Cluster observations of the exterior cusp and its surrounding boundaries under northward IMF

Lavraud, B.; Dunlop, M. W.; Phan, T. D.; Rème, H.; Bosqued, J. M.; Dandouras, I.; Sauvaud, J. A.; Lundin, R.; Taylor, M. G. G. T.; Cargill, P. J.; Mazelle, C.; Escoubet, C. P.; Carlson, C. W.; McFadden, J. P.; Parks, G. K.; Möbius, E.; Kistler, L. M.; Bavassano-Cattaneo, M. B.; Korth, A.; Klecker, B.; Balogh, A.

doi:10.1029/2002gl015464

Cited by 95 publications

(161 citation statements)

References 18 publications

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“…Going from the magnetosheath to the exterior cusp, it is characterized by a decrease in density and an increase in temperature. This property confirms the results obtained in the context of recent case studies by Lavraud et al (2002) and .…”

Section: Characteristics Of the Boundariessupporting

confidence: 81%

“…However, the sizes of the squares (relative to the amount of samples) in this area render this characteristic questionable. We may point out that such properties would not be inconsistent with observations from case studies Lavraud et al, 2002). These were explained in terms of the possible consequences of lobe reconnection, implying plasma precipitation at high-latitudes and a slow sunward field line convection (perpendicular flow).…”

Section: Imf Orientation Dependence Of the Velocity Distributionsmentioning

confidence: 88%

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Cluster survey of the high-altitude cusp properties: a three-year statistical study

Lavraud

Fedorov²,

Budnik³

et al. 2004

Ann. Geophys.

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Abstract. The global characteristics of the high-altitude cusp and its surrounding regions are investigated using a threeyear statistical survey based on data obtained by the Cluster spacecraft. The analysis involves an elaborate orbit-sampling methodology that uses a model field and takes into account the actual solar wind conditions and level of geomagnetic activity. The spatial distribution of the magnetic field and various plasma parameters in the vicinity of the low magnetic field exterior cusp are determined and it is found that: 1) The magnetic field distribution shows the presence of an intermediate region between the magnetosheath and the magnetosphere: the exterior cusp, 2) This region is characterized by the presence of dense plasma of magnetosheath origin; a comparison with the Tsyganenko (1996) magnetic field model shows that it is diamagnetic in nature, 3) The spatial distributions show that three distinct boundaries with the lobes, the dayside plasma sheet and the magnetosheath surround the exterior cusp, 4) The external boundary with the magnetosheath has a sharp bulk velocity gradient, as well as a density decrease and temperature increase as one goes from the magnetosheath to the exterior cusp, 5) While the two inner boundaries form a funnel, the external boundary shows no clear indentation, 6) The plasma and magnetic pressure distributions suggest that the exterior cusp is in equilibrium with its surroundings in a statistical sense, and 7) A preliminary analysis of the bulk flow distributions suggests that the exterior cusp is stagnant under northward IMF conditions but convective under southward IMF conditions.

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Section: Characteristics Of the Boundariessupporting

confidence: 81%

Section: Imf Orientation Dependence Of the Velocity Distributionsmentioning

confidence: 88%

Cluster survey of the high-altitude cusp properties: a three-year statistical study

Lavraud

Fedorov²,

Budnik³

et al. 2004

Ann. Geophys.

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“…[4] Apart from some debate related to the presence of an indentation at high latitudes near the polar cusps [Zhou and Russell, 1997;Dunlop et al, 2000;Lavraud et al, 2002Lavraud et al, , 2004Zhang et al, 2007] and dawn-dusk asymmetries [Dmitriev et al, 2004;Suvorova et al, 2005;Nishino et al, 2008], the shape of the magnetopause is often assumed to be axisymmetric about the aberrated Sun-Earth line, i.e., circular. This hypothesis has been used in most empirical models of the magnetopause [e.g., Sibeck et al, 1991;Petrinec and Russell, 1996;Shue et al, 1997;Kawano et al, 1999], although models using Artificial Neural Network techniques [Dmitriev and Suvorova, 2000] or fits to asymmetric shapes from theoretical expectations [e.g., Zhuang et al, 1981;Boardsen et al, 2000] have also been devised (cf.…”

