Search for spatial variation in the jovian N/N ratio from Cassini/CIRS observations

We have used the spectra obtained by the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft to search for latitudinal variation in the ¹⁵N/¹⁴N ratio on Jupiter. We found no variations statistically significant given the observational and model uncertainties. The absence of latitudinal variations demonstrates that ¹⁵NH₃ is not fractionated in Jupiter's atmosphere, and that the measured ¹⁵N/¹⁴N represents Jupiter's global value. Our mean value for the global jovian ¹⁵N/¹⁴N ratio of (2.22±0.52)×10⁻³ agrees with previous measurements made by Fouchet et al. (2000, Icarus 143, 223-243) and Owen et al. (2001, Astrophys. J. 553, L77-L79). We argue that the jovian isotopic ¹⁵N/¹⁴N ratio must represent the solar nitrogen isotopic composition. The solar ¹⁵N/¹⁴N ratio hence significantly differs from the terrestrial value: (¹⁵N/¹⁴N)_⊕=3.68×10⁻³. This supports the proposition that terrestrial nitrogen originates from a nitrogen reservoir isolated from the main nitrogen reservoir in the proto-solar nebula. The origin and carrier of this isolated reservoir are still unknown.     

Measuring proton energies and fluxes using EIT (SOHO) CCD areas outside the solar disk images

An indirect proton flux measuring tool based on discrimination of the energy deposited by protons in 128 × 128 pixel EIT CCD areas outside the solar disk images is presented. Single pixel intensity events are converted into proton incident energy flux using modeled energy deposition curves for angles of incidence ±60° in four EIT spatial areas with different proton stopping power. The extracted proton flux is corrected for both the loss of one‐pixel events in the range of angles of incidence as well as for the contribution to the single pixel events resulting from scattered middle‐energy protons (low‐energy or high‐energy particles are stopped by the EIT components or pass through them, accordingly). A simple geometrical approach was found and applied to correct for a non‐unique relation between the proton‐associated CCD output signal and the incident proton energy. With this geometrical approximation four unique proton incident energy ranges were determined as 45–49, 145–154, 297–335, and 390–440 MeV. The indirect proton flux measuring tool has been tested by comparing Solar Energetic Particles (SEP) flux temporal profiles extracted from the EIT CCD frames and downloaded from the GOES database for the Bastille Day (BD) of 2000 July 14 and the more recent 2005 January 20 events. The SEP flux temporal profiles and proton spectra extracted from the EIT in the relatively narrow energy ranges between 45 and 440 MeV reported here are consistent with the related GOES profiles. The four additional EIT extracted ranges provide higher energy resolution of the SEP data. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High-resolution spectroscopy of gamma-ray bursts

We report on results from the Goddard germanium Gamma-Ray Burst Spectrometer flown on the ISEE-3 spacecraft. Spectral and temporal studies of two events on 4 and 19 November, 1978 are presented. The power law spectral indices were found to be respectively –1.82 and –1.31, the latter being the hardest event thus far detected. Evidence for two lines in the 4 November event is presented — a broad feature at 420 keV and a narrower one at 740 keV. These are consistent with a common redshift if the parent lines are assumed to be the positron annihilation line (511 keV) and the first excited state of iron (847 keV). If this interpretation is correct, it is shown that additional lines from higher levels of iron and possibly other nuclei are expected and that they may represent a significant contribution to the total spectrum above 1 MeV.Paper presented at the Symposium on Cosmic-Ray Bursts, held at Toulouse, France, 26–29 November, 1979.     

EVIDENCE FOR THE PRESENCE OF LOW MOLECULAR WEIGHT ALCOHOLS AND CARBONYL COMPOUNDS IN THE MURCHISON METEORITE†

Alcohols, aldehydes and ketones identified in the Murchison C2 chondrite include: methanol, ethanol, 2-propanol, butyl alcohols, formaldehyde, acetaldehyde, propionaldehyde, acetone, 2-butanone, 3-pentanone and 2-pentanone.     

The influence of minerals on the pyrolysis of kerogens

The effect of mineral matter on the laboratory pyrolysis of sediments, kerogens and coals, and of coal macerals mixed with either alumina, bentonite, kaolinite, or calcium carbonate has been investigated. Some minerals are more active than others in effecting changes in the composition of the pyrolysate. The relative content of low molecular weight pyrolysis products is higher for kerogens pyrolyzed in a mineral matrix than for isolated kerogens. Our limited data suggests that this is due to both condensation and gasification of higher molecular weight constituents in the ‘primary’ pyrolysate. Differences in the content of aromatic versus aliphatic compounds have been noted when pyrograms from coal macerals are compared with pyrograms from coal maceral-mineral mixtures. We conclude that mineralogy is important in controlling the composition of kerogen pyrolysis products.     

