M. W. Dunlop

Beihang University(BUAA), Peping, Beijing, China

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Publications (609)928.19 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multi-spacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X-line; while using the MITS and FOTE methods, we find it is a magnetic island (O-line). We compare the efficiency and accuracy of these three methods, and find that the most efficient and accurate approach to identify a reconnection event is FOTE. In both the guide- and non-guide-field reconnection regimes, the FOTE method is equally applicable. This study for the first time demonstrates the capability of FOTE in identifying magnetic reconnection events; it would be useful to the forth-coming MMS mission.
    No preview · Article · Jan 2016 · Journal of Geophysical Research: Space Physics
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    H. Y. Lu · J. B. Cao · Y. S. Ge · T. L. Zhang · R. Nakamura · M. W. Dunlop
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    ABSTRACT: In this paper, we established a Hall-finite Larmor radius (FLR) MHD model by including Hall and finite Larmor radius (FLR) effects to study the dipolarization fronts (DFs) produced by the interchange instability in the magnetotail. The results indicate that the Hall effect on the scale of inertial length determines the distributions of electric field at DFs. The FLR effect can not only cause a dawn-dusk asymmetry of the DF structure but also can make the DF drift dawnward. The dawnward drifting of DF can be attributed to the ion diamagnetic velocity, which also causes alteration in the direction of the high-speed flow near the DF.
    Full-text · Article · Dec 2015 · Geophysical Research Letters
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    L.Q. Zhang · J.Y. Wang · W. Baumjohann · H. Rème · L. Dai · M. W. Dunlop · T. Chen · Y. Huang

