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A Comparative Study of the Proton Properties of Magnetospheric Substorms at Earth and Mercury in the Near Magnetotail
Chinese Acad Sci, Inst Geol & Geophys, Key Lab Earth & Planetary Phys, Beijing, Peoples R China.;Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA.;Peking Univ, Sch Earth & Space Sci, Beijing, Peoples R China.;Chinese Acad Sci, Key Lab Lunar & Deep Space Explorat, Natl Astron Observ, Beijing, Peoples R China..
Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 16, p. 7933-7941Article in journal (Refereed) Published
Abstract [en]

The variations of plasma sheet proton properties during magnetospheric substorms at Earth and Mercury are comparatively studied. This study utilizes kappa distributions to interpret proton properties at both planets. Proton number densities are found to be around an order of magnitude higher, temperatures several times smaller, and kappa values broader at Mercury than at Earth. Protons become denser and cooler during the growth phase, and are depleted and heated after the dipolarizations in both magnetospheres. The changes of kappa at Earth are generally small (<20%), indicating that spectrum-preserving processes, like adiabatic betatron acceleration, play an important role there, while variations of kappa at Mercury are large (>60%), indicating the importance of spectrum-altering processes there, such as acceleration due to nonadiabatic cross-tail particle motions and wave-particle interactions. This comparative study reveals important intrinsic properties on the energization of protons in both magnetospheres. Plain Language Summary Earth and Mercury are the only two planets possessing global intrinsic magnetic fields among the four inner planets, which are Mercury, Venus, Earth, and Mars, within the solar system. The interactions between the intrinsic magnetic fields and the continual flow of high-speed solar wind from the Sun form similar magnetospheres at the two planets, although the scale of the magnetosphere is much smaller at Mercury than at Earth. Magnetospheric substorms, a result of solar wind-magnetosphere coupling, occur in both magnetospheres. Comparative study of a similar process between different planets is meaningful as it can help us in understanding the specific process further as well as help us in understanding the intrinsic properties of the magnetospheres. This research paper characterizes the proton properties of magnetospheric substorms of both planets, revealing that different mechanisms control the behavior of protons during the magnetospheric substorms of the two planets.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018. Vol. 45, no 16, p. 7933-7941
Keywords [en]
comparative planetary study, magnetospheric substorm, proton heating, adiabatic and nonadiabatic processes, kappa distribution
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-236022DOI: 10.1029/2018GL079181ISI: 000445612500006Scopus ID: 2-s2.0-85053216058OAI: oai:DiVA.org:kth-236022DiVA, id: diva2:1255508
Note

QC 20181012

Available from: 2018-10-12 Created: 2018-10-12 Last updated: 2018-10-12Bibliographically approved

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