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Published July 2017 | Published
Journal Article Open

Modeling solar energetic particle events using ENLIL heliosphere simulations


Solar energetic particle (SEP) event modeling has gained renewed attention in part because of the availability of a decade of multipoint measurements from STEREO and L1 spacecraft at 1 AU. These observations are coupled with improving simulations of the geometry and strength of heliospheric shocks obtained by using coronagraph images to send erupted material into realistic solar wind backgrounds. The STEREO and ACE measurements in particular have highlighted the sometimes surprisingly widespread nature of SEP events. It is thus an opportune time for testing SEP models, which typically focus on protons ~1–100 MeV, toward both physical insight to these observations and potentially useful space radiation environment forecasting tools. Some approaches emphasize the concept of particle acceleration and propagation from close to the Sun, while others emphasize the local field line connection to a traveling, evolving shock source. Among the latter is the previously introduced SEPMOD treatment, based on the widely accessible and well-exercised WSA-ENLIL-cone model. SEPMOD produces SEP proton time profiles at any location within the ENLIL domain. Here we demonstrate a SEPMOD version that accommodates multiple, concurrent shock sources occurring over periods of several weeks. The results illustrate the importance of considering longer-duration time periods and multiple CME contributions in analyzing, modeling, and forecasting SEP events.

Additional Information

© 2017 American Geophysical Union. Received 2 MAR 2017. Accepted 17 JUN 2017. Accepted article online 21 JUN 2017. Published online 28 JUL 2017. The authors are grateful to the staff of the CCMC for their contributions to deriving the ENLIL cone model parameters, to the SOHO LASCO and STEREO SECCHI investigators for the coronagraph images used, to the GONG Observatory for providing the magnetic synoptic maps used for the ambient solar wind description, to the ACE and STEREO plasma investigation teams for providing 1 AU ENLIL validation data shown here, to the ACE EPAM and GOES EPS Instrument and data providers, and to the MAVEN and Venus Express projects for providing data for the planetary site SEP event model comparisons. This work was supported in part by NASA grant NNX15AG09G to the University of California, Berkeley for the STEREO-IMPACT investigation and by NASA grant NNX15AUo1G to the University of New Hampshire for the STEREO PLASTIC investigation. The model development at UC Berkeley is sponsored by the NSF Award 1322826 through the Living With a Star Program in cooperation with NASA. M.L.M., H.B., and Y.L. acknowledge the support of NASA LWS grant NNX15AB80G. WSA-ENLIL+Cone simulation results have been provided by the Community Coordinated Modeling Center at the Goddard Space Flight Center through their public Runs on Request system (http://ccmc.gsfc.nasa.gov; run numbers Leila_Mays_033115_SH_1, Leila_Mays_052715_SH_1, Leila_Mays_122116_SH_1, Leila_Mays_122116_SH_2). The WSA model was developed by N. Arge at AFRL, and the ENLIL Model was developed by D. Odstrcil at GMU. The ACE EPAM data were obtained via the CDAWeb portal of the Space Physics Data Facility at GSFC (https: spdf.gsfc.nasa.gov), and the GOES data were obtained from the OMNIweb portal (https://omniweb.sci.gsfc.nasa.gov/ftpbrowser/). MAVEN SEP data are available through the Planetary Data System PPI node (http://pds-ppi.igpp.ucla.edu). Venus Express ASPERA-4 background data were provided through personal communication, courtesy of Y. Futaana at IRF in Kiruna (futaana@irf.se).

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August 21, 2023
October 17, 2023