scholarly journals A comparison of small‐scale magnetic fluctuations in the Region 1 and 2 field‐aligned current systems

2017 ◽  
Vol 122 (3) ◽  
pp. 3277-3290 ◽  
Author(s):  
J. Wu ◽  
M. S. Bryant ◽  
C. G. Ridley ◽  
Y. Shen ◽  
L. Yang ◽  
...  
Keyword(s):  
Small Scale ◽  
Magnetic Fluctuations ◽  
Field Aligned Current ◽  
Current Systems

scholarly journals Stationary magnetospheric convection on November 24, 1981. 2. Small-scale structures in the dayside cusp/cleft

1999 ◽  
Vol 17 (3) ◽  
pp. 375-388
Author(s):  
Y. I. Galperin ◽  
J. M. Bosqued ◽  
R. A. Kovrazhkin ◽  
A. G. Yahnin
Keyword(s):  
Ion Beam ◽  
Potential Difference ◽  
Small Scale ◽  
Polar Cap ◽  
Magnetospheric Convection ◽  
Field Aligned Current ◽  
Cross Polar Cap Potential ◽  
Current Systems ◽  
Small Scale Structures

Abstract. A case study of the dayside cusp/cleft region during an interval of stationary magnetospheric convection (SMC) on November, 24, 1981 is presented, based on detailed measurements made by the AUREOL-3 satellite. Layered small-scale field-aligned current sheets, or loops, superimposed to a narrow V-shaped ion dispersion structure, were observed just equatorward from the region of the "cusp proper". The equatorward sheet was accompanied by a very intense and short (less than 1 s) ion intensity spike at 100 eV. No major differences were noted of the characteristics of the LLBL, or "boundary cusp", and plasma mantle precipitation during this SMC period from those typical of the cusp/cleft region for similar IMF conditions. Simultaneous NOAA-6 and NOAA-7 measurements described in Despirak et al. were used to estimate the average extent of the "cusp proper" (defined by dispersed precipitating ions with the energy flux exceeding 10-3 erg cm-2 s-1) during the SMC period, as ~0.73° ILAT width, 2.6-3.4 h in MLT, and thus the recently merged magnetic flux, 0.54-0.70 × 107 Wb. This, together with the average drift velocity across the cusp at the convection throat, ~0.5 km s-1, allowed to evaluate the cusp merging contribution to the total cross-polar cap potential difference, ~33.8-43.8 kV. It amounts to a quite significant part of the total cross-polar cap potential difference evaluated from other data. A "shutter" scenario is suggested for the ion beam injection/penetration through the stagnant plasma region in the outer cusp to explain the pulsating nature of the particle injections in the low- and medium-altitude cusp region.Key words. Magnetospheric physics (current systems; magnetopause · cusp · and boundary layers; solar wind-magnetosphere interactions).

MHD and Ion Kinetic Waves in Field-aligned Flows Observed by Parker Solar Probe

2021 ◽  
Vol 922 (2) ◽  
pp. 188
Author(s):  
L.-L. Zhao ◽  
G. P. Zank ◽  
J. S. He ◽  
D. Telloni ◽  
L. Adhikari ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Whistler Wave ◽  
Spectral Energy ◽  
Small Scale ◽  
The Sun ◽  
Fast Mode ◽  
Magnetic Fluctuations ◽  
Background Magnetic Field ◽  
Ion Cyclotron

Abstract Parker Solar Probe (PSP) observed predominately Alfvénic fluctuations in the solar wind near the Sun where the magnetic field tends to be radially aligned. In this paper, two magnetic-field-aligned solar wind flow intervals during PSP’s first two orbits are analyzed. Observations of these intervals indicate strong signatures of parallel/antiparallel-propagating waves. We utilize multiple analysis techniques to extract the properties of the observed waves in both magnetohydrodynamic (MHD) and kinetic scales. At the MHD scale, outward-propagating Alfvén waves dominate both intervals, and outward-propagating fast magnetosonic waves present the second-largest contribution in the spectral energy density. At kinetic scales, we identify the circularly polarized plasma waves propagating near the proton gyrofrequency in both intervals. However, the sense of magnetic polarization in the spacecraft frame is observed to be opposite in the two intervals, although they both possess a sunward background magnetic field. The ion-scale plasma wave observed in the first interval can be either an inward-propagating ion cyclotron wave (ICW) or an outward-propagating fast-mode/whistler wave in the plasma frame, while in the second interval it can be explained as an outward ICW or inward fast-mode/whistler wave. The identification of the exact kinetic wave mode is more difficult to confirm owing to the limited plasma data resolution. The presence of ion-scale waves near the Sun suggests that ion cyclotron resonance may be one of the ubiquitous kinetic physical processes associated with small-scale magnetic fluctuations and kinetic instabilities in the inner heliosphere.

