Geomagnetic Field Variations Research Articles

From empirical considerations to absolute ages: How geomagnetic field variation may date Teotihuacan mural paintings

Teotihuacan, the most important city of the Americas during the Classic period, developed a deep and complex civilization without any written histories. This millennial culture mostly used pictorial forms of visual communication expressed in numerous mural paintings. Thus, the knowledge of the absolute chronology of some of the most important mural arts is of great importance. Here, we report a comprehensive magnetic survey on two major murals of Palace of Quetzalcoatl, which represent an initial stage of the Teotihuacan archaeology. The magnetic mineralogy of sampled murals is dominated by both magnetite and hematite grains. The contribution of hematite, however, seems to be minor in the Pictorial Remanent Magnetization. Characteristic remanence was successfully isolated for 11 out of 16 analyzed samples belonging to both paintings. Archaeomagnetic dating was achieved using magnetic inclination and declination, yielding an interval between 312 CE and 409 CE as the best estimate of the time of painting of the murals. This study reinforces the early hypothesis that, red color mural paintings may be considered a complementary source of information about the secular variation of the Earth’s Magnetic Field.

Ground-based Observations of the Polar Region Space Environment at the Jang Bogo Station, Antarctica

Jang Bogo Station (JBS), the second Korean Antarctic research station, was established in Terra Nova Bay, Antarctica (74.62°S 164.22°E) in February 2014 in order to expand the Korea Polar Research Institute (KOPRI) research capabilities. One of the main research areas at JBS is space environmental research. The goal of the research is to better understand the general characteristics of the polar region ionosphere and thermosphere and their responses to solar wind and the magnetosphere. Ground-based observations at JBS for upper atmospheric wind and temperature measurements using the Fabry-Perot Interferometer (FPI) began in March 2014. Ionospheric radar (VIPIR) measurements have been collected since 2015 to monitor the state of the polar ionosphere for electron density height profiles, horizontal density gradients, and ion drifts. To investigate the magnetosphere and geomagnetic field variations, a search-coil magnetometer and vector magnetometer were installed in 2017 and 2018, respectively. Since JBS is positioned in an ideal location for auroral observations, we installed an auroral all-sky imager with a color sensor in January 2018 to study substorms as well as auroras. In addition to these observations, we are also operating a proton auroral imager, airglow imager, global positioning system total electron content (GPS TEC)/scintillation monitor, and neutron monitor in collaboration with other institutes. In this article, we briefly introduce the observational activities performed at JBS and the preliminary results of these observations.

Effects Stimulated by Radiation of the SURA Facility in the Geophysical Experiments Program at the International Space Station in 2017

The set of experiments in 2017 included the forecasting of geo- and heliophysical conditions in the ionosphere, the choice of heating regimes at a minimum critical frequency of the F2 ionospheric layer, analysis of the ionosphere radio sounding results and measurements of geomagnetic perturbations using ground-based facilities, study of the potential for higher efficiency and probability of artificial effects on the ionosphere, and the establishment of a correlation between geomagnetic field variations and the radio heating facility cyclogram. The experiments were carried out with a combination of new heating conditions (pulse ratio, period of action, two-frequency and continuous heating, variations in radiated power, polarization, shortwave radiation direction, etc.) in the intervals between recurrent magnetic storms. Geomagnetic field pulsations (in accordance with the cyclogram) and substorm effects were stimulated by the SURA facility against a background of quiet geophysical conditions.

Crustal geomagnetic field and secular variation by regional and global models for Austria

