The Solar Microwave Flux and the Sunspot Number

2010/03/22 by Leif Svalgaard, H. S. Hudson, Svalgaard, Leif +1
Earth and Planetary Sciences · Physics and Astronomy · #FOS: Physical sciences #Geophysics and Gravity Measurements #Solar and Space Plasma Dynamics #Solar and Stellar Astrophysics (astro-ph.SR)

paper · pdf · doi:10.48550/arxiv.1003.4281

openalex publication_date 2010/03/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

The solar F10.7 index is has been a reliable and sensitive activity index since 1947. As with other indices, it has been showing unusual behavior in the Cycle 23/24 minimum. The origins of the solar microwave flux lie in a variety of features, and in two main emission mechanisms: free-free and gyroresonance. In past solar cycles F10.7 has correlated well with the sunspot number SSN. We find that this correlation has broken down in Cycle~23, confirming this with Japanese fixed-frequency radiometric microwave data.

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