Correlations of Sunspot Physical Characteristics during Solar Cycle 23

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Solar Physics
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Valio A.
Spagiari E.
Marengoni M.
Selhorst C.L.
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© 2020, Springer Nature B.V.The behavior of sunspots is governed by the magnetic dynamo acting deep within the convection zone of the Sun. Therefore, knowledge of sunspot physical characteristics and how they evolve in time during a solar cycle can help to improve our understanding of the solar magnetic behavior. This work analyzes the physical characteristics of sunspots during the Solar Activity Cycle 23, detected using computer vision techniques. The main goal is to derive the relationships between sunspot properties. Images in visible light and magnetograms of the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) were used to detect sunspots and to extract their characteristics such as area, intensity (or temperature), and magnetic field magnitude. A total of 32,223 sunspots were analyzed, with longitudes between − 40 ∘ and 40 ∘, throughout the entire Solar Cycle 23, from May 1996 through April 2008. These spots fell mainly into three categories. Most sunspots (85%) did not exhibit a well defined umbra, with average intensities larger than 0.657 relative to disk center, which corresponds to temperatures greater than 5200 K. A second group comprising less than 12% of the spots, was cooler (temperature less than 5200 K) and with more intense magnetic fields (2000 – 4000 G) and mostly presented a well defined umbra. Lastly, only 3% of the spots had large areas and strong magnetic fields with complex umbrae, but intermediate temperatures. The temporal behavior of sunspot physical characteristics throughout the 11 year cycle and the relationships between them were verified. Sunspot physical properties presented variations over time during Solar Cycle 23, such that larger, cooler sunspots with stronger magnetic fields occurred more frequently during periods of maximum activity. Linear correlations were found regarding the logarithm of the area and the intensity with extreme magnetic field, and of the temperature (or intensity) with the area; whereas a quadratic relation was found between magnetic field and temperature of spots.
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