scholarly journals Origin of type-2 thermal-ion upflows in the auroral ionosphere

2005 ◽  
Vol 23 (1) ◽  
pp. 13-24 ◽  
Author(s):  
L. M. Kagan ◽  
J.-P. St.-Maurice
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Collision Frequency ◽  
Frictional Heating ◽  
Electron Collision ◽  
Momentum Balance ◽  
The North ◽  
The Waves ◽  
Ion Upflows

Abstract. The origin of thermal ion outflows exceeding 1km/s in the high-latitude F-region has been a subject of considerable debate. For cases with strong convection electric fields, the "evaporation" of the ions due to frictional heating below 400-500km has been shown to provide some satisfactory answers. By contrast, in the more frequent subclass of outflow events observed over auroral arcs, called type-2, there is no observational evidence for ion frictional heating. Instead, an electron temperature increase of up to 6000° K is observed over the outflow region. In this case, field-aligned electric fields have long been suspected to be involved, but this explanation did not seem to agree with expectations from the ion momentum balance. In the present work we provide a consistent scenario for the type-2 ion upflows based on our case study of an event that occurred on 20 February 1990. We introduce, for the first time, the electron energy balance in the analysis. We couple this equation with the ion momentum balance to study the salient features of the observations and conclude that type-2 ion outflows and the accompanying electron heating events are indeed consistent with the existence of a field-aligned electric field. However, for our explanation to work, we have to require that an allowance be made for electron scattering by high frequency turbulence. This turbulence could be generated at first by the very fast response of the electrons themselves to a newly imposed electric field that would be partly aligned with the geomagnetic field. The high frequencies of the waves would make it impossible for the ions to react to the waves. We have found the electron collision frequency associated with scattering from the waves to be rather modest, i.e. comparable to the ambient electron-ion collision frequency. The field-aligned electric field inferred from the observations is likewise of the same order of magnitude as the normal ambipolar field, at least for the case that we have studied in detail. We propose that the field-aligned electric field is maintained by the north-south motion of an east-west arc. The magnetic perturbation associated with the arc itself converts a small fraction of the perpendicular electric field into a field parallel to the total magnetic field, while the north-south motion ensures that the conversion never stops.

scholarly journals Storm enhanced density: magnetic conjugacy effects

2007 ◽  
Vol 25 (8) ◽  
pp. 1791-1799 ◽  
Author(s):  
J. C. Foster ◽  
W. Rideout
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Ionospheric Disturbance ◽  
Polar Regions ◽  
The North ◽  
Polar Caps ◽  
Source Regions ◽  
Field Lines ◽  
Magnetic Conjugacy ◽  
Early Phases

Abstract. In the early phases of a geomagnetic storm, the low and mid-latitude ionosphere are greatly perturbed. Large SAPS electric fields map earthward from the perturbed ring current overlapping and eroding the outer plasmasphere and mid-latitude ionosphere, drawing out extended plumes of storm enhanced density (SED). We use combined satellite and ground-based observations to investigate the degree of magnetic conjugacy associated with specific features of the stormtime ionospheric perturbation. We find that many ionospheric disturbance features exhibit degrees of magnetic conjugacy and simultaneity which implicate the workings of electric fields. TEC enhancements on inner-magnetospheric field lines at the base of the SED plumes exhibit localized and longitude-dependent features which are not strictly magnetic conjugate. The SED plumes streaming away from these source regions closely follow magnetic conjugate paths. SED plumes can be used as a tracer of the location and strength of disturbance electric fields. The SED streams of cold plasma from lower latitudes enter the polar caps near noon, forming conjugate tongues of ionization over the polar regions. SED plumes exhibit close magnetic conjugacy, confirming that SED is a convection electric field dominated effect. Several conclusions are reached: 1) The SED plume occurs in magnetically-conjugate regions in both hemispheres. 2) The position of the sharp poleward edge of the SED plume is closely conjugate. 3) The SAPS electric field is observed in magnetically conjugate regions (SAPS channel). 4) The strong TEC enhancement at the base of the SED plume in the north American sector is more extensive than in its magnetic conjugate region. 5) The entry of the SED plume into the polar cap near noon, forming the polar tongue of ionization (TOI), is seen in both hemispheres in magnetically-conjugate regions.

Suppression of runaway of electrons in a Lorentz plasma. II. crossed electric and magnetic fields

1970 ◽  
Vol 4 (3) ◽  
pp. 441-450 ◽  
Author(s):  
Barbara Abraham-Shrauner
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electric Field ◽  
Electric Fields ◽  
Cyclotron Frequency ◽  
Collision Frequency ◽  
Uniform Electric Field ◽  
Drift Motion ◽  
Electric And Magnetic Fields ◽  
The Magnetic Field

Suppression of runaway of electrons in a weak, uniform electric field in a fully ionized Lorentz plasma by crossed magnetic and electric fields is analysed. A uniform, constant magnetic field parallel to a constant or harmonically time varying electric field does not alter runaway from that in the absence of the magnetic field. For crossed, constant fields the passage to runaway or to free motion as described by constant drift motion and spiral motion about the magnetic field is lengthened in time for strong magnetic fields. The new ‘runaway’ time scale is roughly the ratio of the cyclotron frequency to the collision frequency squared for cyclotron frequencies much greater than the collision frequency. All ‘runaway’ time scales may be given approximately by t2E Teff where tE is the characteristic time of the electric field and Teff is the ffective collision time as estimated from the appropriate component of the electrical conductivity.

