| 1. |
- Dai, Lei, et al.
(författare)
-
AME : A Cross-Scale Constellation of CubeSats to Explore Magnetic Reconnection in the Solar-Terrestrial Relation
- 2020
-
Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- A major subset of solar-terrestrial relations, responsible, in particular, for the driver of space weather phenomena, is the interaction between the Earth's magnetosphere and the solar wind. As one of the most important modes of the solar-wind-magnetosphere interaction, magnetic reconnection regulates the energy transport and energy release in the solar-terrestrial relation. In situ measurements in the near-Earth space are crucial for understanding magnetic reconnection. Past and existing spacecraft constellation missions mainly focus on the measurement of reconnection on plasma kinetic-scales. Resolving the macro-scale and cross-scale aspects of magnetic reconnection is necessary for accurate assessment and predictions of its role in the context of space weather. Here, we propose the AME (self-Adaptive Magnetic reconnection Explorer) mission consisting of a cross-scale constellation of 12+ CubeSats and one mother satellite. Each CubeSat is equipped with instruments to measure magnetic fields and thermal plasma particles. With multiple CubeSats, the AME constellation is intended to make simultaneous measurements at multiple scales, capable of exploring cross-scale plasma processes ranging from kinetic scale to macro scale.
|
|
| 2. |
- Fu, Huishan, et al.
(författare)
-
Chorus intensification in response to interplanetary shock
- 2012
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. A01203-
-
Tidskriftsartikel (refereegranskat)abstract
- On 3 September 2009, the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites observed a significant intensification of chorus in response to the interplanetary shock in the Earth's dayside plasma trough. We analyze the wave-particle interaction and reveal that the chorus intensification can be caused by the gyroresonance between the chorus and the energetic electrons. When the electrons are scattered from resonance points to low-density regions along the diffusion curves, a part of their energy can be lost and then transferred to amplify the chorus. During the compression of the magnetosphere, the temperature anisotropy of electrons is enhanced. This makes the electron diffusion and chorus intensification very effective. The maximum growth rate after the shock is about 50% greater than that before the shock. The lower-energy (15-25 keV) electrons contribute more to the growth of chorus due to the larger density gradient along the diffusion curve. The < 10 keV electrons are almost isotropic, so they contribute little to the amplification of chorus. We investigate the free energy for the chorus intensification and find that it can be generated through the local betatron acceleration and radial diffusion processes. The local betatron acceleration results from the shock-induced compression of the magnetosphere. The linear and nonlinear growth rates are also compared. We find that the linear diffusion process works well for the present case.
|
|
| 3. |
- Fu, Huishan, et al.
(författare)
-
Electron loss and acceleration during storm time : The contribution of wave-particle interaction, radial diffusion, and transport processes
- 2011
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A10210-
-
Tidskriftsartikel (refereegranskat)abstract
- During the period 19-22 November 2007, the near-equatorial satellites THEMIS D (ThD) and E (ThE) traversed the Earth's morningside magnetosphere once per day and for nearly 2 h the orbits tracked close to each other, providing an excellent opportunity to investigate the evolution of energetic electrons fluxes (EEFs) on two time scales. By analyzing the electrons in the energy range 100-300 keV, we have found that the EEFs undergo different evolutions in the different subregions of Earth's morningside magnetosphere during a moderate storm. The evolutions at three specific locations, showing, respectively, the features of electron loss, acceleration, and conservation, have been analyzed in detail. Our observations reveal that, during storm time, the evolution of EEFs involves five processes: (1) the resonant interaction between chorus and energetic electrons, which can contribute to both loss and acceleration of electrons depending on the distribution of phase space density, (2) the radial diffusion, which is indicated by the good coherence between ULF waves and EEFs and dominates in the region where the chorus is relatively weak; (3) the adiabatic transport, which affects the EEFs at L > 6 during the recovery phase and prefers to work on large time scale (>1 d); (4) the magnetopause shadowing, which can evacuate electrons at L > 7 during the storm main phase but play minor roles during the recovery phase, when the magnetopause was moving outward; (5) the magnetospheric convection, which can significantly affect the dynamics of the <100 keV but not the >100 keV electrons. All these five processes couple to each other and determine the EEFs together.
|
|
| 4. |
- Fu, Huishan, et al.
(författare)
-
Occurrence rate of earthward-propagating dipolarization fronts
- 2012
-
Ingår i: Geophysical Research Letters. - 2000 Florida Ave NW Washington, DC 20009, USA : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 39, s. L10101-
-
Tidskriftsartikel (refereegranskat)abstract
- 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
|
|
| 5. |
- Fu, Huishan S., et al.
(författare)
-
Electric structure of dipolarization front at sub-proton scale
- 2012
-
Ingår i: Geophysical Research Letters. - 2000 Florida Ave NW Washington, DC 20009, USA : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 39, s. L06105-
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 6. |
- Fu, Huishan S., et al.
