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.

Spectral method for processing hydromagnetic survey data at shallow depths

2021 ◽  
Author(s):  
Kirill Kuznetsov ◽  
Kiryukhina Elena ◽  
Bulychev Andrey ◽  
Lygin Ivan
Keyword(s):  
Magnetic Field ◽  
Spectral Method ◽  
Magnetic Field Gradient ◽  
Geophysical Methods ◽  
Temporal Variations ◽  
Magnetic Data ◽  
Field Reconstruction ◽  
Anomalous Magnetic Field ◽  
Single Moment ◽  
Magnetic Field Variations

<p>Magnetic surveys are commonly used for solving variety of geotechnical and geological challenges in offshore areas, jointly with a set of other geophysical methods. The most popular technique employed is hydromagnetic surveying with towed magnetometers. One of the most significant challenges encountered during processing of the magnetic data is related to temporal variations of the Earth's magnetic field. Accounting for diurnal magnetic field variations is often done by carrying out differential hydromagnetic surveys, a technique developed in the 1980-s. It is based on simultaneous measurements of the magnetic field using two sensors towed behind the vessel with a given separation. This technique allows to calculate along-course gradient which is free of magnetic field temporal variations. This measurement system resembles a gradiometer, with the distance between two sensors being referred to as the base of the gradiometer. It is possible to calculate anomalous magnetic field by integrating obtained magnetic field gradient. Studies have shown that accuracy of its reconstruction decreases with increasing base of the gradiometer. This becomes most significant when distance between the sensors and sources of magnetic field anomalies is small. This situation occur when the survey area is located in shallow water (i.e. for shallow marine, river or lake surveys).</p><p>An approach for deriving magnetic anomalies and accounting for diurnal variations in differential hydromagnetic surveys based on the frequency (spectral) representation of the measurements was proposed in 1987 [Melikhov, 1987]. This approach utilizes the fact that it is possible to reconstruct the spectrum of magnetic field anomalies along the vessel course from the spectra of measured signals from the first S<sub>1</sub>(ω) and second S<sub>2</sub>(ω) sensors. Assuming that the sensors are located at the same depth, it can be achieved via the following transform:</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.3d3911bac60061487501161/sdaolpUECMynit/12UGE&app=m&a=0&c=ff23bad5ed5181be02f7ef7ab5e8d6e4&ct=x&pn=gepj.elif&d=1" alt="" width="192" height="43"></p><p>where ω - spatial frequency, <em>l</em> - base of the gradiometer, and <em>i</em> - imaginary unit. Assuming that at a single moment in time magnetic field variations equally affect both sensors, resulting Fourier spectrum T(ω) will correspond the spectrum of anomalous magnetic field, free of the magnetic variations. It should be noted that, similar to the along-course gradient integration approach, anomalous magnetic field is restored to a certain accuracy level.</p><p>Estimates made on model examples showed that accuracy of the field reconstruction using this method is comparable to the accuracy levels of modern marine magnetic surveys (±1-3 nT). It could be noted that for gradiometer bases comparable or larger than depths to magnetic anomaly sources, errors of the field reconstruction are significantly lower for the spectral transformation-based approach compared to along-course gradient integration.</p><p>References:</p><p>Melikhov V.R., Bulychev A.A., Shamaro A.M. Spectral method for solving the problem of separating the stationary and variable components of the geomagnetic field in hydromagnetic gradiometric surveys // Electromagnetic research. - Moscow. IZMIRAN, 1987. - P. 97-109. (in Russian)</p><p> </p>

scholarly journals Study of Interplanetary and Geomagnetic Response of Filament Associated CMEs

2018 ◽  
Vol 13 (S340) ◽  
pp. 83-84
Author(s):  
Kunjal Dave ◽  
Wageesh Mishra ◽  
Nandita Srivastava ◽  
R. M. Jadhav
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Activity ◽  
Space Weather ◽  
Coronal Mass Ejections ◽  
The Sun ◽  
The Earth ◽  
Weather Events ◽  
Terrestrial Magnetic Field

AbstractIt has been established that Coronal Mass Ejections (CMEs) may have significant impact on terrestrial magnetic field and lead to space weather events. In the present study, we selected several CMEs which are associated with filament eruptions on the Sun. We attempt to identify the presence of filament material within ICME at 1AU. We discuss how different ICMEs associated with filaments lead to moderate or major geomagnetic activity on their arrival at the Earth. Our study also highlights the difficulties in identifying the filament material at 1AU within isolated and in interacting CMEs.

