Available potential energy of the daily coastal circulation at Zadar (Croatia)

Summary The aim of this study is the evaluation of the sea breeze speed on the basis of its energy. Energetics of the sea breeze can be studied by means of the available potential energy (APE). Part of this energy is transformed into the kinetic energy of the sea breeze. Some similarity exists between the large scale processes of the circulation and the small coastal air circulation due to the fact that both circulations are triggered by the same physics, i.e., solenoidal activity of the baroclinic atmosphere. To evaluate the sea breeze speed, APE was calculated by use of the Lorenz’s equation (1955), and which is possible if the coastal circulation is considered to be a closed system in a hydrostatic equilibrium. For calculations and verifications hourly sea-surface temperatures, near-ground air temperatures and wind speed measurements, as well as the radio-sounding measurements at 12 UTC were used at the Zadar station (ϕ = 44° 08′ N, λ = 15° 13′ E), which is situated in the central part of the eastern Adriatic coast. Two days with an undisturbed sea breeze circulation were extracted using the methods for minimizing other atmospheric influences. Calculated hourly near ground sea breeze speeds obtained in this way were higher than the measured ones. With the assumption that some of the APE is transformed into the kinetic energy it is possible to obtain characteristic speed of the developed sea breeze with small discrepancies to the near-ground measurements. If 6.6% of the mean daily near ground APE was taken to be transformed to the mean daily kinetic sea breeze energy on the 29th and 4.2% on the 30th September 2002, the best agreement was obtained with the mean daily measured near ground sea breeze speed. This range of values can be attributed to inability to extract precise values for the lapse-rate needed in the APE sea breeze calculations. Results show similarities to the general circulation of the atmosphere, since about 10% of the APE is transformed to the kinetic energy of the sea breeze. On the other hand calculated wind speed at the lower branch of the borderline coastal circulation was not dependent on the integral value of the APE over the land, but on its value at the near-ground level.     

Testing for nonlinearity in European climatic time series by the method of surrogate data

Summary Using temperature and pressure records from Czech meteorological stations and NCEP/NCAR reanalysis series, we tested for the presence of detectable nonlinearity in univariate and multivariate climatic time series. The method of surrogate data was utilized for nonlinearity detection – results of nonlinear prediction for the original series were compared to the results for series whose nonlinear structure was randomized. The prediction was done by means of local linear models in the reconstructed phase space. None or very weak nonlinearity was found in the single (univariate) series, and pressure series generally exhibited stronger nonlinearity than series of temperature (daily mean, minimum or maximum). Distinct nonlinearity was found in all tested multivariate systems, especially when both temperatures and pressures were used simultaneously to form the phase space. Nonlinearity tests were carried out for 30-year and 10-year-long datasets and nonlinear behavior was generally more apparent in the longer versions. In addition, the tested systems showed more substantial nonlinearity when the success of short-range prediction was used as the discriminating statistic; with an increase of the prediction time, detectable nonlinearity became weaker and it disappeared completely for long-term prediction.     

Hazard distribution and risk assessment in the network systems

In the age when transport flows in the railway and road systems, information flows in the internet channels, etc. intensify, hazard distribution in the network systems becomes a more relevant and important issue. In the paper various theoretical hazard type distributions in the network systems are analysed. Conditions and assumptions that hazard in the network system cells would settle and became steady are defined. Cases are analysed, when hazard is initiated in one or several network nodes, while in other nodes hazard is decreased, i.e. they have immunity to the hazard. In all cases hazard distribution equilibrium equations are constructed and their solutions‘ existence conditions are defined. Theoretical results are illustrated by simulation of hazard fuel transportation in the Lithuanian roads. It is shown that using this methodology it is possible to construct an algorithm, which enables to operate and decrease fuel transportation hazard and risk. The novelty of the work is associated with employing Markov process to describe hazard distribution mechanism and to determine limited hazard distribution in the nodes of networks. The hazard of tank trucks in the network of Lithuanian roads has been assessed for the first time.     

