Solar Flux Emergence Simulations

We simulate the rise through the upper convection zone and emergence through the solar surface of initially uniform, untwisted, horizontal magnetic flux, with the same entropy as the nonmagnetic plasma, that is advected into a domain 48 Mm wide by 20 Mm deep. The magnetic field is advected upward by the diverging upflows and pulled down in the downdrafts, which produces a hierarchy of loop-like structures of increasingly smaller scale as the surface is approached. There are significant differences between the behavior of fields of 10 kG and 20 or 40 kG strength at 20 Mm depth. The 10 kG fields have little effect on the convective flows and show small magnetic-buoyancy effects, reaching the surface in the typical fluid rise time from 20 Mm depth of 32 hours. 20 and 40 kG fields significantly modify the convective flows, leading to long, thin cells of ascending fluid aligned with the magnetic field and their magnetic buoyancy makes them rise to the surface faster than the fluid rise time. The 20 kG field produces a large-scale magnetic loop that as it emerges through the surface leads to the formation of a bipolar, pore-like structure.     

Statistical tests of chondrule sorting

Abstract– The variation in sizes of chondrules from one chondrite to the next is thought to be due to some sorting process in the early solar nebula. Hypotheses for the sorting process include chondrule sorting by mass and sorting by some aerodynamic mechanism; one such aerodynamic mechanism is the process of turbulent concentration (TC). We present the results of a series of statistical tests of chondrule data from several different chondrites. The data do not clearly distinguish between various options for the sorting parameter, but we find that the data are inconsistent with being drawn from lognormal or (three‐parameter) Weibull distributions in chondrule radius. We also find that all but one of the chondrule data sets tested are consistent with being drawn from the TC distribution.     

Effect of temperature and mass transport on transition metal isotope fractionation during electroplating

Transition metal stable isotope signatures can be useful for tracing both natural and anthropogenic signals in the environment, but only if the mechanisms responsible for fractionation are understood. To investigate isotope fractionations due to electrochemistry (or redox processes), we examine the stable isotope behavior of iron and zinc during the reduction reaction  + 2e⁻ = M_metal as a function of electrochemical driving force, temperature, and time. In all cases light isotopes are preferentially electroplated, following a mass-dependent law. Generally, the extent of fractionation is larger for higher temperatures and lower driving forces, and is roughly insensitive to amount of charge delivered. The maximum fractionations are δ^56/54Fe = −4.0‰ and δ^66/64Zn = −5.5‰, larger than observed fractionations in the natural environment and larger than those predicted due to changes in speciation. All the observed fractionation trends are interpreted in terms of three distinct processes that occur during an electrochemical reaction: mass transport to the electrode, chemical speciation changes adjacent to the electrode, and electron transfer at the electrode. We show that a large isotope effect adjacent the electrode surface arises from the charge-transfer kinetics, but this effect is attenuated in cases where diffusion of ions to the electrode surface becomes the rate-limiting step. Thus while a general increase in fractionation is observed with increasing temperature, this appears to be a result of thermally enhanced mass transport to the reacting interface rather than an isotope effect associated with the charge-transfer kinetics. This study demonstrates that laboratory experiments can successfully distinguish isotopic signatures arising from mass transport, chemical speciation, and electron transfer. Understanding how these processes fractionate metal isotopes under laboratory conditions is the first step towards discovering what role these processes play in fractionating metal isotopes in natural systems.     

