ALBERT

Description: Impacts of spectral nudging on simulations of Arctic climate in coupled simulations have been investigated in a set of simulations with a regional climate model (RCM). The dominantly circumpolar circulation in the Arctic lead to weak constraints on the lateral boundary conditions (LBCs) for the RCM, which causes large internal variability with strong deviations from the driving model. When coupled to an ocean and sea ice model, this results in sea ice concentrations that deviate from the observed spatial distribution. Here, a method of spectral nudging is applied to the atmospheric model RCA4 in order to assess the potentials for improving results for the sea ice concentrations when coupled to the RCO ocean-sea ice model. The spectral nudging applied to reanalysis driven simulations significantly improves the generated sea ice regarding its temporal evolution, extent and inter-annual trends, compared to simulations with standard LBC nesting. The method is furthermore evaluated with driving data from two CMIP5 GCM simulations for current and future conditions. The GCM biases are similar to the RCA4 biases with ERA-Interim, however, the spectral nudging still improves the surface winds enough to show improvements in the simulated sea ice. For both GCM downscalings, the spectrally nudged version retains a larger sea ice extent in September further into the future. Depending on the sea ice formulation in the GCM, the temporal evolution of the regional sea ice model can deviate strongly.

Description: The increased rate of Tropical Indian Ocean (TIO) surface warming has gained a lot of attention in the recent years mainly due to its regional climatic impacts. The processes associated with this increased surface warming is highly complex and none of the mechanisms in the past studies could comprehend the important features associated with this warming such as the negative trends in surface net heat fluxes and the decreasing temperature trends at thermocline level. In this work we studied a previously unexplored aspect, the changes in large scale surface circulation pattern modulating the surface warming pattern over TIO. We use ocean reanalysis datasets and a suit of Ocean General Circulation Model (OGCM) experiments to address this problem. Both reanalysis and OGCM reveal strengthening large scale surface circulation pattern in the recent years. The most striking feature is the intensification of cyclonic gyre circulation around the thermocline ridge in the southwestern TIO. The surface circulation change in TIO is mainly associated with the surface wind changes and the geostrophic response to sea surface height decrease in the western/southwestern TIO. The surface wind trends closely correspond to SST warming pattern. The strengthening mean westerlies over the equatorial region are conducive to convergence in the central and divergence in the western equatorial Indian Ocean (IO) resulting central warming and western cooling. The resulting east west SST gradient further enhances the equatorial westerlies. This positive feedback mechanism supports strengthening of the observed SST trends in the equatorial Indian Ocean. The cooling induced by the enhanced upwelling in the west is compensated to a large extent by warming due to reduction in mixed layer depth, thereby keeping the surface temperature trends in the west to weak positive values. The OGCM experiments showed that the wind induced circulation changes redistribute the excess heat received in the western TIO to central and east thereby enhancing warming in the central equatorial IO. The increased surface warming in central TIO increases the latent heat loss, and keeps the net heat flux trends negative. Model sensitivity experiments reveal that the subsurface cooling at thermocline level in TIO is contributed by variability in Pacific via Indonesian Through Flow whereas the surface warming trend is mainly induced by the changes in the local forcing. The long term changes in IO Rossby waves are not induced by local atmospheric forcing but are forced by Pacific. The thermocline shoaling in the west is therefore amplified by the remote influence of Pacific via wave transmission through Indonesian archipelago.

Description: Used as fuel cladding in the Gen IV fission reactors, ODS steels would be held at temperatures in the range of 350°C to 600°C for several months. Under these conditions, spinodal decomposition is likely to occur in the matrix, resulting in an increase of material brittleness. In this study, thin films consisting of a modulated composition in Fe and in Cr in a given direction have been elaborated. The time evolution of the composition profiles during aging at 500°C has been characterized by atom probe tomography, indicating an apparent kinetic stasis of the initial microstructure. A computer model has been developed on the basis of the Cahn–Hilliard theory of spinodal decomposition, associated with the mobility form proposed by Martin ( 1990 ). We make the assumption that the initial profile is very close to the amplitude-dependent critical wavelength. Our calculations show that the thin film is unstable relative to wavelength modulations, resulting in the observed kinetic stasis.

