High-beta plasma blobs in the morningside plasma sheet

Equator-S frequently encountered, i.e. on 30%0of the orbits between 1 March and 17 April 1998, strong variations of the magnetic field strength of typically 5–15-min duration outside about 9R_E during the late-night/early-morning hours. Very high-plasma beta values were found, varying between 1 and 10 or more. Close conjunctions between Equator-S and Geotail revealed the spatial structure of these “plasma blobs” and their lifetime. They are typically 5–10° wide in longitude and have an antisymmetric plasma or magnetic pressure distribution with respect to the equator, while being altogether low-latitude phenomena (<15°). They drift slowly sunward, exchange plasma across the equator and have a lifetime of at least 15–30 min. While their spatial structure may be due to some sort of mirror instability, little is known about the origin of the high-beta plasma. It is speculated that the morningside boundary layer somewhat further tailward may be the source of this plasma. This would be consistent with the preference of the plasma blobs to occur during quiet conditions, although they are also found during substorm periods. The relation to auroral phenomena in the morningside oval is uncertain. The energy deposition may be mostly too weak to generate a visible signature. However, patchy aurora remains a candidate for more disturbed periods.     

Estimation of Oxygen Consumption Rate Using T-DO Diagram in the Benthic Layer of Ohmura Bay, Kyushu, Japan

We have observed the temporal variation of oxygen deficient water with short time scale (less than a few days) in the central area of Ohmura Bay, Kyushu, Japan, in summer, 1995 and 1996. The vertical profiles of temperature were similar to those of dissolved oxygen. We noticed a linear relation between temperature and dissolved oxygen in the bottom layer, and applied the T-DO relation to estimate the net oxygen consumption rate, rather than direct evaluation of the advection and diffusion. Oxygen consumption rate just above the bottom was estimated to be about 0.21 g O₂ m^–3day^–1 in July 1995, and about 0.28 g O₂ m^–3day^–1 in August 1996. The net oxygen consumption rate estimated for the bottom layer below the second thermocline was about 0.61 g O₂ m^–3day^–1 with variability from 0.55 to 0.66 g O₂ m^–3day^–1 during July 25 to 29, 1995. This is was about 0.64 g O₂ m^–3day^–1 with variability from 0.18 to 1.4 g O₂ m^–3day^–1 during August 22 to 30, 1996. The net oxygen consumption rates are about half of those measured with a closed system in the Seto Inland Sea.     

Microplastics in the Southern Ocean

A field survey to collect microplastics with sizes < 5 mm was conducted in the Southern Ocean in 2016. We performed five net-tows and collected 44 pieces of plastic. Total particle counts of the entire water column, which is free of vertical mixing, were computed using the surface concentration (particle count per unit seawater volume) of microplastics, wind speed, and significant wave height during the observation period. Total particle counts at two stations near Antarctica were estimated to be in the order of 100,000 pieces km^? 2.     

The S pole distribution on magnetic grains in pyroxenite determined by magnetotactic bacteria

North-seeking bacteria (NSB) with 1 μm diameters migrate to the S pole only. They were applied to identify the S pole determination on a polished surface of magnetite-rich pyroxenite whose natural remanent magnetization (NRM) intensity was 5.64 × 10⁻³ Am² kg⁻¹. The microscopic observations were performed under dark-field illumination in a controlled magnetic field to 10 μT. The NSB formed clusters on limited areas of magnetite grains and scattered over the whole magnetite grains.

The NRM decreased to 1.02 × 10⁻⁵ Am² kg⁻¹ by alternating field (AF) demagnetization to 60 mT but no clusters appeared, while small populations of the NSB scattered on each grain. These scattered bacteria may gather toward the S pole resulting from magnetic domain walls.

When the sample acquired saturation isothermal remanent magnetization (SIRM) to 1 T, the NSB formed dense clusters at the opposite side to the applied field direction on the many grains as expected. This evidence indicated that the NSB can be useful micro-organisms for the determination of fine magnetic structures. Some grains also had NSB clusters at the edge of the grains toward the field direction or did not exhibit any clusters. The complicated distribution of the clusters (the S poles) may be explained by shape anisotropy of the magnetic grains.     

