Radiative Instability of a Barotropic Jet Flow in a Rotating Stratified Atmosphere     

Kalashnik  M. V. 《Izvestiya Atmospheric and Oceanic Physics》2019,55(3):229-234

Izvestiya, Atmospheric and Oceanic Physics - This paper investigates the stability of a jet flow with a piecewise linear velocity profile in a rotating stratified atmosphere. The linearized set of...  相似文献   

Studies of Sedimentary Matter Fluxes along a Long-Term Transoceanic Transect in the North Atlantic and Arctic Interaction Area     

Klyuvitkin  A. A.  Novigatsky  A. N.  Politova  N. V.  Koltovskaya  E. V. 《Oceanology》2019,59(3):411-421

Oceanology - New data are presented on sedimentary matter fluxes and its main components along a meridional transect (59°30′ N) in the North Atlantic under the effect of multidirectional...  相似文献   

Organized Roll Circulation and Transport of Mineral Aerosols in the Atmospheric Boundary Layer     

Vazaeva  N. V.  Chkhetiani  O. G.  Maksimenkov  L. O. 《Izvestiya Atmospheric and Oceanic Physics》2019,55(2):152-166

Izvestiya, Atmospheric and Oceanic Physics - An investigation into mesoscale roll circulation and its transport characteristics in the atmospheric boundary layer (ABL) is carried out. The case...  相似文献   

Prospects for Estimating the Properties of a Loose Surface from the Phase Profiles of Polarization and Intensity of the Scattered Light     

Petrova  E. V.  Tishkovets  V. P.  Nelson  R. M.  Boryta  M. D. 《Solar System Research》2019,53(3):172-180

It has been shown that the model of a scattering medium composed of clusters located in the far zones of each other allows some properties of regolith-like surfaces to be quantitatively estimated from the phase dependences of intensity and polarization measured in the backscattering domain. From the polarization profiles, the sizes of particles, the structure and porosity of the medium, and a portion of the surface area covered with a disperse material can be determined. At the same time, the intensity profiles of the scattered light weakly depend on the sizes and structure of particles; they are mainly controlled by the concentration of scatterers in the medium and the shadow-hiding contribution at small phase angles. Since the latter effect is beyond the considered model, a good agreement between the model and the measured intensity cannot be achieved. Nevertheless, if a portion of the surface that participates in coherent backscattering has been found from the phase profile of polarization, the present model makes it possible to determine the relative contribution of the shadow-hiding effect to the brightness surge measured at zero phase angle. This, in turn, may allow the roughness of the scattering surface to be estimated. The model contains no free parameters, but there is currently no possibility to verify it comprehensively by the data obtained in laboratory measurements of the samples with thoroughly controlled characteristics, because such measurements are rare for a wide range of the properties of particles in a medium, their packing density, and phase angles.

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Petrogenesis of lunar impact melt rock meteorite Oued Awlitis 001     

Axel Wittmann  Randy L. Korotev  Bradley L. Jolliff  Kunihiko Nishiizumi  A. J. Timothy Jull  Marc W. Caffee  Michael Zanetti  Anthony J. Irving 《Meteoritics & planetary science》2019,54(10):2167-2188

Oued Awlitis 001 is a highly feldspathic, moderately equilibrated, clast‐rich, poikilitic impact melt rock lunar meteorite that was recovered in 2014. Its poikilitic texture formed due to moderately slow cooling, which judging from textures of rocks in melt sheets of terrestrial impact structures, is observed in impact melt volumes at least 100 m thick. Such coherent impact melt volumes occur in lunar craters larger than ~50 km in diameter. The composition of Oued Awlitis 001 points toward a crustal origin distant from incompatible‐element‐rich regions. Comparison of the bulk composition of Oued Awlitis 001 with Lunar Prospector 5° γ‐ray spectrometer data indicates a limited region of matches on the lunar farside. After its initial formation in an impact crater larger than ~50 km in diameter, Oued Awlitis 001 was excavated from a depth greater than ~50 m. The cosmogenic nuclide inventory of Oued Awlitis 001 records ejection from the Moon 0.3 Ma ago from a depth of at least 4 m and little mass loss due to ablation during its passage through Earth's atmosphere. The terrestrial residence time must have been very short, probably less than a few hundred years; its exact determination was precluded by a high concentration of solar cosmic ray‐produced ¹⁴C. If the impact that excavated Oued Awlitis 001 also launched it, this event likely produced an impact crater >10 km in diameter. Using petrologic constraints and Lunar Reconnaissance Orbiter Camera and Diviner data, we test Giordano Bruno and Pierazzo as possible launch craters for Oued Awlitis 001.  相似文献   

