Observations of PC5 pulsations near field-aligned current regions     

Alexander Z. Bochev  Karel Kudela  Iren A. Dimitrova  Petko Nenovski  Ashwini K. Sinha  Marián Slivka 《Studia Geophysica et Geodaetica》2009,53(4):537-556

Examples of long period Pc5 magnetic field pulsations near field-aligned current (FAC) regions in the high-latitude magnetosphere, observed by INTERBALL-Auroral satellite during January 11, April 11 and June 28, 1997 are shown. Identification of corresponding magnetosphere regions and subregions is provided by electrons and protons in the energy-range of 0.01–100 keV measured simultaneously onboard the spacecraft. The examined Pc5 pulsations reveal a compressional character. A fairly good correlation is demonstrated between these ULF Pc5 waves and the consecutive injection of magnetosheath low energy protons. The ULF Pc5 wave occurrence is observed in both upward and downward FACs.  相似文献   

On the cumulant expansion up scaling of ground water contaminant transport equation with nonequilibrium sorption     

Hakan Sirin  Miguel A. Mariño 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(4):551-565

The laboratory-scale ground water transport equation with nonequilibrium sorption reaction subjected to unsteady, nondivergence-free, and nonstationary velocity fields is up-scaled to the field-scale by using the ensemble-averaged equations obtained from the cumulant expansion ensemble-averaging method. It is found that existing ensemble-averaged equations obtained with the help of the cumulant expansion method for the system of linear partial differential equations are not second-order exact. Although the cumulant expansion methodology is designed for noncommuting operators, it is found that there are still commudativity requirements that need to be satisfied by the functions and constants exist in the coefficient matrix of the system of ordinary/partial differential equations. A reversibility requirement, which covers the commudativity requirements, is also proposed when applying the cumulant expansion method to a system of partial differential equations/a partial differential equation. The significance of the new velocity correction obtained in this study due to the applied second-order exact cumulant expansion is investigated on a numerical example with a linear trend in the distribution coefficient. It is found that the effect of the new velocity correction can be significant enough to affect the maximum concentration values and the plume center of mass in the case of a trending distribution coefficient in a physically heterogeneous environment.  相似文献   

Curvature derived from LiDAR digital elevation models as simple indicators of debris-flow susceptibility     

Atsuko NONOMURA  Shuichi HASEGAWA  Hideo MATSUMOTO  Mari TAKAHASHI  Mina MASUMOTO  Kazuhito FUJISAWA 《山地科学学报》2019,(1):95-107

To mitigate the damage caused by debris flows resulting from heavy precipitation and to aid in evacuation plan preparation, areas at risk should be mapped on a scale appropriate for affected individuals and communities. We tested the effectiveness of simply identifying debris-flow hazards through automated derivation of surface curvatures using LiDAR digital elevation models. We achieved useful correspondence between plan curvatures and areas of existing debris-flow damage in two localities in Japan using the analysis of digital elevation models(DEMs). We found that plan curvatures derived from 10 m DEMs may be useful to indicate areas that are susceptible to debris flow in mountainous areas. In residential areas located on gentle sloping debris flow fans, the greatest damage to houses was found to be located in the elongated depressions that are connected to mountain stream valleys. Plan curvaturederived from 5 m DEM was the most sensitive indicators for susceptibility to debris flows.  相似文献   

Cretaceous transformation from passive to active continental margin in the Western Carpathians as indicated by the sedimentary record in the Infratatric unit     

Marián Putiš  Hans-Jürgen Gawlick  Wolfgang Frisch  Marián Sulák 《International Journal of Earth Sciences》2008,97(4):799-819

The Cretaceous orogen of the Western Carpathians comprises fragments of the destructed northern Centrocarpathian domain, which is defined as Infratatric unit and formed a continental margin facing the Penninic Ocean in Jurassic and Cretaceous times. The breakup event and opening of the Penninic Ocean occurred in the Early Jurassic (Pliensbachian), which is recorded by an abrupt deepening event from shallow-water sediments to deep-water nodular limestone in the Infratatric sediment succession. The transformation of the passive into an active continental margin by the onset of subduction of the Penninic oceanic crust occurred in Santonian times and is reflected by the beginning of flysch deposition in the Infratatric Belice domain, which took the position of a forearc basin in the convergent margin setting. The forearc basin was supplied by clastic material from the more internal part of the Infratatric unit, which experienced nappe stacking, metamorphism, and subsequent exhumation in Late Cretaceous times. In the frontal part of the forearc basin an accretionary wedge was built up, which formed an outer-arc ridge and delivered detrital material into the forearc basin in Maastrichtian time. Final collision between the European and the Adriatic plate occurred in the Eocene period and is responsible for weak metamorphism in the Infratatric unit.  相似文献   

Temporal changes in pelagic copepod assemblages off Ubatuba,Brazil          下载免费PDF全文

Mauro Melo Júnior  Catarina R. Marcolin  Leonardo K. Miyashita  Rubens M. Lopes 《Marine Ecology》2016,37(4):877-890

The inner shelf waters off Southeastern Brazil are periodically enriched by bottom intrusions of the cold and nutrient‐rich South Atlantic Central Water (SACW), which is transported offshore by the Brazil Current. This study examined the temporal contrasts in abundance and structure of pelagic copepod assemblages in a neritic station off Ubatuba, in relation to hydrography and phytoplankton biomass, to investigate the effects of SACW bottom intrusions on copepod population dynamics during three consecutive years. The water‐column characteristics shifted from a well‐mixed, more turbid and phytoplankton‐poor scenario during subsidence conditions to a stratified, less turbid and high Chl‐a concentration scenario during SACW bottom intrusions, leading to increased copepod diversity, abundance, and biomass. The rise in copepod diversity during SACW intrusions was related to the contribution of oceanic species in addition to coastal water species. The copepod community was numerically dominated by small‐sized species, such as Oncaea waldemari, Oithona plumifera, and clausocalanid and paracalanid copepodids, regardless of seasonality and SACW intrusions. Some large calanoid species contributed considerably to the total copepod biomass during intrusions. In addition to confirming that SACW seasonal intrusions play a key role in pelagic processes off Southeast Brazil, this study showed that the multiannual variability of SACW seasonal intrusions is important in regulating the structure and dynamics of copepod communities in this subtropical area.  相似文献   