Silicon isotopes in the inner Solar System: Implications for core formation, solar nebular processes and partial melting

We report Si isotopic data on a suite of terrestrial mantle-derived samples, meteorites and a lunar sample. Our data on co-existing mantle minerals, peridotites and basalts demonstrate lack of any resolvable high temperature fractionation during igneous processes. We show that the δ³⁰Si of the bulk silicate Earth (BSE) is identical, within analytical uncertainties, to carbonaceous and ordinary chondrites (CHUR). Based on our data the difference between δ³⁰Si_BSE and δ³⁰Si_CHUR is 0.035 ± 0.035. Whole-rock differentiated meteorites from different parent bodies (Mars, Vesta) and a lunar breccia sample also show similar δ³⁰Si suggesting broad-scale Si isotope homogeneity in the inner Solar System with an average δ²⁹Si = −0.20 ± 0.01 and δ³⁰Si = −0.39 ± 0.02 relative to the NBS28 Si isotope standard.A difference between δ³⁰Si_BSE and δ³⁰Si_CHUR of 0.035, as observed in our study, translates to less than 1.67 wt.% Si in the core considering a continuous accretion model whereas estimates using a batch model are even lower. Within uncertainties (±0.035‰) in the δ³⁰Si difference between the BSE and CHUR, a maximum of 3.84 wt.% Si could be present in the Earth’s core whereas at δ³⁰Si_BSE-δ³⁰Si_CHUR = 0, there is no requirement of Si in the Earth’s core. Such low Si in the core necessitates the presence of other light elements in the core to explain its density deficit. Our data also places constraints on the oxidation state of the Earth’s mantle during core segregation. The uncertainties in estimating the concentration of oxidized Fe in the mantle during the first 90% of accretion arise from uncertainties in the estimates of the equilibrium partition coefficient of silicon between metal and silicate at conditions relevant to core formation. For δ³⁰Si_BSE-δ³⁰Si_CHUR = 0.035 ± 0.035, the concentration of oxidized Fe in the mantle during the first 90% of accretion could be as low as ∼1%. However, at δ³⁰Si_BSE-δ³⁰Si_CHUR = 0, the Si isotope data do not require any change in the mantle concentration of oxidized Fe during accretion from the present day value of 6.26%.     

Place Meanings and Participatory Planning Intentions

Interest in integrating human connections and natural areas into resource management decision making has steadily increased. While efforts to validate place meaning dimensions have identified meanings beyond established place dependence and identity concepts, further research to identify tangible and intangible meanings of nature-based recreation areas is needed. This study sought to examine place meanings as a second-order construct consisting of ecological integrity, economic dependency, place dependence, family identity, community identity, and place identity and to determine the influence of place meanings on participatory planning intentions (PPI). Data were collected from Florida Fish and Wildlife Conservation area visitors. Confirmatory factor analysis revealed that six factors were reliable and valid, representing place meanings as an overarching concept. Structural equation modeling showed a significant association between place meanings and PPI. These findings demonstrated the importance of understanding place meanings that influence behavioral intentions, which is relevant to understanding participation in planning processes.     

Transport of Crustacean Larvae Between a Low-Inflow Estuary and Coastal Waters

The effectiveness of larval behavior in regulating transport between well-mixed, low-inflow estuaries and coastal waters in seasonally arid climates is poorly known. We determined the flux of an assemblage of benthic crustacean larvae relative to physical conditions between a shallow estuary and coastal waters on the upwelling coast of northern California (38°18′N, 123°03′W) from 29 to 31 March 2006. We detected larval behaviors that regulate transport in adjacent coastal waters and other estuaries for only two taxa in the low-inflow estuary, but they were apparent for taxa outside the estuary. Vertical mixing in the shallow estuary may have overwhelmed larvae of some species, or salinity fluctuations may have been too slight to cue tidal vertical migrations. Nevertheless, all larval stages of species that complete development in nearshore coastal waters were present in the estuary, because they remained low in the water column reducing seaward advection or they were readily exchanged between the estuary and open coast by tidal flows. Weak tidal flows and gravitational circulation at the head of the estuary reduced seaward transport during development for species that completed development nearshore, whereas larval release during nocturnal ebb tides enhanced seaward transport for species that develop offshore. Thus, nonselective tidal processes dominated larval transport for most species back and forth between the low-inflow estuary and open coastal waters, whereas in adjacent open coastal waters, larval behavior in the presence of wind-induced shear was more important in regulating migrations between adult and larval habitats along this upwelling coast.     