Modeling tippers on a sphere

2021 ◽  
Author(s):  
Alexey Kuvshinov ◽  
Mikhail Kruglyakov
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Transfer Functions ◽  
Three Dimensional ◽  
Vertical Component ◽  
Spherical Geometry ◽  
Magnetic Data ◽  
Period Range ◽  
Continental Scale ◽  
Uniform External Magnetic Field

<p>In the past three decades, a huge amount of long-period magnetic data (from weeks to years of measurements) has been collected around the world either inland or at sea bottom. It makes tempting to estimate from these data magnetotelluric (MT) vertical transfer functions - tippers – in as wide  period range as practicable and further probe with them the three-dimensional (3-D) distribution of electrical conductivity in the upper mantle on a global or semi-global/continental scale. Such problem setup requires modelling MT responses in spherical geometry. It is known that MT impedances in spherical coordinates can be modelled using different polarizations of a uniform external magnetic field. As for tippers, one cannot compute them on a sphere using this type of excitation, because the uniform external magnetic field of any polarization contains a non-zero vertical component. To overcome the problem, we elaborate a model of the source, which leads to valid MT tippers on a sphere or a part thereof. To compute tippers in spherical Earth models with 3-D conductivity distribution we use a novel accurate and computationally efficient solver called GEMMIE. The solver is based on nested integral equations, allowing researchers to calculate high-resolution MT tippers globally and regionally taking into account realistic oceans, sediments, and Earth’s conductivity.</p>

scholarly journals Building a Raspberry Pi School Magnetometer Network in the UK

2018 ◽  
Author(s):  
Ciarán D. Beggan ◽  
Steve R. Marple
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Storms ◽  
Low Cost ◽  
Cost Effective ◽  
Raspberry Pi ◽  
Data Logger ◽  
Weather Events ◽  
Effective System ◽  
The Uk ◽  
Magnetic Field Variations

Abstract. As computing and geophysical sensor components have become increasingly affordable over the past decade, it is now possible to design and build a cost-effective system for monitoring the Earth's natural magnetic field variations, in particular for space weather events. Modern fluxgate magnetometers are sensitive down to the sub-nanotesla level, which far exceeds the level of accuracy required to detect very small variations of the external magnetic field. When the popular Raspberry Pi single-board computer is combined with a suitable digitiser it can be used as a low-cost data logger. We adapted off-the-shelf components to design a magnetometer system for schools and developed bespoke Python software to build a network of low-cost magnetometers across the UK. We describe the system and software and how it was deployed to schools around the UK. In addition, we show the results recorded by the systems from one of the largest geomagnetic storms of the current solar cycle.

scholarly journals Building a Raspberry Pi school magnetometer network in the UK

2018 ◽  
Vol 1 (1) ◽  
pp. 25-34 ◽  
Author(s):  
Ciarán D. Beggan ◽  
Steve R. Marple
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Storms ◽  
Low Cost ◽  
Cost Effective ◽  
Raspberry Pi ◽  
Data Logger ◽  
Weather Events ◽  
Effective System ◽  
The Uk ◽  
Magnetic Field Variations

Abstract. As computing and geophysical sensor components have become increasingly affordable over the past decade, it is now possible to design and build a cost-effective system for monitoring the Earth's natural magnetic field variations, in particular for space weather events. Modern fluxgate magnetometers are sensitive down to the sub-nanotesla (nT) level, which far exceeds the level of accuracy required to detect very small variations of the external magnetic field. When the popular Raspberry Pi single-board computer is combined with a suitable digitiser it can be used as a low-cost data logger. We adapted off-the-shelf components to design a magnetometer system for schools and developed bespoke Python software to build a network of low-cost magnetometers across the UK. We describe the system and software and how it was deployed to schools around the UK. In addition, we show the results recorded by the system from one of the largest geomagnetic storms of the current solar cycle.

