Showing papers on "Dipole model of the Earth's magnetic field published in 1994"

The magnetic field of solar prominences

Abstract: A model is presented which accounts for the formation of coronal magnetic field lines with the appropriate 'dipped' structure to support prominences. The critical ingredients of the model are that the prominence magnetic field is a truly three-dimensional structure with significant variation along the prominence length, and the magnetic field is strongly sheared near the photospheric neutral line. Numerical calculations are presented which demonstrate that these two features lead to dip formation. In addition our model is able to account for the long-puzzling observation of inverse polarity in quiescent prominences.

Properties of the fluctuating magnetic helicity in the inertial and dissipation ranges of solar wind turbulence

Abstract: We investigated the inertial and dissipation ranges of the reduced magnetic helicity spectrum of solar wind fluctuations and have found that this spectrum appears insensitive to solar cycle variations and changes in solar wind flow parameters. In the inertial range of the spectrum, the reduced helicity is large but random and independent of heliocentric distance between 0.3 and 10 AU. At small scales, in the dissipation range of the spectrum, a correlation appears to exist between the average value of the normalized reduced magnetic helicity and the polarity of magnetic sectors, suggesting that these fluctuations, if outward propagating, are predominantly right-hand polarized. In the inertial range the statistical properties of the normalized magnetic helicity are well approximated by a simple model of the magnetic field in which the total magnetic field vector randomly walks with only small variations in magnitude. The behavior of the inertial range spectrum is very similar to that seen in three- and two-and-a-half-dimensional simulations of the incompressible and compressible equations describing magnetohydrodynamic turbulence, consistent with the paradigm that the solar wind is a turbulent magnetofluid.

A coronal magnetic field model with horizontal volume and sheet currents

Abstract: When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside the source surface or by limiting the interaction to thin current sheets between oppositely directed field regions. Yet observations and numerical Magnetohydrodynamic (MHD) calculations suggest the presence of non-force-free volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the magnetostatic equilibria developed by Bogdan and Low and the current-sheet modeling technique developed by Schatten. The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coro nal helmet structures better than the current-sheet model.

Empirical modeling of the quiet time nightside magnetosphere

Abstract: Empirical modeling of plasma pressure and magnetic field for the quiet time nightside magnetosphere is investigated. Two models are constructed for this study. One model, referred to here as T89R, is basically the magnetic field model of Tsyganenko (1989) but is modified by the addition of an inner eastward ring current at a radial distance of approximately 3 RE as suggested by observation. The other is a combination of the T89R model and the long version of the magnetic field model of Tsyganenko (1987) such that the former dominates the magnetic field in the inner magnetosphere while the latter prevails in the distant tail. The distribution of plasma pressure which is required to balance the magnetic force for each of these two field models is computed along the tail axis in the midnight meridian. The occurrence of pressure anisotropy in the inner magnetospheric region is also taken into account by determining an empirical fit to the observed plasma pressure anisotropy. This represents the first effort to obtain the plasma pressure distribution in force equilibrium with magnetic stresses from an empirical field model with the inclusion of pressure anisotropy. The inclusion of pressure anisotropy alters the plasma pressure by as much as a factor of approximately 3 in the inner magnetosphere. The deduced plasma pressure profile along the tail axis is found to be in good agreement with the observed quiet time plasma pressure for geocentric distances between approximately 2 and approximately 35 RE.

NASA/National Space Science Data Center trapped radiation models

Abstract: The National Space Science Data Center (NSSDC) trapped radiation models calculate the integral and differential electron and proton flux for given values of particle energy E, drift shell parameter L, and magnetic field strength normalized to the equatorial/minimum value on the field line B/BQ for either solar maximum or solar minimum conditions. The most recent versions of the series of models, which have been developed and continuously improved over several decades by Vette and co-workers at NSSDC, are AE-8 for electrons and AP-8 for protons. The paper provides a brief history of the modeling efforts at NSSDC and discusses some of the problems encountered when applying the models at low altitudes. Recommendations are made and discussed about the correct use of the trapped particle models in conjunction with geomagnetic field models. Specifically, the importance of using the correct dipole moment and the correct #0 value (i.e., obtained by field line tracing) is illustrated.

