Emil Botev, Tatiana Toteva – Preliminary results of 3-D modeling of the earth crust in SW Bulgaria and some adjacent regions
Abstract. A three-dimensional velocity model of the earth’s crust obtained from the registration of local earthquakes on the territory of Southwestern Bulgaria and the adjacent lands is presented. The picture of the velocity distribution shows a structural subequatorial distribution of the near surface lateral inhomogeneities which is preserved down to 20 km depth. A certain modification occurs at greater depths and the isolines are orientated mainly submerridionally at a level of 30 km. As a whole the low velocity zone at the near surface levels corresponds to the area with the highest seismic activity in the investigated region. The correlation between the configuration of the low velocity zones and the areas of high seismicity continues to a level of 20 km, where the great reduction of the seismic activity is observed.
Key words: earth structure, 3-D modelling

E.Botev, B.Babachkova, B.Dimitrov, S.Velichkova, I.Tzoncheva, K.Donkova– Preliminary data on the seismic events recorded by NOTSSI in July – December 1999
Abstract. A map of the epicentres of 925 earthquakes that occurred in the part of the Balkan Peninsula outlined by longitude l=19°-30°E and latitude j =37°- 47°N is presented. A more detailed analysis of the seismicity of the territory of Bulgaria and its adjacent lands is made.
Key words: seismicity

G. Tenchov– Evolution of the Earth’s gravitational field within the last 500 Ma

Abstract. The possible change in the Earth’s gravitational field is estimated that may have occurred within the last 500 Ma or in the geological time known as Phanerozoi. As possible sources of such events are considered: the change of the Earth’s mass because of meteorites, the change in the Earth’s shape caused by the retardation in its axial rotation, the evolution of the Earth-Moon system and the possible expansion of the Earth. The most significant process is the expansion (or contraction) of the Earth and, the meteorites fallen on the Earth. Both events can produce a change into the Earth’s gravitational field g with a magnitude from 50 mgals to several gals. The second event can produce a variation in g from mgals to several hundred mgals.
Key words: gravitational field, Earth, Phanerozoi

Plamen Muhtarov, Borislav Andonov -Improved relationship between the Interplanetary Magnetic Field component Bz and Kp index
Abstract: An improved dependence of Kp index on IMF Bz component is obtained by introducing a modified Bz function (denoted as Bzm), exhibiting a delayed reaction to Bz changes. Bzm is modeled by using the analogy with an electric circuit consisting of a condenser, a diode rectifier and two resistors. Loading and unloading the condenser, as inertial processes, are described by expressions for the input and output voltages containing respective time constants. These expressions are used in the dependence between Bz and Bzm. The cross-correlation between Kp and Bzm increases to 0.7 compared with -0.4 between Kp and Bz. The mean dependence of Kp on Bzm is approximated by a parabola, by using loading and unloading time constants 0.8 and 9 hours respectively. The time constants are obtained by an optimization method using Bz and Kp data from the whole year of 1981. The Kp model, driven by measured Bz, is capable to predict the three-hour Kp value one step in advance.
Key words: IMF, Kp, prediction of Kp.

Plamen Muhtarov, Ivan Kutiev– Modelling the delayed reaction of ionosphere to geomagnetic forcing
Abstract: A detailed description of the approach of modelling the delayed reaction of F-region ionization to the forcing from auroral latitudes during increased geomagnetic activity is presented. The ionization at the F-layer height is represented by the relative deviation of foF2 from its median (denoted as F), while the geomagnetic activity is characterized by the index Kp. The approach is based on the fact that the F-region reaction (the storm-time variation of F) delays with respect to Kp changes. To evaluate this delay, we introduce a new modified function of Kp, which represents an inertial process, forced by Kp and relaxed with a definite time constant. The modified Kp function is obtained as a solution of the differential equation describing the relaxation of F from a given initial stage, with an imposed perturbation Kp2. The time constant of the relaxation is a measure of the delayed reaction of F to Kp changes. Through the modified Kp function we evaluate the time constant of the delayed reaction of the F-layer to the geomagnetic forcing by a simple fitting to the measured F. We evaluate the time constant on a statistical base, using the cross-correlation function between F and Kp. Using the previously developed model of the cross-correlation function and comparing it with the empirical estimates, obtained on the data from 14 European ionosonde stations over an 11 – year period, we obtain on the average, a time constant of 18 hours.
Key words: Kp index, F-region storms, geomagnetic forcing, delayed reaction of the ionosphere, cross-correlation analysis.

