Showing papers on "Dipole model of the Earth's magnetic field published in 1985"
TL;DR: In this article, the authors measured the electric field at both high and low altitude and found that the large-scale electric field is the same at both altitudes, as expected, but small-scale features with wavelengths less than 100 km which are larger in magnitude at higher altitude.
Abstract: Nearly simultaneous measurements of auroral zone electric fields are obtained by the Dynamics Explorer spacecraft at altitudes below 900 km and above 4,500 km during magnetic conjunctions. The measured electric fields are usually perpendicular to the magnetic field lines. The north-south meridional electric fields are projected to a common altitude by a mapping function which accounts for the convergence of the magnetic field lines. When plotted as a function of invariant latitude, graphs of the projected electric fields measured by both DE-1 and DE-2 show that the large-scale electric field is the same at both altitudes, as expected. Superimposed on the large-scale fields, however, are small-scale features with wavelengths less than 100 km which are larger in magnitude at the higher altitude. Fourier transforms of the electric fields show that the magnitudes depend on wavelength. Outside of the auroral zone the electric field spectrums are nearly identical. But within the auroral zone the high and low altitude electric fields have a ratio which increases with the reciprocal of the wavelength. The small-scale electric field variations are associated with field-aligned currents. These currents are measured with both a plasma instrument and magnetometer on DE-1.
199 citations
TL;DR: In this paper, the evolution of the radial component of the solar photospheric magnetic field during 1976-1984 has been simulated with a spatial resolution of about 34,000 km, and the corresponding evolution of its absolute value averaged over the visible disk is derived.
Abstract: Regarding new bipolar magnetic regions as sources of flux, the evolution of the radial component of the solar photospheric magnetic field during 1976-1984 has been simulated with a spatial resolution of about 34,000 km, and the corresponding evolution of its absolute value averaged over the visible disk is derived. For nominal values of the transport parameters, this simulated gross field is in close, though imperfect, agreement with the observed gross field and its associated indices of solar activity. By analyzing the response of the simulated gross field to variations in the transport parameters and the source properties, it is found that the simulated field originates in newly erupted bipolar regions. The lifetimes of these regions are almost always less than three mo. Consequently, the strength of the simulated gross field is a measure of the current level of solar activity, and any recurrent patterns with lifetimes in excess of six mo must reflect the continuing eruption of new flux at 'active longitudes' rather than the persistence of old flux in long-lived magnetic structures.
110 citations
TL;DR: In this article, an addition of the uniform interplanetary magnetic field and the earth's dipole magnetic field was used to evaluate electric field convection patterns over the polar caps that result from solar wind flow across open geomagnetic field lines.
Abstract: An addition of the uniform interplanetary magnetic field and the earth's dipole magnetic field is used to evaluate electric field convection patterns over the polar caps that result from solar wind flow across open geomagnetic field lines. The model also accounts for field-aligned patterns within, and auroral arcs across, the polar cap. The qualitative predictions derived from the model express the electric field magnitudes, aurora intensity, sunward and antisunward flow, and the dusk-side reversal of the convection field in terms of the x and y components of the interplanetary magnetic field.
97 citations
94 citations
TL;DR: In this paper, the development of currents within an arbitrary distribution of particles trapped in the geomagnetic field is described, these currents combine to form the earth's ring current and thus are responsible for the worldwide depressions of surface magnetic field strength during periods of magnetic activity known as magnetic storms.
Abstract: The development of currents within an arbitrary distribution of particles trapped in the geomagnetic field is described These currents combine to form the earth's ring current and thus are responsible for the worldwide depressions of surface magnetic field strength during periods of magnetic activity known as magnetic storms Following a brief review of trapped particle motion in magnetic fields, ring current development is described and presented in terms of basic field and particle distribution parameters Experimental observations then are presented and discussed within the theoretical framework developed earlier New results are presented which, in the area of composition and charge state observations, hold high promise in solving many long standing ring current problems Finally, available experimental results will be used to assess our present understanding as to ring current sources, generation, and dissipation
60 citations
TL;DR: In this paper, a model of the three-dimensional magnetic field structure around the ionosphere of the night side of the planet Venus is presented. And the results indicate that the magnetosheath plasma flow in the wake region plays an important role in forming the ionospheric holes through deformation of the ionopause.
