Effects Of Field-aligned Currents Research Articles

TEC variations and ionospheric disturbances during the magnetic storm in March 2015 observed from continuous GPS data in the Southeast Asia region

TEC variations and ionospheric disturbances during the magnetic storm in March 2015 observed from continuous GPS data in the Southeast Asia region

Observation of field-aligned and ionospheric currents during space weather month, September 1999

September 1999 was a magnetically active month, with several geomagnetic storms occurring in sequence which influenced the current pattern of the high-latitude ionosphere. The DMI Greenland magnetometers recorded variations of the ionospheric Hall currents while Ørsted, a Danish low-altitude Earth-orbiting satellite, measured the magnetic effect of field-aligned currents (FAC). We discuss a particular dayside event which occurred a few hours after the peak of a moderate storm on Sept. 15, 1999. Ørsted proceeded polebound on a trajectory closely aligned with the Greenland west coast magnetometer chain, and the Sondrestrom Incoherent Scatter Radar was in operation scanning the ionosphere almost parallel to the Østed trajectory. Coincident solar wind (SW) and interplanetary magnetic field (IMF) data were obtained from the ACE spacecraft and ballistically propagated to a nominal subsolar bow shock location at 12 Re. A synoptic view of the data suggests that the dayside field-aligned and ionospheric current system responded quickly (within 5–10 min) to variations of the northward component of the IMF (IMF- B z ). Specifically, the latitude of the boundary between westward and eastward high-latitude Hall currents as well as the latitudes of the maxima of the eastward and westward currents followed closely IMF- B z variations.

The ionospheric E-layer and F-layer dynamos — a tutorial review

Abstract This article reviews the physics of electric currents generated by dynamo action in the ionosphere. The topics discussed include the motions of ions and electrons relative to the neutral air, at different heights in the ionosphere, the ‘voltage generator’ and ‘current generator’ aspects of the ionospheric dynamos, electrical coupling along field lines, and the effects of field-aligned currents.

Instability of the magnetosphere-ionosphere convection and formation of 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.

Finite geometry effects of field‐aligned currents

Traditionally, field‐aligned current densities calculated from gradients in the perturbation magnetic field measured from low‐altitude spacecraft have been based on the assumption that the current regions are infinite in length. However, many measurements clearly indicate that this assumption is invalid. We have performed model calculations of the magnetic field produced by finite current regions that would be measured by a spacecraft‐borne magnetometer. These calculations serve two purposes: (1) to assess the extent to which an infinite current sheet approximation is applicable in calculating field‐aligned current densities by comparing the current density computed from the model perturbation magnetic field assuming an infinite length current region to the model current density; and (2) to assist in the interpretation of the magnetometer signals when the infinite sheet current approximation is clearly inapplicable. For current regions with various aspect (length to width) ratios, we find that the perturbation magnetic fields within the current region more than one current element width from an end produce a calculated current density with less than a 10% departure from the model current density. Certain nonlinear patterns (e.g., V‐shaped signatures) in the correlation plots of the two horizontal components of the perturbation magnetic field can be explained in terms of the end field effects of field‐aligned current regions. Such signatures can be used to determine the configuration of the satellite track through the current region.

The suppressing effect of field-aligned currents on VLF emissions in the magnetosphere

The growth rate of whistler-mode waves is calculated analytically for a bi-Maxwellian plasma in the presence of a beam of cool electrons. This beam is moving in the same direction as the gyroresonant electrons and in the opposite direction to the waves which are considered to propagate parallel (or anti-parallel) to the imposed geomagnetic field. A somewhat surprising result is found. This is that even if the anisotropy is greater than a critical value, which is strongly frequency dependent, the beam reduces the growth of the waves near half the electron gyrofrequency. For a field-aligned current density ~ 1 μA m −2, this mechanism can explain the lack of signals near 1.4 kHz on auroral (return current) flux tubes. It can also explain the observed absorption of signals at half the electron gyrofrequency, around 7 kHz on L = 4 flux tubes, near the equatorial plane and just outside the plasmapause.

