Observation-based modelling of the energetic storm particle event of 14 July 2012

Aims.We model the energetic storm particle (ESP) event of July 14, 2012 using the energetic particle acceleration and transportmodel named ‘PArticle Radiation Asset Directed at Interplanetary Space Exploration’ (PARADISE), together with the solar wind andcoronal mass ejection (CME) model named ‘EUropean Heliospheric FORcasting Information Asset’ (EUHFORIA). The simulationresults illustrate both the capabilities and limitations of the utilised models. We show that the models capture some essential structuralfeatures of the ESP event; however, for some aspects the simulations and observations diverge. We describe and, to some extent,assess the sources of errors in the modelling chain of EUHFORIA and PARADISE, and discuss how they may be mitigated in thefuture.Methods.The PARADISE model computes energetic particle distributions in the heliosphere by solving the focused transport equa-tion in a stochastic manner. This is done using a background solar wind configuration generated by the ideal MHD module ofEUHFORIA. The CME generating the ESP event is simulated by using the spheromak model of EUHFORIA, which approximatesthe CME by a linear force-free spheroidal magnetic field. In addition, a tool was developed to trace CME-driven shock waves in theEUHFORIA simulation domain. This tool is used in PARADISE to (i) inject 50 keV protons continuously at the CME-driven shockand (ii) include a foreshock and a sheath region, in which the energetic particle parallel mean free path,λ‖, decreases towards theshock wave. The value ofλ‖at the shock wave is estimated from in-situ observations of the ESP event.Results.For energies below∼1 MeV, the simulation results agree well with both the upstream and downstream components of theESP event observed by the Advanced Composition Explorer (ACE). This suggests that these low energy protons are mainly the resultof interplanetary particle acceleration. In the downstream region, the sharp drop in the energetic particle intensities is reproduced atthe entry into the following magnetic cloud, illustrating the importance of a magnetised CME model.

Publication year:2022

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