Abstract: Magnetic field structures are analyzed for both the ionospheric hole region and the magnetosheath/ionosphere interaction region of the nightside of Venus, in search of possible coupling between these two regimes. A magnetic coordinate system based on the directions of the solar wind and the interplanetary magnetic field is found to order the data reasonably well, allowing consistent superposition of observational data from individual passes of the Pioneer Venus orbiter. The results indicate that the magnetosheath plasma flow in the wake region plays an important role in forming the ionospheric holes through deformation of the nightside ionopause. The results are combined in a model of the three-dimensional magnetic field structure around the ionosphere of Venus.
59 citations
TL;DR: In this paper, a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology, and the equilibrium of a thin magnetic flux tube with small twist per unit length is calculated.
Abstract: The magnetic field of the solar corona evolves quasistatically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. We show that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, we calculate the equilibrium of a thin magnetic flux tube with small twist per unit length.
44 citations
TL;DR: In this paper, the authors derived satellite magnetic anomaly charts from the measurements by subtracting a global field model regarded as representative of the core field, after removal of the external field effects, and found that the omitted crustal field part is of the same order of magnitude as the rest of the field.
Abstract: Satellite magnetic anomaly charts are derived from the measurements by subtracting a global field model regarded as representative of the core field, after removal of the external field effects. The field model comprises all spherical harmonic terms of the internal field up to a certain degree n, say n = 13. Hence the large-scale constituents of the crustal field are also removed from the anomaly charts. The calculated magnetic field of a global magnetization model of the earth's crust gives an estimate of the lacking lower-order crustal terms. It turns out that the omitted crustal field part is of the same order of magnitude as the rest of the field. The geographic distribution of the omitted model field part on a continental scale is closely correlated with the depth of the Moho. By analogy, the same conclusion is drawn with respect to the actual crustal field. This result accounts for the fact that in the satellite charts the continental margins are not very well reflected. Considerable corrections are therefore required if the anomaly charts are intended to display the whole crustal field.
39 citations
TL;DR: In this paper, a transport equation which describes the evolution of the large-scale magnetic field of the sun was solved numerically and data derived from solar magnetic observations were used to initialize the computations and to account for the emergence of new magnetic flux during the sunspot cycle.
Abstract: A transport equation which describes the evolution of the large-scale magnetic field of the sun was solved numerically Data derived from solar magnetic observations are used to initialize the computations and to account for the emergence of new magnetic flux during the sunspot cycle The objective is to assess the ability of the model to reproduce the observed evolution of the field patterns Recent results from simulations of individual active regions over a few solar rotations and of the magnetic field of the sun over sunspot cycle 21 are discussed
37 citations
TL;DR: In this paper, the magneto-Boussinesq equations are used to perform a linear stability analysis of a static plane layer and several new instability mechanisms are revealed showing previous ideas concerning magnetic buoyancy instabilities to be over simplified.
Abstract: Recent calculations suggest that the bulk of the solar magnetic field may be stored in a thin convectively stable region situated between the convection zone proper and the radiative zone. Determining the stability properties of such a field is therefore important with implications for both the generation and escape of magnetic flux. The magneto-Boussinesq equations are used to perform a linear stability analysis of a static plane layer. Several new instability mechanisms are revealed showing previous ideas concerning magnetic buoyancy instabilities to be over simplified. The most important result is that instability may occur even for fields which increase with height. Detailed results are presented for 2 and 3 dimensional motions for a weakly stratified magnetic field together with a simple calculation for the 2 dimensional instability of a strongly varying field.
