Effects of ocean particles on the upwelling radiance and polarized radiance in the atmosphere-ocean system

Based on a vector radiative transfer model of the atmosphere-ocean system, the influence of oceanic components on radiation processes, including polarization effects, was investigated in the wavelength region ranging from 0.380 to 0.865 μm. The components considered were phytoplankton, inorganic suspended material (sediment), and colored, dissolved organic matter. Due to their important roles in oceanic radiation processes, the sensitivity of the bidirectional reflectance to the rough ocean surface, represented by the wind velocity 10 m above the ocean surface, and aerosol, were taken into account. The results demonstrated that both radiance and polarized radiance just below the ocean surface were sensitive to the change of the concentrations of the considered components, while the dependence of polarized radiance on the observation geometry was more sensitive than radiance. Significant differences in the specular plane existed between the impacts of the phytoplankton and sediment on the degree of polarization just above the ocean surface at 670 nm. At the top of the atmosphere (TOA), polarization was relatively insensitive to changing concentrations of ocean particles at longer wavelengths. Furthermore, the radiance at the TOA in the solar plane was more sensitive to the aerosol optical thickness than wind velocity. In contrast, wind velocity strongly influenced the radiance at the TOA in the sun glint region, while the polarization degree showed less dependence in that region. Finally, a nonlinear optimal inversion method was proposed to simultaneously retrieve the aerosol and wind velocity using radiance measurement.     

Kinematic dynamos associated with large scale fluid motions

Abstract

A standard approach to the kinematic dynamo problem is that pioneered by Bullard and Gellman (1954), which utilizes the toroidal-poloidal separation and spherical harmonic expansion of the magnetic and velocity fields. In these studies, the velocity field is given as a combination of small number of toroidal and poloidal harmonics, with their radial dependences prescribed by some physical considerations. Starting from the original paper of Bullard and Gellman (1954), a number of authors repeated such analyses on different combination of velocity fields, including the most recent and comprehensive effort by Dudley and James (1989). In this paper, we re-examine the previous kinematic dynamo models, using the computer algebra approach initiated by Kono (1990). This method is particularly suited to this kind of research since different velocity fields can be treated by a single program. We used the distribution of magnetic energies in various harmonics to infer the convergence of the results.

The numerical results obtained in this study for the models of Bullard and Gellman (1954), Lilley (1970), Gubbins (1973), Pekeris et al. (1973), Kumar and Roberts (1975), and Dudley and James (1989) are consistent with the previously reported results, in particular, with the extensive calculation of Dudley and James. In addition, we found that the combination of velocities used by Lilley can support the dynamo action if the radial dependence of the velocity is modified.

We also examined the helicity distributions in these dynamo models, to see if there is any correlation between the helicity and the efficiency of dynamo action. A successful dynamo can result both from the cases in which the helicity distributions are symmetric or antisymmetric with respect to the equator. In both cases, it appears that the dynamo action is efficient if the volume integral of helicity over a hemisphere is large.     

Geology of the Kokchetav UHP-HP metamorphic belt, Northern Kazakhstan

Abstract Ultrahigh-pressure metamorphic (UHPM) rocks of the Kokchetav Massif of Kazakhstan contain metamorphic microdiamond and coesite inclusions inside rigid capsules such as garnet and zircon. Precambrian protoliths of the UHPM rocks were metamorphosed at around 530 Ma, at pressures of about 7 GPa, which suggests that crustal protoliths were subducted to depths of over 200 km. Primary UHPM minerals are poorly preserved due to partial obliteration by subsequent Barrovian overprint during exhumation and later collision events in Caledonian times. We report the results of detailed mapping of the Kokchetav Massif and use structural data to propose intrusion and exhumation mechanisms for the UHPM rocks. Detailed mapping revealed that many subvertical structures in the ultrahigh-pressure–high-pressure (UHP–HP) units were formed due to later folding. The primary structure appears to be subhorizontal and the total thickness of the UHP rocks is estimated at around 2 km. The first order structure is sandwich-like; that is, the UHP–HP units are separated from underlying low-P metamorphic rocks of the Daulet Series and from feebly metamorphosed to unmetamorphosed sedimentary strata on the top by subhorizontal faults. Kinematic indicators show top-to-the-south sense of shear along the top, and top-to-the-north displacement along the bottom boundaries. These shear senses, together with the observed metamorphic gradients, suggest that the thin UHPM sheet was extruded toward the north. We consider wedge extrusion to have been the most effective mechanism for the exhumation of the UHPM rocks.     

Distribution of nitrate in groundwater affected by the presence of an aquitard at an agricultural area in Chiba, Japan

Geological and geographical parameters including land use, stratigraphic structure, groundwater quality, and N- and O-isotopic compositions of nitrate in groundwater were investigated to elucidate the mechanism of groundwater pollution by NO₃ ^? in the agricultural area of Katori, Chiba, Japan. An aquitard distributed in the western part of the study area has produced two unconfined aquifers. The average concentrations of NO₃ ^? and dissolved oxygen (DO) were high in the aquifer above the aquitard (7.5 and 7.6 mg/L, respectively) and in the aquifer of the eastern part of the study area that was not influenced by the aquitard (11.9 and 7.8 mg/L, respectively); however, the levels in the aquifer under the aquitard were relatively low (2.2 and 3.7 mg/L, respectively). The δ¹⁵N and δ¹⁸O values of NO₃ ^? generally increased exponentially in the groundwater that flowed into the aquifer under the aquitard as the concentration of NO₃ ^? decreased, although this decrease in NO₃ ^? also occasionally occurred without isotopic changes. These results indicated that the aquitard prevented the penetration of NO₃ ^?, DO, and gaseous O₂. Under the aquitard, denitrification and dilution with unpolluted water that entered from natural forested areas reduced the NO₃ ^? concentrations in the groundwater. The major sources of NO₃ ^? in groundwater in the study area were estimated to be NH₄-chemical fertilizer, livestock waste, and manure.     

