Upgrade of the HadGEM3-A based attribution system to high resolution and a new validation framework for probabilistic event attribution

We present a substantial upgrade of the Met Office system for the probabilistic attribution of extreme weather and climate events with higher horizontal and vertical resolution (60 km mid-latitudes and 85 vertical levels), the latest Hadley Centre atmospheric and land model (ENDGame dynamics with GA6.0 science and JULES at GL6.0) as well as an updated forcings set. A new set of experiments designed for the evaluation and implementation of an operational attribution service are described which consist of pairs of multi-decadal stochastic physics ensembles continued on a season by season basis by large ensembles that are able to sample extreme at- mospheric states possible in the recent past. Diagnostics from these experiments form the HadGEM3-A contribution to the international Climate of the 20th Century Plus (C20Cþ) project and were analysed under the European Climate and Weather Events: Interpretation and Attribution (EUCLEIA) event attribution project as well as contributing to the Climate Science for Service Partnership (CSSP)-China programme. After discussing the framing issues surrounding questions that can be asked with our system we construct a novel approach to the evaluation of atmosphere-only ensembles intended for event attribution, in the process highlighting and clarifying the distinction between hindcast skill and model performance. A framework based around assessing model representation of predictable components and ensuring exchangeability of model and real world statistics leads to a form of detection and attribution to boundary condition forcing as a means of quantifying one degree of freedom of potential model error and allowing for the bias correction of event probabilities and resulting probability ratios. This method is then applied systematically across the globe to assess contributions from anthropogenic influence and specific boundary conditions to the changing probability of observed and record seasonal mean temperatures of four recent 3-month seasons from March 2016–February 2017

DADA: data assimilation for the detection and attribution of weather and climate-related events

A new nudging method for data assimilation, delay‐coordinate nudging, is presented. Delay‐coordinate nudging makes explicit use of present and past observations in the formulation of the forcing driving the model evolution at each time step. Numerical experiments with a low‐order chaotic system show that the new method systematically outperforms standard nudging in different model and observational scenarios, also when using an unoptimized formulation of the delay‐nudging coefficients. A connection between the optimal delay and the dominant Lyapunov exponent of the dynamics is found based on heuristic arguments and is confirmed by the numerical results, providing a guideline for the practical implementation of the algorithm. Delay‐coordinate nudging preserves the easiness of implementation, the intuitive functioning and the reduced computational cost of the standard nudging, making it a potential alternative especially in the field of seasonal‐to‐decadal predictions with large Earth system models that limit the use of more sophisticated data assimilation procedures

Determination of kaolinite and halloysite crystallite size with X-Ray diffraction: implications for industrial applications

To μέσο πάχος και η κατανομή παχών αργιλικών κλασμάτων καολινίτη και αλλουσίτη προσδιορίστηκαν με περιθλασιμετρία ακτίνων-Χ, με χρήση της τεχνικής Bertaut- Warren-Averbach (BWA), η οποία προσδιορίζει τους τομείς συναφούς σκέδασης (CSD). Το μέσο πάχος του καολινίτη και αλλουσίτη ήταν αντίστοιχα 11.8 nm and 10.6 nm, ενώ οι κρύσταλλοι των δύο ορυκτών εμφανίζουν λογαριθμοκανονικές κατανομές πάχους. Το μέσο μέγεθος κόκκου που προσδιορίστηκε με τη μέθοδο της σκέδασης δέσμης laser ήταν πολύ μεγαλύτερο ενώ η κοκκομετρική κατανομή χαρακτηρίζεται από δύο πληθυσμούς (bimodal) λόγω συσσωμάτωσης. Η συσσωμάτωση επηρεάζει αρνητικά οπτικές ιδιότητες ορυκτών κόνεων, όπως η φωτεινότητα λόγω διάχυσης του φωτός. Μεγαλύτερη απόκλιση στο μέγεθος κόκκου που προσδιορίζεται με τις δύο τεχνικές μπορεί να εξηγεί τη μικρή φωτεινότητας που παρατηρείται σε ορισμένα λευκά υλικά.Mean thickness and thickness distribution of kaolinite and halloysite clay fractions was obtained by X-ray diffraction, using the Bertaut-Warren-Averbach (BWA) technique, which determines the coherent scattering domain (CSD). Mean thickness of kaolinite and halloysite was 11.8 nm and 10.6 nm respectively and both minerals are characterized by lognormal thickness distribution. Laser scattering, which is often used by the industry, yielded considerably greater mean grain size and bimodal size distribution for both materials due to particle agglomeration. Agglomeration affects optical properties of mineral powders such as brightness adversely, because of light diffusion. A greater discrepancy in particle size determined by the two techniques might explain lower brightness observed in white powders