(författare)
-
Fermi and betatron acceleration of suprathermal electrons behind dipolarization fronts
- 2011
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 38
-
Tidskriftsartikel (refereegranskat)abstract
- Two dipolarization front (DF) structures observed by Cluster in the Earth midtail region (X(GSM) approximate to -15 R(E)), showing respectively the feature of Fermi and betatron acceleration of suprathermal electrons, are studied in detail in this paper. Our results show that Fermi acceleration dominates inside a decaying flux pileup region (FPR), while betatron acceleration dominates inside a growing FPR. Both decaying and growing FPRs are associated with the DF and can be distinguished by examining whether the peak of the bursty bulk flow (BBF) is co-located with the DF (decaying) or is behind the DF (growing). Fermi acceleration is routinely caused by the shrinking length of flux tubes, while betatron acceleration is caused by a local compression of the magnetic field. With a simple model, we reproduce the processes of Fermi and betatron acceleration for the higher-energy (>40 keV) electrons. For the lower-energy (<20 keV) electrons, Fermi and betatron acceleration are not the dominant processes. Our observations reveal that betatron acceleration can be prominent in the midtail region even though the magnetic field lines are significantly stretched there.
|
|
| 7. |
- Fu, Huishan, et al.
(författare)
-
The role of electrons during chorus intensification : Energy source and energy loss
- 2012
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 80, s. 37-47
-
Tidskriftsartikel (refereegranskat)abstract
- The role of electrons during the shock-induced chorus intensification observed by THEMIS D on 19 November 2007 is investigated in detail. First, the electrons are accelerated through the local betatron acceleration and radial diffusion, which are primarily in the perpendicular direction and result in the positive anisotropy (T-perpendicular to > T-//) of electrons; then they are scattered through the pitch-angle diffusion, during which the electron energies are partially transferred to amplify the chorus. In the case of interest, the energy loss is more efficient for the lower-energy (15 key) electrons because they have larger density gradient along the diffusion curves. The energetic electrons act as the intermediate in this scenario. They transfer the energies carried by the interplanetary shock to the chorus. The energetic electrons injected from magnetotail are not observed; they have no contributions to the energy source in this event.
|
|
| 8. |
- Huang, S. Y., et al.
(författare)
-
Electron acceleration in the reconnection diffusion region : Cluster observations
- 2012
-
Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 39:L11103
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 9. |
- Huang, S. Y., et al.
(författare)
-
Observations of turbulence within reconnection jet in the presence of guide field
- 2012
-
Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 39:L11104
-
Tidskriftsartikel (refereegranskat)abstract
- We present the first comprehensive observations of turbulence properties within high speed reconnection jet in the plasma sheet with moderate guide field. The power spectral density index is about -1.73 in the inertial range, and follows the value of -2.86 in the ion dissipation range. The turbulence is strongly anisotropic in the wave-vector space with the major power having its wave-vector highly oblique to the ambient magnetic field, suggesting that the turbulence is quasi-2D. The measured "dispersion relations" obtained using the k-filtering technique are compared with theory and are found to be consistent with the Alfven-Whistler mode. In addition, both Probability Distribution Functions and flatness results show that the turbulence in the reconnection jet is intermittent (multifractal) at scales less than the proton gyroradius/inertial lengths. The estimated electric field provided by anomalous resistivity caused by turbulence is about 3 mV/m, which is close to the typical reconnection electric field in the magnetotail.
|
|
| 10. |
- Liu, Wenlong, et al.
(författare)
-
On the calculation of electric diffusion coefficient of radiation belt electrons with in situ electric field measurements by THEMIS
- 2016
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:3, s. 1023-1030
-
Tidskriftsartikel (refereegranskat)abstract
- Based on 7years' observations from Time History of Events and Macroscale Interactions during Substorms (THEMIS), we investigate the statistical distribution of electric field Pc5 ULF wave power under different geomagnetic activities and calculate the radial diffusion coefficient due to electric field, , for outer radiation belt electrons. A simple empirical expression of is also derived. Subsequently, we compare to previous D-LL models and find similar Kp dependence with the model, which is also based on in situ electric field measurements. The absolute value of is constantly higher than , probably due to the limited orbital coverage of CRRES. The differences between and the commonly used and models are significant, especially in Kp dependence and energy dependence. Possible reasons for these differences and their implications are discussed. The diffusion coefficient provided in this paper, which also has energy dependence, will be an important contributor to quantify the radial diffusion process of radiation belt electrons.
|
|
| 11. |
- Taubenschuss, Ulrich, et al.
(författare)
-
Different types of whistler mode chorus in the equatorial source region
- 2015
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:20, s. 8271-8279
-
Tidskriftsartikel (refereegranskat)abstract
- The Time History of Events and Macroscale Interactions during Substorms-D spacecraft crossed an active equatorial source region of whistler mode chorus rising tones on 23 October 2008. Rising tones are analyzed in terms of spectral and polarization characteristics, with special emphasis on wave normal angles. The latter exhibit large variations from quasi-parallel to oblique, even within single bursts, but seem to follow a definite pattern, which enables an unambiguous classification into five different groups. Furthermore, we discuss the frequently observed splitting of chorus bursts into a lower and an upper band around one half of the local electron cyclotron frequency. At chorus frequencies close to the gap, we find significantly lowered wave planarities and a tendency of wave normal angles to approach the Gendrin angle.
|
|