A Holistic Approach to Upwelling and Downwelling along the South-West Coast of India     

Phiros Shah  R. Sajeev  K. J. Thara  Grinson George  Muhammad Shafeeque  S. Akash 《Marine Geodesy》2019,42(1):64-84

An attempt has been made to develop a holistic understanding of upwelling and downwelling along the south-west coast of India. The main objective was to elucidate the roles of different forcings involved in the vertical motion along this coast. The south-west coast of India was characterized by upwelling during the south-west monsoon (May to September) and by downwelling during the north-east monsoon and winter (November to February). The average vertical velocity calculated along the south-west coast from the vertical shift of the 26?°C isotherm is 0.57?m/day during upwelling and 0.698?m/day during downwelling. It was concluded that upwelling along the south-west coast of India is driven by offshore Ekman transport due to the alongshore wind, Ekman pumping, horizontal divergence of currents and by the propagation of coastally trapped waves. Whereas downwelling along the coast is driven only by convergence of currents and the propagation of coastally trapped Kelvin waves. Along the west coast of India, the downwelling-favorable Kelvin waves come from the equator and upwelling-favorable waves come from the Gulf of Mannar region.  相似文献   

Testing accretion mechanisms of the H chondrite parent body utilizing nucleosynthetic anomalies     

Sren Grube Pedersen  Martin Schiller  James N. Connelly  Martin Bizzarro 《Meteoritics & planetary science》2019,54(6):1215-1227

Planetary bodies a few hundred kilometers in radii are the precursors to larger planets but it is unclear whether these bodies themselves formed very rapidly or accreted slowly over several millions of years. Ordinary H chondrite meteorites provide an opportunity to investigate the accretion time scale of a small planetary body given that variable degrees of thermal metamorphism present in H chondrites provide a proxy for their stratigraphic depth and, therefore, relative accretion times. We exploit this feature to search for nucleosynthetic isotope variability of ⁵⁴Cr, which is a sensitive tracer of spatial and temporal variations in the protoplanetary disk's solids, between 17 H chondrites covering all petrologic types to obtain clues about the parent body accretionary rate. We find no systematic variability in the mass‐biased corrected abundances of ⁵³Cr or ⁵⁴Cr outside of the analytical uncertainties, suggesting very rapid accretion of the H chondrite parent body consistent with turbulent accretion. By utilizing the μ⁵⁴Cr–planetary mass relationship observed between inner solar system planetary bodies, we calculate that the H chondrite accretion occurred at 1.1 ± 0.4 or 1.8 ± 0.2 Myr after the formation of calcium‐aluminum‐rich inclusions (CAIs), assuming either the initial ²⁶Al/²⁷Al abundance of inner solar system solids determined from angrite meteorites or CAIs from CV chondrites, respectively. Notably, these ages are in agreement with age estimates based on the parent bodies’ thermal evolution when correcting these calculations to the same initial ²⁶Al/²⁷Al abundance, reinforcing the idea of a secular evolution in the isotopic composition of inner disk solids.  相似文献   

Amplitude–Frequency Characteristics of Geomagnetic Noise at Low Frequencies     

Sokol-Kutylovskii  O. L. 《Izvestiya Atmospheric and Oceanic Physics》2019,55(8):905-912

Izvestiya, Atmospheric and Oceanic Physics - The features of the geomagnetic noise distribution over frequencies in different bandwidths and in the signal accumulation mode are investigated. It is...  相似文献   

Long‐term temporal and spatial patterns in bioeroding sponge distribution at the Abrolhos Bank,Brazil, Southwestern Atlantic     

