Calculation of an Equivalent Current System in the PolarERegion

Radio Science ◽  
1971 ◽  
Vol 6 (2) ◽  
pp. 247-253 ◽  
Author(s):  
P. Czechowsky
Keyword(s):  
Current System ◽  
Equivalent Current

scholarly journals Effect of the solar wind conditions on the ionospheric equivalent current systems

2013 ◽  
Vol 31 (3) ◽  
pp. 489-501 ◽  
Author(s):  
J. J. Zhang ◽  
C. Wang ◽  
B. B. Tang ◽  
H. Li
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Wind Speed ◽  
Current System ◽  
Solar Wind Speed ◽  
Lower Latitude ◽  
Equivalent Current ◽  
Mhd Model ◽  
Current Systems ◽  
The Imf

Abstract. We employ a global magnetohydrodynamics (MHD) model, namely the PPMLR-MHD model, to investigate the effect of the solar wind conditions, such as the interplanetary magnetic field (IMF) clock angle, southward IMF magnitude and solar wind speed, on the average pattern of the ionospheric equivalent current systems (ECS). A new method to derive ECS from the MHD model is proposed and applied, which takes account of the oblique magnetic field line effects. The model results indicate that when the IMF is due northward, the ECS are very weak while the current over polar region is stronger than the lower latitude; when the IMF rotates southward, the two-cell current system dominates, the eastward electrojet on the afternoon sector and the westward electrojet on the dawn sector increase rapidly while the westward electrojet is stronger than the eastward electrojet. Under southward IMF, the intensity of the westward electrojet and eastward electrojet both increase with the increase of the southward IMF magnitude and solar wind speed, and the increase is very sharp for the westward electrojet. Furthermore, we compare the geomagnetic perturbations on the ground represented by the simulated average ECS with the observation-based statistical results under similar solar wind conditions. It is found that the model results generally match with the observations, but the underestimation of the eastward equivalent current on the dusk sector is the main limitation of the present model.

Equivalent ionospheric currents above Antarctica during the austral summer

1990 ◽  
Vol 2 (3) ◽  
pp. 267-276 ◽  
Author(s):  
V.O. Papitashvili ◽  
Ya.I. Feldstein ◽  
A.E. Levitin ◽  
B.A. Belov ◽  
L.I. Gromova ◽  
...  
Keyword(s):  
Current System ◽  
Geomagnetic Latitude ◽  
Austral Summer ◽  
Polar Regions ◽  
Ionospheric Currents ◽  
Vortex System ◽  
Geomagnetic Variations ◽  
Mean Values ◽  
Equivalent Current ◽  
Current Systems

A regression analysis was carried out between the ground-based geomagnetic data from the southern polar regions (above −55° corrected geomagnetic latitude) and the interplanetary magnetic field (IMF) components in the geocentric solar-magnetospheric co-ordinate system and solar wind (SW) parameters. Hourly mean values of the geomagnetic field horizontal components H and D from 20 Antarctic observatories and automatic stations of 1978–80 and 1983–84 were examined. Regression coefficients were used as geomagnetic perturbation vectors which were rotated 90° clockwise to plot the equivalent current vector patterns in the “corrected geomagnetic latitude-magnetic local time” co-ordinates. The results which are described in the paper reflect geomagnetic phenomena associated with the IMF and SW parameters for the austral summer season only (November, December, January, February). It was found that, in general, global characteristics of the ionospheric convection patterns agree well for both hemispheres. Geomagnetic variations, which are generated by the interaction of the SW plasma and frozen-in IMF with Earth's magnetosphere, represent three types of equivalent current systems: a) two-vortex system with transpolar current from nightside to dayside, controlled by the “quasi-viscous” interaction and southward IMF; b) zonal current system, controlled by the azimuthal IMF; and c) two-vortex system with transpolar current from noon to midnight controlled by the northward IMF. The southern polar cap (above −75°), which was more densely packed with automatic magnetometers than the northern cap, permit us to investigate the fine structure of the high-latitude current systems in detail.

