Large‐scale crustal magnetization models derived from satellite magnetic anomaly data

1982 ◽  
Author(s):  
M. A. Mayhew
Keyword(s):  
Magnetic Anomaly ◽  
Large Scale ◽  
Crustal Magnetization

A new type of cloud discovered from Earth in the upper Martian atmosphere

2021 ◽  
Author(s):  
Jean Lilensten ◽  
Jean-Luc Dauvergne ◽  
Christophe Pellier ◽  
Marc Delcroix ◽  
Emmanuel Beaudoin ◽  
...  
Keyword(s):  
High Altitude ◽  
Magnetic Anomaly ◽  
Dust Storm ◽  
Large Scale ◽  
Martian Atmosphere ◽  
Ice Clouds ◽  
Large Particles ◽  
Night Side ◽  
Cosmic Particle ◽  
New Type

<p>During the 2020 Mars opposition, we observe from Earth the occurrence of a non-typical large-scale high-altitude clouds system, extending over thousands of km from the equator to 50°S. Over 3 hours, they emerge from the night side at an altitude of 90 (-15/+30) km and progressively dissipate in the dayside. They occur at a solar longitude of 316°, west of the magnetic anomaly and concomitantly to a regional dust storm. Despite their high altitude, they are composed of relatively large particles, suggesting a probable CO<sub>2</sub> ice composition, although H<sub>2</sub>O cannot be totally excluded. Such ice clouds were not reported previously. We discuss the formation of this new type of clouds and suggest a possible nucleation from cosmic particle precipitation.</p>

Three-dimensional numerical modeling of gravity and magnetic anomaly in a mixed space-wavenumber domain

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. G41-G54 ◽  
Author(s):  
Shikun Dai ◽  
Dongdong Zhao ◽  
Shunguo Wang ◽  
Bin Xiong ◽  
Qianjiang Zhang ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Fourier Transform ◽  
Differential Equations ◽  
Numerical Solution ◽  
Magnetic Anomaly ◽  
Large Scale ◽  
Vertical Component ◽  
Wavenumber Domain ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Anomaly

Fast and accurate numerical modeling of gravity and magnetic anomalies is the basis of field-data inversion and quantitative interpretation. In gravity and magnetic prospecting, the computation and memory requirements of practical modeling is still a significant issue, which leads to the difficulty of using efficient and detailed inversions for large-scale complex models. A new 3D numerical modeling method for gravity and magnetic anomaly in a mixed space-wavenumber domain is proposed to mitigate the difficulties. By performing a 2D Fourier transform along two horizontal directions, 3D partial differential equations governing gravity and magnetic potentials in the spatial domain are transformed into a group of independent 1D differential equations wrapped with different wavenumbers. Importantly, the computation and memory requirements of modeling are greatly reduced by this method. A modeling example with 4,040,100 observations can be finished in approximately 28 s on a desktop using a single core, and the independent differential equations are highly parallel among different wavenumbers. The method preserves the vertical component in the space domain, and thus a mesh for modeling can be finer at a shallower depth and coarser at a deeper depth. In general, the new method takes into account the calculation accuracy and the efficiency. The finite-element algorithm combined with a chasing method is used to solve the transformed differential equations with different wavenumbers. In a synthetic test, a model with prism-shaped anomalies is used to verify the accuracy and efficiency of the proposed algorithm by comparing the analytical solution, our numerical solution, and a well-known numerical solution. Furthermore, we have studied the balance between computational accuracy and efficiency using a standard fast Fourier transform (FFT) method with grid expansion and the Gauss-FFT method. A model with topography is also used to explore the ability of modeling topography with our method. The results indicate that the proposed method using the Gauss-FFT method has characteristics of fast calculation speed and high accuracy.

Magnetic exploration of ocean crust for craters of impact origin: Model results

Geophysics ◽  
1991 ◽  
Vol 56 (8) ◽  
pp. 1153-1157 ◽  
Author(s):  
Andrew R. Ochadlick
Keyword(s):  
Magnetic Anomaly ◽  
Deep Ocean ◽  
Point Of View ◽  
Ocean Floor ◽  
Magnetic Data ◽  
Data Sets ◽  
Ocean Crust ◽  
Crustal Magnetization ◽  
Simple Potential ◽  
The Impact

Magnetic data sets over deep ocean areas may contain clues to the existence of craters formed by the impact of an extraterrestrial body with the Earth’s ocean crust. To aid in the magnetic exploration of the ocean crust for oceanic impact craters, basic but effective computations from an impact model are studied from an aeromagnetic point of view. The main assumption of the analysis is that a sufficiently large impact can excavate large volumes of magnetized basalt, vaporize basalt, and raise basalt to temperatures above the Curie temperature (approximately 500°C) to alter the preimpact magnetization of the ocean floor and result in a magnetic anomaly being associated with an oceanic impact crater. In the absence of an existing theory on the influence of impacts on ocean crustal magnetization, the representation of a crater on the ocean floor by a simple potential provides, apparently for the first time, quantitative estimates of the crater’s magnetic anomaly along a horizontal surface. Numerical results from the model suggest that the detection of the anomaly of a Cretaceous‐Tertiary (K-T) type of impact is well within the capabilities of aeromagnetic technology.

