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@Article{RoussosKDKPEMK:2019:CoCaOb,
               author = "Roussos, Elias and Krupp, Norbert and Dialynas, Konstantinos and 
                         Kollmann, Peter and Paranicas, Christopher and Echer, Ezequiel and 
                         Mitchell, Donald G. and Krimigis, Stamatios M.",
          affiliation = "{Max Planck Institute for Solar System Research} and {Max Planck 
                         Institute for Solar System Research} and Office of Space Research 
                         and Technology, Academy of Athens and {Johns Hopkins University 
                         Applied Physics Laboratory} and {Johns Hopkins University Applied 
                         Physics Laboratory} and {Instituto Nacional de Pesquisas Espaciais 
                         (INPE)} and {Johns Hopkins University Applied Physics Laboratory} 
                         and Office of Space Research and Technology, Academy of Athens",
                title = "Jovian cosmic-ray protons in the heliosphere: constraints by 
                         cassini observations",
              journal = "Astrophysical Journal",
                 year = "2019",
               volume = "871",
               number = "2",
                pages = "e223",
                month = "Feb.",
             keywords = "cosmic rays, planets and satellites: gaseous planets, Sun: 
                         heliosphere.",
             abstract = "Measurements of >82 MeV Galactic cosmic-ray (GCR) protons at Earth 
                         indicate that they may be mixed with protons that leak into the 
                         heliosphere from Jupiter's magnetosphere (Jovian cosmic-ray 
                         protons (JCRPs)). A similar to 400 day periodicity in these proton 
                         fluxes, which is similar to the synodic period between Jupiter and 
                         Earth, and an excess proton flux observed when Jupiter and Earth 
                         can be connected through the interplanetary magnetic field were 
                         the basis for this claim. Using nearly 13 yr of GCR measurements 
                         at Saturn with Cassini's Magnetosphere Imaging Instrument, we show 
                         that the similar to 400 day periodicity is also present in greater 
                         than or similar to 100 MeV protons at similar to 9.6 au, although 
                         the synodic period between Saturn and Jupiter is similar to 20 yr. 
                         We also find that the features responsible for this periodicity 
                         were convected from 1 au to Saturn's distance with the solar wind 
                         velocity. Their origin is therefore heliospheric, not Jovian. We 
                         attribute these features to quasi-biennial oscillations, observed 
                         in the solar magnetic field and various heliospheric indices. This 
                         finding indicates that fluxes of JCRPs at 1 au, if present, are 
                         considerably overestimated, because the signal originally 
                         attributed to them represents the amplitude of the similar to 400 
                         day periodic GCR oscillation. This oscillation has to be 
                         subtracted before the resulting proton GCR flux residuals are 
                         analyzed in the context of a possible Jovian source. A 
                         confirmation of the presence of JCRPs over extended regions in the 
                         heliosphere and a constraint on their fractional abundance in GCR 
                         spectra may therefore require further validation and analysis, and 
                         several options are proposed for this purpose.",
                  doi = "10.3847/1538-4357/aafb2f",
                  url = "http://dx.doi.org/10.3847/1538-4357/aafb2f",
                 issn = "0004-637X and 1538-4357",
             language = "en",
           targetfile = "roussos_jovian.pdf",
        urlaccessdate = "05 dez. 2020"
}


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