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  • 1
    Call number: AWI A4-23-95497
    Description / Table of Contents: Extreme weather and climate events are one of the greatest dangers for present-day society. Therefore, it is important to provide reliable statements on what changes in extreme events can be expected along with future global climate change. However, the projected overall response to future climate change is generally a result of a complex interplay between individual physical mechanisms originated within the different climate subsystems. Hence, a profound understanding of these individual contributions is required in order to provide meaningful assessments of future changes in extreme events. One aspect of climate change is the recently observed phenomenon of Arctic Amplification and the related dramatic Arctic sea ice decline, which is expected to continue over the next decades. The question to what extent Arctic sea ice loss is able to affect atmospheric dynamics and extreme events over mid-latitudes has received a lot of attention over recent years and still remains a highly debated topic. In this respect, the objective of ...
    Type of Medium: Dissertations
    Pages: xi, 126 Seiten , Diagramme
    Language: English
    Note: Dissertation, Universität Potsdam, 2023 , CONTENTS 1 SCIENTIFIC BACKGROUND AND RESEARCH QUESTIONS 1.1 Extreme events and attribution 1.2 Arctic climate change and mid-latitude linkages 1.3 Research questions 2 FOUNDATIONS 2.1 Atmospheric basics 2.1.1 Governing equations 2.1.2 Zonal wind and temperature profiles 2.1.3 Atmospheric waves and instabilities 2.1.4 Large-scale variability patterns and blocking 2.2 Atmospheric circulation regimes 2.2.1 Dynamical concepts 2.2.2 Regime computation 2.2.3 Regime number 2.3 Arctic climate change 2.3.1 Recent trends in Arctic sea ice and temperatures 2.3.2 Surface fluxes and energy balance in Arctic regions 2.3.3 Polar amplification mechanisms 2.3.4 Arctic-mid-latitude linkages 2.4 Weather and climate extremes 2.4.1 Recent trends 2.4.2 Dynamical driver of temperature extremes 3 DATA AND METHODS 3.1 ERA5 reanalysis 3.2 Model experiments 3.2.1 The atmospheric general circulation model ECHAM6 3.2.2 Polar Amplification Intercomparison Project data 3.3 Methods 3.3.1 Statistical significance 3.3.2 Extreme definition 4 RESULTS AND DISCUSSION 4.1 Mean circulation in ERA5 and ECHAM6 experiments 4.1.1 Climatological mean states in ERA5 and the reference simulation 4.1.2 Climatological responses in ECHAM6 sensitivity experiments 4.2 Circulation regimes and sea ice-induced frequency changes 4.2.1 Regime structures in ERA5 and ECHAM6 experiments 4.2.2 Regime frequency changes in ERA 4.2.3 Regime frequency changes in ECHAM6 experiments 4.3 Changes in Northern Hemispheric temperature extremes induced by sea ice loss 4.3.1 Extreme occurrence frequency changes 4.3.2 Temperature return level changes 4.4 Links between circulation regimes and extremes over Europe 4.4.1 Winter temperature extremes 4.4.2 Summer heat extremes 4.4.3 Winter wind extremes 4.5 Decomposition of sea ice-induced frequency changes in European winter extremes 4.5.1 Midwinter cold extremes along a SCAN storyline 4.5.2 January warm extremes along a ATl- storyline 4.5.3 February warm extremes along a NAO+ storyline 4.5.4 Comparison with futSST 4.5.5 January wind extremes along a ATL- storyline 4.6 Circulation Analogue-based approach for summer season 4.6.1 ERA5 event definitions 4.6.2 Reference flows and analogues in ERA5 4.6.3 Circulation analogues in ECHAM6 experiments 4.6.4 Decomposition of sea ice-induced changes in European heat extremes 5 CONCLUSION 5.1 Summary 5.2 Final discussion and outlook Appendix A METHODS A.1 Principal Component Analysis A.2 𝑘-Means clustering A.2.1 Algorithm A.2.2 Computation of circulation regimes A.3 Taylor diagram A.4 Regression model for describing ERA5 regime frequency changes A.4.1 General setup A.4.2 Multinomial Logistic Regression A.4.3 Linear predictor A.5 Definition and calculation of return levels A.5.1 Block maxima approach and Generalized Extreme Value distribution A.5.2 Return level estimation A.6 Framework for conditional extreme event attribution Appendix B ADDITIONAL FIGURES B.1 Circulation regimes and sea ice-induced frequency changes B.2 Changes in Northern Hemispheric temperature extremes induced by sea ice loss B.3 Links between circulation regimes and extremes over Europe B.3.1 Conditioned vs. unconditioned ERA5 and wind extreme probabilities B.3.2 Wind and synoptic-scale activity anomalies B.4 Decomposition of sea ice-induced frequency changes in European winter extremes B.5 Circulation Analogue-based approach for summer season B.6 Miscellaneous B.6.1 Recent Arctic sea ice trends B.6.2 futSST forcing field B.6.3 Fluxes over sea ice and ocean surfaces in ECHAM6 BIBLIOGRAPHY
    Location: AWI Reading room
    Branch Library: AWI Library
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  • 2
    Call number: S 93.0427(151) ; ZSP-560-151
    In: Mitteilungen aus dem Institut für Geophysik und Meteorologie der Universität zu Köln
    Type of Medium: Series available for loan
    Pages: viii, 134 S.