    Full-text · Dataset · Dec 2015
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    L. Q. Zhang · L. Dai · W. Baumjohann · H. Rème · M. W. Dunlop · X. H. Wei
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    ABSTRACT: Utilizing multipoint observations by the Cluster satellites, we investigated the ion distributions of the fast bulk flows (FBFs) in the plasma sheet. Simultaneous observation by C1 and C3 revealed that parallel-dominant and perpendicular-dominant components of the flows coexist and correspond to Bx-dominant and Bz-dominant magnetic field regions within the FBFs, respectively. In both cases, the ions distributions are characterized by a single-beam/crescent shape. In particular, no reflected ions are found within the FBFs. Statistical analysis showed that within the FBFs, the strength of the Bx component is typically less than 5nT for Bz-dominant regions and above 10nT for Bx-dominant regions. To distinguish between the parallel-dominant component of the FBFs and the field-aligned beams in the plasma sheet boundary layer (PSBL), we further statistically analyzed the tailward parallel flows (TPF) with positive Bz in the plasma sheet. The results indicated that the FBFs tend to have higher velocity, weaker B, and higher magnetic tilt angle (θMTA) than the TPFs/PSBL beams. Statistically, in the region of B>30nT (θMTA>10°), only PSBL beams can be observed, while in the region of B<10 nT (θMTA>30°), the FBFs are dominant. In the intermediate region (10°<θMTA<30°) of the plasma sheet, the FBFs and the PSBL beams cooccur. These Cluster observations suggest that the X line can produce both perpendicular flow in central plasma sheet and parallel flow in the PSBL. In addition, the parallel-dominant component of the FBFs could be an important origin for the PSBL beams.
    Full-text · Article · Nov 2015 · Journal of Geophysical Research: Space Physics
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    ABSTRACT: During the first several months of the three-spacecraft Swarm mission all three spacecraft came repeatedly into close alignment, providing an ideal opportunity for validating the proposed dual spacecraft method for estimating current density from the Swarm magnetic field data. Two of the Swarm spacecraft regularly fly side-by-side in closely similar orbits, while the third at times approaches the other two. This provides a data set which under certain assumptions of stationarity of the magnetic field, can produce 2, 3, 4, 5 (or more) point measurements, which can be cross-compared. We find that at low Earth orbit the use of time-shifted positions allow stable estimates of current density to be made and can verify temporal effects as well as validating the interpretation of the current components as arising predominantly from field aligned currents. In the case of four-spacecraft configurations we can resolve the full vector current and therefore can check the perpendicular as well as parallel current density components directly, together with the quality factor for the estimates directly (for the first time in situ at low earth orbit).
    No preview · Article · Oct 2015 · Journal of Geophysical Research: Space Physics
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    L.Q. Zhang · J.Y. Wang · W. Baumjohann · H. Rème · L. Dai · M. W. Dunlop · T. Chen · Y. Huang
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    ABSTRACT: Utilizing associated observations of Geotail and ACE satellites from the year of 1998 to 2005, we investigated the X-lines in the near-Earth tail under different interplanetary magnetic field (IMF) conditions. The X-lines are recognized by the tailward fast flows (TFF) with negative Bz. Statistically, the X-lines in the tail can be observed for southward as well as northward IMF, but more frequently observed for southward IMF. A typical case on 26 Apr, 2005 showed clear evidence that the X-line can occur for northward IMF while the geomagnetic activity is particularly quiet. Further analysis showed that the X-line-related solar wind (SW) has stronger Ey and Bz components for southward than northward IMF. In addition, the X-line-related geomagnetic activities are stronger for southward than northward IMF.
    Full-text · Article · Sep 2015 · Journal of Geophysical Research: Space Physics
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    DESCRIPTION: L. Q. Zhang, W. Baumjohann, J. Y. Wang, H. Rème, M. W. Dunlop, and T. Chen
    Full-text · Research · Aug 2015
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    ABSTRACT: Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In this study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of data from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.
    Full-text · Article · Jul 2015 · Journal of Geophysical Research: Space Physics
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    L.Q. Zhang · W. Baumjohann · J.Y. Wang · H. Rème · M. W. Dunlop · T. Chen
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    ABSTRACT: In this paper, we statistically analyzed and compared the earthward flow (EF) and the tailward flow (TF) in the plasma sheet. It is found that the properties of the EF/TF in the central plasma sheet (CPS) of β>1 and the outer plasma sheet (OPS) of 0.1<β<1 are distinctly different. The main conclusions include that: 1) the EF occur in both the CPS and the OPS while the TF mainly occur in the OPS; 2) both flows are dominantly convective in the CPS, and parallel in the OPS; 3) in the CPS, the EF and the TF have similar characteristics, including their bulk velocities and ion densities and Ey components. Both flows tend to have isotropic temperatures; 4) in the OPS, the EF tend to have higher ion velocity, density and Ey than the TF. The EF tend to have anisotropic temperatures, while the TF tend to have more isotropic temperatures. As a whole, combined characteristics of the EF and the TF are consistent with (1) reflection at the “magnetic mirror point” near the Earth for parallel flows in the OPS, and (2) bouncing off/back from the dipolar field closer to the Earth for convective flows in the CPS.
    Full-text · Article · Jul 2015 · Journal of Geophysical Research: Space Physics
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    L. Q. Zhang · J.Y. Wang · W. Baumjohann · H. Rème · M. W. Dunlop
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    ABSTRACT: Utilizing C3/Cluster satellite observations from the year of 2001 to 2006, we investigated the earthward flow (EF) and tailward flow (TF) at Bz > 0 in the plasma sheet. We found that the EF and the TF have similar spatial distributions. Both characteristics are independent of the distance beyond 14 RE. Both flows are deflected while closer to the Earth. Statistical results further showed that the EF/TF occur in the central plasma sheet as well as the plasma sheet boundary layer and can be observed during quiet times and periods of geomagnetic activity. A typical event reveals that the EF and the TF have different plasma population. A transition region (TR) can be formed at the interface between the EF and TF. Very significant duskward components appeared in bulk velocities for both populations. It appears that the vortical-like structure can be formed near the TR. The magnetic field within the TR is twisted and strongly fluctuates. No clear magnetic flux pileups are observed inside the TR.
    Full-text · Article · May 2015 · Journal of Geophysical Research: Space Physics
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    ABSTRACT: We show for the first time, with direct, multispacecraft calculations of electric current density, and other methods, matched signatures of field-aligned currents (FACs) sampled simultaneously near the ionosphere at low (~500 km altitude) orbit and in the magnetosphere at medium (~2.5 RE altitude) orbits using a particular Swarm and Cluster conjunction. The Cluster signatures are interpreted and ordered through joint mapping of the ground/magnetospheric footprints and estimation of the auroral zone boundaries (taken as indication of the boundaries of Region 1 and Region 2 currents). We find clear evidence of both small-scale and large-scale FACs and clear matching of the behavior and structure of the large-scale currents at both Cluster and Swarm. The methodology is made possible through the joint operations of Cluster and Swarm, which contain, in the first several months of Swarm operations, a number of close three-spacecraft configurations.
    Full-text · Article · Apr 2015 · Geophysical Research Letters
