Size and location of cusp diamagnetic cavities observed by Polar

Niehof, J. T.; Fritz, T. A.; Friedel, R. H.; Chen, Jiasheng

doi:10.1029/2009ja014827

Cited by 16 publications

(22 citation statements)

References 45 publications

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“…Though some observations agree with this gradual character for the inner transitions, for example Niehof et al (2010); Nykyri et al (2011a), others describe a much more rapid transition (Lavraud et al, 2002). This may be partly due to the dynamic nature of the cusp region, for instance Nykyri et al (2011b) have shown that some of the local fluctuations in plasma parameters within the CDC may be attributed to the reaction of the CDC to solar wind changes on relatively short timescales.…”

Section: Discussionmentioning

confidence: 80%

3-D mesoscale MHD simulations of magnetospheric cusp-like configurations: cusp diamagnetic cavities and boundary structure

2012

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Abstract. We present results from mesoscale simulations of the magnetospheric cusp region for both strongly northward and strongly southward interplanetary magnetic field (IMF). Simulation results indicate an extended region of depressed magnetic field and strongly enhanced plasma β which exhibits a strong dependence on IMF orientation. These structures correspond to the Cusp Diamagnetic Cavities (CDC's). The typical features of these CDC's are generally well reproduced by the simulation. The inner boundaries between the CDC and the magnetosphere are gradual transitions which form a clear funnel shape, regardless of IMF orientation. The outer CDC/magnetosheath boundary exhibits a clear indentation in both the x-z and y-z planes for southward IMF, while it is only indented in the x-z plane for northward, with a convex geometry in the y-z plane. The outer boundary represents an Alfvénic transition, mostly consistent with a slow-shock, indicating that reconnection plays an important role in structuring the high-altitude cusp region.

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Section: Discussionmentioning

confidence: 80%

3-D mesoscale MHD simulations of magnetospheric cusp-like configurations: cusp diamagnetic cavities and boundary structure

2012

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“…For example, the modeling of cusp soft electron precipitation in a coupled global geospace simulation requires a self‐consistent, dynamic, and accurate specification of the cusp area [e.g., Zhang et al , ]. In global MHD simulations, the area of the polar cusp can be defined by either the spatial extent of the diamagnetic depression [e.g., Niehof et al , ; Adamson et al , ; Walsh et al , ] or the simulated cusp plasma property, viz, relative density enhancement or parallel ion flux at high altitude. The three diagnostic methods give approximately the same area of the polar cusp, and only the results from the diamagnetic depression method are shown in the following section.…”

Section: Resultsmentioning

confidence: 99%

Predicting the location of polar cusp in the Lyon‐Fedder‐Mobarry global magnetosphere simulation

et al. 2013

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[1] In this paper we compare observations of the high-latitude cusp from DMSP data to simulations conducted using the Lyon-Fedder-Mobarry (LFM) global magnetosphere simulation. The LFM simulation is run for the 31 August 2005 to 02 September 2005 moderate storm, from which the solar wind data exhibits a wide range of conditions that enable a statistical representation of the cusp to be obtained. The location of the cusp is identified using traditional magnetic depression and plasma density enhancement at high altitude. A new diagnostic using the parallel ion number flux is also tested for cusp identification. The correlation of the cusp latitude and various solar wind interplanetary magnetic field (IMF) coupling functions is explored using the three different cusp identification methods. The analysis shows (1) the three methods give approximately the same location and size of the simulated cusp at high altitude and (2) the variations of the simulated cusp are remarkably consistent with the observed statistical variations of the low-altitude cusp. In agreement with observations, a higher correlation is obtained using other solar wind coupling functions such as the Kan-Lee electric field. The magnetic local time (MLT) position of the simulated cusp is found to depend upon the IMF B y component, with a lower linear correlation. The width of the simulated cusp in both latitude and MLT is also examined. The size of the cusp is found to increase with the solar wind dynamic pressure with saturation seen when the dynamic pressure is greater than 3 nPa.

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“…proposed local acceleration of particles in the cusp, particularly in diamagnetic cavities. Niehof et al (2010) showed a long-term association between observations of CEPs and cusp diamagnetic cavities; Walsh and Fritz (2011) presented electron observations consistent with local acceleration. Other studies have examined candidate mechanisms for such acceleration.…”

Section: Introductionmentioning

confidence: 99%

“…Cusp passes and CEP events are based on the events from Niehof et al (2010), derived from the Polar satellite observations. Their derivation is briefly summarized here.…”

Section: Data Setsmentioning

confidence: 99%

Association of cusp energetic ions with geomagnetic storms and substorms

2012

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Abstract. Energetic ions observed in the cusp have been explained as a result of processes within the magnetosphere, but also proposed as a driver of some of those same processes. This study assesses potential connections between energetic ions observed in the cusp and geomagnetic storm and substorm activity. These connections may suggest sources of cusp energetic particles (CEPs), or imply effects of these particles on magnetospheric dynamics. We identify CEPs from six years of cusp crossings by the Polar satellite, relating them to storm and substorm onsets. CEPs showed no significant dependence on storms but did show a weak, statistically significant, increase after substorm onsets. CEPs had no significant association with subsequent storm or substorm onsets. We conclude that substorm acceleration may contribute to CEPs but CEPs are unlikely to contribute to global magnetospheric dynamics.

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Size and location of cusp diamagnetic cavities observed by Polar

Cited by 16 publications

References 45 publications

3-D mesoscale MHD simulations of magnetospheric cusp-like configurations: cusp diamagnetic cavities and boundary structure

3-D mesoscale MHD simulations of magnetospheric cusp-like configurations: cusp diamagnetic cavities and boundary structure

Predicting the location of polar cusp in the Lyon‐Fedder‐Mobarry global magnetosphere simulation

Association of cusp energetic ions with geomagnetic storms and substorms

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