SEPMOD

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

SEPMOD is a Fortran code that computes time series of SEP (SolarEnergetic Particle) fluxes at a specified location in the energyrange from a few MeV to 100 MeV using results from an MHD heliosphericsimulation describing the prevailing interplanetary shocks andmagnetic fields. These can be directly compared to observationsor used for forecasting/prediction or other conceptual analyses.

SEPMOD version 1 is designed to work with output from WSA-ENLIL-conemodels as a postprocessing option. Special ENLIL output files arerequired that can be requested. These output files consist of aa sequence of observer-connected field lines, and a file containinginformation 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 everycone model CME injected in the run. (e.g. Separate shock files for eachICME.) Other heliospheric mideks can be used if similar output filesare generated.

This SEPMOD version is currently designed to compute SEP informationfor one observer location at a time, and generates output filescontaining simulated particle flux time profiles at specific energies,plus pitch angle (at 3 of those energies) and energy-time spectrograms.Note that t=0 of the time profile is the time of the first ENLILfieldline snapshot used.

SEPMOD is based on a field line tracer and adiabatic invariantconservation (see Luhmann et al., JASR, 2006, 2010). It is setup with (non-relativistic) protons 10-100 MeV in mind. Energy conservation is assumed following injection at the source. Thusspecified injection energies are the energies of the calculatedSEP flux time series. The current version allows 9 energies to bespecified. A range of default energies is based on IMP-8 detectorchannels.

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

A flare source addition option is available (though WSA-ENLIL modelfield line files provided at this time only trace to the ENLILinner boundary at ~21 Rs- making this this the radius where theflare location is located for SEPMOD). SEPMOD version 1 assumes a single shock source at a time. It allowscontributions from multiple shock sources through superposition(addition) of the flux time series from single shock source runs usingthe same observer field lines but different ENLIL shock files. Thereis no secondary shock acceleration from multiple shock passages. Seedparticles are present only in the sense of background from earlieror 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 injectedflux is based on a shock-velocity dependent empirical fomula derivedby Lario et al. (1995). The shock injections are nominally isotropicand are delta functions in time.

An ESP (Energetic Storm Particle) event option is also included thatintroduces a localized enhancement to the SEP fluxes when the observeris in close proximity to the shock source. This is an ad-hoc descriptionbased on general observations of ESP fluxes and energy spectra -whichare softer than the nominal shock source spectra described above.

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

This models runs on field line and shock output derived from the WSA-ENLIL+Cone model. There fore, an appropriate WSA-ENLIL+Cone model run with the correct settings to produce these outputs must be performed first.

10-100 MeV proton fluxes, pitch angle distributions for three energies, energy vs time spectrogram.