Mineralogy,chemistry, and oxygen isotopes of refractory inclusions from stratospheric interplanetary dust particles and micrometeorites

Abstract— Calcium, aluminum-rich inclusions (CAIs) are characteristic components in carbonaceous chondrites. Their mineralogy is dominated by refractory oxides and silicates like corundum, perovskite, spinel, hibonite, melilite, and Ca-pyroxene, which are predicted to be the first phases to have condensed from the cooling solar nebula. Allowing insights into processes occurring in the early solar system, CAIs in carbonaceous and ordinary chondrites were studied in great detail, whereas only a few refractory inclusions were found and studied in stratospheric interplanetary dust particles (IDPs) and micrometeorites. This study gives a summary of all previous studies on refractory inclusions in stratospheric IDPs and micrometeorites and will present new data on two Antarctic micrometeorites. The main results are summarized as follows: (a) Eight stratospheric IDPs and six micrometeorites contain Ca, Al-rich inclusions or refractory minerals. The constituent minerals include spinel, perovskite, fassaite, hibonite, melilite, corundum, diopside and anorthite. (b) Four of the seven obtained rare-earth-element (REE) patterns from refractory objects in stratospheric IDPs and micrometeorites are related to Group III patterns known from refractory inclusions from carbonaceous chondrites. A Group II related pattern was found for spinel and perovskite in two micrometeorites. The seventh REE pattern for an orthopyroxene is unique and can be explained by fractionation of Gd, Lu, and Tb at highly reducing conditions. (c) The O-isotopic compositions of most refractory objects in stratospheric IDPs and micrometeorites are similar to those of constituents from carbonaceous chondrites and fall on the carbonaceous chondrites anhydrous minerals mixing line. In fact, in most cases, in terms of mineralogy, REE pattern and O-isotopic composition of refractory inclusions in stratospheric IDPs and micrometeorites are in good agreement with a suggested genetic relation of dust particles and carbonaceous chondrites. Only in the case of one Antarctic micrometeorite does the REE pattern obtained for an orthopyroxene point to a link of this particle to enstatite chondrites.     

Zur Frage Kaledonischer Tektonik und Magmabewegung im Variskischen Gebirge Nordostbayerns

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Simulations of an isolated two-dimensional thunderstorm: Sensitivity to cloud droplet size and the presence of graupel

Cloud Resolving Models (CRMs) which are used increasingly to make operational forecasts, employ Bulk Microphysics Schemes (BMSs) to describe cloud microphysical processes. In this study two BMSs are employed in a new Nonhydrostatic σ-coordinate Model to perform two hour simulations of convection initiated by a warm bubble, using a horizontal grid resolution of 500 m. Different configurations of the two BMSs are applied, to test the effects of the presence of graupel with one scheme (2-configurations) and of changing the cloud droplet sizes in the second scheme (4-configurations), on the simulation of idealised thunderstorms. Maximum updrafts in all the simulations are similar over the first 40 minutes, but start to differ beyond this point. The first scheme simulates the development of a second convective cell that is triggered by the cold pool that develops from the outflow of the first storm. The cold pool is more intense in the simulation with graupel because of melting of graupel particles, which results in relatively large raindrops, decreases the temperature through latent heat absorption, causing stronger downdrafts, which all contribute to the formation of a more intense cold pool. The second scheme simulates the development of a second cell in two of its configurations, while two other configurations do not simulate the redevelopment. Two configurations that simulate the secondary redevelopment produce a slightly stronger cold pool just before redevelopment. Our results show that small differences in the microphysics formulations result in simulations of storm dynamics that diverge, possibly due nonlinearities in the model.     

Zur Dynamik von Seichtgewässern

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Die Geländestufen und Geländegräben in der Umgebung von Dresden und ihre Beziehungen zur Entstehung des Elbtales zwischen Pirna und Meißen und zu einem vorgeschichtlichen Erdbeben

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