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  • 1
    Monograph available for loan
    Monograph available for loan
    New York, NY [u.a.] : Wiley
    Call number: G 8860
    Type of Medium: Monograph available for loan
    Pages: X, 610 S. : graph. Darst.
    ISBN: 0471888540
    Location: Upper compact magazine
    Branch Library: GFZ Library
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  • 2
    Publication Date: 2024-01-12
    Description: We investigate the small‐scale magnetic field fluctuations and their associated turbulent nature in the Io flux tube (IFT) connected to Io's footprint tail (IFPT). Our study is based on the recent magnetic field measurements by the Juno spacecraft during the PJ12 Juno flyby. Here, we are interested in understanding what type of turbulence is consistent with the fluctuations in the quasi‐dispersionless frequency range of 0.2–800 Hz as observed by Sulaiman et al. (2020), https://doi.org/10.1029/2020GL088432. Knowledge of the turbulent fluctuations is important to constrain the acceleration mechanisms for ions and electrons in the IFT. In this work, we suggest that the observed temporal fluctuations in the spacecraft frame correspond to Doppler‐shifted spatial fluctuation structured perpendicular to the background magnetic field. This would imply an alternative reinterpretation of the spectral index of the observed magnetic power spectral density to be potentially the result of weak‐MHD and sub‐ion scale kinetic Alfvén wave turbulence in the low‐frequency regime. Our theoretical modelings show that turbulence can be driven both in the torus region and at high‐latitudes rendering results in agreement with the Juno measurements. Calculated turbulence heating rates are consistent with observed energy fluxes in the IFT and represent efficient drivers for particle acceleration. Moreover, a widening of the IFPT structure with respect to the IFT extent is consistent with propagating dispersive Alfvén waves modified by kinetic effects on their group velocities.
    Description: Key Points: Low‐frequency Juno observations in the Io flux tube (IFT) tail represent structures perpendicular to background magnetic field. Magnetic field fluctuations observed in the Io footprint tail (IFPT) are consistent with weak‐MHD and sub‐ion kinetic Alfvén wave turbulence. Dispersion effects on group velocity of Alfvén waves widens the IFT consistent with the observed width of the IFPT.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.17189/1519711
    Description: https://doi.org/10.17189/1522461
    Keywords: ddc:523 ; Io ; Juno observations ; Alfvén waves ; magnetic field fluctuations
    Language: English
    Type: doc-type:article
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  • 3
    Publication Date: 2023-01-12
    Description: Transient magnetic reconnection plays an important role in energetic particle acceleration in planetary magnetospheres. Jupiter's magnetosphere provides a unique natural laboratory to study processes of energy transport and transformation. Strong electric fields in spatially confined structures such as plasmoids can be responsible for ion acceleration to high energies. In this study we focus on the effectiveness of ion energization and acceleration in plasmoids. Therefore, we present a statistical study of plasmoid structures in the predawn magnetotail, which were identified in the magnetometer data of the Juno spacecraft from 2016 to 2018. We additionally use the energetic particle observations from the Jupiter Energetic Particle Detector Instrument which discriminates between different ion species. We are particularly interested in the analysis of the acceleration and energization of oxygen, sulfur, helium, and hydrogen ions. We investigate how the event properties, such as the radial distance and the local time of the observed plasmoids in the magnetotail, affect the ion intensities close to the current sheet center. Furthermore, we analyze if ion acceleration is influenced by magnetic field turbulence inside the plasmoids. We find significant heavy ion acceleration in plasmoids close to the current sheet center which is in line with the previous statistical results based on Galileo observations conducted by Kronberg et al. (2019, https://doi.org/10.1029/2019JA026553). The observed effectiveness of the acceleration is dependent on the position of Juno in the magnetotail during the plasmoid event observation. Our results show no correlation between magnetic field turbulence and nonadiabatic acceleration for heavy ions during plasmoids.
    Description: Key Points: Intensity of heavy ions is strongly increased during plasmoids close to the current sheet center. Significant increase of heavy ion intensities is observed in plasmoids with larger wave power. Acceleration of heavy and light ions in plasmoids due to resonant interaction with the magnetic field fluctuations could not be observed.
