M. W. Dunlop

Peking University, Beijing, Beijing Shi, China

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Publications (322)549.83 Total impact

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    ABSTRACT: [1] In this paper, we test whether time periods with hot proton temperature anisotropy are associated with EMIC waves, and whether the plasma conditions during the observed waves satisfy the linear theory threshold condition. We identify 865 events observed by the Composition DIstribution Function (CODIF) instrument onboard Cluster spacecraft 4 (SC4) during 1 January 2001 – 1 January 2011 that exhibit a positive temperature anisotropy (Ahp = T⊥ h/T∥ h − 1) in the 10-40 keV protons. The events occur over an L range from 4 to 10 in all magnetic local times and at magnetic latitudes (MLAT) within ±50°. Of these Hot Proton Temperature Anisotropy (HPTA) events, only 68 events have electromagnetic ion cyclotron (EMIC) waves. In these 68 HPTA events, for those at 3.81.0 nT2/Hz mainly appear in the region with fEMIC/fH,eq 0.45 * fEMIC/fH,lo, and Ahp/(Ahp + 1) 0.25. By testing a threshold equation for the EMIC instability based on linear theory, we find that for EMIC waves with |MLAT| ≤ 10° in the He, H and > H bands the percentages that satisfy the predicted conditions for wave growth by the threshold equation are 15.2%, 24.6% and 25.6%. For the EMIC waves with |MLAT| > 10° the percentages that satisfy the wave growth predicted conditions are only 2.8%, 2.6% and 0.0%. Finally, possible reasons for the low forecast accuracies of EMIC waves are suggested.
    Journal of Geophysical Research: Space Physics. 01/2014;
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    ABSTRACT: is well accepted that the propagation of electromagnetic ion cyclotron (EMIC) waves are bidirectional near their source regions and unidirectional when away from these regions. The generally believed source region for EMIC waves is around the magnetic equatorial plane. Here we describe a series of EMIC waves in the Pc1 (0.2-5 Hz) frequency band above the local He+ cyclotron frequency observed in situ by all four Cluster spacecraft on 9 April 2005 at midmagnetic latitudes (MLAT = ~33°-49°) with L = 10.7-11.5 on the dayside (MLT = 10.3-10.4). A Poynting vector spectrum shows that the wave packets consist of multiple groups of packets propagating bidirectionally, rather than unidirectionally, away from the equator, while the local plasma conditions indicate that the spacecraft are entering into a region sufficient for local wave excitation. One possible interpretation is that, while part of the observed waves are inside their source region, the others are either close enough to the source region, or mixed with the wave packets from multiple source regions at different latitudes.
    Journal of Geophysical Research 10/2013; 118(10):6266-6278. · 3.17 Impact Factor
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    ABSTRACT: On 14 June 2007, four Time History of Events and Macroscale Interactions during Substorms spacecraft observed a flux transfer event (FTE) on the dayside magnetopause, which has been previously proved to be generated by multiple, sequential X-line reconnection (MSXR) in a 2-D context. This paper reports a further study of the MSXR event to show the 3-D viewpoint based on additional measurements. The 3-D structure of the FTE flux rope across the magnetospheric boundary is obtained on the basis of multipoint measurements taken on both sides of the magnetopause. The flux rope's azimuthally extended section is found to lie approximately on the magnetopause surface and parallel to the X-line direction; while the axis of the magnetospheric branch is essentially along the local unperturbed magnetospheric field lines. In the central region of the flux rope, as distinct from the traditional viewpoint, we find from the electron distributions that two types of magnetic field topology coexist: opened magnetic field lines connecting the magnetosphere and the magnetosheath and closed field lines connecting the Southern and Northern hemispheres. We confirm, therefore, for the first time, the characteristic feature of the 3-D reconnected magnetic flux rope, formed through MSXR, through a determination of the field topology and the plasma distributions within the flux rope. Knowledge of the complex geometry of FTE flux ropes will improve our understanding of solar wind-magnetosphere interaction.
