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Axial tilt angles of sunspot groups
Solar Physics, 1991Digitized Mount Wilson sunspot data from 1917 to 1985 are analyzed to examine tilt angles determined from the area-weighted positions of leading and following sunspots. These spot group tilt angles are examined in relation to other group characteristics to give information which may relate to the formation and evolution of sunspot groups and the ...
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Group Sunspot Numbers: Sunspot Cycle Characteristics
Solar Physics, 2002We examine the "Group" sunspot numbers constructed by Hoyt and Schatten to determine their utility in characterizing the solar activity cycle. We compare smoothed monthly Group Sunspot Numbers to Zurich (International) Sunspot Numbers, 10.7-cm radio flux, and total sunspot area.
David H. Hathaway +2 more
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Solar Physics, 2008
We examine daily records of sunspot group areas (measured in millionths of a solar hemisphere or μHem) for the last 130 years to determine the rate of decay of sunspot group areas. We exclude observations of groups when they are more than 60° in longitude from the central meridian and only include data when at least three days of observations are ...
David H. Hathaway, Debi Prasad Choudhary
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We examine daily records of sunspot group areas (measured in millionths of a solar hemisphere or μHem) for the last 130 years to determine the rate of decay of sunspot group areas. We exclude observations of groups when they are more than 60° in longitude from the central meridian and only include data when at least three days of observations are ...
David H. Hathaway, Debi Prasad Choudhary
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Positions of sunspot groups and solar rotation
Solar Physics, 1981The question is studied whether the one-year solar oscillation found by V. F. Chistyakov for the years 1965–1973 can be traced in the observations of sunspots of 1874–1971 published by Greenwich Observatory. The result is negative. But the study leads to the following two conclusions: (1) The average observable centres of gravity of spot groups are ...
Jaakko Tuominen, Juhani Kyröläinen
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Velocity Oscillations in Active Sunspot Groups
Solar Physics, 1998Time series of two-dimensional spectra were taken with the Gottingen 2D spectrometer at the VTT on Tenerife in 1996. They were investigated for Doppler velocities and velocity oscillations in small spots and pores of rapidly evolving sunspot groups. For the present measurements the magnetically insensitive lines Fe i 557.6 nm and Fe i 709.0 nm were ...
Balthasar, Horst +3 more
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Proper motions of sunspot groups
Hvar Observatory bulletin, 2003.
Ruždjak, Vladimir, Brajša, Roman
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The classification of sunspot groups
Solar Physics, 1990The 3-component McIntosh classification of sunspots was introduced in 1966, adopted for interchange and publication of data in 1969, and has been used increasingly in recent years. The McIntosh classification uses a modified Zurich evolutionary sequence as its first component, class, where two of the Zurich classes are omitted and more quantitative ...
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Common evolution of adjacent sunspot groups
Solar Physics, 1993The evolution of two adjacent bipolar sunspot groups is studied using Debrecen full-disc, white-light photoheliograms and Hα filtergrams as well as Meudon magnetograms. The proper motions of the principal preceding spots of both groups show quite similar patterns; the spots move along almost parallel tracks and change the direction of their motion on ...
L. van Driel-Gesztelyi +6 more
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On the dissolution of sunspot groups
Solar Physics, 1982The behavior of magnetic fluxes from active regions is investigated for times near sunspot disappearance. It is found that the magnetic fluxes decrease on or near the date the spot vanishes. This effect is investigated and it is concluded that it is actually due to changes in the field, rather than through dissipation of the active region fields.
StevenG. Wallenhorst, Robert Howard
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Flare forecasting based on sunspot-groups characteristics
Acta Geophysica, 2008Our comprehension of solar flares is still lacking in many aspects and the possibility of observing active regions during the first phases of flare occurrence is limited by our capability of doing accurate flare forecasting. In order to give a contribution to this aspect, we focused our attention on the characteristics that must be fulfilled by sunspot-
CONTARINO L +5 more
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