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  • 1. Chasapis, A.
    et al.
    Retino, A.
    Sahraoui, F.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Sundkvist, D.
    Greco, A.
    Sorriso-Valvo, L.
    Canu, P.
    Thin Current Sheets and Associated Electron Heating in Turbulent Space Plasma2015Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 804, nr 1, artikel-id L1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Intermittent structures, such as thin current sheets, are abundant in turbulent plasmas. Numerical simulations indicate that such current sheets are important sites of energy dissipation and particle heating occurring at kinetic scales. However, direct evidence of dissipation and associated heating within current sheets is scarce. Here, we show a new statistical study of local electron heating within proton-scale current sheets by using high-resolution spacecraft data. Current sheets are detected using the Partial Variance of Increments (PVI) method which identifies regions of strong intermittency. We find that strong electron heating occurs in high PVI (>3) current sheets while no significant heating occurs in low PVI cases (<3), indicating that the former are dominant for energy dissipation. Current sheets corresponding to very high PVI (>5) show the strongest heating and most of the time are consistent with ongoing magnetic reconnection. This suggests that reconnection is important for electron heating and dissipation at kinetic scales in turbulent plasmas.

  • 2.
    Divin, Andrey
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Lower hybrid drift instability at a dipolarization front2015Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 2, s. 1124-1132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present observations of a reconnection jet front detected by the Cluster satellites in the magnetotail of Earth, which are commonly referred to as dipolarization fronts. We investigate in detail electric field structures observed at the front which have frequency in the lower hybrid range and amplitudes reaching 40mV/m. We determine the frequency and phase velocity of these structures in the reference frame of the front and identify them as a manifestation of the lower hybrid drift instability (LHDI) excited at the sharp density gradient at the front. The LHDI is observed in the nonlinear stage of its evolution as the electrostatic potential of the structures is comparable to approximate to 10% of the electron temperature. The front appears to be a coherent structure on ion and MHD scales, suggesting existence of a dynamic equilibrium between excitation of the LHDI and recovery of the steep density gradient at the front.

  • 3.
    Eriksson, Elin
    et al.
    Uppsala universitet, Institutionen för fysik och astronomi.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri. V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyayintsev, V. M.
    Taras Shevchenko Natl Univ Kyiv, Dept Theoret Phys, Kiev, Ukraine..
    Andre, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Statistics and accuracy of magnetic null identification in multispacecraft data2015Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, s. 6883-6889Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Complex magnetic topologies are ubiquitous in astrophysical plasmas. Analyzing magnetic nulls, regions of vanishing magnetic field, is one way to characterize 3-D magnetic topologies. Magnetic nulls are believed to be important in 3-D reconnection and turbulence. In the vicinity of a null, plasma particles become unmagnetized and can be accelerated to high energies by electric fields. We present the first statistical study of the occurrence of magnetic nulls and their types in the Earth's nightside magnetosphere. We are able to identify the nulls both in the tail and in the magnetopause current sheets. On average, we find one null for every few current sheet crossings. We show that the type identification of magnetic nulls may be sensitive to local fluctuations in the magnetic field. We develop and demonstrate a method to estimate the reliability of the magnetic null type identification.

  • 4.
    Fu, H. S.
    et al.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Cao, J. B.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Cao, D.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Wang, Z.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Vaivads, Andris
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik. Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA.
    Huang, S. Y.
    Wuhan Univ, Sch Elect & Informat, Wuhan, Hubei, Peoples R China.
    Evidence of Magnetic Nulls in Electron Diffusion Region2019Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 1, s. 48-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theoretically, magnetic reconnection—the process responsible for solar flares and magnetospheric substorms—occurs at the X‐line or radial null in the electron diffusion region (EDR). However, whether this theory is correct is unknown, because the radial null (X‐line) has never been observed inside the EDR due to the lack of efficient techniques and the scarcity of EDR measurements. Here we report such evidence, using data from the recent MMS mission and the newly developed First‐Order Taylor Expansion (FOTE) Expansion technique. We investigate 12 EDR candidates at the Earth's magnetopause and find radial nulls (X‐lines) in all of them. In some events, spacecraft are only 3 km (one electron inertial length) away from the null. We reconstruct the magnetic topology of these nulls and find it agrees well with theoretical models. These nulls, as reconstructed for the first time inside the EDR by the FOTE technique, indicate that the EDR is active and the reconnection process is ongoing.

    Plain Language Summary: Magnetic reconnection is a key process responsible for many explosive phenomena in nature such as solar flares and magnetospheric substorms. Theoretically, such process occurs at the X‐line or radial null in the electron diffusion region (EDR). However, whether this theory is correct is still unknown, because the radial null (X‐line) has never been observed inside the EDR due to the lack of efficient technique and the scarcity of EDR measurements. Here we report such evidence, using data from the recent MMS mission and the newly developed FOTE technique.