    ISSN: 0069-5882
    Series Statement: Mitteilungen aus dem Institut für Geophysik und Meteorologie der Universität zu Köln 151
    Classification:
    Meteorology and Climatology
    Language: English
    Location: Lower compact magazine
    Location: Lower compact magazine
    Branch Library: GFZ Library
    Branch Library: GFZ Library
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  • 3
    Publication Date: 2022-09-22
    Description: February‐March 2020 was marked by highly anomalous large‐scale circulations in the Northern extratropical troposphere and stratosphere. The Atlantic jet reached extreme strength, linked to some of the strongest and most persistent positive values of the Arctic Oscillation index on record, which provided conditions for extreme windstorms hitting Europe. Likewise, the stratospheric polar vortex reached extreme strength that persisted for an unusually long period. Past research indicated that such circulation extremes occurring throughout the troposphere‐stratosphere system are dynamically coupled, although the nature of this coupling is still not fully understood and generally difficult to quantify. We employ sets of numerical ensemble simulations to statistically characterize the mutual coupling of the early 2020 extremes. We find the extreme vortex strength to be linked to the reflection of upward propagating planetary waves and the occurrence of this reflection to be sensitive to the details of the vortex structure. Our results show an overall robust coupling between tropospheric and stratospheric anomalies: ensemble members with polar vortex exceeding a certain strength tend to exhibit a stronger tropospheric jet and vice versa. Moreover, members exhibiting a breakdown of the stratospheric circulation (e.g., sudden stratospheric warming) tend to lack periods of persistently enhanced tropospheric circulation. Despite indications for vertical coupling, our simulations underline the role of internal variability within each atmospheric layer. The circulation extremes during early 2020 may be viewed as resulting from a fortuitous alignment of dynamical evolutions within the troposphere and stratosphere, aided by each layer's modification of the other layer's boundary condition.
    Description: Key Points Large‐ensemble simulations are needed to fully characterize coupled extremes in the polar vortex and tropospheric jet in early 2020. Details of the vortex structure play an important role in promoting either reflection or dissipation of upward propagating waves 1 and/or 2. Modulation of lowermost stratospheric circulation from above and below facilitates co‐evolution of tropospheric and stratospheric extremes.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5
    Description: https://doi.org/10.5282/ubm/data.281
    Description: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml
    Keywords: ddc:551.5
    Language: English
    Type: doc-type:article
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  • 4
    Publication Date: 2023-01-19
    Description: Europe has been affected by record‐breaking heat waves in recent decades. Using station data and a gridded reanalysis as input, four commonly used heat wave indices, the heat wave magnitude index daily (HWMId), excess heat factor (EHF), wet‐bulb globe temperature (WBGT) and universal thermal climate index (UTCI), are computed. The extremeness of historical European heat waves between 1979 and 2019 using the four indices and different metrics is ranked. A normalisation to enable the comparison between the four indices is introduced. Additionally, a method to quantify the influence of the input parameters on heat wave magnitude is introduced. The spatio‐temporal behaviour of heat waves is assessed by spatial–temporal tracking. The areal extent, large‐scale intensity and duration are visualized using bubble plots. As expected, temperature explains the largest variance in all indices, but humidity is nearly as important in WBGT and wind speed plays a substantial role in UTCI. While the 2010 Russian heat wave is by far the most extreme event in duration and intensity in all normalized indices, the 2018 heat wave was comparable in size for EHF, WBGT and UTCI. Interestingly, the well‐known 2003 central European heat wave was only the fifth and tenth strongest in cumulative intensity in WBGT and UTCI, respectively. The June and July 2019 heat waves were very intense, but short‐lived, thus not belonging to the top heat waves in Europe when duration and areal extent are taken into account. Overall, the proposed normalized indices and the multi‐metric assessment of large‐scale heat waves allow for a more robust description of their extremeness and will be helpful to assess heat waves worldwide and in climate projections.
