What is weather? Weather describes the state of the atmosphere at any particular time. Weather can be described in terms of temperature, precipitation (snow, rain & hail), wind speed and direction, visibility and cloud amounts.
What is Climate? Climate describes the average weather of a particular part of the world at different times of the year In Britain we would expect cool summers and mild winters with moderate rainfall throughout the year
The Weather Station A weather station makes continuous measurements of different aspects of the weather. Weather stations use standard instruments so that their readings can be compared.
HOWEVER…You can make weather measurements with equipment a lot cheaper and simpler than the kit shown on the previous slide which is an official Met Office station. Please see www.metlink.org for more information.
Temperature Temperature is recorded using thermometers housed inside a Stevenson screen Weather stations record both air temperature and the temperature of the ground
Temperature: The Stevenson Screen Why is the screen painted white? Why is it raised on legs above the ground? Why has it got louvred sides?
Precipitation Rainfall, snow, hail and fog. Rainfall is measured in a raingauge. Some raingauges record rainfall automatically whilst others are emptied everyday by an observer
Wind The direction and strength of the wind are both measured A wind vane measures direction An anemometer records strength Wind strength can also be measured using the Beaufort Scale
Temperature: Summer &Winter In winter the northern hemisphere is tilted away from the sun so the sun’s rays are weaker In summer the northern hemisphere is tilted towards the sun so the sun’s rays are stronger
Temperature: Summer &Winter During the course of the year the Earth tilts towards and away from the sun The mid-points of this cycle are called the equinoxes (spring and autumn)
Temperature: The Sea The North Atlantic Drift is a warm ocean current originating in the Caribbean It moves across the Atlantic keeping the west of Britain warmer than the east in winter
Rainfall In Britain it rains the most in the west and in mountainous areas Rain is brought across Britain from weather systems called depressions In summer showers result from convection on warm days
How it rains The surface is heated by the sun Air rises Air expands and cools Air condenses Water droplets grow to form raindrops Air can rise in different ways
Cyclonic Rainfall Depressions are areas of low pressure formed when cold and warm air meet The warm air rises above the cold air to form a front There are two types of fronts depending on the way in which the air masses are moving.
Cyclonic Rainfall: Fronts Warm fronts form where warm air moves towards cold air Cold fronts form where cold air moves towards warm air As air rises at fronts both are responsible for rain
Convectional rainfall Common on hot summer days inland Hot air rises quickly and condenses to form cumulonimbus Water freezes at the top of the cloud forming hail Associated with lightning
Fair Weather Fair weather is produced by high pressure High pressure forms anticyclones Air sinks and prevents the formation of rain clouds Anticyclones cause heatwaves in summer and frosty/foggy mornings in winter
Forecasting the Weather Modern forecasts use computers to simulate the likely weather based on careful observations from 100s of weather stations round the world Satellite images and radar give a better picture of the weather over a wide area