scholarly journals Possible correlation between the vertical component of lithospheric magnetic field and continental seismicity

2018 ◽  
Vol 70 (1) ◽  
Author(s):  
Yu Lei ◽  
Liguo Jiao ◽  
Huaran Chen
Keyword(s):  
Magnetic Field ◽  
Vertical Component ◽  
Lithospheric Magnetic Field

scholarly journals Properties of the inner penumbral boundary and temporal evolution of a decaying sunspot

2018 ◽  
Vol 620 ◽  
pp. A191 ◽  
Author(s):  
M. Benko ◽  
S. J. González Manrique ◽  
H. Balthasar ◽  
P. Gömöry ◽  
C. Kuckein ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Temporal Evolution ◽  
Vertical Component ◽  
Field Vector ◽  
Linear Increase ◽  
Vertical Magnetic Field ◽  
Magnetic Diffusion ◽  
The Magnetic Field ◽  
Linear Decay

Context. It has been empirically determined that the umbra-penumbra boundaries of stable sunspots are characterized by a constant value of the vertical magnetic field. Aims. We analyzed the evolution of the photospheric magnetic field properties of a decaying sunspot belonging to NOAA 11277 between August 28–September 3, 2011. The observations were acquired with the spectropolarimeter on-board of the Hinode satellite. We aim to prove the validity of the constant vertical magnetic-field boundary between the umbra and penumbra in decaying sunspots. Methods. A spectral-line inversion technique was used to infer the magnetic field vector from the full-Stokes profiles. In total, eight maps were inverted and the variation of the magnetic properties in time were quantified using linear or quadratic fits. Results. We find a linear decay of the umbral vertical magnetic field, magnetic flux, and area. The penumbra showed a linear increase of the vertical magnetic field and a sharp decay of the magnetic flux. In addition, the penumbral area quadratically decayed. The vertical component of the magnetic field is weaker on the umbra-penumbra boundary of the studied decaying sunspot compared to stable sunspots. Its value seem to be steadily decreasing during the decay phase. Moreover, at any time of the sunspot decay shown, the inner penumbra boundary does not match with a constant value of the vertical magnetic field, contrary to what is seen in stable sunspots. Conclusions. During the decaying phase of the studied sunspot, the umbra does not have a sufficiently strong vertical component of the magnetic field and is thus unstable and prone to be disintegrated by convection or magnetic diffusion. No constant value of the vertical magnetic field is found for the inner penumbral boundary.

The reduction of source effect for reliable estimation of geomagnetic transfer functions

2020 ◽  
Vol 221 (1) ◽  
pp. 415-430
Author(s):  
Tomasz Ernst ◽  
Krzysztof Nowożyński ◽  
Waldemar Jóźwiak
Keyword(s):  
Magnetic Field ◽  
Transfer Functions ◽  
Negative Impact ◽  
Vertical Component ◽  
Regional Effect ◽  
Geomagnetic Variations ◽  
Source Effect ◽  
Original Algorithm ◽  
Induction Components ◽  
The Time Domain

SUMMERY We have analysed the literature suggestions regarding possible changes in vertical magnetic transfer function (VTF) over time. We have shown that for periods above 1500 s the observed changes in VTF are caused by the source effect and we proposed how to reduce this negative impact. For calculations we used 1-min recordings of geomagnetic variations registered between 2002 and 2017 in various geomagnetic observatories. In data processing we used frequency-domain Egbert's algorithm and our original algorithm based on the method of least squares in the time domain for some comparisons and tests. We have shown that for periods over 1500 s the VTFs calculated separately from summer and winter data are different. However, our analysis shows that the variability of the VTF values obtained is misleading and results from time-changing presence of magnetic field variations that do not fulfill the assumption of plane wave (there is a vertical component in the incident magnetic field). These variations are much more numerous in summer than in winter. More detailed analysis has shown also that they are usually small at night and big during the day. The vertical components of these variations constitute an error correlated with input signals (horizontal components), which alters the values of the determined VTF. Furthermore, error bars do not take this effect into account. It makes it impossible to improve the accuracy of calculations by increasing the amount of data. Analysing the estimated external parts of vertical components from the Central European observatories we noticed a great similarity of these signals even if the induction components were clearly different, which indicates that this is a regional effect. On this basis, we proposed a procedure to improve the accuracy of VTF determination by means of pre-selection of data.

