scholarly journals Excitation of zero-frequency magnetic field-aligned currents by ionospheric heating

2011 ◽  
Vol 29 (6) ◽  
pp. 1147-1152 ◽  
Author(s):  
A. V. Streltsov ◽  
T. R. Pedersen
Keyword(s):  
Magnetic Field ◽  
Current System ◽  
Three Dimensional ◽  
Characteristic Size ◽  
Ionospheric Heating ◽  
F Region ◽  
Strong Localization ◽  
Frequency Magnetic Field ◽  
Shear Alfven Waves ◽  
Zero Frequency

Abstract. Time-dependent, three-dimensional numerical simulations of the reduced MHD model describing shear Alfvén waves in the magnetosphere provide an interesting prediction superficially similar to results of several ionospheric heating experiments conducted at high altitudes. In these experiments, heating of the ionospheric F-region with a constant/zero-frequency beam of HF waves causes luminous structures in the ionosphere in the form of a ring or a solid spot with a characteristic size comparable to the size of the heated spot. Simulations suggest that spots/rings or similar optical appearance might be associated with a magnetic field-aligned current system produced by the ionospheric heating. Two of the most interesting features of this current system are (1) strong localization across the ambient magnetic field and (2) distinctive non-symmetrical luminous signatures (ring/spot) in magnetically conjugate locations in the ionosphere.

An assessment of how a combination of shears, field-aligned currents and collisions affect F-region ionospheric instabilities

2007 ◽  
Vol 73 (1) ◽  
pp. 69-88 ◽  
Author(s):  
J.-P. ST.-MAURICE ◽  
J.-M. NOËL ◽  
P. J. PERRON
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
Theoretical Framework ◽  
Fluid Limit ◽  
Ambient Magnetic Field ◽  
Acoustic Instability ◽  
F Region ◽  
Ion Acoustic ◽  
Depth Study ◽  
Zero Frequency

Abstract.We present an in depth study of the fluid limit of a kinetically derived collisional, current-driven instability that includes shears in the field-aligned currents as well as collisions. We show how the theory presented here generalizes other theories, including the collisionless current-driven electrostatic ion acoustic instability and its sheared collisionless version. We offer a low-frequency generalization of the zero frequency ion shear driven instability by minimizing the relative drift magnitude as well as the shears themselves. We discuss the implication of our theoretical framework both for strongly field-aligned modes and modes where the wavevectors have arbitrary angles with respect to the ambient magnetic field. We discuss the results in terms of F-region irregularity observations of coherent echoes by ionospheric radars.

Derivation of the full current density vector in the Earth's ionosphere low- and mid-latitude F region using ESA's Swarm satellites

2020 ◽  
Author(s):  
Martin Fillion ◽  
Gauthier Hulot ◽  
Patrick Alken ◽  
Arnaud Chulliat ◽  
Pierre Vigneron
Keyword(s):  
Current Density ◽  
Current System ◽  
Three Dimensional ◽  
Current Density Vector ◽  
F Region ◽  
Swarm Satellites ◽  
Density Vector ◽  
Dynamical Features ◽  
The One ◽  
Swarm Satellite

<p>A new multi-spacecraft method to recover estimates of the average three-dimensional current density in the Earth's ionosphere is presented. It is demonstrated using the ESA's Swarm satellite constellation and by taking advantage of the favorable geometrical configurations during the early phase of the mission. The current density vector is calculated inside prisms whose vortices are defined by the satellite positions. The mathematical formalism differs from previous approaches such as the one known as the ”curlometer”. It makes use of the well-known curl-B technique and involves an inverse problem which allows for error propagation through the calculation. Data from the vector field magnetometers of the three satellites are used and special care is taken to characterize the errors on these data. The method is applied in the low- and mid-latitude F-region on 15 February 2014. It provides latitudinal profiles of the full current density vector together with the associated error bars in the morning and evening sectors. We observe several dynamical features such as clear signatures of field-aligned interhemispheric currents, potential signatures of the wind dynamo current system as well as mid-latitude east-west currents.</p>

scholarly journals Transient production of F-region irregularities associated with TCV passage

2003 ◽  
Vol 21 (7) ◽  
pp. 1531-1541 ◽  
Author(s):  
R. Kataoka ◽  
H. Fukunishi ◽  
K. Hosokawa ◽  
H. Fujiwara ◽  
A. S. Yukimatu ◽  
...  
Keyword(s):  
Electric Fields ◽  
Current System ◽  
Rapid Evolution ◽  
Three Dimensional ◽  
Leading Edge ◽  
Spectral Width ◽  
Plasma Convection ◽  
Plasma Irregularities ◽  
F Region ◽  
Field Aligned Current

Abstract. Transient production of F-region plasma irregularities due to traveling convection vortices (TCVs) was investigated using the Super Dual Auroral Radar Network (SuperDARN) combined with ground magnetometer networks and the POLAR ultraviolet imager. We selected two large-amplitude (100–200 nT) TCV events that occurred on 22 May 1996 and 24 July 1996. It is found that the TCV-associated HF backscatter arises in blobs with spatial scale of a few hundreds km. They traveled following tailward bulk motion of the TCV across the three fields-of-view of the SuperDARN HF radars in the prenoon sector. The spectra in the blobs showed unidirectional Doppler velocities of typically 400–600 m/s, with flow directions away from the radar. These unidirectional velocities correspond to the poleward and/or eastward convective flow near the leading edge of upward field-aligned current. The backscatter blobs overlapped the poleward and westward part of the TCV-related transient aurora. It is likely that the transient backscatter blobs are produced by the three-dimensional gradient drift instabilities in the three-dimensional current system of the TCV. In this case, nonlinear rapid evolution of irregularities would occur in the upward field-aligned current region. The spectral width of the backscatter blob is typically distributed between 50 and 300 m/s, but sometimes it is over 400 m/s. This suggests that the temporal broad spectra over 400 m/s are produced by Pc1–2 bursts, while the background spectral width of 50–300 m/s are produced by the velocity gradient structure of convection vortices themselves.Key words. Ionosphere (Electric fields and currents; Ionospheric irregularities; Plasma convection)

scholarly journals Mid-latitude solar eclipses and their influence on ionospheric current systems

