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  • 551.6  (38)
  • Englisch  (38)
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  • 2020-2022  (38)
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  • Englisch  (38)
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  • 1
    Publikationsdatum: 2021-07-22
    Beschreibung: The variability of the Atlantic meridional overturning circulation (AMOC) and its governing processes during the Last Glacial Maximum (LGM) is investigated in the Kiel Climate Model. Under LGM conditions, multidecadal AMOC variability is mainly forced by the surface heat flux variability linked to the East Atlantic pattern (EAP). In contrast, the multidecadal AMOC variability under preindustrial conditions is mainly driven by the surface heat flux variability associated with the North Atlantic Oscillation. Stand-alone atmosphere model experiments show that relative to preindustrial conditions, the change in AMOC forcing under LGM conditions is tightly linked to the differences in topography.
    Schlagwort(e): 551.6
    Sprache: Englisch
    Materialart: article
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2021-09-27
    Beschreibung: At regional to local scales internal variability is expected to be a dominant source of uncertainty in analyzing precipitation extremes and mean precipitation even far into the 21st century. A debated topic is whether a faster increase in subdaily precipitation extremes can be expected. Here we analyzed seasonal maximum precipitation in various time steps (3 hr, days, and 5 days) from a high-resolution 50-member large-ensemble (CRCM5-LE) and compared them to changes in mean precipitation over Europe. Our results show that the magnitude of change in extreme precipitation varies for season and duration. Subdaily extremes increase at higher rates than daily extremes and show higher scaling with temperature. Northern Europe shows widespread scaling above Clausius-Clapeyron of subdaily extremes in all seasons and for daily extremes in winter/spring. Scaling above Clausius-Clapeyron is also visible over Eastern Europe in winter/spring. For most regions and seasons the forced response emerges from the internal variability by midcentury.
    Schlagwort(e): 551.6 ; large ensembles ; SMILEs ; Regional Climate Model ; precipitation extremes ; subdaily ; Europe
    Sprache: Englisch
    Materialart: map
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2021-09-27
    Beschreibung: An abundance of evidence indicates that the tropics are expanding. Despite many attempts to decipher the cause, the underlying dynamical mechanism driving tropical expansion is still not entirely clear. Here, based on observations, multimodel simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) and purposefully designed numerical experiments, the variations and trends of the tropical width are explored from a regional perspective. We find that the width of the tropics closely follows the displacement of oceanic midlatitude meridional temperature gradients (MMTG). Under global warming, as a first-order response, the subtropical ocean experiences more surface warming because of the mean Ekman convergence of anomalously warm water. The enhanced subtropical warming, which is partially independent of natural climate oscillations, such as the Pacific Decadal Oscillation, leads to poleward advance of the MMTG and drives the tropical expansion. Our results, supported by both observations and model simulations, imply that global warming may have already significantly contributed to the ongoing tropical expansion, especially over the ocean-dominant Southern Hemisphere.
    Schlagwort(e): 551.6 ; Tropical Expansion ; Ocean Circulation ; Jet Stream ; Storm Track ; Mid-latitude Temperature Gradients ; Global Warming
    Sprache: Englisch
    Materialart: map
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2021-09-27
    Beschreibung: Vb cyclones are major drivers of extreme precipitation and floods in the study area of hydrological Bavaria (Germany). When assessing climate change impacts on Vb cyclones, internal variability of the climate system is an important underlying uncertainty. Here, we employ a 50-member single-model initial-condition large ensemble of a regional climate model to study climate variability and forced change on Vb cyclones. An artificial neural network detects cutoff lows over central Europe, which are associated with extreme precipitation Vb cyclones. Thus, machine learning filters the large ensemble prior to cyclone tracking. Our results show a striking change in Vb seasonality with a strong decrease of Vb cyclones in summer (−52%) and a large increase in spring (+73%) under the Representative Concentration Pathway 8.5. This change exceeds the noise of internal variability and leads to a peak shift from summer to spring. Additionally, we show significant increases in the daily precipitation intensity during Vb cyclones in all seasons.
    Schlagwort(e): 551.6 ; Vb-cyclones ; Machine Learning ; Artificial Neural Networks (ANN) ; Single-Model Large Ensembles ; Internal Variability ; Floods
    Sprache: Englisch
    Materialart: map
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2021-09-27
    Beschreibung: 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.
    Schlagwort(e): 551.6 ; FESOM ; ocean model ; climate model ; unstructured mesh ; Finite Volume
    Sprache: Englisch
    Materialart: map
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2021-10-07
    Beschreibung: Land use and climate changes both affect terrestrial ecosystems. Here, we used three combinations of Shared Socioeconomic Pathways and Representative Concentration Pathways (SSP1xRCP26, SSP3xRCP60, and SSP5xRCP85) as input to three dynamic global vegetation models to assess the impacts and associated uncertainty on several ecosystem functions: terrestrial carbon storage and fluxes, evapotranspiration, surface albedo, and runoff. We also performed sensitivity simulations in which we kept either land use or climate (including atmospheric CO2) constant from year 2015 on to calculate the isolated land use versus climate effects. By the 2080–2099 period, carbon storage increases by up to 87 ± 47 Gt (SSP1xRCP26) compared to present day, with large spatial variance across scenarios and models. Most of the carbon uptake is attributed to drivers beyond future land use and climate change, particularly the lagged effects of historic environmental changes. Future climate change typically increases carbon stocks in vegetation but not soils, while future land use change causes carbon losses, even for net agricultural abandonment (SSP1xRCP26). Evapotranspiration changes are highly variable across scenarios, and models do not agree on the magnitude or even sign of change of the individual effects. A calculated decrease in January and July surface albedo (up to −0.021 ± 0.007 and −0.004 ± 0.004 for SSP5xRCP85) and increase in runoff (+67 ± 6 mm/year) is largely driven by climate change. Overall, our results show that future land use and climate change will both have substantial impacts on ecosystem functioning. However, future changes can often not be fully explained by these two drivers and legacy effects have to be considered.
