- What makes air heat up?
- Is the air warmer during the day above the sea or land?
- Why is asphalt so hot in summer?
Air temperature and solar radiation
Air temperature is one of the most important weather elements that people observe. Air temperature, and what happens to air particles when air is heated, was discussed in the earlier chapters. But what causes the temperature to change?
In the morning, the sun is low on the horizon. After a few hours, it gets a little higher. At noon, it is at its highest, and then it begins to descend again. The height of the sun in the sky and the air temperature are closely linked. The higher the angle of the sun's rays falling to the ground, meaning the higher the sun appears in the sky, the more radiation is absorbed by the ground, and the warmer the air becomes above it.
The amount of radiation reaching the ground also depends on whether the weather is clear or cloudy. Some solar radiation that passes through the atmosphere is absorbed by clouds and airborne dust, so it does not reach the ground. Some of the solar radiation is reflected from the clouds, dust and ground.
Warm ground heats up the air above it
Most of the radiation coming from the Sun passes through the atmosphere, reaches the surface of the land or water and is absorbed by it. The warmed surfaces, in turn, heat up the air above them.
Land and water warm up differently, the water warms slower, because the waves mix water and take the warm water deeper, and in addition, on a sunny day there is evaporation from the water's surface, which also uses up heat. The land's surface layer heats up fast, and the air above it is usually warmer than above the water surface.
Think!
- Which surface shown in the figure above has the highest temperature in the air? Where is it the lowest? Why?
What heats up faster, land or water?
- Water
- Land
How does it affect the air temperature above the surfaces?
- Above the faster heating surface, the air heats up faster.
- Above the faster heating surface, the air heats up more slowly.
The amount of radiation absorbed depends on the colour of the surface
It is almost impossible to go barefoot on asphalt on a hot summer day. Light-coloured beach sand is better for this because it is warm, but not too hot. That's because the darker colour absorbs more solar radiation. Have you noticed that the air above the asphalt is much hotter than the air above sand? The warmer the item is, the more heat it gives to the surrounding air.
Rising above ground, the air becomes increasingly cool: the air temperature drops by an average of 6°C per kilometre. Therefore, high mountain peaks are covered with snow even where the mountains are hot at the base year-round.
Which surface heats up more, dark asphalt or light beach sand?
- Asphalt
- Beach sand
How does this affect the air temperature above them?
- Above a light surface, the air temperature is higher.
- Above a dark surface, the air temperature is higher.
I now know that…
The height of the sun in the sky determines how much radiation is absorbed by the ground. The air heats up due to the heated surface below it. A darker surface absorbs more solar radiation, which means that the air above it is warmer.
