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SUMMARY:Visibility of magnetic flux emergence on the Sun - Silvia Dalla (U
 niversity of Central Lancashire)
DTSTART:20091123T160000Z
DTEND:20091123T170000Z
UID:TALK19916@talks.cam.ac.uk
CONTACT:Laurène Jouve
DESCRIPTION:The birth of a new spot on the solar disk indicates the emerge
 nce of\nmagnetic flux through the photosphere\, a process which is key to 
 the solar\ncycle. The presence of a sunspot leads to a solar region being 
 assigned an\nactive region number by the NOAA Space Weather Prediction Cen
 ter so that\nits evolution and activity can be tracked. We analysed data f
 rom the Mount\nWilson solar observatory\, by means of Virtual Observatory 
 tools provided\nby Astrogrid\, to obtain statistics of emergences of 6862 
 sunspot regions.\nThe strong East-West asymmetry in the location of new em
 ergences that we\nobtain\, first reported by A.S.D. Maunder\, allows us to
  derive the\nvisibility function of sunspots\, the rate of magnetic flux e
 mergence and\nthe ratio between the average durations of growth and decay 
 phases of\nsolar active regions. We find that the visibility of small suns
 pots has a\nstrong center-to-limb variation\, far larger than would be exp
 ected from\ngeometrical (projection) effects. This results in a large numb
 er of young\nspots being invisible\, with as many as 44% of new regions em
 erging in the\nWest of the Sun going undetected.
LOCATION:MR14\, DAMTP\, Pav. F
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