Instability of the magnetosphere-ionosphere convection and formation of auroral arcs

1994 ◽  
Vol 12 (7) ◽  
pp. 636-641
Author(s):  
A. E. Kozlovsky ◽  
W. B. Lyatsky
Keyword(s):  
Steady State ◽  
Plasma Sheet ◽  
Electron Precipitation ◽  
Ionospheric Conductivity ◽  
Magnetospheric Convection ◽  
The Earth ◽  
Interchange Instability ◽  
Auroral Arcs

Abstract. In this paper we study an instability of the plasma moving towards the Earth near the inner plasma sheet boundary. We include both the interchange instability of the plasma sheet and the magnetosphere-ionosphere interaction instability caused by an effect of field-aligned currents (connected with electron precipitation) on ionospheric conductivity. The instability leads to the separation of steady-state magnetospheric convection into parallel layers. This instability may be responsible for the appearance of quiet auroral arcs inside region 2 of field-aligned currents flowing out of the ionosphere. This instability allows us to explain also the existence of crossing auroral arcs.

scholarly journals Possible role of magnetosphere-ionosphere coupling in auroral arc generation

2000 ◽  
Vol 18 (9) ◽  
pp. 1108-1117 ◽  
Author(s):  
W. Lyatsky ◽  
A. M. Hamza
Keyword(s):  
Growth Rate ◽  
Plasma Sheet ◽  
Alfven Waves ◽  
The Other ◽  
Alfven Wave ◽  
Alfvén Waves ◽  
Ionospheric Conductivity ◽  
Model Based ◽  
Field Aligned Current ◽  
Auroral Arcs

Abstract. Three models for the magnetosphere-ionosphere coupling feedback instability are considered. The first model is based on demagnetization of hot ions in the plasma sheet. The instability takes place in the global magnetosphere-ionosphere system when magnetospheric electrons drift through a spatial gradient of hot magnetospheric ion population. Such a situation exists on the inner and outer edges of the plasma sheet where relatively cold magnetospheric electrons move earthward through a radial gradient of hot ions. This leads to the formation of field-aligned currents. The effect of upward field-aligned current on particle precipitation and the magnitude of ionospheric conductivity leads to the instability of this earthward convection and to its division into convection streams oriented at some angle with respect to the initial convection direction. The growth rate of the instability is maximum for structures with sizes less than the ion Larmor radius in the equatorial plane. This may lead to formation of auroral arcs with widths about 10 km. This instability explains many features of such arcs, including their conjugacy in opposite hemispheres. However, it cannot explain the very high growth rates of some auroral arcs and very narrow arcs. For such arcs another type of instability must be considered. In the other two models the instability arises because of the generation of Alfven waves from growing arc-like structures in the ionospheric conductivity. One model is based on the modulation of precipitating electrons by field-aligned currents of the upward moving Alfven wave. The other model takes into consideration the reflection of Alfven waves from a maximum in the Alfven velocity at an altitude of about 3000 km. The growth of structures in both models takes place when the ionization function associated with upward field-aligned current is shifted from the edges of enhanced conductivity structures toward their centers. Such a shift arises because the structures move at a velocity different from the E×B drift. Although both models may work, the growth rate for the model, based on the modulation of the precipitating accelerated electrons, is significantly larger than that of the model based on the Alfven wave reflection. This mechanism is suitable for generation of auroral arcs with widths of about 1 km and less. The growth rate of the instability can be as large as 1 s-1, and this mechanism enables us to justify the development of auroral arcs only in one ionosphere. It is hardly suitable for excitation of wide and conjugate auroral arcs, but it may be responsible for the formation of small-scale structures inside a wide arc.Key words: Ionosphere (auroral ionosphere) - Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions)  

scholarly journals Quasi-static MHD processes in Earth's magnetosphere

1988 ◽  
Vol 6 (3) ◽  
pp. 525-537 ◽  
Author(s):  
Gerd-Hannes Voigt
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Plasma Sheet ◽  
Equilibrium Theory ◽  
Flux Tubes ◽  
Earth’S Magnetosphere ◽  
Magnetospheric Convection ◽  
Mhd Equilibrium ◽  
Earth's Magnetosphere ◽  
Flow Velocities