N. Gromkova– Dispersion regulatory model for designing new industrial stacks – software PLUME

Abstract. The product PLUME is one PC utility tool for environmental impact assessments in the vicinity of industrial stacks. The name is borrowed from the conventional Gaussian plume equation, utilized in the physics part of the dispersion model. The method developed, has been funded by the PHARE program, through the Bulgarian Ministry of Environment and Waters (Contract No. 166-1618, 1996) and the project outputs have been approved as a national regulatory standard for designing a new industrial stack with a view not to exceed the environmental standard concentration values as well as for evaluating the air pollution and calculating the maximum preceding pollution from the existing stacks’ configuration. The software package has been coded in Visual Basic and works under WINDOWS’ 9X or NT. Its structure provides an easy way across the tasks, the users had to carry out. The input information is user-friendly, well-provided-to warning messages of missing or restrictions on supplied data.
Keywords: air-pollution, dispersion model, ground-level concentration, industrial stacks.

N.Gromkova – The use of the regulatory PLUME model for the industrial source complex of “Maritza-Iztok” coalmine
Abstract. The dispersion model PLUME has been used to calculate the ground-level concentration for sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon oxide (CO) and dust (PM) from the Maritza-Iztok Ltd. coalmine stacks’ configuration. The meteorological data file, representative for this region, contains sequential hourly records of meteorological parameters, from the month of October 1995 to the month of September 1996. It is shown that the averaged for the all-period pollution fields do not exceed the annual Limit Admissible Concentrations (LAM) for the respective admixtures. The maximum concentration value for all pollutants is evaluated too. The comparison with single LAM shows that only the transient concentration value for sulphur dioxide is higher for the stability class A and wind velocity of 1 m/s.
Key words. Regulatory dispersion model PLUME, industrial stack, ground-level concentration, sequential hourly meteorological data.

R. Dimitrova– Numerical studies of the city heat island

Abstract. The present work aims at studying a 3D mesoscale model sensitivity to the variations of the parameters of the underlying surface and their effects on the city heat island formation. The results from the numerical experiments demonstrate that the applied mesoscale model is reasonably sensitive to the surface parameters variations and so is able to describe the formation of a city heat island and the corresponding local flow systems. The simulations show that the city heat island is formed as a result of a complex interaction of different factors, which explains the complex diurnal course of the heat island intensity.
Key words: city heat island, numerical simulations.

R.Dimitrova, K. Ganev, Ch. Zerefos, A. Vasaras – Exchange of sulfur and nitrogen compounds between Bulgaria and Greece, estimated by a simple three-layer pollution transport model.
Abstract. The simulation of the transport and chemical transformations of Sulfur and Nitrogen pollution from both Greek and Bulgarian sources and estimation of the pollution exchange between Bulgaria and Northern Greece is the objective of the present work. A three-layer Eulerian model, tuned for the cases of complex chemical interactions, is used for the purpose, the simulations being restricted to only two time periods – January and July 1995. The estimations made should be considered as preliminary ones. They still have to be proved by some comparisons with air pollution measurements data. Qualitatively, however, they agree with previous SO2 pollution exchange studies, which is some evidence of the consistency on the simplified pollution transport model.
Key words: pollution transport, chemical transformations of Sulfur and Nitrogen.