Derivation of radial electric fields using kinetic theory in tokamak

2013 ◽  
Vol 79 (5) ◽  
pp. 513-517
Author(s):  
K. NOORI ◽  
P. KHORSHID ◽  
M. AFSARI
Keyword(s):  
Kinetic Theory ◽  
Electric Field ◽  
Electric Fields ◽  
Driving Forces ◽  
Radial Electric Field ◽  
Radial Pressure ◽  
Momentum Balance ◽  
Balance Equations ◽  
Radial Pressure Gradient ◽  
Poloidal Rotation

AbstractIn the current study, radial electric field with fluid equations has been calculated. The calculation started with kinetic theory, Boltzmann and momentum balance equations were derived, the negligible terms compared with others were eliminated, and the radial electric field expression in steady state was derived. As mentioned in previous researches, this expression includes all types of particles such as electrons, ions, and neutrals. The consequence of this solution reveals that three major driving forces contribute in radial electric field: radial pressure gradient, poloidal rotation, and toroidal rotation; rotational terms mean Lorentz force. Therefore, radial electric field and plasma rotation are connected through the radial momentum balance.

Altitude integration effects in the skewness of type-2 coherent echoes

1995 ◽  
Vol 13 (9) ◽  
pp. 946-953 ◽  
Author(s):  
A. V. Kustov ◽  
M. V. Uspensky
Keyword(s):  
Spectral Line ◽  
Density Profile ◽  
Collision Frequency ◽  
Spectral Width ◽  
Electron Density Profile ◽  
Spectral Shape ◽  
Electron Collision ◽  
Turbulent Layer ◽  
Electron Collision Frequency

Abstract. Possible effects of signal reception from different electrojet heights in a skewness of auroral coherent spectra are studied assuming that the "inherent" spectral line due to plasma turbulence is of type-2 and symmetrical. For reasonable ionospheric parameters, the altitude integrated spectra are expected to be skewed negatively for positive mean Doppler shift, in agreement with radar observations at small aspect angles. However, the spectra could be skewed positively if the turbulent layer or the electron density profile is shifted to high altitudes of ~120 km. This change of spectral shape will not be observed experimentally if, at the same time, either the electron collision frequency is enhanced or the "inherent" spectral width is increased. Observational results are discussed in view of the predictions given.

scholarly journals Rocket-borne investigation of auroral patches in the evening sector during substorm recovery

2003 ◽  
Vol 21 (3) ◽  
pp. 719-728 ◽  
Author(s):  
M. A. Danielides ◽  
A. Kozlovsky
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Plasma Flow ◽  
Typical Feature ◽  
The North ◽  
Evening Sector ◽  
Periodical Structure ◽  
S Period ◽  
Electric Fields And Currents ◽  
Auroral Arcs

Abstract. On 11 February 1997 at 08:36 UT after a substorm onset the Auroral Turbulence 2 sounding rocket was launched from Poker Flat Research Range, Alaska into a moderately active auroral region. This experiment has allowed us to investigate evening (21:00 MLT) auroral forms at the substorm recovery, which were discrete multiple auroral arcs stretched to, the east and southeast from the breakup region, and bright auroral patches propagating westward along the arcs like a luminosity wave, which is a typical feature of the disturbed arc. The rocket crossed an auroral arc of about 40 km width, stretched along southeast direction. Auroral patches and associated electric fields formed a 200 km long periodical structure, which propagated along the arc westward at a velocity of 3 km/s, whereas the ionospheric plasma velocity inside the arc was 300 m/s westward. The spatial periodicity in the rocket data was found from optical ground-based observations, from electric field in situ measurements, as well as from ground-based magnetic observations. The bright patches were co-located with equatorward plasma flow across the arc of the order of 200 m/s in magnitude, whereas the plasma flow tended to be poleward at the intervals between the patches, where the electric field reached the magnitude of up to 20 mV/m, and these maxima were co-located with the peaks in electron precipitations indicated by the electron counter on board the rocket. Pulsations of a 70-s period were observed on the ground in the eastern component of the magnetic field and this is consistent with the moving auroral patches and the north-south plasma flows associated with them. The enhanced patch-associated electric field and fast westward propagation suggest essential differences between evening auroral patches and those occurring in the morning ionosphere. We propose the wave that propagates along the plasma sheet boundary to be a promising mechanism for the evening auroral patches.Key words. Ionosphere (auroral ionosphere; electric fields and currents)

Calculation of the transverse conductivity for electrons interacting with waves in strong electric fields

1968 ◽  
Vol 46 (23) ◽  
pp. 2659-2661 ◽  
Author(s):  
Harold N. Spector
Keyword(s):  
Distribution Function ◽  
Electric Field ◽  
Electric Fields ◽  
Optical Lattice ◽  
Transverse Electric ◽  
Lattice Vibrations ◽  
Transverse Electric Fields ◽  
Transverse Conductivity ◽  
Strong Electric Fields ◽  
The Waves