Description: The effect of Hf (0–1 at.%) additions in a Ni-Ti-Pd alloy on P-phase precipitation and martensitic transformations was studied. The addition of hafnium resulted in the refinement of precipitates with an increase in number density. The overlapping strain fields created due to the decrease in inter-precipitate spacing are suspected to reduce the matrix volume to be less than the critical free volume size needed for the martensitic transformation over the temperature range studied (183–573 K). Hafnium was also found to delay the aging time to achieve peak hardness, suggesting a reduction in growth and coarsening kinetics.

Description: We present in situ indentation in a transmission electron microscope on Al-TiN multilayers with individual layer thicknesses of 50 nm and 2.7 nm to explore the effect of length scales on the plastic co-deformability of a metal and a ceramic. At 50 nm, plasticity was confined to the Al layers with brittle fracture in the TiN layers. At 5 nm and below, cracking in TiN was suppressed with co-deformation evident in both layers. The in situ transmission electron microscopy (TEM) straining results demonstrate a profound size effect in enhancing plastic co-deformability in nanoscale metal-ceramic multilayers, as well as direct validation of ex situ and 3-D elastic–plastic deformation models.

Description: Mo-Si-B-alloys are promising materials for high-temperature applications because of their high melting point, excellent phase stability, large alloying capabilities, and reasonable mechanical as well as oxidative properties. A continuing alloy development is, however, required because of the catastrophic oxidation taking place at intermediate temperatures and the rather high density. The addition of Ti stabilizes a new ternary phase field including the Mo 5 Si 3 (T1) phase instead of the Mo 3 Si (A15) phase. Alloys comprising the phases Mo ss , T1 and Mo 5 SiB 2 (T2) show very high creep resistance, improved oxidation behavior and significantly reduced density. The new T1 phase seems to play a crucial role in the improved oxidation resistance of these new materials, since this phase exhibits excellent oxidation behavior at intermediate and high temperatures. The 4-component alloys possess superior creep behavior compared to Mo-Si-B alloys with the same microstructural phase arrangement and size or to the single crystal Ni-base superalloy CMSX-4. The main reason was found to be the formation of Ti-rich silicide precipitates during processing.

Description: High-entropy alloys are multicomponent solid solutions in which various elements with different chemistries and sizes occupy the same crystallographic lattice sites. Thus, none of the atoms perfectly fit the lattice site, giving rise to considerable local lattice distortions and atomic-level stresses. These characteristics can be beneficial for performance under radiation and in a high-temperature environment, making them attractive candidates as nuclear materials. We discuss electronic origin of the atomic-level stresses based upon first-principles calculations using a density functional theory approach.

Description: In this study, the mechanical characteristics of electrospun palm fruit bunch reinforced poly lactic acid (PLA) nanofiber composites using treated and untreated filler was examined. Poly lactic acid–palm fruit bunch–dichloromethane blends were electrospun by varying the concentration of the palm fruit bunch between 0 wt.% and 8 wt.%. A constant voltage of 26 kV was applied, the tip-to-collector distance was maintained at 27.5 cm and PLA-palm fruit bunch-dichloromethane (DCM) concentration of 12.5% (w/v) was used. The results revealed that the presence of untreated palm fruit bunch fillers in the electrospun PLA matrix significantly reduces the average diameters of the fibers, causing the formation of beads. As a result there are reductions in tensile strengths of the fibers. The presence of treated palm fruit bunch fillers in the electrospun PLA matrix increases the average diameters of the fibers with improvements in the mechanical properties. The optimal mechanical responses were obtained at 3 wt.% of the treated palm fruit bunch fillers in the PLA matrix. However, increase in the palm fruit fillers (treated and untreated) in the PLA matrix promoted the formation of beads in the nanofiber composites.

Description: Chitosan, a naturally derived polysaccharide, was covalently linked to chemically converted graphene (CCG) and the properties of the resulting composites were investigated. The composites were prepared using a stable dispersion of CCG in aqueous solvent. The CCG sheets are stabilised in solution by a small number of peripheral charged groups that can be used to form amide linkages with the polymer matrix. Apart from processability and swellability, the synthesized composites exhibited improved mechanical properties and conductivity by the addition of graphene. Graphene incorporation also introduced a control over the extent of swelling in the composites. The synthesized graphene/composites are promising materials for a variety of applications, for example as conducting substrates for the electrically stimulated growth of cells.