  • 5. Fu, H. S.
    et al.
    Cao, J. B.
    Cully, C. M.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Angelopoulos, V.
    Zong, Q. -G
    Santolik, O.
    Macusova, E.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Liu, W. L.
    Lu, H. Y.
    Zhou, M.
    Huang, S. Y.
    Zhima, Z.
    Whistler-mode waves inside flux pileup region: Structured or unstructured?2014Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, nr 11, s. 9089-9100Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During reconnection, a flux pileup region (FPR) is formed behind a dipolarization front in an outflow jet. Inside the FPR, the magnetic field magnitude and Bz component increase and the whistler-mode waves are observed frequently. As the FPR convects toward the Earth during substorms, it is obstructed by the dipolar geomagnetic field to form a near-Earth FPR. Unlike the structureless emissions inside the tail FPR, we find that the whistler-mode waves inside the near-Earth FPR can exhibit a discrete structure similar to chorus. Both upper band and lower band chorus are observed, with the upper band having a larger propagation angle (and smaller wave amplitude) than the lower band. Most chorus elements we observed are rising-tone type, but some are falling-tone type. We notice that the rising-tone chorus can evolve into falling-tone chorus within <3s. One of the factors that may explain why the waves are unstructured inside the tail FPR but become discrete inside the near-Earth FPR is the spatial inhomogeneity of magnetic field: we find that such inhomogeneity is small inside the near-Earth FPR but large inside the tail FPR.

  • 6.
    Fu, H. S.
    et al.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Cao, J. B.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Andre, M.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Dunlop, M.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Liu, W. L.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Lu, H. Y.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Huang, S. Y.
    Wuhan Univ, Sch Elect & Informat, Wuhan 430072, Peoples R China..
    Ma, Y. D.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Eriksson, Elin
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Identifying magnetic reconnection events using the FOTE method2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 2, s. 1263-1272Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multispacecraft 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 nonguide 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 forthcoming Magnetospheric Multiscale (MMS) mission. ion

  • 7.
    Fu, H. S.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Y. V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Andre, M.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Sergeev, V. A.
    Huang, S. Y.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Kronberg, E. A.
    Daly, P. W.
    Pitch angle distribution of suprathermal electrons behind dipolarization fronts: A statistical overview2012Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, nr 12, artikel-id A12221Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We examine the pitch angle distribution (PAD) of suprathermal electrons (> 40 keV) inside the flux pileup regions (FPRs) that are located behind the dipolarization fronts (DFs), in order to better understand the particle energization mechanisms operating therein. The 303 earthward-propagating DFs observed during 9 years (2001-2009) by Cluster 1 have been analyzed and divided into two groups according to the differential fluxes of the > 40 keV electrons inside the FPR. One group, characterized by the low flux (F < 500/cm(2) , s . sr . keV), consists of 153 events and corresponds to a broad distribution of IMF Bz components. The other group, characterized by the high flux (F >= 500/cm(2) . s . sr . keV), consists of 150 events and corresponds to southward IMF Bz components. Only the high-flux group is considered to investigate the PAD of the > 40 keV electrons as the low-flux situation may lead to large uncertainties in computing the anisotropy factor that is defined as A = F-perpendicular to/F-parallel to - 1 for F-perpendicular to > F-parallel to, and A = -F-parallel to/F-perpendicular to + 1 for F-perpendicular to < F-parallel to. We find that, among the 150 events, 46 events have isotropic distribution (vertical bar A vertical bar <= 0.5); 60 events have perpendicular distribution (A > 0.5), and 44 events have field-aligned distribution inside the FPR (A < -0.5). The perpendicular distribution appears mainly inside the growing FPR, where the flow velocity is increasing and the local flux tube is compressed. The field-aligned distribution occurs mainly inside the decaying FPR, where the flow velocity is decreasing and the local flux tube is expanding. Inside the steady FPR, we observed primarily the isotropic distribution of suprathermal electrons. This statistical result confirms the previous case study and gives an overview of the PAD of suprathermal electrons behind DFs.

  • 8.
    Fu, H. S.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Retino, A.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Energetic electron acceleration by unsteady magnetic reconnection2013Ingår i: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 9, nr 7, s. 426-430Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanism that produces energetic electrons during magnetic reconnection is poorly understood. This is a fundamental process responsible for stellar flares(1,2),substorms(34), and disruptions in fusion experiments(5,6).Observations in the solar chromosphere(1) and the Earth's magnetosphere(7-10) indicate significant electron acceleration during reconnection, whereas in the solar wind, energetic electrons are absent(11). Here we show that energetic electron acceleration is caused by unsteady reconnection. In the Earth's magnetosphere and the solar chromosphere, reconnection is unsteady, so energetic electrons are produced; in the solar wind, reconnection is steady(12), so energetic electrons are absent(11). The acceleration mechanism is quasi-adiabatic: betatron and Fermi acceleration in outflow jets are two processes contributing to electron energization during unsteady reconnection. The localized betatron acceleration in the outflow is responsible for at least half of the energy gain for the peak observed fluxes.

  • 9.
    Fu, H. S.
    et al.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China..
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Cao, J. B.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China..
    Olshevsky, V.
    Katholieke Univ Leuven, Ctr Math Plasma Astrophys, Leuven, Belgium..
    Eastwood, J. P.
    Imperial Coll London, Blackett Lab, London, England..
    Retino, A.
    UPMC, Ecole Polytech, CNRS, Lab Phys Plasmas, Palaiseau, France..
    Intermittent energy dissipation by turbulent reconnection2017Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 1, s. 37-43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetic reconnectionthe process responsible for many explosive phenomena in both nature and laboratoryis efficient at dissipating magnetic energy into particle energy. To date, exactly how this dissipation happens remains unclear, owing to the scarcity of multipoint measurements of the diffusion region at the sub-ion scale. Here we report such a measurement by Clusterfour spacecraft with separation of 1/5 ion scale. We discover numerous current filaments and magnetic nulls inside the diffusion region of magnetic reconnection, with the strongest currents appearing at spiral nulls (O-lines) and the separatrices. Inside each current filament, kinetic-scale turbulence is significantly increased and the energy dissipation, Ej, is 100 times larger than the typical value. At the jet reversal point, where radial nulls (X-lines) are detected, the current, turbulence, and energy dissipations are surprisingly small. All these features clearly demonstrate that energy dissipation in magnetic reconnection occurs at O-lines but not X-lines.