    Description: Volkswagen Foundation (VolkswagenStiftung) http://dx.doi.org/10.13039/501100001663
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: NASA
    Description: https://pds-ppi.igpp.ucla.edu/
    Keywords: ddc:523 ; plasmoids ; Juno ; JEDI ; ion acceleration
    Language: English
    Type: doc-type:article
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  • 4
    Publication Date: 2023-01-13
    Description: Recent observations by the Juno spacecraft have shown that electrons contributing to Jupiter's main auroral emission appear to be frequently characterized by broadband electron distributions, but also less often mono‐energetic electron distributions are observed as well. In this work, we quantitatively derive the occurrence rates of the various electron distributions contributing to Jupiter's aurora. We perform a statistical analysis of electrons measured by the JEDI‐instrument within 30–1,200 keV from Juno's first 20 orbits. We determine the electron distributions, either pancake, field‐aligned, mono‐energetic, or broadband, through energy and pitch angles to associate various acceleration mechanisms. The statistical analysis shows that field‐aligned accelerated electrons at magnetic latitudes greater than 76° are observed in 87.6% ± 7.2% of the intervals time averaged over the dipole L‐shells according the main oval. Pancake distributions, indicating diffuse aurora, are prominent at smaller magnetic latitudes (〈76°) with an occurrence rate of 86.2% ± 9.6%. Within the field‐aligned electron distributions, we see broadband distributions 93.0% ± 3.8% of the time and a small fraction of isolated mono‐energetic distribution structures 7.0% ± 3.8% of the time. Furthermore, these occurrence statistics coincide with the findings from our energy flux statistics regarding the electron distributions. Occurrence rates thus also characterize the overall energetics of the different distribution types. This study indicates that stochastic acceleration is dominating the auroral processes in contrast to Earth where the discrete aurora is dominating.
    Description: Plain Language Summary: With the Juno spacecraft arriving in the magnetosphere of Jupiter, first flyby particle measurements have changed the knowledge about the developing process of Jupiter's intense aurora. The observations of auroral particles show a stochastic behavior rather than a preference for specific energy. Our statistical analysis of the first 20 flybys at Jupiter compares the occurrence of different particle distributions and highlights the importance of different generation theories for Jupiter's aurora. A generation via stochastic rather than mono‐energetic behavior is deduced and supports previous observations.
    Description: Key Points: We present a statistical study of Jupiter's auroral electrons within 30–1,200 keV based on Juno's first 20 perijoves. Broadband electron distributions dominates Jupiter's main auroral zone as they are observed in 93% ± 3% of the intervals studied here. Dominance of broadband distributions underlines the importance of a turbulent or stochastic acceleration process.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Universität zu Köln http://dx.doi.org/10.13039/501100008001
    Description: https://lasp.colorado.edu/home/mop/files/2015/02/CoOrd_systems7.pdf
    Description: https://pds-ppi.igpp.ucla.edu/mission/JUNO/JNO/JEDI
    Description: https://lasp.colorado.edu/home/mop/files/2020/04/20190412_Imai_MagFootReader_UIowa_rev.pdf
    Keywords: ddc:523 ; auroral precipitation budget ; particle distribution ; Jupiter ; Juno
    Language: English
    Type: doc-type:article
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  • 5
    Publication Date: 2023-06-19
    Description: Energetic particle acceleration and energization in planetary magnetotails are often associated with dipolarization fronts characterized by a rapid increase of the meridional component of the magnetic field. Despite many studies of dipolarization events in Earth's magnetotail, Jupiter’s magnetotail provides an almost ideal environment to study high‐energetic ion acceleration by dipolarization fronts because of its large spatial scales and plasma composition of heavy and light ions. In this study, we focus on the response of different high‐energetic ion intensities (H, He, S, and O) to prominent magnetic dipolarization fronts inside the Jovian magnetotail. We investigate if ion energization and acceleration are present in the observations around the identified dipolarization fronts. Therefore, we present a statistical study of 87 dipolarization front signatures, which are identified in the magnetometer data of the Juno spacecraft from July 2016 to July 2021. For the ion intensity analysis, we use the energetic particle observations from the Jupiter Energetic Particle Detector Instrument. Our statistical study reveals that less than half of the identified events are accompanied by an increase of the ion intensities, while most of the other events show no significant change in the ion intensity dynamics. In about 40% of the events located in the dawn sector a significant decrease of the energy spectral index is detected indicating ion acceleration by the dipolarization fronts.