    Journal of Geophysical Research 05/2013; 118(5):1904-1911. · 3.17 Impact Factor
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    ABSTRACT: It is widely accepted that the magnetic flux transfer events (FTEs) form a channel between the magnetosphere and magnetosheath to allow transport of solar wind plasma and energy into geospace. On June 14, 2007 four THEMIS spacecraft observed a FTE on the dayside magnetopause which has been previously interpreted as a reconnected flux rope, generated by a double X-line in a two-dimensional (2D) context. This presentation reports a further study of the event to show the three-dimensional (3D) viewpoint based on additional measurements and to confirm that multiple, sequential X-line reconnection (MSXR) is operating. The 3D structure of the FTE flux rope across the magnetospheric boundary is obtained on the basis of multi-point measurements taken on both sides of the magnetopause. The flux rope's azimuthally extended part (leading to the magnetosheath branch of the reconnected flux) is found to lie approximately on the magnetopause surface and parallel to the X-line direction; whilst the axis of the magnetospheric branch is essentially along the local unperturbed magnetospheric field lines. In the central region of the flux rope, as distinct from the traditional viewpoint, we find from the electron distributions that two types of magnetic field topology co-exist: opened magnetic field lines connecting the magnetosphere to the magnetosheath and closed field lines connecting the southern and northern hemispheres. We confirm, therefore, for the first time in-situ, the characteristic feature of the 3D reconnected magnetic flux rope, formed through MSXR, through a determination of the field topology and the plasma distributions within the flux rope. Knowledge of the complex geometry of FTE flux ropes will improve our understanding of solar wind-magnetosphere interaction.
    04/2013;
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    ABSTRACT: works have emphasized the significant influence of the solar wind Alfvén Mach number (MA) 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 MA 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 MA), we also investigate the changes in magnetopause shape as a function of solar wind MA 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 MA, while is it elongated (albeit with moderate statistical significance) along the direction of the IMF during low MA. These findings are consistent with enhanced magnetic forces that prevail in the magnetosheath during low MA. 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.
    Journal of Geophysical Research 03/2013; 118(3):1089-1100. · 3.17 Impact Factor
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    ABSTRACT: An understanding of the transport of solar wind plasma into and throughout the terrestrial magnetosphere is crucial to space science and space weather. For non-active periods, there is little agreement on where and how plasma entry into the magnetosphere might occur. Moreover, behaviour in the high-latitude region behind the magnetospheric cusps, for example, the lobes, is poorly understood, partly because of lack of coverage by previous space missions. Here, using Cluster multi-spacecraft data, we report an unexpected discovery of regions of solar wind entry into the Earth's high-latitude magnetosphere tailward of the cusps. From statistical observational facts and simulation analysis we suggest that these regions are most likely produced by magnetic reconnection at the high-latitude magnetopause, although other processes, such as impulsive penetration, may not be ruled out entirely. We find that the degree of entry can be significant for solar wind transport into the magnetosphere during such quiet times.
    Nature Communications 02/2013; 4:1466. · 10.02 Impact Factor
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    ABSTRACT: 1] We develop a new simple method for inferring the orientation of a magnetic flux rope, which is assumed to be a time-independent cylindrically symmetric structure via the direct single-point analysis of magnetic field structure. The model tests demonstrate that, for the cylindrical flux rope regardless of whether it is force-free or not, the method can consistently yield the axis orientation of the flux rope with higher accuracy and stability than the minimum variance analysis of the magnetic field and the Grad-Shafranov reconstruction technique. Moreover, the radial distance to the axis center and the current density can also be estimated consistently. Application to two actual flux transfer events observed by the four satellites of the Cluster mission demonstrates that the method is more appropriate to be used for the inner part of flux rope, which might be closer to the cylindrical structure, showing good agreement with the results obtained from the optimal Grad-Shafranov reconstruction and the least squares technique of Faraday's law, but fails to produce such agreement for the outer satellite that grazes the flux rope. Therefore, the method must be used with caution., Method for inferring the axis orientation of cylindrical magnetic flux rope based on single-point measurement, J. Geophys. Res., 118, doi:10.1029/2012JA018079.
    Journal of Geophysical Research 01/2013; · 3.17 Impact Factor
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    ABSTRACT: Nonlinear wave-driven processes in plasmas are normally described by either a monochromatic pump wave that couples to other monochromatic waves, or as a random phase wave coupling to other random phase waves. An alternative approach involves a random or broadband pump coupling to monochromatic and/or coherent structures in the plasma. This approach can be implemented through the wave-kinetic model. In this model, the incoming pump wave is described by either a bunch (for coherent waves) or a sea (for random phase waves) of quasi-particles. This approach has been applied to both photon acceleration in laser wakefields and drift wave turbulence in magnetized plasma edge configurations. Numerical simulations have been compared to experiments, varying from photon acceleration to drift mode-zonal flow turbulence, and good qualitative correspondences have been found in all cases.
