S1 Weather and Climate Notes Online version
Weather and climate The weather describes the state of the air around us. It is made up of several components or elements: • • • • • •
temperature precipitation sunshine wind speed wind direction air pressure
how hot or cold it is rain in all its forms (eg snow, hail, sleet) how sunny or cloudy it is how fast the wind is blowing the direction the wind is blowing from the weight of the air on the ground
Temperature changes are usually shown by a line graph. Line graphs are used to show changes over distance or time. Wind speed and air pressure are shown in the same way. Here is a line graph for Glasgow’s temperature:
Daily precipitation is usually shown by a bar graph. A bar graph shows different amounts. Sunshine is shown in the same way. Here is a bar graph for Glasgow’s rainfall:
Wind directions are shown by a wind rose diagram. The length of the arrow tells us how which wind direction is the most frequent.
The climate is the average or typical weather, usually worked out over thirty years. Places in Scotland have a similar climate, but no two places are exactly the same. Climate information can be shown on a climate graph, which is a multiple graph. The temperature is shown by a line. The rainfall is shown with bars Both temperature and rainfall are on the same bar. Here is a climate graph for Loch Ness.
The Climate of the British Isles Rainfall Rainfall is greater in the west of the British Isles than in the east. This is because: • our rain is brought by westerly winds from the Atlantic Ocean. • The west side of Britain is the first to receive these winds and they drop most rain here. • The west side is also wetter because there are uplands here and so they receive extra relief rain. Winter temperatures The west is milder in winter because • it is beside the Atlantic Ocean, which cools down slowly and so is warmer than the land. • Also a warm current of water, called the North Atlantic Drift, washes along the west coast. Winds blowing over the warm ocean and the warm ocean current bring warmer weather to the west side of Britain. Summer temperatures The west is cooler in summer because • it is beside the Atlantic Ocean • This heats up slowly and so is cooler than the land. Places further south are warmer than places in the north because • the midday sun is at a higher angle in the sky. This means the Sun’s rays are concentrated on a smaller area, which makes the land hotter.
In winter and summer temperatures are lower in hilly areas. Temperatures fall by 1 degree Celsius for every 100 metres in height. Example: The temperature at the top of Ben Nevis is 13 degrees colder than the town of Fort William below it. Look how cold the mountain areas are
Causes of rainfall For rain to fall, air must rise. • When air rises, it cools. • The water vapour in the air condenses into water droplets which form clouds. • The droplets become larger until they are heavy enough to fall as rain. There are three reasons why air rises. 1. relief rain This type of rain occurs when air rises to go over mountains. The rain falls on the windward side of the mountain, which is the west side in Britain. As the air descends on the other side of the mountain, the winds become warmer and so bring less rain. This is called a rain-shadow area. Eastern Scotland is an example of a rain-shadow area.
2. convectional rain This type of rain occurs when air rises because it is hot. Air is heated from the land below it. The air in contact with the land heats up and becomes less dense. The air then rises as convection currents. This type of rain is often accompanied by thunder and lightning.
3. frontal rain This type of rain occurs when warm and cold air meet. Where they meet is called a front. Cold and warm air do not mix. The warm air is less dense and rises over the heavier, cold air. As the warm air rises, it cools, the water vapour condenses, clouds form and frontal rain falls.
Air Pressure
Air pressure is the weight of the air on the land below. Sometimes the air pressure is high. This is when the air is descending. It brings dry, calm weather. An area of high pressure is called an anticyclone. At other times, the air pressure is low. This happens when the air is rising. Because it is rising, this often leads to rainfall. Low pressure is associated with wet weather. An area of low pressure which moves is called a depression.
Dry Clear skies Sunny Cold and frosty in winter Warm in summer
Wet Cloudy skies Dull cold damp in winter cool, summer storms
Check point I can draw a temperature graph I can draw a rainfall graph I can draw a wind rose I can take information from a temperature graph I can take information from a rainfall graph I can take information from a wind rose I can give reasons why rainfall is greater in the west I can give reasons why temperature is warmer in the south I can give reasons why the tops of mountains are colder I can describe convectional rain I can describe frontal rain I can describe relief rain I can describe the weather in an anticyclone ( high) I can describe the weather in a cyclone ( depression) I can give reason for global warming I can explain the phrase “global warming� I can give at least three effects of global warming I can suggest at least three solutions to global warming