Mach Number Scaling of Foreshock Magnetic Fluctuations at Quasi-parallel Bow Shocks and Their Role in Magnetospheric Driving Throughout the Solar System
Upstream of quasi-parallel bow shocks, reflected ions generate ion–ion instabilities. The resulting magnetic fluctuations can advect through the shock and interact with planetary magnetospheres. The amplitude of magnetic fluctuations depends on the strength of the shock, quantified by the Alfvén Mac...
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2025-01-01
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| author | Brandon L. Burkholder Li-Jen Chen Katariina Nykyri Norberto Romanelli Menelaos Sarantos Dave Sibeck Jaye Verniero Gina A. DiBraccio Daniel Gershman Martin Lindberg Erin Kincade |
| author_facet | Brandon L. Burkholder Li-Jen Chen Katariina Nykyri Norberto Romanelli Menelaos Sarantos Dave Sibeck Jaye Verniero Gina A. DiBraccio Daniel Gershman Martin Lindberg Erin Kincade |
| author_sort | Brandon L. Burkholder |
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| description | Upstream of quasi-parallel bow shocks, reflected ions generate ion–ion instabilities. The resulting magnetic fluctuations can advect through the shock and interact with planetary magnetospheres. The amplitude of magnetic fluctuations depends on the strength of the shock, quantified by the Alfvén Mach number ( M _A ), which is the ratio of solar wind velocity to the local Alfvén velocity. With increasing heliocentric distance, the solar wind M _A generally increases, such that Mercury typically experiences a lower M _A ∼ 5 compared to Earth ( M _A ∼ 8), and Mars a slightly higher M _A ∼ 9. Farther out in the solar system, Saturn has even higher M _A (∼10). However, the solar wind flow is highly irregular, and on top of solar cycle variations these values for average M _A at each planet do not capture extreme events. Statistical analysis of OMNIWeb observations from 2015 to 2023 shows that sustained (30 minutes or more) high M _A (30–100) occurs at Earth about once a month. Using a selection of events in the ion foreshock regions of Mercury, Earth, Mars, and Saturn, a linear scaling is calculated for the maximum magnetic fluctuation amplitude as a function of M _A . The resulting slope is ∼0.2. Based on the dominant fluctuation frequency for the largest-amplitude events at each planet, it is found that Mars exists in a special regime where the wave period of the magnetic fluctuations can be similar to or longer than the magnetospheric convection timescale, making Mars more susceptible to space weather effects associated with foreshock fluctuations. |
| format | Article |
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| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
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| spelling | doaj-art-62209ee994894b468ed80e9f2bce49f02025-01-30T06:05:45ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-019801710.3847/1538-4357/ada440Mach Number Scaling of Foreshock Magnetic Fluctuations at Quasi-parallel Bow Shocks and Their Role in Magnetospheric Driving Throughout the Solar SystemBrandon L. Burkholder0https://orcid.org/0000-0001-8702-5806Li-Jen Chen1https://orcid.org/0000-0002-4768-189XKatariina Nykyri2https://orcid.org/0000-0002-6905-9487Norberto Romanelli3https://orcid.org/0000-0001-9210-0284Menelaos Sarantos4https://orcid.org/0000-0003-0728-2971Dave Sibeck5Jaye Verniero6Gina A. DiBraccio7Daniel Gershman8https://orcid.org/0000-0003-1304-4769Martin Lindberg9Erin Kincade10University of Maryland Baltimore County , Baltimore, MD 21250, USA; NASA Goddard Space Flight Center , Greenbelt, MD 20771, USANASA Goddard Space Flight Center , Greenbelt, MD 20771, USANASA Goddard Space Flight Center , Greenbelt, MD 20771, USANASA Goddard Space Flight Center , Greenbelt, MD 20771, USA; University of Maryland College Park , College Park, MD 20742, USANASA Goddard Space Flight Center , Greenbelt, MD 20771, USANASA Goddard Space Flight Center , Greenbelt, MD 20771, USANASA Goddard Space Flight Center , Greenbelt, MD 20771, USANASA Goddard Space Flight Center , Greenbelt, MD 20771, USANASA Goddard Space Flight Center , Greenbelt, MD 20771, USADivision of Space and Plasma Physics, KTH Royal Institute of Technology , 114 28 Stockholm, SwedenUS Naval Academy , Annapolis, MD 21402, USAUpstream of quasi-parallel bow shocks, reflected ions generate ion–ion instabilities. The resulting magnetic fluctuations can advect through the shock and interact with planetary magnetospheres. The amplitude of magnetic fluctuations depends on the strength of the shock, quantified by the Alfvén Mach number ( M _A ), which is the ratio of solar wind velocity to the local Alfvén velocity. With increasing heliocentric distance, the solar wind M _A generally increases, such that Mercury typically experiences a lower M _A ∼ 5 compared to Earth ( M _A ∼ 8), and Mars a slightly higher M _A ∼ 9. Farther out in the solar system, Saturn has even higher M _A (∼10). However, the solar wind flow is highly irregular, and on top of solar cycle variations these values for average M _A at each planet do not capture extreme events. Statistical analysis of OMNIWeb observations from 2015 to 2023 shows that sustained (30 minutes or more) high M _A (30–100) occurs at Earth about once a month. Using a selection of events in the ion foreshock regions of Mercury, Earth, Mars, and Saturn, a linear scaling is calculated for the maximum magnetic fluctuation amplitude as a function of M _A . The resulting slope is ∼0.2. Based on the dominant fluctuation frequency for the largest-amplitude events at each planet, it is found that Mars exists in a special regime where the wave period of the magnetic fluctuations can be similar to or longer than the magnetospheric convection timescale, making Mars more susceptible to space weather effects associated with foreshock fluctuations.https://doi.org/10.3847/1538-4357/ada440Planetary bow shocksPlanetary magnetospheres |
| spellingShingle | Brandon L. Burkholder Li-Jen Chen Katariina Nykyri Norberto Romanelli Menelaos Sarantos Dave Sibeck Jaye Verniero Gina A. DiBraccio Daniel Gershman Martin Lindberg Erin Kincade Mach Number Scaling of Foreshock Magnetic Fluctuations at Quasi-parallel Bow Shocks and Their Role in Magnetospheric Driving Throughout the Solar System The Astrophysical Journal Planetary bow shocks Planetary magnetospheres |
| title | Mach Number Scaling of Foreshock Magnetic Fluctuations at Quasi-parallel Bow Shocks and Their Role in Magnetospheric Driving Throughout the Solar System |
| title_full | Mach Number Scaling of Foreshock Magnetic Fluctuations at Quasi-parallel Bow Shocks and Their Role in Magnetospheric Driving Throughout the Solar System |
| title_fullStr | Mach Number Scaling of Foreshock Magnetic Fluctuations at Quasi-parallel Bow Shocks and Their Role in Magnetospheric Driving Throughout the Solar System |
| title_full_unstemmed | Mach Number Scaling of Foreshock Magnetic Fluctuations at Quasi-parallel Bow Shocks and Their Role in Magnetospheric Driving Throughout the Solar System |
| title_short | Mach Number Scaling of Foreshock Magnetic Fluctuations at Quasi-parallel Bow Shocks and Their Role in Magnetospheric Driving Throughout the Solar System |
| title_sort | mach number scaling of foreshock magnetic fluctuations at quasi parallel bow shocks and their role in magnetospheric driving throughout the solar system |
| topic | Planetary bow shocks Planetary magnetospheres |
| url | https://doi.org/10.3847/1538-4357/ada440 |
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