Analytical modelling of wintertime coastal jets in the Adriatic Sea

Two diagnostic models, reproducing circulation generated in a marginal sea by variable density, have been developed. The models’ domain is a 2D transverse section for which analytical solutions have been obtained. They describe the winter situation in the northern Adriatic, with a strong vertical mixing present and the density maximum dominating the centre of the basin. Both models employ Boussinesq-type parametrisation of friction and linear slip at the bottom. The first model allows for frictional departure from hydrostatic equilibrium and includes vertical friction only. The second one is hydrostatic but allows for lateral friction as well. The results obtained by the two models are similar and to some extent dependent on the vertical and bottom friction. They reproduce several well known characteristics of the Adriatic circulation (cyclonic surface flow, downwelling in the central and larger part of the basin compensated by upwelling in the coastal zone) but also predict some phenomena that are still not well understood. A conspicuous feature of the model results are coastal jets, which were observed in the Adriatic on several occasions. The present models show that the distance of jets from the coasts depends on lateral friction: it is found to vary from 1 up to 10 km on the Italian side and between 2 and 15 km on the Croatian side. Both models reproduce the west–east asymmetry, with the wider current on the east side of the basin. The asymmetry is a subject on which conflicting empirical results exist in the Adriatic. In the two models cyclonic flow occupies the whole water column, which disagrees with some recent theoretical findings of the near-bottom anticyclonic flow and thus leaves the issue open.     

Photoelectric analysis of asteroid 216 Kleopatra: Implications for its shape

In some recent theoretical papers it has been suggested that gravitationally bound “rubble piles” in hydrostatic equilibrium possibly exist among the asteroids. For a higher-than-critical value of the angular momentum acquired by such a body, the instability phenomena can produce fission into a binary system. S. J. Weidenschilling [Icarus44, 807–809 (1980)] suggested that 216 Kleopatra may represent a binary asteroid, since it has a large light curve amplitude (1.3–1.4 mag). In this paper new observations of Kleopatra are presented, suggesting the equal plausibility of the single triaxial ellipsoid model. Namely, when phase and aspect effects are taken into account, the actual maximum amplitude is reduced to about 0.9 mag at 90° of aspect which is close to the value predicted by theory for the instability limit. Moreover, multiple-scattering effects [M. Poutanen, E. Bowell, and K. Lumme, Bull. Amer. Astron. Soc.13, 725 (1981)] can reduce the axial ratio a/b even more. If the single-body model is adopted, the density of Kleopatra should be on the order of 1.7 g/cm³. This low value seems reasonable for “rubble pile” models.     

Residual errors in altimetry data detected by combinations of single- and dual-satellite crossovers

 The single- and dual-satellite crossover (SSC and DSC) residuals between and among Geosat, TOPEX/Poseidon (T/P), and ERS 1 or 2 have been used for various purposes, applied in geodesy for gravity field accuracy assessments and determination as well as in oceanography. The theory is presented and various examples are given of certain combinations of SSC and DSC that test for residual altimetry data errors, mostly of non-gravitational origin, of the order of a few centimeters. There are four types of basic DSCs and 12 independent combinations of them in pairs which have been found useful in the present work. These are defined in terms of the `mean' and `variable' components of a satellite's geopotential orbit error from Rosborough's 1st-order analytical theory. The remaining small errors, after all altimeter data corrections are applied and the relative offset of coordinate frames between altimetry missions removed, are statistically evaluated by means of the Student distribution. The remaining signal of `non-gravitational' origin can in some cases be attributed to the main ocean currents which were not accounted for among the media or sea-surface corrections. In future, they may be resolved by a long-term global circulation model. Experience with two current models, neither of which are found either to cover the most critical missions (Geosat & TOPEX/Poseidon) or to have the accuracy and resolution necessary to account for the strongest anomalies found across them, is described. In other cases, the residual signal is due to errors in tides, altimeter delay corrections or El Ni?o. (Various examples of these are also presented.) Tests of the combinations of the JGM 3-based DSC residuals show that overall the long-term data now available are well suited for a gravity field inversion refining JGM 3 for low- and resonant-order geopotential harmonics whose signatures are clearly seen in the basic DSC and SSC sets. Received: 15 January 1999 / Accepted: 9 September 1999     

Experimentally Determined P-Wave Velocity Anisotropy for Rocks Related to the Western Bohemia Seismoactive Region

The elastic properties of granites from Western Bohemia which we measured and published earlier have been supplemented with measurements of olivine nephelinite from the same region and with data on lherzolitic xenolith from the vicinity of elezný Brod. The set of velocities measured under laboratory conditions has been compared with depth profiles suggested for the purpose of locating seismic swarm events which occur in this region. P-wave velocities were measured under pressures of up to 400 MPa. This pressure corresponds to depths of about 15 km for this region. The data were extrapolated for larger depths. Comparing laboratory measurements and seismic profiles, we can conclude that the rocks under study may be constituents of crust structures.     

