Differences in the temporal variations of solar UV flux, 10.7‐cm solar radio flux, sunspot number, and Ca‐K plage data caused by solar rotation and active region evolution

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Abstract
Two types of temporal variations in the solar UV spectral irradiance, caused by solar rotation and active region evolution, are presented and discussed. These particular UV variations differ markedly from the concurrent variations in the 10.7‐cm radio flux and sunspot number. The temporal variations of the modeled UV flux based on Ca‐K plage data are similar to the observed UV flux. The first type of dissimilar temporal behavior occurs when concentrations of solar active regions evolve at solar longitudes nearly 180° apart. Both the UV observations and modeled UV fluxes based on Ca‐K plage data then show strong 13‐day periodicity, while the 10.7‐cm solar radio flux and sunspot number exhibit quite dissimilar temporal variations. This type of dissimilarity is related to the modeled UV flux, having a dependence on the solar central meridian distance that is narrower than that for the 10.7‐cm radio flux or for sunspot numbers. A second case of marked dissimilarity occurs when major new solar active regions arise and dominate the full‐disk fluxes for several rotations. The strongest peaks in 10.7 cm and sunspot numbers tend to occur on their first rotation, for example, during major dips in the total solar irradiance, while the Ca‐K plages and UV enhancements peak on the next rotation and then decay more slowly on subsequent rotations. This type of dissimilarity is related to major active regions having a more rapid growth, peak and decay of sunspots, their strong magnetic fields and related coronal radio emission at centimeter wavelengths than for the Ca‐K plages and their related UV enhancements.

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