  • 10.
    Fu, H. S.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Olshevsky, V.
    Katholieke Univ Leuven, Ctr Math Plasma Astrophys, Dept Math, Leuven, Belgium.;Main Astron Observ NAS, Kiev, Ukraine..
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Cao, J. B.
    Beihang Univ, Space Sci Inst, Sch Astronaut, Beijing 100191, Peoples R China..
    Huang, S. Y.
    Ecole Polytech, CNRS, UPMC, Lab Phys Plasmas, F-91128 Palaiseau, France.;Wuhan Univ, Sch Elect & Informat, Wuhan 430072, Peoples R China.
    Retino, A.
    Ecole Polytech, CNRS, UPMC, Lab Phys Plasmas, F-91128 Palaiseau, France..
    Lapenta, G.
    Katholieke Univ Leuven, Ctr Math Plasma Astrophys, Dept Math, Leuven, Belgium..
    How to find magnetic nulls and reconstruct field topology with MMS data?2015Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 5, s. 3758-3782Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, we apply a new method-the first-order Taylor expansion (FOTE)-to find magnetic nulls and reconstruct magnetic field topology, in order to use it with the data from the forthcoming MMS mission. We compare this method with the previously used Poincare index (PI), and find that they are generally consistent, except that the PI method can only find a null inside the spacecraft (SC) tetrahedron, while the FOTE method can find a null both inside and outside the tetrahedron and also deduce its drift velocity. In addition, the FOTE method can (1) avoid limitations of the PI method such as data resolution, instrument uncertainty (Bz offset), and SC separation; (2) identify 3-D null types (A, B, As, and Bs) and determine whether these types can degenerate into 2-D (X and O); (3) reconstruct the magnetic field topology. We quantitatively test the accuracy of FOTE in positioning magnetic nulls and reconstructing field topology by using the data from 3-D kinetic simulations. The influences of SC separation (0.05 similar to 1 d(i)) and null-SC distance (0 similar to 1 d(i)) on the accuracy are both considered. We find that (1) for an isolated null, the method is accurate when the SC separation is smaller than 1 d(i), and the null-SC distance is smaller than 0.25 similar to 0.5 d(i); (2) for a null pair, the accuracy is same as in the isolated-null situation, except at the separator line, where the field is nonlinear. We define a parameter xi vertical bar(lambda(1) +lambda(2) +lambda(3))vertical bar/vertical bar lambda vertical bar(max) in terms of the eigenvalues (lambda(i)) of the null to quantify the quality of our method-the smaller this parameter the better the results. Comparing to the previously used parameter (eta vertical bar del center dot B vertical bar/vertical bar del x B vertical bar), xi is more relevant for null identification. Using the new method, we reconstruct the magnetic field topology around a radial-type null and a spiral-type null, and find that the topologies are well consistent with those predicted in theory. We therefore suggest using this method to find magnetic nulls and reconstruct field topology with four-point measurements, particularly from Cluster and the forthcoming MMS mission. For the MMS mission, this null-finding algorithm can be used to trigger its burst-mode measurements.

  • 11.
    Fu, H. S.
    et al.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Xu, Y.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Super-efficient Electron Acceleration by an Isolated Magnetic Reconnection2019Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 870, nr 2, artikel-id L22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetic reconnection-the process typically lasting for a few seconds in space-is able to accelerate electrons. However, the efficiency of the acceleration during such a short period is still a puzzle. Previous analyses, based on spacecraft measurements in the Earth's magnetotail, indicate that magnetic reconnection can enhance electron fluxes up to 100 times. This efficiency is very low, creating an impression that magnetic reconnection is not good at particle acceleration. By analyzing Cluster data, we report here a remarkable magnetic reconnection event during which electron fluxes are enhanced by 10,000 times. Such acceleration, 100 times more efficient than those in previous studies, is caused by the betatron mechanism. Both reconnection fronts and magnetic islands contribute to the acceleration, with the former being more prominent.

  • 12.
    Fu, Huishan
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Huang, S. Y.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Occurrence rate of earthward-propagating dipolarization fronts2012Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, artikel-id L10101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The occurrence rate of earthward-propagating dipolarization fronts (DFs) is investigated in this paper based on the 9 years (2001-2009) of Cluster 1 data. For the first time, we select the DF events by fitting the characteristic increase in B-z using a hyperbolic tangent function. 303 earthward-propagating DFs are found; they have on average a duration of 4 s and a B-z increase of 8 nT. DFs have the maximum occurrence at Z(GSM) approximate to 0 and r approximate to 15 R-E with one event occurring every 3.9 hours, where r is the distance to the center of the Earth in the XYGSM plane. The maximum occurrence rate at Z(GSM) approximate to 0 can be explained by the steep and large increase of B-z near the central current sheet, which is consistent with previous simulations. Along the r direction, the occurrence rate increases gradually from r approximate to 20 to r approximate to 15 R-E but decreases rapidly from r approximate to 15 to r approximate to 10 R-E. This may be due to the increasing pileup of the magnetic flux from r approximate to 20 to r approximate to 15 R-E and the strong background magnetic field at r <similar to 13 R-E, where the magnetic field changes from the tail-like to dipolar shape. The maximum occurrence rate of DFs (one event per 3.9 hours) is comparable to that of substorms, indicating a relation between the two.

