Title: Towards the understanding of coronal hole occurrence during the Schwabe cycle
Authors: M. Storini, M.Y. Hofer, J. Sykora
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Description: The search for substructures in the latitude/time distribution of long-lived isolated coronal holes (age > 5 Carrington rotations) during sunspot cycles 21 and 22 reveals that they are organized into two populations: (i) class-I, occurring around the maximum phase of the solar activity, made up by long-lived holes of both magnetic field polarities and lying on a medium-term (time extent: 2-4 years) diagonal area, from middle heliographic latitudes towards the equator and beyond; (ii) class-II, characterized by long-lived holes having a high probability to occur on a long-term ( ~18 years, i.e. lasting for more than a solar activity cycle) diagonal region, one for each magnetic field polarity. Moreover, the slopes and the lengths of the diagonals for the class-I holes are different for the two cycles analysed, while the ones for the class-II are similar. While clues for class-I existence were found in the past, class-II identification based on the CH magnetic field polarity is made here for the first time. The discussion points out implications for the odd-even Schwabe cycle pairs.
Reference: Advances in Space Research 38 (2006), 912-920
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Date and Time: 18.6. 2018 21:43:35 CEST
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