4,591 research outputs found

    The role of brine release and sea ice drift for winter mixing and sea ice formation in the Baltic Sea

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    Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics 1.0: A General Circulation Model for Simulating the Climates of Rocky Planets

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    Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics (ROCKE-3D) is a 3-Dimensional General Circulation Model (GCM) developed at the NASA Goddard Institute for Space Studies for the modeling of atmospheres of Solar System and exoplanetary terrestrial planets. Its parent model, known as ModelE2 (Schmidt et al. 2014), is used to simulate modern and 21st Century Earth and near-term paleo-Earth climates. ROCKE-3D is an ongoing effort to expand the capabilities of ModelE2 to handle a broader range of atmospheric conditions including higher and lower atmospheric pressures, more diverse chemistries and compositions, larger and smaller planet radii and gravity, different rotation rates (slowly rotating to more rapidly rotating than modern Earth, including synchronous rotation), diverse ocean and land distributions and topographies, and potential basic biosphere functions. The first aim of ROCKE-3D is to model planetary atmospheres on terrestrial worlds within the Solar System such as paleo-Earth, modern and paleo-Mars, paleo-Venus, and Saturn's moon Titan. By validating the model for a broad range of temperatures, pressures, and atmospheric constituents we can then expand its capabilities further to those exoplanetary rocky worlds that have been discovered in the past and those to be discovered in the future. We discuss the current and near-future capabilities of ROCKE-3D as a community model for studying planetary and exoplanetary atmospheres.Comment: Revisions since previous draft. Now submitted to Astrophysical Journal Supplement Serie

    Experimental investigations on the characteristics of snow accretion using the EMU-320 model train

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    This paper presents a snow accretion test conducted in a climate wind tunnel to investigate the icing process on a model train. The model used within this experiment was the cleaned-up and 2/3-scaled version of EMU-320, which is a high-speed train in Korea. The model was designed without an electronic power source or heat source so that the wheels did not rotate and snow accretion on the model did not occur due to heat sources. To investigate snow accretion, four cases with different ambient temperatures were considered in the climate wind tunnel on Rail Tec Arsenal. Before analyzing the snow accretion on the train, the snow flux and liquid water content of snow were measured so that they could be used as the input conditions for the simulation and to ensure the analysis of the icing process was based on the characteristics of the snow. Both qualitative and quantitative data were obtained, whereby photographs was used for qualitative analysis, and the density of the snow sample and the thickness of snow accreted on the model were used for quantitative analysis. Based on the visual observations, it was deduced that as the ambient temperature increased, the range of the snow accreted was broader. The thickness of snow accreted on the model nose was the largest on the upper and lower part at -3 oC, and on the middle part at -5 oC. Additionally, the cross section of snow accreted was observed to be trench-like. Similar icing processes were observed to occur on the slope of nose. Snow accreted on all components of the bogie, and for all cases, the thickness of snow at wheel was the largest at an arc angle of 40 to 70 o. These detailed data of experimental conditions can be applied as an input to simulations to improve simulations of ice conditions. Thus, they can facilitate the development of appropriate anti-icing designs for trainsComment: 31 pages, 23 Figures, 8 Table

    Phase change of molten-salt flows in energy systems

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    The possibility of molten salt freezing in pipe flow systems is a key concern for the solar-energy industry and a safety issue in the Generation-IV molten-salt reactors, worthy of careful consideration. The overriding aim of this thesis is to address this issue by providing an approach to quantify the solidification of molten salts in piping systems (in terms of mass build-up, effect on the flow and heat transfer, etc.). In light of this aim, several aspects needed to be investigated which affect how molten salt solidification can be predicted. Specifically, the work described in this thesis is hereby described: 1) An experimental method was developed to measure the thermal conductivity of molten salts, whose uncertainties significantly affect further modelling efforts. The method can be applied to measure the thermal conductivity of molten salts up to temperatures around 760 K, with an overall error better than 4%. 2) The thermal conductivities of NaNO3 -NaNO2 -KNO3 eutectic (HTS) and LiCl -KCl eutectic were measured up to temperatures of 700 K and 760 K respectively. In addition, data in the literature were re-evaluated by taking into account the thermal losses present in a particular experimental apparatus; the revised results were found to be in good agreement with other studies. These re-evaluated data and the measurements conducted in the present study were used to critically review and suggest the values of the thermal conductivities of common salts, including FLiNaK. 3) A 1-dimensional thermo-hydraulic model was developed under the steady state assumption and validated to predict transient freezing in internal pipe flows. The model can be incorporated in standard thermo-hydraulic codes and can be used to predict the solidi cation process in complex piping system where CFD is computationally expensive. 4) An experimental apparatus equipped with laser-based diagnostic measurement techniques was built to measure the growing thickness of an ice layer in contact with a cold surface and liquid water flow. The developed freezing model was validated against these experimental data and the discrepancies were considered. 5) The freezing model was then applied to study the behaviour of the Direct Reactor Auxiliary Cooling System (DRACS) under Loss of Forced Circulation (LOFC) with blackout. DRACS was found to be prone to failure due to freezing in the molten salt/air heat exchanger; its transient response was characterised and discussed.Open Acces

    The effects of climate change on hailstorms

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    Hailstorms are dangerous and costly phenomena that are expected to change in response to a warming climate. In this Review, we summarize current knowledge of climate change effects on hailstorms. As a result of anthropogenic warming, it is generally anticipated that low-level moisture and convective instability will increase, raising hailstorm likelihood and enabling the formation of larger hailstones; the melting height will rise, enhancing hail melt and increasing the average size of surviving hailstones; and vertical wind shear will decrease overall, with limited influence on the overall hailstorm activity, owing to a predominance of other factors. Given geographic differences and offsetting interactions in these projected environmental changes, there is spatial heterogeneity in hailstorm responses. Observations and modelling lead to the general expectation that hailstorm frequency will increase in Australia and Europe, but decrease in East Asia and North America, while hail severity will increase in most regions. However, these projected changes show marked spatial and temporal variability. Owing to a dearth of long-term observations, as well as incomplete process understanding and limited convection-permitting modelling studies, current and future climate change effects on hailstorms remain highly uncertain. Future studies should focus on detailed processes and account for non-stationarities in proxy relationships
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