Multiple, discrete arcs on sunward convecting field lines in the 14‐15 MLT region

Abstract: Ionospheric plasma flow measurements and simultaneous observations of thin (∼0.2° invariant latitude (ILAT)), multiple, longitudinally extended auroral arcs of transient nature within 74°-76° ILAT and 1030-1130 UT (∼14-15 MLT) on January 12, 1989, are reported. The auroral structures appeared within the luminous belt of strong 630.0-nm emissions located predominantly on sunward convecting field lines equatorward of the convection reversal boundary as identified by the European Incoherent Scatter UHF radar. The events occurred during a period of several hours quasi-steady solar wind speed (∼ 700 km s−1) and a radially orientated interplanetary magnetic field (IMF) with a weak northward tilt (IMF Bz>0). These typical dayside auroral features are related to previous studies of auroral activity related to the upward region 1 current in the postnoon sector. The discrete auroral events presented here may result from magnetosheath plasma injections into the low-latitude boundary layer (LLBL) and an associated dynamo mechanism. An alternative explanation invokes kinetic Alfven waves, triggered either by Kelvin-Helmholtz instability at the inner (or outer) edge of the LLBL or by pressure pulse induced magnetopause surface waves.

Empirical models of the magnetospheric magnetic field

Abstract: A general overview of magnetospheric modeling is given, along with a more detailed discussion of several empirical models which are widely used. These models are composed of representations of the Earth's main internal field (basically a bipolar field), plus external field contributions due to ring currents (carried by the particles in the Van Allen radiation belts), magnetopause currents (the boundary surface between the Earth's magnetic field and interplanetary magnetic field carried by the solar wind), and tail currents (carried by particles in the neutral sheet of the magnetotail). The empirical models presented here are the Mead-Fairfield, Olsen-Pfitzer tilt-dependent (1977), Tsyganenko-Usamo, Tsyganenko (1987), Olsen-Pfitzer dynamic (1988), Tsyganenko (1989), and Hilmer-Voight models. The derivations, agreement with quiet time and storm time data from the two satellite programs, Spacecraft Charging at High Altitudes (SCATHA) and Combined Release Radiation Effects Satellite (CRRES), and computational requirements of these models are compared.

Magnetic field evolution with Hall drift in neutron stars

Abstract: The role of the Hall current in plasma physics is studied in a model of neutron star magnetic fields. We calculate the evolution of the neutron star magnetic field with and without the Hall current effect. In our model, it is assumed that the magnetic field is confined to the crust and that the field dissipates through ohmic decay. The decay rates are expected to increase with the multipole moments if there is no Hall current and the dipole field is likely to survive. The presence of the Hall current causes coupling among the different modes, and the energy is transferred among them. We find that the dipole magnetic field does not always survive, and the decay features depend on the configuration of the fields

A study of quasi-periodic ELF-VLF emissions at three Antarctic stations: evidence for off-equatorial generation?

Abstract: The spatial extent and temporal behaviour of quasi-periodic (QP) intensity modulations of 0.5-2 kHz ELF-VLF signals were investigated in a comparative study of data collected at the Antarctic stations of South Pole (L=14), Halley (L=4), and Siple (L=4). Frequently, the waveforms of ELF-VLF signals simultaneously received at each site were identical. Although of similar frequency structure, the waveforms of the accompanying Pc3 magnetic pulsations did not show a one-to-one association. Whereas both are dayside phenomena, QP emissions occur over a smaller range of local times, and have a maximum of occurrence later in the day closer to local noon. QP emissions are identified with the periodic modulation of the electron pitch-angle distribution by the propagation of ULF compressional fast-mode waves through a region. However, contrary to previous ideas, rising-tone emissions do not represent the frequency-time signatures of such waves. In addition to generation close to the equatorial plane, we propose an additional high-latitude source of QP emissions. These emissions are associated with regions of minimum B produced by the dayside compression of the magnetosphere close to the magnetopause. Model magnetic field calculations of these minimum-B regions as a function of magnetic local time and invariant latitude are presented.

