Showing papers on "Dipole model of the Earth's magnetic field published in 2016"

The magnetic field vector of the Sun-as-a-star

Abstract: Direct comparison between stellar and solar magnetic maps are hampered by their dramatic differences in resolution. Here, we present a method to filter out the small-scale component of vector fields, in such a way that comparison between solar and stellar (large-scale) magnetic field vector maps can be directly made. Our approach extends the technique widely used to decompose the radial component of the solar magnetic field to the azimuthal and meridional components as well. For that, we self-consistently decompose the three-components of the vector field using spherical harmonics of different $l$ degrees. By retaining the low $l$ degrees in the decomposition, we are able to calculate the large-scale magnetic field vector. Using a synoptic map of the solar vector field at Carrington Rotation CR2109, we derive the solar magnetic field vector at a similar resolution level as that from stellar magnetic images. We demonstrate that the large-scale field of the Sun is not purely radial, as often assumed -- at CR2109, $83\%$ of the magnetic energy is in the radial component, while $10\%$ is in the azimuthal and $7\%$ is in the meridional components. By separating the vector field into poloidal and toroidal components, we show that the solar magnetic energy at CR2109 is mainly ($>90\%$) poloidal. Our description is entirely consistent with the description adopted in several stellar studies. Our formalism can also be used to confront synoptic maps synthesised in numerical simulations of dynamo and magnetic flux transport studies to those derived from stellar observations.

Evolution of the dipole geomagnetic field. Observations and models

Abstract: The works on paleomagnetic observations of the dipole geomagnetic field, its variations, and reversals in the last 3.5 billion years have been reviewed. It was noted that characteristic field variations are related to the evolution of the convection processes in the liquid core due to the effect of magnetic convection and solid core growth. Works on the geochemistry and energy budget of the Earth's core, the effect of the solid core on convection and the generation of the magnetic field, dynamo models are also considered. We con� sider how core growth affects the magnetic dipole generation and variations, as well as the possibility of mag� netic field generation up to the appearance of the solid core. We also pay attention to the fact that not only the magnetic field but also its configuration and time variations, which are caused by the convection evolution in the core on geological timescales, are important factors for the biosphere.

The global distribution of magnetic helicity in the solar corona

Abstract: By defining an appropriate field line helicity, we apply the powerful concept of magnetic helicity to the problem of global magnetic field evolution in the Sun's corona. As an ideal-magnetohydrodynamic invariant, the field line helicity is a meaningful measure of how magnetic helicity is distributed within the coronal volume. It may be interpreted, for each magnetic field line, as a magnetic flux linking with that field line. Using magneto-frictional simulations, we investigate how field line helicity evolves in the non-potential corona as a result of shearing by large-scale motions on the solar surface. On open magnetic field lines, the helicity injected by the Sun is largely output to the solar wind, provided that the coronal relaxation is sufficiently fast. But on closed magnetic field lines, helicity is able to build up. We find that the field line helicity is non-uniformly distributed, and is highly concentrated in twisted magnetic flux ropes. Eruption of these flux ropes is shown to lead to sudden bursts of helicity output, in contrast to the steady flux along the open magnetic field lines.

Modelling the magnetic dipole

Abstract: Three different models of a magnetic dipole, viz., a uniformly magnetised sphere, a circular current loop and a pair of fictitious magnetic charges, have been systematically analysed within the formalism based on the vector potential of the magnetic field. The expressions of the potentials and magnetic fields produced by each dipole model have been obtained. A computer code has been put forward in order to visualise magnetic field lines for different dipole models. It has been shown that the magnetic field outside the uniformly magnetised sphere coincides with that of a point dipole. The other two models give considerably different results at distances small or intermediate in comparison with the dipole size.