Abstract Using 12-year-long series of data (2001-2012) from geomagnetic observatories and repeat stations in Austria and its neighboring countries, a regional spatial-temporal (ST) model is developed based on the polynomial expansion consisting of latitude, longitude, and time of the geomagnetic field components and total magnetic field F. Additionally, we have used three different global models (CHAOS-5, POMME-9, and EMM2015), which are built on spherical harmonics up to a maximum degree Lmax and give the core field and crustal field separately. The normal field provided by the ST model and its “model bias”, which comprise the residuals of the differences between measured and predicted values, are calculated and the respective maps are shown. The residuals are considered an estimate of the local crustal field. In the case of global models, we have applied for each of these three methods to calculate the “model bias”: residuals of the differences between observed values and predicted values of the model, residuals of the differences between observed values and core field values of the model, and the average bias for the period 2001-2012. The normal field of the region of Austria provided by each global model is also calculated. Generally, the regional and global models yield relatively similar crustal fields for the Austrian region, especially when the first method is used. The normal fields calculated by them are in good agreement with each other. Each of the global models directly provides the crustal field, and they are compared with the aeromagnetic data provided by aeromagnetic surveys over the Austrian region. The ST model is in better agreement with aeromagnetic data. We have also analyzed the secular variation over the region, which is calculated from the rate of change of normal field given by the ST and global models.

Field Validation of a Magnetic Sensor to Monitor Borehole Deviation during Tunnel Excavation.

In this article, a magnetic sensor is proposed to monitor borehole deviation during tunnel excavation. It is made by piling four super-strong N42 NdFeB cylinder magnets and then encasing them in an aluminum alloy hollow cylinder. The distribution of the magnetic field produced by the magnetic sensor and its summation with the geomagnetic field (GMF) in a global coordinate system are derived based on the theory of magnetic fields. An algorithm is developed to localize the position of the magnetic sensor. The effect of the GMF variation on the effective monitoring range of the magnetic sensor is also studied numerically. Field validation tests are conducted at Jinzhai Pumped-Storage hydroelectric power station, during the excavation of an inclined tunnel in Anhui Province of China. Test results show that the algorithm and the magnetic sensor are used successfully to detect the deviation of the borehole with an estimated error of approximately 0.5 m. The errors are mainly from the measurement errors of the coordinates, of both the test and the measurement points. The effective monitoring range of the magnetic sensor is dependent on the direction of the magnetic sensor as well as the variation of the GMF.

A Comparison of Model‐Based Ionospheric and Ocean Tidal Magnetic Signals With Observatory Data

AbstractObserved tidal geomagnetic field variations are due to a combination of electric currents in the ionosphere, ocean, and their induced counterparts. Using these variations to constrain subsurface electrical conductivity in oceanic regions is a promising frontier; however, properly separating the ionospheric and oceanic tidal contributions of the magnetic field is critical for this. We compare semidiurnal lunar tidal magnetic signals (i.e., the signals due to the M2 tidal mode) estimated from 64 global observatories to physics‐based forward models of the ionospheric M2 magnetic field and the oceanic M2 magnetic field. At ground level, predicted ionospheric M2 amplitudes are strongest in the horizontal components, whereas the predicted oceanic amplitudes are strongest in the vertical direction. There is good agreement between the predicted and estimated M2 phases for the Y component; however, the F and X components experience deviations that may be indicative of unmodeled ionospheric processes or unmodeled coastal effects. Overall, we find that the agreement between the physics‐based model predictions and the observations is very encouraging for electromagnetic sensing applications, especially since the predicted ionospheric vertical component is very weak.

Geomagnetic Field Variations During Solar Eclipses and the Geographic Location of Observing Sites

Geomagnetic Field Variations During Solar Eclipses and the Geographic Location of Observing Sites

Possible Effect of Stratospheric QBO on The Ionospheric E-Region Current Densities

It is known that ionospheric winds cause the ions to drift in the geomagnetic field. This drift set up a current which produces ground-level geomagnetic field variations.  In this study, the relationship between stratospheric QBO and the ionospheric E- region current densities (Jx and Jy) for low latitudes (01.22 N, 103.55 E) have been statistically investigated using the multiple regression model.  Also the effect of F10.7 solar flux index was included in the investigation.  As a result of the investigation using the multiple regression model, it was determine that an increase/a decrease of 1 s.f.u in the F10.7 solar flux caused an increase/a decrease of 1.5x10-2 A/km and 2.5x10-2 A/km on Jx and Jy current density, respectively. On the other hand, an increase/ a decrease of 1 m / s in the QBO caused a decrease/ an increase of 3x10-3 A/km and 4x10-3 A/km on Jx and Jy current densities, respectively.
 