Description: The reductive acid leaching kinetics of synthetic cadmium-bearing zinc ferrite was investigated, and the influence of reaction temperature, sulfuric acid and hydrazine sulfate were studied. The results illustrated that an increase in the reaction temperature, initial sulfuric acid and hydrazine sulfate significantly enhanced the extraction efficiencies of cadmium, zinc and iron. The leaching kinetics were controlled by a surface chemical reaction based on a shrinking core model. The empirical equation \( 1 - (1 - X)^{{{\raise0.7ex\hbox{\(1\)} \!\mathord{\left/ {\vphantom {1 3}}\right.\kern-0pt} \!\lower0.7ex\hbox{\(3\)}}}} = k_{\text{r}} t \) applied was found to fit well with the kinetics analysis; the leaching processes of cadmium, zinc and iron were similar and the activation energies were 79.9 kJ/mol, 77.9 kJ/mol and 79.7 kJ/mol, respectively. The apparent orders of cadmium-bearing zinc ferrite dissolution with respect to sulfuric acid concentration were 0.83, 0.83 and 0.84 for Cd, Zn and Fe, respectively.

Description: The irradiation behavior of Al x CoCrFeNi ( x  = 0.1, 0.75, and 1.5) high entropy alloys was studied under 3 MeV Au-ions irradiation. The microstructural change and volume swelling due to irradiation were investigated using transmission electron microscopy and atomic force microscopy. The results showed that, with increasing the Al contents, the phase crystal structures of the as-cast samples evolved from face-centered cubic (FCC), to FCC + body-centered cubic (BCC), and BCC and irradiation-induced volume swelling increased. All alloys showed exceptional structural stability when irradiated up to over 50 displacement per atom at 298 K, and the irradiation-induced volume swellings in Al x CoCrFeNi HEAs were significantly lower than conventional nuclear materials under similar irradiation dosages.

Description: Sn whiskers/hillocks are believed to form due to stress in the layers, but the dependence on the stress has been difficult to quantify. We therefore used the thermal expansion mismatch between Sn thin films and Si substrates to induce controlled stress by heating. This enables us to measure the average stress in the layer (using wafer curvature) at the same time as we monitor the nucleation rate (using optical microscopy). Scanning electron microscopy of the surface after intervals of heating is also used to quantify the whisker volume as a function of stress and time. The results allow us to determine the dependence of the whisker nucleation rate and the growth rate on the applied stress. They also show that whisker formation is not the dominant mode of plastic strain relaxation in the Sn layer.

Description: An on-line, ensemble-based data assimilation (DA) method is performed to reconstruct the climate for 1750–1850 AD, and the performance is evaluated on large and small spatial scales. We use a low-resolution version of the Max Planck Institute for Meteorology MPI-ESM model and assimilate the PAGES 2K continental mean temperature reconstructions for the Northern Hemisphere (NH). The ensembles are generated sequentially for sub-periods based on the analysis of previous sub-periods. The assimilation has good skill for large-scale temperatures, but there is no agreement between the DA analysis and proxy-based reconstructions for small-scale temperature patterns within Europe or with reconstructions for the North Atlantic Oscillation (NAO) index. To explain the lack of added value in small spatial scales, a maximum covariance analysis (MCA) of links between NH temperature and sea level pressure is performed based on a control simulation with MPI-ESM. For annual values, winter and spring the Northern Annular Mode (NAM) is the pattern that is most closely linked to the NH continental temperatures, while for summer and autumn it is a wave-like pattern. This link is reproduced in the DA for winter, spring and annual means, providing potential for constraining the NAM/NAO phase and in turn regional temperature variability. It is shown that the lack of actual small-scale skill is likely due to the fact that the link might be too weak, as the NH continental mean temperatures are not the best predictors for large-scale circulation anomalies, or that the PAGES 2K temperatures include noise. Both factors can lead to circulation anomalies in the DA analysis that are substantially different from reality, leading to unrealistic representation of small-scale temperature variability. Moreover, we show that even if the true amplitudes of the leading MCA circulation patterns were known, there is still a large amount of unexplained local temperature variance. Based on these results, we argue that assimilating temperature reconstructions with a higher spatial resolution might improve the DA performance.