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    ABSTRACT: On 18 May 2011, the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observed whistler-mode waves associated with a magnetic dip behind a dipolarization front (DF) structure in the bursty bulk flow (BBF) braking region. For the first time, we find that whistler-mode waves are generated at the edges of magnetic dip, rather than at the center (also known as “minimum-B-pocket”). Detailed wave analysis indicates that the waves are likely lower and upper band whistler-mode chorus. We examine electron pitch angle distributions at the edges of dip, and compare them with those at the center and far outside the magnetic dip. Results confirm that the positive temperature anisotropy and pancake distributions at the edges of magnetic dip provide free energy source for growth of the whistler-mode waves. We also interpret the whole physical process of how whistler-mode waves generate in this event.
    Full-text · Article · Mar 2015 · Journal of Geophysical Research: Space Physics
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    Tieyan Wang · Jinbin Cao · Huishan Fu · Wenlong Liu · Malcolm Dunlop
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    ABSTRACT: :On April 13 2002, four Cluster spacecraft with separations up to 127 km measured similar turbulence in the exterior cusp during northward interplanetary magnetic field (IMF) Bz. Both the power spectra of magnetic and electric field fluctuations resemble the classical Kolmogorov power law with the scaling f –1.7 under the proton gyrofrequency fcp (~0.3 Hz), breaks near fcp and then steepens with the scalings f –2.8 and f –2.0 up to 10 Hz, respectively. The observed ratio of the electric to magnetic field is in agreement with the theoretical values of |δE/δB| for the quasi perpendicular kinetic Alfvén waves (KAWs), which reflects the features of Alfvén turbulence. The wave vector and dispersion relation of the turbulence are obtained using k-filtering technique. The results show that the waves propagate quasi-perpendicularly to the background magnetic field. The similarity between the experimental and the theoratical dispersion relations indicates that the measured waves are kinetic Alfvén wave. The waves have right handed elliptical polarization in the plane perpendicular to k. The main axis of polarization ellipse is perpendicular to the average magnetic field. These features furthermore indicate that the turbulence properties agree well with those of KAW mode. The observed KAW is much possibly produced through resonance mode conversion. We calculate the density gradient vector using multi-point density data and found that the waves propagate basically towards high density region. The density gradient in the exterior cusp provides a favorable condition for the resonance converted KAW.
    Full-text · Article · Dec 2014 · Journal of Geophysical Research: Space Physics
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    ABSTRACT: Knowing the magnetic field distribution in the magnetotail current sheet (CS) is essential for exploring magnetotail dynamics. In this study, using a joint dataset of Cluster/TC-1, the radial profile of the magnetic field in the magnetotail CS with radial distances covering 8<r<20 RE under different geomagnetic activity states (i.e., AE≤100 nT for quiet intervals while AE>100 nT for active times) and solar wind parameters are statistically surveyed. Our new findings demonstrate that, independent of the activity state, the field strength and Bz component (GSM coordinates) start the monotonic increase prominently as r decreases down to ∼11.5RE, which means the dipole field starts to make a significant contribution from there. At least in the surveyed radial range, the Bz component is found to be weaker in the midnight and dusk sectors than that in the dawn sector, displaying a dawn-dusk asymmetry. The occurrence rate of negative Bz in active times also exhibits a similar asymmetric distribution, which implies active dynamics may occur more frequently at midnight and dusk flank. In comparison with that in quiet intervals, several features can be seen in active times: (1) a local Bz minimum between 10.5<r<12.5 RE is found in the dusk region, (2) the Bz component around the midnight region is generally stronger and experiences larger fluctuations, and (3) a sharp positive/negative-excursion of the By component occurs at the dawn/dusk flank regions inside r<10 RE. The response to solar wind parameters revealed that the Bz component is generally stronger under higher dynamic pressure (Pdy>5 nPa), which may support the dawn-dusk squeezing effect as presented by Miyashita et al. (2010). The CS By is generally correlated with the interplanetary magnetic field (IMF) By component, and the correlation quality is found to be better with higher penetration coefficient (the ratio of CS By to IMF By) when IMF Bz is positive. The implications of the present results are discussed.
    Full-text · Article · Nov 2014 · Planetary and Space Science
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    A.Y. Duan · J. B. Cao · M. Dunlop · Z.Q. Wang
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    ABSTRACT: We studied energetic electron (40-250 keV) bursts (EEB) in the plasma sheet (PS) and their relation to bursty bulk flows (BBF) using the data recorded by Cluster from 2001 to 2009. The EEBs in the PS can be classified into four types. Three types of EEBs are dispersionless, including EEBs accompanied with BBFs (V > 250 km/s) but without DF, EEBs accompanied with both dipolarization front (DF) and BBF, and EEBs accompanied with DF and fast flow with V < 250 km/s. One type of EEB, i.e. EEBs not accompanied with BBFs and DFs, is dispersed. The energetic electrons (40 -130 keV) can be easily transported earthward by BBFs due to the strong dawn-dusk electric field embedded in BBFs. The DFs in BBFs can produce energetic electrons (40 to 250 keV). For the EEBs with DF and BBFs, the superposed epoch analyses show that the increase of energetic electron flux has two phases: gradual increase phase before DF and rapid increase phase concurrent with DF. In the PS around x = -18 RE, 60%-70% of EEBs are accompanied with BBFs, indicating that although hitherto there have been various acceleration mechanisms of energetic electrons, most of energetic electrons in the PS are related with magnetic reconnection, and they are produced either directly by magnetic reconnection or indirectly by the DFs within BBFs. In the BBF's braking region of -12 RE < x < -10 RE, 20% of EEBs are accompanied with BBFs. The corresponding ratio between EEBs and BBFs shows a dawn-dusk asymmetry.
    Full-text · Article · Nov 2014 · Journal of Geophysical Research: Space Physics
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    Full-text · Dataset · Oct 2014
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    Full-text · Dataset · Oct 2014
  • W.S. Shang · Q.Q. Shi · A.M. Tian · M.W. Dunlop · Z.H. Yao
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    ABSTRACT: Combining with ARTEMIS (P1 and P2) and Wind data, we have investigated the magnetic field and plasma properties in the distant magnetotail during the period January to December 2012. Of particular interest is their characteristic of density near the neutral sheet. We present the discovery of high speed flow of high density in the distant tail under the northward interplanetary magnetic field (IMF) conditions. Multi-satellite observations can present the tailward high speed flow accompany with high density plasma when the satellites were crossing the neutral sheet in the north of the ecliptic plane under the active interplanetary condition. And in this case, single satellite observation shows that the earthward high speed flow accompany with high density plasma because of the influence of solar wind dynamic pressure. And the other satellite observed the tailward high speed flow due to solar wind entry into the magnetotail.
    No preview · Article · Oct 2014
  • X.C. Gou · Q.Q. Shi · A.M. Tian · S.Y. Fu · Q.G. Zong · M.W. Dunlop · Z.Y. Pu
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    ABSTRACT: In this paper, using Cluster multi-spacecrafts observation data during January to April of each year from 2001 to 2006, we have studied the solar wind penetration events into the Earth's high-latitude magnetosphere. When the IMF is northward, although the formation of the entry layers depends on the direction of IMF, we pointed out that it mainly depends on the IMF Bx component and the influences of IMF By component could be weak.
    No preview · Article · Oct 2014
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    Full-text · Dataset · Aug 2014

