Effects of Random Flows on the Solar f Mode: I. Horizontal Flow     

Nils Mole  Andrea Kerekes  Robert Erdélyi 《Solar physics》2008,251(1-2):453-468

We examine the effect of random horizontal flows on the dispersion relation of high-degree solar f modes. We follow the approach of Murawski and Roberts (Astron. Astrophys. 272, 595, 1993), addressing some limitations of that paper, and extending the results to include damping and to apply for a general turbulent spectrum. We find a reduction in frequency below the classical result that is about three times that observed. For large wavenumber the damping rate is larger than the frequency correction by a factor of the order of the nondimensional wavenumber, which appears to be consistent with observation.  相似文献   

Simulating the diurnal cycle of rainfall in global climate models: resolution versus parameterization   总被引：1，自引：1，他引：0  

Paul A. Dirmeyer  Benjamin A. Cash  James L. Kinter III  Thomas Jung  Lawrence Marx  Masaki Satoh  Cristiana Stan  Hirofumi Tomita  Peter Towers  Nils Wedi  Deepthi Achuthavarier  Jennifer M. Adams  Eric L. Altshuler  Bohua Huang  Emilia K. Jin  Julia Manganello 《Climate Dynamics》2012,39(1-2):399-418

The effects of horizontal resolution and the treatment of convection on simulation of the diurnal cycle of precipitation during boreal summer are analyzed in several innovative weather and climate model integrations. The simulations include: season-long integrations of the Non-hydrostatic Icosahedral Atmospheric Model (NICAM) with explicit clouds and convection; year-long integrations of the operational Integrated Forecast System (IFS) from the European Centre for Medium-range Weather Forecasts at three resolutions (125, 39 and 16 km); seasonal simulations of the same model at 10 km resolution; and seasonal simulations of the National Center for Atmospheric Research (NCAR) low-resolution climate model with and without an embedded two-dimensional cloud-resolving model in each grid box. NICAM with explicit convection simulates best the phase of the diurnal cycle, as well as many regional features such as rainfall triggered by advancing sea breezes or high topography. However, NICAM greatly overestimates mean rainfall and the magnitude of the diurnal cycle. Introduction of an embedded cloud model within the NCAR model significantly improves global statistics of the seasonal mean and diurnal cycle of rainfall, as well as many regional features. However, errors often remain larger than for the other higher-resolution models. Increasing resolution alone has little impact on the timing of daily rainfall in IFS with parameterized convection, yet the amplitude of the diurnal cycle does improve along with the representation of mean rainfall. Variations during the day in atmospheric prognostic fields appear quite similar among models, suggesting that the distinctive treatments of model physics account for the differences in representing the diurnal cycle of precipitation.  相似文献   

Seismic hazard parameter estimation of the Mount Cameroon volcanic region (Cameroon) based on a combination of mixed catalogs     

Wetie Ngongang  Ariane  Lenhardt  Nils  Smit  Ansie 《Natural Hazards》2019,96(1):369-388

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Energy dissipation within the wave run-up at stepped revetments     

Nils B. Kerpen  Daniel B. Bung  Daniel Valero  Torsten Schlurmann 《中国海洋大学学报(英文版)》2017,16(4):649-654

To understand the processes and energy dissipation performance caused by turbulence during the wave run-up over a stepped revetment, hydraulic model tests with steady flow conditions are conducted and correlated with unsteady flow conditions of the wave run-up within a short time frame. Under irregular waves, the run-up reduction over a stepped revetment is dependent on the Iribarren number and decreases for decreasing Iribarren numbers. Velocity gradients are found to be similar in a steady and unsteady flow regime near the pseudo-bottom.  相似文献   

Petrology, magnetostratigraphy and geochronology of the Miocene volcaniclastic Tepoztlán Formation: implications for the initiation of the Transmexican Volcanic Belt (Central Mexico)     

Nils Lenhardt  Harald Böhnel  Klaus Wemmer  Ignacio S. Torres-Alvarado  Jens Hornung  Matthias Hinderer 《Bulletin of Volcanology》2010,72(7):817-832