Description: We analyse the impact of migration and strength of Southern Hemisphere westerly winds on the ocean carbon cycle in a systematic sensitivity study with the University of Victoria Earth System Climate Model. We find that changes in the biological pump are mainly driven by changes in ocean residence times while changes in export production are negligible. Changes in the biological and physical pumps are always of opposite sign; with the physical pump being dominant for southward shifts and the biological pump being dominant for northward shifts. Furthermore, changes in the Pacific Ocean carbon budget dictate the overall changes in global marine and atmospheric carbon. Overall, atmospheric \(\hbox {CO}_2\) increases (and \(\Delta ^{14}\hbox {C}\) decreases) for northward shifts or a strengthening in wind forcing. The opposite is true for a southward shift or a weakening in wind forcing. Combining forcings (shift and intensity change) results in a combination of their impacts with the direction of the shift being the first order forcing. The terrestrial carbon reservoir absorbs (releases) 50–70 % of the net oceanic carbon loss (increase), counterbalancing the effect on atmospheric \(\hbox {CO}_2\) .

Description: Effects of wind and fresh water on the Atlantic meridional overturning circulation (AMOC) are investigated using a fully coupled climate model. The AMOC can change significantly when perturbed by either wind stress or freshwater flux in the North Atlantic. This study focuses on wind stress effect. Our model results show that the wind forcing is crucial in maintaining the AMOC. Reducing wind forcing over the ocean can cause immediately weakening of the vertical salinity diffusion and convection in the mid-high latitudes Atlantic, resulting in an enhancement of vertical salinity stratification that restrains the deep water formation there, triggering a slowdown of the thermohaline circulation. As the thermohaline circulation weakens, the sea ice expands southward and melts, providing the upper ocean with fresh water that weakens the thermohaline circulation further. The wind perturbation experiments suggest a positive feedback between sea-ice and thermohaline circulation strength, which can eventually result in a complete shutdown of the AMOC. This study also suggests that sea-ice variability may be also important to the natural AMOC variability on decadal and longer timescales.

Description: The relationship between the large-scale circulation dynamics and regional precipitation regime in the Tibetan Plateau (TP) has so far not been well understood. In this study, we classify the circulation types using the self-organizing maps based on the daily field of 500 hPa geopotential height and link them to the precipitation climatology in the eastern and central TP. By virtue of an objective determining method, 18 circulation types are quantified. The results show that the large amount of precipitation in summer is closely related to the circulation types in which the enhanced and northward shifted subtropical high (SH) over the northwest Pacific and the obvious cyclconic circulation anomaly over the Bay of Bengal are helpful for the Indian summer monsoon and East Asian summer monsoon to take abundant low-latitude moisture to the eastern and southern TP. On the contrary, the dry winter in the central and eastern Tibet corresponds to the circulation types with divergence over the central and eastern TP and the water vapor transportations of East Asian winter monsoon and mid-latitude westerly are very weak. Some circulation types are associated with some well-known circulation patterns/monsoons influencing the TP (e.g. East Atlantic Pattern, El Niño Southern Oscillation, Indian Summer Monsoon and the mid-latitude westerly), and exhibit an overall good potential for explaining the variability of regional seasonal precipitation. Moreover, the climate shift signals in the late 1970s over the eastern Pacific/North Pacific Oceans could also be reflected by both the variability of some circulation types and their correspondingly composite precipitations. This study extends our understandings for the large-scale atmospheric dynamics and their linkages with regional precipitation and is beneficial for the climate change projection and related adaptation activities in the highest and largest plateau in the world.

