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  • 1
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    Air‐Sea Interactions and Water Mass Transformation During a Katabatic Storm in the Irminger Sea (2022)
    Details
    Publication Date: 2022-10-04
    Description: We use a global 5‐km resolution model to analyze the air‐sea interactions during a katabatic storm in the Irminger Sea originating from the Ammassalik valleys. Katabatic storms have not yet been resolved in global climate models, raising the question of whether and how they modify water masses in the Irminger Sea. Our results show that dense water forms along the boundary current and on the shelf during the katabatic storm due to the heat loss caused by the high wind speeds and the strong temperature contrast. The dense water contributes to the lightest upper North Atlantic Deep Water as upper Irminger Sea Intermediate Water and thus to the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). The katabatic storm triggers a polar low, which in turn amplifies the near‐surface wind speed due to the superimposed pressure gradient, in addition to acceleration from a breaking mountain wave. Overall, katabatic storms account for up to 25% of the total heat loss (20 January 2020 to 30 September 2021) over the Irminger shelf of the Ammassalik area. Resolving katabatic storms in global models is therefore important for the formation of dense water in the western boundary current of the Irminger Sea, which is relevant to the AMOC, and for the large‐scale atmospheric circulation by triggering polar lows.
    Description: Plain Language Summary: Katabatic storms are outbursts of cold air associated with strong winds from coastal valleys of Greenland, in particular from the Ammassalik valleys in southeast Greenland. These storms are not resolved in global climate models because of their small spatial extent. However, they are important for the formation of dense water on the Irminger Sea shelf, because they induce a substantial heat loss from the coastal water. In this study, we resolve katabatic storms for the first time in a global climate model and analyze the water transformation caused by a single storm before quantifying the importance of katabatic storms for the entire simulation period. We find that a water mass is formed during the katabatic storm that is dense enough to contribute to the cooling and sinking of the global conveyor belt in the subpolar North Atlantic. Overall, katabatic storms account for up to 25% of the heat loss over the Irminger shelf of the Ammassalik area.
    Description: Key Points: For the first time, the direct effect of a katabatic storm on the Irminger Sea has been simulated in a global climate model. The katabatic storm induces strong heat loss and dense water formation over the Irminger shelf (Sermilik Trough) and in the boundary current. Dense water forming in the western boundary current during katabatic storms contributes to the lightest upper North Atlantic Deep Water.
    Description: Collaborative Research Centre TRR181 funded by DFG
    Description: Max Planck Society for Advancement of Science
    Description: NextGEMS
    Description: European Union’s Horizon 2020
    Description: https://hdl.handle.net/21.11116/0000-0008-ECF1-E
    Description: https://cera-www.dkrz.de/WDCC/ui/Compact.jsp?acronym=DKRZ_LTA_033_ds00010
    Description: https://mpimet.mpg.de/en/science/modeling-with-icon/code-availability
    Keywords: ddc:551.5
    Language: English
    Type: doc-type:article
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  • 2
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    Hydrologic Turnover Matters — Gross Gains and Losses of Six First‐Order Streams Across Contrasting Landscapes and Flow Regimes (2022)
    Details
    Publication Date: 2023-01-20
    Description: Gross gains and losses of stream water and the consequent hydrologic turnover may modify the composition of stream water and drive in‐stream ecological functioning. We evaluated over 500 breakthrough curves of conservative tracer additions to analyze the channel water balance resulting in gross gains and losses, net exchange, and hydrologic turnover. During the hydrological year 2019, seven tracer experiments had been carried out in six first‐order streams along 400 m study reaches. All streams are located in the Holtemme catchment (Central Germany) with three each dominated by forested and agricultural land use. Four of the six streams were characterized by net‐losing conditions. The overall median of gross exchange was five times higher than net exchange. On average, subsurface gains replaced 50% of the original stream water over less than one kilometer of stream length. We even observed cases where over 95% of the stream water turned over within 100 m. Gross exchange was relatively higher in forested than in agricultural streams. Patterns of exchange in the forested streams persisted spatially and were temporally independent of streamflow, whereas in the agricultural ones, variable spatial patterns and streamflow dependence occurred. Overall, moderate flow coincided with highest relative gross exchange. Our results support previous findings that in‐stream solute concentrations could heavily depend on location and magnitude of gains and losses. Gross exchange embodies a permanent but variable control of downstream solute concentrations interacting with the signal of biogeochemical activity. We highlight the importance to include reach‐scale hydrological processes in studies on nutrient spiraling.
