B. Tsenova, R. Mitseva – The impact of in-cloud characteristics and graupel surface properties on graupel surface temperature in the dry growth regime
Abstract. The impact of in-cloud characteristics (effective water content, air temperature and pressure, size of freezing droplets) and graupel properties (graupel size and velocity, graupel shape) on graupel surface temperature were considered. For the calculations of graupel surface temperature the equation of Macklin and Payne, 1967 was used. The study reveals that graupel surface temperature is affected significantly by all of the studied parameters, and that at medium variation of air pressure the impact on graupel surface temperature is negligible.
Key words: rime, graupel growth, effective water content, non-inductive charging.

K. Ganev, D. Syrakov, Ch. Zerefos, M. Prodanova, R. Dimitrova, A. Vasaras– On some cases of extreme sulfur pollution in Bulgaria or Northern Greece
Abstract. Extensive air pollution simulations were carried out in the framework of a joint research project (Grant ENVIR.LG 973343) and a long-term evaluation of the SO2 exchange between Bulgaria and Northern Greece was performed. From both scientific and practical points of view, however, not only large-term pollution characteristics and country to country pollution exchange characteristics are of interest. The study of episodes with especially large air pollution in a selected region and their analysis with respect to the meteorological conditions and the pollution sources configuration is also important. That is why the present work aims at a more detailed study of the SO2 origin for some days of 1995 with particularly large mean concentrations over Bulgaria or Northern Greece. The method of functions of influence was applied in the study. The general conclusion from the simulations is that in most of the cases more than 50% of the extreme surface SO2 pollution in Northern Greece (up to 82% in some cases) originates from Bulgarian sources, with a particularly large contribution of the “Maritza” power plants (in one of the episodes nearly 80%). There are cases, however, when the SO2 pollution in Northern Greece is formed mostly (more than 60%) from Greek sources. In all the cases studied, more than 70% of the extreme SO2 pollution in Bulgaria is caused by Bulgarian sources. The present results are in good agreement with some previous studies, where the numerical evaluations were convincingly confirmed by the experimental data.
Key words: air pollution, functions of influence, conjugated equations.

E.Botev, B.Babachkova, B.Dimitrov, S.Velichkova, I.Tzoncheva, K.Donkova, S.Dimitrova– Preliminary data on the seismic events recorded by NOTSSI in January – June 2001
Abstract. A map of the epicentres of 565 earthquakes occurring in the part of the Balkan Peninsula outlined by longitude l=190-300E and latitude j =370- 470N is presented. A more detailed analysis of the seismicity of the territory of Bulgaria and its very close adjacent lands is made.
Key words: seismicity

L. D. Stoyanov, R. A. Ivanov -Design of the new Bulgarian Gravity Basic Network

Abstract. The dynamic interactive network design for derivation of an optimal observational scheme of a new Gravity Basic Network for Bulgaria is proposed. This design has been obtained by a special case of sequential optimization. As a result a homogeneous network with minimal variances of the gravity values is suggested. The absolute gravity stations are included in the modeling by the establishment of national Gravity Datum and scale. The optimizing procedure is applied to the existing Bulgarian gravity network.
Key words: Gravity Basic Network, optimization, absolute gravity stations.

I. Georgiev, Ya. Chapanov– Analysis of laser ranging data to the geodynamic satellites Lageos 1 and Lageos 2 for the period 1984 – 2000
Abstract. Long series of laser ranging data to the geodynamic satellites Lageos (LAser GEOdynamic Satellite) 1 and 2 with spanning periods April 1984 – December 2000 and January 1993 – December 2000, respectively, are processed and analyzed. The data reduction and analysis of the observations are made by the new version – 4.0 of the program SLRP (Satellite Laser Ranging Processor), developed at the Central Laboratory of Geodesy (CLG). In the new version of the program some new dynamic models are included and the parameters estimation strategy is refined. The solution obtained, beside coordinates and velocities of the laser stations and Earth Orientation Parameters (EOP), contains estimates of some Earth’s dynamic and geometric parameters, such as: geogravitational constant; part of the Earth’s geopotential coefficients; Love and Shida numbers; amplitudes and phases of the ocean tides; parameters connected with the satellites motion and laser observations modeling. The present paper shortly describes the laser ranging data processing emphasising on the improvements made, both in the orbital dynamic and parameters estimation strategy. Some of the important results derived are outlined.
Key words: Satellite Laser Ranging, dynamic and geometric parameters of the Earth