2009 ◽  
Vol 27 (12) ◽  
pp. 4449-4461 ◽  
Author(s):  
A. T. Tomás ◽  
H. Lühr ◽  
M. Rother
Keyword(s):  
Magnetic Field ◽  
Current System ◽  
Magnetic Field Data ◽  
Ionospheric Conductivity ◽  
Ionospheric Current ◽  
Zonal Winds ◽  
Northern Summer ◽  
F Region ◽  
June Solstice ◽  
Current Systems

Abstract. Using CHAMP magnetic field data we study the behaviour of the geomagnetic field during two mid latitude eclipses on 21 June 2001 and 22 September 2006. The possible influence of the eclipses on different ionospheric current systems, as seen in the magnetic field measured by CHAMP, is discussed. It is expected that the blocking of solar radiation during an eclipse causes a reduction of the ionospheric conductivity and therefore has an effect on the different current systems. We address in particular the effects of the eclipses on the inter-hemispheric field-aligned currents and on the Sq current system. The two events studied occur under different seasonal conditions, e.g. June solstice and September equinox, therefore quite different aspects can be investigated. We find that the eclipses might affect the direction and intensity of the inter-hemispheric currents and possibly influence the direction of zonal winds, therefore changing the direction of the prevailing F-region dynamo currents. The eclipse in the Southern Hemisphere during September equinox caused inter-hemispheric currents similar to those observed in northern summer. Reverse inter-hemispheric currents were recorded after the end of the eclipse. A large variety of atypical currents was observed during the June event. Most of them might be related to a reversed F-region dynamo in the morning sector and an enhanced conductivity difference between the hemispheres. The eclipse in the south seems to enhance the June solstice conditions considerably.

Generation of shear Alfvén waves by a rotating magnetic field source: Three-dimensional simulations

2011 ◽  
Vol 18 (3) ◽  
pp. 032113 ◽  
Author(s):  
A. V. Karavaev ◽  
N. A. Gumerov ◽  
K. Papadopoulos ◽  
Xi Shao ◽  
A. S. Sharma ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Alfven Waves ◽  
Rotating Magnetic Field ◽  
Alfvén Waves ◽  
Field Source ◽  
Shear Alfven Waves ◽  
Three Dimensional Simulations

A three-dimensional kinematic dynamo

1975 ◽  
Vol 344 (1637) ◽  
pp. 235-258 ◽  
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Characteristic Size ◽  
Steady Flows ◽  
Dynamo Action ◽  
Ohmic Dissipation ◽  
The Earth ◽  
Induction Equation ◽  
High Degree ◽  
The Magnetic Field

A number of steady (marginal) solutions of the induction equation governing the magnetic field created by a particular class of threedimensional flows in a sphere of conducting fluid surrounded by an insulator are derived numerically. These motions possess a high degree of symmetry which can be varied to confirm numerically that the corresponding asymptotic limit of Braginsky is attained. The effect of altering the spatial scale of the motions without varying their vigour can also be examined, and it is found that dynamo action is at first eased by decreasing their characteristic size. There are, however, suggestions that the regenerative efficiency does not persistently increase to very small length scales, but ultimately decreases. It is further shown that time varying motions, in which the asymmetric components of flow travel as a wave round lines of latitude, can sustain fields having co-rotating asymmetric parts. It is demonstrated that, depending on their common angular velocity, these may exist at slightly smaller magnetic Reynolds numbers than the corresponding models having steady flows and fields. The possible bearing of the integrations on the production of the magnetic field of the Earth is considered, and the implied ohmic dissipation of heat in the core of the Earth is estimated for different values of the parameters defining the model.

scholarly journals Afternoon mid-latitude current system and low-latitude geomagnetic field asymmetry during geomagnetic storms

1997 ◽  
Vol 15 (12) ◽  
pp. 1537-1547 ◽  
Author(s):  
A. Grafe ◽  
P. A. Bespalov ◽  
V. Y. Trakhtengerts ◽  
A. G. Demekhov
Keyword(s):  
Magnetic Field ◽  
Ring Current ◽  
Geomagnetic Storms ◽  
Current System ◽  
Three Dimensional ◽  
Low Latitude ◽  
Electrojet Current ◽  
The Relationship ◽  
Current Systems ◽  
Correlative Relationship

Abstract. For four geomagnetic storms of middle intensity the relationship between the low-latitude magnetic field asymmetry using ASY indices and the intensity of the auroral eastward and westward electrojet was considered. It was asked whether there exists a connection between ASY and the eastward electrojet. To answer this question equivalent current systems were estimated in mid-latitudes. It was found that the observations obviously show no correlative relationship between the low-latitude magnetic-field asymmetry and the eastward electrojet, whereas one exists between ASY and the westward electrojet. To explain the generally accepted common three-dimensional current system between the partial ring current and the eastward electrojet, a condensor model of the three-dimensional current system was developed. It could be shown that the short periodic variations of the partial ring current are shielded by the condensor and cannot influence the eastward-electrojet current.

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