Geomagnetic activity and variations of the geomagnetic field
The Department of Geomagnetism runs the Geomagnetic Observatory ESI SAS in Hurbanovo. Since 1997, the Observatory has been a member of INTERMAGNET, the global network of observatories. Within the scope of the observatory research also the distribution of the geomagnetic field in the territory of Slovakia is investigated. The research into geomagnetic activity is focused on modeling of the geomagnetic activity associated with various phenomena that take place in the interplanetary space.
Paleomagnetic Research
Paleomagnetic research focuses mainly on geodynamic, palaeogeographic and magnetostratigraphic studies of the Western Carpathian tectonic units in close co-operation with foreign research groups mainly from Hungary, Poland, Czech Republic and Belgium. Archeomagnetic research has also been performing on several archeological localities in Slovakia and Czech Republic, aiming to date most precisely individual archeological artifacts, especially pottery, bricks from pottery kilns, and ancient fireplaces.
Origin of cosmic magnetic fields
Theoretical research devoted to possible processes of cosmic magnetic fields generation and their variations. Rapidly rotating cosmic bodies possess magnetic fields which are considered to be generated in liquid, electrically conductive parts of these bodies. Dynamics of such complex systems is manifested by variations of magnetic fields on the surface of a body. By solving the corresponding physical equations under some presumed conditions, particular mechanisms as causes of these changes can be inferred.
Rotating magnetoconvection; anisotropic diffusivities influence
Research devoted to the influence of anisotropy of thermal diffusivity and viscosity on the models of rotating magnetoconvection in the horizontal plane layer. Various models of rotating plane layer are investigated, where the layer rotates around the horizontal axis in the x-direction (H-case) or around the vertical axis in the z-direction (V-Case). The layer is permeated with a homogeneous magnetic field in the horizontal y-direction. The layer is heated from below and cooled from above and a uniform temperature gradient is sustained. The instabilities, i.e. stationary and/or nonstationary convection, are investigated in the form of horizontal rolls. The critical parameters of the onset of the convection are searched for by linear stability analysis. The stabilising or destabilising effects of the anisotropy of diffusive coefficients at the onset of the convection are investigated.
Dynamics of the Earth's Core
The core of the Earth is at least partially molten. We study how the molten part of the Earth's core solidified from the centre outwards. At the solidification front (outer/inner core boundary), some of the alloy elements are incorporated into the solid inner core while others are expelled into the liquid outer core. Compositional convection is generated because the density of the released fluid is lower than that of the melt. The strength of compositional convection has an impact on the strength of the Earth's magnetic field. Our focus is on a systematic study of diffusive and convective dynamics of multicomponent systems with the aim to understand their role in planetary magnetic field generation.
The Earth's Crust and Upper Mantle
Electromagnetic methods significantly contribute to understanding and exploring processes in the Earth's Crust and Upper Mantle. The group contributes to research related to tectonic and geodynamic processes particularly in the Carpatho-Pannonian region or continent-continent collision areas in south Asia. The research group applied the results from shallow structures investigation to the research into strategic energy and mineral resources assessment. Electromagnetic methods allow the characterization and identification of the spatial distribution of the physical parameters of the geological structures based on electrical conductivity, particularly for structures with high conductivity contrast. They are used for mapping of sedimentary basins and fluids (geothermal water aquifers), active and passive faults and fractures, and for description of porosity and permeability, i.e. transport properties, of the rocks.
Integrated modeling of the crustal structures
An interpretation of the crustal structure of the Western Carpathians using the combined modeling of geophysical and tectonic data. New modeling of magnetotelluric data measured in several profiles. Use of gravimetric, magnetic and seismic data for integrated geophysical modeling. Interpretation of a deep structure based on the General geological map of the Slovak Republic, scale 1: 200 000. Identification of major tectonic fault zones and areas with anomalous manifestations of the geophysical field. Geological interpretation of the geophysical anomalies.