Long-term variations in the second sectorial Stokes harmonics on the basis of TOPEX/POSEIDON altimetry between 1993 and 2000

The long-term variations in the second degree sectorial Stokes parameters of the geopotential have been determined from TOPEX-POSEIDON (T/P) satellite altimeter data, covering the period of January 1, 1993 to January 3, 2001 (T/P cycles 11-305). It is the first attempt to determine the variations in the second sectorial harmonics in the Earth’s inertia tensor due to the ocean dynamics. The variations amount to about 1 × 10⁻¹⁰ (J ₂ ⁽²⁾ ≈ 1.6 × 10⁻⁶ and S ₂ ⁽²⁾ ≈ −0.9 × 10⁻⁶). The variations are about 5% of the tidal effect. This corresponds to variations in the directions of the equatorial axes of the Earth’s inertia ellipsoid of up to 10 arc-seconds. Consequently, the annual and semi-annual variations of the Earth’s equatorial flattening is about 10⁻⁹; i.e. it corresponds to a change of 8 units of its denominator of 91 030. (The equatorial flattening ≈ 1/91 030). Since the coverage of the Earth’s ocean surface is not worldwide, and the inclination of T/P is i = 66°, it is only 58.2% (min. depth of the ocean 2 000 m) of the Earth’s surface which is processed, the torque, resulting from the seasonal transfer of masses within a sea surface layer, is not zero. It amounts up to 10¹⁶ kg m²s⁻², which is comparable to the total indirect tidal torque due to the Moon and the Sun, ∼ 3.9 × 10¹⁶ kg m²s⁻². However, the above estimate strongly depends on the adopted thickness of the sea surface layer, ΔR = 50 m. For a larger thickness of ΔR = 100 m, the seasonal torque amounts to about ∼ 2.3 × 10¹⁶ kg m²s⁻².     

Recent Advances and Difficulties of Infrasonic Wave Investigation in the Ionosphere

Acoustic waves have a remarkable ability to transfer energy from the ground up to the uppermost layers of the atmosphere. On the ground, there are many permanent sources of infrasound, and also pulsed and/or sporadic sources (e.g., sea waves, infrasonic and sonic noise of cities, lightning, earthquakes, explosions, etc.). The infrasonic waves carry away the major part of their energy upwards through the atmosphere. What are the consequences of the upward energy transfer? What heights of the atmosphere are supplied by energy from various sources of an infrasonic wave? In most cases, the answers to these questions are not well known at present. The only opportunity to monitor the propagation of an infrasonic wave to high altitudes is to watch for its influence on the ionospheric plasma. Unfortunately, most of standard equipment for ionospheric sounding, as a rule, cannot detect plasma fluctuations in the infrasonic range. Besides, the form of an infrasonic wave strongly varies during propagation due to nonlinear effects. However, the development of the Doppler method of radiosounding of the ionosphere has enabled progress to be made. Simultaneously, the ionospheric method for sensing aboveground and underground explosions has been developed. Its main advantage is the remote observation of an explosion in the near field zone by means of short radio waves, i.e., the radio sounding of the ionosphere directly above the explosion. The theory of propagation of an acoustic pulse produced by an explosion on the ground up to ionospheric heights has been developed better than the theory for other sources, and has been quantitatively confirmed by experiments. A review of some advances in the area of infrasound investigations at ionospheric heights is given and some current problems are presented.     

Ray-centred coordinate systems in anisotropic media

Whereas the ray-centred coordinates for isotropic media by Popov and Pšenčík are uniquely defined by the selection of the basis vectors at one point along the ray, there is considerable freedom in selecting the ray-centred coordinates for anisotropic media. We describe the properties common to all ray-centred coordinate systems for anisotropic media and general conditions, which may be imposed on the basis vectors. We then discuss six different particular choices of ray-centred coordinates in an anisotropic medium. This overview may be useful in choosing the ray-centred coordinates best suited for a particular application. The equations are derived for a general homogeneous Hamiltonian of an arbitrary degree and are thus applicable both to the anisotropic-ray-theory rays and anisotropic common S-wave rays.     