Section: Introductionmentioning

confidence: 99%

Asymmetry of magnetosheath flows and magnetopause shape during low Alfvén Mach number solar wind

et al. 2013

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[1] Previous works have emphasized the significant influence of the solar wind Alfvén Mach number (M A ) on magnetospheric dynamics. Here we report statistical, observational results that pertain to changes in the magnetosheath flow distribution and magnetopause shape as a function of solar wind M A and interplanetary magnetic field (IMF) clock angle orientation. We use all Cluster 1 data in the magnetosheath during the period 2001-2010, using an appropriate spatial superposition procedure, to produce magnetosheath flow distributions as a function of location in the magnetosheath relative to the IMF and other parameters. The results demonstrate that enhanced flows in the magnetosheath are expected at locations quasi-perpendicular to the IMF direction in the plane perpendicular to the Sun-Earth line; in other words, for the special case of a northward IMF, enhanced flows are observed on the dawn and dusk flanks of the magnetosphere, while much lower flows are observed above the poles. The largest flows are adjacent to the magnetopause. Using appropriate magnetopause crossing lists (for both high and low M A ), we also investigate the changes in magnetopause shape as a function of solar wind M A and IMF orientation. Comparing observed magnetopause crossings with predicted positions from an axisymmetric semi-empirical model, we statistically show that the magnetopause is generally circular during high M A , while is it elongated (albeit with moderate statistical significance) along the direction of the IMF during low M A . These findings are consistent with enhanced magnetic forces that prevail in the magnetosheath during low M A . The component of the magnetic forces parallel to the magnetopause produces the enhanced flows along and adjacent to the magnetopause, while the component normal to the magnetopause exerts an asymmetric pressure on the magnetopause that deforms it into an elongated shape.

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“…Here we define it as the low magnetic field region located at large radial distances. It has recently been shown as more or less stagnant under northward IMF (Lavraud et al, 2002) while rather largely convective under southward IMF (Cargill et al, 2004). It often shows, however, disordered plasma flows and fields (Haerendel, 1978;Savin et al, 2004) and transient flows associated with recently reconnected flux tubes .…”

Section: Introductionmentioning

confidence: 99%

“…One region that stands out is the exterior cusp. This region has been the subject of various terminology (Haerendel, 1978;Savin et al, 2004;Lavraud et al, 2002). Here we define it as the low magnetic field region located at large radial distances.…”

Section: Introductionmentioning

confidence: 99%

Cluster observations of high-frequency waves in the exterior cusp

et al. 2004

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Abstract.We study wave emissions, in the frequency range from above the lower hybrid frequency up to the plasma frequency, observed during one of the Cluster crossings of a high-beta exterior cusp region on 4 March 2003. Waves are localized near narrow current sheets with a thickness a few times the ion inertial length; currents are strong, of the order of 0.1-0.5 µA/m 2 (0.1-0.5 mA/m 2 when mapped to ionosphere). The high frequency part of the waves, frequencies above the electron-cyclotron frequency, is analyzed in more detail. These high frequency waves can be broad-band, can have spectral peaks at the plasma frequency or spectral peaks at frequencies below the plasma frequency. The strongest wave emissions usually have a spectral peak near the plasma frequency. The wave emission intensity and spectral character change on a very short time scale, of the order of 1 s. The wave emissions with strong spectral peaks near the plasma frequency are usually seen on the edges of the narrow current sheets. The most probable generation mechanism of high frequency waves are electron beams via bump-on-tail or electron two-stream instability. Buneman and ion-acoustic instability can be excluded as a possible generation mechanism of waves. We suggest that high frequency waves are generated by electron beams propagating along the separatrices of the reconnection region.

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Cluster observations of the exterior cusp and its surrounding boundaries under northward IMF

Cited by 95 publications

References 18 publications

Cluster survey of the high-altitude cusp properties: a three-year statistical study

Cluster survey of the high-altitude cusp properties: a three-year statistical study

Asymmetry of magnetosheath flows and magnetopause shape during low Alfvén Mach number solar wind

Cluster observations of high-frequency waves in the exterior cusp

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