What does this paragraph mean? Why is the air sinking over the desert and how does it rise with rain systems thousands of kilometers away?
In fact, it has been calculated that the Sahara Desert actually loses more infrared radiation than it gains solar radiation from the sun. This net loss of radiant energy is balanced by the sinking air over the desert, which warms as it is compressed. The air over the desert is, in turn, being forced to sink by rising within rain systems hundreds or thousands of miles away. Thus, in some sense, rain can be considered the cause of deserts(!).
This paragraph is discussing the phenomenon of sinking air over the Sahara Desert and its relationship with rain systems. Let me break it down for you:
The paragraph begins by stating that the Sahara Desert loses more infrared radiation than it gains solar radiation from the sun. This means that the desert is radiating away more energy than it receives from sunlight. This creates a net loss of radiant energy.
To balance this net loss, the air over the desert sinks and becomes compressed. As the air sinks, it warms up due to compression. This warming effect occurs because as the air descends, it encounters increasing pressure, which causes the air molecules to become more tightly packed together. This compression leads to an increase in temperature.
Now, you might be wondering, why does the air over the desert sink in the first place? This is where the second part of the paragraph comes in. The sinking air over the desert is actually being forced to sink by rising air within rain systems that are located hundreds or thousands of miles away.
When rain systems develop, air rises within them, and this upward motion creates a kind of "void" or low-pressure area above the rain systems. Air naturally moves from areas of higher pressure to areas of lower pressure, so the sinking air over the desert flows towards these low-pressure regions created by the rising air in the rain systems.
Therefore, in a way, rain systems can be considered the cause of deserts because they are responsible for creating the sinking air over the desert. The sinking air over the Sahara Desert, in turn, leads to the dry and arid conditions typically found in desert regions.
In summary, the paragraph explains that the air over the Sahara Desert sinks and warms due to compression, which is a result of the desert's net loss of radiant energy. This sinking air is caused by the rising air within rain systems located far away.