  • 13.
    Fu, Huishan S.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Huang, S. Y.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Electric structure of dipolarization front at sub-proton scale2012Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, s. L06105-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using Cluster data, we investigate the electric structure of a dipolarization front (DF) - the ion inertial length (c/omega(pi)) scale boundary in the Earth's magnetotail formed at the front edge of an earthward propagating flow with reconnected magnetic flux. We estimate the current density and the electron pressure gradient throughout the DF by both single-spacecraft and multi-spacecraft methods. Comparison of the results from the two methods shows that the single-spacecraft analysis, which is capable of resolving the detailed structure of the boundary, can be applied for the DF we study. Based on this, we use the current density and the electron pressure gradient from the single-spacecraft method to investigate which terms in the generalized Ohm's law balance the electric field throughout the DF. We find that there is an electric field at ion inertia scale directed normal to the DF; it has a duskward component at the dusk flank of DF but a dawnward component at the dawn flank of DF. This electric field is balanced by the Hall (j x B/ne) and electron pressure gradient (del P-e/ne) terms at the DF, with the Hall term being dominant. Outside the narrow DF region, however, the electric field is balanced by the convection (V-i x B) term, meaning the frozen-in condition for ions is broken only at the DF itself. In the reference frame moving with the DF the tangential electric field is almost zero, indicating there is no flow of plasma across the DF and that the DF is a tangential discontinuity. The normal electric field at the DF constitutes a potential drop of similar to 1 keV, which may reflect and accelerate the surrounding ions. 

  • 14.
    Graham, Daniel B.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Andre, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Electrostatic solitary waves and electrostatic waves at the magnetopause2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 4, s. 3069-3092Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrostatic solitary waves (ESWs) are characterized by localized bipolar electric fields parallel to the magnetic field and are frequently observed in space plasmas. In this paper a study of ESWs and field-aligned electrostatic waves, which do not exhibit localized bipolar fields, near the magnetopause is presented using the Cluster spacecraft. The speeds, length scales, field strengths, and potentials are calculated and compared with the local plasma conditions. A large range of speeds is observed, suggesting different generation mechanisms. In contrast, a smaller range of length scales normalized to the Debye length lambda(D) is found. For ESWs the average length between the positive and negative peak fields is 9 lambda(D), comparable to the average half wavelength of electrostatic waves. Statistically, the lengths and speeds of ESWs and electrostatic waves are shown to be similar. The length scales and potentials of the ESWs are consistent with predictions for stable electron holes. The maximum ESW potentials are shown to be constrained by the length scale and the magnetic field strength at the magnetopause and in the magnetosheath. The observed waves are consistent with those generated by the warm bistreaming instability, beam-plasma instability, and electron-ion instabilities, which account for the observed speeds and length scales. The large range of wave speeds suggests that the waves can couple different electron populations and electrons with ions, heating the plasma and contributing to anomalous resistivity.

  • 15.
    Graham, Daniel B.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Electrostatic solitary waves with distinct speeds associated with asymmetric reconnection2015Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, nr 2, s. 215-224Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrostatic solitary waves (ESWs) are observed at the magnetopause with distinct time scales. These ESWs are associated with asymmetric reconnection of the cold dense magnetosheath plasma with the hot tenuous magnetospheric plasma. The distinct time scales are shown to be due to ESWs moving at distinct speeds and having distinct length scales. The length scales are of order 5-50 Debye lengths, and the speeds range from approximate to 50 km s(-1) to approximate to 1000 km s(-1). The ESWs are observed near the reconnection separatrices. The observation of ESWs with distinct speeds suggests that multiple instabilities are occurring. The implications for reconnection at the magnetopause are discussed.

  • 16.
    Graham, Daniel B.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Fazakerley, A. N.
    Electron Dynamics in the Diffusion Region of an Asymmetric Magnetic Reconnection2014Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 112, nr 21, s. 215004-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During a magnetopause crossing near the subsolar point Cluster observes the ion diffusion region of antiparallel magnetic reconnection. The reconnecting plasmas are asymmetric, differing in magnetic field strength, density, and temperature. Spatial changes in the electron distributions in the diffusion region are resolved and investigated in detail. Heating of magnetosheath electrons parallel to the magnetic field is observed. This heating is shown to be consistent with trapping of magnetosheath electrons by parallel electric fields.