High-resolution observations of the polar magnetic fields of the sun

Abstract: High-resolution magnetograms of the solar polar region were used for the study of the polar magnetic field. In contrast to low-resolution magnetograph observations which measure the polar magnetic field averaged over a large area, we focused our efforts on the properties of the small magnetic elements in the polar region. Evolution of the filling factor - the ratio of the area occupied by the magnetic elements to the total area - of these magnetic elements, as well as the average magnetic field strength, were studied during the maximum and declining phase of solar cycle 22, from early 1991 to mid-1993. We found that during the sunspot maximum period, the polar regions were occupied by about equal numbers of positive and negative magnetic elements, with equal average field strength. As the solar cycle progresses toward sunspot minimum, the magnetic field elements in the polar region become predominantly of one polarity. The average magnetic field of the dominant polarity elements also increases with the filling factor. In the meanwhile, both the filling factor and the average field strength of the non-dominant polarity elements decrease. The combined effects of the changing filling factors and average field strength produce the observed evolution of the integrated polar flux over the solar cycle. We compared the evolutionary histories of both filling factor and average field strength, for regions of high (70°–80°) and low (60°–70°) latitudes. For the south pole, we found no significant evidence of difference in the time of reversal. However, the low-latitude region of the north pole did reverse polarity much earlier than the high-latitude region. It later showed an oscillatory behavior. We suggest this may be caused by the poleward migration of flux from a large active region in 1989 with highly imbalanced flux.

Solar wind electrons as tracers of the Martian magnetotail topology

Abstract: Simultaneous measurements of electrons and magnetic field are used to study the topology of the Martian magnetosphere Halo solar wind electrons streaming along magnetic field lines replicate variations of the Bx component, thus tracing the interplanetary magnetic field draping in most parts of the Martian tail This suggests that the magnetic field observed near the equatorial plane of Mars is mainly induced However, there are regions where this perfect tracing is violated This could be considered as evidence for an intrinsic planetary field An alternative interpretation involves the relationship between these regions and ionospheric holes

Convective motions in the Earth's fluid core

Abstract: Convection in the Earth's core is affected by Lorentz and Coriolis forces. The relative importance of these is measured by the Elsasser number Λ. Previous work suggested that the optimum condition for convection occurs when the Elsasser number Λ is O(1); in particular, the critical modified Rayleigh number R* had a minimum value at some O(1) value of Λ. This gave rise to the view that the size of the magnetic field generated by the dynamo would adjust to this Λ-value because it optimised the convection. We have investigated convection in a rotating spherical shell with magnetic field distributions satisfying appropriate boundary conditions in the form of the toroidal decay modes which we believe are more realistic for the Earth's core. Our results are rather different from the classical picture. We find no optimum Elsasser number that minimises R*, but instead a monotonic decay of R* as Λ increases. At Λ ∼ 10, R* goes negative, so that rolls are driven by magnetic instability rather than convection. Naturally, as this regime is entered the rolls must be destroying magnetic field rather than creating it by dynamo action. This suggests that in the Earth's fluid outer core, the field strength is such that 1 < Λ < 10, so that the magnetic field is stable and the corresponding convection is dominated by large scales and is efficient. Another important feature of these solutions is that the azimuthal flow is primarily two-dimensional. This is surprising, as it has generally been believed that a magnetic field of this strength would break the Taylor-Proudman constraint. However, it appears that the magnetic field adjusts to preserve two-dimensionality even in the range 1 < Λ < 20.

