Page 221 - PPL-engelsk 2025

Meteorology

Without the greenhouse effect, Earth's temperature would be 20–30°C lower

than it is today!

When the air is dry, the greenhouse effect is small. On clear days, you will notice

the temperature drops rapidly after sunset.

3.3.2.5 Earth's surface temperature

The Earth's surface temperature depends on the nature of the surface. Not all

surfaces are equally good at conducting heat.

For example, rocky areas can store much more heat, while sandy surfaces only

become warm on the surface. This means that, in the evening, after the sun's

radiation has stopped, rocky areas retain heat better than sandy ones. Think

about the large daily temperature differences in the desert: 45°C during the day
and 8°C at night.

Water surfaces are good at absorbing heat. This heat causes movement in the

water, and the warmth is spread over a large area.

The daily temperature variation is less significant in coastal areas compared to

inland areas.

On the illustration next page, you can see how different surfaces retain heat.

You can also observe the impact of surface temperature on the air above it.

From warm surfaces, air rises because warm air expands. The air cools at higher

altitudes and forms tiny water droplets that combine to form clouds. The clouds

created by this convection (rising warm air) are vertically developed clouds,

called cumulus clouds.

Over cold areas, the air sinks. Where air sinks, the temperature increases

because pressure increases. This results in a decrease in the air’s relative

humidity, and no clouds form.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 221