Space-temporal characteristic of the magnetic field of the Ukraine

Paper type: 
Oral presentation

SPACE-TEMPORAL CHARACTERISTIC OF THE MAGNETIC FIELD OF THE UKRAINE

M.I.Orliuk, A.O.Romenets, Yu.P. Sumaruk, T.P.Sumaruk

Institute of Geophysics of the National Academy of Sciences of the Ukraine, Kyiv

orlyuk@igph.kiev.ua;  sumar@mail.lviv.ua

 

The Earth’s magnetic field (EMF)is one of the principal geophysical factors concerning the processes in a different planet covers and the planet in whole. Numerous phenomena in magnetosphere, ionosphere, atmosphere and biosphere are due to the magnetic field state as well as to the geomagnetic activity. Space-temporal structure of the Earth’s magnetic field B is defined by field total from different sources:

B= Bn+ Bа+ Be+δBv

whereBnis the Earth’s normal main field that is generated by the processes in the liquid core and at the border with the mantle and that is defining global space and temporal structure of the planet field; Bаis the anomalous magnetic field (lithospheric one) that is due generally to the rocks magnetization; Beis the external field that is due to the influence of solar and cosmic radiation as well as to the Sun magnetic field and circumterrestrial space;δBvis the variations field.

Geomagnetic anomaly of the total scalar ∆Bof the territory of the Ukraine has a very complex character (after the data of surface and airborne survey). Anomalies sizes and intensities are depending on the geological structure of the Earth crust and on the magnetic sources.

Continuous registration of the EMF induction as well as of the induction of northernВх,  eastern Вуand vertical Вzcomponentsis carrying out by magnetic observatories (MO). On the territory of the Ukraine during long period of time there are three MO: Kiev(KIV), Lviv (LVV) and Odessa(ODE). After the survey data it is shown that the principal changes have place in the main EMF, especially for the territory of the Ukraine the value is upon the averageВ=1200 nТfor the last 50 years. We used this field with aim to evaluate the magnetizingeffect in the magnetic field secular variations(BSV).   

Magnetic field secular variationsBSV  are defined as a difference between successive average annual values of three orthogonal components and total intensity of the geomagnetic field that is observed uninterruptedly by MO. Calculating those differences it is assumed that the variations with the periods less that one year and that are generated by external sources are excluded automatically. However the variations of the geomagnetic field generated by the ring magnetic current that are reflected in the horizontal(δВН) and vertical(δВz) field components are of the same sign. Therefore during magnetically active years δВН-component is always smaller and δВz-component is bigger than in the quiet years. The same effect is produced by the solar-dayvariation δВs. Under the influence of the external sources the secular variations BSVobtained by average annual values will have the components connected with solar activity and, correspondingly, with magnetic one.

Changing magnetic field from the external sources is induced by the currents in the main Earth’s layers whose magnetic field is overlapping the dipole field. So the average annual intensity values of the geomagnetic field and its components have (besides a dipole field) a contributions from external sources as well as from the magnetizingeffect and induction currents in the main layers of the Earth. A very actual goal is to disjoint field by components from every source.

Magnetic observatories of the Ukraine are placed in the regions with different geological structure that is reflected by the magnetic field intensity. MO “Kievis located in the region of weakly intensive Kiev regional magnetic anomaly ∆B= 85 nТ, MO “Lviv” on the periphery of the intensive Lviv anomaly∆B= 250 nТ, and MO “Odessa – in the gradient zone of Odessa anomaly ∆B= - 20 nТ. Thereby it follows to expect a different value of the Earth’s structure under the observatories.

To separate a component connected with external and internal sources, we need to subtract from average observatory annual field value its main part generated by currents at the core-mantle border. Main field value ВIGRFas well as the values of all EMF components were calculated from IGRF 1945-2010 Model Coefficients 2010.

It is necessary to divide the obtained difference into two parts: one from external magnetospheric and ionospheric currents, another from magnetization of the magnetic sources and currents in the cushion courses. External sources influence on the average annual values of the geomagnetic field is reflected best of all in the horizontal ВH-component, internal sources influence – in the vertical ВZand total fieldcomponent В.

Contribution of the external sources for all the observatories are evaluated by the difference of average annual values for all the days and by the quiet days (ВН– ВSq).

At present for MOs “Kiev”, “Lviv” and “Odesa” using a new criterion to estimate EMF disturbance the anomalies that occurred due to the magnetizingeffect in the anomalies BSVare calculated. They originated from the change of the rocks magnetizing field value. It follows from the supposition that in case the inductive component IiHis conditioning the total rocks magnetization the proportion ∆D= B/2Bn must be constant for any time interval. The calculations shown that this field component during last 50 years make: -0,75 nТ for MO “Odesa”, 2,25 nТ for MO “Kiev” and 6,3 nТfor MO “Lviv”.

Thus in the report the space-temporal structure of the EMF on the territory of the Ukraine during last 50 years is evaluated, the technique to define the contribution of external and internal sources in the secular variation anomaly is proposed as well as first numerous estimations after the data of the Ukrainian observatories are obtained.

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