Spatial and time variations in critical frequencies of the ionospheric <Emphasis Type="Italic">F</Emphasis> region above the zone of equatorial earthquake preparation

Spatial and time variations in the critical frequencies foF2 before the strong earthquake of August 15, 1963, with the magnitude M = 7.75 are analyzed. The epicenter of the earthquake was located in the vicinity of the magnetic equator in the American longitudinal sector. The data of the topside ionosonde on board Alouette-1 and of the series of ground-based ionosondes has been used for this purpose. The ground-based ionosondes made it possible to detect an insignificant anomalous decrease in foF2 within the zone of earthquake preparation a few days prior to the earthquake. This result confirms the conclusion drawn earlier on the basis of the satellite data. The modification of the ionosphere at the F-region level is more evident in the satellite than in the ground-based data. It is also noted that the character of the time variations in foF2 a day before the earthquake is similar to the so called “quiet time” Q-disturbances in the ionosphere, when the electron concentration at the F region maximum differs from the median values by more than 20% under undisturbed geophysical conditions.     

Anthropogenic hillslope terraces and swidden agriculture in Jiuzhaigou National Park, northern Sichuan, China

Small, irregular terraces on hillslopes, or terracettes, are common landscape features throughout west central China. Despite their prevalence, there is limited understanding of the nature of these topographic features, the processes that form them, and the role humans played in their formation. We used an interdisciplinary approach to investigate the geology, ecology, and cultural history of terracette development within Jiuzhaigou National Park, Sichuan Province, China. Terracettes occur on south facing, 20° slopes at 2500 m elevation, which appears to coincide with places people historically preferred to build villages. Ethnographic interviews suggest that traditional swidden agricultural cycles removed tree roots, causing the loess sediments to lose cohesion, slump, and the terrace risers to retreat uphill over time. This evidence is supported by landslide debris at terracette faces. Archaeological analysis of terracette sites reveal remains of rammed spread soil structures, bones, stone tools, and ceramics dating from at least 2200 years before present within a distinct paleosol layer. Radiocarbon and optically stimulated luminescence dating of terracette sediments ranged in age from between 1500 and 2000 ¹⁴C yr BP and between 16 and 0.30 ka, respectively. These multiple lines of evidence indicate a long history of human habitation within Jiuzhaigou National Park and, taken together, suggest strong links between terracette formation and human-landuse interactions.     

The dynamics of central Main Ethiopian Rift waters: Evidence from δD, δO and Sr/Sr ratios

Water samples from cold and geothermal boreholes, hot springs, lakes and rivers were analyzed for δD, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr compositions in order to investigate lake water–groundwater mixing processes, water–rock interactions, and to evaluate groundwater flow paths in the central Main Ethiopian Rift (MER) of the Ziway–Shala basin. Different ranges of isotopic values were recorded for different water types: hot springs show δ¹⁸O −3.36 to +3.69 and δD −15.85 to +24.23, deep Aluto-Langano geothermal wells show δ¹⁸O −4.65 to −1.24 and δD −12.39 to −9.31, groundwater wells show δ¹⁸O −3.99 to +5.14 and δD −19.69 to +32.27, whereas the lakes show δ¹⁸O and δD in the range +3.98 to +7.92 and +26.19 to +45.71, respectively. The intersection of the Local Meteoric Water Line (LMWL: δD = 7 δ¹⁸O + 11.2, R² = 0.94, n = 42) and the Local Evaporation Line (LEL: δD = 5.63δ¹⁸O + 8, n = 14, R² = 0.82) was used to estimate the average isotopic composition of recharge water into the basin (δD = −5.15 and δ¹⁸O = −2.34). These values are depleted if compared with the modern-day average precipitation, presumably indicating paleo-groundwater components recharged during previous humid climatic phases. The measured stable isotope values indicate that the geothermal wells, some of the hot springs and groundwater wells mainly consist of meteoric water. The Sr isotopic signatures in all waters are within the range of the Sr isotopic composition of the rift basalts and rhyolites. The variability of Sr isotopic data also pinpoints complex water–rock interaction and mixing processes in groundwater and surface water. The ⁸⁷Sr/⁸⁶Sr ratio ranges from 0.70445 to 0.70756 in the hot springs, from 0.70426 to 0.70537 in two deep geothermal wells, and from 0.70673 to 0.70721 in the rift lakes Ziway, Langano, Shala and Awasa. The radiogenic composition recorded by the lakes indicates that the input water was predominantly affected by progressive interaction with rhyolitic volcanics and lacustrine sediments.     

