We present the Hylaty geophysical station, a high-sensitivity and low-noise facility for extremely low frequency (ELF, 0.03-300 Hz) electromagnetic field measurements, which enables a variety of geophysical and climatological research related to atmospheric, ionospheric, magnetospheric, and space weather physics. The first systematic observations of ELF electromagnetic fields at the Jagiellonian University were undertaken in 1994. At the beginning the measurements were carried out sporadically, during expeditions to sparsely populated areas of the Bieszczady Mountains in the southeast of Poland. In 2004, an automatic Hylaty ELF station was built there, in a very low electromagnetic noise environment, which enabled continuous recording of the magnetic field components of the ELF electromagnetic field in the frequency range below 60 Hz. In 2013, after 8 years of successful operation, the station was upgraded by extending its frequency range up to 300 Hz. In this paper we show the station's technical setup, and how it has changed over the years. We discuss the design of ELF equipment, including antennas, receivers, the time control circuit, and power supply, as well as antenna and receiver calibration. We also discuss the methodology we developed for observations of the Schumann resonance and wideband observations of ELF field pulses. We provide examples of various kinds of signals recorded at the station.

[1] Asymmetric resonance curves are observed in various resonance systems occurring in nature. The reason for such a shape of the resonance curves is an interaction of the standing waves field in the resonator with the field of traveling waves which transmit energy from sources to the resonator. This behavior can be observed in strongly damped electromagnetic resonators. The ELF wave propagation inside the Earth-ionosphere cavity is a good example of the simultaneous occurrence of resonance and transmission phenomena. In this paper we show that the transmission field component depends on the attenuation rate of the Earth-ionosphere cavity and the observer-source distance. Besides, the resonance curve asymmetry causes an evident diurnal variability of the resonance frequencies. The superposition of the two components at any point of the resonator makes the analysis of the Schumann resonance (SR) difficult. Here we suggest a field decomposition method that allows separating the resonance component from the transmission one. Owing to the decomposition, having a single measurement of the E or B field, it is possible, independently of the observer position, to study the physical properties of the resonator as well as to determine the localization and the intensity of sources. The field decomposition permits defining new resonator parameters such as reduced resonance frequencies and reduced quality factors, independent of the observer position inside the cavity. We believe that the application of the decomposition method in the analysis of the ELF observations yields a possibility of improving the accuracy of the determination of both the distances and intensities of the sources exciting the Earthionosphere resonator, as well as its own parameters.

[1] Observations of resonant electromagnetic fields caused by global lightning activity are employed in determining the averaged parameters of the lower ionosphere. Using the twodimensional telegraph equation (TDTE) transmission line model described by Kul / ak et al.[2003], we have computed the attenuation rate of the Earth-ionosphere waveguide from diurnal observations of the N-S magnetic component of the ELF field performed irregularly for 6 years in the East Carpathian mountains. As the measurements were carried out during both the minimum and the maximum of the solar cycle 23 we present how solar activity influence the first Schumann resonance frequency and the attenuation rate. The analysis of all the data indicates that the first Schumann resonance frequency increases from 7.75 Hz at solar minimum to about 7.95 Hz at solar maximum while the global mean attenuation rate a at 8 Hz varies from 0.31 dB/Mm at minimum to about 0.26 dB/Mm at maximum.

[1] Measurements of extremely low frequency (ELF) transients can be used to obtain model parameters and rates of the strong cloud-to-ground (CG) lightning discharges that generate them. In this study, we present an analytical description of a CG lightning discharge which takes into account both a return stroke and a continuing current. Using quasi-TEM (q-TEM) solutions for the Earth-ionosphere waveguide for distances within the near zone we show that the ELF spectrum of transients strongly depends on the percentage contribution of the continuing current to the discharge process. It is supposed that during typical observational conditions the only parameter of an ELF transient that can be measured sufficiently accurately is the impulse amplitude. In relation to the observational conditions the consequences of the calibration of ELF receivers on the measured ELF impulse amplitude are discussed, particularly the role of antialias filters. It is demonstrated that measurements of the ELF transient amplitude at a known distance to the source allows the total dipole moment of the discharge to be calculated and allows contributions of the return stroke and continuing current to this process to be estimated. Furthermore, some techniques of the signal spectral filtration that enable independent measurements of the return and continuing phase of the discharge are discussed.

