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  • 1
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    Evaluation of FESOM2.0 Coupled to ECHAM6.3: Preindustrial and HighResMIP Simulations (2021)
    Details
    Publication Date: 2021-09-27
    Description: A new global climate model setup using FESOM2.0 for the sea ice-ocean component and ECHAM6.3 for the atmosphere and land surface has been developed. Replacing FESOM1.4 by FESOM2.0 promises a higher efficiency of the new climate setup compared to its predecessor. The new setup allows for long-term climate integrations using a locally eddy-resolving ocean. Here it is evaluated in terms of (1) the mean state and long-term drift under preindustrial climate conditions, (2) the fidelity in simulating the historical warming, and (3) differences between coarse and eddy-resolving ocean configurations. The results show that the realism of the new climate setup is overall within the range of existing models. In terms of oceanic temperatures, the historical warming signal is of smaller amplitude than the model drift in case of a relatively short spin-up. However, it is argued that the strategy of “de-drifting” climate runs after the short spin-up, proposed by the HighResMIP protocol, allows one to isolate the warming signal. Moreover, the eddy-permitting/resolving ocean setup shows notable improvements regarding the simulation of oceanic surface temperatures, in particular in the Southern Ocean.
    Keywords: 551.6 ; FESOM ; ocean model ; climate model ; unstructured mesh ; Finite Volume
    Language: English
    Type: map
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    CITATION GEO-LEO
  • 2
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    Atmospheric Wind Biases: A Challenge for Simulating the Arctic Ocean in Coupled Models? (2021)
    Details
    Publication Date: 2022-03-23
    Description: Many state‐of‐the‐art climate models do not simulate the Atlantic Water (AW) layer in the Arctic Ocean realistically enough to address the question of future Arctic Atlantification and its associated feedback. Biases concerning the AW layer are commonly related to insufficient resolution and excessive mixing in the ocean component as well as unrealistic Atlantic‐Arctic Ocean exchange. Based on sensitivity experiments with FESOM1.4, the ocean–sea‐ice component of the global climate model AWI‐CM1, we show that even if all impediments for simulating AW realistically are addressed in the ocean model, new biases in the AW layer develop after coupling to an atmosphere model. By replacing the wind forcing over the Arctic with winds from a coupled simulation we show that a common bias in the atmospheric sea level pressure (SLP) gradient and its associated wind bias lead to differences in surface stress and Ekman transport. Fresh surface water gets redistributed leading to changes in halosteric height distribution. Those changes lead to strengthening of the anticyclonic surface circulation in the Canadian Basin, so that the deep counterflow carrying warm AW gets reversed and a warm bias in the Canadian Basin develops. The SLP and anticyclonic wind bias in the Nordic Seas weaken the cyclonic circulation leading to reduced AW transport into the Arctic Ocean through Fram Strait but increased AW transport through the Barents Sea Opening. These effects together lead to a cold bias in the Eurasian Basin. An underestimation of sea ice concentration can significantly amplify the induced ocean biases.
    Description: Plain Language Summary: Coupled global climate models are used to predict anthropogenic climate change along with its impacts. The Arctic has experienced amplified warming in the recent decades compared to global mean warming and therefore is one region of intense climate research. In this context Atlantification of the Arctic Ocean has become a high priority topic. Atlantification describes the increasing impact of oceanic heat from the Atlantic Water (AW) layer of the Arctic Ocean on the sea ice cover. In climate models, the direction and strength of simulated AW circulation around the Arctic Ocean is known to be sensitive to ocean grid resolution, parametrization, boundary and surface forcing or a combination thereof. Here we show that biases in the atmospheric component of climate models can interrupt and even reverse the simulated AW circulation at depth. Such biases can be further amplified by a negative bias in simulated sea ice cover. This study shows how these surface biases can negatively impact the deep ocean circulation.
    Description: Key Points: Many state‐of‐the‐art climate models fail to simulate the properties of the Atlantic Water layer in the Arctic Ocean realistically. Biases in Arctic sea level pressure and surface winds in atmosphere models can reverse Atlantic Water circulation. The underestimation of sea‐ice cover amplifies this problem further.
    Description: European Union's Horizon 2020 Research and Innovation program
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Keywords: ddc:551.46
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 3
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    A natural basis for efficient brain-actuated control (2000)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The prospect of noninvasive brain-actuated control of computerized screen displays or locomotive devices is of interest to many and of crucial importance to a few 'locked-in' subjects who experience near total motor paralysis while retaining sensory and mental faculties. Currently several groups are attempting to achieve brain-actuated control of screen displays using operant conditioning of particular features of the spontaneous scalp electroencephalogram (EEG) including central mu-rhythms (9-12 Hz). A new EEG decomposition technique, independent component analysis (ICA), appears to be a foundation for new research in the design of systems for detection and operant control of endogenous EEG rhythms to achieve flexible EEG-based communication. ICA separates multichannel EEG data into spatially static and temporally independent components including separate components accounting for posterior alpha rhythms and central mu activities. We demonstrate using data from a visual selective attention task that ICA-derived mu-components can show much stronger spectral reactivity to motor events than activity measures for single scalp channels. ICA decompositions of spontaneous EEG would thus appear to form a natural basis for operant conditioning to achieve efficient and multidimensional brain-actuated control in motor-limited and locked-in subjects.
