Fridrich Valach

The intense magnetic storm of March 1918 as recorded by observatory Ógyalla (present day Hurbanovo)

This paper presents an analysis of the magnetic storm on March 8, 1918, on the basis of a preserved analogue magnetogram that was recorded by observatory Ógyalla, present day Hurbanovo. It is inferred that much of the spectacular phenomena that were attributed to this storm, such as effects in telegraph lines, were likely caused by rapid changes of the geomagnetic field during two consecutive substorms. The storm sudden commencement that preceded the magnetic storm was probably also potent in this regard. This supports the recent findings that argue against the inevitable major role of the ring current in extreme magnetic disturbances at mid latitudes.

Report on the magnetic survey in Slovakia for the 2014.5 epoch

Abstract The models of the distribution of the elements of the geomagnetic field must be updated regularly. For this purpose geomagnetic measurements have to be carried out repeatedly at geomagnetic observatories as well as at temporary observation points. In this paper the results of the geomagnetic survey that was carried out in Slovakia in the year 2014 are presented. The measurements were performed at 12 observation points and they were reduced to the 2014.5 epoch. The secular variation between 2007.5 and 2014.5 was also calculated. The obtained values of the geomagnetic elements were used for calculating a 1st-degree polynomial model for the distribution of magnetic declination, inclination and total field. The comparison with the IGRF model showed that the polynomial model provided more accurate results for magnetic inclination and total field. For magnetic declination, on the contrary, the IGRF model produced slightly better results than the polynomial model.

Modeling of CME and CIR driven geomagnetic storms by means of artificial neural networks

Abstract A model of geomagnetic storms based on the method of artificial neural networks (ANN) combined with an analytical approach is presented in the paper. Two classes of geomagnetic storms, caused by coronal mass ejections (CMEs) and those caused by corotating interaction regions (CIRs), of medium and week intensity are subject to study. As the model input, the hourly solar wind parameters measured by the ACE satellite at the libration point L1 are used. The time series of the Dst index is obtained as the model output. The simulated Dst index series is compared with the corresponding observatory data. The model reliabilty is assessed using the skill scores, namely the correlation coefficient CC and the prediction efficiency PE. The results show that the model performance is better for the CME driven storms than for the CIR driven storms. At the same time, it appears that in the case of medium and weak storms the model performance is worse than in the case of intense storms

Substitution for lost one-hour means of the geomagnetic elements for the first half of the 20-th century at the Hurbanovo Geomagnetic Observatory by means of neural networks

Abstract The existence of long-acting observatories by itself does not guarantee that their historical magnetograms are available or complete. In the archive of the Hurbanovo Geomagnetic Observatory (acronym HRB; geographical coordinates 47.86 ◦ N, 18.19 ◦ E), records of the geomagnetic field made on photo paper covering the period between the two World Wars were found for which the values of the baselines are unknown. We studied if a feed-forward neural network with one hidden layer can be used to supplement one-hour means of the geomagnetic elements D, H and Z of observatory HRB, using for this purpose the geomagnetic data of observatories Potsdam, Seddin and Niemegk (all of them being referenced to Niemegk). We focused our interest on the first half of the 20-th century. The neural-network model for element D proved to be applicable to substitute for the lost data of the magnetic declination at observatory HRB; however, the usability of the model for both elements H and Z turned out to be limited to a few years close to beginning or end of data gaps. Further we supplemented the time series of annual means of geomagnetic elements D, H and Z at observatory HRB with the model data.

Magnetic ground survey of Slovakia for the 2007.5 epoch – accuracy of geomagnetic elements distribution maps

Abstract Magnetic ground or repeat station surveys are performed to determine the geomagnetic field (GMF) spatial distribution, which is of great importance for scientific purposes as well as for many applications, for instance the aerial navigation. In for the information about the GMF distribution to be complete, the accuracy of the geomagnetic maps need to be known. It is a custom in the papers dealing with magnetic surveys that the precision of the instruments employed for the measurements are listed there. However, such information is not sufficient to answer the question about the quality of the geomagnetic maps because our experience shows that the spatial variations at a distance of several kilometers often exceed the precisions of the instruments. In the paper we proposed a simple method for the evaluation of the accuracy of the GMF distribution maps. We applied it to the maps which were the results of the magnetic ground survey carried out in Slovakia in the 2007.5 epoch. The method is based on the following procedure which is accomplished for each observation point of the magnetic ground survey network: A single point drops out of the data base, then the map is generated in a standard way, whereupon the observed value of the geomagnetic element for the dropped out observation point is compared with the value of the geomagnetic element which is determined from the map. Thus the image of the accuracy of the complete map can be tagged together for the surveyed territory

New Slovak geomagnetic repeat station network

Six geomagnetic repeat stations were established over the territory of Slovakia. The locations of the observation points were chosen in a way to provide long time series of geomagnetic measurements at the same places (or nearly the same ones). Thus the series start in the middle of the 19th century. In this paper, the long time series of three geomagnetic elements D, H and I are reviewed. Results of the last geomagnetic measurements at the six observation points (reduced to the 2004.5 epoch) are presented and linear models of the distribution of geomagnetic elements and of their secular variations are shown.