  • 17. Huang, S. Y.
    et al.
    Fu, H. S.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Yuan, Z. G.
    Pang, Y.
    Zhou, M.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Deng, X. H.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Zhang, L.
    Fu, S.
    Li, H. M.
    Wang, D. D.
    Dawn-dusk scale of dipolarization front in the Earth's magnetotail: multi-cases study2015Ingår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 357, nr 1, artikel-id 22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We analyze three dipolarization front (DF) events to investigate their dawn-dusk scales in the Earth's magnetotail using the Cluster measurements in year 2007, when the spacecraft separation is about 1.8 Re (Re is the Earth's radius) and is appropriate for investigating the DF scale. Based on the Minimum Variance Analysis (MVA) and the general shape of the DF, we found that Cluster detected the center and the flank (or just beyond the flank) of DF in the same event. This means that the scale of DF is about 3.6 Re in the dawn-dusk direction, larger than that reported in previous studies. Using the semicircle function to fit the observations, we got the dawn-dusk scale of similar to 3.2-3.6 Re, consistent with the rough estimation. Considering large separation among the spacecraft, the timing analysis cannot be used to obtain the normal of DF and the propagation velocity along the normal. One should be careful when performing timing analysis of DF using the Cluster data, and have to carry on MVA analysis to check the normal of DF before do timing analysis.

  • 18.
    Huang, S. Y.
    et al.
    Wuhan Univ, Sch Elect Informat, Wuhan, Peoples R China.;UPMC, Lab Phys Plasmas, CNRS, Ecole Polytech, Palaiseau, France..
    Fu, H. S.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China..
    Yuan, Z. G.
    Wuhan Univ, Sch Elect Informat, Wuhan, Peoples R China..
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Retino, A.
    UPMC, Lab Phys Plasmas, CNRS, Ecole Polytech, Palaiseau, France..
    Zhou, M.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Peoples R China..
    Graham, Daniel B.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Fujimoto, K.
    Natl Astron Observ Japan, Div Theoret Astron, Mitaka, Tokyo, Japan..
    Sahraoui, F.
    UPMC, Lab Phys Plasmas, CNRS, Ecole Polytech, Palaiseau, France..
    Deng, X. H.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Peoples R China..
    Ni, B.
    Wuhan Univ, Sch Elect Informat, Wuhan, Peoples R China..
    Pang, Y.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Peoples R China..
    Fu, S.
    Wuhan Univ, Sch Elect Informat, Wuhan, Peoples R China..
    Wang, D. D.
    Wuhan Univ, Sch Elect Informat, Wuhan, Peoples R China..
    Zhou, X.
    Liaoning Univ, Sch Phys, Shenyang, Peoples R China..
    Two types of whistler waves in the hall reconnection region2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 7, s. 6639-6646Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Whistler waves are believed to play an important role during magnetic reconnection. Here we report the near-simultaneous occurrence of two types of the whistler-mode waves in the magnetotail Hall reconnection region. The first type is observed in the magnetic pileup region of downstream and propagates away to downstream along the field lines and is possibly generated by the electron temperature anisotropy at the magnetic equator. The second type, propagating toward the X line, is found around the separatrix region and probably is generated by the electron beam-driven whistler instability or erenkov emission from electron phase-space holes. These observations of two different types of whistler waves are consistent with recent kinetic simulations and suggest that the observed whistler waves are a consequence of magnetic reconnection.

  • 19.
    Huang, S. Y.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Zhou, M.
    Fu, Huishan
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Retino, A.
    Deng, X. H.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Cully, Christopher M.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    He, J. S.
    Sahraoui, F.
    Yuan, Z. G.
    Pang, Y.
    Electron acceleration in the reconnection diffusion region: Cluster observations2012Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, nr L11103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present one case study of magnetic islands and energetic electrons in the reconnection diffusion region observed by the Cluster spacecraft. The cores of the islands are characterized by strong core magnetic fields and density depletion. Intense currents, with the dominant component parallel to the ambient magnetic field, are detected inside the magnetic islands. A thin current sheet is observed in the close vicinity of one magnetic island. Energetic electron fluxes increase at the location of the thin current sheet, and further increase inside the magnetic island, with the highest fluxes located at the core region of the island. We suggest that these energetic electrons are firstly accelerated in the thin current sheet, and then trapped and further accelerated in the magnetic island by betatron and Fermi acceleration.

  • 20.
    Huang, S. Y.
    et al.
    Wuhan Univ, Sch Elect Informat, Wuhan, Hubei, Peoples R China.
    Yuan, Z. G.
    Wuhan Univ, Sch Elect Informat, Wuhan, Hubei, Peoples R China.
    Fu, H. S.
    Beihang Univ, Sch Astronaut, Space Sci Inst, Beijing, Peoples R China.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Sahraoui, F.
    UPMC, EcolePolytech, CNRS, Lab Phys Plasmas, Palaiseau, France.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Retino, A.
    UPMC, EcolePolytech, CNRS, Lab Phys Plasmas, Palaiseau, France.
    Zhou, M.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Jiangxi, Peoples R China.
    Graham, Daniel B.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Fujimoto, K.
    Natl Astron Observ Japan, Div Theoret Astron, Mitaka, Tokyo, Japan.
    Deng, X. H.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Jiangxi, Peoples R China.
    Ni, B. B.
    Wuhan Univ, Sch Elect Informat, Wuhan, Hubei, Peoples R China.
    Pang, Y.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Jiangxi, Peoples R China.
    Fu, S.
    Wuhan Univ, Sch Elect Informat, Wuhan, Hubei, Peoples R China.
    Wang, D. D.
    Wuhan Univ, Sch Elect Informat, Wuhan, Hubei, Peoples R China.
    Observations of Whistler Waves in the Magnetic Reconnection Diffusion Region2018Ingår i: 2ND URSI ATLANTIC RADIO SCIENCE MEETING (AT-RASC), IEEE , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Whistler waves are believed to play an important role during magnetic reconnection. In this paper, we report the simultaneous occurrence of two types of the whistler waves in the magnetotail reconnection diffusion region. The first type is observed in the pileup region of downstream and propagates away along the field lines to downstream, and is possibly generated by the electron temperature anisotropy at the magnetic equator. The second type is found around the separatrix region and propagates towards the X-line, and is possibly aenerated by the electron beam-driven whistler instability or Cerenkov emission from electron phase-space holes. Our observations of two different types of whistler waves are well consistent with recent kinetic simulations, and suggest that the observed whistler waves are the consequences of magnetic reconnection.Moreover, we statistically investigate the whistler waves in the magnetotail reconnection region, and construct the global distribution and occurrence rate of the whistler waves based on the two-dimensional reconnection model. It is found that the occurrence rate of the whistler waves is large in the separatrix region (113,1B0j>0.4) and pileup region ([B,./Bol<0.2, 161>45'), but very small in the X-line region. The statistical results are well consistent with the case study.

