* K. Bojadgiev, V. Hristov, B. Srebrov,T. Harinarayana, K. Veeraswamy* – Temperature investigations in Polyanovo hydrothermal reservoir (se Bulgaria)

**Abstract.**Polyanovo hydrothermal reservoir located in the southeastern part of Bulgaria mainly consist of fractured sediment and volcano-sedimentary Upper Cretaceous rocks. Water temperature varies from 15 to 49oC. Temperature depth profiles are carried out in 17 wells where varying depths are from 100 to 500m. Temperature distribution maps at three depth levels below the surface – 50, 100 and 150m and geothermal gradient map have been prepared and analyzed together with existing geophysical results of gravity, magnetic, electric resistivity and well logging. The unchanged temperature anomaly location on the three levels and high horizontal temperature gradient (at depths 100 and 150 m) are indicators for a sub vertical water heat transfer to the surface.The obtained results are base for developing a reservoir structural model.

**Key words**: hydrothermal reservoir, temperature-depth profiles, temperature and geothermal gradient maps

* P. Trifonova, Zh. Zhelev, T. Petrova *– Curie point depths of the Bulgarian territory inferred from geomagnetic observations

**Abstract**. During last years spectral analysis of geomagnetic data has often been applied to estimate Curie point depths. It is used to delineate thermal and crustal structures on the basis of geomagnetic observations. The most popular mathematical model on which the spectral analysis is applied was introduced by Spector and Grant (1970) and comprises a collection of rectangular prisms with constant magnetization. The expectation value of the spectrum for the model is the same as that of a single body with the average parameters for the collection. .A satisfactory algorithm based on this model is used in the present research to calculate the thickness of magnetically active part of the lithosphere on the Bulgarian territory. The algorithm estimates x0, y0 and z0, the coordinates of the centroid, and depth to the top zt of the source distribution, trough least-squares fit of a straight line to the log averaged power spectrum in the lowest part of the radial frequency’s range. The depth to the bottom (Curie point depth) is zb,= 2z0,- zt. An useful compilation of data was made merging Bulgarian and South Romanian geomagnetic maps which allows to expand the result’s area. Calculated values of the Curie point depths of Bulgarian territory range between 17 and 35km. Several anomalous zones are delineated, mostly in the southern part of the area. As a criterion of reliability a correlation with the heat flow data of Bulgarian territory was used.

**Key words:**curie point depth, geomagnetic, spectral analysis, geothermal.

* L.M. Abramova , D.Yu. Abramova* – Some results of magnetovariational observations in the east Bulgaria

**Abstract.**The study of the floor structure, particularly in active zones, is primary importance for geodynamics and geochronology. The results of the magnetovariational observations in different parts of the Bulgarian continental offshore and land-based magnetovariational observations in Bulgaria are discussed in this report. The geomagnetic variations in the water were measured by the bottom three-component (H, D, Z) flux-gate magnetometers. As a result electrical conductivity functions in the period range of 10 min to 3-4 h were calculated. Analysis shows very small values of the magnetic field vertical component on the south part of Bulgarian territory and adjacent continental shelf. Magnetic variations at the north Bulgarian shelf differ very strong from these at south. Non-uniform thinsheet model was applied to invert this data. Both the electromagnetic (EM) measurement data themselves and their joint analysis with the data of other geophysical methods determine the crust conducting zone existence both under south part of the Bulgarian offshore of the Black Sea and under the east part of Rhodope massif. The crust conductivity layer is about 3 km thick, with a resistance of 3 m and conductance approximately of 1000 S. To some Bulgarian hydrogeologists thinking autochthonous in this shear is the thick layer of karst marbles what they describe as a large deep bedding artesian basin with hydrothermal karst and ascending underground flow. Waterproof layer is the plate building by the Rhodope granitoides series. Taking into account results of the EM investigations and the data of other geophysical methods it is possible to speak about an opportunity of existence of conducting astenosphere layer under East Rhodopean and south part of the Bulgarian offshore which begins from 50 km depth. A possible explanation for this phenomenon is that the upper mantle beneath the Aegean region is heated by hot asthenospheric material that penetrates the lithosphere through convection. These results conform to the high values of the heat flow observed here and are in concordance with modern view on the deep structure of the neighbouring regions.

**Key words:**el.magnetic soundings,conductivity anomalies,coast effect,3-D modeling.

* I. Butchvarov* – Processing and organization of the data obtained from the analog magnetograms of Panagjuriste geomagnetic observatory

**Abstract.**A brief history of the Panagjuriste Geomagnetic Observatory sins its establishment in 1937 to the present day is given. The data processing in the past and the contemporary geomagnetic data organization are described (Fig. 1). A brief description of the programming software for post-processing of the observed geomagnetic data in machine-readable form for PC is given. A few tables elaborated with this software are presented. More information and details are available on the telephone numbers and E-mails given in item 2.