scholarly journals Inverse Energy Cascade in Advanced MHD Turbulence (the RNG Method)

1993 ◽  
Vol 157 ◽  
pp. 255-261
Author(s):  
N. Kleeorin ◽  
I. Rogachevskii
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Magnetic Field Effect ◽  
Magnetic Reynolds Number ◽  
Energy Cascade ◽  
Small Scale ◽  
Magnetic Fluctuations ◽  
Mhd Turbulence ◽  
Inverse Energy Cascade ◽  
Large Scale Magnetic Field

The nonlinear (in terms of the large-scale magnetic field) effect of the modification of the magnetic force by an advanced small-scale magnetohydrodynamic (MHD) turbulence is considered. The phenomenon is due to the generation of magnetic fluctuations at the expense of hydrodynamic pulsations. It results in a decrease of the elasticity of the large-scale magnetic field.The renormalization group (RNG) method was employed for the investigation of the MHD turbulence at the large magnetic Reynolds number. It was found that the level of the magnetic fluctuations can exceed that obtained from the equipartition assumption due to the inverse energy cascade in advanced MHD turbulence.This effect can excite an instability of the large-scale magnetic field due to the energy transfer from the small-scale turbulent pulsations. This instability is an example of the inverse energy cascade in advanced MHD turbulence. It may act as a mechanism for the large-scale magnetic ropes formation in the solar convective zone and spiral galaxies.

scholarly journals On the probability distribution function of small-scale interplanetary magnetic field fluctuations

2004 ◽  
Vol 22 (10) ◽  
pp. 3751-3769 ◽  
Author(s):  
R. Bruno ◽  
V. Carbone ◽  
L. Primavera ◽  
F. Malara ◽  
L. Sorriso-Valvo ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Robust Statistics ◽  
Interplanetary Space ◽  
Parametric Instability ◽  
Field Vector ◽  
Small Scale ◽  
Magnetic Fluctuations ◽  
Mhd Turbulence ◽  
The One

Abstract. In spite of a large number of papers dedicated to the study of MHD turbulence in the solar wind there are still some simple questions which have never been sufficiently addressed, such as: a) Do we really know how the magnetic field vector orientation fluctuates in space? b) What are the statistics followed by the orientation of the vector itself? c) Do the statistics change as the wind expands into the interplanetary space? A better understanding of these points can help us to better characterize the nature of interplanetary fluctuations and can provide useful hints to investigators who try to numerically simulate MHD turbulence. This work follows a recent paper presented by some of the authors which shows that these fluctuations might resemble a sort of random walk governed by Truncated Lévy Flight statistics. However, the limited statistics used in that paper did not allow for final conclusions but only speculative hypotheses. In this work we aim to address the same problem using more robust statistics which, on the one hand, forces us not to consider velocity fluctuations but, on the other hand, allows us to establish the nature of the governing statistics of magnetic fluctuations with more confidence. In addition, we show how features similar to those found in the present statistical analysis for the fast speed streams of solar wind are qualitatively recovered in numerical simulations of the parametric instability. This might offer an alternative viewpoint for interpreting the questions raised above.

scholarly journals An investigation of the field-aligned currents associated with a large-scale ULF wave using data from CUTLASS and FAST

2005 ◽  
Vol 23 (2) ◽  
pp. 487-498 ◽  
Author(s):  
H. C. Scoffield ◽  
T. K. Yeoman ◽  
D. M. Wright ◽  
S. E. Milan ◽  
A. N. Wright ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Detection Threshold ◽  
Field Measurements ◽  
Energy Detection ◽  
Alfven Wave ◽  
Small Scale ◽  
Resonance Model ◽  
Ulf Wave ◽  
Field Aligned Current

Abstract. On 14 December 1999, a large-scale ULF wave event was observed by the Hankasalmi radar of the SuperDARN chain. Simultaneously, the FAST satellite passed through the Hankasalmi field-of-view, measuring the magnetic field oscillations of the wave at around 2000km altitude, along with the precipitating ion and electron populations associated with these fields. A simple field line resonance model of the wave has been created and scaled using the wave's spatial and temporal characteristics inferred from SuperDARN and IMAGE magnetometer data. Here the model calculated field-aligned current is compared with field-aligned currents derived from the FAST energetic particle spectra and magnetic field measurements. This comparison reveals the small-scale structuring and energies of the current carriers in a large-scale Alfvén wave, a topic, which at present, is of considerable theoretical interest. When FAST traverses a region of the wave involving low upward field-aligned current densities, the current appears to be carried by unstructured downgoing electrons of energies less than 30eV. A downward current region appears to be carried partially by upgoing electrons below the FAST energy detection threshold, but also consists of a mixture of hotter downgoing magnetospheric electrons and upgoing ionospheric electrons of energies <30eV, with the hotter upgoing electrons presumably representing those upgoing electrons which have been accelerated by the wave field above the low energy detection threshold of FAST. A stronger interval of upward current shows that small-scale structuring of scale ~50km has been imposed on the current carriers, which are downgoing magnetospheric electrons of energy 0-500eV.