An empirical RBF model of the magnetosphere parameterized by interplanetary and ground‐based drivers

Abstract: In a recent paper [Andreeva and Tsyganenko, 2016], a novel method was proposed to model the magnetosphere directly from spacecraft data, with no a priori knowledge nor ad hoc assumptions about the geometry of the magnetic field sources The idea was to split the field into the toroidal and poloidal parts and then expand each part into a weighted sum of radial basis functions (RBF) In the present work we take the next step forward by having developed a full-fledged model of the near magnetosphere, based on a multi-year set of space magnetometer data (1995–2015) and driven by ground-based and interplanetary input parameters The model consolidates the largest ever amount of data and has been found to provide the best ever merit parameters, in terms of both the overall rms residual field and record-high correlation coefficients between the observed and model field components By experimenting with different combinations of input parameters and their time averaging intervals, we found the best so far results to be given by the ram pressure Pd, Sym-H, and N-index by Newell et al [2007] In addition, the IMF By has also been included as a model driver, with a goal to more accurately represent the IMF penetration effects The model faithfully reproduces both externally and internally induced variations in the global distribution of the geomagnetic field and electric currents Stronger solar wind driving results in a deepening of the equatorial field depression and a dramatic increase of its dawn-dusk asymmetry The Earth's dipole tilt causes a consistent deformation of the magnetotail current sheet and a significant north-south asymmetry of the polar cusp depressions on the dayside Next steps to further develop the new approach are also discussed

The influences of solar wind pressure and interplanetary magnetic field on global magnetic field and outer radiation belt electrons

Abstract: Using the Van Allen Probe in situ measured magnetic field and electron data, we examine the solar wind dynamic pressure and interplanetary magnetic field (IMF) effects on global magnetic field and outer radiation belt relativistic electrons (≥1.8 MeV). The dynamic pressure enhancements (>2 nPa) cause the dayside magnetic field increase and the nightside magnetic field reduction, whereas the large southward IMFs (Bz-IMF 4), the pitch angles of relativistic electrons are mainly pancake distributions with a flux peak around 90° (corresponding anisotropic index A > 0.1), and the higher-energy electrons have stronger pancake distributions (the larger A), suggesting that the compression-induced betatron accelerations enhance the dayside pancake distributions. However, in the nighttime decreased magnetic field region (MLT ~ 18:00–06:00, and L ≥ 5), the pitch angles of relativistic electrons become butterfly distributions with two flux peaks around 45° and 135° (A < 0). The spatial range of the nighttime butterfly distributions is almost independent of the relativistic electron energy, but it depends on the magnetic field day-night asymmetry and the interplanetary conditions. Themore » dynamic pressure enhancements can make the nighttime butterfly distribution extend inward. The large southward IMFs can also lead to the azimuthal expansion of the nighttime butterfly distributions. As a result, these variations are consistent with the drift shell splitting and/or magnetopause shadowing effect.« less

A model of Earth’s magnetic field derived from 2 years of Swarm satellite constellation data

Abstract: More than 2 years of magnetic field data taken by the three-satellite constellation mission Swarm are used to derive a model of Earth’s magnetic field and its time variation. This model is called SIFMplus. In addition to the magnetic field observations provided by each of the three Swarm satellites, explicit advantage is taken of the constellation aspect of Swarm by including East–West magnetic intensity and vector field gradient information from the lower satellite pair. Along-track differences of the magnetic intensity as well as of the vector components provide further information concerning the North–South gradient. The SIFMplus model provides a description of the static lithospheric field that is very similar to models determined from CHAMP data, up to at least spherical harmonic degree $$n=75$$ . Also the core field part of SIFMplus, with a quadratic time dependence for $$n \le 6$$ and a linear time dependence for $$n=7$$ –15, demonstrates the possibility to determine high-quality field models from only 2 years of Swarm data, thanks to the unique constellation aspect of Swarm. To account for the magnetic signature caused by ionospheric electric currents at polar latitudes we co-estimate, together with the model of the core, lithospheric and large-scale magnetospheric fields, a magnetic potential that depends on quasi-dipole latitude and magnetic local time.

Precise numerical estimation of the magnetic field generated around recombination

Abstract: We investigate the generation of magnetic fields from nonlinear effects around recombination. As tight-coupling is gradually lost when approaching $z\ensuremath{\simeq}1100$, the velocity difference between photons and baryons starts to increase, leading to an increasing Compton drag of the photons on the electrons. The protons are then forced to follow the electrons due to the electric field created by the charge displacement; the same field, following Maxwell's laws, eventually induces a magnetic field on cosmological scales. Since scalar perturbations do not generate any magnetic field as they are curl-free, one has to resort to second-order perturbation theory to compute the magnetic field generated by this effect. We reinvestigate this problem numerically using the powerful second-order Boltzmann code SONG. We show that: (i) all previous studies do not have a high enough angular resolution to reach a precise and consistent estimation of the magnetic field spectrum; (ii) the magnetic field is generated up to $z\ensuremath{\simeq}10$; (iii) it is in practice impossible to compute the magnetic field with a Boltzmann code for scales smaller than 1 Mpc. Finally we confirm that for scales of a few Mpc, this magnetic field is of order $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}29}\text{ }\text{ }\mathrm{G}$, many orders of magnitude smaller than what is currently observed on intergalactic scales.