Advanced mosasaurs from the Upper Cretaceous Nakaminato Group in Japan

Plotosaurus is a highly aquatically adapted mosasaur, which is supposed to inhabit the deep ocean basin. The geographic occurrence of this genus has been limited only to the west coast of North America. In this study, two Plotosaurus-type mosasaur caudal vertebrae derived from the Upper Cretaceous Nakaminato Group in Ibaraki Prefecture, Japan, are described with discussion on the paleobiogeographic significance of the Late Cretaceous mosasaur fauna in the Northwestern Pacific region. The two specimens are an intermediate caudal vertebra found in a beach cobble, which presumably originated from the Hiraiso Formation (upper Campanian), and a terminal caudal vertebra found in situ in the lower Isoai Formation (lower Maastrichtian). Because their relative centrum lengths (ratio of centrum length/centrum height, ~0.7) are very close to that of Plotosaurus, the specimens are referred to cf. Plotosaurus sp. The two specimens provide the first evidence that highly specialized Plotosaurus-type mosasaurs inhabited the Northwestern Pacific Ocean, suggesting that such forms had a wider distribution than previously recognized and might have existed since the late Campanian in the Northwestern Pacific Ocean.     

Phase transition of zircon at high P-T conditions

Abstract In situ observations of the zircon-reidite transition in ZrSiO₄ were carried out using a multianvil high-pressure apparatus and synchrotron radiation. The phase boundary between zircon and reidite was determined to be P (GPa) = 8.5+0.0017×(T-1200) (K) for temperatures between 1100–1900 K. When subducted slabs, including igneous rocks and sediments, descend into the upper mantle, the zircon in the subducted slab transforms into reidite at pressures of about 9 GPa, corresponding to a depth of 270 km. Reidite found in an upper Eocene impact ejecta layer in marine sediments is thought to have been transformed from zircon by a shock event. The peak pressure generated by the shock event in this occurrence is estimated to be higher than 8 GPa.Editorial responsibility: J. Hoefs     

Tomographic imaging of seismic velocity structure in and around the Onikobe volcanic area, northeastern Japan: implications for fluid distribution

We estimated three-dimensional P- (V_p) and S-wave velocity (V_s) and V_p/V_s structures in and around the Onikobe volcanic area, northeastern Japan, by local travel time tomography. We used travel time data from source and receiver pairs located within and outside the study area, which plays an important role in obtaining the optimum ray coverage and in elucidating the deeper structure more accurately. Detailed information on deeper structures is essential for imaging the complete volcanic system from the magmatic source zone through areas of shallow hydrothermal circulation. More than 50 000 travel time data for the P-waves and 35 000 for the S-waves were used to image the velocity structure. Our results show the following dominant features: (1) two conduits in the upper crust with low V_p and low V_s indicative of H₂O-rich fluid pathways: one lying beneath Naruko volcano, the other beneath the focal area of the 1962 Northern Miyagi earthquake (M6.5); (2) an underlying broad region in the lower crust with low V_p, low V_s and high V_p/V_s, suggestive of a zone of partial melt, from which the fluids in (1) are derived; and (3) low V_p/V_s areas near the surface of the Sanzugawa and Onikobe calderas, suggesting a diffuse vapor-saturated cap.     

The Water-Ammonia Phase Diagram up to 300 MPa: Application to Icy Satellites

We performed high-pressure experiments on the crystallization of water ice I and III in the ammonia-water (NH₃)_x(H₂O)_(1−x) system, and apply the results to the interiors of icy bodies in the Solar System. Phase equilibrium lines between an entirely liquid solution and a liquid solution in which water ice forms (liquidus lines) were determined for ammonia concentration by mass X equal to 0.034, 0.0472, 0.111, 0.176, and 0.229. Growth-melting of ice I as well as ice III crystals were observed. Application of the results to icy satellites that are potential bearers of ammonia shows that ammonia admixture decreases the depth of the liquidus surface. A shift of the liquidus temperature within a satellite depends on three parameters: the ammonia concentration, X; the temperature gradient, α; and the product of density and gravity, ρg.     

Modelling radiation quantities and photolysis frequencies in the troposphere

STAR (System for Transfer of Atmospheric Radiation) was developed to calculate accurately and efficiently the irradiance, the actinic flux, and the radiance in the troposphere. Additionally a very efficient calculation scheme to computer photolysis frequencies for 21 different gases was evolved. STAR includes representative data bases for atmospheric constituents, especially aerosol particles. With this model package a sensitivity study of the influence of different parameter on photolysis frequencies in particular of O₃ to Singlet D oxygen atoms, of NO₂, and of HCHO was performed. The results show the quantitative effects of the influence of the solar zenith angle, the ozone concentration and vertical profile, the aerosol particles, the surface albedo, the temperature, the pressure, the concentration of NO₂, and different types of clouds on the photolysis frequencies.Notation I _A(, ) actinic flux - I _H(, ) irradiance - L(, , , ) radiance - wavelength - azimuth angle - cosine of zenith angle - _s cosine of solar zenith angle - optical depth - _s scattering coefficient - _c extinction coefficient - _o single scattering albedo - p _mix mixed phase function - g _mix mixed asymmetry factor - J _gas photolysis frequency