Influence of molecular outflows from young stellar objects on molecular clouds

In this paper it is investigated whether molecular outflows can support the turbulence in molecular clouds against decay. In the momentum-driven regime of molecular flows the time scale of the replenishment of the fluctuations is longer than the dissipation time scale of pure hydrodynamical supersonic turbulence.     

Correction of precipitation based on off-site weather information

Owing to aerodynamic errors, correction of precipitation measurements, liquid, mixed or solid, is often carried out by means of an explicit mathematical statistical model. The magnitude of correction, e.g., calculated as a correction factor to the observed amount of precipitation, is the dependent variable, and wind speed, temperature and a measure of precipitation intensity are independent variables entering the correction model. Usually these independent variables are accessible on site where the precipitation measurements are recorded. However, in many standard precipitation networks the gauge measurements are not accompanied by on site information of these variables, and information from remote stations must be used. The aim of the paper is to describe how the statistical models can be used in evaluating if the set of remote information of the independent variables can be used for the estimation of a reliable correction factor on site. The technique is then applied to an example of precipitation network in Denmark where the typical situation for the standard gauges is that only the amount of precipitation is available. It is expected that not only can the methods be adapted to other countries, but for landscapes similar to Denmark even the conclusions can be applied directly: extrapolation of all independent variables from remote sites should be conducted with caution, wind speed information can be extrapolated from remote sites not farther away than approximately 50 km, while information on rain intensity and temperature can be safely extrapolated across longer distances.     

Melt‐bearing impactites (suevite and impact melt rock) within the Gardnos structure,Norway

Abstract– Melt‐bearing impactites dominated by suevite, and with a minor content of clast‐rich impact melt rock, are found within the central part of the Gardnos structure. They are preserved as the eroded remnants in the relatively small complex impact structure with a present diameter of 5 km. These rocks have been mapped in the field and in the Branden drill core, and described according to mineralogy/petrology, including matrix, litho clast, and melt content, as well as geochemistry. Based on our extensive field mapping, a simple 3‐D model of the original crater was constructed to estimate tentative volumes for the melt‐bearing impactites. The variations in lithic and melt fragment content and chemistry of suevite matrix can mostly be explained by incorporation of mafic rocks into a dominant mixture of granitic, gneissic, and quartzitic target rocks, reflecting mixing of material from different parts of the crater. Melt fragments within suevite occur with a variety of shapes and textures, probably related to different original target rock composition, to the various temperatures the individual fragments were subjected to during the impact event and deposition processes. This study discusses the impact‐related deposits based on a sedimentological approach. Their overall composition and structures indicate dominating gravity flow processes in the final transportation and deposition of the suevite.     

A non-magmatic iron projectile for the Gardnos impact event

The goal of this study is to identify the type of projectile responsible for the formation of the late Precambrian Gardnos impact structure in Norway. Fifteen impactite samples, predominantly impact breccias and suevites from the central and northeastern part of the structure, were analyzed for platinum group elements (PGE) and Au using nickel-sulfide fire assay combined with inductively coupled plasma mass spectrometry (ICP-MS). Major and trace elements were measured in the same samples using X-ray fluorescence (XRF). In addition, the concentrations of siderophile elements Ni, Cr, and Co were determined by ICP-MS after acid digestion. The samples collected at the contact between suevite and the sedimentary infill yielded the highest PGE concentrations (Ir = 1.926 ng/g, Ru = 3.494 ng/g, Pt = 4.716 ng/g, Rh = 0.766 ng/g, Pd = 2.842 ng/g for GC6). The CI-normalized PGE patterns are characterized by Ru and Rh enrichments suggesting a non-chondritic impactor. Concentration plots of the different PGE display an excellent correlation (R > 0.99), indicative of a single source for the PGE enrichment. The Ni/Cr ratio of the Gardnos impactor (2.56 ± 0.20) agrees with that of chondrites (2 to 7), whereas Ir is depleted relative to Ni in this projectile (Ni/Ir ratio of 92 000 ± 8000 compared to an average Ni/Ir ratio of 23 150 ± 4250 for chondrites). There is no clear indication of selective post-depositional remobilization of the characteristic highly siderophile elements. The Ni/Ir and Cr/Ir data combined with the non-chondritic PGE ratios probably indicate a differentiated projectile. Based on (1) the similarity of the inter-element ratios of the impactor with the iron phase of non-magmatic iron meteorites and (2) the presence of characteristics of both chondrites and iron meteorites (Ni/Cr and Ni/Ir ratios), an IA or IIIC non-magmatic iron meteorite is a very plausible impactor.     

Ensemble Kalman filtering with shrinkage regression techniques

The classical ensemble Kalman filter (EnKF) is known to underestimate the prediction uncertainty. This can potentially lead to low forecast precision and an ensemble collapsing into a single realisation. In this paper, we present alternative EnKF updating schemes based on shrinkage methods known from multivariate linear regression. These methods reduce the effects caused by collinear ensemble members and have the same computational properties as the fastest EnKF algorithms previously suggested. In addition, the importance of model selection and validation for prediction purposes is investigated, and a model selection scheme based on cross-validation is introduced. The classical EnKF scheme is compared with the suggested procedures on two-toy examples and one synthetic reservoir case study. Significant improvements are seen, both in terms of forecast precision and prediction uncertainty estimates.     

Surface ocean temperatures in the north-east Atlantic during the last 500 000 years: evidence from foraminiferal census data

Abstract Changes in North Atlantic sea surface temperature (SST) are regarded as a key element of the climate during the Quaternary. However, there are relatively few long-term records providing quantitative SST estimates from this region. Using planktic foraminiferal-derived SSTs together with changes on species level and iceberg-rafted debris, the last 500 ka were studied. Pronounced SST changes, as determined from the last glacial–interglacial cycle, characterize most colder periods. Peak interglacial temperatures were found for marine isotope stages (MIS) 1, 5e and 11, the latter two being the warmest. The warm substages within MIS 7 and 9 are marked by enhanced dissimilarity coefficients, indicating that SSTs obtained for these times appear to be overestimated. This is corroborated by differences within the species assemblage, which show enhanced cold water components. It is therefore concluded that detailed analysis down to species level is a crucial prerequisite to better reconstructions of SST.