Ionospheric effects of magnetospheric and thermospheric disturbances on March 17–19, 2015

Abstract: Using vertical and oblique radio-sounding data, we analyze the ionospheric and thermospheric disturbances during the magnetic storm that occurred in northeastern Russia on March 17–19, 2015. We consider the heliospheric sources that induced the magnetic storm. During the main and early recovery phases, the midlatitude stations are characterized by extremely low values of electron density at the F2 layer maximum. Using oblique sounding data, we recorded signals that propagated outside the great circle arc. In evening and night hours, no radio signals were found to pass along the Norilsk–Irkutsk and Magadan–Irkutsk paths. The observed ionospheric effects are shown to be caused by a sharp shift of the boundaries of the main ionospheric trough to the invariant latitude 46° N during the main phase of the magnetic storm. The negative ionospheric disturbance during the recovery phase of the storm, which was associated with significant variations in the composition of the neutral atmosphere, led to a change in the mode composition of received radio signals and a decline in observed maximal frequencies in daytime hours of March 18, 2015 by more than 2 times.

Long-period variations in the magnetic field of small-scale solar structures

Abstract: Thirty small-scale structures in the solar atmosphere, i.e., facula nodes at ±(20°–46°) latitudes, have been studied in order to analyze quasi-periodic variations in the magnetic field. SDO/HMI magnetograms have been used for this purpose. Long-period variations in the magnetic field strength of the considered objects in the 60–280 min range have been revealed as a result of data processing. It has been shown that there are no dependences between the magnetic field and period, nor between the magnetic field and object area. It has been assumed that the discovered variations are not natural oscillations of the magnetic field strength.

Charged dust grain dynamics subject to solar wind, Poynting-Robertson drag, and the interplanetary magnetic field

Abstract: We investigate the combined effect of solar wind, Poynting-Robertson drag, and the frozen-in interplanetary magnetic field on the motion of charged dust grains in our solar system. For this reason we derive a secular theory of motion by the means of averaging method and validate it with numerical simulations of the un-averaged equations of motions. The theory predicts that the secular motion of charged particles is mainly affected by the z-component of the solar magnetic axis, or the normal component of the interplanetary magnetic field. The normal component of the interplanetary magnetic field leads to an increase or decrease of semi-major axis depending on its functional form and sign of charge of the dust grain. It is generally accepted that the combined effects of solar wind and photon absorption and re-emmision (Poynting-Robertson drag) lead to a decrease in semi-major axis on secular time scales. On the contrary, we demonstrate that the interplanetary magnetic field may counteract these drag forces under certain circumstances. We derive a simple relation between the parameters of the magnetic field, the physical properties of the dust grain as well as the shape and orientation of the orbital ellipse of the particle, which is a necessary conditions for the stabilization in semi-major axis.

One year in the Earth's magnetosphere: A global MHD simulation and spacecraft measurements

Abstract: The response of the Earth's magnetosphere to changing solar wind conditions is studied with a 3-D Magnetohydrodynamic (MHD) model. One full year (155 Cluster orbits) of the Earth's magnetosphere is simulated using Grand Unified Magnetosphere Ionosphere Coupling simulation (GUMICS-4) magnetohydrodynamic code. Real solar wind measurements are given to the code as input to create the longest lasting global magnetohydrodynamics simulation to date. The applicability of the results of the simulation depends critically on the input parameters used in the model. Therefore, the validity and the variance of the OMNIWeb data are first investigated thoroughly using Cluster measurement close to the bow shock. The OMNIWeb and the Cluster data were found to correlate very well before the bow shock. The solar wind magnetic field and plasma parameters are not changed significantly from the L1 Lagrange point to the foreshock; therefore, the OMNIWeb data are appropriate input to the GUMICS-4. The Cluster SC3 footprints are determined by magnetic field mapping from the simulation results and the Tsyganenko (T96) model in order to compare two methods. The determined footprints are in rather good agreement with the T96. However, it was found that the footprints agree better in the Northern Hemisphere than the Southern one during quiet conditions. If the By is not zero, the agreement of the GUMICS-4 and T96 footprint is worse in longitude in the Southern Hemisphere. Overall, the study implies that a 3-D MHD model can increase our insight of the response of the magnetosphere to solar wind conditions.