Long-term high-frequency measurements of dibromomethane in the atmosphere at algae-rich and algae-poor coastal sites

Dibromomethane (CH₂Br₂), a natural stratospheric ozone depleting substance, is mostly emitted from the ocean, but the relative importance of coastal (or macroalgae) and open ocean emissions is unknown. We made long-term high-frequency measurements of CH₂Br₂ concentrations at two remote coastal sites in Japan, on the subtropical Hateruma Island (poor in macroalgae) and at Cape Ochiishi (rich in macroalgae). CH₂Br₂ concentrations at Hateruma showed prominent seasonal variation, being lower in summer (around 0.94 ppt) than in winter (around 1.23 ppt). In contrast, CH₂Br₂ concentrations at Ochiishi were highly variable, often exceeding 2 ppt in the summer but with minimum baseline concentrations close to those from Hateruma; in the winter the concentrations were almost constant at about 1.3 ppt. Analysis of the data suggested that (1) emissions from macroalgae were not likely to extend offshore, but instead were localized near the shore, (2) strong macroalgal emissions of CH₂Br₂ were almost limited to the summer, but it was not reflected in the seasonality of the baseline concentrations of CH₂Br₂ in the atmosphere, and therefore (3) macroalgal or coastal emissions of CH₂Br₂ in the temperate zone might have a rather limited contribution to the global CH₂Br₂ sources. These findings are especially important for the understanding of the tropospheric and stratospheric bromine budget.     

Space weathered rims found on the surfaces of the Itokawa dust particles

On the basis of observations using Cs‐corrected STEM, we identified three types of surface modification probably formed by space weathering on the surfaces of Itokawa particles. They are (1) redeposition rims (2–3 nm), (2) composite rims (30–60 nm), and (3) composite vesicular rims (60–80 nm). These rims are characterized by a combination of three zones. Zone I occupies the outermost part of the surface modification, which contains elements that are not included in the unchanged substrate minerals, suggesting that this zone is composed of sputter deposits and/or impact vapor deposits originating from the surrounding minerals. Redeposition rims are composed only of Zone I and directly attaches to the unchanged minerals (Zone III). Zone I of composite and composite vesicular rims often contains nanophase (Fe,Mg)S. The composite rims and the composite vesicular rims have a two‐layered structure: a combination of Zone I and Zone II, below which Zone III exists. Zone II is the partially amorphized zone. Zone II of ferromagnesian silicates contains abundant nanophase Fe. Radiation‐induced segregation and in situ reduction are the most plausible mechanisms to form nanophase Fe in Zone II. Their lattice fringes indicate that they contain metallic iron, which probably causes the reddening of the reflectance spectra of Itokawa. Zone II of the composite vesicular rims contains vesicles. The vesicles in Zone II were probably formed by segregation of solar wind He implanted in this zone. The textures strongly suggest that solar wind irradiation damage and implantation are the major causes of surface modification and space weathering on Itokawa.     

Consistent DOF reduction of tall steel frames

This paper presents an energy‐consistent approach for reducing the number of degrees‐of‐freedom (DOFs) in tall steel frames. In the present approach, the moment resistance of beams and columns in each story is represented by the moment resistance of a rotational spring and a beam‐column element, respectively. The shear resistance provided by braces in each story is represented by the shear resistance of a shear spring. Furthermore, the resistance to the overturning moment provided by axial resistance of columns in each story is represented by the moment resistance of a rotational spring. These representations are carried out by achieving the equivalence between the strain energy stored and dissipated in the elements in the full (unreduced) DOF models and the strain energy stored and dissipated in the corresponding elements in the reduced DOF models. The accuracy of the present approach is demonstrated through numerical examples, which compare the results of nonlinear time history analyses obtained using the full and reduced DOF models. In the numerical examples, the response is estimated for 20‐story and 40‐story steel frames with and without buckling‐restraint braces subjected to a suite of near‐fault and far‐fault ground motions. The present approach is useful in estimating the response of tall steel frames having non‐regular member arrangements to a suite of intense ground motions including near‐fault ones, where it is crucial to capture the influence of higher mode effects on collapse mechanisms. Copyright © 2017 John Wiley & Sons, Ltd.     

