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Uncertainties in surface mass balance projections of the Greenland Ice Sheet
No full textAs a result of global warming, the Greenland Ice Sheet (GrIS) will bemajor contributor to the future mean sea level rise (SLR). Its contribution will be led by the meltwater production at the surface of the ice sheet, gauged by the surface mass balance (SMB, the sum of surface ice mass gains and losses). Various physical processes enhanced the current melt of the ice sheet through positive feedbacks. These feedbacks add uncertainties to SMB projections due to their poor representation in climate modelling. The purpose of this thesis is to estimate the uncertainties related to the influence of two of these feedbacks on the GrIS SMB projections.
The SMB is computed in this work by a regional climate model, the Modèle Atmosphérique Régional (MAR), developed at ULiège and specifically designed to represent the interactions of the atmosphere with snow-covered or ice-covered surfaces. The first objective was to evaluate the influence of recent circulation changes associated with summer blocking events on the SMB in a context of atmospheric warming up to + 2°C. We highlighted that if such events continue to occur, the increase in SMB due to global warming alone may be underestimated by a factor of 2 in the current projections. We then assessed the representation of such circulation changes in the new generation of global climate models (the CMIP6 models) used to perform the climate projections to 2100. We concluded that none of these models can represent the currently observed circulation changes, nor do they project such changes to 2100. Finally, the last objective was to
study the long-term (2200) influence of extreme atmospheric warming (+ 7 °C compared to 1961-1990) on the GrIS contribution to SLR, and on the method to represent the feedback between melt and surface elevation, causing an enhancing of melt. This was achieved by coupling MAR with an ice sheet model (PISM), thus enabling the explicit consideration of the melt-elevation feedback. While not considering this feedback results in an underestimation of more than 10 % of the a contribution to SLR, the alternative method of representing this feedback, the offline correction of SMB results, overestimates this contribution by 2.5 %. This overestimation is due to mitigation of the feedback in the coupled simulation due to local changes in atmospheric circulation with evolving surface topography (the ice sheet is retreating and the slope is changing), making the correction invalid on the ice sheet margins.
In conclusion, we studied the influence of two positive feedbacks that can cause the enhancing of GrIS melt. The influence of the melt-elevation feedback can be considered through the coupling of an atmospheric model and an ice dynamics model. The alternative method of an offline correction, which avoids a costly coupling in terms of computing time, is no longer valid at the margins of the ice sheet, resulting in additional uncertainties in the SMB projections, which are less large than the uncertainty associated with not accounting for the feedback. Nevertheless, this underlines the importance of considering the local atmospheric processes influencing the SMB. On the other hand, circulation changes aregreater source of uncertainty since they could double the increase in SMB if they persist in the future. Moreover, these changes are still not represented by
the global models used for climate projections. The latter could therefore be underestimated if these changes in circulation are not linked to natural climate
variability. Finally, the causes of these blocking events and the links with current global warming are still poorly understood
Quel réchauffement l'inlandsis du Groenland peut-il supporter ?
No full textGreenland Ice sheet (GrIS) is considered as one of the main contributor to sea level rise (SLR) for the end of the 21 st century. What if it is already to late to reverse the ice loss of GrIS ?
The mass balance (MB) resulting from the coupling between the Modèle Atmosphérique Régional (MAR, ULiège) and the Parallel Ice Sheet Model (PISM, PIK) over Greenland with CESM2 ssp585 as large scale forcing indicates that even if we stop the CESM2 warming in 2100 and continue with a climate of + 7 °C until 2200 compared to the reference period (1961-1990), the GrIS is still losing ice masse up to 60 cm of SLR contribution in 2200. Starting from this coupling experiment, we launch several coupled simulations by stabilizing the warming at different threshold (+ 1, 2, 3, … °C) compared to our reference period throughout the 21st century. Another experiment launched is to reverse the CESM2-imposed climate starting in 2100 to 2000. The aim is first to highlight a kind of tipping point of the GrIS to determine whether the stabilization of the climate at a certain warming would result in a new equilibrium state of the GrIS or if the total MB will continue to decrease. The reverse experiment highlight that if we go back to a climate as warm as currently, GrIS could gain ice mass again
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Evaluation of summer Greenland blocking index of the CMIP6 models