Determination of kaolinite and halloysite crystallite size with X-Ray diffraction: implications for industrial applications

To μέσο πάχος και η κατανομή παχών αργιλικών κλασμάτων καολινίτη και αλλουσίτη προσδιορίστηκαν με περιθλασιμετρία ακτίνων-Χ, με χρήση της τεχνικής Bertaut- Warren-Averbach (BWA), η οποία προσδιορίζει τους τομείς συναφούς σκέδασης (CSD). Το μέσο πάχος του καολινίτη και αλλουσίτη ήταν αντίστοιχα 11.8 nm and 10.6 nm, ενώ οι κρύσταλλοι των δύο ορυκτών εμφανίζουν λογαριθμοκανονικές κατανομές πάχους. Το μέσο μέγεθος κόκκου που προσδιορίστηκε με τη μέθοδο της σκέδασης δέσμης laser ήταν πολύ μεγαλύτερο ενώ η κοκκομετρική κατανομή χαρακτηρίζεται από δύο πληθυσμούς (bimodal) λόγω συσσωμάτωσης. Η συσσωμάτωση επηρεάζει αρνητικά οπτικές ιδιότητες ορυκτών κόνεων, όπως η φωτεινότητα λόγω διάχυσης του φωτός. Μεγαλύτερη απόκλιση στο μέγεθος κόκκου που προσδιορίζεται με τις δύο τεχνικές μπορεί να εξηγεί τη μικρή φωτεινότητας που παρατηρείται σε ορισμένα λευκά υλικά.Mean thickness and thickness distribution of kaolinite and halloysite clay fractions was obtained by X-ray diffraction, using the Bertaut-Warren-Averbach (BWA) technique, which determines the coherent scattering domain (CSD). Mean thickness of kaolinite and halloysite was 11.8 nm and 10.6 nm respectively and both minerals are characterized by lognormal thickness distribution. Laser scattering, which is often used by the industry, yielded considerably greater mean grain size and bimodal size distribution for both materials due to particle agglomeration. Agglomeration affects optical properties of mineral powders such as brightness adversely, because of light diffusion. A greater discrepancy in particle size determined by the two techniques might explain lower brightness observed in white powders

Characterising loss and damage from climate change

Policy-makers are creating mechanisms to help developing countries cope with loss and damage from climate change, but the negotiations are largely neglecting scientific questions about what the impacts of climate change actually are. Mitigation efforts have failed to prevent the continued increase of anthropogenic greenhouse gas (GHG) emissions. Adaptation is now unlikely to be sufficient to prevent negative impacts from current and future climate change1. In this context, vulnerable nations argue that existing frameworks to promote mitigation and adaptation are inadequate, and have called for a third international mechanism to deal with residual climate change impacts, or “loss and damage”2. In 2013, the United Nations Framework Convention on Climate Change (UNFCCC) responded to these calls and established the Warsaw International Mechanism (WIM) to address loss and damage from the impacts of climate change in developing countries3. An interim Executive Committee of party representatives has been set up, and is currently drafting a two-year workplan comprising meetings, reports, and expert groups; and aiming to enhance knowledge and understanding of loss and damage, strengthen dialogue among stakeholders, and promote enhanced action and support. Issues identified as priorities for the WIM thus far include: how to deal with non-economic losses, such as loss of life, livelihood, and cultural heritage; and linkages between loss and damage and patterns of migration and displacement2. In all this, one fundamental issue still demands our attention: which losses and damages are relevant to the WIM? What counts as loss and damage from climate change