scholarly journals Some theoretical aspects of the two-level magnetovariational method

1997 ◽  
Vol 40 (6) ◽  
Author(s):  
M. Vellante
Keyword(s):  
Magnetic Field ◽  
Transfer Function ◽  
Apparent Resistivity ◽  
Vertical Component ◽  
Horizontal Magnetic Field ◽  
Source Field ◽  
Earth Models ◽  
The Vertical Distribution ◽  
Magnetic Field Variations

We discuss some theoretical aspects of the two-level magnetovariational method for the determination of the underground electrical structure. The properties of two new apparent resistivity functions, respectively depending on gain and phase of the transfer function of the horizontal magnetic field variations between the Earth's surface and a given depth, are examined for two-layer Earth models. The effects of a finite wavelength of the source field are also investigated. It is shown that the measurement of the attenuation of the magnetic vertical component generated by an inhomogeneous source field can provide further information on the vertical distribution of the Earth's conductivity. In particular, it is shown that the measurement of the transfer function of both vertical and horizontal components between two levels can be used to estimate the average conductivity of the interlying medium.

scholarly journals Geomagnetic Activity at Lampedusa Island: Characterization and Comparison with the Other Italian Observatories, Also in Response to Space Weather Events

2021 ◽  
Vol 13 (16) ◽  
pp. 3111
Author(s):  
Domenico Di Mauro ◽  
Mauro Regi ◽  
Stefania Lepidi ◽  
Alfredo Del Corpo ◽  
Guido Dominici ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Space Weather ◽  
Current System ◽  
Low Frequency ◽  
The Other ◽  
Quality Data ◽  
Individual Response ◽  
High Quality ◽  
Superposed Epoch Analysis ◽  
Weather Events

Regular automatic recordings of the time series of the magnetic field, together with routine manual absolute measurements for establishing dynamic baselines at Lampedusa Island—south of Sicily—Italy (geographic coordinates 35∘31’N; 12∘32’E, altitude 33 m a.s.l.), show a signature of very low electromagnetic noise. The observatory (provisional IAGA code: LMP) lays inside a restricted and remote wildlife reserve, far away from the built-up and active areas of the island, which at present is the southernmost location of the European territory for such observations. The availability of high-quality data from such site, whose survey started in 2005, is valuable for filling the spatial gap due to the lack of observatories in the whole south Mediterranean and North African sectors. We compare observations at Lampedusa, in both time and frequency domains, with those at the other Italian observatories (Castello Tesino and Duronia-L’Aquila), operating since the 1960s of last century, allowing us to report even the secular variation. Using data recorded in the last few years, we investigate higher frequency variations (from diurnal to Pc3-4 pulsations) in order to magnetically characterize the Italian territory and the local response to external forcing. In particular, we present a characterization in terms of diurnal variation and its seasonal dependence for the three observatories. This latter feature is in good agreement with a geomagnetic Sq-model, leading us to speculate about the position of the north Sq-current system vortex and its seasonal displacement with respect to the geographic positions of the observatories. We also study the geomagnetic individual response to intense space weather events by performing Superposed Epoch Analysis (SEA), with an ad-hoc significance test. Magnetic responses in the Ultra Low Frequency range (ULF) from spectral, local Signal-to-Noise Ratio (SNR) analyses under different local time, and polarization rates are computed. These latter studies lead us to search for possible signatures of magnetic field line resonances during intense space weather events, using cross-phase multi-observatory analysis, revealing the promising detection capability of such technique even at low latitudes. The geomagnetic observatories prove to be important points of observation for space weather events occurring at different spatial and time scales, originating in both upstream and ionospheric regions, here analyzed by several well-established methodologies and techniques. The quiet environmental site of LMP, providing high-quality geomagnetic data, allows us such investigations even at inner Earth’s magnetospheric shell.