    Journal of Plasma Physics 12/2012; 76(06):903-914. · 0.76 Impact Factor
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    ABSTRACT: 1] We present a generalized multipoint analysis of physical quantities, such as magnetic field and plasma flow, based on spatial gradient properties, where the multipoint data may be taken by irregular (distorted) configurations of any number of spacecraft. The methodology is modified from a previous, fully 3-D gradient analysis technique, designed to apply strictly to 4-point measurements and to be stable for regular spacecraft configurations. Here, we adapt the method to be tolerant against distorted configurations and to return a partial result when fewer spacecraft measurements are available. We apply the method to a variety of important physical quantities, such as the electric current density and the vorticity of plasma flows based on Cluster and THEMIS multiple-point measurements. The method may also have valuable applications on the coming Swarm mission. Citation: Shen, C., et al. (2012), Spatial gradients from irregular, multiple-point spacecraft configurations, J. Geophys. Res., 117, A11207, doi:10.1029/2012JA018075.
    Journal of Geophysical Research 11/2012; · 3.17 Impact Factor
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    ABSTRACT: A substorm dispersionless injection event observed during the storm recovery phase on 11 March 1998 at geosynchronous orbit is carefully studied. The event shows the notable characteristics that for energetic ions the flux enhancement ratio before and after injection increases and remains elevated with increasing energy, while for energetic electrons it tends to decrease with increasing energy. In order to explain the unique injection feature, the authors propose a possible mechanism that velocity space diffusion in common to electric acceleration adjusts the particle injection state. Spectral characteristics of four different phases (pregrowth phase, the growth phase, the substorm expansion phase, and the recovery phase) have been investigated. The differential fluxes of electrons from 50 keV to 1.5 Mev and ions from 50 keV to 1.2 MeV measured by Synchronous Orbit Plasma Analyzer (SOPA) instrument onboard LANL satellite 1991-080 are found to be best fitted with the three-parameter kappa distribution function (f ˜ A0 · E[1 + E / (κE0)]-κ-1) by Levenberg-Marquardt and Universal Global Optimization methods. The evolutions of the three parameters in the above kappa distribution in different substorm phases have been depicted for both electrons and ions. In each phase, E0 and κ show an approximately linear relationship κ(E0) = κ0 + ηE0. This linear relationship can be obtained by solving the velocity space diffusion equation with an initial superthermal kappa distribution. Ion and electron are found to have opposite trend of parameters κ0 and η in each phase, which indicates that the different species of particles exert different velocity space diffusion processes so that their flux enhancement ratios before and after injection are rather different. This implies that not only electric field acceleration, but also velocity space diffusion plays a very important role in the particle injection.
    Journal of Geophysical Research 11/2012; 117(A11):11210-. · 3.17 Impact Factor
  • A. T. Y. Lui, Q.-G. Zong, C. Wang, M. W. Dunlop
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    ABSTRACT: We examine the strength of the electron source associated with dipolarization at the outer boundary of the radiation belts using multisatellite observations from THEMIS. This topic is relevant to the determination on the relative roles of inward radial diffusion versus internal local acceleration for the origin of the relativistic electrons in the outer radiation belt. We focus on the electron phase space density (PSD) as a function of the first adiabatic invariant (μ) for equatorially mirroring population over a broad energy range. It is found that the source strength associated with dipolarization for non-storm periods at the outer boundary of the radiation belts can be well above the observed fluxes of relativistic electrons inside the outer radiation belt. The PSD change due to the magnetic field strength variation dominates over PSD change from the energy flux increase with dipolarization, resulting in a strong anticorrelation between magnetic field strength and PSD values at a given μ. If observations from closely spaced satellites during the same event can be used to indicate radial transport of electrons with dipolarization, then the observed PSD at these satellites indicates frequent occurrence of non-adiabatic process during their radial transport.