Effect of geomagnetic storms on VHF scintillations observed at low latitude

A geomagnetic storm affects the dynamics and composition of the ionosphere and also offers an excellent opportunity to study the plasma dynamics. In the present study, we have used the VHF scintillations data recorded at low latitude Indian station Varanasi ($$\hbox {Geomag. latitude}\,=\,14^{^{\circ }}55^{\prime }$$N, long. = $$154^{^{\circ }}\hbox {E}$$) which is radiated at 250 MHz from geostationary satellite UFO-02 during the period 2011–2012 to investigate the effects of geomagnetic storms on VHF scintillation. Various geomagnetic and solar indices such as Dst index, Kp index, IMF Bz and solar wind velocity (Vx) are used to describe the geomagnetic field variation observed during geomagnetic storm periods. These indices are very helpful to find out the proper investigation and possible interrelation between geomagnetic storms and observed VHF scintillation. The pre-midnight scintillation is sometimes observed when the main phase of geomagnetic storm corresponds to the pre-midnight period. It is observed that for geomagnetic storms for which the recovery phase starts post-midnight, the probability of occurrence of irregularities is enhanced during this time and extends to early morning hours.

Methodology of Individual Brain Activity Monitoring in Interrelations with Geomagnetic Field Variations in the Arctic

Methodology of Individual Brain Activity Monitoring in Interrelations with Geomagnetic Field Variations in the Arctic

Electrical Conductance Map for Saurashtra Region, Gujarat, India

In the present study, we have deployed 35 fluxgate magnetometers and 20 long-period magnetotelluric sites to derive the electrical conductivity distribution of Saurashtra region, Gujarat, India. Geomagnetic field variations (X-north–south, Y-east–west and Z-vertically downward components) recorded at the above sites are investigated to obtain single-station vertical field transfer functions. Maps of induction arrows suggest that the offshore basins are more conducting than inland basins of the region. Thin sheet modelling of the induction features suggests that the anomalous behaviour is strongly influenced by the offshore and shelf edge sedimentary basins that contain thick depo centres of Mesozoic sediments. Jamnagar, Ulva and Mesozoic sedimentary basins on land are also reflected as high conductivity anomalies that could be related to the presence of carbonate/shale sediments. Release of carbon (in the form of thin films) due to thermal activity of Reunion hotspot on carbonate rich sediments may give rise to high conductivity anomalies.

Variability of Geomagnetic Field with Interplanetary Magnetic Field at Low, Mid and High Latitudes

The fluctuations in the Interplanetary Magnetic Field significantly affect the state of geomagnetic field particularly during the Coronal Mass Ejection (CME) events. In the present investigation we have studied the influence of Interplanetary Magnetic Field changes on the geomagnetic field components at high, low and mid latitudes. To carry out this investigation we have selected three stations viz. Alibag (18.6°N, 72.7°E), Beijing MT (40.3°N, 116.2°E) and Casey (66.2°S, 110.5°E) one each in the low, mid and high latitude regions. Then we selected geomagnetic storm events of three types namely weak (-50≤Dst≤-20), moderate (100≤Dst≤-50) and intense (Dst≤-100nT). In each storm category 10 events were considered. From our study we conclude that geomagnetic field components are significantly affected by the changes in the IMF at all the three latitudinal regions during all the storm events. At the same time we also found that the magnitude of change in geomagnetic field components is highest at the high latitudes during all types of storm events while at low and mid latitude stations the magnitude of effect is approximately the same.

Mathematical Simulation of Convective Processes in the Liquid Core of the Earth and Implications for the Interpretation of Geomagnetic Field Variations in Polar Latitudes

The flow structure induced by thermal convection in a rotating spherical shell with viscous boundary conditions is considered under the assumption that the differential rotation of the core relative to the mantle is absent. The radial, azimuthal, and meridional components of the flow’s velocity and helicity are studied. With the magnetic field assumed to be frozen into a liquid (frozen-flux hypothesis), it is shown that the numerical results fit the observations of the geomagnetic field variations close to the pole.

