scholarly journals An improved 50-degree spherical harmonic model of the magnetic field of Mars derived from both high-altitude and low-altitude data

2002 ◽  
Vol 107 (E10) ◽  
Author(s):  
Jafar Arkani-Hamed
Keyword(s):  
Magnetic Field ◽  
High Altitude ◽  
Spherical Harmonic ◽  
Harmonic Model ◽  
Low Altitude ◽  
Spherical Harmonic Model ◽  
The Magnetic Field

scholarly journals Retrieving lithospheric magnetisation distribution from magnetic field models

2019 ◽  
Author(s):  
V Lesur ◽  
F Vervelidou
Keyword(s):  
Magnetic Field ◽  
Cost Function ◽  
Spherical Harmonic ◽  
Field Model ◽  
Harmonic Model ◽  
Whole Process ◽  
Magnetic Field Model ◽  
The Cost ◽  
Spherical Harmonic Model ◽  
The Magnetic Field

Summary We investigate to which extent the radially averaged magnetisation of the lithosphere can be recovered from the information content of a spherical harmonic model of the generated magnetic field when combined with few simple hypotheses. The results obtained show firstly that a hypothesis of magnetisation induced by a field of internal origin, even over a localised area, is not sufficient to recover uniquely the radially averaged magnetisation and, secondly, that this magnetisation can be recovered when a constant magnetisation direction is assumed. An algorithm to recover the magnetisation direction and distribution is then described and tested over a synthetic example. It requires to introduce a cost function that vanishes when estimated in a system of coordinates with its Z axis aligned with the magnetisation direction. Failing to find a vanishingly small value for the cost function is an indication that a constant magnetisation direction is not a valid hypothesis for the studied magnetic field model. The range of magnetisation directions that are compatible with the magnetic field model and a given noise level, can also be estimated. The whole process is illustrated by analysing a local, isolated maximum of the Martian magnetic field.

scholarly journals Cusp-like plasma in high altitudes: a statistical study of the width and location of the cusp from Magion-4

2002 ◽  
Vol 20 (3) ◽  
pp. 311-320 ◽  
Author(s):  
J. Mĕrka ◽  
J. Šafránková ◽  
Z. Nĕmeček
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Altitudes ◽  
Data Set ◽  
Latitudinal Dependence ◽  
Merging Process ◽  
Low Altitude ◽  
Field Lines ◽  
The Magnetic Field ◽  
Dipole Tilt

Abstract. The width of the cusp region is an indicator of the strength of the merging process and the degree of opening of the magnetosphere. During three years, the Magion-4 satellite, as part of the Interball project, has collected a unique data set of cusp-like plasma observations in middle and high altitudes. For a comparison of high- and low-altitude cusp determination, we map our observations of cusp-like plasma along the magnetic field lines down to the Earth’s surface. We use the Tsyganenko and Stern 1996 model of the magnetospheric magnetic field for the mapping, taking actual solar wind and IMF parameters from the Wind observations. The footprint positions show substantial latitudinal dependence on the dipole tilt angle. We fit this dependence with a linear function and subtract this function from observed cusp position. This process allows us to study both statistical width and location of the inspected region as a function of the solar wind and IMF parameters. Our processing of the Magion-4 measurements shows that high-altitude regions occupied by the cusp-like plasma (cusp and cleft) are projected onto a much broader area (in magnetic local time as well as in a latitude) than that determined in low altitudes. The trends of the shift of the cusp position with changes in the IMF direction established by low-altitude observations have been confirmed.Key words. Magnetospheric physics (magnetopause, cusp and boundary layer; solar wind – magnetosphere interactions)

scholarly journals The Optimal Degree of Gravity Spherical Harmonic Model Calculation for Gravity Disturbance Compensation in Inertial Navigation

2018 ◽  
Vol 160 ◽  
pp. 07004
Author(s):  
Junbo TIE ◽  
Meiping WU ◽  
Juliang Cao ◽  
Junxiang Lian ◽  
Shaokun Cai ◽  
...  
Keyword(s):  
Frequency Band ◽  
Spherical Harmonic ◽  
Inertial Navigation ◽  
Gravity Disturbance ◽  
Harmonic Model ◽  
Response Characteristics ◽  
Optimal Degree ◽  
Amplitude Frequency Response ◽  
Navigation Error ◽  
Spherical Harmonic Model

In recent years, the significant improvement of inertial navigation, leaves the gravity disturbance as the important factor which affects the accuracy of inertial navigation. This paper focus on the compensation for gravity disturbance with gravity spherical harmonic model, especially the optimal degree of gravity spherical harmonic model with which to calculate the gravity disturbance. The effect of gravity disturbance on inertial navigation is analysed based on the amplitude-frequency response characteristics of inertial navigation error differential equation, then the dominantly influential frequency band of gravity disturbance can be found which is the target of compensation. Combination the dominantly influential frequency band with the spatial resolution of the Earth’s gravity spherical harmonic model EGM2008 which is used to calculate the gravity disturbance, the optimal degree can be determined based on an algorithm proposed in this paper. Finally, shipborne inertial navigation experiment confirms the correctness and effectiveness of the proposed algorithm.

scholarly journals Observations of vortex-like structure in the cusp-magnetosheath region during northward IMF orientation

2008 ◽  
Vol 26 (11) ◽  
pp. 3375-3387 ◽  
Author(s):  
O. Tkachenko ◽  
J. Šafránková ◽  
Z. Němeček ◽  
J. Šimůnek ◽  
L. Přech
Keyword(s):  
Magnetic Field ◽  
High Altitude ◽  
Plasma Flow ◽  
Alternative Explanation ◽  
Regular Feature ◽  
Hot Plasma ◽  
Large Vortex ◽  
Small Structure ◽  
The Magnetic Field ◽  
Statistical Results

Abstract. Two-point observations made by the Interball spacecraft pair unveiled a presence of a large vortex-like structure filled by slow and heated plasma in the outer cusp during periods of the positive BZ interplanetary magnetic field (IMF) component. We have observed the rotation of the magnetic field and the decrease of its magnitude connected with the presence of a hot plasma population inside the vortex. The structure starts with a clear reversal of the plasma flow caused by reconnection tailward of the cusp that turns a part of the magnetosheath plasma into the cusp. We compare the observations of two spacecraft in detail, discuss the differences between them and suggest the way of a formation such structure. Moreover, the statistical results have confirmed that this phenomenon is probably a regular feature of the high-altitude cusp, however, this relatively small structure cannot be observed too often. The alternative explanation of presented observations as a flapping of the magnetopause is taken into account and discussed.

Spherical tensor approach to multipole expansions. II. Magnetostatic interactions

1976 ◽  
Vol 54 (5) ◽  
pp. 513-518 ◽  
Author(s):  
C. G. Gray ◽  
P. J. Stiles
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Interaction Energy ◽  
Current Distribution ◽  
Spherical Harmonic ◽  
Magnetostatic Interaction ◽  
Multipole Expansions ◽  
The Magnetic Field ◽  
A Current ◽  
Magnetostatic Interactions

The magnetic field due to a given current distribution, the interaction energy of a current distribution with an arbitrary external magnetic field, and the magnetostatic interaction energy between two current distributions are decomposed into multipolar components using spherical harmonic expansions. Diamagnetic interactions and the spin contributions to the multipole expansions are also discussed.

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