CISM SEP Modeling Background The major SEP events come from the CME-generated coronal and interplanetary shock(s) These “gradual”events can have a “prompt” portion that is related to the observer field line connection to the shock when it is close to the Sun, and a second maximum that occurs when the shock arrives, depending on the geometry of the field line connection to the strongest parts of the shock.

The CISM SEP Model Goal: A generalized test particle code that uses the time-dependent fields and shock information from the CISM heliospheric MHD simulation for transport and (shock) source descriptions Approach: Adapt a field-line tracer to a guiding-center particle tracer for MeV/n ions of any mass and charge

Assumptions of the Model Conservation of the first adiabatic invariant Default mode is scatter-free (assumes field-aligned or parallel propagation – neglects cross-field diffusion and gradient curvature drifts) E=-VxB electric field is negligible at the ion energies of the model B field and shock source descriptions can be isolated in code subroutines

Model Approach Details B field subroutine takes an x,y,z and gives back Bx,By,Bz at that location (Development version uses PFSS coronal field and a Parker Spiral outside the source surface) Shock source is represented by a moving point source that travels along the observer- connected field line at the shock speed and has an evolving strength (Development version injects isotropic particles with a power law energy spectrum. Evolving shock strength is represented by a radially dependent weighting function applied to the injections.)

Development Path For testing the SEP model concept we selected an event sequence in late March-early April First we analyzed the magnetic field connections to the erupting active region.

Step 1-Identify Field Lines Connected to the SEP Source In the case of these events during CR1974, open field lines from the erupting active region map to the ecliptic plane We had to specify the source along each field line as a function of time Each of the three events had a different CME speed and a different perspective:

Perspectives

Step 2-Determine Source Descriptions Our Development version uses a prescribed shock source weighting function (top panel) –here assumed at 10, 50 and 100 MeV (green, blue and red) The shock is assumed to move at the observed CME speed The Bottom panel shows single field line SEP “time profiles” at 1 AU for the three energies for the three shock speeds with the same radial and energy weighting prescription

Step 3-From the sequence of profiles on encountered field lines construct the observer’s SEP profile

Development Plans Incorporate the CISM heliospheric B field description and shock location in the transport code, using a sequence of MHD simulation field “snapshots”-see Ledvina presentation Develop an ion-kinetic hybrid model-based lookup table for the shock source description (flux, energy spectrum, pitch angle distribution)- see Krauss-Varban presentation Incorporate the above in the transport code

A Lesson from PFSS Model Fields The Balch (1999) Protons Model traces Parker Spiral Field Lines directly to flare sites The PFSS model illustrates that this mapping can often be tens of degrees off Field line lengths (inferred from velocity dispersions) of Prompt SEP arrivals can also be underestimated

SEP code near-term challenges Determine the frequency of field model snapshots needed (will depend on shock speed) Decide how to treat shock “revisits” Evaluate the need for including scattering away from the source Work on the May 12, 1997 event

SEP code longer term challenges Add coronal shock portion using an improved version of MAS/ENLIL Determine an appropriate treatment for the flux increase at the shock (in strong events at >10 MeV) Play with ion composition source description(s)

CISM May 12 ’97 Event Characteristics

CISM May 12 ’97 Event (cont.) This was a very small event relative to those of SEC interest It had a classic shock source profile for a near- central meridian CME We plan to use the “cone model” MAS/ENLIL simulation fields to further develop the framework

A note about other approaches: Zank, Li et al. and Kota use a modified Boltzmann eq. approaches, solving for the distribution function “f(p)”. Limitations include the underlying assumptions of their Boltzmann eqs. which entail field geometry and the degree of isotropy/anisotropy of f, and the presumption of the importance of diffusive motion. Our approach is more general, allowing any description of the field, the scattering, and the source.