High Resolution Doppler Spectrum Measurements of 3-meter Auroral Irregularities at Large Magnetic Aspect Angles

Doppler spectral properties of 50 MHz auroral echoes observed at several magnetic aspect angles are presented. The measurements were made with high resolution CW Doppler systems at 10 different aspect angles ranging between 1 and 14 degrees, during a series of experiments carried out the summers of 1981, 1982 and 1983 in western Canada. The extensive data set was representative of several backscatter periods and different geomagnetic conditions. We found that three basic spectral types associated with different irregularity groups and classified as type 1, 2 and 3, existed throughout the aspect angle range. Type 1 and 2 spectra are reminiscent of those observed in both the equatorial and auroral backscatter at small aspect angles, whereas type 3 is a newly established spectral signature possibly related to electrostatic ion cyclotron waves. The evidence suggests that 3 m primary and secondary plasma waves can exist in aurora with k||/k⊥ wavenumber ratios perhaps larger than 0.25. Statistical analysis of the data showed the magnetic aspect angle effect upon the Doppler spectrum properties to be weak for all types of irregularities at 50 MHz. It is now clear that equatorial E region instability theories, which had been applied directly to aurora, need important modifications, and possibly the inclusion of field aligned current effects, to account for the magnetic aspect angle observations.

A magnetohydrodynamic model of whistler duct structure in the magnetosphere

In this study, the physical structure for the propagation of whistler waves within a duct in the Earth's magnetosphere is investigated by means of magnetohydrodynamic (MHD) theory. Expressions for the current density and induced magnetic field are determined analytically and evaluated in terms of two models for the duct plasma density distribution. It is found that once the duct is formed, forces associated with the current structure will maintain it. MHD instabilities are examined briefly and found to be unlikely to threaten duct maintenance in regions where whistlers are typically observed. Examination of some effects of field-aligned currents suggest that this may be a viable mechanism for duct formation.

Effect of field-aligned currents in the polar cap at the recovery phase of a magnetic storm

Unusually great fluctuations in the ΔB module of the geomagnetic field have been observed in the polar cap from the satellite Cosmos-321. They are explained by small-scale two-sheet field-aligned current systems which exist during the periods when magnetic fields having a considerable northward B z ( B z ⩾ 10 nT) component are observed in interplanetary space.

Triaxial magnetic measurements of field-aligned currents at 800 kilometers in the auroral region: Initial results

A three-axis magnetometer experiment for measuring the magnetic effects of field-aligned currents at auroral latitudes is described. Some of the results obtained to date are presented, and some preliminary conclusions are discussed. (WDM)

Discussion of paper by L. P. Block and C.-G. Fälthammar, ‘Effects of field-aligned currents on the structure of the ionosphere’

Journal of Geophysical Research (1896-1977)Volume 74, Issue 14 p. 3747-3748 Letters Discussion of paper by L. P. Block and C.-G. Fälthammar, ‘Effects of field-aligned currents on the structure of the ionosphere’ Robert Schunk, Robert SchunkSearch for more papers by this authorJames C. G. Walker, James C. G. WalkerSearch for more papers by this author Robert Schunk, Robert SchunkSearch for more papers by this authorJames C. G. Walker, James C. G. WalkerSearch for more papers by this author First published: 1 July 1969 https://doi.org/10.1029/JA074i014p03747Citations: 6AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume74, Issue14Space Physics1 July 1969Pages 3747-3748 RelatedInformation

Reply [to “Discussion of paper by L. P. Block and C.-G. Fäilthammar, ‘Effects of field-aligned currents on the structure of the ionosphere’”

Reply [to “Discussion of paper by L. P. Block and C.-G. Fäilthammar, ‘Effects of field-aligned currents on the structure of the ionosphere’”

Effects of field-aligned currents on the structure of the ionosphere

The influence of electric currents along the magnetic field lines on the high-latitude F-layer ionosphere is investigated theoretically. It is shown that a current of either sign leads to a reduction of the total electron content and the maximum density, if the charge carriers have to be produced in the ionosphere. Low-energy precipitation leads to a corresponding increase. Extremely low densities in the topside ionosphere may be reached for ion currents of the order of 10-6 amp/m2 or electron currents of 10-3 amp/m2. Observational evidence exists for currents at least of the order of 10-6 amp/m2. It is suggested that the ionospheric trough, the F-layer storm, and other similar effects may be explained by field-aligned currents or plasma diffusion, which is also quantitatively accounted for by the present theory.