Dynamos at extreme magnetic Prandtl numbers: insights from shell models

Abstract: We present a magnetohydrodynamic (MHD) shell model suitable for computation of various energy fluxes of MHD turbulence for very small and very large magnetic Prandtl numbers Pm; such computations are inaccessible to direct numerical simulations. For small Pm, we observe that both kinetic and magnetic energy spectra scale as k−5/3 in the inertial range, but the dissipative magnetic energy scales as k−11/3exp (− k/kη). Here the kinetic energy at large length scale feeds the large-scale magnetic field that cascades to small-scale magnetic field, which gets dissipated by Joule heating. The large-Pm dynamo has a similar behaviour except that the dissipative kinetic energy scales as k−13/3. For this case, the large-scale velocity field transfers energy to the large-scale magnetic field, which gets transferred to small-scale velocity and magnetic fields; the energy of the small-scale magnetic field also gets transferred to the small-scale velocity field, and the energy thus accumulated is dissipated by t...

The Decay of a Weak Large-Scale Magnetic Field in Two-dimensional Turbulence

Abstract: We investigate the decay of a large-scale magnetic field in the context of incompressible, two-dimensional magnetohydrodynamic turbulence. It is well established that a very weak mean field, of strength significantly below equipartition value, induces a small-scale field strong enough to inhibit the process of turbulent magnetic diffusion. In the light of ever-increasing computer power, we revisit this problem to investigate fluids and magnetic Reynolds numbers that were previously inaccessible. Furthermore, by exploiting the relation between the turbulent diffusion of the magnetic potential and that of the magnetic field, we are able to calculate the turbulent magnetic diffusivity extremely accurately through the imposition of a uniform mean magnetic field. We confirm the strong dependence of the turbulent diffusivity on the product of the magnetic Reynolds number and the energy of the large-scale magnetic field. We compare our findings with various theoretical descriptions of this process.

Stability of rotating self-gravitating filaments: effects of magnetic field

Abstract: We have performed systemmatic local linear stability analysis on a radially stratified infinite self-gravitating cylinder of rotating plasma under the influence of magnetic field. In order to render the system analytically tractable, we have focussed solely on the axisymmetric modes of perturbations. Using cylindrical coordinate system, we have derived the critical linear mass density of a non-rotating filament required for gravitational collapse to ensue in the presence of azimuthal magnetic field. Moreover, for such filaments threaded by axial magnetic field, we show that the growth rates of the modes having non-zero radial wavenumber are reduced more strongly by the magnetic field than that of the modes having zero radial wavenumber. More importantly, our study contributes to the understanding of the stability property of rotating astrophysical filaments that are more often than not influenced by magnetic fields. In addition to complementing many relevant numerical studies reported the literature, our results on filaments under the influence of magnetic field generalize some of the very recent analytical works (e.g.,~\citet{jog2014}, etc.). For example, here we prove that even a weak magnetic field can play a dominant role in determining stability of the filament when the rotation timescale is larger than the free fall timescale. A filamentary structure with faster rotation is, however, comparatively more stable for the same magnetic field. The results reported herein, due to strong locality assumption, are strictly valid for the modes for which one can ignore the radial variations in the density and the magnetic field profiles.

Relativity and the Solar Wind: The Maxwell-Equation Origins of the Solar-Wind Motional Electric Field

Abstract: The motional electric field of the solar wind as seen by the Earth is examined theoretically and with spacecraft measurements. As it flows outward from the sun, the solar-wind plasma carries a spatially structured magnetic field with it. To calculate the motional electric field of the solar wind the spatially structured magnetic field is Lorentz transformed; for a full physical understanding, it is also necessary to Lorentz transform the current densities and charge densities in the solar wind. Referring to Maxwell’s equations, two related questions are asked: 1) Is the source of the solar-wind motional electric field charge density in the solar wind, time derivatives of current densities in the solar wind, or both? 2) Is the solar-wind motional electric field at Earth an electrostatic field, an induction field, or a superposition of the two? A Helmholtz decomposition of the motional electric field of the solar wind is made into a divergence-origin (electrostatic) and a curl-origin (induction) electric field. The global electric field associated with the outward advection of the global Parker-spiral magnetic field is found to be electrostatic with its origin being a distributed charge density in the solar-wind plasma. The electrostatic versus induction nature of the time-varying electric field associated with the advection of mesoscale magnetic structure varies with time as differently shaped magnetic structures in the solar-wind plasma pass the Earth; the mesoscale structure of the solar-wind plasma contains sheets of space charge and sheets wherein the current density has nonzero time derivatives.