R. B. Raykova, S. B. Nikolova – Review of digital formats for exchange and processing of seismological data.
Abstract. The aim of this paper is to review some commonly used digital seismic formats. The most widespread seismic formats for exchange of waveform data are SEED (Standard for the Exchange of Earthquake Data), GSE (Global Seismic Exchange), and SAC (Seismic Analysis Code) formats. Available seismological software products for waveform analysis usually create and use its own digital format. A recent tendency in development of seismological software packages is the possibility to use some of the existing digital formats. Some of these software packages and formats are AH (Ad Hoc), SEISAN (Seismic Analysis), PITSA (Programmable Interactive Tool for Seismic Analysis), SEGY (Society of Exploration Geophysicists – Y format), CSS (Center for Seismic Studies), miniSEED. The contents of SEED, GSE, SAC, and CSS formats are described here in details. The addresses of the corresponding web sites are given for more information.
Key words: digital seismic data formats, SEED, SAC, CSS, GSE.

S. M. Stankov – The oxygen-helium ion transition level during low solar activity: II. A new empirical model
Abstract. A new empirical model of the O+ – He+ ion transition level during low solar activity is developed using in-situ measurements from the Atmosphere Explorer – C satellite. It simulates the level’s longitudinal, latitudinal, seasonal and diurnal variations.
Keywords: transition level, satellite measurements, empirical modelling

D.K.Teodosiev – Effects of particles acceleration on parametrically induced waves

Abstract. The possibility of charged particles fluxes formation under the influence of powerful VLF-transmitters on the upper ionosphere plasma is considered. The processes of particles acceleration by parametrically induced waves are discussed in detail. Experimental data of the satellites “Aureol-3”, “Cosmos-1809” and “Intercosmos-Bulgaria-1300” are used in the numerical calculation. It is known that as a result of disintegration of the initial VLF wave, ion-cyclotron waves are formed most effectively. Evalutions concerning the contribution of the diffusion and flux terms in the diffusion equation about the charge particles distribution function are obtained for the cyclotronic interaction of waves with particles. It is shown that in the three-wave decays only the particles which are in the “tail” of the equilibrium distribution function interact effectively. The inhomogeneous plasma is considered. This inhomogeneity is particularly important for ion acceleration at the cyclotronic resonance as the energy of the cross component of particle velocity is transformed into an energy of its parallel component. As a result of the numerical calculation performed, the dependence of the sizes of the fluxes of accelerated oxygen ions on the energy is obtained at different pitch-angles, for heights 1000 km and 1500 km. The particles flux with large pitch-angles is equal to 3.104 cm-2s-1 eV-1.
Key words: ionosphere, plasma waves, parametrical instabilities.

A.P.Venedikov, B. Ducarme – Determination of the Earth tide constituents generated by the tidal potentials of degree 3 and 4 for large series of observations made by superconducting gravimeters.
Abstract. According to the theory of the tidal deformation, the Earth has different responses to the tide generating potentials P2, P3 and P4, of degree 2, 3 and 4 respectively. Usually, the study of the reaction to P3 and P4 is restricted to the separation of the higher frequency tidal groups M3, generated mainly by P3 and M4, generated by P4. This paper is an attempt to estimate the parameters of the P3 and P4 waves within the diurnal and semi-diurnal tidal bands, as well as the P4 waves within the third diurnal band. The numerical results are derived from the analysis of six large series of very high quality gravity tidal data. Some of these results are obtained and published for the first time in the tidal domain. In particular, the separation of the new tidal group 4TD is the first determination of P4 tides outside the P4 group M4. In addition, the estimates of 4TD appeared to be considerably more reliable than the estimates of M4.
Key words: Earth tides, tide generating potential, Tamura tidal potential, tidal analysis.

Science – in service of society

R. Glavcheva – L. Christoskov: “Earthquakes – Danger and Mitigation” M&M, Sofia, 2000, 62p., (in Bulgarian)