  • 21.
    Johlander, Andreas
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Gingell, Imogen
    Schwartz, Steven J
    Giles, Barbara L
    Torbert, Roy B
    Russell, Christopher T
    Shock ripples observed by the MMS spacecraft: ion reflection and dispersive properties2018Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, artikel-id 125006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Shock ripples are ion-inertial-scale waves propagating within the front region of magnetized quasi-perpendicular collisionless shocks. The ripples are thought to influence particle dynamics and acceleration at shocks. With the four magnetospheric multiscale (MMS) spacecraft, it is for the first time possible to fully resolve the small scale ripples in space. We use observations of one slow crossing of the Earth’s non-stationary bow shock by MMS. From multi-spacecraft measurements we show that the non-stationarity is due to ripples propagating along the shock surface. We find that the ripples are near linearly polarized waves propagating in the coplanarity plane with a phase speed equal to the local Alfvén speed and have a wavelength close to 5 times the upstream ion inertial length. The dispersive properties of the ripples resemble those of Alfvén ion cyclotron waves in linear theory. Taking advantage of the slow crossing by the four MMS spacecraft, we map the shock-reflected ions as a function of ripple phase and distance from the shock. We find that ions are preferentially reflected in regions of the wave with magnetic field stronger than the average overshoot field, while in the regions of lower magnetic field, ions penetrate the shock to the downstream region.

  • 22.
    Johlander, Andreas
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Retinò, A.
    Dandouras, I.
    Univ Toulouse 3, F-31062 Toulouse, France.;CNRS, IRAP, Toulouse, France..
    Ion Injection At Quasi-Parallel Shocks Seen By The Cluster Spacecraft2016Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 817, nr 1, artikel-id L4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Collisionless shocks in space plasma are known to be capable of accelerating ions to very high energies through diffusive shock acceleration (DSA). This process requires an injection of suprathermal ions, but the mechanisms producing such a suprathermal ion seed population are still not fully understood. We study acceleration of solar wind ions resulting from reflection off short large-amplitude magnetic structures (SLAMSs) in the quasi-parallel bow shock of Earth using in situ data from the four Cluster spacecraft. Nearly specularly reflected solar wind ions are observed just upstream of a SLAMS. The reflected ions are undergoing shock drift acceleration (SDA) and obtain energies higher than the solar wind energy upstream of the SLAMS. Our test particle simulations show that solar wind ions with lower energy are more likely to be reflected off the SLAMS, while high-energy ions pass through the SLAMS, which is consistent with the observations. The process of SDA at SLAMSs can provide an effective way of accelerating solar wind ions to suprathermal energies. Therefore, this could be a mechanism of ion injection into DSA in astrophysical plasmas.

  • 23.
    Li, Wenya
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Andre, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Graham, Daniel B.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Toledo-Redondo, S.
    European Space Agcy, Sci Directorate, ESAC, Madrid, Spain..
    Norgren, Cecilia
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Henri, P.
    CNRS, LPC2E, Orleans, France..
    Wang, C.
    Natl Space Sci Ctr, Beijing, Peoples R China..
    Tang, B. B.
    Natl Space Sci Ctr, Beijing, Peoples R China..
    Lavraud, B.
    Univ Toulouse UPS, Inst Rech Astrophys & Planetol, Toulouse, France.;CNRS, UMR 5277, Toulouse, France..
    Vernisse, Y.
    Univ Toulouse UPS, Inst Rech Astrophys & Planetol, Toulouse, France..
    Turner, D. L.
    Aerosp Corp, Dept Space Sci, El Segundo, CA 90245 USA..
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Blake, J. B.
    Aerosp Corp, Dept Space Sci, El Segundo, CA 90245 USA..
    Mauk, B.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Giles, B.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C.
    Denali Sci, Healy, AL USA..
    Fennell, J.
    Aerosp Corp, Dept Space Sci, El Segundo, CA 90245 USA..
    Jaynes, A.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Saito, Y.
    Japan Aerosp Explorat Agcy, Tokyo, Japan..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Kinetic evidence of magnetic reconnection due to Kelvin-Helmholtz waves2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 11, s. 5635-5643Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Kelvin-Helmholtz (KH) instability at the Earth's magnetopause is predominantly excited during northward interplanetary magnetic field (IMF). Magnetic reconnection due to KH waves has been suggested as one of the mechanisms to transfer solar wind plasma into the magnetosphere. We investigate KH waves observed at the magnetopause by the Magnetospheric Multiscale (MMS) mission; in particular, we study the trailing edges of KH waves with Alfvenic ion jets. We observe gradual mixing of magnetospheric and magnetosheath ions at the boundary layer. The magnetospheric electrons with energy up to 80keV are observed on the magnetosheath side of the jets, which indicates that they escape into the magnetosheath through reconnected magnetic field lines. At the same time, the low-energy (below 100eV) magnetosheath electrons enter the magnetosphere and are heated in the field-aligned direction at the high-density edge of the jets. Our observations provide unambiguous kinetic evidence for ongoing reconnection due to KH waves.