36 citations
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TL;DR: In this paper, the basic features of the solar activity mechanism are explained in terms of the dynamo theory of mean magnetic fields, and the field generation sources are the differential rotation and the mean helicity of turbulent motions in the convective zone.
Abstract: The basic features of the solar activity mechanism are explained in terms of the dynamo theory of mean magnetic fields. The field generation sources are the differential rotation and the mean helicity of turbulent motions in the convective zone. A nonlinear effect of the magnetic field upon the mean helicity results in stabilizing the amplitude of the 22-year oscillations and forming a basic limiting cycle. When two magnetic modes (with dipole and quadrupole symmetry) are excited nonlinear beats appear, which may be related to the secular cycle modulation.
TL;DR: The relationship between solar magnetic fields and the transient variations of the interplanetary magnetic field (IMF) at 1 AU, flares from unusual north-south oriented active regions, large IMF B(Z) events, and large flares with comprehensive flare index higher than 12 were collected in this article.
Abstract: In order to study the relationship between solar magnetic fields and the transient variations of the north-south component B(Z) of the interplanetary magnetic field (IMF) at 1 AU, flares from unusual north-south oriented active regions, large IMF B(Z) events, and large flares with comprehensive flare index higher than 12 were collected. The associated IMF B(Z) changes or the magnetic field of the initiating flares are investigated. For those cases where an association between a transient B(Z) variation and an initiating flare is plausible, it is found that, for a given flare field, the orientation of the corresponding transient variation of B(Z) may be in agreement with the flare field, opposite to it, or more often, fluctuating in both magnitude and direction. Conversely, an IMF B(Z) event may originate in a flare field in the same magnetic orientation, opposite to it, or in the east-west orientation.
TL;DR: Sondrestrom radar observations reveal that the dawn-dusk (By) component of the interplanetary magnetic field (IMF) strongly influences the nightside polar convection.
Abstract: Sondrestrom radar observations reveal that the dawn-dusk (By) component of the interplanetary magnetic field (IMF) strongly influences the nightside polar convection. This effect is quite complex. The convection for one orientation of By is not the mirror image of the other orientation. A positive By (i.e., pointing toward dusk) seems to organize the velocities such that, at all local times, they are predominantly westward within the radar field-of-view (approximately 68 deg-to-82 deg invariant latitude). Between dusk and midnight, on one such occasion, sunward flow is observed within the polar cap. In the midnight and dawn sectors, when By is negative, the plasma velocities often appear shifted toward early hours such that large southward velocities are observed about 3 hours before midnight. These are the only times when the predominant velocity component is southward.
TL;DR: In this article, the authors investigate plasma flow in the vicinity of the model magnetosphere, especially in the tail region Luminous thermal plasma is injected by means of a newly designed plasma emitter called the powered double probe (PDP) and time exposure photographs show luminosity along the magnetic field lines which cross the position of the PDP.
Abstract: Using laboratory simulation experiments, we investigate plasma flow in the vicinity of the model magnetosphere, especially in the tail region Luminous thermal plasma is injected by means of a newly designed plasma emitter called the powered double probe (PDP) Time exposure photographs show luminosity along the magnetic field lines which cross the position of the PDP The results obtained from different positions of the PDP show four regions of illumination The dependence of the illumination width of such artificial plasma on the PDP positions yields information on energetic particles and their diamagnetic effect Artificial plasma injection illuminates trajectories of energetic particles produced in the nightside magnetosphere In particular, when the PDP is located in the tail at a geocentric distance corresponding to about 15 to 18 RE, an especially bright luminous line was found to form It is suggested that this phenomenon results from plasma intrusion into the magnetosphere through the dayside cusp region In order to examine the effect of the intrusion of the interplanetary magnetic field (IMF) into the magnetosphere, an external quasi-static magnetic field is applied that simulates the IMF The result reveals the structural form of magnetic field lines which indicate characteristics of a stable “open” magnetosphere In the presence of southward IMF, a neutral line was formed at about the location where the linear sum of the external vaccum magnetic field (IMF) and the distorted dipole field BM (without BZ) becomes null This result seems to imply a direct IMF control of energy coupling between the solar wind and the magnetosphere
TL;DR: In this paper, the authors compared data recorded by Defense Meteorological Satellite Program, Tiros and P-78-1 satellites for the CDAW 6 event on March 22, 1979, have been compared with a statistical model of precipitating electron fluxes.
