Comparing observations of closely located JUICE and STEREO-A spacecraft during the widespread 13 May 2024 solar energetic particle event
: Rodríguez-García, L.; Palmerio, E.; Pinto, M.; Dresing, N.; Cohen, C. M. S.; Gómez-Herrero, R.; Gieseler, J.; Santos, F.; Espinosa Lara, F.; Cernuda, I.; Mewes, M.; Vallat, C.; Witasse, O.; Altobelli, N.
Publisher: EDP SCIENCES S A
: 2025
: Astronomy and Astrophysics
: A13
: 701
: 0004-6361
: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202555301
: https://doi.org/10.1051/0004-6361/202555301
: https://research.utu.fi/converis/portal/detail/Publication/500324323
Context. Following its launch in April 2023, JUICE is now in its cruise phase to Jupiter, where it is scheduled to arrive in July 2031. JUICE carries a radiation monitor, namely the RADiation hard Electron Monitor (RADEM) to measure protons, electrons, and ions, detecting particles coming mainly from the anti-Sunwards direction. On 13 May 2024, a large solar energetic particle (SEP) event took place in association with an eruption close to the western limb of the Sun, as seen from Earth. Providentially, at that time, JUICE was located very close to STEREO-A, separated by only 0.13 au in radial distance, 0.3 degrees in latitude, and 1.6 degrees in longitude.
Aims. Our main aims are to characterise the observations within the interplanetary (IP) context whereby SEPs propagated to near-Earth, JUICE, and STEREO-A observers, while performing a first comparison of energetic particle instruments on board JUICE and STEREO-A spacecraft.
Methods. We analysed the IP context using in situ measurements and studied the proton anisotropies measured by near-Earth spacecraft and STEREO-A. We focussed on an isotropic period during the decay phase of the SEP event to compute the proton energy spectrum. We fit the STEREO-A spectrum and compared it to the one measured by SOHO and JUICE.
Results. We find the proton spectral indices measured by JUICE, SOHO, and STEREO-A to be similar. The proton fluxes measured by RADEM are in agreement with those from STEREO-A, with a deviation of less than 25%.
Conclusions. The RADEM instrument aboard JUICE is a valuable tool for measuring SEP events in the heliosphere, providing an excellent opportunity to study and characterise the energetic particle environment in the solar wind between 0.65 and 5.2 au. The intercalibration factors between the fluxes measured by STEREO-A and JUICE at the effective energies of 6.9 MeV, 13.3 MeV, 21.6 MeV, and 31.2 MeV are 1.02, 1.23, 1.12, and 0.95, respectively. We note that these intercalibration factors are valid only until 2024 July 10, when the configuration of the RADEM instrument was changed.
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L.R.-G. acknowledges support through the European Space Agency (ESA) research fellowship programme. L.R.-G. and E.P. acknowledge support from ESA through the Science Faculty – Funding reference ESA-SCI-E-LE-050. E.P. also acknowledges support from NASA’s HGI-O (no. 80NSSC23K0447), LWS (no. 80NSSC19K0067), and LWS-SC (no. 80NSSC22K0893) programmes. N.D. and J.G. acknowledge funding from the European Union’s Horizon Europe research and innovation programme under grant agreement No. 101134999 (SOLER). The paper reflects only the authors’ view and the European Commission is not responsible for any use that may be made of the information it contains. Work in the University of Turku was performed under the umbrella of Finnish Centre of Excellence in Research of Sustainable Space (FORESAIL) funded by the Research Council of Finland (grant No. 352847). N.D. is grateful for support by the Research Council of Finland (SHOCKSEE, grant No. 346902). We also thank the members of the Data Analysis Working Group at the Space Research Laboratory of the University of Turku, Finland for useful discussions. The UAH team acknowledges the financial support of MICIU/AEI/10.13039/501100011033 and FEDER, UE through project PID2023-150952OB-I00. C.M.S.C. acknowledges additional partial funding from NASA grants 80NSSC22K0893, 80NSSC21K1327, 80NSSC20K1815, and 80NSSC19K0067. The authors thank NASA’s Community Coordinated Modeling Center (CCMC; https://ccmc.gsfc.nasa.gov) for supporting the WSA–ENLIL+Cone simulation efforts presented in this work. The WSA model was developed by C. N. Arge (currently at NASA Goddard Space Flight Center) and the ENLIL model was developed by D. Odstrcil (currently at George Mason University). The WSA–ENLIL+Cone simulation run employed in this work can be accessed online at https://ccmc.gsfc.nasa.gov/ungrouped/SH/Helio_main.php (run id: Laura_Rodriguez-Garcia_092424_SH_1).