Theoretical study of onset conditions for solar eruptive processes: Influence of the boundaries

Abstract: We investigate the influence of the finite extent of the computational domain and of specific boundary conditions on a theoretical model for solar eruptive processes originally proposed by Zwingmann (1987). In this model, the slow pre-onset time evolution of arcade-like solar coronal magnetic field structures is described by quasi-static equilibrium sequences. The magnetic field is represented by Euler potentials which allow for a realistic description of the photospheric boundary conditions, because the pressure and the magnetic footpoint displacement can be prescribed separately. We use an improved numerical method suitable for computing equilibrium sequences, allowing for larger domains and higher resolution than used in the previous work. With this method, we are able to show that, in contradiction to a supposition made by Zwingmann (1987), the results of the computations do strongly depend on the size of the computing domain. This has consequences for a possible physical interpretation of the model. We furthermore show that with the boundary conditions used in this model a shearing motion of the magnetic footpoints inevitably leads to the formation of singular current layers at the separatrix between field lines cutting the upper boundary (open field lines) and field lines which are only connected with the photosphere (closed field lines).

Alfvénic disturbances in the equatorial solar wind with a spiral magnetic field

Abstract: We study a two-dimensional propagation of Alfvenic perturbations within the solar equatorial plane (SEP) in the solar wind with a spiral magnetic field. Analytical solutions within the entire frequency range are derived at large radial distance r. Numerical solutions which smoothly pass through the Alfven critical point rA are also obtained. Since the spiral magnetic field caused by the solar rotation scales as ∼r−1 at large r, the velocity and magnetic field perturbations, which are perpendicular to the SEP, remain small relative to the wind parameters in the entire radial range. The frequency criterion for the non-WKB radial scalings of the perturbation variables to appear is (f + mf⊙)² < fc², where f is the perturbation frequency, f⊙ is the solar rotation frequency, m is the azimuthal wavenumber, and fc is the well-known characteristic frequency determined by the wind parameters. We demonstrate that the process of continuous reflection in a spiral magnetic field and the effect of superposing Alfvenic perturbations with various f and m can lead to variations of the relative magnetic field fluctuation, the normalized cross helicity σc, the Alfven ratio ra, the magnetic perturbation energy density Eb, and the kinetic perturbation energy density Eυ, which differ from the predictions of the conventional WKB theory. In particular, the non-WKB radial scalings of the perturbation variables can appear at any timescales with appropriate values of m. The relevance of these results to data analyses on interplanetary fluctuations is discussed, and we emphasize the importance of obtaining fluctuation spectrum with respect to both f and m in the outer heliosphere.

Induced magnetosphere of comet Halley: 2. Magnetic field and electric currents

Abstract: An induced magnetosphere of a comet rotates around the Sun-comet line along with the interplanetary magnetic field (IMF) vector. During the Giotto flyby near comet Halley the direction of the IMF changed several times. For this reason, the trajectory of the Giotto spacecraft, being represented in the IMF-related coordinate system, covered rather well the transverse cross section of the comet Halley magnetosphere. As a result, two-dimensional distributions of both the magnetic field and electric current density have been calculated in the transverse cross section of the induced magnetosphere of comet Halley. The distributions reveal the following facts. The magnetic barrier is axially symmetric (within the accuracy of the grid ∼ 10³ km). Such a behavior is associated with the fact that the magnetic field strength in the barrier is governed by the dynamic pressure of the solar wind and does not depend on the ion-neutral friction (which affects only the location of the magnetic field maximum). Along with draping about the dayside of a comet, magnetic field lines also drape about its flanks (where the magnetic field turns out to be enhanced). As a result, the Lorentz electric field inside the cometary ionosphere decreases. Lines of the electric current drape about the cometary ionosphere in a manner resembling the magnetic field lines. The region of the magnetic barrier in front of the contact surface is shown to be an electric load for the MHD generator arising as a result of the solar wind interaction with a comet.

