scholarly journals Auroral Current and Electrodynamics Structure (ACES) observations of ionospheric feedback in the Alfvén resonator and model responses

2013 ◽  
Vol 118 (6) ◽  
pp. 3288-3296 ◽  
Author(s):  
I. J. Cohen ◽  
M. R. Lessard ◽  
S. R. Kaeppler ◽  
S. R. Bounds ◽  
C. A. Kletzing ◽  
...  
Keyword(s):  
Alfven Resonator ◽  
Auroral Current

The splitting effect of the mode structure of the ionospheric alfven resonator

2015 ◽  
Vol 21 (1(92)) ◽  
pp. 58-63
Author(s):  
N.A. Baru ◽  
◽  
A.V. Koloskov ◽  
Y.M. Yampolski ◽  
◽  
...  
Keyword(s):  
Mode Structure ◽  
Ionospheric Alfvén Resonator ◽  
Alfven Resonator ◽  
Ionospheric Alfven Resonator ◽  
Splitting Effect

Characterization of auroral current systems in Saturn's magnetosphere: High-latitude Cassini observations

2009 ◽  
Vol 114 (A6) ◽  
pp. n/a-n/a ◽  
Author(s):  
D. L. Talboys ◽  
C. S. Arridge ◽  
E. J. Bunce ◽  
A. J. Coates ◽  
S. W. H. Cowley ◽  
...  
Keyword(s):  
High Latitude ◽  
Auroral Current ◽  
Current Systems

Pc 1 waves and ionospheric Alfvén resonator: Generation or filtration?

2000 ◽  
Vol 27 (23) ◽  
pp. 3805-3808 ◽  
Author(s):  
A. G. Demekhov ◽  
V. Yu. Trakhtengerts ◽  
T. Bösinger
Keyword(s):  
Ionospheric Alfvén Resonator ◽  
Alfven Resonator ◽  
Ionospheric Alfven Resonator

scholarly journals Dynamics of Alfvén waves in the night-side ionospheric Alfvén resonator at mid-latitudes

2005 ◽  
Vol 23 (2) ◽  
pp. 499-507 ◽  
Author(s):  
V. V. Alpatov ◽  
M. G. Deminov ◽  
D. S. Faermark ◽  
I. A. Grebnev ◽  
M. J. Kosch
Keyword(s):  
Pulse Duration ◽  
Alfven Waves ◽  
Fundamental Period ◽  
Alfvén Waves ◽  
Shear Mode ◽  
Q Factor ◽  
Trapped Waves ◽  
Alfven Resonator ◽  
Ionospheric Alfven Resonator ◽  
The Waves

Abstract. A numerical solution of the problem on dynamics of shear-mode Alfvén waves in the ionospheric Alfvén resonator (IAR) region at middle latitudes at nighttime is presented for a case when a source emits a single pulse of duration τ into the resonator region. It is obtained that a part of the pulse energy is trapped by the IAR. As a result, there occur Alfvén waves trapped by the resonator which are being damped. It is established that the amplitude of the trapped waves depends essentially on the emitted pulse duration τ and it is maximum at τ=(3/4)T, where T is the IAR fundamental period. The maximum amplitude of these waves does not exceed 30% of the initial pulse even under optimum conditions. Relatively low efficiency of trapping the shear-mode Alfvén waves is caused by a difference between the optimum duration of the pulse and the fundamental period of the resonator. The period of oscillations of the trapped waves is approximately equal to T, irrespective of the pulse duration τ. The characteristic time of damping of the trapped waves τdec is proportional to T, therefore the resonator Q-factor for such waves is independent of T. For a periodic source the amplitude-frequency characteristic of the IAR has a local minimum at the frequency π/ω=(3/4)T, and the waves of such frequency do not accumulate energy in the resonator region. At the fundamental frequency ω=2π/T the amplitude of the waves coming from the periodic source can be amplified in the resonator region by more than 50%. This alone is a basic difference between efficiencies of pulse and periodic sources of Alfvén waves. Explicit dependences of the IAR characteristics (T, τdec, Q-factor and eigenfrequencies) on the altitudinal distribution of Alfvén velocity are presented which are analytical approximations of numerical results.