Description: The current work aims to reveal the effects of solute atoms (TM = Ag, Zn, and Zr) on the age hardening of Mg-Gd-based alloys via the density functional theory and electron work function (EWF) approaches. The 10H LPSO phases of Mg-Gd-TM alloys are selected as the model case due to the improved strength and ductility such long periodic stacking ordered precipitates (LPSOs) offer. The CALPHAD-modeling method is applied to predict the EWF in the ternary Mg-Gd-TM alloys. The obtained EWFs of these Mg alloys are shown to match well with previous experimental and theoretical results. Moreover, the variation of EWF in the ternary Mg-Gd-TM alloys is attributed to the structure contribution [i.e., the formation of face-centered cubic (fcc)-type fault layers] and the chemical effect of solute atoms (i.e., electron redistributions). With the knowledge of bonding charge density between the solute and solvent atoms, the present work provides insight into the correlations between the EWF and hardness of Mg-Gd-TM alloys.

Description: Anodic potential, morphology and phase composition of the anodic layer, corrosion morphology of the metallic substrate, and oxygen evolution behavior of Pb-Ag anode in H 2 SO 4 solution without/with fluoride ion were investigated and compared. The results showed that the presence of fluoride ions contributed to a smoother anodic layer with lower PbO 2 concentration, which resulted in lower double layer capacity and higher charge transfer resistance for the oxygen evolution reaction. Consequently, the Pb-Ag anode showed a higher anodic potential (about 35 mV) in the fluoride-containing electrolyte. In addition, the fluoride ions accelerated the detachment of loose flakes on the anodic layer. It was demonstrated that the anodic layer formed in the fluoride-containing H 2 SO 4 solution was thinner. Furthermore, fluoride ions aggravated the corrosion of the metallic substrate at interdendritic boundary regions. Hence, the presence of fluoride ions is detrimental to oxygen evolution reactivity and increases the corrosion of the Pb-Ag anode, which may further increase the energy consumption and capital cost of zinc plants.

Description: The nanomechanical behavior of the Co 20 Cr 20 Fe 20 Mn 20 Ni 20 high-entropy alloy was investigated in as-cast, rolled, annealed, and thin-film forms. Dislocation nucleation was studied by repeated indents at a low load for each of the different processing conditions. Distinct displacement bursts (pop in) were observed in the loading curve marked by incipient plasticity for all the samples. The as-cast and annealed samples showed pop ins for 100% of the indents, whereas the rolled and thin-film samples showed a much lower fraction of displacement bursts. This was explained by the high density of dislocations for the cold-worked and thin-film conditions. The strong depth dependence of hardness was explained by geometrically necessary dislocations. The nanomechanical behavior and twinned microstructure indicate low stacking-fault energy for this high-entropy alloy.

Description: Based on the historical and RCP8.5 experiments from 25 Coupled Model Intercomparison Project phase 5 (CMIP5) models, the impacts of sea surface temperature (SST) warming in the tropical Indian Ocean (IO) on the projected change in summer rainfall over Central Asia (CA) are investigated. The analysis is designed to answer three questions: (1) Can CMIP5 models reproduce the observed influence of the IO sea surface temperatures (SSTs) on the CA rainfall variations and the associated dynamical processes? (2) How well do the models agree on their projected rainfall changes over CA under warmed climate? (3) How much of the uncertainty in such rainfall projections is due to different impacts of IO SSTs in these models? The historical experiments show that in most models summer rainfall over CA are positively correlated to the SSTs in the IO. Furthermore, for models with higher rainfall-SSTs correlations, the dynamical processes accountable for such impacts are much closer to what have been revealed in observational data: warmer SSTs tend to favor the development of anti-cyclonic circulation patterns at low troposphere over north and northwest of the Arabian Sea and the Bay of Bengal. These anomalous circulation patterns correspond to significantly enhanced southerly flow which carries warm and moisture air mass from the IO region up to the northeast. At the same time, there is a cyclonic flow over the central and eastern part of the CA which further brings the tropical moisture into the CA and provides essential moist conditions for its rainfall generation. In the second half of twenty-first century, although all the 25 models simulate warmed SSTs, significant uncertainty exists in their projected rainfall changes over CA: half of them suggest summer rainfall increases, but the other half project rainfall decreases. However, when we select seven models out of the 25 based on their skills in capturing the dynamical processes as observed, then the model projected changes are much closer. Five out of the seven models predicted more rainfall over CA. Such a result is helpful for allowing us to attribute part of the observed upward rainfall trend in the CA region in the last several decades to the IO SST warming.