    Journal of Geophysical Research 10/2012; 117(A10):10224-. · 3.17 Impact Factor
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    ABSTRACT: We report a clear transition through a reconnection layer at the low-latitude magnetopause which shows a complete traversal across all reconnected field lines during northwestward interplanetary magnetic field (IMF) conditions. The associated plasma populations confirm details of the electron and ion mixing and the time history and acceleration through the current layer. This case has low magnetic shear with a strong guide field and the reconnection layer contains a single density depletion layer on the magnetosheath side which we suggest results from nearly field-aligned magnetosheath flows. Within the reconnection boundary layer, there are two plasma boundaries, close to the inferred separatrices on the magnetosphere and magnetosheath sides (S sp and S sh) and two boundaries associated with the Alfvén waves (or Rotational Discontinuities, RD sp and RD sh). The data are consistent with these being launched from the reconnection site and the plasma distributions are well ordered and suggestive of the time elapsed since reconnection of the field lines observed. In each sub-layer between the boundaries the plasma distribution is different and is centered around the current sheet, responsible for magnetosheath acceleration. We show evidence for a velocity dispersion effect in the electron anisotropy that is consistent with the time elapsed since reconnection. In addition, new evidence is presented for the occurrence of partial reflection of magnetosheath electrons at the magnetopause current layer. Citation: Zhang, Q.-H., et al. (2012), Inner plasma structure of the low-latitude reconnection layer, J. Geophys. Res., 117, A08205, doi:10.1029/2012JA017622.
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    ABSTRACT: 1] We report a clear transition through a reconnection layer at the low-latitude magnetopause which shows a complete traversal across all reconnected field lines during northwestward interplanetary magnetic field (IMF) conditions. The associated plasma populations confirm details of the electron and ion mixing and the time history and acceleration through the current layer. This case has low magnetic shear with a strong guide field and the reconnection layer contains a single density depletion layer on the magnetosheath side which we suggest results from nearly field-aligned magnetosheath flows. Within the reconnection boundary layer, there are two plasma boundaries, close to the inferred separatrices on the magnetosphere and magnetosheath sides (S sp and S sh) and two boundaries associated with the Alfvén waves (or Rotational Discontinuities, RD sp and RD sh). The data are consistent with these being launched from the reconnection site and the plasma distributions are well ordered and suggestive of the time elapsed since reconnection of the field lines observed. In each sub-layer between the boundaries the plasma distribution is different and is centered around the current sheet, responsible for magnetosheath acceleration. We show evidence for a velocity dispersion effect in the electron anisotropy that is consistent with the time elapsed since reconnection. In addition, new evidence is presented for the occurrence of partial reflection of magnetosheath electrons at the magnetopause current layer. Citation: Zhang, Q.-H., et al. (2012), Inner plasma structure of the low-latitude reconnection layer, J. Geophys. Res., 117, A08205, doi:10.1029/2012JA017622.
    Journal of Geophysical Research 08/2012; 117:A08205,. · 3.17 Impact Factor
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    ABSTRACT: The Kelvin-Helmholtz Instability (KHI) can drive waves at the magnetopause. These waves can grow to form rolled-up vortices and facilitate transfer of plasma into the magnetosphere. To investigate the persistence and frequency of such waves at the magnetopause we have carried out a survey of all Double Star 1 magnetopause crossings, using a combination of ion and magnetic field measurements. Using criteria originally used in a Geotail study made by Hasegawa et al. (2006) (forthwith referred to as H2006), 17 candidate events were identified from the entire TC-1 mission (cover-ing ∼623 orbits where the magnetopause was sampled), a majority of which were on the dayside of the terminator. The relationship between density and shear velocity was then in-vestigated, to identify the predicted signature of a rolled up vortex from H2006 and all 17 events exhibited some level of rolled up behavior. The location of the events had a clear dawn-dusk asymmetry, with 12 (71 %) on the post noon, dusk flank suggesting preferential growth in this region.
    Annales Geophysicae 06/2012; 30:1025-1035. · 1.52 Impact Factor
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    ABSTRACT: 1] The strong magnetic field B y component (in GSM coordinates) has been increasingly noticed to play an important role in the dynamics of tail current sheet (CS). The distribution profile of strong B y components in the tail CS (i.e., those with guide field), however, is not well known. In the present work, by using the simultaneous multipoint observations of Cluster satellites, the profile of a strong B y component in tail current sheets is explored, through detailed case studies, as well as in a statistical study. It is discovered that around the midnight meridian, the strength of the strong B y component, i.e., |B y |, is basically enhanced at the center of the CS relative to that in the CS boundaries and lobes and forms a north-south symmetric distribution about the center of CS. Generally, however, for strong guide field cases in the non-midnight meridian, the profile of B y strength basically becomes north-south asymmetric, the strength of the B y component in the northern side of the CS is found to be either stronger or weaker than that in the counterpart southern side. By considering the modulation of the tail flaring magnetic field with magnetic local time, we propose an interpretation to account for the variation of the B y -profile, which is supported by the statistical survey. These results offer an observation basis for further studies. Citation: Rong, Z. J., et al. (2012), Profile of strong magnetic field B y component in magnetotail current sheets, J. Geophys. Res., 117, A06216, doi:10.1029/2011JA017402.
