The Role of Magnetic Connectivity and SEP Event History in Determining Seed Populations and Large SEP Events
ROSES ID: NNH20ZDA001N Selection Year: 2020
Program Element: Focused Science Topic
Principal Investigator: Christina O Lee
Affiliation(s): University of California, Berkeley
Project Member(s):
Lynch, Benjamin J Co-I University of California, Berkeley
Luhmann, Janet G. Co-I University of California, Berkeley
Arge, Charles N Collaborator NASA Goddard Space Flight Center
Odstrcil, Dusan Collaborator George Mason University
Mays, Leila Collaborator NASA Goddard Space Flight Center
Summary:
Forecasting large SEP events continues to be an outstanding challenge in solar and heliospheric physics. We do not directly observe the timing/location of particle acceleration regions, the transport of SEPs along magnetic field lines, or properties of the pre-event seed populations. Multipoint observations have shown that enhanced SEP fluxes can be detected at widely separated locations in the inner heliosphere, especially during active times, when multiple interplanetary shocks are present. Using data-driven modeling of shock evolution, we will determine the connectivity to the observing spacecraft and the spatial relationship between the shock(s) and observer(s). Results will be compared with multipoint measurements to determine the contribution of cross-field transport by evaluating how far away from the shock-connected regions SEPs are still detected.
Hypotheses for the origin of the seed populations associated with large SEP events include: (a) variations in the suprathermal tail of the nominal solar wind distribution at the Sun or in the heliosphere; (b) suprathermal ions from prior or current solar flares; and (c) previously shock-energized particles as a heliospheric source. We propose a combined data analysis and modeling approach to quantify the potential contribution of each of these by investigating the spatiotemporal extent and variability of:
1. SEP (shock) origin in the heliosphere: We will use Wang-Sheeley-Arge (WSA)-Enlil with SEPMOD to examine the field line connectivity and determine how much cross-field transport is necessary to explain the spatial extent of SEP events observed at multiple locations (e.g., L1, STA, PSP). Can the connectivity to CME-driven shock fronts explain the entire longitudinal extent of SEP events?
2. Magnetic geometry near the Sun: We will examine topological structures like pseudostreamers, S-web arcs, and narrow open-field channels into or near the flare site/CME source. Each of these regions has a large squashing factor, i.e., a small angular difference at 1Rs but a large angular difference at the source surface or 21.5Rs. As a result, any flare or CME dynamics could greatly enhance the longitudinal extent available to SEPs.
3. Pre-event conditions and remnant seed particles in the heliosphere: We will use WSA-Enlil+Cone with SEPMOD to investigate how often the observer field lines intersect multiple shocks. The modeled shock parameters will be used as input for detailed shock acceleration calculations with the resulting seed population(s) injected onto WSA-Enlil field lines. As the shock evolves, different field lines will encounter different suprathermal properties.
4. CME-driven shocks near the Sun: We will examine the shock structure in the low corona (<21.5Rs) from MHD simulations of CME eruptions and couple the field line connectivity information to that from WSA-Enlil to investigate the coronal source of the seed population. Additionally, we will examine open field lines that have reconnected in the eruption process, the evolution of the magnetic topology disturbed by the eruption, and the longitudinal extent at 21.5Rs of flare/shock-connected field lines.
The results of our project will build a better understanding of multipoint observations of large SEP events. Without a first-order knowledge of magnetic connectivity to interplanetary shocks, it is difficult to evaluate the importance of perpendicular transport in the context of real events. Our project will make significant progress towards the LWS FST objectives to understand the relative roles of solar flares and CMEs in producing large SEP events and understand particle transport, mixing, and other effects that result in the observed variability in the properties of SEP events at 1AU. Our project is highly relevant to the LWS Strategic Science Areas SSA-II (Solar Eruptive and Transient Heliospheric Phenomena) and SSA-III (Acceleration Transport of Solar Energetic Particles).
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