    Description: Plain Language Summary: The vitality of stream ecosystems largely relies on the exchange of water between surface and groundwater. This comprises all gains and losses of stream water from and to the subsurface and is referred to as gross exchange. We investigated gross exchange for six headwater streams in the Holtemme catchment (Central Germany) during the hydrological year 2019. By applying salt tracer experiments we calculated the extent of exchange. Consistently, the investigated stream reaches lost more water than they gained. On average, half of the stream water was replaced by newly added groundwater along less than one km of stream length and, in few cases, almost the entire volume was exchanged within 100 m distance. Streams surrounded by forest exchanged more water than streams in agricultural landscapes. The location and direction of exchange remained similar in the forested streams, but varied temporarily for the agricultural streams. We could show that groundwater represents an important volume of our streams and that the true gross exchange can easily be underestimated if only the sum of gains and losses is measured. Therefore, solute concentrations can be strongly modified by gross exchange, which is important to better understand the transport of solutes in streams.
    Description: Key Points: In over 90% of the cases, gross exchange equals five times the net exchange, which impacts interpretations of nutrient uptake. Gross exchange and hydrologic turnover show spatiotemporal patterns persisting over discharge at forested, but not at agricultural sites. Moderate discharge exhibits the highest relative gross exchange.
    Keywords: ddc:551.48 ; gross gain and loss ; hydrologic turnover ; headwater streams ; reach scale ; losing streams ; land use
    Language: English
    Type: doc-type:article
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  • 3
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    ICON‐O: The Ocean Component of the ICON Earth System Model—Global Simulation Characteristics and Local Telescoping Capability (2022)
    Details
    Publication Date: 2023-01-25
    Description: We describe the ocean general circulation model Icosahedral Nonhydrostatic Weather and Climate Model (ICON‐O) of the Max Planck Institute for Meteorology, which forms the ocean‐sea ice component of the Earth system model ICON‐ESM. ICON‐O relies on innovative structure‐preserving finite volume numerics. We demonstrate the fundamental ability of ICON‐O to simulate key features of global ocean dynamics at both uniform and non‐uniform resolution. Two experiments are analyzed and compared with observations, one with a nearly uniform and eddy‐rich resolution of ∼10 km and another with a telescoping configuration whose resolution varies smoothly from globally ∼80 to ∼10 km in a focal region in the North Atlantic. Our results show first, that ICON‐O on the nearly uniform grid simulates an ocean circulation that compares well with observations and second, that ICON‐O in its telescope configuration is capable of reproducing the dynamics in the focal region over decadal time scales at a fraction of the computational cost of the uniform‐grid simulation. The telescopic technique offers an alternative to the established regionalization approaches. It can be used either to resolve local circulation more accurately or to represent local scales that cannot be simulated globally while remaining within a global modeling framework.
    Description: Plain Language Summary: Icosahedral Nonhydrostatic Weather and Climate Model (ICON‐O) is a global ocean general circulation model that works on unstructured grids. It rests on novel numerical techniques that belong to the class of structure‐preserving finite Volume methods. Unstructured grids allow on the one hand a uniform coverage of the sphere without resolution clustering, and on the other hand they provide the freedom to intentionally cluster grid points in some region of interest. In this work we run ICON‐O on an uniform grid of approximately 10 km resolution and on a grid with four times less degrees of freedom that is stretched such that in the resulting telescoping grid within the North Atlantic the two resolutions are similar, while outside the focal area the grid approaches smoothly ∼80 km resolution. By comparison with observations and reanalysis data we show first, that the simulation on the uniform 10 km grid provides a decent mesoscale eddy rich simulation and second, that the telescoping grid is able to reproduce the mesoscale rich circulation locally in the North Atlantic and on decadal time scales. This telescoping technique of unstructured grids opens new research directions.
    Description: Key Points: We describe Icosahedral Nonhydrostatic Weather and Climate Model (ICON‐O) the ocean component of ICON‐ESM 1.0, based on the ICON modeling framework. ICON‐O is analyzed in a globally mesoscale‐rich simulation and in a telescoping configuration. In telescoping configuration ICON‐O reproduces locally the eddy dynamics with less computational costs than the uniform configuration.
    Description: https://swiftbrowser.dkrz.de/public/dkrz_07387162e5cd4c81b1376bd7c648bb60/kornetal2021
    Description: https://mpimet.mpg.de/en/science/modeling-with-icon/code-availability
    Keywords: ddc:551.46 ; ocean modeling ; ocean dynamics ; unstructured grid modeling ; local refinement ; structure preservation numerics
    Language: English
    Type: doc-type:article
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  • 4
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    The glass transition, crystallization and melting in Au-Pb-Sb alloys (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The glass transition, crystallization and melting of Au(55)Pb(22.5)Sb(22.5) alloys have been studied by differential scanning calorimetry DSC. Crystallization on heating above the glass transition temperature Tg (45 C) begins at 64 C. Further crystallization events are observed at 172 C and 205 C. These events were found to correspond to the formation of the intermetallic compounds AuSb2, Au2Pb, and possibly AuPb2, respectively. Isothermal DSC scans of the glassy alloy above Tg were used to monitor the kinetics of crystallization. The solidification behavior and heat capacity in the glass-forming composition range were determined with droplet samples. An undercooling level of 0.3T(L) below the liquidus temperature T(L) was achieved, resulting in crystallization of different stable and metastable phases. The heat capacity C(P) of the undercooled liquid was measured over an undercooling range of 145 C.