scholarly journals Time evolution of the South Atlantic Magnetic Anomaly

2009 ◽  
Vol 81 (2) ◽  
pp. 243-255 ◽  
Author(s):  
Gelvam A. Hartmann ◽  
Igor G. Pacca
Keyword(s):  
Time Evolution ◽  
Magnetic Anomaly ◽  
Large Scale ◽  
Outer Core ◽  
South Atlantic ◽  
Historical Period ◽  
Total Field ◽  
The South ◽  
The North ◽  
Area Of Influence

The South Atlantic Magnetic Anomaly (SAMA) is one of the most outstanding anomalies of the geomagnetic field. The SAMA secular variation was obtained and compared to the evolution of other anomalies using spherical harmonic field models for the 1590-2005 period. An analysis of data from four South American observatories shows how this large scale anomaly affected their measurements. Since SAMA is a low total field anomaly, the field was separated into its nondipolar, quadrupolar and octupolar parts. The time evolution of the non-dipole/total, quadrupolar/total and octupolar/total field ratios yielded increasingly high values for the South Atlantic since 1750. The SAMA evolution is compared to the evolution of other large scale surface geomagnetic features like the North and the South Pole and the Siberia High, and this comparison shows the intensity equilibrium between these anomalies in both hemispheres. The analysis of non-dipole fields in historical period suggests that SAMA is governed by (i) quadrupolar field for drift, and (ii) quadrupolar and octupolar fields for intensity and area of influence. Furthermore, our study reinforces the possibility that SAMA may be related to reverse fluxes in the outer core under the South Atlantic region.

Limitations of the long‐wavelength components of the North American magnetic anomaly map

Geophysics ◽  
1990 ◽  
Vol 55 (12) ◽  
pp. 1577-1588 ◽  
Author(s):  
J. Arkani‐Hamed ◽  
W. J. Hinze
Keyword(s):  
Magnetic Anomaly ◽  
North American ◽  
Data Set ◽  
Long Wavelength ◽  
Related Data ◽  
The North ◽  
North American Data ◽  
Crustal Magnetization ◽  
Anomaly Map ◽  
Lateral Variations

The magnetic anomaly map of North America and its related data set provide the opportunity not only to view the obvious short‐wavelength anomalies (<300 km) in a continental context, but to isolate and analyze the longer wavelength anomalies. However, care must be used in analyzing the longer wavelengths because of the effects of noncrustal sources on these anomalies. Inversion of the anomalies into lateral variations of crustal magnetization suggests that the long‐wavelength anomalies (>2600 km) are strongly affected by core field components that have not been completely removed from the North American data set. Furthermore, the piecewise matching of the magnetic anomalies of adjacent survey areas in the map compilation has contaminated the intermediate wavelength anomalies (300–2600 km).

MAGNETIC ANOMALY EFFECTS DUE TO APPROXIMATING INFINITE RECTANGULAR PRISM SOURCES BY INFINITE LINE OR INFINITE SHEET SOURCES

Geophysics ◽  
1975 ◽  
Vol 40 (3) ◽  
pp. 530-537 ◽  
Author(s):  
J. N. Shapiro ◽  
G. Weynand ◽  
A. F. Gangi
Keyword(s):  
Magnetic Anomaly ◽  
Plate Tectonics ◽  
Rectangular Prism ◽  
Magnetization Distribution ◽  
The World ◽  
Simplifying Assumptions ◽  
Crustal Magnetization ◽  
Infinite Line ◽  
Ridge System

The inversion of oceanic magnetic anomaly data to obtain the crustal magnetization requires some assumptions regarding the magnetization distribution (Parker and Huestis, 1974). Two simplifying assumptions typically made for data near ridge systems are that the source magnetization is lineated parallel to the ridge system and that it is unidirectional. These assumptions follow directly from the theory of plate tectonics and have been used near the major ridge systems of the world. The presence of transform faulting can offset the lineations usually observed and render the first assumption invalid. In this note, only those cases in which both assumptions are valid will be considered.

scholarly journals Retrieval of large volcanomagnetic effects observed during the 1981 eruption of Mt.Etna

1997 ◽  
Vol 40 (2) ◽  
Author(s):  
C. Del Negro ◽  
F. Ferrucci ◽  
R. Napoli
Keyword(s):  
Magnetic Anomaly ◽  
Geomagnetic Field ◽  
Large Scale ◽  
Joint Effect ◽  
Mt Etna ◽  
Significant Extension

A large temporal anomaly was retrieved in the total geomagnetic field series recorded in 1981 on Mt. Etna at two continuously recording magnetometers, and associated with the March 17-23 eruption of the volcano. Variations were of such large scale that a 10 nT anomaly was observed at a distance of some 7 km from the eruptive events, calling for a significant extension and depth of the magnetic anomaly source. We discuss here some models which may account for such magnetic changes in relation to the eruption mechanism inferred by other data. The anomaly is thought to be accounted for by the joint effect of piezomagnetism of the country rocks and thermal demagnetisation engendered by a large intrusive dyke.

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