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Low-frequency oscillatory flow signatures and high-speed flows in the Earth's magnetotail
Umeå University, Faculty of Science and Technology, Department of Physics.ORCID iD: 0000-0003-1167-8055
Umeå University, Faculty of Science and Technology, Department of Physics.ORCID iD: 0000-0002-2043-4442
Umeå University, Faculty of Science and Technology, Department of Physics.ORCID iD: 0000-0002-5681-0366
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 7, p. 7042-7056Article in journal (Refereed) Published
Abstract [en]

Using plasma sheet data from Cluster 1 spacecraft from 2001 till 2011, we statistically investigate oscillatory signatures in the plasma bulk flow. These periodic oscillations are compared to high-speed and quiet flows. Periodic oscillations are observed approximately 8% of the time, while high-speed flows and quiet flows are observed around 0.5% and 12% of the time, respectively. We remark that periodic oscillations can roughly occur everywhere for x(gsm) < -10 R-E and |y(gsm)| < 10 RE, while quiet flows mainly occur toward the flanks of this region and toward x = -10 R-E. The relation between the geomagnetic and solar activity and the occurrence of periodic oscillations is investigated and reveal that periodic oscillations occur for most Kp values and solar activity, while quiet flows are more common during low magnetospheric and solar activity. We find that the median oscillation frequency of periodic oscillations is 1.7 mHz and the median duration of the oscillation events is 41 min. We also observe that their associated Poynting vectors show a tendency to be earthward (S-x >= 0). Finally, the distribution of high-speed flows and periodic oscillations as a function of the velocity is investigated and reveals that thresholds lower than 200 km/s should not be used to identify high-speed flows as it could result in misinterpreting a periodic oscillations for a high-speed flow.

Place, publisher, year, edition, pages
Washington: American Geophysical Union (AGU), 2017. Vol. 122, no 7, p. 7042-7056
Keywords [en]
bursty bulk flows, plasma sheet, cluster observations, magnetic field, neutral sheet, magnetosphere, dependence, midtail
National Category
Fluid Mechanics and Acoustics Subatomic Physics
Identifiers
URN: urn:nbn:se:umu:diva-139015DOI: 10.1002/2017JA024076ISI: 000407627100008Scopus ID: 2-s2.0-85021756656OAI: oai:DiVA.org:umu-139015DiVA, id: diva2:1141176
Funder
Swedish National Space Board, 271/14Available from: 2017-09-14 Created: 2017-09-14 Last updated: 2023-03-24Bibliographically approved
In thesis
1. There and back again... An Earth magneto-tale: understanding plasma flows in the magnetotail
Open this publication in new window or tab >>There and back again... An Earth magneto-tale: understanding plasma flows in the magnetotail
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Bort och hem igen... En magnetosfärs äventyr : studier av plasmaflöden i jordens magnetsvans
Abstract [en]

On average, the Earth's magnetotail plasma sheet seems to be a calm region of the magnetosphere where the plasma moves slowly towards Earth. However, the plasma sheet actually hosts many phenomena, some of which can affect Earth. For example, high-speed flows of plasma with speed larger than 400 km/s are observed in the plasma sheet and they can lead to aurorae. Such dynamical phenomena and the impact they may have on Earth naturally makes the plasma sheet an important region of study. Even though these high-speed flows can affect Earth, they are observed less than 5% of the time, meaning that most of the time, other disturbances take place in the plasma sheet. Our aim is to investigate and better understand the plasma dynamics in the plasma sheet.

The plasma above and below the cross-tail current sheet was previously thought to convect in the same direction. However, we find that under clearly non-zero Interplanetary Magnetic Field (IMF)By (dawn-dusk component), the plasma has a tendency to convect in opposite dawn-dusk direction across the current sheet near the midnight sector depending on the sign of IMF By.

The high-speed plasma flows are known to be associated with an increase of the northward component of the magnetic field as they propagate toward Earth. Using simulations, we notice that the magnetic field lines are bent by the high-speed flows and dents can appear. The deformation of the magnetic field is such that it may be directed towards the tail above the cross-tail current sheet and towards the Earth below it. This is opposite to the expected orientation of the magnetic field thus making this feature important in order to properly identify the region in which a spacecraft is located.

At times, the plasma can be seen to move back and forth in an oscillatory manner. We investigate statistically such oscillatory behaviour and compare them to high-speed flows and to time periods when the plasma is calm. These oscillatory flows are observed about 8% of the time in the plasma sheet. They typically have a frequency of about 1.7 mHz (~10 min period) and usually last about 41 min.

Some oscillations of the plasma velocity are observed along the magnetic field. The particles measured by the satellite initially have a velocity parallel to the magnetic field and towards Earth. Gradually with time, the measured velocity of the particles turns around to first become more perpendicular to the magnetic field and then be along the magnetic field but away from Earth. These signatures are interpreted simply as being due to mirroring particles injected tailward of the satellite and move toward Earth. The particles are then reflected, and move away from Earth. We investigate the general features of such oscillations along the magnetic field and find that the source of the particles is typically located less than 25 RE (Earth's radii) tailward of the satellite.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2020. p. 54
Keywords
Plasma dynamics, Earth magnetosphere, magnetotail, plasma sheet flows, oscillatory flows, burst bulk flows, tailward flows
National Category
Fusion, Plasma and Space Physics
Research subject
Space Physics; Space and Plasma Physics
Identifiers
urn:nbn:se:umu:diva-170347 (URN)978-91-7855-290-0 (ISBN)978-91-7855-289-4 (ISBN)
Public defence
2020-06-02, Umeå University, N360, Umeå, 09:00 (English)
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Supervisors
Note

Posting sheet: Wrongly stated number of pages. Digital ISBN missing. 

Thesis: Lacking information regarding digital/print ISBN.

New location for the defence.

Available from: 2020-05-12 Created: 2020-05-04 Last updated: 2020-05-26Bibliographically approved

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De Spiegeleer, AlexandreHamrin, MariaPitkänen, TimoMann, IngridNorqvist, PatrikVaverka, Jakub

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