Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011apj...734...64s&link_type=abstract
The Astrophysical Journal, Volume 734, Issue 1, article id. 64 (2011).
Astronomy and Astrophysics
Astronomy
Sun: Activity, Sun: Faculae, Plages, Sun: General, Sun: Radio Radiation
Scientific paper
The current solar minimum has surprised the entire solar community because the spotless period is presently almost 2-3 years longer than the usual minima. To better understand this, we studied the variation of the solar radius and the polar limb brightening at 17 GHz, comparing the results from the minimum at the end of cycle XXIII with those of the previous one. Daily maps obtained by the Nobeyama Radioheliograph (NoRH) from 1992 through 2010 were analyzed. Whereas the variation of the solar radius at radio frequencies indicates the heating of the solar atmosphere due to solar activity, the limb brightening intensity depends on the organization of the polar magnetic field of the Sun, including the global dipole and the features formed around it. These features are more prominent during minima periods. As a common result, researchers have observed a decrease in both radius and limb brightness intensity at 17 GHz during the present minimum when compared with the previous one. The mean solar radius is 0farcs9 ± 0farcs6 smaller and the limb brightening reduced its intensity by around 20%. Both decrements are interpreted in terms of the weaker solar chromospheric activity of the present cycle. Measurement of the radius and limb brightening at 17 GHz can be used as an alternative solar activity index and should be included in the set of parameters used to predict future cycles.
Costa Joaquim E. Rezende
Guillermo Gimenez de Castro Carlos
Selhorst Caius L.
Shibasaki Kazuo
Valio Adriana
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