Fernando Coreixas de Moraes  Fernanda Cervi  Cludia S. Karez  Leonardo T. Salgado  Rodrigo L. Moura  Gabriella A. Leal  Alex C. Bastos  Gilberto M. Amado‐Filho 《Marine Ecology》2019,40(3)

Bioeroding sponges belong to the most dominant bioeroders, significantly contributing to the erosion of coral reefs. Some species are tolerant or even benefit from environmental conditions such as ocean warming, acidification, and eutrophication. In consequence, increases in sponge bioerosion have been observed on some coral reefs over the last decades. The Abrolhos Bank is the largest coral reef system in the South Atlantic. It has been affected by sedimentation, eutrophication, overfishing, and climate change, mainly affecting coastal reefs, and at lesser intensity outer ones as well. This study aimed to describe spatial and temporal patterns in bioeroding sponge distribution in carbonate substrates in the Abrolhos Bank. Photo‐quadrats were used to compare bioeroding sponge abundance between two shallow reefs: a coastal, Pedra de Leste (PL), and an outer reef, Parcel dos Abrolhos (PAB). Each individual was delimitated over the substrate by determining the sponge surface through a line connecting the outermost papillae. The study was conducted over 6 years in 2008–2009 and 2013–2016. Four species of bioeroding sponges were identified: Cliona carteri Ridley, 1881, C. delitrix Pang, 1973, C. cf. schmidtii Ridley, 1881, and Siphonodictyon coralliphagum Rützler, 1971. The distribution and abundance of species varied between the inner and outer reefs and across the years, and displayed certain selectivity for the calcareous substrates recorded. Crustose coralline algae (CCA) were the main substrate excavated by the most abundant bioeroding species, C. carteri, and represented 70% of the substrate types occupied by this sponge (CCA, coral overgrown by CCA and plain coral). The highest abundance of bioeroding sponges observed in photo‐quadrats was 21.3 individuals/m² at the outer reefs (PAB) in 2014. The abundances or areal extents of bioeroding sponges were up to 10 times greater on the outer reefs than on the coastal ones, where sedimentation is higher and more strongly influenced by siliciclastic material. Moreover, a higher herbivorous fish biomass has been reported on outer reefs which could also influence the higher abundance of bioeroding sponges in outer reefs. During the study period of 6 years, an increase in bioeroding sponge abundance was observed at the outer reefs (PAB), with the sea surface temperature increase. As CCA have an important role in reefal cementation and carbonate production in the Abrolhos reefs, a bioerosion impact might be expected, in particular, on the outer reefs.  相似文献   

Zircon fission‐track ages from Newfoundland—A proxy for high geothermal gradients and exhumation before opening of the Central Atlantic Ocean     

Arne P. Willner  Stuart N. Thomson  Johannes Glodny  Hans‐Joachim Massonne  Rolf L. Romer  Cees R. van Staal  Alexandre Zagorevski 《地学学报》2019,31(1):1-10

Following Appalachian orogenesis, metamorphic rocks in central Newfoundland were exhumed and reburied under Tournaisian strata. New zircon fission‐track (ZFT) ages of metamorphic rocks below the Tournaisian unconformity yield post‐depositionally reset ages of 212–235 Ma indicating regional fluid‐absent reheating to at least ≥220°C. Post‐Tournaisian sedimentary thicknesses in surrounding basins show that burial alone cannot explain such temperatures, thus requiring that palaeo‐geothermal gradients increased to ≥30–40°C/km before final late Triassic accelerated cooling. We attribute these elevated palaeo‐geothermal gradients to localized thermal blanketing by insulating sediments overlying radiogenic high‐heat‐producing granitoids. Late Triassic rifting and magmatism before break up of Pangaea likely also contributed to elevated heat flow, as well as uplift, triggering late Triassic accelerated cooling and exhumation. Thermochronological ages of 240–200 Ma are seen throughout Atlantic Canada, and record rifting and basaltic magmatism on the conjugate margins of the Central Atlantic Ocean preceding the onset of oceanic spreading at ~190 Ma.  相似文献