Dynamics and spatial boundaries of retardation of the plasma cloud of an explosion in a dipole magnetic field

Abstract: In the framework of the ideal MHD approximation, we shall discuss the dynamics of a 3-D expansion of a spherical cloud of rarefied plasma into a vacuum in the presence of a nonuniform external magnetic field of dipole structure. When the plasma expands rapidly, for example, as a result of the energy released by the explosion, at the stage of an expansion that is nearly radial, an effective retardation of the boundaries of the cloud takes place as a result of the interaction of induced surface currents with the magnetic field. It is necessary to find the configuration and location of the plasma front as a function of time, and also to determine the limits of its propagation, which are caused by the retardation effect. Interest in this problem is primarily due to the study of nonstationary processes of an explosive nature in the cosmic plasma [1], in particular, to the analysis of the global instability of the earth's magnetosphere in estimates of the effectiveness of explosive methods of its protection from collisions with asteroids and comets [2, 3]. The problem was studied in a similar formulation only in the simplest case, i.e., in a uniform external field [4]. The case with a dipole field was examined in [5] for comparatively low explosion energies and correspondingly small deviations of the shape of the plasma formation from a sphere. In [6], we estimated the size and configuration of the retardation region in the field of a point dipole. On the whole, the problem has been little-studied because of the absence of the necessary 3-D nonstationary numerical models owing to the complexity of creating them. The proposed study is based on some simple relationships for generalized characteristics of motion - energy and pressure - and does not allow for the role of magnetic diffusion, which makes it possible to find the basic principles of the 3-D dynamics of retardation with a minimum number of initial parameters. The calculation model is compared with the results of an experiment on the expansion of laser plasma clouds in a dipole field on a KI-1 stand [7]. This approach is aimed at estimating the possibilities of the hydrodynamic method and obtaining preliminary data necessary for constructing more rigorous models. 1. Analysis of the Retardation Model. As in [4], which discussed the problem of expansion of a superconducting sphere in a uniform external magnetic field, it can readily be shown that the work of ponderomotive forces A on particles of an ideally conducting plasma cloud of changing shape during its expansion time t in a field of arbitrary configuration is equal to the work of forces of magnetic pressure Bs2/87r on its surface S, written in the form t

Plasma pressure and anisotropy inferred from the Tsyganenkomagnetic field model

Abstract: A numerical procedure has been developed to deduce the plasma pressure and anisotropy from the Tsyganenko magnetic field model. The Tsyganenko empirical field model, which is based on vast satellite field data, provides a realistic description of magnetic field configuration in the magnetosphere. When the force balance under the static condition is assumed, the electromagnetic J×B force from the Tsyganenko field model can be used to infer the plasma pressure and anisotropy distributions consistent with the field model. It is found that the J×B force obtained from the Tsyganenko field model is not curl-free. The curl-free part of the J×B force in an empirical field model can be balanced by the gradient of the isotropic pressure, while the nonzero curl of the J×B force can only be associated with the pressure anisotropy. The plasma pressure and anisotropy in the near-Earth plasma sheet are numerically calculated to obtain a static equilibrium consistent with the Tsyganenko field model both in the noon-midnight meridian and in the equatorial plane. The plasma pressure distribution deduced from the Tsyganenko 1989 field model is highly anisotropic and shows this feature early in the substorm growth phase. The pressure anisotropy parameter P, defined as P=1-P\VertP⊥, is typically \sim0.3 at x\approx-4.5RE and gradually decreases to a small negative value with an increasing tailward distance. The pressure anisotropy from the Tsyganenko 1989 model accounts for 50% of the cross-tail current at maximum and only in a highly localized region near x\sim-10RE. In comparison, the plasma pressure anisotropy inferred from the Tsyganenko 1987 model is much smaller. We also find that the boundary conditions have significant effects on the plasma pressure distributions and have to be considered carefully.

A mechanism of magnetic flux rope formation in the ionosphere of Venus

Abstract: Magnetic field observations in the dayside ionosphere of Venus revealed the existence of magnetic flux ropes. The general properties of these small-scale magnetic field structures can be explained by a theory of magnetic fluctuations excited by random magnetohydrodynamic flows of ionospheric plasma. The local spatial distribution of the magnetic field is random: the field is concentrated inside flux tubes separated by regions with weak fields. A mechanism of amplification of magnetic fluctuations in the presence of zero mean field, proposed by Zeldovich, is applied to the nonlinear theory of flux rope formation by means of a nonlinear equation derived from the induction equation; the nonlinearity is associated with the Hall effect. The equation describes the evolution of the correlation function of the magnetic field and resembles the Schrodinger equation except for a variable mass and the absence of the imaginary unit in the time-derivative term. In the limit of large Reynolds number the formulation is amenable to treatment by a modified WKB method. On the basis of this theory it is possible to explain why flux ropes are not observed if there is a strong regular large-scale magnetic field caused by the lowering of the ionopause. The theory predicts correctly the cross section of the flux ropes in the ionosphere of Venus and the maximum value of the magnetic field inside the flux rope.

