Fridrich Valach

Fridrich Valach
Slovak Academy of Sciences | SAV · Earth Science Institute

PhD

About

46
Publications
4,963
Reads
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220
Citations
Additional affiliations
July 2015 - present
Earth Science Institute of the Slovak Academy of Sciences
Position
  • Researcher
August 1996 - June 2015
Geophysical Institute of the Slovak Academy of Sciences
Position
  • Researcher
Education
August 1996 - May 2000
Comenius University Bratislava
Field of study
  • Geophysics (Geomagnetism)
September 1990 - July 1992
Comenius University Bratislava
Field of study
  • Teacher education, Physics
September 1986 - July 1991
Comenius University Bratislava
Field of study
  • Solid state physics

Publications

Publications (46)
Article
Full-text available
Some recent studies point out that currents related to the auroral oval, electrojets and Field Aligned Currents (FACs), are serious candidates for the mechanism of the intense mid-latitude magnetic storms. It is interesting to re-analyse historical data under the light of this modern knowledge. In this aim, we analysed two intense magnetic storms t...
Article
Full-text available
Magnetic observations at the Clementinum Observatory were started in July 1839 and data up to 1917 were published in yearbooks. In addition to regular daily observations with a typical 2‐hr time step, two categories of data with a higher cadence were provided in the first decade. The first category captures 73 magnetic storms with their magnitude b...
Article
Full-text available
The historical magnetic observatory Clementinum operated in Prague from 1839 to 1926. The data from the yearbooks that recorded the observations at Clementinum have recently been digitized and were subsequently converted, in this work, into the physical units of the International System of Units (SI). Introducing a database of geomagnetic data from...
Preprint
Full-text available
The historical magnetic observatory Clementinum operated in Prague from 1839 to 1926. The data from the yearbooks that recorded the observations at Clementinum have recently been digitized and were subsequently converted in this work into the physical units of the International System of Units (SI). Introducing a database of geomagnetic data from t...
Book
Kniha vysvetľuje fyziku magnetických búrok a súvisiace procesy v blízkom kozmickom okolí Zeme. (Prvé vydanie.)
Conference Paper
Full-text available
ABSTRAKT In 2018, the geomagnetic field was measured at six observation points in Slovakia and the results were reduced to the epoch 2018.5. The reduction procedure was carried out utilising the data of the Hurbanovo Geomagnetic Observatory. The information about the geomagnetic elements D, I, and F (declination, inclination, and total field, respe...
Conference Paper
Full-text available
Owing to geomagnetically induced currents, extreme mid-latitude geomagnetic disturbances might cause serious damages to some vulnerable technological systems. A part of the space weather research has therefore to be focused on deeper understanding of the origins and mechanisms of these phenomena. In this study three cases of mid-latitude geomagneti...
Article
Full-text available
Records of the past geomagnetic field can be divided into two main categories. These are instrumental historical observations on the one hand, and field estimates based on the magnetization acquired by rocks, sediments and archaeological artefacts on the other hand. In this paper, a new database combining historical, archaeomagnetic and volcanic reco...
Poster
Full-text available
Recently, several geomagnetic storms were identified which probably do not conform with the conventional understanding of the dominant role of the ring current for the development of extreme magnetic disturbances. Some events of the most severe disturbances that were observed at mid-latitudes rather seem to be connected with the auroral currents th...
Article
The Dynamic Global Core Plasma Model (DGCPM) is an empirical dynamical model of the plasmasphere which, despite its simple mathematical form, or perhaps because of its simple mathematical form, has enjoyed wide use in the space physics modeling community. In this paper we present some recent observations from the European quasi-Meridional Magnetome...
Conference Paper
Full-text available
In this paper we investigate the differences between values of the geomagnetic field that were produced by the global geomagnetic model IGRF and the values that were obtained by direct measurements. The measurements were carried out at various observation points in Slovakia; therefore, the relation between the differences on one side and the distan...
Article
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...
Article
It is generally accepted that the geomagnetic K indices derived by experienced observers are of great value. The interactive method (IM) based on the traditional hand-scaling methodology is tested in this study. The tests are performed utilising the data from the Hurbanovo and Budkov magnetic observatories. These data include both digital records o...
Article
Full-text available
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...
Article
This paper reports on an interactive computer method for producing K indices. The method is based on the traditional hand-scaling methodology that had been practised at Hurbanovo Geomagnetic Observatory till the end of 1997. Here, the performance of the method was tested on the data of the Kakioka Magnetic Observatory. We have found that in some ra...
Article
Full-text available
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 in...
Conference Paper
Full-text available
Pokiaľ sme si vedomí, už dlhšiu dobu v slovenskej odbornej literatúre nebol publikovaný aktuálny prehľad o kozmickom počasí, ktorý by mohol slúžiť ako ucelený informačný zdroj pre študentov a vedeckých pracovníkov v oblasti geofyziky. Pritom problematika kozmického počasia v dnešnej technologicky vyspelej spoločnosti naberá na význame a potreba tak...
Article
A model to forecast one-hour lead Dst index is proposed. Our approach is based on artificial neural networks (ANN) combined with an analytical model of the solar wind-magnetosphere interaction. Previously, the hourly solar wind parameters have been considered in the analytical model, all of them provided by registration of the ACE satellite. They w...
Article
Full-text available
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...
Article
Full-text available
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...
Article
The paper deals with the relation of the southern orientation of the north-south component BzBz of the interplanetary magnetic field to geomagnetic activity (GA) and subsequently a method is suggested of using the found facts to forecast potentially dangerous high GA. We have found that on a day with very high GA hourly averages of BzBz with a nega...
Article