    Description: Europe has been affected by record‐breaking heat waves in recent decades. Using station data and a gridded reanalysis, the extremeness of European heat waves between 1979 and 2019 is ranked using four indices: heat wave magnitude index daily (HWMId), excess heat factor (EHF), wet‐bulb globe temperature (WBGT) and universal thermal climate index (UTCI). In order to assess heatwaves worldwide and in climate projections, the spatial extent, large‐scale intensity and duration of heatwaves are visualized using bubble plots.
    Description: AXA Research Fund http://dx.doi.org/10.13039/501100001961
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Karlsruher Institut für Technologie http://dx.doi.org/10.13039/100009133
    Keywords: ddc:551.5 ; duration ; heat wave ; indices ; intensity ; large‐scale ; spatial extent
    Language: English
    Type: doc-type:article
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  • 5
    Publication Date: 2023-11-02
    Description: Extra‐tropical cyclones are an important source of weather variability in the mid‐latitudes. Multiple occurrences in a short period of time at a particular location are denominated serial cyclone clustering (SCC), and potentially lead to large societal impacts. We investigate the relationship between SCC affecting Western Europe and large‐scale weather regimes (WRs) in the North Atlantic‐European region in boreal winter. We find that SCC in low latitudes (45°N) is predominantly associated with the anticyclonic Greenland Blocking WR. In contrast, SCC in mid and high latitudes (55°N, 65°N) is mostly linked to different cyclonic WRs. Thereby, SCC occurs typically within a well‐established WR that builds up prior to SCC and decays after SCC. Thus, SCC events are closely associated with recurrent, quasi‐stationary and persistent large‐scale flow patterns (WRs). This mutual relationship reveals the potential of WRs in forecasting storm series and associated impacts on sub‐seasonal to seasonal time scales.
    Description: Plain Language Summary: Serial cyclone clustering describes the occurrence of multiple extra‐tropical cyclones within a certain time frame and a spatially restricted region. Since extra‐tropical cyclones can be associated with strong winds and heavy precipitation, multiple occurrences can lead to large cumulative impacts in the affected areas. We analyze the relationship between serial cyclone clustering (SCC) in Western Europe and so‐called weather regimes (WRs) in the North Atlantic‐European region in boreal winter. These regimes describe slow evolving and enduring large‐scale atmospheric circulation patterns. Relationships with certain regime types are identified but depend on the latitude at which the clustered frequency of extra‐tropical cyclones is found. When SCC occurs in low latitudes (45°N), it mostly appears coincident with anticyclonic large‐scale flow patterns. In contrast, SCC in mid and high latitudes (55°N, 65°N) often occurs simultaneously with different cyclonic regimes. We find that periods of SCC occur typically within WR life cycles pointing to the fact that both, the WRs and SCC periods, are interlinked. This relationship may facilitate forecasting storm series and associated impacts on time scales beyond 2 weeks.
    Description: Key Points: A close relationship is found between serial cyclone clustering (SCC) at 5°W and weather regimes (WRs) in the North Atlantic‐European region. SCC in mid and high latitudes (55°N, 65°N) is mainly associated with cyclonic and in low latitudes (45°N) with anticyclonic WR life cycles. Regardless of the selected latitude, SCC occurs mostly during an active regime life cycle and is manifested in a well‐established WR.
