Oscillations in radiation-driven outflows

In this paper we investigate the dynamical behaviour of radiation-driven winds, specifically winds that arise when Compton scattering transfers momentum from the radiation field to the gas flow. Such winds occur during strong X-ray bursts from slowly accreting neutron stars, and also may be driven from the inner regions of a black hole or neutron star accretion disc when the mass transfer rate is very high. By linearizing the radiation hydrodynamic equations around steady spherical outflow, we evaluate the time-dependent response of these winds to perturbations introduced at their inner boundaries. We find that although radiation-driven winds are generally stable, they act as mechanical filters that should produce quasi-periodic oscillations or peaked noise in their radiation output when perturbations force them stochastically. This behaviour may underlie the photospheric oscillations observed in some strong Type I X-ray bursts.     

Paläozoische und frühmesozoische Orogenesen am pazifischen Rand Gondwanas

Zusammenfassung In Südamerika, in der Antarktis und in Australien läßt sich gleichermaßen vom Kambrium bis in die Trias ein pazifikwärtiges Wandern der orogenen Aktivität beobachten. Aus der relativen Lage dieser Orogene ergibt sich, daß vor dem Jura die Antarktische Halbinsel westlich der Südspitze von Südamerika gelegen hat.

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In South America, Antarctica and Australia, from the Cambrian to the Triassic Pacificward shifting of the orogenic activity is observed. From the relative position of these orogenes is deduced that before the Jurassic the Antarctic Peninsula was situated west of the southern tip of South America.

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Resumen Tanto en Sudamérica como en la Antártida y en Australia desde el Cámbrico hasta el Triásico se observa una transposición continua de la actividad orogénica hacia el Pacífico. De la posición relativa de estos orógenos se concluye que antes del Jurásico la Península Antártica fue situada al Oeste de la punta Sur de Sudamérica.

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Age and intensity of thermal events by fission track analysis: The Ries impact crater

A thermal event reduces the number of previously registered fission tracks in a mineral dependent upon the track retention properties of the individual mineral. Apatite, sphene and zircon have retention properties over a wide range of temperatures (from 100° to 550°C); apatite data reveal information at lowest temperatures while sphene and zircon data are useful for higher temperatures.Thermal events within this temperature range of 100°C to about 550°C are suitable for study with this technique. The age of the event is determined from samples in which the fission tracks are completely erased, while minerals containing partially removed (erased) tracks provide information on the temperatures occurring during the thermal event.As a test case, the analysis of the temperatures developed by the meteorite impact which produced the Ries crater at 14.7 m.y. ago is presented.     

Do paleoclimate proxies agree? A test comparing 19 late Holocene climate and sea‐ice reconstructions from Icelandic marine and lake sediments

Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down‐core comparisons with instrumental climate data. Multi‐proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi‐proxy assessment comparing 19 sub‐centennially resolved late Holocene proxy records, covering the period 300–1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea‐ice biomarker IP₂₅, allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea‐ice proxies, correlate strongly with each other over multi‐centennial timescales, and thus do appear to record changes in regional climate. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessing the Measurement Consistency Between the Jason-2/AMR and SARAL/AltiKa/DFMR Microwave Radiometers Using Simultaneous Nadir Observations

SARAL/AltiKa has a Dual Frequency Microwave Radiometer (DFMR), and Jason-2 has an Advanced Microwave Radiometer (AMR). Both microwave radiometer sensors include a 23.8 GHz primary water sensing channel. The measurement consistencies between DFMR and AMR are important for establishing a consistent altimetry data set between SARAL/AltiKa and Jason-2 in order to accurately assess sea level rise in a long-term time series. This study investigates the measurement consistency in the 23.8 GHz channel between DFMR and AMR at the Simultaneous Nadir Overpasses (SNO's) between the two satellites and also at coldest ocean brightness temperature locations. Preliminary results show that while both instruments show no significant trends over the one year since the launch of SARAL, a consistent relative bias of 2.88 K (DFMR higher than AMR) with a standard deviation of 0.98 K is observed. The relative bias at the lowest brightness temperature from the SNO method (-3.82 K) is consistent with that calculated from coldest ocean method (-3.74 K). The relative bias exhibits strong latitude (and scene temperature) dependency, changing from -3.82 K at high latitudes to -0.92 K near the equator. There also exists an asymmetry between the northern and southern hemisphere. The relative bias increases toward the lower end of brightness temperature.     

Emerging coral diseases: a temperature‐driven process?

In the last few decades there has been a surge in research focusing on coral disease. While climate change, specifically rising sea surface temperature, has been proposed as a major and growing driver of the emergence of marine diseases, to date a solid connection between disease epizootics and elevated sea surface temperature has not been established. However, a wealth of data now exists, compiled from many different perspectives, that may support such a connection. In this work we provide a comprehensive review targeting one coral disease, black band disease, that spans the infection process, pathobiology, and epizootiology, and links specific mechanisms of the disease process to increasing temperatures. This temperature‐driven pattern of infection can be expanded to include similar processes associated with other temperature‐related coral diseases. The conclusions presented here are based upon the results of many studies using a diverse suite of approaches that have been synthesized to argue that the emergence and continuing spread of black band disease is linked to warming sea surface temperatures. In summary, as global ocean temperatures increase seasonally and over decades, the environment shifts to become more favorable for the growth of potentially pathogenic microorganisms endemic to the immediate environment of the reef. The increase in the relative number of potential pathogens in the microbial community produces microenvironments conducive to the growth of other potential pathogens, leading to infection by a polymicrobial consortium. This consortium is easily perturbed by a (seasonal) temperature decrease, but remains associated with the coral host and can be reactivated with a subsequent seasonal increase in temperature, resulting in a cycle of temperature‐dependent disease emergence.