Can Core Flows inferred from Geomagnetic Field Models explain the Earth's Dynamo?

Abstract: We test the ability of large scale velocity fields inferred from geomagnetic secular variation data to produce the global magnetic field of the Earth. Our kinematic dynamo calculations use quasi-geostrophic (QG) flows inverted from geomagnetic field models which, as such, incorporate flow structures that are Earth-like and may be important for the geodynamo. Furthermore, the QG hypothesis allows straightforward prolongation of the flow from the core surface to the bulk. As expected from previous studies, we check that a simple quasi-geostrophic flow is not able to sustain the magnetic field against ohmic decay. Additional complexity is then introduced in the flow, inspired by the action of the Lorentz force. Indeed, on centenial time-scales, the Lorentz force can balance the Coriolis force and strict quasi-geostrophy may not be the best ansatz. When the columnar flow is modified to account for the action of the Lorentz force, magnetic field is generated for Elsasser numbers larger than 0.25 and magnetic Reynolds numbers larger than 100. This suggests that our large scale flow captures the relevant features for the generation of the Earth's magnetic field and that the invisible small scale flow may not be directly involved in this process. Near the threshold, the resulting magnetic field is dominated by an axial dipole, with some reversed flux patches. Time-dependence is also considered, derived from principal component analysis applied to the inverted flows. We find that time periods from 120 to 50 years do not affect the mean growth rate of the kinematic dynamos. Finally we notice the footprint of the inner-core in the magnetic field generated deep in the bulk of the shell, although we did not include one in our computations.

Markov properties of the magnetic field in the quiet solar photosphere

Abstract: The observed magnetic field on the solar surface is characterized by a very complex spatial and temporal behaviour. Although feature-tracking algorithms have allowed us to deepen our understanding of this behaviour, subjectivity plays an important role in the identification, tracking of such features. In this paper we study the temporal stochasticity of the magnetic field on the solar surface \textit{without} relying neither on the concept of magnetic feature nor on subjective assumptions about their identification and interaction. The analysis is applied to observations of the magnetic field of the quiet solar photosphere carried out with the IMaX instrument on-board the stratospheric balloon {\sc Sunrise}. We show that the joint probability distribution functions of the longitudinal ($B_\parallel$) and transverse ($B_\perp$) components of the magnetic field, as well as of the magnetic pressure ($B^2=B^2_\perp+B^2_\parallel$), verify the necessary and sufficient condition for the Markov chains. Therefore we establish that the magnetic field, as seen by IMaX with a resolution of 0.15\arcsec-0.18\arcsec and $33$~sec cadence, can be considered as a memoryless temporal fluctuating quantity.

Modeling the sun’s small-scale global photospheric magnetic field

Abstract: We present a new model for the Sun's global photospheric magnetic field during a deep minimum of activity, in which no active regions emerge. The emergence and subsequent evolution of small-scale magnetic features across the full solar surface is simulated, subject to the influence of a global supergranular flow pattern. Visually, the resulting simulated magnetograms reproduce the typical structure and scale observed in quiet Sun magnetograms. Quantitatively, the simulation quickly reaches a steady state, resulting in a mean field and flux distribution that are in good agreement with those determined from observations. A potential coronal magnetic field is extrapolated from the simulated full Sun magnetograms to consider the implications of such a quiet photospheric magnetic field on the corona and inner heliosphere. The bulk of the coronal magnetic field closes very low down, in short connections between small-scale features in the simulated magnetic network. Just 0.1% of the photospheric magnetic flux is found to be open at 2.5 R ⊙, around 10–100 times less than that determined for typical Helioseismic and Magnetic Imager synoptic map observations. If such conditions were to exist on the Sun, this would lead to a significantly weaker interplanetary magnetic field than is currently observed, and hence a much higher cosmic ray flux at Earth.

