Download Geography Knowledge Map: Year 9: Weather and Climate

Geography Knowledge Map: Year 9: Weather and Climate
What causes weather?
There are 2 main causes of weather.
 The Sun
 Water Vapour
The sun is the most important one.
1. The sun heats the Earth. But it does this unevenly as the Earth is
round. So the North and South Pole do no warm up too much.
2. The Earth heats the air, so the air also warms unevenly. Warm air
rises; colder air comes in to replace it as wind.
3. The sun also warms the oceans. This causes evaporation, creating
water vapour – the 2nd cause of weather.
4. Water vapour condenses to form clouds; these are made up of tiny
water droplets.
5. Droplets join together making them heavier, they then fall from the
sky as rain.
6. If the air is very cold these droplets may fall as snow, sleet or hail
instead.
7. Water vapour may also condense lower down in the air; it may
condense around us forming fog.
8. Or it may hang in the air as mist, or condense on cold grass as dew.
Rain and clouds.
There are 3 types of rainfall.
 Convectional rainfall – Air rises because the ground heats it. The air
rises as currents of warm air. We call these convection currents, so
we call the rain convectional rainfall.
 Relief rainfall – Wind is moving air, when the wind meets a line of
high hills or mountains, the wind has to travel upwards. So the air
rises and cools, creating rain. We call this relief rainfall.
 Frontal rainfall – Huge blocks of air called air masses move around
the Earth. When a warm air mass meets a cold one, the warm air is
forced to rise. This causes condensation and we get frontal rainfall.
From weather to climate.
Factors that influence climate.
Weather – the state of the atmosphere at a given time. Weather can change from
hour to hour and day to day.
Climate – the average weather in a place, it tells you what the weather is usually
like in any given month.
The climate varies in the UK. We can divide the country up into 4 climate zones.
Why does weather change?
Some parts of the Earth ae hot, some are cold. This causes the air to
move around. Warm air always moves from a warm place to a cold one,
this pushes cold air back towards the warmer place.
There are also 3 types of clouds.



Cumulus – result of warm air rising really fast. For example when
the ground heats the air really quickly on a hot day.
Stratus – result of air rising more slowly, over a wide area. For
example when a warm air mass slides up and over a colder one.
Cirrus – an early sign that a warm front is approaching.
The air moves in huge blocks called air masses. Air masses can be warm,
cold, damp or dry depending on where it came from.
Cold + Dry – Air mass comes from the North Pole.
Warm + Damp – Air mass comes from a warm ocean.
Climates around the world.
1. Latitude (how far away a place is from the equator) – The further
away the cooler it is. That’s because the Earth is curved. The poles
receive very little heat from the sun; the equator receives a lot of
heat from the sun. That is why the equator is always hot and poles
are always cold.
2. The Earth’s tilt – The Earth travels nonstop around the Sun and it
tilts as it travels. It is this tilt that means climate can be different in
different months. It is the tilt that gives us our seasons. In June the
northern hemisphere is tilted towards the sun, so we have summer
but in December the northern hemisphere is tilted away so we have
winter.
3. Distance from the sea – The Sea is cooler than the land in summer
and warmer in winter. So a sea breeze keeps the coast cool in
summer and warmer in winter.
The climate is changing; the Earth is getting warmer – as you should
remember from our climate change unit!
50 years from now, a world climate map could look very different, since
the Earth is getting warmer. Places that are now dry could become very
wet and vice versa.