Article
Using the WSA Model to Test the Parker Spiral Approximation for SEP Event Magnetic Connections
Solar Physics
(2016)
Abstract
In studies of solar energetic (E >10 MeV) particle (SEP) events the Parker spiral
(PS) field approximation, based only on the measured 1 AU solar wind (SW) speed V sw, is
nearly always used to determine the coronal or photospheric source locations of the 1 AU
magnetic fields. There is no objective way to validate that approximation, but here we seek
guidelines for optimizing its application. We first review recent SEP studies showing the
extensive use of the PS approximation with various assumptions about coronal and photospheric
source fields. We then run the Wang–Sheeley–Arge (WSA) model over selected
Carrington rotations (CRs) to track both the photospheric and 5 R source locations of
the forecasted 1 AU SW, allowing us to compare those WSA sources with the PS sources
inferred from the WSA V sw forecast. We compile statistics of the longitude differences
(WSA–PS) for all the CRs and discuss the limitations of using the WSA model to validate
the PS approximation. Over nearly all of each CR the PS and WSA source longitudes agree
to within several degrees. The agreement is poor only in the slow–fast SW interaction regions
characterized by high-speed events (HSEs), where the longitude differences can reach
several tens of degrees. This result implies that SEP studies should limit use of the PS approximation
around HSEs and use magnetic field polarities as an additional check of solar
source connections.
Keywords
- Energetic particles Acceleration,
- magnetic fields Models,
- cocoronal mass ejections Low coronal signatures
Disciplines
Publication Date
Summer June 27, 2016
DOI
10.1007/s11207-016-0934-x
Citation Information
S. W. Kahler, C. N. Arge and David Alan Smith. "Using the WSA Model to Test the Parker Spiral Approximation for SEP Event Magnetic Connections" Solar Physics Vol. 291 Iss. 6 (2016) p. 1829 Available at: http://works.bepress.com/david-smith/9/