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SUMMARY:Globally Non-Simultaneous Forbush Decrease Events
DTSTART;VALUE=DATE-TIME:20070704T194500Z
DTEND;VALUE=DATE-TIME:20070704T194500Z
DTSTAMP;VALUE=DATE-TIME:20260607T170118Z
UID:indico-contribution-804@cern.ch
DESCRIPTION:Speakers: Dr. OH\, Su Yeon (Department of Astronomy and Space 
 Science\, Chungnam National University)\nIt is generally believed that For
 bush Decrease (FD) events happen \nsimultaneously over the globe of the Ea
 rth. However\, there have been reports \non non-simultaneous FD events. We
  investigate the properties of non-\nsimultaneous FD events in order to de
 termine what solar wind conditions lead \nto global simultaneity of FD eve
 nts. \n\n  We examined the hourly data of the Oulu Neutron Monitor (NM) st
 ation from \n1998 to 2006. We have selected FD events that have greater th
 an 3.5 % \nintensity reductions. Global simultaneity was determined by com
 paring the time \nprofiles of these FD events with those recorded by other
  NM stations at Inuvik \nand Magadan. These three NM stations are located 
 at approximately the same \nhigh latitude\, but fairly evenly spaced in lo
 ngitudes.\n\n  Most FD event onsets are observed simultaneously by each NM
  station in \nuniversal time (UT) regardless of the location of the statio
 n\, whereas some \nother FD events are not simultaneously detected\, but a
 t similar local times (LT). \nThe stronger FD events tend to be simultaneo
 us events\, but the weaker FD \nevents non-simultaneous. The latter occurs
  only if the main phase of the FD is \nsuperposed in phase with the declin
 ing phase of diurnal variation\, which has \nthe maximum around noon and t
 he minimum around midnight. The \nsimultaneous FD events might occur when 
 the high speed strong magnetic \nbarrier (IP shock sheath and MC) overtake
 s the Earth\, whereas the non-\nsimultaneous FD events might occur only wh
 en the slow moving weak magnetic \nbarrier passes by on the dusk side of t
 he Earth. The global simultaneity of FD \nevents depends on speed and IMF 
 strength of solar wind overtaking Earth's \nmagnetosphere and its propagat
 ion direction. This model of FD simultaneity can \nbe tested by the STEREO
  mission.\n\nhttps://indico.nucleares.unam.mx/event/4/session/8/contributi
 on/804
LOCATION:Merida\, Mexico Regency (Hyatt)
URL:https://indico.nucleares.unam.mx/event/4/session/8/contribution/804
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