Gravity anomaly modeling of sedimentary basins by means of multiple structures and exponential density contrast-depth variations: A space domain approach

An automatic modeling scheme is developed in the space domain to interpret the gravity anomalies of sedimentary basins, among which the density contrast decreases exponentially with depth. Forward modeling is realized in the space domain using a combination of both analytical and numerical approaches. A collage of vertical prisms having equal widths, whose depths are to be estimated, describes the geometry of a sedimentary basin. Initial depths of a sedimentary basin are predicted using the Bouguer slab formula and subsequently updated, iteratively, based on the differences between the observed and theoretical gravity anomalies until the modeled gravity anomalies mimic the observed ones. The validity and applicability of the method is demonstrated with a synthetic and two real field gravity anomalies, one each over the Chintalpudi sub-basin in India and the other over the San Jacinto graben, California. In case of synthetic example, the assumed structure resembles a typical intracratonic rift basin formed by normal block faulting and filled with thick section of sediments. The proposed modeling technique yielded information that is consistent with the assumed parameters in the case of synthetic structure and with the available/drilling depths in case of field examples.     

Geochemical transport modelling of drainage from experimental mine tailings cells covered by capillary barriers

The use of covers with capillary barrier effects (CCBEs) for reducing acid mine drainage (AMD) from sulphidic mine tailings is simulated using the MIN3P finite volume model for coupled groundwater flow, O₂ diffusion and multi-component reactive transport. The model is applied to simulate five pilot-scale in situ test cells containing reactive tailings from the Manitou mine site, Val d’Or, Que., Canada. Four of the cells were constructed with CCBEs over the tailings, while the fifth tailings cell was left uncovered. Observed and simulated discharge from the base of each cell showed that the capillary barrier covers significantly reduced sulphide oxidation and AMD. Compared to acidic discharge from the uncovered cell, discharge from the four CCBE-covered cells had neutral pH levels and 1–7 orders of magnitude lower concentrations of SO₄, Fe, Zn, Cu and Al. The simulations showed that the moisture retaining layer of the CCBEs reduced AMD by inhibiting O₂ diffusion into the underlying reactive wastes. Provided the moisture-retention layer of the CCBE remains close to saturation, its thickness had a relatively minor effect. Under such near-saturated conditions, O₂ availability is limited by its diffusion rate through the bulk porous medium and not by the diffusion rate through the oxidized grain shells. The model is providing important new insights for comparing design alternatives for reducing or controlling AMD.     

Studies of sodar‐observed dot echo structures

Abstract

During moist weather under stably stratified and light wind conditions very often “dot” shaped echoes, either distributed randomly or arranged in a stratified layer, have been observed on sodar echograms. They last from a couple of hours to ten hours. Their horizontal widths are up to 200 m while their vertical sizes are up to 40 m. It is argued that dot echoes represent clusters of water vapour translated by the wind in the boundary layer, the back‐scattered acoustic energy being the contribution of correlated fluctuations in temperature and humidity (turbulent mixing) in the inertial subrange.     

Global plasmaspheric TEC and its relative contribution to GPS TEC

The plasmaspheric electron content is directly estimated from the global positioning system (GPS) data onboard JASON-1 Satellite for the first time. Similarly, the ground-based GPS total electron content (TEC) is estimated using about 1000 GPS receivers distributed around the globe. The relative contribution of the plasmaspheric electron content to the ground-based GPS TEC is then estimated globally using these two independent simultaneous measurements; namely ground-based GPS TEC and JASON-1 GPS TEC. Results presented here include data from 3 months of different solar cycle conditions (October 2003, May 2005, and December 2006). The global comparison between the two independent measurements was performed by dividing the data into three different regions; equatorial, mid- and high-latitude regions. This division is essential as the GPS raypaths traverse different distances through the plasmasphere at different latitudes. The raypath length through the plasmasphere decreases as latitude increases. The relative contribution of the plasmaspheric electron content exhibits a diurnal variation that depends on latitude with minimum contribution (10%) during daytime and maximum (up to 60%) at night. The contribution is also maximum at the equatorial region where the GPS raypath traverses a long distance through the plasmasphere compared to its length in mid- and high-latitude regions. Finally, the solar cycle variation of plasmaspheric contribution is also reported globally.     

Baryon loading and the Weibel instability in gamma-ray bursts

The dynamics of two counter-streaming electron–positron–ion unmagnetized plasma shells with zero net charge is analysed in the context of magnetic field generation in gamma-ray burst internal shocks due to the Weibel instability. The effects of large thermal motion of plasma particles, arbitrary mixture of plasma species and space charge effects are taken into account. We show that, although thermal effects slow down the instability, baryon loading leads to a non-negligible growth rate even for large temperatures and different shell velocities, thus guaranteeing the robustness and the occurrence of the Weibel instability for a wide range of scenarios.