Radon
Radon (222R) is the most important source of ionizing radiation among natural radionuclides. Investigation of radon activity concentration is performed both in the atmosphere and water. The research is realized in a natural environment (caves, galleries, boreholes) and in dwellings. Measurements are performed continually, as well as by integrating methods and grab sampling. In data series recorded during long-time continual monitoring the influence of meteorological conditions on daily, multi-day and annual radon variations is evaluated.
Spatial and temporal variations of the geomagnetic activity
Written by : Vladimir Pohanka | Published in: Geomagnetic field |Spatial and temporal variations of the geomagnetic activity as seen by an observer from outer space
Vladimír Pohánka and Fridrich Valach
The magnetic field which is observed by the geomagnetic observatories located on the Earth's surface (let us call it the geomagnetic field) is not invariable. It shows temporal as well as spatial variations. To understand these variations, one must consider some knowledge about the sources of the magnetic field - there are several of them:
(1) The main part of the geomagnetic field is produced in the molten, liquid and highly conductive Earth's core. Here the relevant processes are described by the physical theory which is called magnetohydrodynamics. This field changes slowly, the corresponding time scales are years, centuries, even millenia.
(2) Another source of the geomagnetic field is presented by magnetic rocks in the Earth's crust, for instance by well known magnetite. Neither this component of the geomagnetic field can change quickly.
(3) Finally,certain part of the observed geomagnetic field originates in the near-Earth space environment. It is generated by current systems flowing in the conductive part of the Earth's atmosphere - ionosphere; for instance, complex systems of electric currents exist in auroral regions. Important are also the magnetic fields that are caused by electric currents in magnetosphere - both in inner magnetosphere and in the distant magnetospheric tail. The processes in the near-Earth space environment are very dynamic and they are driven by explosive processes that take part in the solar atmosphere and in the
interplanetary space (e.g. coronal mass ejections and co-rotating interactive regions).
These changes of the geomagnetic field may seriously affect the life on the Earth: in the past, the violent changes of the geomagnetic field already inflicted a lot of damage. Examples are wide-area failures of the electricity supply lasting for hours; these were caused by melting the windings in saturated transformers by geomagnetically induced currents (GICs). Reported were also fires at telegraphic stations that were set by the GICs. For our modern society, which is immensely dependent on the vulnerable technological systems, the extreme magnetic storms represent the hazard that might cause even more severe damage.
We are not able to see the above mentioned temporal and spatial changes of the geomagnetic field by own eyeball. We can just directly see auroras, which are related to these changes indirectly. The aim of this short paper is to visualise the Earth magnetic field and its changes over the whole Earth surface.
MT measurements - Vysoké Tatry 2016
Written by : Dusan Bilcik | Published in: Magnetotelluric measurements |
In the period 17/09 - 24/09/2016 additional magnetotelluric measurements were carried out on the selected positions in Belianske Tatras and Spišská Magura mountains.
These measurements were accomplished in the framework of bilateral cooperation with Geophysical Institute of the Czech Academy of Sciences.
Understanding 1D magnetotelluric apparent resistivity and phase
Written by : Alexandra Marsenić | Published in: Magnetotelluric measurements |
This study represents a new view on the 1D magnetotelluric problem on a layered half-space. Emphasis is put on the physical aspect of the matters. No wave effects are allowed and the electric field undergoes subsequent decay with the rate depending on the conducting properties of the subsurface. It is also claimed that the magnetic field inside a layer is produced by local currents according to Ampère’s law. The presented analysis led to explicit formulas for apparent resistivity and impedance phase – the key characteristics of the magnetotelluric research – as functions of frequency. This is significant because understanding of these behaviours can help in interpretation of measured data – in other words, it can help to "read" the sounding curves. It is shown that as to how the apparent resistivity reacts on a change in local resistivity by increase or decrease, the impedance phase reacts on the same factor by change of its curvature. This finding is a base for design of a straightforward method to recover physical parameters of the model. Once properties of the sounding curves are known, the layered half-space in question can be easily reconstructed.
Computed apparent resistivity and phase difference between the electric and magnetic fields for Half-space 1 consisting of 3 layers (1000 m, 100 Ωm; 3000 m, 1000 Ωm; 2000 m, 10 Ωm) and substratum (100 Ωm). The violet curves are obtained by using Wait’s recursion formula, the green ones are obtained by explicit formulas as the results of this study. The presented dependences embody abrupt changes which reflect sharp transitions in physical conditions on interfaces between the layers whose resistivities are marked in orange. The smooth recursive solution provides a basis for validation of the present approach.