Magnetic Field Variations in Alaska: Recording Space Weather Events on Seismic Stations in Alaska

2020 ◽  
Vol 110 (5) ◽  
pp. 2530-2540 ◽  
Author(s):  
Adam T. Ringler ◽  
Robert E. Anthony ◽  
David C. Wilson ◽  
Abram C. Claycomb ◽  
John Spritzer
Keyword(s):  
Magnetic Field ◽  
Ground Motion ◽  
Space Weather ◽  
Vertical Component ◽  
Environmental Data ◽  
Magnetic Data ◽  
Seismic Stations ◽  
Weather Events ◽  
S Period ◽  
Magnetic Field Variations

ABSTRACT Seismometers are highly sensitive instruments to not only ground motion but also many other nonseismic noise sources (e.g., temperature, pressure, and magnetic field variations). We show that the Alaska component of the Transportable Array is particularly susceptible to recording magnetic storms and other space weather events because the sensors used in this network are unshielded and magnetic flux variations are stronger at higher latitudes. We also show that vertical-component seismic records across Alaska are directly recording magnetic field variations between 40 and 800 s period as opposed to actual ground motion during geomagnetic events with sensitivities ranging from 0.004 to 0.48  (m/s2)/T. These sensitivities were found on a day where the root mean square variation in the magnetic field was 225 nT. Using a method developed by Forbriger (2007, his section 3.1), we show that improving vertical seismic resolution of an unshielded sensor by as much as 10 dB in the 100–400 s period band using magnetic data from a collocated three-component magnetometer is possible. However, due to large spatial variations in Earth’s magnetic field, this methodology becomes increasingly ineffective as the distance between the seismometer and magnetometer increases (no more than 200 km separation). A potential solution to this issue may be to incorporate relatively low-cost magnetometers as an additional environmental data stream at high-latitude seismic stations. We demonstrate that the Bartington Mag-690 sensors currently deployed at Global Seismographic Network sites are not only acceptable for performing corrections to seismic data, but are also capable of recording many magnetic field signals with similar signal-to-noise ratios, in the 20–1000 s period band, as the observatory grade magnetometers operated by the U.S. Geological Survey Geomagnetism Program. This approach would densify magnetic field observations and could also contribute to space weather monitoring by supplementing highly calibrated magnetometers with additional sensors.

Recording the Aurora at Seismometers across Alaska

2020 ◽  
Vol 91 (6) ◽  
pp. 3039-3053 ◽  
Author(s):  
Carl Tape ◽  
Adam T. Ringler ◽  
Don L. Hampton
Keyword(s):  
Magnetic Field ◽  
Seismic Data ◽  
Vertical Component ◽  
Seismic Array ◽  
Magnetic Shielding ◽  
Data Sets ◽  
S Waves ◽  
Auroral Activity ◽  
Seismic Sensors ◽  
Magnetometer Data

Abstract We examine three continuously recording data sets related to the aurora: all-sky camera images, three-component magnetometer data, and vertical-component, broadband seismic data as part of the EarthScope project (2014 to present). Across Alaska there are six all-sky cameras, 13 magnetometers, and >200 seismometers. The all-sky images and magnetometers have the same objective, which is to monitor space weather and improve our understanding of auroral activity, including the influence on magnetic fields in the ground. These variations in the magnetic field are also visible on seismometers, to the extent that during an auroral event, the long-period (40–800 s) waves recorded by a seismometer are magnetic field variations, not true ground motion. Although this is a problem—one that can be rectified with magnetic shielding at each seismometer site—it is also an opportunity because the present seismic array in Alaska is much broader than the coverage by magnetometers and all-sky cameras. Here we focus on three aurora events and document a direct link between aurora images in the night sky and seismometer recordings on ground. Simultaneous recordings by magnetometers provide a critical link between the sky images and the seismometer recordings. We document qualitative correlations among sky, magnetic, and seismic data. The findings suggest that the signature of auroral activity is widespread across seismometers in Alaska, implying that the seismic array could be used to enhance the spatial resolution of the existing network of all-sky cameras and magnetometers. Future efforts to improve the multisensor seismic stations in Alaska, for the purpose of monitoring seismic and auroral activity, should consider installation of all-sky cameras, installation of magnetometers, and magnetic shielding of seismic sensors.