The dynamic cusp at low altitudes: a case study utilizing Viking, DMSP-F7, and Sondrestrom incoherent scatter radar observations

Abstract: . Coincident multi-instrument magnetospheric and ionospheric observations have made it possible to determine the position of the ionospheric footprint of the magnetospheric cusp and to monitor its evolution over time. The data used include charged particle and magnetic field measurements from the Earth-orbiting Viking and DMSP-F7 satellites, electric field measurements from Viking, interplanetary magnetic field and plasma data from IMP-8, and Sondrestrom incoherent scatter radar observations of the ionospheric plasma density, temperature, and convection. Viking detected cusp precipitation poleward of 75.5° invariant latitude. The ionospheric response to the observed electron precipitation was simulated using an auroral model. It predicts enhanced plasma density and elevated electron temperature in the upper E- and F-regions. Sondrestrom radar observations are in agreement with the predictions. The radar detected a cusp signature on each of five consecutive antenna elevation scans covering 1.2 h local time. The cusp appeared to be about 2° invariant latitude wide, and its ionospheric footprint shifted equatorward by nearly 2° during this time, possibly influenced by an overall decrease in the IMF Bz component. The radar plasma drift data and the Viking magnetic and electric field data suggest that the cusp was associated with a continuous, rather than a patchy, merging between the IMF and the geomagnetic field.

Balloon observations of nightside Pc 5 quasi-electrostatic waves above the south pole

Abstract: The authors report here a unique Pc 5 band quasi-electrostatic wave event ({approximately}300-s period) observed near local geomagnetic midnight at an invariant latitude of 75{degrees}. The electric field signal was obtained from one of the eight high-latitude balloon payloads launched above the south geographic pole during the South Pole Balloon Champaign in the 1985-86 austral summer. The balloon payloads were instrumented with double-probe electric field detectors and bremsstrahlung X-ray detectors. The electric field data from one flight of particular interest have been compared with ground-based magnetometer and micropulsation data in an attempt to understand the nature of the wave event. The Pc 5 waves were linearly polarized in the electric field, the electric field components had amplitudes of 20 to 30 mV/m, and the event persisted for an interval of more than 3 hours from 0000 to 0330 UT (2030 to 2400 MLT) on December 22, 1985. The magnetic activity was quiet during this time period. Detailed power spectra are presented in the paper. No evidence was found suggesting that the event was produced by an artifact. The event was not associated with atmospheric neutral waves, weather processes, or upward propagating gravity waves. The event was produced in the ionospheremore » by a process other than the convection of irregularities. The authors suggest that ULF magnetosonic waves originating at the magnetopause produced the signals that were observed. 61 refs., 9 figs.« less

Theory of Passive Magnetic Field Transport

Abstract: In recent years, our knowledge of photospheric magnetic fields went through a thorough transformation—nearly unnoticed by dynamo theorists. It is now practically certain that the overwhelming majority of the unsigned magnetic flux crossing the solar surface is in turbulent form (intranetwork and hidden fields). Furthermore, there are now observational indications (supported by theoretical arguments discussed in this paper) that the net polarity imbalance of the turbulent field may give a significant or even dominant contribution to the weak large-scale background magnetic fields outside unipolar network areas. This turbulent magnetic field consists of flux tubes with magnetic fluxes below 1010 Wb (1018 Mx). The motion of these thin tubes is dominated by the drag of the surrounding flows, so the transport of this component of the solar magnetic field must fully be determined by the kinematics of the turbulence (i.e. it is “passive”), and it can be described by a one-fluid model like mean-field theory (MFT). The recent advance in the direct and indirect observation of turbulent fields is therefore of great importance for MFT as these are the first-ever observations on the Sun of a field to which MFT may be applied. However, in order to utilize the observations of turbulent fields and their large-scale patterns as a possible diagnostic of MFT dynamo models, the transport mechanisms linking the surface field to the dynamo layer must be thoroughly understood.

