IMF dependence of the azimuthal direction of earthward magnetotail fast flows

Pitkänen, Timo; Hamrin, Maria; Norqvist, Patrik; Karlsson, Tomas; Nilsson, Hans

doi:10.1002/2013gl058136

Cited by 22 publications

(67 citation statements)

References 38 publications

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“…Grocott et al, 2005). The azimuthal directions within the fast flow are also consistent with the statistical results of Pitkänen et al (2013) of IMF-dependent favourable azimuthal flow directions of convective fast flows, which they suggested possibly to be originated from untwisting.…”

Section: Discussionsupporting

confidence: 86%

“…Walsh et al (2009) suggested that the flow shear could be related to untwisting, but could not rule out a possibility of it to be related to internal flow patterns within the fast flow channel (depleted bubble), since the flow shear was observed only by one spacecraft. Besides these two studies, also Pitkänen et al (2013) have reported an indication of an azimuthal velocity shear across the neutral sheet during a fast flow in their fast flow example event. However, they showed only single satellite measurements and did not discuss the event any further.…”

Section: Introductionmentioning

confidence: 89%

“…Whether this is true even for the degree of magnetic field line twisting remains to be shown. One possible interpretation of the results by Pitkänen et al (2013) is that the untwisting process could be occurring in the tail to some extent for all nonzero IMF B y conditions, and not only limited to those of northward and B y dominating IMF. This possibility should be studied further.…”

Section: Introductionmentioning

confidence: 90%

“…Recently, motivated by the results by Grocott et al (2007), Pitkänen et al (2013) using Cluster data conducted a statistical investigation of a possible IMF dependence (and hence twist-dependence) of the direction of the azimuthal convection velocity component of the Earthward magnetotail fast flows. It was found that the azimuthal flow direction of the fast flows and the orientation of the IMF show a correlation and in such a manner that is consistent with the untwisting hypothesis.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we analyse and discuss the flow shear event identified by Pitkänen et al (2013) in more detail. We will extend their preliminary single spacecraft analysis by taking the full advantage of the Cluster multispacecraft observations.…”

Section: Introductionmentioning

confidence: 99%

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Azimuthal velocity shear within an Earthward fast flow – further evidence for magnetotail untwisting?

et al. 2015

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Abstract.It is well known that nonzero interplanetary magnetic field B y conditions lead to a twisted magnetotail configuration. The plasma sheet is rotated around its axis and tail magnetic field lines are twisted, which causes an azimuthal displacement of their ionospheric footprints. According to the untwisting hypothesis, the untwisting of twisted field lines is suggested to influence the azimuthal direction of convective fast flows in the nightside geospace. However, there is a lack of in situ magnetospheric observations, which show actual signatures of the possible untwisting process. In this paper, we report detailed Cluster observations of an azimuthal flow shear across the neutral sheet associated with an Earthward fast flow on 5 September 2001. The observations show a flow shear velocity pattern with a V ⊥y sign change, near the neutral sheet (B x ∼ 0) within a fast flow during the neutral sheet flapping motion over the spacecraft. Firstly, this implies that convective fast flows may not generally be unidirectional across the neutral sheet, but may have a more complex structure. Secondly, in this event tail B y and the flow shear are as expected by the untwisting hypothesis. The analysis of the flow shear reveals a linear dependence between B x and V ⊥y close to the neutral sheet and suggests that Cluster crossed the neutral sheet in the dawnward part of the fast flow channel. The magnetospheric observations are supported by the semi-empirical T96 and TF04 models. Furthermore, the ionospheric SuperDARN convection maps support the satellite observations proposing that the azimuthal component of the magnetospheric flows is enforced by a magnetic field untwisting. In summary, the observations give strong supportive evidence to the tail untwisting hypothesis. However, the T96 ionospheric mapping demonstrates the limitations of the model in mapping from a twisted tail.

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Section: Discussionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Azimuthal velocity shear within an Earthward fast flow – further evidence for magnetotail untwisting?

et al. 2015

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Cross‐tail expansion of dipolarizing flux bundles

et al. 2015

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Dipolarizing flux bundles (DFBs), magnetotail flux tubes with stronger, more dipolar magnetic field than the background magnetotail plasma, which are led by dipolarization fronts, typically propagate earthward within bursty bulk flows. Although DFBs are localized (typically 1–3 RE) in the cross‐tail direction, many of them may combine to cause global effects, such as the substorm current wedge. Knowledge of how this local‐to‐global coupling happens is crucial for understanding magnetotail dynamics. We investigate how the coupling happens using multipoint observations from the Time History of Events and Macroscale Interactions during Substorms mission. Our results show that most DFBs expand in the cross‐tail direction as they propagate earthward. Through such expansion, azimuthally localized DFBs can cover a wide region to cause global effects when they arrive at the inner edge of the plasma sheet.

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Direct observations of the full Dungey convection cycle in the polar ionosphere for southward interplanetary magnetic field conditions

Zhang

Lockwood

Foster³

et al. 2015

JGR Space Physics

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Tracking the formation and full evolution of polar cap ionization patches in the polar ionosphere, we directly observe the full Dungey convection cycle for southward interplanetary magnetic field (IMF) conditions. This enables us to study how the Dungey cycle influences the patches' evolution. The patches were initially segmented from the dayside storm enhanced density plume at the equatorward edge of the cusp, by the expansion and contraction of the polar cap boundary due to pulsed dayside magnetopause reconnection, as indicated by in situ Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations. Convection led to the patches entering the polar cap and being transported antisunward, while being continuously monitored by the globally distributed arrays of GPS receivers and Super Dual Auroral Radar Network radars. Changes in convection over time resulted in the patches following a range of trajectories, each of which differed somewhat from the classical twin‐cell convection streamlines. Pulsed nightside reconnection, occurring as part of the magnetospheric substorm cycle, modulated the exit of the patches from the polar cap, as confirmed by coordinated observations of the magnetometer at Tromsø and European Incoherent Scatter Tromsø UHF radar. After exiting the polar cap, the patches broke up into a number of plasma blobs and returned sunward in the auroral return flow of the dawn and/or dusk convection cell. The full circulation time was about 3 h.

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IMF dependence of the azimuthal direction of earthward magnetotail fast flows

Cited by 22 publications

References 38 publications

Azimuthal velocity shear within an Earthward fast flow – further evidence for magnetotail untwisting?

Azimuthal velocity shear within an Earthward fast flow – further evidence for magnetotail untwisting?

Cross‐tail expansion of dipolarizing flux bundles

Direct observations of the full Dungey convection cycle in the polar ionosphere for southward interplanetary magnetic field conditions

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