Geomagnetic field variations observed by INTERMAGNET during 4 total solar eclipses

We investigate variations of the geomagnetic field observed by INTERMAGNET geomagnetic observatories over which the totality path passed during a total solar eclipse. As a result, we have presented results of examining the geomagnetic field data observed by 6 geomagnetic observatories during the 4 total solar eclipses (11 August 1999, 1 August 2008, 11 July 2010, and 20 March 2015). These total solar eclipses are the only total solar eclipse, since 1991 when the INTERMAGNET began to work, during which the umbra of the Moon swept an INTERMAGNET geomagnetic observatory and simultaneously variations of the geomagnetic field are recorded at the geomagnetic observatory. We have confirmed previous reports that, at least on average, during the solar eclipse characteristic increase of Y component of the geomagnetic field Y and decreases of X,Z and F are conspicuous. Interestingly, we have noted that variations of X,Y,Z and F observed during the total solar eclipse at Isla de Pascua Mataveri (Easter Island) in Chile (IPM) in the southern hemisphere show distinct decrease of Y and increases of X and Z on the contrary. We have found, however, that variations of X,Y,Z and F observed at Hornsund in Norway (HRN) at 77°N in latitude seem to be dominated by other geomagnetic occurrence since the solar activity is near maximum, and the geomagnetic field is disturbed on the day of eclipse. We further discuss a possibility of exploring an effect of the solar eclipse on the amplitude of harmonic components of the geomagnetic field using the wavelet analysis technique, which has revealed suppression in the amplitude during the middle of a solar eclipse. Finally, we conclude by discussing implications of what we have found.

Variações de intensidade do campo geomagnético em Santa Maria (Brasil) para os últimos 3 mil anos

Earth magnetic field variations at secular scales and at hundred quilometers have internal origin at the outer core. The most important feature associated with this internal field is the South Atlantic Magnetic Anomaly (SAMA), which covers the South America and it is characterized by the lowest total field intensity at the surface. Here, we investigate the geomagnetic field variations in Santa Maria (Brazil) over the past 3 ka. Results indicate that the intensities observed in Santa Maria are the lowest of the geomagnetic field over the past 3 ka. The consequences of these field features could be the increase in the electrically charged particles reaching the low Earth atmosphere that may generate problems in the communications systems or climate changes.

Magnetospheric Effects during the Approach of the Chelyabinsk Meteoroid

We have analyzed the observational results for variations in the main geomagnetic field and its fluctuations in the range of periods 1–1000 s that accompanied the approach of the Chelyabinsk space body to the magnetosphere and ionosphere of the Earth. The measurements were conducted with a magnetometerfluxmeter near the city of Kharkiv, as well as with the network of magnetometers located at the observatories of Novosibirsk, Kyiv, Lviv, Almaty, Khabarovsk, Arti, Borok, and Yakutsk. Variations in the main geomagnetic field and its fluctuations approximately 33–47 min prior to the explosion of the Chelyabinsk meteoroid have been discovered; they persisted for 25–35 min and were probably associated with meteoroid passage through the magnetosphere. The amplitude of variations reached 1–6 nT. We have proposed a model of the generation of aperiodic, quasi-periodic, and noise-like variations in the geomagnetic field induced by the approach of a space body.

On the Occurrence of Afternoon Counter Electrojet Over Indian Longitudes During June Solstice in Solar Minimum

