Low-frequency magnetic variations at the high-<i>β</i> Earth bow shock
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Published:2019-09-24
Issue:5
Volume:37
Page:877-889
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ISSN:1432-0576
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Container-title:Annales Geophysicae
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language:en
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Short-container-title:Ann. Geophys.
Author:
Petrukovich Anatoli A.,Chugunova Olga M.,Shustov Pavel I.
Abstract
Abstract. Observations of Earth's bow shock during high-β (ratio of thermal
to magnetic pressure) solar wind streams are rare.
However, such shocks are ubiquitous in astrophysical plasmas.
Typical solar wind parameters related to high β (here β>10) are as follows: low speed, high density, and a very low interplanetary magnetic field of 1–2 nT. These conditions are usually quite transient
and need to be verified immediately upstream of the observed shock crossings.
In this report, three characteristic crossings by the Cluster project (from the 22 found) are studied using multipoint analysis, allowing us to determine spatial scales.
The main magnetic field and density spatial scale
of about a couple of hundred of kilometers generally corresponds to the increased proton convective gyroradius.
Observed magnetic variations are different from those for supercritical shocks, with β∼1.
Dominant magnetic variations in the shock transition
have amplitudes much larger than the background field and have a
frequency of ∼ 0.3–0.5 Hz (in some events – 1–2 Hz). The wave polarization has no stable phase
and is closer to linear, which complicates the determination of the
wave propagation direction. Spatial scales (wavelengths) of variations
are within several tens to a couple of hundred of kilometers.
Funder
Russian Science Foundation
Publisher
Copernicus GmbH
Subject
Space and Planetary Science,Earth and Planetary Sciences (miscellaneous),Atmospheric Science,Geology,Astronomy and Astrophysics
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