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Abstract We conduct a global hybrid simulation of an observation event to affirm that an interplanetary (IP) shock can drive significant suprathermal (tens to hundreds of eV) H+outflows from the polar cap. The event showed that a spacecraft in the lobe at ∼6.5 REaltitude above the polar cap observed the appearance of suprathermal outflowing H+ions about 8 min after observing enhanced downward DC Poynting fluxes caused by the shock impact. The simulation includes H+ions from both the solar wind and the ionospheric sources. The cusp/mantle region can be accessed by ions from both sources, but only the outflow ions can get into the lobe. Despite that upward flowing solar wind ions can be seen within part of the cusp/mantle region and their locations undergo large transient changes in response to the magnetosphere compression caused by the shock impact, the simulation rules out the possibility that the observed outflowing H+ions was due to the spacecraft encountering the moving cusp/mantle. On the other hand, the enhanced downward DC Poynting fluxes caused by the shock impact drive more upward suprathermal outflows, which reach higher altitudes a few minutes later, explaining the observed time delay. Also, these simulated outflowing ions become highly field‐aligned in the upward direction at high altitudes, consistent with the observed energy and pitch‐angle distributions. This simulation‐observation comparison study provides us the physical understanding of the suprathermal outflow H+ions coming up from the polar cap.
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Suprathermal Outflowing H + Ions in the Lobe Driven by an Interplanetary Shock: 1. An Observation Event
Abstract To better understand how sharp changes in the solar wind and interplanetary magnetic field conditions affect the ionosphere outflows at high latitudes, we analyze an event observed on 17 July 2002 showing suprathermal (tens to hundreds of eV) outflowing H+ions in the lobe driven by the impact of an interplanetary (IP) shock. A spacecraft in the lobe at altitudes of ∼6.5REfirst observed enhanced downward DC Poynting fluxes ∼2 min after the shock impact and then, another 8 min later, the appearance of suprathermal outflowing H+ions as ion beams and ion conics. The increasing downward DC Poynting fluxes and the increasing outflowing H+fluxes that appeared later were highly correlated because they shared a similar increasing trend with a time scale of ∼5 min. To explain such time delay and correlation, we conclude that a plausible scenario was that the enhanced DC Poynting fluxes reached down to lower altitudes, drove processes to accelerate the pre‐existing polar wind ions to ion beams and ion conics, and then these newly generated suprathermal ions flowed upward to the spacecraft altitudes. This event indicates that an IP shock can drive a significant amount of suprathermal H+outflows from the polar cap.
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- PAR ID:
- 10614287
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 129
- Issue:
- 9
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2024JA032557