scholarly journals The upper atmospheres of Uranus and Neptune

2020 ◽  
Vol 378 (2187) ◽  
pp. 20190478 ◽  
Author(s):  
Henrik Melin
Keyword(s):  
Magnetic Field ◽  
Joule Heating ◽  
Critical Role ◽  
Upper Atmosphere ◽  
Heating Rates ◽  
James Webb Space Telescope ◽  
Vertical Distributions ◽  
Auroral Current ◽  
First Time ◽  
The Magnetic Field

We review the current understanding of the upper atmospheres of Uranus and Neptune, and explore the upcoming opportunities available to study these exciting planets. The ice giants are the least understood planets in the solar system, having been only visited by a single spacecraft, in 1986 and 1989, respectively. The upper atmosphere plays a critical role in connecting the atmosphere to the forces and processes contained within the magnetic field. For example, auroral current systems can drive charged particles into the atmosphere, heating it by way of Joule heating. Ground-based observations of H 3 + provides a powerful remote diagnostic of the physical properties and processes that occur within the upper atmosphere, and a rich dataset exists for Uranus. These observations span almost three decades and have revealed that the upper atmosphere has continuously cooled between 1992 and 2018 at about 8 K/year, from approximately 750 K to approximately 500 K. The reason for this trend remain unclear, but could be related to seasonally driven changes in the Joule heating rates due to the tilted and offset magnetic field, or could be related to changing vertical distributions of hydrocarbons. H 3 + has not yet been detected at Neptune, but this discovery provides low-hanging fruit for upcoming facilities such as the James Webb Space Telescope and the next generation of 30 m telescopes. Detecting H 3 + at Neptune would enable the characterization of its upper atmosphere for the first time since 1989. To fully understand the ice giants, we need dedicated orbital missions, in the same way the Cassini spacecraft explored Saturn. Only by combining in situ observations of the magnetic field with in-orbit remote sensing can we get the complete picture of how energy moves between the atmosphere and the magnetic field. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems’.

scholarly journals Ionospheric Alfvén resonator revisited: Feedback instability

2001 ◽  
Vol 106 (A11) ◽  
pp. 25813-25824 ◽  
Author(s):  
Oleg A. Pokhotelov ◽  
V. Khruschev ◽  
M. Parrot ◽  
S. Senchenkov ◽  
V. P. Pavlenko
Keyword(s):  
Ionospheric Alfvén Resonator ◽  
Alfven Resonator ◽  
Ionospheric Alfven Resonator

scholarly journals A linear auroral current-voltage relation in fluid theory

2004 ◽  
Vol 22 (5) ◽  
pp. 1719-1728 ◽  
Author(s):  
J. Vedin ◽  
K. Rönnmark
Keyword(s):  
Kinetic Model ◽  
Large Scale ◽  
Equations Of State ◽  
Potential Drop ◽  
Fluid Models ◽  
Linear Current ◽  
Current Voltage ◽  
Auroral Phenomena ◽  
Auroral Current ◽  
Current Voltage Relation

Abstract. Progress in our understanding of auroral currents and auroral electron acceleration has for decades been hampered by an apparent incompatibility between kinetic and fluid models of the physics involved. A well established kinetic model predicts that steady upward field-aligned currents should be linearly related to the potential drop along the field line, but collisionless fluid models that reproduce this linear current-voltage relation have not been found. Using temperatures calculated from the kinetic model in the presence of an upward auroral current, we construct here approximants for the parallel and perpendicular temperatures. Although our model is rather simplified, we find that the fluid equations predict a realistic large-scale parallel electric field and a linear current-voltage relation when these approximants are employed as nonlocal equations of state. This suggests that the concepts we introduce can be applied to the development of accurate equations of state for fluid simulations of auroral flux tubes.Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions) – Space plasma physics (kinetic and MHD theory)

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