Category Science

As the Earth spins on its axis, it orbits about the Sun. This means that at different times of year, different parts of the world directly face the Sun in the middle of the day. In January, places about 2,000 kilometres south of the equator have the hottest weather. In July, the hottest weather is about 2,000 kilometres north of the equator. This means that the warmest season in the northern parts of the world is during July and in the southern part during January.

Many climates further away from the equator have four seasons. The weather in winter is often too cold for most plants to grow, and there is a good deal of frost. In summer and winter the weather is often stable for longer periods of time. The weather in spring and autumn often changes from day to day, with high winds and sudden showers. The main season of growth is spring.

As the hottest regions change, the directions of winds and positions of fronts change around the world. These winds and fronts affect rainfall, and so some regions have distinct rainy and dry seasons. In India, for example, there is a very rainy summer season, called the wet ‘monsoon’, but little or no rain from December to April.

The wet monsoon often causes flooding.

Around the world, weather stations record the type of weather every day – they monitor the temperature continuously, the amount of rainfall and the hours of sunshine. Air pressure, which affects the weather, is also recorded. Measuring the ‘humidity’, or amount of moisture in the air, helps to predict clouds, fog or rain.

Satellites can be used in long-range weather forecasting – predicting the weather for a period of weeks. They orbit the Earth photographing it and recording weather patterns. Information sent back to the Earth could include warnings of a fast-developing storm in the tropics, or of a sudden snow melt in a mountainous region.

Recording sunshine

A sunshine recorder uses a large round lens to focus the Sun’s rays and burn a mark onto a piece of card. As the Sun moves across the sky, the burn mark leaves a trail showing how long the Sun has been shining.

The weather satellite Tiros orbits the Earth recording the weather.

Most people like to know in advance what the weather will be like. Weather forecasters often look for signs of fronts approaching – as a warm front approaches, the air pressure decreases and as a cold front approaches the air pressure increases. These changes in pressure often bring rain. A steady area of high pressure often says we can expect dry weather, cold in winter, warm in summer. Professional weather forecasters may use radar to watch how the clouds are moving. Information can also be processed by a computer to show, for example, temperature differences.

Satellite images can show a storm developing.

Pine cones are also a tool for the amateur weather forecaster. When the air is moist, just before rainfall, pine cones close their scales. In dry weather, the scales open again.

Many well-known sayings help amateur weather forecasters to predict the weather. “Red sky at night, shepherds delight”, says that a red sunset will bring dry and warm weather.

The fluffy, white clouds you see on fine, summer days are called ‘cumulus’ clouds. When these rise up to form dark ‘cumulo-nimbus’ thunderclouds, there is a good chance of a heavy shower or a thunderstorm.

‘Cirrus’ clouds are the thin, wispy clouds you sometimes see very high in the sky on dry days. They usually mean a front is arriving, so you can expect the weather to change. As a front moves nearer, the cloud gets lower, turning into ‘alto-stratus’ or small ‘alto-cumulus’. Tall heaps of alto-cumulus means there may be a storm. Lower down, grey ‘nimbo-stratus’ clouds often cause continuous rain. ‘Stratus’ clouds form as a low sheet and often cause fog.