    Journal of Geophysical Research 06/2012; · 3.17 Impact Factor
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    ABSTRACT: A number of poleward-moving events were observed between 1130-1300 UT on 11 Feb 2004, during periods of southward interplanetary magnetic field (IMF), while the steerable antenna of the EISCAT Svalbard Radar (ESR) and the Tromsø VHF Radar pointed nearly northward at low elevation. In this interval, simultaneous SuperDARN CUTLASS Finland radar measurements showed poleward-moving radar aurora forms (PMRAFs) which appeared very similar to the density enhancements observed by the ESR northward-pointing antenna. These events appeared quasi-periodically with a period of about 10 minutes. Comparing the observations from the above three radars, it is inferred that there is an almost one-to-one correspondence between the Poleward-Moving Plasma Concentration Enhancements (PMPCEs) observed by the ESR and the VHF radar, and the PMRAFs measured by the CUTLASS Finland radar. These observations are consistent with the interpretation that the polar cap patch material was generated by photo-ionisation at sub-auroral latitudes, and that the plasma was structured by bursts of magnetopause reconnection giving access to the polar cap. There is clear evidence that plasma structuring into patches was dependent on the variability in IMF |BY|. The duration of these events implies that the average evolution time of the newly opened flux tubes from the sub-auroral region to the polar cap was about 33 minutes.
    04/2012;
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    ABSTRACT: The combined magnetic effect of the Earth's ring current (RC), the system of connecting field aligned currents (FACs) and the ionospheric polar currents, forms the dominant external influence on the measured Geomagnetic field. These induced magnetic signals have significant effect at low Earth orbit (LEO), and will be surveyed by the three Swarm spacecraft. SWARM observations will benefit from other spacecraft information, however, and present indices, such as Dst, are presently not good indicators (the RC can be different during storm development and recovery for similar Dst). A space based indicator is needed, for example, which maps RC response, in particular, to better define these influences and provide corrections to the main geomagnetic field models. In anticipation of the direct comparison of SWARM and other spacecraft, preliminary study of the influence of the RC using Cluster, Champ and other LEO data is in progress, including a full-circle determination of the RC vector directly from Cluster 4-spacecraft perigee observations, under non-storm conditions (Dst > -30 nT). The results confirm that the in situ average measured current density (in the radial range 4-4.5RE) is asymmetric in MLT, ranging from 9 to 27 nAm-2 (growing from 10 to 27 nAm-2 as azimuth reduces from about 12:00MLT to 03:00 and falling from 20 to 10 nAm-2 less steadily as azimuth reduces from 24:00 to 12:00MLT). This result is consistent with the operation of region-2 field aligned-currents (FACs), which are expected to flow upward into the ring current around 09:00MLT and downward out of the ring current around 14:00MLT. We note, however, that it is also consistent with a possible asymmetry in the radial distribution profile of current density and that part of the enhanced current could reflect an increase in the mean AE activity (during the periods in which Cluster samples those MLT). A specific problem is therefore to match the interpretation of the magnetic signals seen at LEO and those measured directly within the central RC region, where dawn-dusk RC asymmetries, seen both under storm and non-storm conditions, have some discrepancy between near-Earth and in-situ estimates. This could result from FAC connectivity, but at least call for a new consideration of the Dst correction in main field modeling.