Publication Stats

7k Citations
928.19 Total Impact Points

Institutions

  • 2014-2015
    • Beihang University(BUAA)
      • School of Astronautics
      Peping, Beijing, China
  • 1-2015
    • Imperial College London
      • Department of Physics
      Londinium, England, United Kingdom
  • 2013
    • Science and Technology Facilities Council
      Swindon, England, United Kingdom
  • 2012
    • Chinese Academy of Sciences
      Peping, Beijing, China
  • 2008
    • University of California, Berkeley
      • Space Sciences Laboratory
      Berkeley, CA, United States
  • 1993-2007
    • Technische Universität Braunschweig
      • Institute for Geophysics and Extraterrestrial Physics
      Brunswyck, Lower Saxony, Germany
  • 2002
    • Research Associates Laboratory
      Dallas, Texas, United States
    • KTH Royal Institute of Technology
      • School of Electrical Engineering (EE)
      Tukholma, Stockholm, Sweden
  • 2001
    • The University of Sheffield
      • Department of Automatic Control and Systems Engineering
      Sheffield, England, United Kingdom
  • 1999
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
  • 1991
    • Space Research Institute
      Moskva, Moscow, Russia
  • 1990
    • University of Cologne
      • Institute of Geophysics and Meteorology
      Köln, North Rhine-Westphalia, Germany