Description: The use of duplex stainless steels (DSS) in nuclear power generation systems is limited by thermal instability that leads to embrittlement in the temperature range of 204°C to 538°C. New lean-grade alloys, such as 2101, offer the potential to mitigate these effects. Thermal embrittlement was quantified through impact toughness and hardness testing on samples of alloy 2101 after aging at 427°C for various durations (1–10,000 h). Additionally, atom probe tomography (APT) was utilized in order to observe the kinetics of α – α ′ separation and G-phase formation. Mechanical testing and APT data for two other DSS alloys, 2003 and 2205, were used as a reference to 2101. The results show that alloy 2101 exhibits superior performance compared to the standard-grade DSS alloy 2205 but inferior to the lean-grade alloy 2003 in mechanical testing. APT data demonstrate that the degree of α – α ′ separation found in alloy 2101 closely resembles that of 2205 and greatly exceeds 2003. Additionally, contrary to what was observed in 2003, 2101 demonstrated G-phase like precipitates after long aging times, although precipitates were not as abundant as was observed in 2205.

Description: Cyclonic windstorms are one of the most important natural hazards for Europe, but robust climate projections of the position and the strength of the North Atlantic storm track are not yet possible, bearing significant risks to European societies and the (re)insurance industry. Previous studies addressing the problem of climate model uncertainty through statistical comparisons of simulations of the current climate with (re-)analysis data show large disagreement between different climate models, different ensemble members of the same model and observed climatologies of intense cyclones. One weakness of such evaluations lies in the difficulty to separate influences of the climate model’s basic state from the influence of fast processes on the development of the most intense storms, which could create compensating effects and therefore suggest higher reliability than there really is. This work aims to shed new light into this problem through a cost-effective “seamless” approach of hindcasting 20 historical severe storms with the two global climate models, ECHAM6 and GA4 configuration of the Met Office Unified Model, run in a numerical weather prediction mode using different lead times, and horizontal and vertical resolutions. These runs are then compared to re-analysis data. The main conclusions from this work are: (a) objectively identified cyclone tracks are represented satisfactorily by most hindcasts; (b) sensitivity to vertical resolution is low; (c) cyclone depth is systematically under-predicted for a coarse resolution of T63 by both climate models; (d) no systematic bias is found for the higher resolution of T127 out to about three days, demonstrating that climate models are in fact able to represent the complex dynamics of explosively deepening cyclones well, if given the correct initial conditions; (e) an analysis using a recently developed diagnostic tool based on the surface pressure tendency equation points to too weak diabatic processes, mainly latent heating, as the main source for the under-prediction in the coarse-resolution runs. Finally, an interesting implication of these results is that the too low number of deep cyclones in many free-running climate simulations may therefore be related to an insufficient number of storm-prone initial conditions. This question will be addressed in future work.

Description: Extreme precipitation and flood episodes in the Himalayas are oftentimes traced to synoptic situations involving connections between equatorward advancing upper level extratropical circulations and moisture-laden tropical monsoon circulation. While previous studies have documented precipitation characteristics in the Himalayan region during severe storm cases, a comprehensive understanding of circulation dynamics of extreme precipitation mechanisms is still warranted. In this study, a detailed analysis is performed using rainfall observations and reanalysis circulation products to understand the evolution of monsoon-extratropical circulation features and their interactions based on 34 extreme precipitation events which occurred in the Western Himalayas (WEH) during the period 1979–2013. Our results provide evidence for a common large-scale circulation pattern connecting the extratropics and the South Asian monsoon region, which is favorable for extreme precipitation occurrences in the WEH region. This background upper level large-scale circulation pattern consists of a deep southward penetrating midlatitude westerly trough, a blocking high over western Eurasia and an intensifying Tibetan anticyclone. It is further seen from our analysis that the key elements of monsoon-midlatitude interactions, responsible for extreme precipitation events over the WEH region, are: (1) midlatitude Rossby wave breaking, (2) west-northwest propagation of monsoon low-pressure system from the Bay of Bengal across the Indian subcontinent, (3) eddy shedding of the Tibetan anticyclone, (4) ageostrophic motions and transverse circulation across the Himalayas, and (5) strong moist convection over the Himalayan foothills. Furthermore, high-resolution numerical simulations indicate that diabatic heating and mesoscale ageostrophic effects can additionally amplify the convective motions and precipitation in the WEH region.