  • 24.
    Norgren, Cecilia
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Graham, Daniel. B.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri. V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Slow electron holes in multicomponent plasmas2015Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, nr 18, s. 7264-7272Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrostatic solitary waves (ESWs), often interpreted as electron phase space holes, are commonly observed in plasmas and are manifestations of strongly nonlinear processes. Often slow ESWs are observed, suggesting generation by the Buneman instability. The instability criteria, however, are generally not satisfied. We show how slow electron holes can be generated by a modified Buneman instability in a plasma that includes a slow electron beam on top of a warm thermal electron background. This lowers the required current for marginal instability and allows for generation of slow electron holes for a wide range of beam parameters that covers expected plasma distributions in space, for example, in magnetic reconnection regions. At higher beam speeds, the electron-electron beam instability becomes dominant instead, producing faster electron holes. The range of phase speeds for this model is consistent with a statistical set of observations at the magnetopause made by Cluster.

  • 25.
    Norgren, Cecilia
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Slow electron phase space holes: Magnetotail observations2015Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, nr 6, s. 1654-1661Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report multispacecraft observations of slow electrostatic solitary waves in the plasma sheet boundary layer. The electrostatic solitary waves are embedded in a region with field-aligned electron flows and are interpreted as electron phase space holes. We make unambiguous velocity and length estimates of the electron holes, v(EH)approximate to 500 km/s and l(||)approximate to 2-4(De), where l(||) is the parallel half width. We do not detect any magnetic signature of the holes. The electrostatic potentials of the holes are of the order e/k(B)T(e)approximate to 10%, indicating that they can affect electron motion and further couple the electron and ion dynamics.

  • 26.
    Norgren, Cecilia
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Lower Hybrid Drift Waves: Space Observations2012Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, nr 5, artikel-id 055001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lower hybrid drift waves (LHDWs) are commonly observed at plasma boundaries in space and laboratory, often having the strongest measured electric fields within these regions. We use data from two of the Cluster satellites (C3 and C4) located in Earth's magnetotail and separated by a distance of the order of the electron gyroscale. These conditions allow us, for the first time, to make cross-spacecraft correlations of the LHDWs and to determine the phase velocity and wavelength of the LHDWs. Our results are in good agreement with the theoretical prediction. We show that the electrostatic potential of LHDWs is linearly related to fluctuations in the magnetic field magnitude, which allows us to determine the velocity vector through the relation integral delta Edt . v = phi(delta B parallel to). The electrostatic potential fluctuations correspond to similar to 10% of the electron temperature, which suggests that the waves can strongly affect the electron dynamics.

  • 27.
    Schwartz, Steven J.
    et al.
    Imperial Coll London, London, England;Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Avanov, Levon
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Turner, Drew
    Aerosp Corp, POB 92957, Los Angeles, CA 90009 USA.
    Zhang, Hui
    Univ Alaska Fairbanks, Geophys Inst, Fairbanks, AK 99775 USA.
    Gingell, Imogen
    Imperial Coll London, London, England.
    Eastwood, Jonathan P.
    Imperial Coll London, London, England.
    Gershman, Daniel J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Johlander, Andreas
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Russell, Christopher T.
    Univ Calif Los Angeles, Earth Planetary & Space Sci, Los Angeles, CA USA.
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA.
    Dorelli, John C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Eriksson, Stefan
    Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Ergun, Robert E.
    Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Fuselier, Stephen A.
    Southwest Res Inst, San Antonio, TX USA;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX USA.
    Giles, Barbara L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Goodrich, Katherine A.
    Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Lavraud, Benoit
    Imperial Coll London, London, England;Univ Toulouse, UPS, CNRS, Inst Rech Astrophys & Planetol,CNES, Toulouse, France.
    Lindqvist, Per-Arne
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Oka, Mitsuo
    Imperial Coll London, London, England;Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.
    Phan, Tai-Duc
    Strangeway, Robert J.
    Univ Calif Los Angeles, Earth Planetary & Space Sci, Los Angeles, CA USA.
    Trattner, Karlheinz J.
    Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Torbert, Roy B.
    Imperial Coll London, London, England;Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO 80309 USA;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Wei, Hanying
    Univ Calif Los Angeles, Earth Planetary & Space Sci, Los Angeles, CA USA.
    Wilder, Frederick
    Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Ion Kinetics in a Hot Flow Anomaly: MMS Observations2018Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 21, s. 11520-11529Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hot Flow Anomalies (HFAs) are transients observed at planetary bow shocks, formed by the shock interaction with a convected interplanetary current sheet. The primary interpretation relies on reflected ions channeled upstream along the current sheet. The short duration of HFAs has made direct observations of this process difficult. We employ high resolution measurements by NASA's Magnetospheric Multiscale Mission to probe the ion microphysics within a HFA. Magnetospheric Multiscale Mission data reveal a smoothly varying internal density and pressure, which increase toward the trailing edge of the HFA, sweeping up particles trapped within the current sheet. We find remnants of reflected or other backstreaming ions traveling along the current sheet, but most of these are not fast enough to out-run the incident current sheet convection. Despite the high level of internal turbulence, incident and backstreaming ions appear to couple gyro-kinetically in a coherent manner. Plain Language Summary Shock waves in space are responsible for energizing particles and diverting supersonic flows around planets and other obstacles. Explosive events known as Hot Flow Anomalies (HFAs) arise when a rapid change in the interplanetary magnetic field arrives at the bow shock formed by, for example, the supersonic solar wind plasma flow from the Sun impinging on the Earth's magnetic environment. HFAs are known to produce impacts all the way to ground level, but the physics responsible for their formation occur too rapidly to be resolved by previous satellite missions. This paper employs NASA's fleet of four Magnetospheric Multiscale satellites to reveal for the first time clear, discreet populations of ions that interact coherently to produce the extreme heating and deflection.

