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  • 1
    Publication Date: 2016-05-06
    Description: Knowledge of sediment dynamics in rivers is of great importance for various practical purposes. Despite its high relevance in riverine environment processes, the monitoring of sediment rates remains a major and challenging task for both suspended and bedload estimation. While the measurement of suspended load is currently an active area of testing with non-intrusive technologies (optical and acoustic), bedload measurement does not mark a similar progress. This paper describes an innovative combination of measurement techniques and analysis protocols that establishes the proof-of-concept for a promising technique, labeled herein Acoustic Mapping Velocimetry (AMV). The technique estimates bedload rates in rivers developing bedforms using a non-intrusive measurements approach. The raw information for AMV is collected with acoustic multi-beam technology that in turn provides maps of the bathymetry over longitudinal swaths. As long as the acoustic maps can be acquired relatively quickly and the repetition rate for the mapping is commensurate with the movement of the bedforms, successive acoustic maps capture the progression of the bedform movement. Two-dimensional velocity maps associated with the bedform migration are obtained by implementing algorithms typically used in particle image velocimetry to acoustic maps converted in gray-level images. Furthermore, use of the obtained acoustic and velocity maps in conjunction with analytical formulations (e.g., Exner equation) enables estimation of multi-directional bedload rates over the whole imaged area. This paper presents a validation study of the AMV technique using a set of laboratory experiments. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2015-05-17
    Description: Plasmaspheric virtual resonance (PVR) model has been proposed as one of source mechanisms for low-latitude Pi2 pulsations. Since PVR-associated Pi2 pulsations are not localized inside the plasmasphere, simultaneous multipoint observations inside and outside the plasmasphere require to test the PVR model. Until now, however, there are few studies using simultaneous multisatellite observations inside and outside the plasmasphere for understanding the radial structure of Pi2 pulsation. In this study, we focus on the Pi2 event observed at low-latitude Bohyun (BOH, L = 1.35) ground station in South Korea in the postmidnight sector (magnetic local time (MLT) = 3.0) for the interval from 1730 to 1900 UT on 12 March 2013. By using electron density derived from the frequency of the upper hybrid waves detected at Van Allen Probe-A (VAP-A) and Van Allen Probe-B (VAP-B), the plasmapause is identified. At the time of the Pi2 event, VAP-A was outside the plasmasphere near midnight (00:55 MLT and L = ~ 6), while VAP-B was inside the plasmasphere in the postmidnight sector (02:15 MLT and L = ~ 5). VAP-B observed oscillations in the compressional magnetic field component ( B z ) and the dawn-to-dusk electric field component ( E y ), having high coherence with the BOH Pi2 pulsation in the H component. The H − B z and H − E y cross phases at VAP-B inside the plasmasphere were near −180° and −90°, respectively.These phase relationships among B z , E y , and H are consistent with a radially standing oscillation of the fundamental mode reported in previous studies. At VAP-A outside the plasmasphere, B z oscillations were highly correlated with BOH Pi2 pulsations with ~−180° phase delay, and the H-E y cross phase is near -90°. From these two-satellite observations, we suggest that the fundamental PVR mode is directly detected by VAP-A and VAP-B.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
  • 4
    Publication Date: 2015-01-10
    Description: The contributions of the equatorial waves to the quasi-biennial oscillation (QBO) are investigated using a version of the Hadley Centre Global Environment Model (HadGEM2). A gravity-wave parameterization that couples its source spectrum to the convection is used. The equatorial wave modes are identified in the spectral domain, based on their distinct characteristics associated with momentum and heat fluxes. The Kelvin waves and parameterized gravity waves (PGWs) transport westerly momentum into the equatorial stratosphere by ~0.35 and 0.8 mPa, respectively, while easterly momentum is carried primarily by the PGWs (~0.75 mPa). The resolved inertio-gravity (IG) waves transport both easterly and westerly momentum by ~0.2 mPa. In the lowermost stratosphere, gradual dissipation of the Kelvin waves occurs, and the remaining waves induce eastward forcing in the westerly-shear layer by 3–5 m s −1 month −1 . The PGWs primarily dissipate within the sheared layer and provide large easterly and westerly forcing in the middle stratosphere (~17 m s −1 month −1 ), while the forcing in the lower stratosphere is comparable to the Kelvin wave forcing. The IG wave forcing is small because of the small wave dissipation rate. The Rossby and mixed Rossby-gravity (MRG) waves contribute to the westerly-to-easterly QBO transition by ~2 m s −1 month −1 . The magnitudes of the simulated Kelvin and Rossby wave forcings are comparable with the Modern-Era Retrospective Analysis for Research and Applications (MERRA), whereas the MRG and IG wave forcings are underestimated in the lower stratosphere. Differences between the simulation and reanalysis and the uncertainties in both are discussed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2015-03-29
