1.      Narayan, J. P. (2006): Numerical study of island effects on Rayleigh waves. Geofizika, 23, 1-12. 

 

ABSTRACT:

 

           To improve our understanding of Rayleigh wave generation and propagation in oceans, the effects of the presence of an island on the Rayleigh wave features are simulated. The analysis of results reveals Rayleigh wave generation in ocean near the island. In the water column, a decrease of amplitude in the vertical component and an increase of amplitude in the radial component of Rayleigh wave with depth are observed. The path of particle motion is elliptical clockwise, vertically polarised at the surface and horizontally polarised at the base of the water column. An increase of Rayleigh wave amplitude with island-slope (20° – 60°) is obtained, in contrast to the decrease of Rayleigh wave amplitude with increase of slope of basin-edge in the basin.. The effect of island-slope is greater in the vertical component, as compared to the radial one. Responses of different submersed islands (0 – 75 m below water surface) reveal decrease of amplitude of island-induced Rayleigh waves with depth. The obtained results help us to understand the characteristics and the generation of Rayleigh waves near islands.

 

Keywords: Island effects, Rayleigh wave generation and propagation in oceans.

 

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2.  Verbanac, G., L. Hermann and M. Rother (2006): Evidence of the ring current effect in geomagnetic observatories annual means. Geofizika, 23, 13-20. 

 

ABSTRACT:

 

           The purpose of this study is to identify the physical sources of the major disturbance in the observatory annual means caused by the external geomagnetic field. The observatory annual means are widely used, especially in the modeling of the main field and its secular variations, although it is known that they are contaminated by parts of the field that come from outside the Earth. We consider data from 46 European observatories spanning the time period 1960–2001. The core field was removed using the Comprehensive Model, CM4 (Sabaka et al., 2004). With a suitable parameterization of the POMME model (Maus et al., 2005), we were able to reconstruct the signal of the residuals which can be linked to the ring current. This investigation paves a way for the more detail study of the external field influence on the observatory annual means, which as a consequence can bring a proposal for their correction.

 

Keywords: geomagnetic observatory, annual means, ring current, POMME model

 

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3.    Niwas, S., and O. A. L. de Lima (2006): Unified equation for straightforward inversion scheme on vertical electrical sounding data. Geofizika, 23, 21-35.

 

ABSTRACT:

 

            A unified apparent resistivity equation is derived encompassing eight electrode configurations for Straightforward Inversion Scheme (SIS) on Vertical Electrical Sounding (VES) data. Suitable parameters are worked out to convert unified equation to a particular configuration viz. Wenner, Pole-Pole, Schlumberger, Pole-Dipole, Radial Dipole, Perpendicular Dipole, Parallel Dipole and Azimuthal Dipole. The derived equation is validated by forward computations of VES data for a 5-layer earth model that compares well with that of VES data obtained using existing individual equations for a particular configuration. SIS scheme is briefly described and a Schlumberger synthetic sounding data is generated using the unified equation over model riddled with equivalence /suppression and subsequently inverted using SIS to show the resolving power of the scheme via-a-vis low resistivity contrast between the layers. Two examples of field Schlumberger soundings from known lithology on a paleochannel in Mario Island in Northern Brazil are also included and the inverted continuous resistivity variation is presented to show the efficacy of the scheme.

 

 

Keywords: unified equation, straightforward inversion, vertical electrical sounding.

 

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4.  Herceg Bulić, I., and Č. Branković (2006): Seasonal climate sensitivity to the sea-ice cover in an intermediate complexity AGCM. Geofizika, 23, 37-58.

 

ABSTRACT:

 

           The sensitivity of the atmospheric circulation to a different specification of sea-ice temperature and its seasonal cycle is analysed from the 50-year long integrations with SPEEDY, an intermediate complexity atmospheric general circulation model (AGCM). This impact is inferred from the difference between model atmospheric states obtained with and without the inclusion of the thermodynamic effects of sea ice. The two experiments with sea ice were made – the first one used climatological monthly mean temperatures for sea ice (derived from ERA–15 data), whereas in the second experiment the sea-ice temperature was determined by a thermodynamic model embedded into the SPEEDY code.

It is shown that the thermodynamic model tends to amplify the seasonal cycle of temperature. In the boreal winter, the inclusion of the thermodynamic model for sea-ice temperature leads to a general cooling of the model atmosphere at high latitudes (when compared with the experiment with climatological sea ice), associated with the reduction in geopotential heights and the strengthening of zonal winds. It also reduces the extent and amount of cloud cover in the mid- and high latitudes. Atmospheric cooling could be directly linked to the increased sea-ice seasonal cycle, because the increased albedo over sea ice reduces incoming solar radiation and further stabilises already cold air. Some of the changes induced by sea ice extend throughout the whole depth of the model atmosphere and could be linked directly to strong meridional differential temperature gradients. In addition, some seasonally varying symmetry between the Northern and the Southern Hemisphere is also found.

In summer when the receding sea ice is included in model integration, the opposite effects are seen: differential temperature gradients are of the opposite sign, the atmosphere is warmed thus effecting a reduction in zonal winds and an increase in cloudiness. These effects are stronger in amplitude than those associated with the maximum winter extent of sea ice, suggesting that ocean heat flux from the ice-free water together with increased solar radiation and convection bear a strong mark on the model atmosphere.

 

 

Keywords: seasonal climate sensitivity, thermodynamic effects of sea-ice, intermediate complexity AGCM

 

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5.     Juras, J., and Z. Pasarić (2006): Application of tetrachoric and polychoric correlation coefficients to forecast verification. Geofizika, 23, 59-82.

 

ABSTRACT:

 

           The measure of association in 2 x 2 (K x K) contingency tables known as tetrachoric (polychoric) correlation coefficient is recalled. These measures rely on two assumptions: 1) there exist continuous latent variables underlying the contingency table and 2) joint distribution of corresponding standard normal deviates is bivariate normal. It is shown that, in practice, the tetrachoric (polychoric) correlation coefficient is an estimate of Pearson correlation coefficient between the latent variables. Consequently, these measures do not depend on bias nor on marginal frequencies of the table, which implies a natural and convenient partition of information (carried by the contingency table), between association, bias and probability of the event and subsequently enables the analysis of how other scores depend on bias and marginal frequencies. Results extended to K ´ K tables lead to eventual reduction in dimensionality from K2 to 2K. The theoretical findings are illustrated through analysis of real-life, 6 ´ 6 contingency tables on verification of quantitative precipitation forecasts.

 

 

Keywords: tetrachoric correlation coefficient, contingency table, forecast evaluation

 

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