[1] The primary purpose of the research presented is to study solar variations in extremely low frequency (ELF) propagation parameters using Schumann resonance (SR) data from our irregular observations carried out in the East Carpathian mountains. The natural electromagnetic ELF fields in the Earth-ionosphere cavity (the global resonator) are strongly dependent on its resonance and propagation properties as well as on the global thunderstorm activity. Thus a determination of the global resonator parameters from Schumann resonances needs information about such signal properties, which depend only on physical conditions of the Earth-ionosphere cavity. To seek such signal properties, we consider the two-dimensional telegraph equation (TDTE) approach for describing propagation of ELF electromagnetic waves in a two-dimensional spherical transmission line model of the Earth-ionosphere cavity. We have set up a model consisting of a network of finite, homogeneous, one-dimensional transmission lines covering the sphere; with the square root dependence of the attenuation rate from frequency as a sufficient model for the study of the solar influence on global properties of the Earth-ionosphere cavity. Using this model, we have constructed useful formulae and algorithms connecting the observed parameters of Schumann resonances with the attenuation rate. This enables us to study the solar influence on the attenuation rate from diurnal observations of the NS-magnetic component of the ELF field measured at one station. As the measurements were carried out during both the minimum and the maximum of the solar cycle 23, we present in the work of KuÀ lak et al. [2003] evidence for a change in the ELF attenuation rate in the Earth-ionosphere cavity with solar activity.

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Abstract. Three types of observations: the daily values of the solar radio flux at 7 frequencies, the daily international sunspot number and the daily Stanford mean solar magnetic field were processed in order to find all the periodicities hidden in the data. Using a new approach to the radio data, two time series were obtained for each frequency examined, one more sensitive to spot magnetic fields, the other to large magnetic structures not connected with sunspots. Power spectrum analysis of the data was carried out separately for the minimum (540 days from 1 March 1996 to 22 August 1997) and for the rising phase (708 days from 23 August 1997 to 31 July 1999) of the solar cycle 23. The Scargle periodograms obtained, normalized for the effect of autocorrelation, show the majority of known periods and reveal a clear difference between the periodicities found in the minimum and the rising phase. We determined the rotation rate of the "active longitudes" in the rising phase as equal to 444.4 ± 4 nHz (26.The results indicate that appropriate and careful analysis of daily radio data at several frequencies allows the investigation of solar periodicities generated in different layers of the solar atmosphere by various phenomena related to the periodic emergence of diverse magnetic structures.

In the modern forestry paradigm, many factors influence the amount of coarse woody debris (CWD). The present paper analyzes the effects of both local (national) programs (special functions of forests) and European programs (Natura 2000 sites), as well as the individual characteristics of forest stands. The study was conducted on 2,752 sampling plots distributed over an area of about 17,500 ha and located in lowland stands having a species composition typical of large areas in central Europe. Natura 2000 areas contained significantly more CWD (8.4 m 3 /ha) than areas not covered by the program (4.8 m 3 / ha). However, this is due to the fact that Natura 2000 sites involve well-preserved forest areas, such as nature reserves (26.6 m 3 /ha). In the managed forests that have been covered by the Natura 2000 program over the past several years, the volume of CWD has not increased. Forests with ecological and social functions differed slightly in the amount of CWD. More CWD occurred in protected animal areas (8.7 m 3 /ha) than in stands damaged by industry (3.9 m 3 /ha). Intermediate CWD levels were found in water-protection forests and in forests located around cities and military facilities. In managed forests, the lowest CWD volume was observed in middle-aged stands. The species composition of the stand had little effect on the volume of CWD. Only stands with a predominance of ash and alder had higher CWD levels (13.5 m 3 /ha). More CWD was found in stands whose species composition did not represent the potential site quality (6.4 m 3 /ha) than in habitats with the optimum species composition (3.8 m 3 /ha). CWD volume should be systematically increased taking into consideration local natural conditions. Such efforts should be focused on particularly valuable regions, and especially on Natura 2000 sites, where the threshold values reported from other European forests should be reached. Leaving some trees to die naturally and retaining reasonable amounts of such trees ought to be incorporated into CWD management practice in Poland.