The influence of carbon source on abiotic organic synthesis and carbon isotope fractionation under hydrothermal conditions

A series of laboratory experiments were performed to investigate the relative contributions of CO and other single-carbon compounds to abiotic synthesis of organic compounds in hydrothermal environments. Experiments were conducted by heating aqueous solutions of CO, CO₂, HCOOH, or CH₄ at 250 °C under reducing conditions, and observing production of CH₄ and other hydrocarbons. Native Fe was included in the experiments as a source of H₂ through reaction with water and as a potential catalyst. Experiments with CO or HCOOH as the carbon source resulted in rapid generation of CH₄ and other hydrocarbons that closely resembled typical products of Fischer-Tropsch organic synthesis. In contrast, experiments using CO₂ or CH₄ as the carbon source yielded no detectable hydrocarbon products. Carbon isotope measurements of reaction products from the CO experiments indicate that the CH₄ and other hydrocarbons were substantially depleted in ¹³C, with CH₄ δ¹³C values 30 to 34‰ lighter than the initial CO. Most of the fractionation apparently occurs during attachment of CO to the catalyst surface and subsequent reduction to surface-bound methylene. The initial step in polymerization of these methylene units to form hydrocarbons involves a small, positive fractionation, so that ethane and ethene are slightly enriched in ¹³C relative to CH₄. However, subsequent addition of carbon molecules to the growing hydrocarbon chain proceeds with no net observable fractionation, so that the isotopic compositions of the C₃₊ light hydrocarbons are controlled by isotopic mass balance. This result is consistent with a previously proposed model for carbon isotopic patterns of light hydrocarbons in natural samples. The abundance and isotopic composition of light hydrocarbons produced with HCOOH as the carbon source were similar to those generated with CO, but the isotopic compositions of non-volatile hydrocarbons diverged, suggesting that the higher hydrocarbons were formed by different mechanisms in the CO and HCOOH experiments. The experiments indicate that CO, and possibly HCOOH, may be critical intermediates in the abiotic formation of organic compounds in geologic environments, and suggest that the low levels of these compounds present in most hydrothermal systems could represent a bottleneck restricting the extent of abiotic organic synthesis in some circumstances.     

Late Eocene–Pliocene basin evolution in the Eastern Cordillera of northwestern Argentina (25°–26°S): regional implications for Andean orogenic wedge development

Important aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from Eocene–Pliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (Pucará–Angastaco and La Viña areas) provide an Eocene (ca. 38 Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca. 14 Ma and the coarse‐grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial‐lacustrine intramontane setting. By ca. 4 Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐Eocene strata (Santa Barbara Subgroup) within the region.     

Statistical dependence in input data of national greenhouse gas inventories: effects on the overall inventory uncertainty

An uncertainty assessment of the Austrian greenhouse gas inventory provided the basis for this analysis. We isolated the factors that were responsible for the uncertainty observed, and compared our results with those of other countries. Uncertainties of input parameters were used to derive the uncertainty of the emission estimate. Resulting uncertainty using a Monte Carlo approach was 5.2% for the emission levels of 2005 and 2.4 percentage points for the 1990–2005 emission trend. Systematic uncertainty was not assessed. This result is in the range expected from previous experience in Austria and other countries. The determining factor for the emission level uncertainty (not the trend uncertainty) is the uncertainty associated with soil nitrous oxide N₂O emissions. Uncertainty of the soil N₂O release rate is huge, and there is no agreement even on the magnitude of the uncertainty when country comparisons are made. In other words, reporting and use of N₂O release uncertainty are also different between countries; this is important, as this single factor fully determines a country’s national greenhouse gas inventory uncertainty. Inter-country comparisons of emission uncertainty are thus unable to reveal much about a country’s inventory quality. For Austria, we also compared the results of the Monte Carlo approach to those obtained from a simpler error propagation approach, and find the latter to systematically provide lower uncertainty. The difference can be explained by the ability of the Monte Carlo approach to account for statistical dependency of input parameters, again regarding soil N₂O emissions. This is in contrast to the results of other countries, which focus less on statistical dependency when performing Monte Carlo analysis. In addition, the error propagation results depend on treatment of skewed probability distributions, which need to be translated into normal distributions. The result indicates that more attention needs to be given to identifying statistically dependent input data in uncertainty assessment.     

