Dalla, S., Fletcher, L. and Walton, N. A. (2008) Invisible sunspots and rate of solar magnetic flux emergence. Astronomy and Astrophysics, 479 (1). L1-L4. ISSN 0004-6361
- Published Version
Official URL: http://dx.doi.org/10.1051/0004-6361:20078800
We study the visibility of sunspots and its influence on observed values of sunspot region parameters.
We use Virtual Observatory tools provided by AstroGrid to analyse a sample of 6862 sunspot regions. By studying the distributions of locations where sunspots were first and last observed on the solar disk, we derive the visibility function of sunspots, the rate of magnetic flux emergence and the ratio between the durations of growth and decay phases of solar active regions.
We demonstrate that the visibility of small sunspots has a strong centre-to-limb variation, far larger than would be expected from geometrical (projection) effects. This results in a large number of young spots being invisible: 44% of new regions emerging in the west of the Sun go undetected. For sunspot regions that are detected, large differences exist between actual locations and times of flux emergence, and the apparent ones derived from sunspot data. The duration of the growth phase of solar regions has been, up to now, underestimated.
|Uncontrolled Keywords (separate with ;):||sunspots ; Sun: photosphere ; Sun: magnetic fields ; Sun: activity|
|Subjects:||Physical sciences > Physics|
|Schools:||College of Science and Technology > School of Physical Sciences and Computing > Jeremiah Horrocks Institute|
|Deposited By:||Helen Cooper|
|Deposited On:||20 Mar 2012 13:37|
|Last Modified:||17 May 2016 12:29|
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