Fast Variations of Spectra of Comet Halley

Results of the analysis of the Comet Halley spectrophotometry,which has been carried out by H.K. Nazarchuk in 1985 with the TVscanner of the 6-meter telescope (SAO, Russia) are presented. Timevariations in the intensities of the CN, CH, C₂ and NH₂bands were investigated using the series of spectra obtained inthe spectral region λλ=410÷ 510 nm. Theauto-correlation functions for all the bands, thecross-correlation functions for C₂ lines and their Fouriertransformations are calculated to determine the frequencies andperiods of the variations. A possibility is considered thathigh-amplitude fast variations of spectral lines in Comet Halleyare caused by solar flares. The daily numbers of solar spots andproton fluxes with energies of more then 1 MeV are compared withthe spectral variations of these lines. It is shown that in theobservation periods the comet was projected onto an active regionof the Sun, but, among all the kinds of solar activity, mainlythe solar proton flux with energies less than 4 MeV coincides intime with fast intensity variations in the spectral lines. Analgorithm of cross-correlation analysis of discrete samplingseries with gaps is built, and average cross-correlation coefficientsare calculated.     

Bioluminescence potential during polar night: impact of behavioral light sensitivity and water mass pathways

During polar nights of 2012 and 2017, bioluminescence (BL) potential surveys demonstrated high emissions at depths around and below 100 m at offshore stations to the north of a Svalbard fjord (Rijpfjorden). We demonstrated that the highest bioluminescent emissions for offshore stations are located at depths below depths of modelled/ambient light intensities corresponding to the reported irradiance thresholds for the behavioral light sensitivity of krill and copepods, and suggest that behavioral light sensitivity is one of the reasons for high values of BL potential observed below 100 m at offshore stations. In order to understand sources of bioluminescent taxa responsible for the observed high values of BL potential in offshore waters, we have investigated the origin and pathways of water masses circulating to the north, offshore of the fjord Rijpfjorden by using a hydrodynamic model. For both 2012 and 2017, the model water masses mostly originate from the west, where the Atlantic water is flowing northward, then along the shelf and shelf slope of northern Svalbard, and to the offshore of the fjord. This indicates that the advection of zooplankton by North Atlantic Water is one possible source of bioluminescent organisms offshore of northern Svalbard. In 2012, water masses also originated from the inflow through Hinlopen trench and strait, while, in 2017, the offshore water was advected and upwelled into the fjord on time scales less than 10 days, and after that there was a recirculation back from the fjord to offshore on time scales larger than 10 days. This recirculation from the fjord might be another source of bioluminescent organisms in the offshore waters.

     

A Model of an Active Region on the Surface of a Cometary Nucleus

An active region on the surface of a cometarynucleus is considered as a conic hole in the surface dust mantle with icy bottom and dusty side-walls. This conic structureshould concentrate solar energy onto the bottom andtherefore enhance sublimation. Preliminary results of thecalculation of this effect are given. The temperature distributionat the bottom of the crater is calculated for different sets ofits geometrical parameters. Effects of intensified sublimation depending on the geometrical parameters areconsidered for the specific case when a single active region islocated exactly at the pole of the nucleus and the pole is directed tothe Sun.     

Bioluminescence potential modeling with an ensemble approach

Ocean Dynamics - The approach for modeling bioluminescence (BL) potential is proposed. The approach consists of (1) estimation of the adjoint (by backward in time integration of the adjoint model),...     

The Pliocene Yafo Formation in Israel: Hydrogeologically inert or active?

For several decades the “Saqiye beds” (later renamed Yafo Formation) underlying the Coastal Plain aquifer (Kurkar Group) aquifer of Israel, were regarded as an extremely thick, tectonically undisturbed, and absolutely impervious aquiclude. Following intensive groundwater exploitation from the overlying Kurkar Group aquifer, brackish and saline waters were locally encountered in the lower parts of this aquifer and always at the contact with the underlying Yafo Formation aquiclude. The present study revealed that this aquiclude is not a uniform and impervious rock unit, but rather an alternation of pervious and impervious strata within the Yafo Formation containing highly pressured fluids of different — mostly high — salinities. The permeable beds are at an angular unconformity and in direct contact with the overlying Kurkar Group aquifer. The Yafo Formation and the underlying and overlying rock units are dislocated by numerous fault systems, which facilitate accessibility of brines into the Kurkar Group aquifer. The mobilization of the saline fluids and their injection into the Kurkar Group aquifer could be due either to diffusion of saline fluids occurring in the permeable horizons of the Petah Tiqva Member through the clays of the Yafo Formation or to their upconing following intensive pumping in the Coastal Plain aquifer. It could have also been caused by up-dip movement of saline water as the result of overpressure generated by major accumulation of gas in the permeable horizons. Another possible mechanism could be hydraulic contact with pressurized brines up-flowing along fault zones from deep-seated Jurassic or Cretaceous reservoirs. The squeezing of saline interstitial water from the clays of the Yafo Formation into the overlying Kurkar Group aquifer, is of secondary importance for groundwater salinization (its input is comparable with salt input from rain).     