    Keywords: METALLIC MATERIALS
    Type: Materials Science and Engineering (ISSN 0025-5416); 97; 301-305
    Format: text
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  • 5
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    Gamma heating in thin heavy-element absorbers. (1968)
    In:  Other Sources
    Details
    Publication Date: 2011-08-12
    Description: Gamma heating rate measured by aqueous dosimeter converted to rate in thin tungsten detector in water shield through transport theory calculations, obtaining correction factors
    Keywords: NUCLEAR ENGINEERING
    Type: ; ADEMIE DES SCIENCES
    Format: text
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  • 6
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    Molecular structure of r/GCG/d/TATACGC/ - A DNA-RNA hybrid helix joined to double helical DNA (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The molecule r(GCG)d(TATACGC) is self-complementary and forms two DNA-RNA hybrid segments surrounding a central region of double helical DNA; its molecular structure has been solved by X-ray analysis. All three parts of the molecule adopt a conformation which is close to that seen in the 11-fold RNA double helix. The conformation of the ribonucleotides is partly determined by water molecules bridging between the ribose O2' hydroxyl group and cytosine O2. The hybrid-DNA duplex junction contains no structural discontinuities. However, the central DNA TATA sequence has some structural irregularities.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Nature; 299; Oct. 14
    Format: text
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  • 7
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    Description, characteristics and testing of the NASA airborne radar (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Presented here is a description of a coherent radar scattermeter and its associated signal processing hardware, which have been specifically designed to detect microbursts and record their radar characteristics. Radar parameters, signal processing techniques and detection algorithms, all under computer control, combine to sense and process reflectivity, clutter, and microburst data. Also presented is the system's high density, high data rate recording system. This digital system is capable of recording many minutes of the in-phase and quadrature components and corresponding receiver gains of the scattered returns for selected spatial regions, as well as other aircraft and hardware related parameters of interest for post-flight analysis. Information is given in viewgraph form.
    Keywords: AIR TRANSPORTATION AND SAFETY
    Type: Airborne Wind Shear Detection and Warning Systems: Third Combined Manufacturers' and Technologists' Conference, Part 2; p 937-978
    Format: application/pdf
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  • 8
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    COSMIC: Carbon Monoxide and Soot in Microgravity Inverse Combustion (2001)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Almost seventy percent of deaths in accidental fires are caused by inhalation of toxins such as carbon monoxide (CO) and smoke (soot) that form during underventilated burning. The COSMIC project examines the formation mechanisms of CO and soot during underventilated combustion, achieved presently using laminar, inverse diffusion flames (IDFs) formed between an air jet and surrounding fuel. A major hypothesis of the project is that the IDF mimics underventilated combustion because carbon-containing species that form on the fuel side of the flame (such as CO and soot) can escape without passing through an oxidizing flame tip. An IDF literature review was presented at the last microgravity workshop, and a few additional IDF papers have appeared since that meeting. The COSMIC project is entering the third year of its four-year funding cycle. The first two years have been devoted to designing and constructing a rig for use in the NASA 2.2-second drop tower. A few computations and laboratory experiments have been performed. The goals of this paper are to discuss the use of numerical simulation during burner design, to present computational and experimental results that support the hypothesis that IDFs are similar to underventilated flames, and to delineate future plans.
    Keywords: Inorganic, Organic and Physical Chemistry
    Type: Sixth International Microgravity Combustion Workshop; 177-180; NASA/CP-2001-210826
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  • 9
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    The development and testing of a lightweight flight prototype ion engine system. (1966)
    In:  Other Sources
    Details
    Publication Date: 2019-05-30
    Description: Lightweight flight prototype mercury ion engine system development and testing
    Keywords: PROPULSION SYSTEMS
    Type: AIAA PAPER 66-216
    Format: text
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  • 10
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    Evaluation of high temperature stranded hook-up wire (1966)
    In:  CASI
    Details
    Publication Date: 2019-05-30
    Description: High temperature insulation materials, silver alloy, and copper wires tested for aerospace electric conductor application
    Keywords: ELECTRONIC EQUIPMENT
    Type: NASA-TM-X-53522
    Format: application/pdf
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