Abstract: Data recorded by Defense Meteorological Satellite Program, Tiros and P-78-1 satellites for the CDAW 6 event on March 22, 1979, have been compared with a statistical model of precipitating electron fluxes. Comparisons have been made on both an orbit-by-orbit basis and on a global basis by sorting and binning the data by AE index, invariant latitude, and magnetic local time in a manner similar to which the model was generated. It is concluded that the model flux agrees with the data to within a factor of two, although small features and the exact locations of features are not consistently reproduced. In addition, the latitude of highest electron precipitation usually occurs about 3 deg more poleward in the model than in the data. This discrepancy is attributed to ring current inflation of the storm time magnetosphere.
TL;DR: In this paper, the advantages of the approximation of the Earth's magnetic field by means of the field of the so-called natural magnetic sources are discussed, and a new theory about the Earth evolution is proposed.
TL;DR: In this article, a study of the dependence of the interplanetary magnetic field structure on the distribution and evolutionary properties of solar magnetic fields has been made by direct comparison of a sequence of synoptic charts of the photospheric magnetic field with the interplane magnetic field, and by applying the method of correlation analysis.
Abstract: For the period 1969–1975, a study has been made of the dependence of the interplanetary magnetic field structure on the distribution and evolutionary properties of solar magnetic fields. By direct comparison of a sequence of synoptic charts of the photospheric magnetic field with the interplanetary magnetic field, and by applying the method of correlation analysis, it is shown that to areas with an unstable polarity of the interplanetary magnetic field there correspond regions with a complicated inverse polarity line that forms either narrow gulfs and islands against a background of the dominant polarity, or bipolar magnetic regions and their clusters. At the time of reconstruction of the photospheric magnetic field the correlation between the photospheric and interplanetary magnetic field element distributions worsens. An asymmetry of the correlation between the interplanetary and photospheric magnetic field structures of different hemispheres is found. During the period of study, the interplanetary field structure shows a better correlation with the distribution of the photospheric magnetic field at middle and lower latitudes (0°–40°) of the southern hemisphere.
TL;DR: To validate the program for locating the dipole, theoretical calculations and computer programs related to the total magnetic field vector resulting from a hypothetical current source within a homogeneous sphere were generated and the errors in calculations of the current dipole depth and strength are presented.
01 Aug 1985
TL;DR: In this paper, a survey of low energy proton bidirectional anisotropies measured on ISEE-3 in the interplanetary medium between August 1978 and May 1982, together with magnetic field data from the same spacecraft are presented.
Abstract: It is known that the interplanetary medium in the period approaching solar maximum is characterized by an enhancement in the occurrence of transient solar wind streams and shocks and that such systems are often associated with looplike magnetic structures or clouds. There is observational evidence that bidirectional, field aligned flows of low energy particles could be a signature of such looplike structures, although detailed models for the magnetic field configuration and injection mechanisms do not exist at the current time. Preliminary results of a survey of low energy proton bidirectional anisotropies measured on ISEE-3 in the interplanetary medium between August 1978 and May 1982, together with magnetic field data from the same spacecraft are presented.
TL;DR: In this paper, the main parameters of a flare stream-its velocity, magnetic field intensity, plasma density, and temperature -depend on the mutual orientation of magnetic fields in the main body of the stream and within its compressed solar wind region.
Abstract: The main parameters of a flare stream-its velocity, magnetic field intensity, plasma density, and temperature - are shown to depend on the mutual orientation of magnetic fields in the main body of the stream and within its compressed solar wind region. In particular, the plasma velocity and frozen-in magnetic-field intensity within the main body of the stream, as well as the plasma density and temperature, and the magnetic field intensity within the compressed solar wind region, are maximum when the magnetic fields in the two regions are antiparallel to each other, and minimum when the fields are parallel.