Description: This paper examines the difference in the Atlantic Meridional Overturning Circulation (AMOC) mean state between free and assimilative simulations of a common ocean model using a common interannual atmospheric forcing. In the assimilative simulation, the reproduction of cold cores in the Nordic Seas, which is absent in the free simulation, enhances the overflow to the North Atlantic and improves AMOC with enhanced transport of the deeper part of the southward return flow. This improvement also induces an enhanced supply of North Atlantic Deep Water (NADW) and causes better representation of the Atlantic deep layer despite the fact that correction by the data assimilation is applied only to temperature and salinity above a depth of 1750 m. It also affects Circumpolar Deep Water in the Southern Ocean. Although the earliest influence of the improvement propagated by coastal waves reaches the Southern Ocean in 10–15 years, substantial influence associated with the arrival of the renewed NADW propagates across the Atlantic Basin in several decades. Although the result demonstrates that data assimilation is able to improve the deep ocean state even if there is no data there, it also indicates that long-term integration is required to reproduce variability in the deep ocean originating from variations in the upper ocean. This study thus provides insights on the reliability of AMOC and the ocean state in the Atlantic deep layer reproduced by data assimilation systems.

Description: The present work is concerned with the study of the relationship between microstructure and ductility of nanostructured bainite. The tensile behavior of two steels treated at the same temperature during different times has been analyzed. Special attention has been paid to the role that the retained austenite mechanical stability plays in enhancing the ductility through its contribution to the work-hardening and the damage resistance of these materials. The results have shown that the relative mechanical properties of the phases present affect both the martensitic transformation behavior and the total elongation.

Description: The southeast region of Brazil experienced in austral summer 2014 a major drought event leading to a number of impacts in water availability for human consumption, agricultural irrigation and hydropower production. This study aims to perform a diagnostic analysis of the observed climate conditions during this event, including an inspection of the occurred precipitation anomalies in the context of previous years, and an investigation of possible relationships with sea surface temperatures and atmospheric circulation patterns. The sea surface temperature analysis revealed that the southwestern South Atlantic Ocean region near the coast of southeast Brazil showed strong negative association with precipitation over southeast Brazil, indicating that increased sea temperatures in this ocean region are consistent with reduced precipitation as observed in summer 2014. The circulation analysis revealed prevailing anti-cyclonic anomalies at lower levels (850 hPa) with northerly anomalies to the west of southeast Brazil, channeling moisture from the Amazon towards Paraguay, northern Argentina and southern Brazil, and drier than normal air from the South Atlantic Ocean towards the southeast region of Brazil. This circulation pattern was found to be part of a large-scale teleconnection wave train linked with the subsidence branch of the Walker circulation in the tropical east Pacific, which in turn was generated by an anomalous tropical heat source in north/northeastern Australia. A regional Hadley circulation with an ascending branch to the south of the subsidence branch of the Walker circulation in the tropical east Pacific was identified as an important component connecting the tropical and extratropical circulation. The ascending branch of this Hadley circulation in the south Pacific coincided with an identified Rossby wave source region, which contributed to establishing the extratropical component of the large-scale wave train connecting the south Pacific and the Atlantic region surrounding southeast Brazil. This connection between the Pacific and the Atlantic was confirmed with Rossby ray tracing analyses. The local circulation response was associated to downward air motion (subsidence) over Southeast Brazil, contributing to the expressive negative precipitation anomalies observed during summer 2014, and leading to a major drought event in the historical context. The analysis of atmospheric and oceanic patterns of this event helped defining a schematic framework leading to the observed drought conditions in southeast Brazil, including the involved teleconnections, blocking high pressure, radiative and humidity transport effects.