The volcaniclastic Tepoztlán Formation (TF) represents an important rock record to unravel the early evolution of the Transmexican Volcanic Belt (TMVB). Here, a depositional model together with a chronostratigraphy of this Formation is presented, based on detailed field observations together with new geochronological, paleomagnetic, and petrological data. The TF consists predominantly of deposits from pyroclastic density currents and extensive epiclastic products such as tuffaceous sandstones, conglomerates and breccias, originating from fluvial and mass flow processes, respectively. Within these sediments fall deposits and lavas are sparsely intercalated. The clastic material is almost exclusively of volcanic origin, ranging in composition from andesite to rhyolite. Thick gravity-driven deposits and large-scale alluvial fan environments document the buildup of steep volcanic edifices. K-Ar and Ar-Ar dates, in addition to eight magnetostratigraphic sections and lithological correlations served to construct a chronostratigraphy for the entire Tepoztlán Formation. Correlation of the 577 m composite magnetostratigraphic section with the Cande and Kent (1995) Geomagnetic Polarity Time Scale (GPTS) suggests that this section represents the time intervall 22.8–18.8 Ma (6Bn.1n-5Er; Aquitanian-Burdigalian, Lower Miocene). This correlation implies a deposition of the TF predating the extensive effusive activity in the TMVB at 12 Ma and is therefore interpreted to represent its initial phase with predominantly explosive activity. Additionally, three subdivisions of the TF were established, according to the dominant mode of deposition: (1) the fluvial dominated Malinalco Member (22.8–22.2 Ma), (2) the volcanic dominated San Andrés Member (22.2–21.3 Ma) and (3) the mass flow dominated Tepozteco Member (21.3–18.8 Ma).  相似文献   

Reduction of nitrogen compounds in oceanic basement and its implications for HCN formation and abiotic organic synthesis     

Nils G Holm  Anna Neubeck 《Geochemical transactions》2009,10(1):9-11

Hydrogen cyanide is an excellent organic reagent and is central to most of the reaction pathways leading to abiotic formation of simple organic compounds containing nitrogen, such as amino acids, purines and pyrimidines. Reduced carbon and nitrogen precursor compounds for the synthesis of HCN may be formed under off-axis hydrothermal conditions in oceanic lithosphere in the presence of native Fe and Ni and are adsorbed on authigenic layer silicates and zeolites. The native metals as well as the molecular hydrogen reducing CO₂ to CO/CH₄ and NO₃ ^-/NO₂ ^- to NH₃/NH₄ ⁺ are a result of serpentinization of mafic rocks. Oceanic plates are conveyor belts of reduced carbon and nitrogen compounds from the off-axis hydrothermal environments to the subduction zones, where compaction, dehydration, desiccation and diagenetic reactions affect the organic precursors. CO/CH₄ and NH₃/NH₄ ⁺ in fluids distilled out of layer silicates and zeolites in the subducting plate at an early stage of subduction will react upon heating and form HCN, which is then available for further organic reactions to, for instance, carbohydrates, nucleosides or even nucleotides, under alkaline conditions in hydrated mantle rocks of the overriding plate. Convergent margins in the initial phase of subduction must, therefore, be considered the most potent sites for prebiotic reactions on Earth. This means that origin of life processes are, perhaps, only possible on planets where some kind of plate tectonics occur.  相似文献   

The transmission of mass and angular momentum from a satellite or planetary system to its primary     

Nils Aall Barricelli 《Astrophysics and Space Science》1972,15(3):479-501

In this paper main implication of basic properties detected in the satellite systems of Jupiter, Saturn and Uranus, and presented by the author in an earlier contribution (Barricelli, 1971b) are investigated. The similarity between the primary periods in the three systems, their apparent relation to the axial rotation periods of the three planets and other features suggesting that collisions with the planetary surfaces may have played a role in the evolution of the three satellite systems are interpreted by assuming that in each case a satellite of unusually large size was originally disintegrated at the Roche limit of its primary. The disintegration of large satellites and their fusion with the respective planets is assumed to be a normal feature in the latest stage of planetary growth and the main cause of axial rotation in the respective planets.These assumptions make it possible to give a selfconsistent interpretation of the similarity between the axial rotation periods of the three planets and their relation to the primary periods (as defined by Barricelli, 1971b) in the three systems.Similar assumptions when applied to the Earth-Moon system make it possible to understand why the Moon, in its closest approach to the Earth is found to have been almost exactly at the Roche limit (Gerstenkorn, 1955; MacDonald, 1964), a coincidence which is too good to be accidental. According to this interpretation our Moon is a portion (representing about one third) of our original satellite, which survived its approach to the Roche limit and the ensuing fusion process with the Earth. It can be shown (see text) that under certain conditions this could leave a residual satellite with a stationary distance from the Earth (which in retrospect would be identified as its lowest distance from the Earth) at the Roche limit.The only other case in which we have observational evidence of parts of a satellite surviving its fusion process at the Roche limit is represented by the rings of Saturn and possibly the small innermost satellite Janus which seems to have been feeding on the rings.  相似文献   