TL;DR: In this paper, a non-constant shearing magnetic field is introduced into the magnetohydrostatic equations, and it is found that a critical amount of shearing is needed for a magnetic island to form and then break out to form an open magnetic configuration in which resistive tearing-mode instability may occur, and may initiate a two-ribbon flare.
Abstract: With the assumption that the magnetic field lines are radial at some quite high level in the solar corona, a non-constant shearing magnetic field is introduced into the magnetohydrostatic equations. It is found that a same critical amount of shearing a magnetic island is formed and then breaks out to form an open magnetic configuration in which resistive tearing-mode instability may occur, and may initiate a two-ribbon flare. In addition, high shearing magnetic fields are investigated. It is shown that high shearing magnetic configurations are weak two-dimensional neutral sheets, the instability of which has been studied by Janicke (1982).
01 Aug 1985
TL;DR: In this article, a method to determine the directional differential intensity (d.d.i.), expressed in terms of spherical harmonics, from sectored particle data, concurrent interplanetary magnetic field (IMF) and solar wind velocity is presented.
Abstract: A method to determine the directional differential intensity (d.d.i.), expressed in terms of spherical harmonics, from sectored particle data, concurrent interplanetary magnetic field (IMF) and solar wind velocity is presented.
01 Oct 1985
TL;DR: In this article, the response of heliospheric quantities to the solar phenomena is discussed from a statistical point of view, and the magnetic parameters defined by some combinations of the heliosperic quantities including magnetic field intensity are the physical characteristics that measure, distinguish or identify the influence of various solar phenomena on the heliosphere.
Abstract: The response of heliospheric quantities to the solar phenomena is discussed in this paper from a statistical point of view. An important result obtained is that the magnetic parameters defined by some combinations of the heliosperic quantities including magnetic field intensity are the physical characteristics that measure, distinguish or identify the influence of various solar phenomena on the heliospherie. Among these magnetic parameters the ratio of the magnetic to thermal pressure μ_p is one of the heliospheric characteristics that measures the influence of sunspot activity, distinguishes especially the influence exerted by the major flare activity, but also identifies the predecessor in the ascending and maximum phases for the region with a stable high-speed stream from cornal hole in the post-maximum phases. The magnetic sonic speed C_(as) possesses a considerably stable helio-longitudinal distribution in all the phases of the solar cycle, which implies a common feature for the region with a magnetically strong stream in the ascending and maximum phases and the region with a stable high-speed stream in the post-maximum phases. The other magnetic parameters such as the Alfven wave speed C_a as well as the ratios of the magnetic and total pressure to the kinetic energy density μk and Π_k~* respectively, reflect also the above features to a certain extent.
TL;DR: In this article, the upper critical field Hc2 of the series PbxLa1-xMo6Se8 was measured in high magnetic fields up to 35 T. The temperature dependence of Hc 2 was found to be explained by the term of orbital critical field.
Abstract: The upper critical field Hc2 of the series PbxLa1-xMo6Se8 was measured in high magnetic fields up to 35 T. The temperature dependence of Hc2 was found to be explained by the term of orbital critical field.
01 Jan 1985
TL;DR: In this paper, a selected region of the quiet Sun near the center of the disc was analyzed in order to deduce parameters concerning regions of highly concentrated magnetic field, including network elements.
Abstract: A selected region of the quiet Sun near the center of the disc was analyzed in order to deduce parameters concerning regions of highly concentrated magnetic field, including network elements. The present analysis covers a sequence of spectra corresponding to a total time laps of 6 min over the same region. Spectra of both magnetically sensitive and insensitive lines were measured in detail in order to deduce the velocity distribution around magnetic flux tubes. Large amplitude five minute oscillatory components were removed using an averaging over time procedure. Preliminary results are discussed as well as factors which could affect their interpretation.