The purpose of this paper is to demonstrate how the MHD equilibrium theory can be used to describe the global magnetic field configuration of Earth's magnetosphere and its time evolution under the influence of magnetospheric convection. The MHD equilibrium theory represents magneto-hydrodynamics in the slow-flow approximation. In this approximation time scales are long compared to typical Alfvén wave travel times, and plasma flow velocities are small compared to the Alfvén speed. Under those conditions, the inertial term ρ(dv/dt) in the MHD equation of motion is a small second order term which can be neglected. The MHD equilibrium theory is not a static theory, though, because time derivatives and flow velocities remain first order quantities in the continuity equation, in the thermodynamic equation of state, and in the induction equation. Therefore one can compute slowly time-dependent processes, such as magnetospheric convection, in terms of series of static equilibrium states. However, those series are not arbitrary; they are constrained by thermodynamic conditions according to which the magnetosphere evolves in time.It is an interesting question, whether or not the magnetosphere, driven by slow, lossless, adiabatic, earthward convection of magnetotail flux tubes, can reach a steady state. There exist magnetospheric equilibria in which magnetotail flux tubes satisfy the steady-state condition d/dt (Pρ−γ) = 0. Those configurations exhibit a deep magnetic field minimum in the equatorial plane, near the inner edge of the tail plasma sheet. The magnetosphere becomes tearing-mode unstable in the neighborhood of such a minimum, thus leading to periodic onsets of substorms in the inner plasma sheet. This explains why distinct magnetic field minima have not been observed in this region. Magnetic substorms seem to be an inevitable element of the global convection cycle which inhibit the establishment of an ultimate steady state.MHD equilibria discussed in this paper result from linear and non-linear solutions to the two-dimensional Grad-Shafranov equation for isotropic thermal plasma pressure.

scholarly journals Ion shell distributions as free energy source for plasma waves on auroral field lines mapping to plasma sheet boundary layer

2004 ◽  
Vol 22 (6) ◽  
pp. 2115-2133 ◽  
Author(s):  
A. Olsson ◽  
P. Janhunen ◽  
W. K. Peterson
Keyword(s):  
Boundary Layer ◽  
Free Energy ◽  
Plasma Sheet ◽  
Wave Activity ◽  
Plasma Sheet Boundary Layer ◽  
In Situ Data ◽  
Bernstein Waves ◽  
Field Lines ◽  
Auroral Arcs ◽  
Polar Satellite

Abstract. Ion shell distributions are hollow spherical shells in velocity space that can be formed by many processes and occur in several regions of geospace. They are interesting because they have free energy that can, in principle, be transmitted to ions and electrons. Recently, a technique has been developed to estimate the original free energy available in shell distributions from in-situ data, where some of the energy has already been lost (or consumed). We report a systematic survey of three years of data from the Polar satellite. We present an estimate of the free energy available from ion shell distributions on auroral field lines sampled by the Polar satellite below 6 RE geocentric radius. At these altitudes the type of ion shells that we are especially interested in is most common on auroral field lines close to the polar cap (i.e. field lines mapping to the plasma sheet boundary layer, PSBL). Our analysis shows that ion shell distributions that have lost some of their free energy are commonly found not only in the PSBL, but also on auroral field lines mapping to the boundary plasma sheet (BPS), especially in the evening sector auroral field lines. We suggest that the PSBL ion shell distributions are formed during the so-called Velocity Dispersed Ion Signatures (VDIS) events. Furthermore, we find that the partly consumed shells often occur in association with enhanced wave activity and middle-energy electron anisotropies. The maximum downward ion energy flux associated with a shell distribution is often 10mWm-2 and sometimes exceeds 40mWm-2 when mapped to the ionosphere and thus may be enough to power many auroral processes. Earlier simulation studies have shown that ion shell distributions can excite ion Bernstein waves which, in turn, energise electrons in the parallel direction. It is possible that ion shell distributions are the link between the X-line and the auroral wave activity and electron acceleration in the energy transfer chain for stable auroral arcs.

scholarly journals IMF B y Influence on Magnetospheric Convection in Earth's Magnetotail Plasma Sheet

2019 ◽  
Vol 46 (21) ◽  
pp. 11698-11708 ◽  
Author(s):  
T. Pitkänen ◽  
A. Kullen ◽  
K. M. Laundal ◽  
P. Tenfjord ◽  
Q. Q. Shi ◽  
...  
Keyword(s):  
Plasma Sheet ◽  
Magnetospheric Convection

Effects of spatial diffusion in the inner plasma sheet and the structure of the diffusion tensor

1995 ◽  
Vol 13 (2) ◽  
pp. 111-117 ◽  
Author(s):  
V. E. Zakharov ◽  
M. I. Pudovkin
Keyword(s):  
Flux Tube ◽  
Plasma Sheet ◽  
Diffusion Tensor ◽  
Plasma Pressure ◽  
Spatial Diffusion ◽  
Angle Distribution ◽  
Inner Magnetosphere ◽  
Electron Population ◽  
Magnetospheric Convection ◽  
Isotropic Pitch

Abstract. A standard pair of equations is used to describe the behaviour of a single monoenergetic particle (proton or electron) population on a geomagnetic flux tube drifting in the magnetosphere. When particle losses from the drifting flux tube into the ionosphere are neglected, this behaviour is adiabatic in a thermodynamic sense. For a population of particles with an isotropic pitch-angle distribution, the generalization of that system of equations is obtained by adding radial and azimuthal spatial diffusion terms. The magnetic field is taken to be dipolar in the inner magnetosphere. The potential electric field is assumed to consist of magnetospheric convection and corotation components. Experimental data are used to estimate the radial equatorial profiles of the plasma sheet pressure. Assuming that the local time and L-shell variations are separable and supposing steady-state conditions, the expressions for the diffusion tensor components are evaluated. The influence of spatial diffusion on the radial and azimuthal profiles of the plasma pressure in the inner plasma sheet is also discussed.