    Schlagwort(e): 333.7 ; 551.6 ; land use change ; climate change projections ; terrestrial ecosystems ; vegetation modeling ; ecosystem service indicators ; legacy effects
    Sprache: Englisch
    Materialart: map
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2021-10-07
    Beschreibung: Abstract One of the most intriguing facets of the climate system is that it exhibits variability across all temporal and spatial scales; pronounced examples are temperature and precipitation. The structure of this variability, however, is not arbitrary. Over certain spatial and temporal ranges, it can be described by scaling relationships in the form of power laws in probability density distributions and autocorrelation functions. These scaling relationships can be quantified by scaling exponents which measure how the variability changes across scales and how the intensity changes with frequency of occurrence. Scaling determines the relative magnitudes and persistence of natural climate fluctuations. Here, we review various scaling mechanisms and their relevance for the climate system. We show observational evidence of scaling and discuss the application of scaling properties and methods in trend detection, climate sensitivity analyses, and climate prediction.
    Schlagwort(e): 551.6 ; scaling ; climate variability ; memory ; scaling mechanisms ; paleoclimate ; power law
    Sprache: Englisch
    Materialart: map
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2021-10-07
    Beschreibung: We reconstructed the variability of the Earth's strongest hydrological system, the Indian monsoon, over the interval 6.24 to 4.91 Ma at International Ocean Discovery Program (IODP) Expedition 353 Site U1448 in the Andaman Sea. We integrated high-resolution benthic and planktic foraminiferal carbon and oxygen isotopes with Mg/Ca measurements of the mixed layer foraminifer Trilobatus sacculifer to reconstruct the isotopic composition of seawater (δ18Osw) and the gradient between planktic and benthic foraminiferal δ13C. A prominent increase in mixed layer temperatures of ~4°C occurred between 5.55 and 5.28 Ma, accompanied by a change from precession- to obliquity-driven variability in planktic δ18O and δ18Osw. We suggest that an intensified cross-equatorial transport of heat and moisture, paced by obliquity, led to increased summer monsoon precipitation during warm stages after 5.55 Ma. Transient cold stages were characterized by reduced mixed layer temperatures and summer monsoon failure, thus resembling late Pleistocene stadials. In contrast, an overall cooler background climate state with a strengthened biological pump prevailed prior to 5.55 Ma. These findings highlight the importance of internal feedback processes for the long-term evolution of the Indian monsoon.
    Schlagwort(e): 551.6 ; Indian monsoon ; Miocene-Pliocene transition ; Bay of Bengal ; Mg/Ca paleothermometry ; stable isotopes ; orbital forcing
    Sprache: Englisch
    Materialart: map
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2021-10-07
    Beschreibung: Forest canopies present irregular surfaces that alter both the quantity and spatiotemporal variability of precipitation inputs. The drop size distribution (DSD) of rainfall varies with rainfall event characteristics and is altered substantially by the forest stand properties. Yet, the influence of two major European tree species, European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. karst), on throughfall DSD is largely unknown. In order to assess the impact of these two species with differing canopy structures on throughfall DSD, two optical disdrometers, one above and one below the canopy of each European beech and Norway spruce, measured DSD of both incident rainfall and throughfall over 2 months at a 10-s resolution. Fractions of different throughfall categories were analysed for single-precipitation events of different intensities. While penetrating the canopies, clear shifts in drop size and temporal distributions of incoming rainfall were observed. Beech and spruce, however, had different DSD, behaved differently in their effect on diameter volume percentiles as well as width of drop spectrum. The maximum drop sizes under beech were higher than under spruce. The mean ± standard deviation of the median volume drops size (D50) over all rain events was 2.7 ± 0.28 mm for beech and 0.80 ± 0.04 mm for spruce, respectively. In general, there was a high-DSD variability within events indicating varying amounts of the different throughfall fractions. These findings help to better understand the effects of different tree species on rainfall partitioning processes and small-scale variations in subcanopy rainfall inputs, thereby demonstrating the need for further research in high-resolution spatial and temporal properties of rainfall and throughfall.
    Schlagwort(e): 551.6 ; canopy drip ; canopy interaction ; disdrometer ; droplets ; interception ; rain intensity ; rain rate ; splash droplets
    Sprache: Englisch
    Materialart: map
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2021-10-07
    Beschreibung: Precipitation extremes with devastating socioeconomic consequences within the South American Monsoon System (SAMS) are expected to become more frequent in the near future. The complexity in SAMS behavior, however, poses severe challenges for reliable future projections. Thus, robust paleomonsoon records are needed to constrain the high spatiotemporal variability in the response of SAMS rainfall to different climatic drivers. This study uses Ti/Ca ratios from X-ray fluorescence scanning of a sediment core retrieved off eastern Brazilian to trace precipitation changes over the past 322 Kyr. The results indicate that despite the spatiotemporal complexity of the SAMS, insolation forcing is the primary pacemaker of variations in the monsoonal system. Additional modulation by atmospheric pCO2 suggests that SAMS intensity over eastern Brazil will be suppressed by rising CO2 emissions in the future. Lastly, our record reveals an unprecedented strong and persistent wet period during Marine Isotope Stage 6 driven by anomalously strong trade winds.
    Schlagwort(e): 551.6 ; South American Monsoon System (SAMS)
    Sprache: Englisch
    Materialart: map
    Standort Signatur Erwartet Verfügbarkeit
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