What phenomenon increases in correlation with the appearance of sunspots?

The correct choice highlights the relationship between sunspots and solar radiation. Sunspots are dark spots on the Sun's surface, associated with magnetic activity. When the number of sunspots increases, it often correlates with a rise in solar activity, including solar radiation emitted from the Sun. This increase in solar radiation can enhance various solar phenomena, leading to more pronounced effects in space weather.

In contrast, while magnetic storms may be influenced by solar activity spikes linked to sunspot cycles, they are more directly a result of solar flares and coronal mass ejections, rather than sunspots alone. Similarly, solar wind, which consists of charged particles released from the Sun, can be affected by sunspots but is not as directly correlated with their appearance as solar radiation is. Lastly, space weather encompasses the overall conditions in space influenced by solar activity and is impacted by various factors, including but not limited to sunspot activity. Thus, while there are connections to magnetic storms and space weather, the primary phenomenon that shows a direct correlation with the increase of sunspots is solar radiation.