Observing upper troposphere–lower stratosphere climate with radio occultation data from the CHAMP satellite

High quality observations of the atmosphere are particularly required for monitoring global climate change. Radio occultation (RO) data, using Global Navigation Satellite System (GNSS) signals, are well suited for this challenge. The special climate utility of RO data arises from their long-term stability due to their self-calibrated nature. The German research satellite CHAllenging Minisatellite Payload for geoscientific research (CHAMP) continuously records RO profiles since August 2001 providing the first opportunity to create RO based climatologies for a multi-year period of more than 5 years. A period of missing CHAMP data from July 3, 2006 to August 8, 2006 can be bridged with RO data from the GRACE satellite (Gravity Recovery and Climate Experiment). We have built seasonal and zonal mean climatologies of atmospheric (dry) temperature, microwave refractivity, geopotential height and pressure with 10° latitudinal resolution. We show representative results with focus on dry temperatures and compare them with analysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Although we have available only about 150 CHAMP profiles per day (compared to millions of data entering the ECMWF analyses) the overall agreement between 8 and 30 km altitude is in general very good with systematic differences <0.5 K in most parts of the domain. Pronounced systematic differences (exceeding 2 K) in the tropical tropopause region and above Antarctica in southern winter can almost entirely be attributed to errors in the ECMWF analyses. Errors resulting from uneven sampling in space and time are a potential error source for single-satellite climatologies. The average CHAMP sampling error for seasonal zonal means is <0.2 K, higher values occur in restricted regions and time intervals which can be clearly identified by the sampling error estimation approach we introduced (which is based on ECMWF analysis fields). The total error of this new type of temperature climatologies is estimated to be <0.5 K below 30 km. The recently launched Taiwan/U.S. FORMOSAT-3/COSMIC constellation of 6 RO satellites started to provide thousands of RO profiles per day, but already now the single-satellite CHAMP RO climatologies improve upon modern operational climatologies in the upper troposphere–lower stratosphere and can act as absolute reference climatologies for validation of more bias-sensitive climate datasets and models.     

The effects of spatially distributed ionisation sources on the temperature structure of H <Emphasis Type="SmallCaps">ii</Emphasis> regions

Spatially resolved studies of star-forming regions show that the assumption of spherical geometry is not realistic in most cases, with a major complication posed by the gas being ionised by multiple non-centrally located stars or star clusters. Geometrical effects including the spatial configuration of ionising sources affect the temperature and ionisation structure of these regions. We try to isolate the effects of multiple non-centrally located stars, via the construction of 3D photoionisation models using the 3D Monte Carlo photoionisation code mocassin with very simple gas density distributions, but various spatial configurations for the ionisation sources.Emission-line spectra from H?ii regions are often used to study the metallicity of star-forming regions, as well as for providing a constraint on temperatures and luminosities of the ionising sources. Empirical metallicity diagnostics must often be calibrated with the aid of photoionisation models. However, most studies so far have been carried out by assuming spherical or plane-parallel geometries, with major limitations on the allowed gas and dust density distributions and with the spatial distribution of multiple, non-centrally located ionising sources not being accounted for. We compare integrated emission-line spectra from our models and quantify any systematic errors caused by the simplifying assumption of a single, central location for all ionising sources. We find that the dependence of the metallicity indicators on the ionisation parameter causes a clear bias, due to the fact that models with a fully distributed configuration of stars always display lower ionisation parameters than their fully concentrated counterparts. The errors found imply that the geometrical distribution of ionisation sources may partly account for the large scatter in metallicities derived using model-calibrated empirical methods.     

Stability of inclined orbits of terrestrial planets in habitable zones

In long-term stability studies of terrestrial planets moving in the habitable zone (HZ) of a sun-like star, we distinguish four different configurations: (i) planets moving in binary star systems, (ii) the inner type (where the gas giant moves outside the HZ), (iii) the outer type (where the gas giant is closer to the star, than the HZ) and (iv) the Trojan type (where the gas giant moves in the HZ). Since earlier calculations indicated, that the stability of the motion in the HZ also depends on the inclination of the terrestrial planet orbits, we present a detailed numerical investigation to show correlations between the eccentricity, the mass and the distance of the giant planet for various inclinations of the terrestrial planets. The orbital stability of the HZ was examined for all four configurations stated above. While we could find hardly any stable orbits for the first three types for inclinations higher than 40^°, the Trojan planets can be stable up to an inclination of 60^°. Additionally, we could also find some stabilizing effects of the inclination for the first three types. As dynamical model we used the elliptic restricted three-body problem, which consists of two massive and one mass-less body. This allows an application to all detected and future extrasolar single planet systems.