We have obtained the transverse a.c. conductivity for electrons interacting with waves in the presence of strong d.c. electric fields. The presence of the d.c. electric field leads to the introduction of a drifted distribution function for the electrons and a complex, field-dependent temperature. The expression for the transverse a.c. conductivity can be used to find the effects of the electric field on the propagation and absorption of waves in solids which induce transverse electric fields. We have applied our results to the interaction of electrons with transverse optical lattice vibrations and find that for all values of ql, it is the drifted distribution function which leads to the amplification of the waves.

scholarly journals Nonlinear Effects of Tropical Instability Waves on the Equatorial Pacific Circulation

2010 ◽  
Vol 40 (2) ◽  
pp. 381-393 ◽  
Author(s):  
Jaclyn N. Brown ◽  
J. Stuart Godfrey ◽  
Susan E. Wijffels
Keyword(s):  
Low Frequency ◽  
Nonlinear Effects ◽  
Equatorial Pacific ◽  
Momentum Balance ◽  
Equatorial Pacific Ocean ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
The North ◽  
The Waves ◽  
Frequency State

Abstract In a numerical model of the equatorial Pacific Ocean, the ∼20-day period tropical instability waves, excited in the eastern half of the domain, are found to damp the strong zonal mean currents. The waves generate large, nonlinear, advection terms in the momentum balance, change the vorticity balance, and thus modulate the low-frequency state. The authors explore whether the effect of tropical instability waves on the background flow can instead be adequately parameterized by a constant-coefficient Laplacian friction scheme. On annual mean, a Laplacian friction coefficient that varies in space is required, for the coefficient is twice as large along the equator and a few degrees more to the north than elsewhere. In addition, wave activity varies in time. During active phases, such as the second half of the year and during La Niñas, the activity increases, which would require the Laplacian coefficient of friction to be at least twice as strong as during the inactive phases. Thus, a more sophisticated damping parameterization than simple Laplacian friction is required in ocean models that do not explicitly resolve tropical instability waves.

scholarly journals On the role of neutral flow in field-aligned currents

2018 ◽  
Vol 36 (1) ◽  
pp. 53-57 ◽  
Author(s):  
Anthony J. Mannucci ◽  
Olga P. Verkhoglyadova ◽  
Xing Meng ◽  
Ryan McGranaghan
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Rest Frame ◽  
Geomagnetic Storms ◽  
Electron Flow ◽  
Lower Ionosphere ◽  
Momentum Balance ◽  
Neutral Atmosphere ◽  
Magnetospheric Dynamics

Abstract. In this brief note we explore the role of the neutral atmosphere in magnetosphere–ionosphere coupling. We analyze momentum balance in the ion rest frame to form hypotheses regarding the role of neutral momentum in the lower ionosphere during geomagnetic storms. Neutral momentum that appears in the ion rest frame is likely the result of momentum imparted to ionospheric ions by solar wind flow and the resultant magnetospheric dynamics. The resulting ion-neutral collisions lead to the existence of an electric field. Horizontal electron flow balances the momentum supplied by this electric field. We suggest a possible role played by the neutral atmosphere in generating field-aligned currents due to local auroral heating. Our physical interpretation suggests that thermospheric neutral dynamics plays a complementary role to the high-latitude field-aligned currents and electric fields resulting from magnetospheric dynamics. Keywords. Ionosphere (ionosphere–magnetosphere interactions; polar ionosphere) – magnetospheric physics (magnetosphere–ionosphere interactions)

Tuning the Electric Field Response of MOFs by Rotatable Dipolar Linkers

2019 ◽  
Author(s):  
Johannes P. Dürholt ◽  
Babak Farhadi Jahromi ◽  
Rochus Schmid
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Structural Changes ◽  
Dielectric Behavior ◽  
Two Dimensions ◽  
Dielectric Constants ◽  
Electric Response ◽  
Dipole Strength ◽  
Metal Organic ◽  
Dynamics Simulations

Recently the possibility of using electric fields as a further stimulus to trigger structural changes in metal-organic frameworks (MOFs) has been investigated. In general, rotatable groups or other types of mechanical motion can be driven by electric fields. In this study we demonstrate how the electric response of MOFs can be tuned by adding rotatable dipolar linkers, generating a material that exhibits paralectric behavior in two dimensions and dielectric behavior in one dimension. The suitability of four different methods to compute the relative permittivity κ by means of molecular dynamics simulations was validated. The dependency of the permittivity on temperature T and dipole strength μ was determined. It was found that the herein investigated systems exhibit a high degree of tunability and substantially larger dielectric constants as expected for MOFs in general. The temperature dependency of κ obeys the Curie-Weiss law. In addition, the influence of dipolar linkers on the electric field induced breathing behavior was investigated. With increasing dipole moment, lower field strength are required to trigger the contraction. These investigations set the stage for an application of such systems as dielectric sensors, order-disorder ferroelectrics or any scenario where movable dipolar fragments respond to external electric fields.

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