Significance of stemflow in groundwater recharge. 1: Evaluation of the stemflow contribution to recharge using a mass balance approach

Stemflow was evaluated in a water balance and its contribution to groundwater recharge determined. Gross precipitation, throughfall and stemflow were measured for one year in a pine forest (Tsukuba, Japan) to determine each component of the water balance in the forest. Groundwater recharge rates by stemflow and throughfall were calculated from a mass balance method using chloride in subsurface waters. The stemflow in the water balance was relatively small when estimated as a value per canopy projected area of the tree in the forest. However, the results for the mass balance of chloride in subsurface waters indicated that it was impossible to disregard the stemflow in determining groundwater recharge. Although the ratio of stemflow to the net precipitation was small in the water balance, the effect of stemflow on groundwater recharge was relatively large.     

Effects of Larval Settlement and Post-Settlement Mortality on the Distribution Pattern and Abundance of the Spirorbid Tube Worm Neodexiospira brasiliensis (Grube) (Polychaeta) Living on Seagrass Leaves

Abstract. The role of larval settlement, post-settlement mortality and competition with a red algae in determining the patterns of abundance and distribution of the spirorbid tube worm Neodexiospira brasiliensis (Grube) (Polychaeta: Spirorbidae) on leaves of three seagrass species: Zostera marina Linnaeus, Zostera asiatica Miki and Phyllospadix iwatensis Makino were examined in Aininkap, Akkeshi Bay, Akkeshi, Hokkaido, Japan. Field collections of seagrass shoots were made at about 1-week intervals. The density of newly settled larvae (< 0.3 mm in tube diameter) increased significantly on Z. asiatica and P. iwatensis , but not on Z. marina during the sampling period. It was highest on Z. asiatica among the three seagrass species, followed by P. iwatensis and Z. marina . Newly settled larvae occurred more on the basal part of younger leaves of each seagrass species. Mortality tended to be high on Z. marina , followed by Z. asiatica and P. iwatensis , although the differences were not great. Size-specific mortality showed the existence of high mortality in early post-settlement stages on Z. asiatica and P. iwatenisis . Relatively high mortality was also suffered by individuals with a tube diameter over 1.5 mm. Growth in tube diameter of N. brasiliensis was slower on P. iwatensis than on the other two seagrasses. The effect of a calcareous red algae on larval settlement was investigated with removal experiments; however, no effect of red algae was detected. Patterns in the distribution and abundance of N. brasiliensis on leaves of three seagrass species resulted from the heterogeneity of larval settlement rather than from post-settlement mortality or competition with red algae. Different densities of larval settlement among the three seagrass species or on a leaf are likely to relate to larval behaviour, such as negative phototaxis.     

Physicochemical Environment during the Formation of the Mozumi Skarn-type Pb–Zn–Ag Deposit at the Kamioka Mine, Central Japan: A Thermochemical Study

Abstract: The physicochemical environment during the ore formation of the Mozumi skarn-type Pb–Zn–Ag deposit, Kamioka mine, Central Japan is discussed with silicate phase equilibria using calculated phase diagrams. The mineral assemblages, mineral chemistry, and fluid inclusion data are coupled with thermodynamic calculation to estimate the stability fO2–XCO2condition of the mineral assemblages at each ore formation stage. The skarn was approximated by the model system CaO–A12O3–FeO–SiO2–O2–CO2–H2O including grossular-andradite garnet and clinozoisite-epidote solid solutions. The solid solutions are combined into the calculation using "pseudocompound approximation", and real boundary of the mineral assemblages other than simple activity corrected diagram was provided. The diagrams also show isoplethal contour for garnet and epidote.