The multipole nature of the extraneous field of a magnetic field wireless power transfer system

Abstract: Because efficiency is paramount, magnetic field wireless power transfer (MF-WPT) systems are tuned in a manner similar to some tuned linear transformers, such as IF transformers, in which the primary and secondary circuits are each tuned to the same resonant frequency (synchronous tuning) and then the load resistance adjusted for critical coupling. This causes the primary and secondary currents to be 90° out of phase with one another. The phase difference gives rise to a unique extraneous electromagnetic field consisting primarily of contributions from a magnetic dipole and a linear magnetic quadrupole. At great distance, the dipole moment contribution dominates. However, in the immediate vicinity of the system, the contribution from the quadrupole moment can dominate and thus there exists a certain distance from the system (dependent on direction) at which the dipole and quadrupole contributions are of the same order. We determine this distance for typical MF-WPT designs at ground level and find that the contribution of the dipole moment dominates the magnetic field at distances frequently specified in EMC standards, e.g. 3 and 10 meters. This conclusion has implications for characterization procedures which involve the the measurement of only the magnetic dipole moment.

Reversals in the six-jet Geodynamo model

Abstract: We describe a large-scale geodynamo model based on hypothesis about 6-cells convection in the Earth’s core. This hypothesis suggests indirect data of inhomogeneities in the density of the Earth?s core. The convection pattern is associated with a spherical harmonic Y 2 4 which defines the basic poloidal component of velocity. The model takes into account the feedback effect of the magnetic field on convection. It was ascertained that the model contains stable regimes of field generation with reversals. The velocity of convection and the dipole component of the magnetic field are similar to the observed ones.

Three‐dimensional full‐kinetic simulation of the solar wind interaction with a vertical dipolar lunar magnetic anomaly

Abstract: A detailed understanding of the solar wind interaction with lunar magnetic anomalies (LMAs) is essential to identify its implications for lunar exploration and to enhance our physical understanding of the particle dynamics in a magnetised plasma. We present the first three-dimensional full-kinetic electromagnetic simulation case study of the solar wind interaction with a vertical dipole, resembling a medium-size LMA. In contrast to a horizontal dipole, we show that a vertical dipole twists its field lines and cannot form a mini-magnetosphere. Instead, it creates a ring-shaped weathering pattern and reflects up to 21% (4 times more as compared to the horizontal case) of the incoming solar wind ions electrostatically through the normal electric field formed above the electron shielding region surrounding the cusp. This work delivers a vital piece to fully comprehend and interpret lunar observations as we find the amount of reflected ions to be a tracer for the underlying field structure.

Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models

Abstract: . When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.

Electric Power Generation from Earth’s Rotation through its Own Magnetic Field

Abstract: There is a simple proof that it is impossible to produce electricity using Earth's rotation through the nonrotating component of its own magnetic field. However, the authors have identified a loophole in that proof, and it appears that power generation could be possible in a laboratory system. Experimental verification of this result could carry implications for a clean-energy future.

Theoretical Methods for Studying Distance and Frequency Scaling for AC Magnetic Fields in Satellite Missions

Abstract: In this paper, magnetic source models based on physical phenomena are introduced for the purpose of studying ac magnetic cleanliness. More explicitly, a theoretical analysis of the magnetic behavior of current loops has been carried out with respect to several parameters, i.e., shape, area, frequency, and current type. The parameters were studied individually, resulting in different power laws of the magnetic field. The present research focuses on frequency and distance scaling of the magnetic field, resulting in indicative power laws for several magnetic loop types. This approach can form a basis to identify the parameters of the magnetic loops inside equipment under test by measuring the magnetic field falloff.

Induced magnetic field due to reaction wheel shielding

Abstract: In situ magnetic field measurements are of critical importance to unanswered questions on the inner heliosphere, such as: how the corona and solar wind are accelerated and heated; how the solar magnetic field evolves over a solar cycle; and how this field links into space. However, accurate spacecraft magnetometer measurements require reliable in-flight calibration. The magnetic interference caused by reaction wheels on magnetometer measurements in space is well known, and a common mitigation method is to use magnetic shielding. However, the presence of high-permeability material in-flight has the side-effect of distorting the true ambient field. We present a theoretical analysis of this distortion, and suggest a transfer function that can be used to recover the ambient field from the distorted dataset. Experimental measurements on a shield prototype for the Solar Orbiter mission agree with predictions to within an order of magnitude, demonstrating a distortion of approximately 1 part in 104.