Interannual fluctuations in recruitment of walleye pollock in the Oyashio region related to environmental changes     

Osamu Shida  Tomonori Hamatsu  Akira Nishimura  Akifumi Suzaki  Jun Yamamoto  Kazushi Miyashita  Yasunori Sakurai 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2822

The Japanese Pacific walleye pollock (Theragra chalcogramma) stock is the largest stock of this species in Japanese waters. It is a key component of the Oyashio ecosystem. In southern Hokkaido waters, these fish spawn mainly during January and February near the mouth of Funka Bay (FB), and most eggs and larvae are transported into FB. During midsummer juvenile pollock migrate along the southern coast of Hokkaido to a nursery ground on the continental shelf off eastern Hokkaido (Doto area). However, some eggs and larvae are transported southward to the Tohoku region (TR). Transport depends largely on the Oyashio, which generally flows southward along the eastern coasts of Hokkaido and Tohoku. Thus, this stock has two different recruitment routes: FB–Doto and FB–TR. In the 1980s, when the southward flow of the Oyashio was strong, the number of age-2 pollock estimated from a virtual population analysis (VPA) indicated that recruitment to the entire stock remained at a medium level. In the 1990s, when the Oyashio weakened, strong year-classes occurred in 1991, 1994, and 1995, but not in the latter half of the 1990s. Juvenile catches in the TR by commercial fisheries, which can be taken as indices of recruitment level via FB–TR, were high during the 1980s and decreased in the 1990s. Although there was no significant difference in the average number of recruits between the 1980s and the 1990s as estimated from a VPA, the recruitment patterns differed between the two decades. Here, we propose that recruitment routes of this stock shifted in response to environmental changes.  相似文献   

Diurnal changes in the acoustic-frequency characteristics of Japanese anchovy (Engraulis japonicus) post-larvae "shirasu" inferred from theoretical scattering models     

Miyashita  Kazushi 《ICES Journal of Marine Science》2003,60(3):532-537

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Target strength of mesopelagic lanternfishes (family Myctophidae) based on swimbladder morphology   总被引：3，自引：1，他引：3  

Yasuma  Hiroki; Sawada  Kouichi; Ohshima  Tatsuki; Miyashita  Kazushi; Aoki  Ichiro 《ICES Journal of Marine Science》2003,60(3):584-591

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2-Gyr Simulation of the Oort-Cloud Formation. I. Introduction on a New Model of the Outer Oort-Cloud Formation     

Luboš Neslušan  Piotr A. Dybczyński  Giuseppe Leto  Marián Jakubík  Tomáš Paulech 《Earth, Moon, and Planets》2009,105(2-4):257-261

The study of the reservoirs of small bodies in the Solar System can help us to refine our theory of the origin and evolution of the whole planetary system we live in. In this contribution, we introduce a simulation of the evolution of an initial proto-planetary disc (PPD) for 2 Gyr period, in which 10,038 studied test particles (TPs), representing the disc, are perturbed by four giant planets in their current orbits and having their current masses. In addition, Galactic-tide and stellar perturbations are considered. The outer Oort cloud (OC) appears to be formed within about 0.5 Gyr. At 2 Gyr, only 0.14% of all TPs reside in the outer OC, according to our simulation. This is the largest discrepancy with the results of previous authors. The TPs in the outer OC originate from almost all regions of the PPD. Specifically, 14, 7, 29, 21, and 29% of all TPs, that are the members of the outer OC at 2 Gyr, originate in the Jupiter, Saturn, Uranus, Neptune, and Edgeworth-Kuiper-belt regions, respectively. The largest number of the TPs, 6,669 (66.4%), was ejected into the interstellar space. Besides other results, we found a dominance of high galactic inclinations of outer-OC orbits. Obviously, this is a consequence of the action of Galactic tide.  相似文献   

Few Comments on the Relation Between the Initial Proto-planetary Disc Model and the Oort Cloud Formation     

Tomáš Paulech  Marián Jakubík  Luboš Neslušan  Piotr A. Dybczyński  Giuseppe Leto 《Earth, Moon, and Planets》2009,105(2-4):367-371

A fraction of small bodies from the once existing proto-planetary disc was ejected, by the giant planets, to large heliocentric distances and start to build the comet Oort cloud. Considering four models of initial proto-planetary disc, we attempt to roughly map a dependence between the initial disc’s structure and some properties of the Oort cloud. We find that it is difficult to construct the proto-planetary disc if (i) the amount of heavy chemical elements in Jupiter and Saturn is as high as currently accepted and (ii) the total mass of the minimum-mass solar nebula is assumed to be lower than $\approx0.05\,\hbox{M}_{\odot}.$ The behaviour of the Oort cloud formation does not crucially depend on the initial disc model. Some differences in its structure are obvious: since the cloud is known to be filled mainly by Uranus and Neptune, the efficiency of its formation is higher when the initial amount of particles in the Uranus-Neptune region is relatively higher. A significantly large number of Jupiter Trojans in our simulation appears, however, only in the case of the initially non-gapped disc, with the particles situated also close to the Jupiter’s orbit.  相似文献