Properties of flux tubes and the relation with solar irradiance variability

Abstract. At the solar surface the magnetic field is bundled into discrete elements of concentrated flux, often referred to as magnetic flux tubes, which cover only a small fraction of the solar surface. Flux tubes span a whole spectrum of sizes, ranging from sunspots to features well below the best currently obtainable spatial resolution. Whereas sunspots have been well studied, our knowledge of the true brightness of small-scale magnetic features is hampered by the insuffi-cient spatial resolution of the observations. A better understanding of the thermal and magnetic properties of these small-scale features, however, is crucial for an understanding of (climate-relevant) long-term solar irra-diance variations. Key words. Irradiance—flux tube—sunspot—plage. 1. Solar irradiance variations Space-borne measurements of solar irradiance reveal a remarkably inconstant Sun with variations on time-scales of minutes up to the length of the solar cycle. Mos