    Description: German Research Foundation
    Description: AXA Research Fund http://dx.doi.org/10.13039/501100001961
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: BMBF ClimXtreme
    Description: https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era-interim
    Keywords: ddc:551.5 ; serial cyclone clustering ; weather regimes ; atmospheric dynamics ; sub‐seasonal prediction
    Language: English
    Type: doc-type:article
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  • 6
    Publication Date: 2024-01-12
    Description: Regional and local wind systems are often complex, particularly near coastal areas with a highly variable orography. Thus, the realistic representation of regional wind systems in weather and climate models is of strong relevance. Here, we evaluate the ability of a 13‐year convection‐permitting climate simulation in reproducing the interaction of several regional summer wind systems over the complex orography in the eastern Mediterranean region. The COSMO‐CLM simulations are driven by hourly ERA‐5 reanalysis and have a spatial resolution of 2.8 and 7.0 km. The simulated near‐surface wind fields are compared with unique very high‐resolution wind observations collected within the “Dead Sea Research Venue” project (DESERVE) and data from the Israel Meteorological Service synop network. The high‐resolution COSMO‐CLM simulations largely reproduce the main characteristics of the regional wind systems (Mediterranean and Dead Sea breeze, slope winds in the Judean Mountains and winds along the Jordan Rift valley), whereas ERA‐5 is only able to represent the Mediterranean Sea breeze. The high‐resolution simulations substantially improve the representation of regional winds, particularly over complex orography. Indeed, the 2.8 km simulation outperforms the 7.0 km run, on 88% of the days. Two mid‐July 2015 case studies show that only the 2.8 simulation can realistically simulate the penetration of the Mediterranean Sea Breeze into the Jordan Rift valley and complex interactions with other wind systems like the Dead Sea breeze. Our results may have profound implications for regional weather and climate prediction since very high‐resolution information seems to be necessary to reproduce the main summertime climatic features in this region. We envisage that such simulations may also be required at other regions with complex orography.
    Description: In this paper we show that COSMO‐CLM regional climate model simulations at 7.0 (CLM‐7.0) and 2.8km (CLM‐2.8) resolution can realistically reproduce near‐surface regional and local wind systems over the complex orography of the eastern Mediterranean as opposite to coarser resolutions (ERA‐5, 31 km). The Mediterranean and local Dead Sea breezes, slope winds over the Judean Mountains, and winds along the Jordan Rift valley are well represented both climatologically and on individual days. CLM‐2.8 captures the small‐scale variability of the wind field better than CLM‐7.0 particularly near the Dead Sea and on 88% of the days CLM‐2.8 represents wind speed even more realistically than CLM‐7.0. image
    Description: German Helmholtz Association (“Changing Earth” program)
    Description: AXA Research Fund http://dx.doi.org/10.13039/501100001961
    Description: Ministry of Science, Research and Arts
    Description: Helmholtz Association of German Research Centers
    Keywords: ddc:551.6 ; complex orography ; convection permitting ; COSMO‐CLM ; Dead Sea ; eastern Mediterranean ; grid spacing ; regional climate modelling ; sea breeze
    Language: English
    Type: doc-type:article
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  • 7
    Publication Date: 2024-04-25
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Dansgaard‐Oeschger (D‐O) climate variability during the last glaciation was first evidenced in ice cores and marine sediments, and is also recorded in various terrestrial paleoclimate archives in Europe. The relative synchronicity across Greenland, the North Atlantic and Europe implies a tight and fast coupling between those regions, most probably effectuated by an atmospheric transmission mechanism. In this study, we investigated the atmospheric changes during Greenland interstadial (GI) and stadial (GS) phases based on regional climate model simulations using two specific periods, GI‐10 and GS‐9 both around 40 ka, as boundary conditions. Our simulations accurately capture the changes in temperature and precipitation as reconstructed by the available proxy data. Moreover, the simulations depict an intensified and southward shifted eddy‐driven jet during the stadial period. Ultimately, this affects the near‐surface circulation toward more southwesterly and cyclonic flow in western Europe during the stadial period, explaining much of the seasonal climate variability recorded by the proxy data, including oxygen isotopes, at the considered proxy sites.〈/p〉
    Description: Plain Language Summary: The climate during the last ice age varied between colder and warmer periods on timescales ranging from hundreds to thousands of years. This variability was first detected in Greenland ice cores and marine sediment cores of the North Atlantic, as well as in continental geological records in Europe. The variation between the colder and warmer periods occur mostly simultaneously in Greenland and in Europe, which is why the atmosphere is assumed to have an important role in transferring the climate signals. We simulated two different periods of the last ice age, one colder and one warmer around 40,000 years ago, using a regional climate model. The aim was to study how the climate and atmospheric circulation changed during these two periods. We find the eddy‐driven jet over the North Atlantic intensified and shifted southward during the colder period. The jet influences the near‐surface atmospheric circulation and leads to more southwesterly and cyclonic flow in western Europe. Oxygen isotope variations observed in western European paleoclimate records may be partly explained by different, more southern moisture sources on top of changes in seasonal temperatures.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Simulated temperatures agree with proxy data; precipitation is biased but GI‐10 versus GS‐9 differences are well captured〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The stadial winter jet stream is intensified and shifted southward, consistent with dominant southwesterly/cyclonic flow in western Europe〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Oxygen isotope signal changes at western European proxy sites may be explained not only by temperature but also by varying moisture sources〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: NRDIO