Solar energetic particle (SEP) modelling has gained great interest in the community, specifically in connection with the safety of crews and the protection of technological systems of spacecraft situated outside the shielding of Earth's magnetosphere. Two models for the prediction of SEP events are presented in this paper. The models are based on a...
Conference Paper
Full-text available
Our modern society with its advanced technology is becoming increasingly vulnerable to the Earth's system disorders originating in explosive processes on the Sun. Coronal mass ejections (CMEs) blasted into interplanetary space as gigantic clouds of ionized gas can hit Earth within a few hours or days and cause, among other effects, geomagnetic stor...
Article
Full-text available
A model of the magnetic storm of August 4, 2010, is presented in the paper. Simulated Dst index series is obtained from an empirical model of the solar wind magnetosphere interaction and is compared with real data. In broader context, the underlying study can be conceived as an example of the space weather modeling. A brief survey of the approaches...
Article
Full-text available
New geomagnetic ground survey was carried out in years 2006-2008. The survey was accomplished under fair geomagnetic-activity conditions during the minimum phase of a solar activity cycle No. 23. The measurements of the geomagnetic field were reduced to the 2007.5 epoch using magnetograms of the Hurbanovo Geomagnetic Observatory. The distribution o...
Article
Full-text available
Coronal mass ejections (CMEs) are believed to be the principal cause of increased geomagnetic activity. They are regarded as being in context of a series of related solar energetic events, such as X-ray flares (XRAs) accompanied by solar radio bursts (RSPs) and also by solar energetic particle (SEP) flux. Two types of the RSP events are known to be...
Article
Full-text available
A forecasting scheme of geomagnetic activity is presented, based on the analysis of the geoeffectiveness of X-ray flares, accompanied by Type II and/or Type IV radio bursts (RSP) observed on the solar disc in the years 1996–2004. The neural network was used to construct this scheme enabling us to determine the probability, with which flares will be...
Article
Full-text available
Data concerning solar energetic events, published in 1996–2004 by the USAF/NOAA in the form of daily reports, have been collected. The analysis of the particular event types indicates that the degree of their geoeffectiveness depends on their size and on their solar disc location. The mere information that a solar X-flare (XRA) event or a Long Dura...
Article
Full-text available
The Slovak repeat station network consists of six stations. It was established in 2004 in a way to provide long time series of geomagnetic measurements at the same, or nearly the same, places, with the beginning in the middle of the 19th century. The new geomagnetic network was measured first time in 2004. It was reoccupied in the middle of 2006. I...
Article
Full-text available
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 geom...
Article
Full-text available
The geomagnetic field changes with time and space. For the study of this changes it is necessary to determine the distribution of the geomagnetic field from geomagnetic surveys. The question is, at which geomagnetic activity it is possible to carry out these measurements not to have rank error. The differences in the total field F between 8 observa...
Article
Full-text available
In the paper a new neural network (NN) model for prediction of Kp indices during geomagnetic storms is proposed. The model consists of 34 individually trained three-layer networks that are fed with solar wind parameters B z, n, and V measured at libration point L1. One-hour averages of those are used. Four geomagnetic storm intervals (14-18 May 199...
Article
Full-text available
Several neural network (NN) models for the prediction of the Kp index have been proposed recently. Usually only solar wind data are used as inputs. In this paper an attempt is made to consider ground-based observations of geomagnetic variations as input to the NN model. The horizontal component H variations of the geomagnetic field from the Hurbano...
Article
Full-text available
The paper is devoted to the results of the last geomagnetic repeat station survey in Slovakia that was carried out in 2004. The geomagnetic elements at the observation points of the repeat station network were reduced to the 2004.5 epoch. The rates of their secular changes were derived for the period between 1995.5 and 2004.5. Linear models for the...
Conference Paper
Full-text available
Summary SPACE WEATHER VARIABILITY AND ITS FORECASTING The analysis of occurrence of magnetic storms within the 7-11 November 2004 time interval allows to understand the notion of space weather, conditions of its formation and variability. The utilization of data with different time resolution makes it possible to follow the tight relationship betwe...
Conference Paper
Full-text available
Výskumy slnečných energetických eventov v rokoch 1996-2004 ukazujú, že miera ich geoefektívnosti závisí na ich mohutnosti, a tiež na mieste ich výskytu na slnečnom disku. V práci sa zaoberáme analýzou geoefektívnosti rentgenových erupcií doprevádzaných rádiovým vzplanutím typu II a IV. Použili sme umelú neurónovú sieť na vytvorenie modelu, ktorý pr...
Article
Full-text available
The paper is devoted to choosing suitable sites for repeat stations of a new geomagnetic network. Six stations we planned to be established over the territory of Slovakia. This intention is in accordance with the agreement made during Workshop on European Magnetic Repeat Station Surveys (Niemegk, February 20th and 21st, 2003). The authors proposed...
Article
The best known manifestations of the solar wind impact on the Earth's magnetosphere are the geomagnetic storms. At middle latitudes, the magnetic storm is best described in terms of the horizontal component of the geomagnetic field. We use the method of neural networks which is suitable for nonlinear dynamical systems modeling and for the nowcastin...
Article
Full-text available
The auroral electrojet index (AE) was introduced in 1966 to describe the global activity of the auroral zone electric currents using the information from 12 stations which are located almost evenly around the northern magnetic pole of the Earth. Missing data deteriorate the determination of the AE index. To ensure the proper determination of the au...
Article
GMINV is a computer program for inversion of potencial field data using damped approximate technique. In this paper we evaluate the results of geomagnetic field measuring in the area of Kolárovo basin magnetic anomaly, south-west Slovakia. In order to achieve more precise evaluation of the location and geometry of the perturbative body we use some...

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