. The lighter warmer air rises over the heavier, colder air.

3. As the warm air rises condensation occurs, clouds form and rain falls along the front.

4. First a warm front passes over, bringing rain and warm air, then a cold front passes bringing more rain and cold air.

Frontal Rainfall Diagram

Layers of the Atmosphere

Troposphere

Stratosphere

Mesosphere

Thermosphere

Exosphere

Troposphere

It is the lowest layer of the atmosphere.

Almost all weather occurs in this layer and this is the

layer where planes usually fly.

Starts at Earth’s surface and is around 20km high.

The temperature is about 17ºC

Stratosphere

The second layer of the atmosphere is the stratosphere.

The stratosphere is very dry and so doesn’t contain many clouds.

The stratosphere extends around 50km down to anywhere from 6-20km above the Earth surface

The temperature is about -15ºC at the top of the stratosphere.

Mesosphere

This is the third layer of the atmosphere.

Here different gases mix together and meteors

vapourise.

This layer extends from about 50km to 85km above

the earth’s surface.

The temperature is about -90ºC.

Thermosphere

This is the fourth layer of atmosphere.

Space shuttles orbit in this layer.

It is about 90km to 5,000km above our planet.

Temperatures can reach 500ºC.

Exosphere

This the last layer of our atmosphere.

Here atoms and molecules are released into space.

It is over 5,000km above our planet.

The temperature can reach thousands of Celsius.

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