Telluric currents play a big role in interpreting geomagnetic variations

2020 ◽  
Author(s):  
Ari Viljanen ◽  
Liisa Juusola
Keyword(s):  
Current System ◽  
Time Derivative ◽  
Space Physics ◽  
Reasonable Assumption ◽  
Geomagnetically Induced Currents ◽  
Geomagnetic Variations ◽  
Near Surface ◽  
Equivalent Current ◽  
Internal Part ◽  
Telluric Currents

<p>Fast geomagnetic variations of periods from seconds to hours and days are primarily produced by currents in the ionosphere and magnetosphere. There is always an associated secondary (internal, telluric) current system induced in the conducting ground and contributing to the total variation field measured by ground magnetometers. Mathematically, it is possible to fully explain the variation field by two equivalent current systems, one at the ionospheric altitude and another just below the ground. In practice, this separation is feasible using dense magnetometer networks.</p><p>A common way in space physics has been to implicitly neglect the internal part and interpret the ground field only in terms of ionospheric currents. As known from previous studies, this is often a reasonable assumption, since a typical internal contribution is about 30%. However, the situation is much different when the time derivative of the magnetic field (dB/dt) is considered. For the north European IMAGE magnetometer network, the internal part exceeds the external one nearly at all stations. The largest effects due to telluric currents occur at coastal sites close to highly-conducting ocean water and at inland locations close to highly-conducting near-surface anomalies.</p><p>This finding gives a new viewpoint for studies of geomagnetically induced currents (GIC), which are closely related to dB/dt. One key question is to understand which are the ionospheric drivers of big GIC events. We will demonstrate how the telluric currents can strongly modify field variations and especially dB/dt, and how this is correspondingly seen in equivalent current patterns. Consequently, it is recommended that the field separation is performed whenever it is feasible, i.e. a dense observation network is available.</p>

scholarly journals A determination of the hydromagnetic waves polarization from their perturbations on the terminator

1996 ◽  
Vol 14 (6) ◽  
pp. 647-658 ◽  
Author(s):  
L. Alperovich ◽  
B. Fidel ◽  
O. Saka
Keyword(s):  
Frequency Dependence ◽  
Current System ◽  
Orientation Angle ◽  
Temporal Analysis ◽  
Alfven Waves ◽  
Equatorial Region ◽  
Alfven Wave ◽  
Alfvén Waves ◽  
Equivalent Current ◽  
Magnetospheric Waves

Abstract. The influence of the homogeneous and inhomogeneous ionosphere on the orientation angle of the horizontal magnetic vectors of the long-time geomagnetic pulsations is under consideration in this study. It was realized that this angle is small in the case of the homogeneous ionosphere for both the Alfvén  and magnetosonic types of oscillations. An increase in the ionospheric electric field was discovered as the ionospheric conductivity changes during the switch from day to night conditions. It is valid only for the initial Alfvén wave. The ionospheric equivalent current systems excited by the initial magnetospheric waves of Alfvén  and magnetosonic types as well as their behavior near the terminator were studied for different seasons. For the Alfvén source, seasonal variations of the orientation angle close to sunrise at the equator depend on the type of source: odd or even modes of Alfvén oscillations excite observable pulsations. It was found that the ionospheric two-vortex equivalent current system of the long-period pulsations arising in high-latitudes in the equatorial region alters not only its direction, but its intensity too. The largest anomaly (~25% of the source value) would be expected near the terminator. A new experimental method was suggested to recognize the type of incident magnetospheric waves by implementing observations either at a single observatory or at a couple of observatories. In the case of a single observatory it is proposed to study the frequency dependence of the orientation angle of their magnetic components close to sunrise. If the initial wave is magnetosonic, this angle must not be changed as a function of the local time within the wide frequency range of pulsations. When pulsations have an orientation angle sensitive to the presence of the terminator, they may be classified as both Alfvén and magnetosonic. For the Alfvén waves no frequency dependence of the orientational angle is peculiar. On the contrary, magnetosonic waves should be determined as oscillations with an orientational angle proportional to the frequency. These oscillations may be revealed at observatories located on the high-resistance cross sections. The example of the spectral-temporal analysis of pulsation at the equatorial observatory in Huancayo was demonstrated to confirm the proposed experimental technique. A weak dependence of the orientation angle anomaly on the frequency near the terminator was found. The latter is evidence for the dominant contribution of the Alfvén waves to low-latitude and equatorial oscillations.

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