scholarly journals A high resolution lithospheric magnetic field model over southern Africa based on a joint inversion of CHAMP, Swarm, WDMAM and ground magnetic field data

2018 ◽  
Author(s):  
Foteini Vervelidou ◽  
Erwan Thébault ◽  
Monika Korte
Keyword(s):  
Magnetic Field ◽  
Southern Africa ◽  
Field Model ◽  
Joint Inversion ◽  
Field Measurements ◽  
Magnetic Field Data ◽  
Magnetic Field Model ◽  
Lithospheric Magnetic Field ◽  
The Mean ◽  
Ground Magnetic

Abstract. We derive a lithospheric magnetic field model up to equivalent Spherical Harmonic degree 1000 over southern Africa. We rely on a joint inversion of satellite, near-surface and ground magnetic field data. The input data set consists of magnetic field vector measurements from the CHAMP satellite, across-track magnetic field differences from the Swarm mission, the World Digital Magnetic Anomaly Map and magnetic field measurements from repeat stations and three local INTERMAGNET observatories. For the inversion scheme, we use the Revised-Spherical Cap Harmonic Analysis (R-SCHA), a regional analysis technique able to deal with magnetic field measurements obtained at different altitudes. The model is carefully assessed and displayed at different altitudes and its spectral content is compared to high resolution global lithospheric field models. By comparing the shape of its spectrum to a statistical power spectrum of Earth's lithospheric magnetic field, we infer the mean magnetic thickness and the mean magnetization over southern Africa.

scholarly journals Geomagnetic field influences upward movement of young Chinook salmon emerging from nests

2018 ◽  
Vol 14 (2) ◽  
pp. 20170752 ◽  
Author(s):  
Nathan F. Putman ◽  
Michelle M. Scanlan ◽  
Amanda M. Pollock ◽  
Joseph P. O'Neil ◽  
Ryan B. Couture ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Chinook Salmon ◽  
Geomagnetic Field ◽  
Oncorhynchus Tshawytscha ◽  
Dimensional Space ◽  
Spatial Scales ◽  
Vertical Component ◽  
Life Cycles ◽  
Upward Movement ◽  
The Magnetic Field

Organisms use a variety of environmental cues to orient their movements in three-dimensional space. Here, we show that the upward movement of young Chinook salmon ( Oncorhynchus tshawytscha ) emerging from gravel nests is influenced by the geomagnetic field. Fish in the ambient geomagnetic field travelled farther upwards through substrate than did fish tested in a field with the vertical component inverted. This suggests that the magnetic field is one of several factors that influences emergence from the gravel, possibly by serving as an orientation cue that helps fish determine which way is up. Moreover, our work indicates that the Oncorhynchus species are sensitive to the magnetic field throughout their life cycles, and that it guides their movements across a range of spatial scales and habitats.

scholarly journals Analysis of geomagnetic measurements prior the Maule (2010), Iquique (2014) and Illapel (2015) earthquakes, in the Pacific Ocean sector of the Southern Hemisphere

2019 ◽  
Author(s):  
Enrique G. Cordaro ◽  
Patricio Venegas-Aravena ◽  
David Laroze
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Seismic Event ◽  
Vertical Component ◽  
Time Lapse ◽  
Radial Component ◽  
Cumulative Number ◽  
Research Groups ◽  
Low Frequencies ◽  
Ocean Sector