The axial rotation of planets and transfer of mass and angular momentum from a satellite system to its primary     

Nils Aall Barricelli 《Earth, Moon, and Planets》1988,41(1):1-43

The main topic of this paper is to investigate the exchange of mass and angular momentum between a satellite or planetary system and its primary, and the effects of this exchange to axial rotations and satellite orbits. Various applications on the calculation of axial rotations, present and past satellite masses and orbits and other implications of the theory are presented.  相似文献   

Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution. II. Formation constants for the monosilicate ions SiO(OH)3− and SiO2(OH)22−. A precision study at 25°C in a simplified seawater medium     

Staffan Sjöberg  Agneta Nordin  Nils Ingri 《Marine Chemistry》1981,10(6):521-532

The hydrolysis of silicic acid, Si(OH)₄, was studied in a simplified seawater medium (0.6 M Na(Cl)) at 25°C. The measurements were performed as potentiometric titrations (hydrogen electrode) in which OH^? was generated coulometrically. The total concentration of Si(OH)₄, B, and log[H⁺] were varied within the limits 0.00075 ? B ? 0.008 M and 2.5 ? -log[H⁺] ? 11.7, respectively. Within these ranges the formation of SiO(OH)₃^? and SiO₂(OH)₂^2? with formation constants log β_?11(Si(OH)₄ ? SiO(OH)₃^? + H⁺) = ?9.472 ±0.002 and log β_?21(Si(OH)₄ ? SiO₂(OH)₂^2? + 2H⁺) = ?22.07 ± 0.01 was established. With B > 0.003 M polysilicate complexes are formed, however, with $\text{-}\text{log[H}{}^{\mathrm{+}}\text{] ? 10.7}$ their formation does not significantly affect the evaluated formation constants. Data were analyzed with the least squares computer program LETAGROPVRID.  相似文献   

Redox cycling of iron and manganese in sediments of the Kalix River estuary, Northern Sweden     

Anders Widerlund  Johan Ingri 《Aquatic Geochemistry》1996,2(2):185-201

Iron and manganese redox cycling in the sediment — water interface region in the Kalix River estuary was investigated by using sediment trap data, pore-water and solid-phase sediment data. Nondetrital phases (presumably reactive Fe and Mn oxides) form substantial fractions of the total settling flux of Fe and Mn (51% of Fe_total and 84% of Mn_total). A steady-state box model reveals that nondetrital Fe and Mn differ considerably in reactivity during post-depositional redox cycling in the sediment. The production rate of dissolved Mn (1.6 mmol m^–2 d^–1) exceeded the depositional flux of nondetrital Mn (0.27 mmol m^–2 d^–1) by a factor of about 6. In contrast, the production rate of upwardly diffusing pore-water Fe (0.77 mmol m^–2 d^–1) amounted to only 22% of the depositional flux of nondetrital Fe (3.5 mmol m^–2 d^–1). Upwardly diffusing pore-water Fe and Mn are effectively oxidized and trapped in the oxic surface layer of the sediment, resulting in negligible benthic effluxes of Fe and Mn. Consequently, the concentrations of nondetrital Fe and Mn in permanently deposited, anoxic sediment are similar to those in the settling material. Reactive Fe oxides appear to form a substantial fraction of this buried, non-detrital Fe. The in-situ oxidation rates of Fe and Mn are tentatively estimated to be 0.51 and 0.16–1.7 mol cm^–3 d^–1, respectively.  相似文献