Numerical Modeling of Meteorological Sea Level Oscillations in the Black Sea

Oceanology - To study the features of short-period meteorological sea level oscillations, adaptation of the numerical Princeton Ocean Model (POM) to the Black Sea conditions was performed. The...     

Pole tide in the Baltic Sea

The pole tide, which is driven by the Chandler Wobble, has a period of about 14 months and typical amplitudes in the World Ocean of ～0.5 cm. However, in the Baltic Sea the pole tide is anomalously high. To examine this effect we used long-term hourly sea level records from 23 tide gauges and monthly records from 64 stations. The lengths of the series were up to 123 years for hourly records and 211 years for monthly records. High-resolution spectra revealed a cluster of neighboring peaks with periods from 410 to 440 days. The results of spectral analysis were applied to estimate the integral amplitudes of pole tides from all available tide gauges along the coast of the Baltic Sea. The height of the pole tide was found to gradually increase from the entrance (Danish Straits, 1.5–2 cm) to the northeast end of the sea. The largest amplitudes—up to 4.5–7 cm—were observed in the heads of the Gulf of Finland and the Gulf of Bothnia. Significant temporal fluctuations in amplitudes and periods of the pole tide were observed during the 19th and 20th centuries.     

Geochemical features of metabasite inclusions in gray gneisses of the Baidarik block (Central Mongolia)

The Baidarik block of the Dzavhan microcontinent (Central Asian Fold Belt) includes the Upper Archean Baidaragin gray-gneiss complex. Among gray plagiogneisses, there are metabasic bodies, which are probably relics of early volcanics. By composition, the metabasites are divided into three petrochemical groups, whose protoliths were tholeiitic basalts, Al-undepleted and Al-depleted basaltic komatiites. Only a few samples are similar in REE composition to these protoliths. We have found metabasites with crustal-contamination features. The unusual geochemical properties of the metabasites (LREE enrichment and Nb, Zr, and Ti depletion) are related to their metasomatism.     

Spectrum of mesoscale sea level oscillations in the northern Black Sea: Tides,seiches, and inertial oscillations

Long-term data from 23 tide gauges were used to analyze the spectrum of mesoscale sea level variability of the Black Sea. The tides have sharp spectral peaks, and they are detected at diurnal and semidiurnal frequencies for all stations. A local wide spectral peak associated with inertial oscillations is located between the diurnal and semidiurnal tidal peaks. This peak is well known in the spectra of the current velocity variations of the Black Sea, but in the sea level spectrum it has been identified for the first time. At frequencies of >3 cpd, sea level spectra of the Black Sea have (1) wide maxima in the continuous spectrum, which correspond to the main eigenmodes of the sea with periods of 5.6, 4.8, 4.1, and 3.1 h, and (2) sharp peaks of radiational harmonics S₃, S₄, S₅, and S₆. The periods of seiches calculated in this study are close to the periods of eigenmodes of the Black Sea, obtained by the numerical modeling of other authors. The main factors influencing the formation of radiational tides in the Black Sea are presumably breezes and runoff from large rivers. The significant predominance of a harmonic with frequency of 5 cpd (S₅) over other radiational harmonics is caused by the influence of an eigenmode, with a frequency of about 5 cpd. The proximity of the periods of these oscillations leads to resonant amplification and to a corresponding increase in amplitude of the radiational harmonic S₅.     

Determination of the orbits of near-Earth asteroids from observations at the first opposition

Observations at the first opposition are used to determine the orbits of 16 near-Earth asteroids with two or more observed oppositions. The orbits are improved by the differential method. This paper considers two modifications of the improvement technique, which are compared to the classical method based on the principle of the least square method (LSM). The first modification uses the principle of least absolute deviations (LAD). In the second modification, the differences O - C (between the observed and calculated positions) are transformed to fit into a new coordinate system whereby the axes go parallel and perpendicular to the asteroid’s apparent path (the modified differential method (MDM)). The orbits determined from one opposition by the classical LSM, LAD, and MDM are compared to a more accurate orbit calculated by the LSM from all the available oppositions. The calculations show that in 13 cases out of 16, the asteroid orbits calculated by LAD are more accurate than those calculated by the classical LSM. The improvement by the modified differential method, which includes the O - C transformation, does not produce any perceptible increase in accuracy when compared to the orbits calculated by the classical method.     

Dynamics of Slope Processes in the Geysernaya River Valley (Kamchatka) According to the Interpretation Data of Multi-Temporal Space Images

Doklady Earth Sciences - The interpretation of high-resolution satellite images (0.5–3 m) of three time slices (1964, 2009, and 2017) allowed us to identify the areas of activation of modern...