An Augmented Iteratively Re-weighted and Refined Least Squares Method for lp Minimization Problem in Inverse Modeling of Potential Field Magnetic Data

2020 ◽  
Vol 1 (3) ◽  
Author(s):  
Maysam Abedi
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Least Squares ◽  
Minimization Problem ◽  
Potential Field ◽  
Field Data ◽  
Least Squares Method ◽  
Porphyry Copper ◽  
Magnetic Data ◽  
Magnetic Field Data

The presented work examines application of an Augmented Iteratively Re-weighted and Refined Least Squares method (AIRRLS) to construct a 3D magnetic susceptibility property from potential field magnetic anomalies. This algorithm replaces an lp minimization problem by a sequence of weighted linear systems in which the retrieved magnetic susceptibility model is successively converged to an optimum solution, while the regularization parameter is the stopping iteration numbers. To avoid the natural tendency of causative magnetic sources to concentrate at shallow depth, a prior depth weighting function is incorporated in the original formulation of the objective function. The speed of lp minimization problem is increased by inserting a pre-conditioner conjugate gradient method (PCCG) to solve the central system of equation in cases of large scale magnetic field data. It is assumed that there is no remanent magnetization since this study focuses on inversion of a geological structure with low magnetic susceptibility property. The method is applied on a multi-source noise-corrupted synthetic magnetic field data to demonstrate its suitability for 3D inversion, and then is applied to a real data pertaining to a geologically plausible porphyry copper unit.  The real case study located in  Semnan province of  Iran  consists  of  an arc-shaped  porphyry  andesite  covered  by  sedimentary  units  which  may  have  potential  of  mineral  occurrences, especially  porphyry copper. It is demonstrated that such structure extends down at depth, and consequently exploratory drilling is highly recommended for acquiring more pieces of information about its potential for ore-bearing mineralization.

The High-Frequency Decay Slope of Spectra (Kappa) for M≥3.5 Earthquakes on Rock Sites in Eastern and Western Canada

2020 ◽  
Vol 110 (2) ◽  
pp. 471-488 ◽  
Author(s):  
Samantha M. Palmer ◽  
Gail M. Atkinson
Keyword(s):  
Ground Motion ◽  
Classical Method ◽  
Vertical Component ◽  
Western Canada ◽  
S Wave ◽  
Motion Modeling ◽  
Eastern Canada ◽  
General Observation ◽  
Anelastic Attenuation ◽  
Two Parameters

ABSTRACT Spectral decay of ground-motion amplitudes at high frequencies is primarily influenced by two parameters: site-related kappa (κ0) and regional Q (quality factor, inversely proportional to anelastic attenuation). We examine kappa and apparent Q-values (Qa) for M≥3.5 earthquakes recorded at seismograph stations on rock sites in eastern and western Canada. Our database contains 20 earthquakes recorded on nine stations in eastern Canada and 404 earthquakes recorded on eight stations in western Canada, resulting in 105 and 865 Fourier amplitude spectra, respectively. We apply two different methods: (1) a modified version of the classical S-wave acceleration method; and (2) a new stacking method that is consistent with the use of kappa in ground-motion modeling. The results are robust with respect to the method used and also with respect to the frequency band selected, which ranges from 9 to 38 Hz depending on the region, event, and method. Kappa values obtained from the classical method are consistent with those of the stacked method, but the stacked method provides a lower uncertainty. A general observation is that kappa is usually larger, and apparent Q is smaller, for the horizontal component in comparison to the vertical component. We determine an average regional κ0=7  ms (horizontal) and 0 ms (vertical) for rock sites in eastern Canada; we obtain κ0=19  ms (horizontal) and 14 ms (vertical) for rock sites in western Canada. We note that kappa measurements are quite sensitive to details of data selection criteria and methodology, and may be significantly influenced by site effects, resulting in large site-to-site variability.

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