    Keywords: Man/System Technology and Life Support
    Type: IEEE transactions on rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society (ISSN 1063-6528); Volume 8; 2; 208-11
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    NASA TECHNICAL REPORTS
  • 4
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    Awareness during drowsiness: dynamics and electrophysiological correlates (2000)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: During drowsy periods, performance on tasks requiring continuous attention becomes intermittent. Previously, we have reported that during drowsy periods of intermittent performance, 7 of 10 participants performing an auditory detection task exhibited episodes of non-responding lasting about 18 s (Makeig & Jung, 1996). Further, the time patterns of these episodes were repeated precisely in subsequent sessions. The 18-s cycles were accompanied by counterbalanced power changes within two frequency bands in the vertex EEG (near 4 Hz and circa 40 Hz). In the present experiment, performance patterns and concurrent EEG spectra were examined in four participants performing a continuous visuomotor compensatory tracking task in 15-20 minute bouts during a 42-hour sleep deprivation study. During periods of good performance, participants made compensatory trackball movements about twice per second, attempting to keep a target disk near a central ring. Autocorrelations of time series representing the distance of the target disk from the ring centre showed that during periods of poor performance marked near-18-s cycles in performance again appeared. There were phases of poor or absent performance accompanied by an increase in EEG power that was largest at 3-4 Hz. These studies show that in drowsy humans, opening and closing of the gates of behavioural awareness is marked not by the appearance of (12-14 Hz) sleep spindles, but by prominent EEG amplitude changes in the low theta band. Further, both EEG and behavioural changes during drowsiness often exhibit stereotyped 18-s cycles.
    Keywords: Life Sciences (General)
    Type: Canadian journal of experimental psychology = Revue canadienne de psychologie experimentale (ISSN 1196-1961); Volume 54; 4; 266-73
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    NASA TECHNICAL REPORTS
  • 5
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    Unifying view of transient responses for determining lifetime and surface recombination velocity in silicon diodes and back-surface-field solar cells, with application to experimental short-circuit-current decay (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Electron Devices (ISSN 0018-9383); ED-31; 588-595
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Analysis and visualization of single-trial event-related potentials (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: In this study, a linear decomposition technique, independent component analysis (ICA), is applied to single-trial multichannel EEG data from event-related potential (ERP) experiments. Spatial filters derived by ICA blindly separate the input data into a sum of temporally independent and spatially fixed components arising from distinct or overlapping brain or extra-brain sources. Both the data and their decomposition are displayed using a new visualization tool, the "ERP image," that can clearly characterize single-trial variations in the amplitudes and latencies of evoked responses, particularly when sorted by a relevant behavioral or physiological variable. These tools were used to analyze data from a visual selective attention experiment on 28 control subjects plus 22 neurological patients whose EEG records were heavily contaminated with blink and other eye-movement artifacts. Results show that ICA can separate artifactual, stimulus-locked, response-locked, and non-event-related background EEG activities into separate components, a taxonomy not obtained from conventional signal averaging approaches. This method allows: (1) removal of pervasive artifacts of all types from single-trial EEG records, (2) identification and segregation of stimulus- and response-locked EEG components, (3) examination of differences in single-trial responses, and (4) separation of temporally distinct but spatially overlapping EEG oscillatory activities with distinct relationships to task events. The proposed methods also allow the interaction between ERPs and the ongoing EEG to be investigated directly. We studied the between-subject component stability of ICA decomposition of single-trial EEG epochs by clustering components with similar scalp maps and activation power spectra. Components accounting for blinks, eye movements, temporal muscle activity, event-related potentials, and event-modulated alpha activities were largely replicated across subjects. Applying ICA and ERP image visualization to the analysis of sets of single trials from event-related EEG (or MEG) experiments can increase the information available from ERP (or ERF) data. Copyright 2001 Wiley-Liss, Inc.
    Keywords: Life Sciences (General)
    Type: Human brain mapping (ISSN 1065-9471); 14; 3; 166-85
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    NASA TECHNICAL REPORTS
  • 7
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    Circuit for Lifetime and Surface-Recombination Measurements (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Test circuit for silicon solar cells suppresses spurious effects. New circuit increases accuracy of measurements of recombination lifetime and effective surface recombination velocity in silicon solar cell. Fast electronic switch, circuit grounds forward-biased cell so rapidly transient voltage to be measured not affected significantly.