Full text linkThe Greenland blocking index (GBI), an indicator of the synoptic-scale circulation over Greenland, has been anomalously positive during summer since the end of the 1990s. The GBI is negatively correlated with the North Atlantic Oscillation (NAO), which has been consistently negative during the same period. These changes in atmospheric circulation have led to an increase in Greenland summer temperatures, a decrease in cloud cover and greater ice sheet surface melt. The GBI is therefore a key indicator of melting in Greenland. However, the fifth phase of the Coupled Model Intercomparison Project (CMIP5) models do not represent any increase in GBI as indicated by observations. Until 2100, no oscillation of the GBI, and therefore no circulation changes, are projected. In this study we evaluate the new generation CMIP6 models in order to analyze the evolution of the future GBI. Our initial analysis reveals a general trend towards a decrease of the GBI until 2100. Additionally, still no model reproduces the strong increase in GBI observed over the last few decades, similar to the CMIP5 models. It is therefore important to note that significant melting events related to a highly positive GBI, as observed this summer 2019 for example, are still not considered by CMIP6 models and therefore the projected mass balance decrease could be underestimated if such general circulation change will occur in future
Main output data used in "Coupling the regional climate MAR model with the ice sheet model PISM mitigates the melt-elevation positive feedback" (Delhasse et al., 2023)
No full text<p>Outputs used in:</p>
<p><em>Delhasse, A., Beckmann, J., Kittel, C., & Fettweis, X.: Coupling the regional climate MAR model with the ice sheet model PISM mitigates the melt-elevation positive feedback, The Cryosphere Discuss. [preprint], https://doi.org/10.5194/tc-2023-15, in review, 2023.</em></p>
<p>MAR-PISM coupling experiments outputs over 1991-2200. The main experiments are:</p>
<ul>
<li>MAPI-2w: 2-way coupling, consideration <em>online</em> of the melt-elevation feedback (evolving topography in MAR).</li>
<li>MAPI-1w: 1-way coupling, consideration of the melt-elevation feedback only with the <em>offline</em> correction (Franco <em>et al.</em>, 2012) of the MAR outputs (fixed topography in MAR).</li>
<li>MAPI-0w: 0-way coupling, no consideration of the melt-elevation feedback (fixed topography in MAR and no correction during interpolation).</li>
</ul>
<p>MAR files contain yearly SMB (surface mass balance) and ST (surface temperature) interpolated (with correction) on the PISM-4.5km grid. Gradients used for the correction of the melt-elevation feedback are also given for both variables. SMB and ST are the two required MAR fields to couple MAR with PISM. </p>
<p>PISM files contain yearly ice thickness (THK) and ice mask (MASK) as simulated by PISM for each of the three experiments. </p>
<p>The MAR code used in this dataset is tagged as v3.11.3 on https://gitlab.com/Mar-Group/MARv3# (last access: 23 January 2024) (MARTeam, 2024). The PISM code used is tagged as PISMv1.2.2 on <a href="https://github.com/pism/pism/releases/tag/v1.2.2" target="_blank" rel="noopener noreferrer">https://github.com/pism/pism/releases/tag/v1.2.2</a> (last access: 23 January 2024). Other coupling scripts are also available upon request by email (<a href="mailto:[email protected]" target="_blank" rel="noopener noreferrer">[email protected]</a>).</p>
<p>If you need other variables from MAR or PISM, send us an email ([email protected], [email protected]) and we will be glad to help you. We will also be happy to share the scripts we have developed to analyse the outputs and make the figures in this paper if needed. Please cite the paper if you use these MAR-PISM outputs.<br><br>Data usage notice:</p>
<p>If you use any of these results, please acknowledge the work of the people involved in producing them. Acknowledgments should be similar to the one below that contains information related to MAR and PISM. To document MAR scientific impact and enable ongoing support of the model, users are likely encouraged to contact me to add their works to the list of MAR-related publications. </p>
<p>"We thank A. Delhasse and J. Beckmann, as well as the MAR and PISM teams which make available the model outputs. We also thank agencies (F.R.S - FNRS, CÉCI, and the Walloon Region) that provided computational resources for MAR-PISM simulations. "</p>
<p>You should also refer to and cite the following paper in its latest version:</p>
<p><em>Delhasse, A., Beckmann, J., Kittel, C., & Fettweis, X.: Coupling the regional climate MAR model with the ice sheet model PISM mitigates the melt-elevation positive feedback, The Cryosphere Discuss. [preprint], https://doi.org/10.5194/tc-2023-15, in review, 2023.</em></p>
<p>Reference</p>
<p><em>Franco, B., Fettweis, X., Lang, C., and Erpicum, M.: Impact of spatial resolution on the modelling of the Greenland ice sheet surface mass balance between 1990–2010, using the regional climate model MAR, The Cryosphere, 6, 695–711, https://doi.org/10.5194/tc-6-695-2012, 2012.</em></p>
<p><em>MARTeam: MARv3.11, GitLab [data set], <span><a href="https://gitlab.com/Mar-Group/MARv3" target="_blank" rel="noopener">https://gitlab.com/Mar-Group/MARv3#</a></span> (last access: 28 May 2022), 2021.</em></p>
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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