Interplay of bubble injections in the plasma sheet dynamics as inferred from RCM-I simulations

2020 ◽  
Author(s):  
Sina Sadeghzadeh ◽  
Jian Yang
Keyword(s):  
Plasma Sheet ◽  
High Speed ◽  
Space Environment ◽  
Inner Magnetosphere ◽  
Near Earth Space ◽  
Hot Plasma ◽  
Plasma Distribution ◽  
Rice Convection Model ◽  
Convection Model ◽  
Interchange Instability

<p><span>Understanding the transport of hot plasma from tail towards the inner magnetosphere is of great importance to improve our perception of the near-Earth space environment. In accordance with the recent observations, the contribution of bursty bulk flows (BBFs)/bubbles in the inner plasma sheet especially in the storm-time ring current formation is nonnegligible. These high-speed plasma flows with depleted flux tube/entropy are likely formed in the mid tail due to magnetic reconnection and injected earthward as a result of interchange instability. In this presentation, we investigate the interplay of these meso-scale structures on the average magnetic field and plasma distribution in various regions of the plasma sheet, using the Inertialized Rice Convection Model (RCM-I). We will discuss the comparison of our simulation results with the observational statistics and data-based empirical models.</span></p>

Modeling particle precipitation and effects on the ionospheric conductivity

2020 ◽  
Author(s):  
Yiqun Yu ◽  
Xingbin Tian ◽  
Minghui Zhu ◽  
Shreedevi Pr
Keyword(s):  
Ring Current ◽  
Transport Model ◽  
Current Model ◽  
Electron Precipitation ◽  
Plasma Convection ◽  
Particle Precipitation ◽  
Ionospheric Conductivity ◽  
Emic Wave ◽  
Intense Storm ◽  
Stream Transport

<p>Particle precipitation originated from the magnetosphere provides important energy source to the upper atmosphere, leading to ionization and enhancement of conductivity, which in turn changes the electric potential in the MI system to influence the plasma convection in the magnetosphere. In this study, we simulate ring current particle precipitation caused by several important loss mechanisms, including electron precipitation due to whistler wave scattering, ion precipitation due to EMIC wave diffusion and field line curvature scattering. These physical mechanisms are implemented in the kinetic ring current model via diffusion equation with associated pitch angle diffusion coefficients. The precipitation is subsequently input to a two-stream transport model at the top of ionosphere in order to examine its impact on the ionsopheric conductivity. It is found that during intense storm time, electron precipitation of tens of keV dominates in the dawn sector and leads to significant enhancement of conductivity at low altitudes. On the other hand, proton precipitation on the nightside mostly occurs for energy below 10 keV, and contributes to ionization above 100 km, resulting in enhancement of conductivity there. Consequently, the height profile of both Pedersen and Hall conductivity exhibits two layers, potentially complicating the current closure in the ionosphere system.</p>

Determining latitudinal extent of energetic electron precipitation using MEPED on-board NOAA POES

2020 ◽  
Author(s):  
Eldho Midhun Babu ◽  
Hilde Nesse Tyssøy ◽  
Christine Smith-Johnsen ◽  
Ville Aleksi Maliniemi ◽  
Josephine Alessandra Salice ◽  
...  
Keyword(s):  
Solar Wind ◽  
Radiation Belt ◽  
Climate Models ◽  
Stratospheric Ozone ◽  
Energetic Electron ◽  
Radiation Belts ◽  
Atmospheric Dynamics ◽  
Electron Precipitation ◽  
Atmospheric Effects ◽  
The Earth

<p>Energetic electron precipitation (EEP) from the plasma sheet and the radiation belts, can collide with gases in the atmosphere and deposit their energy. EEP increase the production of NOx and HOx, which will catalytically destroy stratospheric ozone, an important element of atmospheric dynamics. The particle precipitation also causes variation in the radiation belt population. Therefore, measurement of latitudinal extend of the precipitation boundaries is important in quantifying atmospheric effects of Sun-Earth interaction and threats to spacecrafts and astronauts in the Earth’s radiation belt. <br>This study uses measurements by MEPED detectors of six NOAA/POES and EUMETSAT/METOP satellites during the year 2010 to determine the latitudinal boundaries of EEP and its variability with geomagnetic activity and solar wind drivers. Variation of the boundaries with respect to different particle energies and magnetic local time is studied. The result will be a key element for constructing a model of EEP variability to be applied in atmosphere climate models.</p>

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