129 research outputs found
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Simultaneous geomagnetic measurements on an ice island surface and 1000 feet below
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Magnetic anomalies caused by two-dimensional structure : their computation by digital computers and their interpretation
The clustering of polarity reversals of the geomagnetic field
Often in nature the temporal distribution of inhomogeneous stochastic point
processes can be modeled as a realization of renewal Poisson processes with a
variable rate. Here we investigate one of the classical examples, namely the
temporal distribution of polarity reversals of the geomagnetic field. In spite
of the commonly used underlying hypothesis, we show that this process strongly
departs from a Poisson statistics, the origin of this failure stemming from the
presence of temporal clustering. We find that a Levy statistics is able to
reproduce paleomagnetic data, thus suggesting the presence of long-range
correlations in the underlying dynamo process.Comment: 4 pages, in press on PRL (31 march 2006?
Hydrous Carbonatitic Liquids Drive CO2 Recycling From Subducted Marls and Limestones
This research was supported by the Italian Ministry of Education, University, and Research (MIUR) program PRIN2017 and by the Deep Carbon Observatory (DCO). We are greatly indebted to Andrea Risplendente for careful examination of run charges at the Electron Microprobe.Pelagic limestones are subducted in a variety of subduction zones worldwide. Despite the geochemical relevance
of systems enriched in CaCO3, previous experimental investigations mostly focused on carbonated pelites, with
low Ca/(Ca+Mg+Fe) ratio. We present the compositions and the formation conditions of liquids in the model
system CaO‐Al2O3‐SiO2‐H2O‐CO2 (CASHC), building on phase relationships in the subsystems CHC and
CSHC, where a second critical endpoint was suggested at temperatures as low as 515 °C, and 3.2 GPa. Multianvil
experiments were performed at 4.2 and 6.0 GPa on five bulk compositions at variable Ca/Si/Al ratios. H2O
contents
vary from 5.6 to 21 wt%. Aragonite + kyanite + vapor and minor lawsonite form at 700 °C, replaced by
zoisite/grossular at 800 °C. Between 850 °C and 950 °C, a complex sequence of textural features is observed
upon quenching of a single volatile‐rich liquid phase formed at run conditions. Precipitates include dendritic
CaCO3, silicate glass, and Al‐rich whiskers. The bulk composition of such hydrous carbonatitic liquids is
retrieved by image analysis on X‐ray maps, showing Ca/Si ratio increasing with pressure and temperature.
Hydrous Ca‐carbonatitic liquids are efficient media for scavenging volatiles from subducted crustal material and
for metasomatizing the mantle wedge.Ministry of Education, Universities and Research (MIUR)Deep Carbon Observatory (DCO
Determination of Interstellar O Parameters Using the First Two Years of Data from the Interstellar Boundary Explorer
The direct measurements of interstellar matter by the Interstellar Boundary Explorer ( IBEX ) mission have opened a new and important chapter in our study of the interactions that control the boundaries of our heliosphere. Here we derive for the quantitative information about interstellar O flow parameters from IBEX low-energy neutral atom data for the first time. Specifically, we derive a relatively narrow four-dimensional parameter tube along which interstellar O flow parameters must lie. Along the parameter tube, we find a large uncertainty in interstellar O flow longitude, 76°.0 ± 3°.4 from χ 2 analysis and 76°.5 ± 6°.2 from a maximum likelihood fi t, which is statistically consistent with the fl ow longitude derived for interstellar He, 75°.6 ± 1°.4. The best-fit O and He temperatures are almost identical at a reference flow longitude of 76°, which provides a strong indication that the local interstellar plasma near the Sun is relatively unaffected by turbulent heating. However, key differences include an oxygen parameter tube for the interstellar speed (relation between speed and longitude) that has higher speeds than those in the corresponding parameter tube for He, and an upstream flow latitude for oxygen that is southward of the upstream flow latitude for helium. Both of these differences are likely the result of enhanced filtration of interstellar oxygen due to its charge-exchange ionization rate, which is higher than that for helium. Furthermore, we derive an interstellar O density near the termination shock of - + - 5 .8 X 10^-5 cm that, within uncertainties, is consistent with previous estimates. Thus, we use IBEX data to probe the interstellar properties of oxygen
One Solar Cycle of Heliosphere Observations with the Interstellar Boundary Explorer: Energetic Neutral Hydrogen Atoms Observed with IBEX-Lo from 10 eV to 2 keV
The Interstellar Boundary Explorer (IBEX) is a NASA satellite in Earth orbit, dedicated to observing both
interstellar neutral atoms entering the heliosphere and energetic neutral atoms (ENAs) from the interstellar
boundaries from roughly 10 eV to 6 keV. This work presents the averaged maps, energy spectra, and temporal
variability of heliospheric ENA intensities measured with the IBEX-Lo instrument at 1 au at energies between
10 eV and 2 keV, covering one entire solar cycle from 2009 through 2019. These results expand the range in time
and energy for studying the globally distributed ENA flux and the IBEX Ribbon. The observed ENA intensities
exceed model predictions, in particular below 500 eV. Moreover, the ENA intensities between 50–200 eV energy
show an unexpected rise and fall around the year 2015 in most sky regions
A Study of ^3He Spectra and Abundances in Impulsive Solar Energetic Particle Events - Results from Measurements with ACE/SEPICA, ACE/SIS and SOHO/HSTOF
Energy spectra of the He isotopes and the energy dependence of the ^3He/^4He ratio during a number of impulsive solar energetic particle events (SEP) observed between September 1997 and December 1998 are analyzed. Data covering the energy range from 0.1 to 10 MeV/amu were supplied by three instruments with complementary energy ranges: the Solar Energetic Particle Ionic Charge Analyzer (SEPICA) and the Solar Isotope Spectrometer (SIS) on ACE, and the time-of-flight mass spectrometer HSTOF on SOHO. We confirm the trend of a monotonic increase of the 3He abundance with energy up to a maximum in the region of a few MeV/amu found in previous ISEE studies and extend the analysis to events of intermediate 3He enrichment. We briefly discuss the observational data and their relation to existing theoretical work on selection and acceleration mechanisms in impulsive flares
Heliospheric Neutral Atom Spectra Between 0.01 and 6 keV fom IBEX
Since 2008 December, the Interstellar Boundary Explorer (IBEX) has been making detailed observations of neutrals from the boundaries of the heliosphere using two neutral atom cameras with overlapping energy ranges. The unexpected, yet defining feature discovered by IBEX is a Ribbon that extends over the energy range from about 0.2 to 6 keV. This Ribbon is superposed on a more uniform, globally distributed heliospheric neutral population. With some important exceptions, the focus of early IBEX studies has been on neutral atoms with energies greater than approx. 0.5 keV. With nearly three years of science observations, enough low-energy neutral atom measurements have been accumulated to extend IBEX observations to energies less than approx. 0.5 keV. Using the energy overlap of the sensors to identify and remove backgrounds, energy spectra over the entire IBEX energy range are produced. However, contributions by interstellar neutrals to the energy spectrum below 0.2 keV may not be completely removed. Compared with spectra at higher energies, neutral atom spectra at lower energies do not vary much from location to location in the sky, including in the direction of the IBEX Ribbon. Neutral fluxes are used to show that low energy ions contribute approximately the same thermal pressure as higher energy ions in the heliosheath. However, contributions to the dynamic pressure are very high unless there is, for example, turbulence in the heliosheath with fluctuations of the order of 50-100 km/s
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