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SEPMOD (v2.20221228)

SEP Model

Model Description

SEPMOD was developed as part of the coupled Sun-to-Earth space weather model system created under CISM (Center for Integrated Space weather Modeling) -and NSF STC led by BU (Dir., J. Hughes, see JASTP v66,2004). 

SEPMOD is a Fortran code that computes time series of SEP (Solar Energetic Particle) fluxes at a specified location in the energy range from a few MeV to 100 MeV using results from an MHD heliospheric simulation describing the prevailing interplanetary shocks and magnetic fields. These can be directly compared to observations or used for forecasting/prediction or other conceptual analyses.

SEPMOD version 1 is designed to work with output from WSA-ENLIL-cone models as a postprocessing option. Special ENLIL output files are required that can be requested. These output files consist of aa sequence of observer-connected field lines, and a file containing information on a particular ICME shock identified on the field lines. The cadence of ENLIL 'snapshots' used by SEPMOD is about 6 minutes.Note that the special ENLIL output contains one shock file for every cone model CME injected in the run. (e.g. Separate shock files for each ICME.) Other heliospheric models can be used if similar output files are generated.

This SEPMOD version (2) is currently designed to compute SEP information for one observer location at a time, and generates output files containing simulated particle flux time profiles at specific energies and energy-time spectrograms. Note that t=0 of the time profile is the time of the first ENLIL fieldline snapshot used.

SEPMOD is based on a field line tracer and adiabatic invariant conservation (see Luhmann et al., JASR, 2006, 2010). It was originally setup with (non-relativistic) protons 10-100 MeV in mind. Energy conservation is assumed following injection at the source. Thus specified injection energies are the energies of the calculated SEP flux time series. The current version allows 9 energies to be specified. A range of default energies is based on IMP-8 detector channels.  This version expands this range to GOES-like detector channels up to 1000 MeV with relativistic protons.  The model contains a flare source addition option but this is not yet available for CCMC Runs on Request. 

The current approach assumes parallel (to the field) propagation and scatter-free transport along the observer field line.

SEPMOD version 1 assumes a single shock source at a time. It allows contributions from multiple shock sources through superposition(addition) of the flux time series from single shock source runs using the same observer field lines but different ENLIL shock files. There is no secondary shock acceleration from multiple shock passages. Seed particles are present only in the sense of background from earlier or other shock injections occurring around the same time.  

The currently assumed shock source energy *spectrum* is a power law based on the Jones-Ellison formula for diffusive shock acceleration.The spectrum power exponent (gamma) depends on the ENLIL shock (density)compression at the observer shock connection location. The injected *flux* is based on a shock-velocity dependent empirical formula derived by Lario et al. (1995). The shock injections are nominally isotropic and are delta functions in time.

An ESP (Energetic Storm Particle) event option is also included that introduces a localized enhancement to the SEP fluxes when the observer is in close proximity to the shock source. This is an ad-hoc description based on general observations of ESP fluxes and energy spectra -which are softer than the nominal shock source spectra described above.

ENLIL runs with field lines extended out to ~5 AU allow inclusion of particles generated after the shock has passed a 1-2 AU observer. However, because the ENLIL model only extends in to ~21 Rs, coronal shocks, which can be important for the initial phases of large/fast CME events, are not currently included. Also, the cone model interplanetary disturbance does not include coronal magnetic field 'ejecta' following the cone model pressure wave. Thus it primarily includes transport effects related to shock and sheath portions of the ICME beyond ~21Rs. Future heliospheric models that include these other effects can be used by SEPMOD through the used field line and shock input files.

Model Figure(s) :

Model Inputs Description

SEPMOD runs using field line and shock output derived from the WSA-ENLIL+Cone model. Therefore, an appropriate WSA-ENLIL+Cone model run with the correct settings to produce these outputs must be performed first.  ENLIL runs intended for use with SEPMOD must be set up such that: (1) they contain CME(s), (2) the number of simulation blocks is one greater than the number of CMEs (nblk=ncmes+1), and (3) the 3D simulation output time step is one hour (tstep=1). To submit an ENLIL run intended for SEPMOD use, please use the beta ENLIL v2.8f submission interface, https://ccmc.gsfc.nasa.gov/requests/SH/E28/enlil_options.php, (allows time-dependent inner boundary) with the advanced run setup option.  Please contact the model host contact listed below with any questions.

Model Outputs Description

proton fluxes, pitch angle distributions, energy vs time spectrogram.

Model Caveats

Change Log

ROR bug fixes: Added in relativistic correction for particle speeds; corrected problem with ESP on/off option not being picked up by script; corrected graphics legend to include tens place for energies; corrected spectra graphics x and y axes label which were swapped.

Model Acknowledgement/Publication Policy (if any)

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Curator: Chiu Wiegand | NASA Official: Dr. Masha Kuznetsova | Privacy and Security Notices | Accessibility | CCMC Data Collection Consent Agreement