**Key words:**Geomagnetic data; Geomagnetic Observatory. Panagjuriste.

* А.Anufriev, M.Tassev* – On the flow in the earth’s liquid core

**Abstract.** The momentum equation for the flow in the Earth’s liquid core which depends on two small parameters (the Ekman, E, and the Rossby, Ro numbers), is transformed to a form which depends on other two parameters:ЦE and l = ЦE/Ro . The first of them is still small, but the other one exceeds ЦE approximately with six orders of magnitude. The Ekman suction boundary conditions for the inviscid flow in the bulk of the Earth’s core also depend on the first parameter only. Therefore we search for the solution of the hydrodynamic problem in the form of the decomposition in the small parameter ЦE . The equations obtained show that the flow of the leading approximation in ЦE decomposition depends on the only parameter l . This means that for fast rotating fluids Ц2Wn/V1 becomes the universal parameter (as e.g. the Reynolds number R= V1L1/n in the hydrodynamics) and all flows can be classified only by it. The whole flow is presented as a sum of the force and the geostrophic flows. The first one can be directly determined in terms of integrals of the force. The second one obeys the equations which depend on time derivative of the geostrophic velocity. So the geostrophic flow is the only part of the whole flow which has its own time behavior. It evolves together with magnetic field and temperature distributions. In the opposite, the force flow fits instantly to the force and its time behavior is defined entirely by that of the force distribution. There are two (the inviscid l®0 and the viscous controlled l®0) limits in which the whole flow does not depend on l and hence on E. Therefore the flow converts in Taylor state in these limits. Depending on the viscosity, the parameter l for the Earth’s core changes from 3.3×10-1 for the kinematic viscosity to 2.3×10-2 for the greatest value of the turbulent viscosity nT=h where h is the magnetic diffusivity. So both types of the Taylor state flows can be realized in the Earth’s core. From computer simulations point of view the viscous controlled case is especially important, because all the simulations use implicitly l » 1. For example, Glatzmaier and Roberts (1995, 1996) in fact carried out their simulations for l ~ 103 . Thus their asymptotic (at l®Ґ ) solution is approximately suitable for the Earth’s core conditions with the “turbulent” l 3.3×101. It is not trivial, since if we adopt the same values of n(=nT=h) and V1 for Venus where W is with two orders of magnitude smaller, then l becomes of order of 1 and the viscous controlled numerical results become unapplicable to this planet. Moreover, being independent of l (and respectively of E), the viscous controlled computer simulated flows convert into Taylor state and so describe adequately the flow in the Earth’s core for the turbulent viscosity. This is also a non-trivial conclusion, taking into account that the typical values of the Ekman numbers in computer simulations typically exceed these in the Earth core with ten orders! Though the computer simulations describe satisfactory the flows with large l , they are unapplicable to solve the problem with smaller values of l and especially in the inviscid limit l®0 , due to the necessity of resolution of the thin boundary layers. We believe that this difficulty can be overcome by creating computer codes on the base of the equations presented here which are free of this necessity.

**Key words:** geodynamo, Taylor state, inviscid limit

* A. Savtchenko, R. Mitzeva *– Sprites and parent thunderstorms

**Abstract.** Sprites are a very fascinating member of the huge and varied family of Transient Luminous Events (TLEs), sometimes called also “high-altitude lightning”. Topic of extensive scientific research in the past decade, they are thought to be an interesting addition to the tropospheric lightning activity and an important participant in affecting the global atmospheric electric circuit and atmospheric circulation. Several theories have tried to explain the strange nature of sprites though there are still many unanswered question waiting to be uncovered. The present paper summarizes the known facts related to sprites according to the existing literature in the field of sprite research. The physical and optical properties of sprites are revealed as well as the physical mechanisms for their generation. The methods of detection are briefly introduced and some concepts of the numerical modeling of sprites are given. An attention is paid also to the characteristics of sprite-parent lightning and thunderstorms.

**Key words:** Sprites, positive cloud-to-ground lightning, thunderstorms

* S. Petrova, R. Mitzeva* – The impact of ice crystal nucleation mechanism on cloud microphysics and dynamics – numerical study

**Abstract.**Numerical simulations are carried out to investigate the effect of ice crystals formation mechanism on the dynamics and microphysics of mixed-phase convective clouds. Three different in power convective clouds are simulated by 1-D numerical model with bulk-water microphysical parameterization. Two types of parameterizations of ice crystals formation are used: primary nucleation given by Fletcher approximation and Hallet-Mossop mechanism (secondary nucleation) parameterized by constant enhancement factor in specific temperature band. The results reveal that precipitation starts earlier and at lower levels in the three simulated clouds when secondary nucleation is taken into account in comparison with the case when only primary (Fletcher) nucleation is used. However, the simulations indicate that the impact of ice nucleation (primary and secondary) depends on the power of the simulated cloud: there is an increase in the precipitation of most powerful cloud and decrease in the other two clouds when the secondary nucleation is included.

**Key words:**ice crystals formation mechanism, numerical cloud models

* D. Yordanov, M. Kolarova , U. Rizza , C. Mangia , T. Tirabassi, D.Syrakov*– Evaluation of wind and turbulent parameterisations for short range air pollution modeling

**Abstract.**Most of the air quality dispersion models used for regulatory applications are based on K-diffusion formulations. In this paper, two turbulent parameterisations for dispersion models in the atmospheric boundary layer are evaluated with experimental data. The first scheme is based on a similarity approach and provides wind and eddy diffusivity profiles on the basis of a diagnostic PBL model. The second one provides an eddy diffusivity profile based on the Taylor statistical diffusion theory and on the spectral properties of turbulence. The two parameterisations have been included in a numerical grid model and tested with the Copenhagen data set. Results show tha: i) the dispersion model with both turbulent schemes, produces a good fitting of the measured ground-level concentration data for all the experimental conditions considered; ii) there are no significant differences between the two schemes in the range of experimental data – the profiles are close to each other in the lower layers while they show larger differences in the layer above the surface layer. Therefore, both parameterisations give a realistic description of the dispersion processes in the lower PBL, and can be used for short range air pollution models and ground level concentrations.

**Key words**: turbulence parameterisations, planetary boundary layer, eddy diffusivities, air pollution modelling.