Simultaneous determination of Earth orientation parameters and station coordinates from combination of results of different observation techniques

Described is a method for non-regular combination of different techniques, where the normal equations matrix cannot be restored, to obtain a representative set of Earth orientation parameters and station coordinates. The method is based on combining station position vectors transformed to the celestial reference frame, where they are functions of both the EOP and the station coordinates. Three types of constraints are applied to stabilize the system, separate celestial pole offset from polar motion and, to tie the EOP between individual epochs. VLBI, GPS, SLR and Doris data as collected for the ‘IERS SINEX Combination Campaign’ was used to check the method. After combination, dispersion of station coordinates decreased from 0.040 to 0.031 m. The effect of the combination on EOP is of the order of 0.2 mas and it can be seen in Figs. 3 and 4 as a difference of the final and a priori values.     

Behaviour of zircon in high-grade metamorphic rocks: evidence from Hf isotopes,trace elements and textural studies

Hf isotopic data of minerals in a mafic pyroxene granulite from the southern Bohemian Massif, together with their major and trace element composition and petrological observations were used to decipher the metamorphic history and behaviour of zircon in the granulite. The Hf isotopic composition in the minerals was used to estimate whether the decompression reaction, namely the consumption of garnet and rutile, could have provided Zr for the formation of newly grown metamorphic zircon. The age of the decompression reaction indicated by the evolution of Hf isotopes in garnet and orthopyroxene is between 333 and 331 Ma, i.e. ca. 7 Ma younger than the available U–Pb zircon ages from the Moldanubian granulites and than the newly obtained 343 ± 2 Ma laser ablation ICP-MS U–Pb age of zircons. The combination of bulk and in-situ Hf isotopic data, major and trace element composition and petrological modeling of P–T evolution revealed that the formation of zircons can not be related to the decompression phase of the evolution of the mafic granulites. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Magmatic history of granite-derived mylonites from the southern Desná Unit (Silesicum, Czech Republic)

Summary In the southern part of the Hruby Jeseník Mts. (Silesicum, Bohemian Massif) granitic orthogneisses and quartz-feldspars mylonites occur that were variously deformed, metamorphosed and imbricated with the overlaying Devonian volcano-sedimentary complex during the Variscan orogeny. Based on combined mapping, petrologic and geochemical studies, three main rock groups are distinguished. The fairly primitive nature of the tonalite suite is shown by low ⁸⁷Sr/⁸⁶Sr₅₅₀ ratios (0.7034–0.7038) and positive ε _Nd ⁵⁵⁰ values (+3.8 and +3.1). Isotopic composition of the metagranite suite is similar (ε _Nd ⁵⁵⁰ = +1.9 to +2.9). Both suites probably belong to a single Cadomian calc-alkaline tonalite–granite association, which can be correlated with acid-intermediate plutonic rocks of the eastern Brunovistulicum (Slavkov Terrane). All these units are interpreted as representing dismembered fragments of the same continental margin magmatic arc system. The leucogranite suite is most likely early Variscan in age. The initial Nd isotopic composition (ε _Nd ³³⁰ = +0.8 and +2.3) is consistent with its formation by a Variscan remelting of the metaigneous Cadomian crust represented by the rocks of the tonalite–granite association. The within-plate granite affinity of the leucogranite suite is most likely related to the break-up of the Brunovistulicum during the Variscan orogeny.     

Hydrogeological characteristics of some deep siphonal springs in Serbia and Montenegro karst

In terms of hydrogeological, engineering-geological, and hydrotechnical tapping in karst in relation to ground waters, karst channels, springs and ponors, speleodiving is the only research method which enables direct observation, studying and exact geological mapping of karst channels and caverns. Data collected during speleodiving research contribute considerably to the analysis of karst evolution process in the given region, which is very important in evaluating the depth of karstification and determining the main direction of the groundwater flow. In the past 30 years in Serbia and Montenegro, speleodivers have investigated over 40 siphonal springs, active cave channels and ponors, of which more than 20 are proof of deep siphonal circulation in karstic aquifers. The karstic springs are the most interesting phenomenon from a hydrogeological view point, and their investigations need particular attention. Most of significant karstic springs are on the rims of erosion basins—perimeters of karst poljes, river valleys, sea coasts and contact areas between karst aquifers and hydrogeological barriers. General characteristics of the spring regime are the direct correlation between precipitation and spring discharge. Moreover, the hydrogeological regime of these springs also depends on the size of the catchment area, karstic aquifer retardation capacity, total porosity, as well as lithological and structural characteristics.