Modeling studies of the bioluminescence potential dynamics in a high Arctic fjord during polar night

Ocean Dynamics - During polar nights in January 2012 and 2017, significantly higher bioluminescence (BL) potential emissions in the upper 50 m were observed in the fjord Rijpfjorden...     

Submesoscale features and their interaction with fronts and internal tides in a high-resolution coupled atmosphere-ocean-wave model of the Bay of Bengal

Large freshwater fluxes into the Bay of Bengal by rainfall and river discharges result in strong salinity fronts in the bay. In this study, a high-resolution coupled atmosphere-ocean-wave model with comprehensive physics is used to model the weather, ocean circulation, and wave field in the Bay of Bengal. Our objective is to explore the submesoscale activity that occurs in a realistic coupled model that resolves mesoscales and allows part of the submesoscale field. Horizontal resolution in the atmosphere varies from 2 to 6 km and is 13 km for surface waves, while the ocean model is submesoscale permitting with resolutions as high as 1.5 km and a vertical resolution of 0.5 m in the upper 10 m. In this paper, three different cases of oceanic submesoscale features are discussed. In the first case, heavy rainfall and intense downdrafts produced by atmospheric convection are found to force submesoscale currents, temperature, and salinity anomalies in the oceanic mixed layer and impact the mesoscale flow. In a second case, strong solitary-like waves are generated by semidiurnal tides in the Andaman Sea and interact with mesoscale flows and fronts and affect submesoscale features generated along fronts. A third source of submesoscale variability is found further north in the Bay of Bengal where river outflows help maintain strong salinity gradients throughout the year. For that case, a comparison with satellite observations of sea surface height anomalies, sea surface temperature, and chlorophyll shows that the model captures the observed mesoscale eddy features of the flow field, but in addition, submesoscale upwelling and downwelling patterns associated with ageostrophic secondary circulations along density fronts are also captured by the model.     

Finite-Element-Berechnungen zur Auswertung herdmechanischer Daten und deren Beziehungen zum Störungsmuster des Ägäis-Raumes

Zusammenfassung Für den Ägäis-Raum liegt seitRitsema 1974 ein umfangreiches Material herdmechanischer Daten vor. In der vorliegenden Studie wird daher die Rekonstruktion der Spannungsfelder aus den Richtungen der maximalen Kompression über ein ebenes Finite-Element-Modell versucht. Die auf diese Weise simulierten Bruchstrukturen werden mit den aus Luftbild- und Satellitenbild-Interpretation ermittelten Photolineationen sowie mit den Ergebnissen bathymetrischer und reflexions-seismischer Untersuchungen verglichen, um zu Aussagen über symmetrologische Beziehungen zwischen rezentem bzw. subrezentem Störungsmuster und rezenten Spannungsverteilungen zu gelangen.

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SinceRitsema 1974 a large amount of focal plane data exists for the Aegean. In this study the reconstruction of the stress field due to the direction of maximum compression as found inRitsema is attempted in a Finite-Element model. The fracture patterns thus simulated are compared with the results of photolineations ascertained from airphotos and satellite images as well as bathymetric and reflection — seismic investigations, in order to determine if a relation exists between the recent or subrecent fracture pattern and the recent stress distribution.

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Résumé DepuisRitsema 1974 un matériel considerable de données existe sur les mécanismes aux foyers des tremblements de terre de la région égéenne. Dans l'étude présente nous essayons done de reconstruire le champ des contraintes à partir des directions de la compression maximale au moyen d'un modèle d'élément-finite. Afin d'arriver à une conclusion sur des relations symmétrologiques entre les directions des failles récentes, respectivement subrécentes, et les répartitions de contraintes récentes, on doit comparer les failles ainsi simulées avec des photolinéations déterminées au moyen de l'interprétation des photos aériennes et satellites d'une part, et des résultats obtenus des recherches bathymétriques et réflexion-sismiques d'autre part.

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