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- Title
Effect of Rapid Changes of Solar Wind Conditions on the Pickup Ion Velocity Distribution.
- Authors
Bower, J. S.; Moebius, E.; Berger, L.; Farrugia, C.; Keilbach, D.; Lee, M. A.; Quinn, P. R.; Schwadron, N.; Taut, A.
- Abstract
We performed the first systematic analysis of pickup ion (PUI) cutoff speed variations, across compression regions and due to fast fluctuations in solar wind (SW) speed and magnetic field strength. This study is motivated by the need to remove or correct for systematic effects on the determination of the interstellar flow longitude based on the longitudinal variation of the PUI cutoff. Using 2007–2014 STEREO A PLASTIC observations, we identified SW compression regions and accumulated the contained PUI velocity distributions in a superposed epoch analysis. The shift of the cutoff in velocity, interpreted as PUI energization, varies systematically across the compression region and increases approximately linearly with the speed gradient of the compression. Additionally, the shift remains positive into the negative speed gradient at the beginning of the rarefaction region. A similar response is found when PUI distributions are sorted according to the strength of fast fluctuations in SW speed, density, and magnetic field strength. These parameters remain high in the first part of the rarefaction region, suggesting a possible PUI energization through compressive turbulence. Based on these results, we removed the strongest compression regions from the interstellar flow analysis, finding no significant change in direction or uncertainty. Thus, we have revealed the influence of adiabatic compression and compressive turbulence, increasing the PUI cutoff energy, and we have demonstrated that the determination of the interstellar inflow direction via analysis of PUI distributions is robust for a multiyear data set, even in the presence of SW interaction regions. Key Points: The cutoff speed of the pickup ion helium distribution function is shown to systematically increase in solar wind compression regionsThe magnitude of the pickup ion cutoff shift scales approximately linearly with the solar wind speed gradient in the compression regionThe interstellar flow longitude obtained from the pickup ion cutoff is largely unaffected by compressions, when using multiyear data sets
- Subjects
SOLAR wind; VELOCITY distribution (Statistical mechanics); IONS; MAGNETIC flux density; METEOROLOGICAL observations
- Publication
Journal of Geophysical Research. Space Physics, 2019, Vol 124, Issue 8, p6418
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2019JA026781