    Description: We present methane (CH 4 ) emissions for East Asia from a Bayesian inversion of CH 4 mole fraction and stable isotope (δ 13 C-CH 4 ) measurements. Emissions were estimated at monthly resolution from 2000 to 2011. A posteriori, the total emission for East Asia increased from 43 ± 4 to 59 ± 4 Tg y −1 between 2000 and 2011, owing largely to the increase in emissions from China, from 39 ± 4 to 54 ± 4 Tg y −1 , while emissions in other East Asian countries remained relatively stable. For China, South Korea, and Japan, the total emissions were smaller than the prior estimates (i.e., EDGAR-4.2 FT2010 for anthropogenic emissions) by an average of 29%, 20%, and 23%, respectively. For Mongolia, Taiwan, and North Korea, the total emission was less than 2 Tg y −1 and was not significantly different from the prior. The largest reductions in emissions, compared to the prior, occurred in summer in regions important for rice agriculture suggesting that this source is overestimated in the prior. Furthermore, analysis of the isotope data suggests that the prior underestimates emissions from landfills and ruminant animals for winter 2010 to spring 2011 (no data available for other times). The inversion also found a lower average emission trend for China, 1.2 Tg y −1 compared to 2.8 Tg y −1 in the prior. This trend was not constant, however, and increased significantly after 2005, up to 2.0 Tg y −1 . Overall, the changes in emissions from China explain up to 40% of the increase in global emissions in the 2000s.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2017-09-10
    Description: We investigated the biogeochemical cycling of dissolved zinc (Zn) in the western and central subarctic North Pacific during the GEOTRACES GP 02 cruise. The relationship between dissolved Zn and silicate in the subarctic North Pacific plotted as a concave curve. Values of Zn* were strongly positive in the intermediate waters (26.6–27.5 σ θ ) of both the western and the central subarctic North Pacific. There was a distinct kink in the relationship between dissolved Zn and soluble reactive phosphorus (SRP) at the transition from shallow to intermediate water, which is similar to what has been reported for other open oceans. The high Zn:SRP ratio and high Zn* in the intermediate water suggests that intermediate water masses play an important role in the decoupling of dissolved Zn and silicate in the subarctic North Pacific, which implies that the biogeochemical processes that control dissolved Zn and silicate in the intermediate water are different from those in other oceanic regions.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2017-10-11
    Description: We examine magnetic and electric field perturbations associated with a sudden commencement (SC), caused by an interplanetary (IP) shock passing over the Earth's magnetosphere on 16 February 2013. The SC was identified in the magnetic and electric field data measured at THEMIS-E (THE-E: MLT = 12.4, L = 6.3), Van Allen Probe-A (VAP-A: MLT = 3.2, L = 5.1), and Van Allen Probe-B (VAP-B: MLT = 0.2. L = 4.9) in the magnetosphere. During the SC interval, THE-E observed a dawnward-then-duskward electric (E) field perturbation around noon, while VAP-B observed a duskward E-field perturbation around midnight. VAP-A observed a dawnward-then-duskward E-field perturbation in the postmidnight sector, but the duration and magnitude of the dawnward E-perturbation are much shorter and weaker than that at THE-E. That is, the E-field signature changes with local time during the SC interval. The SuperDARN radar data indicate that the ionospheric plasma motions during the SC are mainly due to the E-field variations observed in space. This indicates that the SC-associated E-field in space plays a significant role in determining the dynamic variations of the ionospheric convection flow. By comparing previous SC MHD simulations and our observations, we suggest that the E-field variations observed at the spacecraft are produced by magnetospheric convection flows due to deformation of the magnetosphere as the IP shock sweeps the magnetopause.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2017-04-19
    Description: Vertically propagating low-frequency inertia-gravity waves (IGWs) are retrieved from meteor radar winds observed at King Sejong Station (KSS: 62.22 ∘ S, 58.78 ∘ W), Antarctica. IGW horizontal winds extracted from temporal band-pass filtering in regular time-height bins show the frequent occurrence of IGWs with the downward phase progression and the counterclockwise rotation of their horizontal wind vectors with time (i.e., upward energy propagation) near the mesopause region throughout the whole year of 2014. The vertical wavelengths of the observed IGWs roughly range from 14 km to more than 20 km, which is consistent with previous observational studies on the mesospheric IGWs over Antarctica. Stokes parameters and rotary spectra computed from the hodographs of the IGW horizontal wind components reveal that the intrinsic frequencies of the upward propagating IGWs are | f |–3| f | with seasonal variations of the relative predominance between | f |–2| f | and 2| f |–3| f |, where f is the Coriolis parameter at KSS. The hodograph analysis also indicates that the N–S propagation is dominant in austral summer, while the NE–SW propagation is pronounced in austral winter. The propagation direction is discussed in relation to the generation of IGWs due to dynamical imbalances occurring in the tropospheric and stratospheric jet-flow systems. Ray-tracing results indicate that the N–S propagation in summer may be due to the jet-flow systems roughly north of KSS and the NE–SW propagation in winter may be either the SW propagation from the jet-flow systems northeast of KSS or the NE propagation (around the South pole) from the south of Australia and Southern Indian and Pacific Oceans.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 9
    Publication Date: 2018-03-01
    Print ISSN: 0002-1962
    Electronic ISSN: 1435-0645
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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  • 10
    Publication Date: 2017-11-01
    Print ISSN: 0002-1962
    Electronic ISSN: 1435-0645
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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