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SUMMARY:Coronal voids and their magnetic nature
DTSTART;VALUE=DATE-TIME:20230509T080000Z
DTEND;VALUE=DATE-TIME:20230509T081500Z
DTSTAMP;VALUE=DATE-TIME:20240704T115653Z
UID:indico-contribution-311@meetings.aip.de
DESCRIPTION:Speakers: Jonathan David Nölke (Max Planck Institute for Sola
 r System Research)\nExtreme ultraviolet (EUV) observations of the quiet su
 n corona have revealed extended regions of reduced emission. These coronal
  voids are on average around 30% less intense than the quiet Sun and can h
 ave sizes corresponding to several supergranular cells. At least the large
 r of these voids can exist for many hours with their boundaries to the qui
 et Sun remaining more or less unchanged. The aim of our study is to unders
 tand what causes the reduced emission through an investigation of the unde
 rlying magnetic features in the photopshere. \n\nAt least two scenarios co
 uld explain why the voids appear dark: \n(1) The coronal voids could be ma
 gnetic structures that are (locally) open similar to coronal holes and app
 ear dark for the same reason as those do. (2) they could also be areas of 
 lower (magnetic) heating due to lower magnetic field strength in the photo
 sphere below\, when compared to the typical quiet Sun.\n\nTo distinguish b
 etween the two scenarios\, we combine quiet Sun data from the high-resolut
 ion EUV-channel at 17.4 nm of the Extreme Ultraviolet Imager (EUI)\, showi
 ng coronal plasma close to 1 MK\, and magnetograms obtained with the high-
 resolution telescope of the Polarimetric and Helioseismic Imager (PHI)\, b
 oth onboard Solar Orbiter. \n\nOur results show the average unsigned magne
 tic field inside the voids to be reduced by $\\sim$ 25% with respect to th
 e entire observed quiet Sun region. Specifically\, there is little or no n
 etwork structure visible inside the coronal voids. Observed flux imbalance
 s are within the range of flux imbalances found in quiet Sun areas of simi
 lar size. Hence\, the flux imbalances we find in the voids are not signifi
 cant. Consequently\, it is highly unlikely that these voids are true minia
 ture versions of coronal holes.\nInstead\, we find that in general the uns
 igned magnetic flux in the photosphere below the voids is significantly sm
 aller than in the quiet Sun\, and the vast majority of stronger magnetic p
 atches is located outside the voids. The weaker photospheric field below t
 he voids will produce a Poynting flux smaller than in the surrounding quie
 t Sun. Consequently\, the coronal part above will be heated less and the v
 oids will appear darker in coronal emission.\n\nWe started a subsequent st
 udy into the temporal evolution of coronal voids on time scales from hours
  to several days. Our initial results for a time scale of a few hours indi
 cate that at least larger structures persist\, and their outer boundaries 
 remain mostly unchanged during this time.\n\nhttps://meetings.aip.de/event
 /24/contributions/311/
LOCATION:Haus H\, Telegrafenberg
URL:https://meetings.aip.de/event/24/contributions/311/
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