    Description: Key Points: Eighty‐seven prominent dipolarization front signatures are observed in the MAG data during Juno's prime mission during 21:00–05:30 local time. Less than half of the identified events are accompanied by an increase of the ion intensities. In 40% of the events observed on the dawn side a significant decrease of the energy spectral index indicates ion acceleration by the fronts.
    Description: Volkswagen Foundation http://dx.doi.org/10.13039/501100001663
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.17189/1519711
    Description: https://doi.org/10.17189/1519713
    Keywords: ddc:523 ; Juno ; Jovian magnetotail ; energetic ions ; dipolarization fronts ; JEDI
    Language: English
    Type: doc-type:article
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  • 6
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 118 (2013): 273–286, doi:10.1029/2012JC008154.
    Description: The shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas. Including such effects in numerical models demands improvements in the understanding of several aspects of the energetics, especially those relating to turbulence generation, and observations are needed to build this understanding. To address some of these issues in the estuarine context, we undertook an intensive field program for 10 days in the summer of 2008 in the St. Lawrence Estuary. The sampling involved shore-based photogrammetry, ship-based surveys, and an array of moorings in the shoaling region that held both conventional and turbulence-resolving sensors. The measurements shed light on many aspects of the wave shoaling process. Wave arrivals were generally phase-locked with the M2 tide, providing hints about far-field forcing. In the deeper part of the study domain, the waves propagated according to the predictions of linear theory. In intermediate-depth waters, the waves traversed the field site perpendicularly to isobaths, a pattern that continued as the waves transformed nonlinearly. Acoustic Doppler velocimeters permitted inference of the turbulent energetics, and two main features were studied. First, during a period of shoaling internal waves, turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude. Second, the evolving spectral signatures associated with a particular wave-shoaling event suggest that the turbulence is at least partly locally generated. Overall, the results of this study suggest that parameterizations of wave-induced mixing could employ relatively simple dynamics in deep water, but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions.
    Description: The work was supported by the Killam Foundation, the Natural Sciences and Engineering Research Council of Canada, the Canadian Foundation for Innovation, the Canadian Foundation for Climate and Atmospheric Sciences, and the Canadian Department of Fisheries and Oceans.
    Description: 2013-07-30
    Keywords: Internal waves ; Turbulence ; Estuary
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 7
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 72 (2014): 21-33, doi:10.1016/j.csr.2013.10.019.
    Description: Two-dimensional, nonlinear and nonhydrostatic field-scale numerical simulations are used to examine the resuspension, dispersal and transport of mud-like sediment caused by the shoaling and breaking of long internal solitary waves on uniform slopes. The patterns of erosion and transport are both examined, in a series of test cases with varying conditions. Shoreward sediment movement is mainly within boluses, while seaward movement is within intermediate nepheloid layers. Several relationships between properties of the suspended sediment and control parameters are determined such as the horizontal extent of the nehpeloid layers, the total mass of resuspended sediment and the point of maximum bed erosion. The numerical results provide a plausible explanation for acoustic backscatter patterns observed during and after the shoaling of internal solitary wavetrains in a natural coastal environment. The results may further help interpret sedimentary structures that may have been shaped by internal waves and add an another e ective mechanism for o shore dispersal of muddy sediments.
    Description: This research was funded by the Natural Sciences and Engineering Research Council of Canada (D. Bourgault) and by the Spanish Research Project CGL2009-13254 (M. Morsilli).
    Keywords: Internal solitary wave ; Sediment ; Nepheloid layer ; Numerical modelling ; Sedimentary structures
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: application/pdf
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  • 8
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 1735–1756, doi:10.1175/JPO-D-14-0238.1.