AbstractStudies made earlier using ground‐based observations of geomagnetic field over the Indian longitudes revealed that the occurrence of equatorial counter electrojet (CEJ) events in afternoon hours is more frequent during June solstice (May‐June‐July‐August) in solar minimum than in other periods. In general, the June solstice solar minimum CEJ events occur between 1500 local time (LT) and 1800 LT with peak strength of about −10 nT at around 1600 LT. In order to understand the frequent occurrence of these CEJ events, an investigation is carried out using an equatorial electrojet model (Anandarao, 1976, https://doi.org/10.1029/GL003i009p00545) and the empirical vertical drift model by Fejer et al. (2008, https://doi.org/10.1029/2007JA012801). The strength, duration, peak value, and the occurrence time of CEJ obtained using electrojet model match remarkably well with the corresponding observation of average geomagnetic field variations. The occurrence of CEJ is found to be due to solar quiet (Sq) electric field in the westward direction which is manifested as downward drift in Fejer et al. (2008, https://doi.org/10.1029/2007JA012801) model output during 1500–1800 LT. Further, the occurrence of afternoon reversal of Sq electric field in this season is shown to be consistent with earlier studies from Indian sector. Therefore, this investigation provides explicit evidence for the role of westward Sq electric field on the generation of afternoon CEJ during June solstice in solar minimum periods over the Indian sector indicating the global nature of these CEJ events.

Ionospheric Conductance Spatial Distribution During Geomagnetic Field Reversals

AbstractThe conductivity of the ionosphere is extremely important in geophysical processes and plays a critical role in magnetosphere‐ionosphere‐thermosphere coupling. Understanding its nature is essential to understand the physics of ionospheric electrodynamics. Earth's magnetic field, which varies greatly in geological time scales, is among the main variables involved in ionospheric conductivity. The present field can be approximated by a magnetic dipole that accounts for ~80% of the magnetic field at the Earth's surface, plus multipolar components making up the remaining ~20%. During a polarity transition the field magnitude diminishes to about 10% of its normal value at the expense, most likely, of decreasing the dipolar component and becoming mostly multipolar in nature. The effects of geomagnetic field variations on the spatial structure of Hall and Pedersen conductances are analyzed in the present work considering some possible reversal scenarios. The spatial structure of both conductances changes significantly with sharp spatial gradients. The conductivity peak heights also change, moving to upper heights as expected for weaker field configurations.

Advances in Residential Design Related to the Influence of Geomagnetism.

Since the origin of the Modern Movement, there has been a basic commitment to improving housing conditions and the well-being of occupants, especially given the prediction that 2/3 of humanity will reside in cities by 2050. Moreover, a compact model of the city with tall buildings and urban densification at this scale will be generated. Continuous constructive and technological advances have developed solid foundations on safety, energy efficiency, habitability, and sustainability in housing design. However, studies on improving the quality of life in these areas continue to be a challenge for architects and engineers. This paper seeks to contribute health-related information to the study of residential design, specifically the influence of the geomagnetic field on its occupants. After compiling information on the effects of geomagnetic fields from different medical studies over 23 years, a case study of a 16-story high-rise building is presented, with the goal of proposing architectural design recommendations for long-term occupation in the same place. The purpose of the present work is three-fold: first, to characterize the geomagnetic field variability of buildings; second, to identify the causes and possible related mechanisms; and third, to define architectural criteria on the arrangement of uses and constructive elements for housing.

Statistical analysis of geomagnetic field variations during solar eclipses

We investigate the geomagnetic field variations recorded by INTERMAGNET geomagnetic observatories, which are observed while the Moon’s umbra or penumbra passed over them during a solar eclipse event. Though it is generally considered that the geomagnetic field can be modulated during solar eclipses, the effect of the solar eclipse on the observed geomagnetic field has proved subtle to be detected. Instead of exploring the geomagnetic field as a case study, we analyze 207 geomagnetic manifestations acquired by 100 geomagnetic observatories during 39 solar eclipses occurring from 1991 to 2016. As a result of examining a pattern of the geomagnetic field variation on average, we confirm that the effect can be seen over an interval of 180 min centered at the time of maximum eclipse on a site of a geomagnetic observatory. That is, demonstrate an increase in the Y component of the geomagnetic field and decreases in the X component and the total strength of the geomagnetic field. We also find that the effect can be overwhelmed, depending more sensitively on the level of daily geomagnetic events than on the level of solar activity and/or the phase of solar cycle. We have demonstrated it by dividing the whole data set into subsets based on parameters of the geomagnetic field, solar activity, and solar eclipses. It is suggested, therefore, that an evidence of the solar eclipse effect can be revealed even at the solar maximum, as long as the day of the solar eclipse is magnetically quiet.