Answer:
The given blank can be filled with sunspots.
Step-by-step explanation:
The solar radiation, which reaches the surface of the Earth is known as insolation. It is determined by the concentration of solar energy reaching per square centimeter in a minute. The concentration of the solar radiation reaching the surface of the Earth can be affected by the sunspots.
Sunspots refer to the temporary process taking place on the photosphere of the Sun, which seems as darker spots in comparison to the surrounding regions. The maximum sunspot activity is related to a very slight upsurge in the energy output from the Sun. There will be a dramatic elevation in the ultraviolet radiation at the time of high sunspot activity that can exhibit a huge influence on the atmosphere of the Earth. The reverse is true at the time of least sunspot activity.