    Description: The Lofoten basin of the Nordic Seas is recognized as a crucial component of the meridional overturning circulation in the North Atlantic because of the large horizontal extent of Atlantic Water and winter surface buoyancy loss. In this study, hydrographic and current measurements collected from a mooring deployed in the Lofoten basin from July 2010 to September 2012 are used to describe water mass transformation and the mesoscale eddy field. Winter mixed layer depths (MLDs) are observed to reach approximately 400 m, with larger MLDs and denser properties resulting from the colder 2010 winter. A heat budget of the upper water column requires lateral input, which balances the net annual heat loss of ~80 W m−2. The lateral flux is a result of mesoscale eddies, which dominate the velocity variability. Eddy velocities are enhanced in the upper 1000 m, with a barotropic component that reaches the bottom. Detailed examination of two eddies, from April and August 2012, highlights the variability of the eddy field and eddy properties. Temperature and salinity properties of the April eddy suggest that it originated from the slope current but was ventilated by surface fluxes. The properties within the eddy were similar to those of the mode water, indicating that convection within the eddies may make an important contribution to water mass transformation. A rough estimate of eddy flux per unit boundary current length suggests that fluxes in the Lofoten basin are larger than in the Labrador Sea because of the enhanced boundary current–interior density difference.
    Description: The work was supported by NSF OCE 0850416.
    Description: 2015-12-01
    Keywords: Circulation/ Dynamics ; Atmosphere-ocean interaction ; Boundary currents ; Eddies ; Fluxes ; Mesoscale processes ; Atm/Ocean Structure/ Phenomena ; Thermohaline circulation
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 9
    Publication Date: 2019-04-30
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wagner, T. J. W., Straneo, F., Richards, C. G., Slater, D. A., Stevens, L. A., Das, S. B., & Singh, H. Large spatial variations in the flux balance along the front of a Greenland tidewater glacier. Cryosphere, 13(3), (2019):911-925, doi:10.5194/tc-13-911-2019.
    Description: The frontal flux balance of a medium-sized tidewater glacier in western Greenland in the summer is assessed by quantifying the individual components (ice flux, retreat, calving, and submarine melting) through a combination of data and models. Ice flux and retreat are obtained from satellite data. Submarine melting is derived using a high-resolution ocean model informed by near-ice observations, and calving is estimated using a record of calving events along the ice front. All terms exhibit large spatial variability along the ∼5 km wide ice front. It is found that submarine melting accounts for much of the frontal ablation in small regions where two subglacial discharge plumes emerge at the ice front. Away from the subglacial plumes, the estimated melting accounts for a small fraction of frontal ablation. Glacier-wide, these estimates suggest that mass loss is largely controlled by calving. This result, however, is at odds with the limited presence of icebergs at this calving front – suggesting that melt rates in regions outside of the subglacial plumes may be underestimated. Finally, we argue that localized melt incisions into the glacier front can be significant drivers of calving. Our results suggest a complex interplay of melting and calving marked by high spatial variability along the glacier front.
    Description: We acknowledge support from the Woods Hole Oceanographic Institution Ocean and Climate Change Institute Arctic Research Initiative, and NSF OPP-1418256 and OPP-1743693, to Fiamma Straneo and Sarah B. Das. Till J. W. Wagner was further supported by NSF OPP award 1744835. Geospatial support for this work was provided by the Polar Geospatial Center under NSF OPP awards 1043681 and 1559691. DEMs provided by the Polar Geospatial Center under NSF OPP awards 1043681, 1559691, and 1542736. Donald A. Slater acknowledges the support of Scottish Alliance for Geoscience, Environment and Society early-career research exchange funding.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 10
    Publication Date: 2023-02-17
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(10), (2022): 1525–1539, https://doi.org/10.1175/jtech-d-21-0186.1.
    Description: The static and dynamic performances of the RBRargo3 are investigated using a combination of laboratory-based and in situ datasets from floats deployed as part of an Argo pilot program. Temperature and pressure measurements compare well to co-located reference data acquired from shipboard CTDs. Static accuracy of salinity measurements is significantly improved using 1) a time lag for temperature, 2) a quadratic pressure dependence, and 3) a unit-based calibration for each RBRargo3 over its full pressure range. Long-term deployments show no significant drift in the RBRargo3 accuracy. The dynamic response of the RBRargo3 demonstrates the presence of two different adjustment time scales: a long-term adjustment O(120) s, driven by the temperature difference between the interior of the conductivity cell and the water, and a short-term adjustment O(5–10) s, associated to the initial exchange of heat between the water and the inner ceramic. Corrections for these effects, including dependence on profiling speed, are developed.
    Keywords: Data processing/distribution ; In situ oceanic observations ; Profilers ; Oceanic
    Repository Name: Woods Hole Open Access Server
    Type: Article
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