Field-aligned current systems in the magnetospheric ground state

1998 ◽  
Vol 103 (A4) ◽  
pp. 6853-6869 ◽  
Author(s):  
Masakazu Watanabe ◽  
Takesi Iijima ◽  
Masayuki Nakagawa ◽  
Thomas A. Potemra ◽  
Laurence J. Zanetti ◽  
...  
Keyword(s):  
Ground State ◽  
Field Aligned Current ◽  
Current Systems

scholarly journals Multi-spacecraft observations of small-scale fluctuations in density and fields in plasmaspheric plumes

2012 ◽  
Vol 30 (3) ◽  
pp. 623-637 ◽  
Author(s):  
H. Matsui ◽  
F. Darrouzet ◽  
J. Goldstein ◽  
P. A. Puhl-Quinn ◽  
Yu. V. Khotyaintsev ◽  
...  
Keyword(s):  
Electric Fields ◽  
Small Scale ◽  
Fast Mode ◽  
Magnetic Fluctuations ◽  
Density Enhancement ◽  
Non Local ◽  
Similar Location ◽  
Local Generation ◽  
Alfven Velocity ◽  
Measured Density

Abstract. In this event study, small-scale fluctuations in plasmaspheric plumes with time scales of ~10 s to minutes in the spacecraft frame are examined. In one event, plasmaspheric plumes are observed by Cluster, while IMAGE measured density enhancement at a similar location. Fluctuations in density exist in plumes as detected by Cluster and are accompanied by fluctuations in magnetic fields and electric fields. Magnetic fluctuations are transverse and along the direction of the plumes. The E/B ratio is smaller than the Alfvén velocity. Another similar event is briefly presented. We then consider physical properties of the fluctuations. Alfvén mode modulated by the feedback instability is one possibility, although non-local generation is likely. It is hard to show that the fluctuations represent a fast mode. Interchange motion is possible due to the consistency between measurements and expectations. The energy source could be a pressure or density gradient in plasmaspheric plumes. When more events are accumulated so that statistical analysis becomes feasible, this type of study will be useful to understand the time evolution of plumes.

Field-aligned current ordering in ground and space measurements

2020 ◽  
Author(s):  
Malcolm Dunlop ◽  
Junying Yang ◽  
Xiangcheng Dong ◽  
Mervyn Freeman ◽  
Neil Rogers ◽  
...  
Keyword(s):  
Large Scale ◽  
Correlation Coefficients ◽  
Lower Latitude ◽  
Time Shift ◽  
Small Scale ◽  
Maximum Correlation ◽  
Substorm Activity ◽  
The Mean ◽  
Field Aligned Current ◽  
Statistical Trends

&lt;p&gt;The orientation of field-aligned current sheets (FACs) can be inferred from dual-spacecraft correlations of the FAC signatures between two Swarm spacecraft (A and C), using the maximum correlations obtained from sliding data segments. Statistical analysis of both the correlations and the inferred orientations shows clear trends in magnetic local time (MLT) which reveal behaviour of both large and small scale currents. The maximum correlation coefficients show distinct behaviour in terms of either the time shift, or the shift in longitude between Swarm A and C for various filtering levels. The lower-latitude FACs show the strongest correlations for a broad range of MLT centred on dawn and dusk, with a higher correlation coefficient on the dusk-side and lower correlations near noon and midnight, and broadly follow the mean shape of the auroral boundary for the lower latitudes corresponding to Region 2 FACs (and are most well-ordered on the dusk side). Individual events sampled by higher altitude spacecraft (e.g. the 4 Cluster spacecraft), in conjunction with Swarm (mapping both to region 1 and 2), also show two different domains of FACs: time variable, small-scale (10s km), and more stationary large-scale (&gt;100 km) FACs. We investigate further how these FAC regimes are dependent on geomagnetic activity, focusing on high activity events. Both the statistical trends, and individual conjugate events, show comparable effects seen in the ground magnetometer signals (dH/dt) during storm/substorm activity and show distributions that are similar.&lt;/p&gt;

Altitudinal comparison of dayside field-aligned current signatures by Viking and DMSP-F7: Intermediate-scale field-aligned current systems

1996 ◽  
Vol 101 (A7) ◽  
pp. 15297-15310 ◽  
Author(s):  
S. Ohtani ◽  
L. G. Blomberg ◽  
P. T. Newell ◽  
M. Yamauchi ◽  
T. A. Potemra ◽  
...  
Keyword(s):  
Intermediate Scale ◽  
Scale Field ◽  
Field Aligned Current ◽  
Current Signatures ◽  
Current Systems
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