Measurements of radon activity in houses
Written by : Iveta Smetanová | Published in: Radon activity measurements |Exposure to radon gas in the home accounts for about half of all non-medical exposure to ionizing radiation. Indoor radon activity concentration (RAC) depends on many factors, for example building material, local geology, design of a house, ventilation, and contact of a room with the subsoil.
According to the Regulation from the Ministry of Health SR No. 528/ 2007, an action level 400 Bq/m3 is recommended for an annual average RAC for existing residential buildings and 200 Bq/m3 for new and reconstructed residential buildings. A reference level recommended by the Council Directive 2013/59/EURATOM is 300 Bq/m3 in average per year.
Integration measurement of indoor RAC in houses was performed from March 2012 to February 2013 in the framework of the project “Harmonization of determining the radiation dose of the population originating from radon in V4 countries”. The objective of the project was to elaborate a common measurement protocol of the Visegrad countries for the measurement of indoor radon (222Rn) and thoron (220Rn) concentration (the placement of detectors, type of detectors, questionnaire).
In Slovakia, the radon survey was performed in three localities: Záhorská Bystrica, Ružomberok and Mochovce are (Nevidzany and Čifáre). Fours sets of passive alpha track detectors Raduet (Radosys, Hungary) were used, sets were replaced after three months of exposure to compare the changes in RAC activities during the year. Two detectors were placed in a house, preferably in rooms on the ground floor in which the inhabitants spent the most of their time.
Indoor RAC in selected houses ranged (40-740) Bq/m3 in average per year. In 66 % of monitored rooms the average RAC per year was less than 200 Bq/m3. However, in 10 % RAC exceeded 400 Bq/m3. Increased radon levels in houses without a cellar were confirmed. The seasonal variation of RAC with the minimum in summer and maximum in winter months was observed, probably due to the intensive ventilation of a room in the summer season.
Paleomagnetic research of the Central Western Carpathians
Written by : Jozef Madzin | Published in: Paleomagnetism |During the ongoing project APVV-0212-12 „TRANSFER“, a detailed structural research has been performed as well as more than three hundred individually drilled and oriented samples were taken from the Hronic Unit which forms the highest cover nappe system of the Central Western Carpathians. The paleomagnetic study involved Permian volcanic rocks of the Ipoltica Group from the Malé Karpaty Mts. and Nízke Tatry Mts. and Triassic carbonate sediments from the latter. Demagnetisation, standard paleomagnetic and anisotropy of magnetic susceptibility (AMS) measurements were carried out in three laboratories (Modra, Budapest and Warsaw).
For most localities statistically well-defined paleomagnetic directions were obtained which significantly differ from the local direction of the present Earth magnetic field, indicating long-term stability of the paleomagnetic signal. The general picture outlined by the tilt corrected paleomagnetic vectors is moderate to large clockwise (CW) rotation with respect to the present orientation.
The Permian localities exhibit much larger CW rotations in the western and eastern part of the study area than from the localities in-between. This can be attributed to differencial movements during nappe transport or post-emplacement disturbance. The possibility of complete remagnetisation can also not be excluded.
The younger Triassic localities yielding quite good results of moderate CW rotation represent only a limited area, so sampling of more geographically distributed localities are needed to prove their tectonic significance.
Paleomagnetic sampling of the Upper Eocene sediments of the
Central Carpathian Paleogene Basin at Kvacianka stream in Orava area.
During the summer 2016 we also sampled Upper Eocene sediments of the Central Carpathian Paleogene Basin (CCPB), at two localities in Liptov and Orava area, which directly cover the Hronic nappe system. The obtained paleomagnetic vectors, after tectonic corrections, exhibit large counterclockwise (CCW) rotations similar to the published paleomagnetic studies performed on the equivalent sediments of the CCPB from the Levoča Mts. and Podhale Basin in Poland.