Clay minerals as indicators of late quaternary sedimentation constraints in the Mendeleev Rise, Amerasian Basin, Arctic Ocean

The results of study of six cores taken from different morphostructural zones in the Mendeleev Ridge area are discussed. Average contents of minerals of the illite group, chlorite, kaolinite, and smectite are about 60, 21, 12, and 5%, respectively. It was found that fluctuations of minerals along the section correlate with variations in sedimentation constraints in the Late Quaternary. Peaks of kaolinite usually coincide with increased contents of the sand fraction, probably, due to its delivery by icebergs. In contrast, illite shows good correlation with the pelite fraction, testifying to its transport mainly by ices and currents. Minerals of the chlorite and smectite groups in the studied cores are less informative.     

Relationships between the color and chemical composition of quaternary bottom sediments from the southern part of the Mendeleev Rise and the continental slope of the East Siberian Sea

This paper addresses the problem of relationships between the chemical composition and color of Quaternary marine sediments using the data of X-ray fluorescence analysis for the region of the Mendeleev Rise (Arctic Ocean). The contributions of sedimentation and diagenetic factors to color formation were estimated. It was shown that lithostratigraphic correlations should be performed (with certain limitations) using only sediment layers of dark brown and pink color.     

A Long-Term Decrease of the Mid-Size Segmentation Lengths Observed in the He <Emphasis Type="SmallCaps">ii</Emphasis> (30.4 nm) Solar EUV Emission

Power spectra of segmentation-cell length (a dominant length scale of EUV emission in the transition region) from full-disk He?ii extreme ultraviolet (EUV) images observed by the Extreme ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during periods of quiet-Sun conditions for a time interval from 1996 to 2015 were analyzed. The spatial power as a function of the spatial frequency from about 0.04 to 0.27 (EIT) or up to 0.48 (AIA) Mm^?1 depends on the distribution of the observed segmentation-cell dimensions – a structure of the solar EUV network. The temporal variations of the spatial power reported by Didkovsky and Gurman (Solar Phys. 289, 153, 2014) were suggested as decreases at the mid-spatial frequencies for the compared spectra when the power curves at the highest spatial frequencies of 0.5 pix^?1 were adjusted to match each other. This approach has been extended in this work to compare spectral ratios at high spatial frequencies expressed in the solar spatial frequency units of Mm^?1. A model of EIT and AIA spatial responses allowed us to directly compare spatial spectral ratios at high spatial frequencies for five years of joint operation of EIT and AIA, from 2010 to 2015. Based on this approach, we represent these ratio changes as a long-term network transformation that may be interpreted as a continuous dissipation of mid-size network structures to the smaller-size structures in the transition region. In contrast to expected cycling of the segmentation-cell dimension structures and associated spatial power in the spectra with the solar cycle, the spectra demonstrate a significant and steady change of the EUV network. The temporal trend across these structural spectra is not critically sensitive to any long-term instrumental changes, e.g. degradation of sensitivity, but to the change of the segmentation-cell dimensions of the EUV network structure.     

GPS for real-time earthquake source determination and tsunami warning systems

We identify the key design aspects of a GPS-based system (and in the future, GNSS-based systems) that could contribute to real-time earthquake source determination and tsunami warning systems. Our approach is based on models of both transient and permanent displacement of GPS stations caused by large earthquakes, while considering the effect of GPS errors on inverted earthquake source parameters. Our main conclusions are that (1) the spatial pattern, magnitude, and timing of permanent displacement of GPS stations can be inverted for the earthquake source and so predict the 3D displacement field of the ocean bottom, thus providing the initial conditions for tsunami models, and (2) there are no inherently limiting factors arising from real-time orbit and positioning errors, provided sufficient near-field GPS stations are deployed. This signal could be readily exploited by GPS networks currently in place, and will be facilitated by the IGS Real-Time Project as it comes to fruition.