Cooling Radius vs. Absorption Size of Galaxies

The discussion of the relationship between cooling radius in two-phaseadiabatic halo models and observationally established maximal radiusof absorption in luminous galaxies at low redshift is presented. It isof paramount importance that any viable model of the halo is able toreproduce empirical value of the absorption cross-section of normalgalaxies and its scaling with luminosity. Several ways for bringingthe theoretical and observational values into agreement are outlined.It is of great methodological importance to fully assess the difficultiesany model is likely to encounter when testing predicted extent ofabsorption and column density distribution against recently obtainedlow-redshift Ly absorption data.     

Power-law spectra of 1–2 GHz narrowband dm-spikes

Twelve examples of clouds of narrowband dm-spikes, observed by the Ondejov radiospectrograph in the 1–2 GHz frequency range, are analyzed. After transforming of the frequency scales to heights in the solar atmosphere, the indices of the power-law power spectra are determined. The derived power-law indices are scattered in a broad range of values (–0.80––2.85). In some cases they considerably deviate from the previously found value of –5/3. A change of the power-law index above logk2.5 was also found in some cases. In the two longest events the time evolution of their power spectra as well as their indices were studied. While in most parts of the radio spectra the spectral index remains constant, in one part its absolute value increases with the spike intensity increase. Finally, the results, especially the broad range of power-law indices, are briefly discussed.     

Synthetic Proper Elements for Outer Main Belt Asteroids

For the orbits with low to moderate inclination and eccentricity, in the asteroid main belt, the analytically computed proper elements are accurate to a level very close to the best result achievable by any analytical theory. This fundamental limitation results from the infinite web of resonances and because of the occurrence of chaotic motions. Still, there are some regions of the belt in which these proper elements are of degraded accuracy, thus preventing a reliable definition of asteroid families and detailed studies of the dynamical structure. We have used a different method to compute asteroid proper elements, following the approach introduced in the LONGSTOP project to describe the secular dynamics of the major outer planets. By applying purely numerical techniques, we produced so-called synthetic proper elements for a catalog of 10,256 asteroids with osculating semimajor axes between 2.5 and 4.0AU.The procedure consisted of simultaneous integration of asteroid and planetary orbits for 2Myr, with online filtering of the short-periodic perturbations. The output of the integration was spectrally resolved, and the principal harmonics (proper values) extracted from the time series. For each asteroid we have also tested the accuracy and stability in time of the proper elements, and estimated the maximum Lyapunov Characteristic Exponent to monitor the chaotic behaviors. This provided information on the reliability of the data for each orbit, in particular allowing to select 1,852 cases for an extended integration (10Myr) of the orbits showing instability. The results indicate that for more than half of the cases the proper elements have a time stability improved by more than a factor 3 with respect to the elements computed by the previous analytical theory. But of course there are also unstable cases for which the proper elements are less accurate and reliable, the extreme examples being 23 orbits exhibiting hyperbolic escape from the solar system. This form of escape from the asteroid belt could be responsible for a significant mass loss over the age of the solar system.     

Katabatic flow with Coriolis effect and gradually varying eddy diffusivity

Katabatic flows over high-latitude long glaciers experience the Coriolis force. A sloped atmospheric boundary-layer (ABL) flow is addressed which partly diffuses upwards, and hence, becomes progressively less local. We present the analytical and numerical solutions for (U ,V, θ) depending on (z, t) in the katabatic flow, where U and V are the downslope and cross-slope wind components and θ is the potential temperature perturbation. A Prandtl model that accounts for the Coriolis effect, via f, does not approach a steady state, because V diffuses upwards in time; the rest, i.e., (U, θ), are similar to that in the classic Prandtl model. The V component behaves in a similar manner as the solution to the 1st Stokes (but inhomogeneous) problem. A WKB approach to the problem of the sloped ABL winds is outlined in the light of a modified Ekman-Prandtl model with gradually varying eddy diffusivity K(z). Ideas for parameterizing these high-latitude persistent flows in climate models are revealed. After Wentzel, Kramers and Brillouin, who popularized the method in theoretical physics.     

Adsorptive removal of eight heavy metals from aqueous solution by unmodified and modified agricultural waste: tangerine peel

Analysis was carried out using tangerine peel aiming its use as a potential adsorbent of eight heavy metal ions (Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) from aqueous solution. This agricultural waste was tested both in its untreated and also chemically modified form. Based on Fourier transformation infrared spectra, a comparison of biosorbent structure before and after chemical treatment was made. Batch adsorption tests were conducted at different pH and mass of sorbent to examine the influence on the effectiveness of simultaneous removal of tested ions. Kinetic studies were conducted at optimum pH 5.0 and sorbent dosage 300 mg. The pseudo-second-order kinetic model best fit the experimental data with high correlation coefficients (r² > 0.9997). By optimizing listed parameters, high removal efficiencies (> 89%) were achieved. According to the results obtained in this study, the remediation of water polluted with heavy metals could be done using modified tangerine peel as an agricultural waste material.