The deformation of flux tubes in the solar wind with applications to the structure of magnetic clouds and CMEs

Abstract: Two dimensional magnetohydrodynamic simulations of the distortion of a magnetic flux tube, accelerated through ambient solar wind plasma, are presented. Vortices form on the trailing edge of the flux tube, and couple strongly to its interior. If the flux tube azimuthal field is weak, it deforms into an elongated banana-like shape after a few Alfven transit times. A significant azimuthal field component inhibits this distortion. In the case of magnetic clouds in the solar wind, it is suggested that the shape observed at 1 AU was determined by distortion of the cloud in the inner heliosphere. Distortion of the cloud beyond 1 AU takes many days. It is estimated that effective drag coefficients slightly greater than unity are appropriate for modeling flux tube propagation. Synthetic magnetic field profiles as would be seen by a spacecraft traversing the cloud are presented.

Magnetic fields of celestial bodies

Abstract: Principles of Measurement of Magnetic Fields of Celestial Bodies Techniques for the Measurement of Magnetic Fields of Celestial Bodies The Magnetic Fields of Sunspots Background and Local Magnetic Fields on the Solar Surface Magnetic Fields of the Solar Atmosphere The General Magnetic Field of the Sun Magnetic Fields of the Solar System Stellar Magnetic Fields Magnetic Fields of Galaxies and Intergalactic Space Some Theoretical Problems of Cosmic Magnetic Fields.

Distinction between the Climatic Effects of the Solar Corpuscular and Electromagnetic Radiation

Abstract: We study the possibilities of the separation of solar electromagnetic and corpuscular impacts on the terrestrial lower atmosphere by examining their characteristic differences. We focus on the behaviour of the solar-meteorological correlation with respect to characteristic magnetic properties. Examples are given that the solar meteorological correlation — the efficiency of the solar impact — depends on the Sun-Earth attitude, the polarity of the solar main dipole field (and IMF) and the type of the geomagnetic events. This can explain the virtual disappearance or reversal of certain solar-meteorological effects.

The determination of interplanetary magnetic field polarities around sector boundaries using E greater than 2 keV electrons

Abstract: The determination of the polarities of interplanetary magnetic fields (whether the field direction is outward from or inward toward the sun) has been based on a comparison of observed field directions with the nominal Parker spiral angle. These polarities can be mapped back to the solar source field polarities. This technique fails when field directions deviate substantially from the Parker angle or when fields are substantially kinked. We introduce a simple new technique to determine the polarities of interplanetary fields using E greater than 2 keV interplanetary electrons which stream along field lines away from the sun. Those electrons usually show distinct unidirectional pitch-angle anisotropies either parallel or anti-parallel to the field. Since the electron flow direction is known to be outward from the sun, the anisotropies parallel to the field indicate outward-pointing, positive-polarity fields, and those anti-parallel indicate inward-pointing, negative-polarity fields. We use data from the UC Berkeley electron experiment on the International Sun Earth Explorer 3 (ISSE-3) spacecraft to compare the field polarities deduced from the electron data, Pe (outward or inward), with the polarities inferred from field directions, Pd, around two sector boundaries in 1979. We show examples of large (greater than 100 deg) changes in azimuthal field direction Phi over short (less than 1 hr) time scales, some with and some without reversals in Pe. The latter cases indicate that such large directional changes can occur in unipolar structures. On the other hand, we found an example of a change in Pe during which the rotation in Phi was less than 30 deg, indicating polarity changes in nearly unidirectional structures. The field directions are poor guides to the polarities in these cases.