RHEOLOGICAL PROPERTIES OF PALYGORSKITE-SMECTITE SUSPENSIONS FROM THE VENTZIA BASIN, W. MACEDONIA, GREECE

In this contribution we examine the rheological properties of palygorskite rich clays from the Ventzia Basin, W. Macedonia, Greece. The clays consist of palygorskite and/or dioctahedral Fe-rich smectite (nontronite) and quartz as main components, and serpentine, amphibole and sepiolite as minor constituents. The apparent and plastic viscosity and yield point increase with increasing concentration of clay in the suspension. Flow is Newtonian for 1% suspensions, becoming gradually Bingham plastic (3% clay suspensions) and then pseudoplastic with yield point described by the Herschel Bulckley flow model. In the case of suspensions cf smectite-free clays Bingham plastic flow behaviour was not observed. Addition of 1M NaCl electrolyte deteriorates the rheological behaviour of the smectite-bearing palygorskite clays but it does not affect significantly the smectite-free, palygorskite rich clays. The different rheological properties of the palygorskite compared to smectite is due to the different morphological and crystal-chemical properties of these two minerals. It is suggested that the palygorskite-rich clays can be used successfully as drilling muds in seawater based drilling fluids, in which smectite-based drilling muds tend to flocculate

Evaluation of the HadGEM3-A simulations in view of detection and attribution of human influence on extreme events in Europe

A detailed analysis is carried out to assess the HadGEM3-A global atmospheric model skill in simulating extreme temperatures, precipitation and storm surges in Europe in the view of their attribution to human influence. The analysis is performed based on an ensemble of 15 atmospheric simulations forced with observed Sea Surface Temperature of the 54 year period 1960-2013. These simulations, together with dual simulations without human influence in the forcing, are intended to be used in weather and climate event attribution. The analysis investigates the main processes leading to extreme events, including atmospheric circulation patterns, their links with temperature extremes, land-atmosphere and troposphere-stratosphere interactions. It also compares observed and simulated variability, trends and generalized extreme value theory parameters for temperature and precipitation. One of the most striking findings is the ability of the model to capture North Atlantic atmospheric weather regimes as obtained from a cluster analysis of sea level pressure fields. The model also reproduces the main observed weather patterns responsible for temperature and precipitation extreme events. However, biases are found in many physical processes. Slightly excessive drying may be the cause of an overestimated summer interannual variability and too intense heat waves, especially in central/northern Europe. However, this does not seem to hinder proper simulation of summer temperature trends. Cold extremes appear well simulated, as well as the underlying blocking frequency and stratosphere-troposphere interactions. Extreme precipitation amounts are overestimated and too variable. The atmospheric conditions leading to storm surges were also examined in the Baltics region. There, simulated weather conditions appear not to be leading to strong enough storm surges, but winds were found in very good agreement with reanalyses. The performance in reproducing atmospheric weather patterns indicates that biases mainly originate from local and regional physical processes. This makes local bias adjustment meaningful for climate change attribution

Understanding the rapid summer warming and changes in temperature extremes since the mid-1990s over Western Europe

Analysis of observations indicates that there was a rapid increase in summer (June-August, JJA) mean surface air temperature (SAT) since the mid-1990s over Western Europe. Accompanying this rapid warming are significant increases in summer mean daily maximum temperature, daily minimum temperature, annual hottest day temperature and warmest night temperature, and an increase in frequency of summer days and tropical nights, while the change in the diurnal temperature range (DTR) is small. This study focuses on understanding causes of the rapid summer warming and associated temperature extreme changes. A set of experiments using the atmospheric component of the state-of-the-art HadGEM3 global climate model have been carried out to quantify relative roles of changes in sea surface temperature (SST)/sea ice extent (SIE), anthropogenic greenhouse gases (GHGs), and anthropogenic aerosols (AAer). Results indicate that the model forced by changes in all forcings reproduces many of the observed changes since the mid-1990s over Western Europe. Changes in SST/SIE explain 62.2% ± 13.0% of the area averaged seasonal mean warming signal over Western Europe, with the remaining 37.8% ± 13.6% of the warming explained by the direct impact of changes in GHGs and AAer. Results further indicate that the direct impact of the reduction of AAer precursor emissions over Europe, mainly through aerosol-radiation interaction with additional contributions from aerosol-cloud interaction and coupled atmosphere-land surface feedbacks, is a key factor for increases in annual hottest day temperature and in frequency of summer days. It explains 45.5% ± 17.6% and 40.9% ± 18.4% of area averaged signals for these temperature extremes. The direct impact of the reduction of AAer precursor emissions over Europe acts to increase DTR locally, but the change in DTR is countered by the direct impact of GHGs forcing. In the next few decades, greenhouse gas concentrations will continue to rise and AAer precursor emissions over Europe and North America will continue to decline. Our results suggest that the changes in summer seasonal mean SAT and temperature extremes over Western Europe since the mid-1990s are most likely to be sustained or amplified in the near term, unless other factors intervene