Abstract. It has been possible to detect variations in the vertical component of the geomagnetic field (Bz) through its first and second derivate in a range of frequencies (microHz); these seem to be roughly related with some major seismic subduction events. We studied the period 2010–2015, analysing the daily values of magnetic records over periods close to the last three significant events that occurred through the Chilean margin, i. e., along a boundary between convergent plates that is characterized by the occurrence of seismic events of magnitude greater than Mw8. These are the events of Iquique 2014, Illapel 2015 and Maule 2010, all at different latitudes, on different dates and characterized by different types of margin (erosive or accretionary). Certain similarities were found in the associated magnetic field variations: 1) Variation in the radial or z component of the geomagnetic field and its first and second temporal derivative, modelled as a small jump, and small oscillations in the second derivative, generating a frequency band between 1c / 48.9 hours and 1c / 79.13 Hrs. 2) A variable time lapse of between 30 and 120 days; and 3) The seismic event. Furthermore, when analysing spectrograms for the second temporal derivate of the radial component, different behaviour is found related to its spectral density. This takes the form of an increase in ultra-low frequencies (0.01–0.4 mHz) between the start of the magnetic jump and the seismic event. These frequencies are lower than those found during the last years by research groups that related magnetic field and earthquakes, furthermore the concept of time lapse close to 30 days is in agreement with those research groups. The previous analyses may not be so robust, this is why additionally a new method is used with stations closer to the events and time periods of two years. We analysed the daily cumulative number of anomalous behaviour in z component of magnetic field on ground based magnetometers. The results show an increase in the number of magnetic anomalies prior to the occurrence of the three earthquakes. The behavior of the anomalies is similar to those presented by other authors for other earthquakes with similar methods in ionosphere. All this magnetic features might recover seismic information of the events and could be related with Lithosphere-Atmosphere-Ionosphere Coupling.

AN ELECTROMAGNETIC INTERPRETATION PROBLEM IN GEOPHYSICS

Geophysics ◽  
1951 ◽  
Vol 16 (3) ◽  
pp. 431-449 ◽  
Author(s):  
L. B. Slichter
Keyword(s):  
Magnetic Field ◽  
Electrical Properties ◽  
Magnetic Field Intensity ◽  
Vertical Component ◽  
Single Frequency ◽  
Magnetic Intensity ◽  
Conductivity Function ◽  
The Magnetic Field ◽  
Surface Observations ◽  
Interpretation Problem

An interpretation problem in electromagnetic prospecting is discussed. A flat earth in which the three electrical properties of material vary only with depth is subjected to an alternating inducing field produced by a dipole above the surface with axis perpendicular to the surface. Observations of the horizontal or of the vertical component of the magnetic intensity at the ground’s surface are supposed to be available at all distances. From these observations solutions for the three unknown functions are developed. When the magnetic permeability is variable, the solutions for the permeability and dielectric functions require observations at two different frequencies. The conductivity function may be found from observations at a single frequency. It is shown that the horizontal and vertical components of the magnetic field intensity are mutually dependent in the region above the ground’s surface; and formulae independent of the ground’s characteristics are deduced for expressing [Formula: see text] in terms of [Formula: see text], and vice‐versa. Here [Formula: see text] denotes a plane coincident with or above and parallel to, the earth’s surface.

scholarly journals 29. The internal constitution of sunspots

1958 ◽  
Vol 6 ◽  
pp. 263-274 ◽  
Author(s):  
A. Schlüter ◽  
S. Temesváry
Keyword(s):  
Magnetic Field ◽  
Physical Properties ◽  
Flux Tube ◽  
Energy Transport ◽  
Convection Zone ◽  
Vertical Component ◽  
Relative Distribution ◽  
Physical Processes ◽  
Internal Constitution ◽  
The Magnetic Field

The constitution of stationary single sunspots of circular shape is considered. Account is taken of the mechanical effects of the magnetic field, including those which arise from the curvature of the lines of force. To make the system of magneto-hydrostatic equations manageable, it is assumed that the relative distribution of the vertical component of the magnetic field is the same across the flux-tube of the spot in all depths. Preliminary results indicate that suppression of convective energy transport by the magnetic field in those depths in which ionization of hydrogen takes place, will give the essential observable properties of sunspots, relatively independent on the asumptions about the physical processes in greater depths. There the physical properties of matter can deviate but very little from those of the indisturbed hydrogen convection zone.

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