    Description: AXA Research Fund http://dx.doi.org/10.13039/501100001961
    Description: https://doi.org/10.5065/1dfh-6p97
    Keywords: ddc:551.6 ; Dansgaard‐Oeschger cycle ; regional atmospheric dynamics ; regional climate modeling ; continental paleoclimate proxy ; Europe
    Language: English
    Type: doc-type:article
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Multimedia tools and applications 1 (1995), S. 245-262 
    ISSN: 1573-7721
    Keywords: hypermedia ; multimedia ; human computer interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This paper report on recent and on going work related to the design of a set of hypermedia authoring tools intended to produce courseware, to be used for self learning or distance learning and training environments in a cooperative way. These tools have roots in a standalone hypermedia editor developed to create courseware, to which were added other tools to enhance its usability, namely a hypermedia player to view courseware in self study mode, and a hypermedia browser to create, to navigate and to display graphically the hypermedia document structure. The underlying metaphors are the overhead projector, the transparency and the layer. This system was developed for the MS-Windows environment, supporting OLE technology. We discuss the impact that such technology might have on the “look and feel” of hypermedia learning material and we describe the implementation of a Hypermedia Editor, Browser and Player tools. Part of this work is carried out in the context of the Co-Learn European project, which is aiming to design and to implement a third generation cooperative learning environment.
    Type of Medium: Electronic Resource
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  • 9
    Publication Date: 2020-07-06
    Description: Climate simulations for the North Atlantic and Europe for recent and future conditions simulated with the regionally coupled ROM model are analyzed and compared to the results from the MPI‐ESM. The ROM simulations also include a biogeochemistry and ocean tides. For recent climate conditions, ROM generally improves the simulations compared to the driving model MPI‐ESM. Reduced oceanic biases in the Northern Atlantic are found, as well as a better simulation of the atmospheric circulation, notably storm tracks and blocking. Regarding future climate projections for the 21st century following the RCP 4.5 and 8.5 scenarios, MPI‐ESM and ROM largely agree qualitatively on the climate change signal over Europe. However, many important differences are identified. For example, ROM shows an SST cooling in the Subpolar Gyre which is not present in MPI‐ESM. Under the RCP8.5 scenario, ROM Arctic sea ice cover is thinner and reaches the seasonally ice‐free state by 2055, well before MPI‐ESM. This shows the decisive importance of higher ocean resolution and regional coupling for determining the regional responses to global warming trends. Regarding biogeochemistry, both ROM and MPI‐ESM simulate a widespread decline in winter nutrient concentration in the North Atlantic of up to ~35%. On the other hand, the phytoplankton spring bloom in the Arctic and in the North‐Western Atlantic starts earlier and the yearly primary production is enhanced in the Arctic in the late 21st century. These results clearly demonstrate the added value of ROM to determine more detailed and more reliable climate projections at the regional scale.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 10
    Publication Date: 2018-08-27
    Description: The climate in Mexico and Central America is influenced by the Pacific and the Atlantic oceanic basins and atmospheric conditions over continental North and South America. These factors and important ocean–atmosphere coupled processes make the region’s climate a great challenge for global and regional climate modeling. We explore the benefits that coupled regional climate models may introduce in the representation of the regional climate with a set of coupled and uncoupled simulations forced by reanalysis and global model data. Uncoupled simulations tend to stay close to the large-scale patterns of the driving fields, particularly over the ocean, while over land they are modified by the regional atmospheric model physics and the improved orography representation. The regional coupled model adds to the reanalysis forcing the air–sea interaction, which is also better resolved than in the global model. Simulated fields are modified over the ocean, improving the representation of the key regional structures such as the Intertropical Convergence Zone and the Caribbean Low Level Jet. Higher resolution leads to improvements over land and in regions of intense air–sea interaction, e.g., off the coast of California. The coupled downscaling improves the representation of the Mid Summer Drought and the meridional rainfall distribution in southernmost Central America. Over the regions of humid climate, the coupling corrects the wet bias of the uncoupled runs and alleviates the dry bias of the driving model, yielding a rainfall seasonal cycle similar to that in the reanalysis-driven experiments.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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