    04/2012;
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    ABSTRACT: Magnetic holes with relatively small scale sizes, detected by Cluster and TC-1 in the magnetotail plasma sheet, are studied in this paper. It is found that these magnetic holes are spatial structures and they are not magnetic depressions generated by the flapping movement of the magnetotail current sheet. Most of the magnetic holes (93%) were observed during intervals with Bz larger than Bx, i.e. they are more likely to occur in a dipolarized magnetic field topology. Our results also suggest that the occurrence of these magnetic holes might have a close relationship with the dipolarization process. The magnetic holes typically have a scale size comparable to the local proton Larmor radius and are accompanied by an electron energy flux enhancement at a 90° pitch angle, which is quite different from the previously observed isotropic electron distributions inside magnetic holes in the plasma sheet. It is also shown that most of the magnetic holes occur in marginally mirror-stable environments. Whether the plasma sheet magnetic holes are generated by the mirror instability related to ions or not, however, is unknown. Comparison of ratios, scale sizes and propagation direction of magnetic holes detected by Cluster and TC-1, suggests that magnetic holes observed in the vicinity of the TC-1 orbit (~7-12 RE) are likely to be further developed than those observed by Cluster (~7-18 RE).
    Annales Geophysicae 03/2012; 30(3):583-595. · 1.52 Impact Factor
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    ABSTRACT: The plasmasheet boundary layer (PSBL) has been found to be a region of intense mass, energy, and momentum transfer. Clear entry of streaming O+ from the lobe into the PSBL is often observed in the ~20 Re magnetotail, and the energy of the O+ gradually increases as it enters. In our previous study, by testing for the invariance of the phase space density, we showed that while the high velocity of the O+ observed in the tail lobes is mostly due to the velocity filter effect, the energetic O+ beams observed within the PSBL actually have been accelerated. The energy increase is up to several keV. How these ions inside the PSBL are accelerated is an interesting question. Observations show that the electric field is much stronger in the PSBL than in the lobes. As a result, streaming O+ will experience a strong EXB drift that can increase the velocity of O+. A close look at the distribution function shows that streaming O+ experiences some kind of acceleration/heating inside the PSBL as well as the strong EXB effect. Many energization mechanisms have been proposed, including electrostatic and electromagnetic wave heating and acceleration parallel to the electric field due to non-adiabatic motion. In order to determine the energization mechanism that is responsible for heating the streaming O+ inside the PSBL, we use several case studies to determine how the distribution function changes as the O+ enters the PSBL, and how the changes correlate with the electric field and with wave activity. Invariants and features of the streaming O+ energization in the PSBL are presented and possible energization mechanisms are discussed.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: The Earth's magnetic field is influenced by the interplanetary magnetic field (IMF), specially at the magnetopause where both magnetic fields enter in direct contact and magnetic reconnection can be initiated. In the polar regions, the polar cusp that extends from the magnetopause down to the ionosphere is also directly influenced. The reconnection not only allow ions and electrons from the solar wind to enter the polar cusp but also give an impulse to the magnetic field lines threading the polar cusp through the reconnection electric field. A dispersion in energy of the ions is subsequently produced by the motion of field lines and the time-of-flight effect on down-going ions. If reconnection is continuous and operates at constant rate, the ion dispersion is smooth and continuous. On the other hand if the reconnection rate varies, we expect interruption in the dispersion forming energy steps or staircase. Similarly, multiple entries near the magnetopause could also produce steps at low or mid-altitude when a spacecraft is crossing subsequently the field lines originating from these multiple sources. Cluster with four spacecraft following each other in the mid-altitude cusp can be used to distinguish between these "temporal" and "spatial" effects. We will show two Cluster cusp crossings where the spacecraft were separated by a few minutes. The energy dispersions observed in the first crossing were the same during the few minutes that separated the spacecraft. In the second crossing, two ion dispersions were observed on the first spacecraft and only one of the following spacecraft, about 10 min later. The detailed analysis indicates that these steps result from spatial structures.
    AGU Fall Meeting Abstracts. 12/2011;

Publication Stats

2k Citations
549.83 Total Impact Points

Institutions

  • 2013
    • Peking University
      • School of Earth and Space Sciences
      Beijing, Beijing Shi, China
  • 1–2011
    • Imperial College London
      • Department of Physics
      Londinium, England, United Kingdom
  • 2007
    • Technische Universität Braunschweig
      • Institute for Geophysics and Extraterrestrial Physics
      Brunswyck, Lower Saxony, Germany
  • 2005
    • University of California, Los Angeles
      • Institute of Geophysics and Planetary Physics
      Los Angeles, CA, United States
  • 1997
    • University of Leicester
      • Department of Physics and Astronomy
      Leicester, ENG, United Kingdom
  • 1995
    • Imperial Valley College
      Imperial, California, United States
  • 1990
    • University of Cologne
      • Institute of Geophysics and Meteorology
      Köln, North Rhine-Westphalia, Germany