  • 28.
    Soucek, J.
    et al.
    Acad Sci Czech Republic, Inst Atmospher Phys, Prague, Czech Republic..
    Åhlén, Lennart
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Bale, S.
    UCB, Space Sci Lab, Berkeley, CA USA..
    Bonnell, J.
    UCB, Space Sci Lab, Berkeley, CA USA..
    Boudin, N.
    ESA ESTEC, Noordwijk, Netherlands..
    Brienza, D.
    IAPS, Rome, Italy..
    Carr, C.
    Imperial Coll, London, England..
    Cipriani, F.
    ESA ESTEC, Noordwijk, Netherlands..
    Escoubet, C. P.
    ESA ESTEC, Noordwijk, Netherlands..
    Fazakerley, A.
    UCL, Mullard Space Sci Lab, Dorking, Surrey, England..
    Gehler, M.
    ESA ESTEC, Noordwijk, Netherlands..
    Genot, V.
    IRAP, Toulouse, France..
    Hilgers, A.
    ESA ESTEC, Noordwijk, Netherlands..
    Hanock, B.
    UCL, Mullard Space Sci Lab, Dorking, Surrey, England..
    Jannet, G.
    LPC2E, Orleans, France..
    Junge, A.
    ESA ESTEC, Noordwijk, Netherlands..
    Khotyaintsev, Yuri
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    De Keyser, J.
    BIRA IASB, Brussels, Belgium..
    Kucharek, H.
    Univ New Hampshire, Durham, NH 03824 USA..
    Lan, R.
    Acad Sci Czech Republic, Inst Atmospher Phys, Prague, Czech Republic..
    Lavraud, B.
    IRAP, Toulouse, France..
    Leblanc, F.
    Plasma Phys Lab, Paris, France..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Mansour, M.
    Plasma Phys Lab, Paris, France..
    Marcucci, M. F.
    IAPS, Rome, Italy..
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Nemecek, Z.
    Charles Univ Prague, Prague, Czech Republic..
    Owen, C.
    UCL, Mullard Space Sci Lab, Dorking, Surrey, England..
    Phal, Y.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Retino, A.
    Plasma Phys Lab, Paris, France..
    Rodgers, D.
    ESA ESTEC, Noordwijk, Netherlands..
    Safrankova, J.
    Charles Univ Prague, Prague, Czech Republic..
    Sahraoui, F.
    Plasma Phys Lab, Paris, France..
    Vainio, R.
    Univ Turku, Turku, Finland..
    Wimmer-Schweingruber, R.
    Univ Kiel, Kiel, Germany..
    Steinhagen, J.
    Univ Kiel, Kiel, Germany..
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Wielders, A.
    ESA ESTEC, Noordwijk, Netherlands..
    Zaslavsky, A.
    Observ Paris, LESIA, Ifeudon, France..
    EMC Aspects Of Turbulence Heating Observer (THOR) Spacecraft2016Ingår i: Proceedings Of 2016 Esa Workshop On Aerospace Emc (Aerospace Emc), Institute of Electrical and Electronics Engineers (IEEE), 2016, artikel-id 7504544Konferensbidrag (Refereegranskat)
    Abstract [en]

    Turbulence Heating ObserveR (THOR) is a spacecraft mission dedicated to the study of plasma turbulence in near-Earth space. The mission is currently under study for implementation as a part of ESA Cosmic Vision program. THOR will involve a single spinning spacecraft equipped with state of the art instruments capable of sensitive measurements of electromagnetic fields and plasma particles. The sensitive electric and magnetic field measurements require that the spacecraft-generated emissions are restricted and strictly controlled; therefore a comprehensive EMC program has been put in place already during the study phase. The THOR study team and a dedicated EMC working group are formulating the mission EMC requirements already in the earliest phase of the project to avoid later delays and cost increases related to EMC. This article introduces the THOR mission and reviews the current state of its EMC requirements.

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