J/ApJ/908/5ivo://CDS.VizieR/J/ApJ/908/5doi:10.26093/cds/vizier.19080005CDSBelov A.Papaioannou A.Abunina M.Dumbovic M.Richardson I.G.,Heber B.Kuhl P.Herbst K.Anastasiadis A.Vourlidas A.Eroshenko E.,Abunin A.2022-09-05T14:09:51Z2022-07-07T09:33:11ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsolar-systemthe-sunThe rigidity dependence of all Forbush Decreases (FDs) recorded from 1995 to 2015 has been determined using neutron monitor (NM) and Solar and Heliospheric Observatory (SOHO) (EPHIN) spacecraft data, covering the energy (rigidity) range from ~433MeV (1GV) to 9.10GeV (10GV). We analyzed a total of 421 events and determined the spectrum in rigidity with an inverse power-law fit. As a result, the mean spectral index was identified to be <{gamma}F>=0.46{+/-}0.02. The majority (~66%) of the FDs have {gamma}F within the range 0.3-0.7. The remaining one-third of the events (~33%) have either (very) soft or hard FD spectra, with the latter being more common than the former. Significant variations of {gamma}F occur within almost every FD event. During the initial FD decay phase the spectrum becomes gradually harder, in contrast to the recovery phase, when it becomes softer. Additionally, low energies (rigidities) seem to be better suited for studying the fine structure of interplanetary disturbances (primarily interplanetary coronal mass ejections) that lead to FDs. In particular, FDs recorded by the EPHIN instrument on SOHO better capture a two-step structure than FDs observed by NMs. Finally, the ejecta of an ICME, especially when identified as a magnetic cloud, often leads to abrupt changes in the slope of {gamma}F.2021ApJ...908....5Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/908/5CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/ApJ/896/133 : 2001-2019 ICME associate Forbush decrease events (Light+, 2020)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/908/5https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/908/5http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/908/5https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/908/5https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/908/5http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/908/5GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/ApJ/908/5/table1The list of Forbush Decreases recorded at EPHIN onboard SOHO from 1995 to 2015recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNumID[1/421] Event numbermeta.id;meta.mainintDate[1995/2015] Event date; yeartime.epochTimeForbush decrease onset time; hh:mmtime.epochcharAS[0.6/16.8] Forbush decrease amplitude by EPHIN%phot.mag;arith.ratiofloatAE[0.3/9] Forbush decrease magnitude by neutron monitors%phot.magfloatgammaF[-0.68/1.26] Mean spectral indexspect.indexfloate_gammaF[0.03/0.7] Uncertainty in gammaFstat.errorfloatTypeStructure type; Corotating Interaction Regions and/or Interplanetary Coronal Mass Ejectionsmeta.notecharEPHIN[0/1] A two-step Forbush decrease from EPHIN? 0=No, 1=Yesmeta.codeintNMs[0/1] A two-step Forbush decrease from NMs? 0=No, 1=Yesmeta.codeint