Ya. Chapanov, I. Georgiev– Secular drifts of the low degree zonal coefficients obtained from Satellite Laser Ranging to the geodynamic satellites Lageos 1 and Lageos 2

G. G. Tenchov – Physical properties of the inner core’s substance

Abstract. Using PREM model data and the Legander-Roshe hypothesis it was confirmed that the inner core is a homogenous body. Some data were obtained about the inner core density and dilatation at its temperature and pressure. They confirmed there was a steep decrease of Vs and increase of the Vp/Vs ratio near the border of the inner-outer core. No phase transformation was outlined. All these support the proposed idea that the inner core is made of a relatively pure substance. The equations for the gradient of the P and S waves in the inner core are obtained and it is shown that the incompressibility derived by the PREM density model and by the seismic waves data are not equal. This is probably caused by the problems in the velocity determination of P and S waves into the inner core. Because of the lack of experimental data at megabars pressure and temperatures up to 40000C it is not possible to define the chemical composition of the inner core’s substance.
Key words: inner core, high pressure, Earth interior.

I. Georgiev, L. Pashova, G. Nikolov, E. Botev, D. Dimitrov, Sl. Gospodinov, I. Zdravchev, B. Alexandrov– Regional geodynamic GPS network in SW Bulgaria: geological and geophysical background, status and perspectives
Abstract: The initial scientific studies performed in the framework of the research project “Multidisciplinary study on the active geodynamic setting of Southwestern Bulgaria” (Project funded by the Scientific Research Department at the University of Architecture, Civil Engineering and Geodesy, Sofia) are presented. The establishment of a geodynamic network that covers the main tectonic structures in the region of Southwestern Bulgaria is of great importance. The paper gives the main geological features, an analysis of the seismic data for the last 10 years, the stages of planning and setting up the GPS network. The first GPS campaign performed in August-September 2001 is briefly outlined. We expect in the framework of this project to establish the present-day kinematics in the studied region. The obtained results can be used to bring up-to-date assessment of the seismic risk and the seismic zoning of that part of the country.
Key words: recent geodynamics, seismicity, GPS network, SW Bulgaria

Zheljo Zhelev, Totka Petrova, Fuensanta Montesinos, Ricardo Vieira, Jose Arnoso, Antonio Camacho – Some new results of the analysis of the Lanzarote (Canary Islands) gravity anomaly with elementary sources
Abstract. As is known, the method of D. Zidarov concerning the solution of the inverse problems of the potential fields with elementary sources through optimization permits obtaining approximate information about the distribution of the underground density inhomogeneities on the basis of the corresponding observations. Here, this technique is used to study the deep underground structure of the Lanzarote (Canary Islands). For this purpose a network of 296 gravity stations distributed over the whole island and a digital terrain model of about 45, 000 terrestrial and oceanic data (to determine the corresponding terrain corrections) are used. The resulting Bouguer anomaly is analysed by the above mentioned method, which gives a mean level of observational noise of about 1.7 mGal. The final solution is presented by 14 point masses and a polynomial trend, obtaining the approximate location of the anomalies sources and their masses.The main quantity of masses (corresponding probably to the main intrusive body) is concentrated under the central area and can correspond to a dilated volcanic activity (of shield formation) . The center of this body is located at a depth of about 8 – 10 km. Besides, the SW extreme area of the island shows a smaller positive body, approximately at the same depth, interpreted as a less developed magmatic intrusion. Similar results are obtained also in the previous works on the same subject. Here, however, no intrusion is established in the NE extreme area of the island. Probably the observed anomaly in this region is provoked by much deeper masses, located far away NE from this place. To clear out more exactly this problem however, some more detailed additional observations in this region are needed in the future. All these results seem to be more or less in agreement with the information known of other sources.
Key words: Lanzarote Island, Bouguer gravity anomaly, numerical modeling

News in brief

R. Glavcheva – Third Meeting of Asian Seismological Commission and a Symposium on Seismology, Earthquake Hazard Assessment and Earth’s Interior Related Topics
I. Kutiev – In Memoriam: Dimitar Mishev 1933-2003