    Keywords: ELECTRONIC COMPONENTS AND CIRCUITS
    Type: NPO-16752 , NASA Tech Briefs (ISSN 0145-319X); 10; 6; P. 30
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    NASA TECHNICAL REPORTS
  • 8
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    Factors influencing Northern Hemisphere winter mean atmospheric circulation anomalies during the period 1960/61 to 2001/02 (2012)
    Royal Meteorological Society
    In:  Quarterly Journal of the Royal Meteorological Society, 138 . pp. 1970-1982.
    Details
    Publication Date: 2019-09-23
    Description: Influences from the Tropics, the stratosphere and the specification of observed sea surface temperature and sea-ice (SSTSI) on Northern Hemisphere winter mean circulation anomalies during the period 1960/61 to 2001/02 are studied using a relaxation technique applied to the ECMWF model. On interannual time-scales, the Tropics strongly influence the Pacific sector but also the North Atlantic sector, although weakly. The stratosphere is found to be influential on the North Atlantic Oscillation (NAO) on interannual time-scales but is less important over the Pacific sector. Adding the observed SSTSI to the tropical relaxation runs generally improves the model performance on interannual time-scales but degrades/enhances the model’s ability to capture the 42-year trend over the Pacific/Atlantic sector. While relaxing the stratosphere to the reanalysis fails to capture the trend over the whole 42-year period, the stratosphere is shown to be influential on the upward trend of the NAO index from 1965 to 1995, but with reduced amplitude compared to previous studies. Influence from the Tropics is found to be important for the trend over both time periods and over both sectors although, across all experiments, we can account for only 30% of the amplitude of the hemispheric trend. Copyright c� 2012 Royal Meteorological Society
    Type: Article , PeerReviewed
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    PAPER (OCEANREP)
  • 9
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    An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part I: Sea ice and solid freshwater (2016)
    Elsevier
    In:  Ocean Modelling, 99 . pp. 110-132.
    Details
    Publication Date: 2020-11-04
    Description: Highlights: • Arctic sea ice extent and solid freshwater in 14 CORE-II models are inter-compared. • The models better represent the variability than the mean state. • The September ice extent trend is reasonably represented by the model ensemble mean. • The descending trend of ice thickness is underestimated compared to observations. • The models underestimate the reduction in solid freshwater content in recent years. Abstract: The Arctic Ocean simulated in fourteen global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE II) is analyzed. The focus is on the Arctic sea ice extent, the solid freshwater (FW) sources and solid freshwater content (FWC). Available observations are used for model evaluation. The variability of sea ice extent and solid FW budget is more consistently reproduced than their mean state in the models. The descending trend of September sea ice extent is well simulated in terms of the model ensemble mean. Models overestimating sea ice thickness tend to underestimate the descending trend of September sea ice extent. The models underestimate the observed sea ice thinning trend by a factor of two. When averaged on decadal time scales, the variation of Arctic solid FWC is contributed by those of both sea ice production and sea ice transport, which are out of phase in time. The solid FWC decreased in the recent decades, caused mainly by the reduction in sea ice thickness. The models did not simulate the acceleration of sea ice thickness decline, leading to an underestimation of solid FWC trend after 2000. The common model behavior, including the tendency to underestimate the trend of sea ice thickness and March sea ice extent, remains to be improved.
    Type: Article , PeerReviewed
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  • 10
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    An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part II: Liquid freshwater (2016)
    Elsevier
    In:  Ocean Modelling, 99 . pp. 86-109.
    Details
    Publication Date: 2020-11-04
    Description: Highlights: • Arctic liquid freshwater budget simulated in 14 CORE-II models is studied. • The models better represent the temporal variability than the mean state. • Multi-model mean (MMM) FW fluxes compare well with observations. • MMM FWC shows an upward trend in the recent years, with an underestimated rate. • FW flux interannual variability is more consistent where volume flux determines it. Abstract: The Arctic Ocean simulated in 14 global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE-II) is analyzed in this study. The focus is on the Arctic liquid freshwater (FW) sources and freshwater content (FWC). The models agree on the interannual variability of liquid FW transport at the gateways where the ocean volume transport determines the FW transport variability. The variation of liquid FWC is induced by both the surface FW flux (associated with sea ice production) and lateral liquid FW transport, which are in phase when averaged on decadal time scales. The liquid FWC shows an increase starting from the mid-1990s, caused by the reduction of both sea ice formation and liquid FW export, with the former being more significant in most of the models. The mean state of the FW budget is less consistently simulated than the temporal variability. The model ensemble means of liquid FW transport through the Arctic gateways compare well with observations. On average, the models have too high mean FWC, weaker upward trends of FWC in the recent decade than the observation, and low consistency in the temporal variation of FWC spatial distribution, which needs to be further explored for the purpose of model development.
    Type: Article , PeerReviewed
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