Description: The strengthening mechanisms of Co 21 Cr 22 Cu 22 Fe 21 Ni 14 multiple-principal element alloy processed by high pressure torsion (HPT) and annealing were examined. Two face-centered cubic (FCC) phases were observed in the as-cast alloy; one was a Cu-rich phase and the other was a Cu-lean one. In the HPT process, the microhardness increased from 190 HV to 470 HV at a strain of 157 due to strain hardening and grain refinement hardening. X-ray diffraction showed that the lattice parameters of the two FCC phases became closer to each other at higher HPT strain, indicating the alloying of Cu into the Cu-lean matrix. The HPT processed specimens were annealed at 500°C, 550°C, 600°C, and 650°C. The microhardness increased to 540 HV after annealing at temperatures lower than 650°C, whereas it decreased when the specimen was annealed at 650°C. The mean grain size of the specimens annealed at temperatures lower than 650°C was much smaller than 100 nm, and Cu-rich clusters with sizes ranging from 2 nm to 32 nm were distributed homogeneously. The reasons for the formation of the Cu-rich nano-clusters were discussed from a perspective of the positive mixing enthalpy of Cu in the alloy and thermalenergy for Cu diffusion at a given temperature. The dissolution and partitioning of two FCC phases played a key role in strengthening the Co 21 Cr 22 Cu 22 Fe 21 Ni 14 system.

Description: The existence of cut-off lows (COLs) over South Pacific and South America is often associated with adverse weather events such as intense precipitation over the central region of South America, frost episodes in southern Brazil and the development of Andes lee cyclones and intense cyclones over the southern coast of Brazil. Despite this importance, the formation and maintenance mechanisms of the COLs are not well understood. To detail the significant variability in terms of the eddy kinetic energy equation for fifty cases of COLs that formed over the southeastern Pacific Ocean is the aim of this study. Only the cases of COLs that formed over the ocean and remained there during most of their life were chosen. The main terms of the equation [ageostrophic flux convergence (AFC), baroclinic conversion (BRC) and barotropic conversion (BRT)] were calculated using the 6-hourly gridded data from the National Centers for Environmental Prediction/Department of Energy reanalysis. The formation mechanism of the COLs was associated with BRC and AFC. During the midlife period, the BRC term converted eddy kinetic energy to eddy potential energy and the AFC had a positive contribution until 6 h after the midlife point. In the dissipation phase, the BRC term remained positive and AFC became negative. The BRT extracted kinetic energy from the COL during the entire life cycle. The AFC term was the most important in all phases of the cut-off lifetime, and it was the responsible for extending the cut-off lifetime while the others terms were negatives.

Description: The present study examines the ability of high resolution (T382) National Centers for Environmental Prediction coupled atmosphere–ocean climate forecast system version 2 (CFS T382) in simulating the salient spatio-temporal characteristics of the boreal summertime mean climate and the intraseasonal variability. The shortcomings of the model are identified based on the observation and compared with earlier reported biases of the coarser resolution of CFS (CFS T126). It is found that the CFS T382 reasonably mimics the observed features of basic state climate during boreal summer. But some prominent biases are noted in simulating the precipitation, tropospheric temperature (TT) and sea surface temperature (SST) over the global tropics. Although CFS T382 primarily reproduces the observed distribution of the intraseasonal variability over the Indian summer monsoon region, some difficulty remains in simulating the boreal summer intraseasonal oscillation (BSISO) characteristics. The simulated eastward propagation of BSISO decays rapidly across the Maritime Continent, while the northward propagation appears to be slightly slower than observation. However, the northward propagating BSISO convection propagates smoothly from the equatorial region to the northern latitudes with observed magnitude. Moreover, the observed northwest-southeast tilted rain band is not well reproduced in CFS T382. The warm mean SST bias and inadequate simulation of high frequency modes appear to be responsible for the weak simulation of eastward propagating BSISO. Unlike CFS T126, the simulated mean SST and TT exhibit warm biases, although the mean precipitation and simulated BSISO characteristics are largely similar in both the resolutions of CFS. Further analysis of the convectively coupled equatorial waves (CCEWs) indicates that model overestimates the gravest equatorial Rossby waves and underestimates the Kelvin and mixed Rossby-gravity waves. Based on analysis of CCEWs, the study further explains the possible reasons behind the realistic simulation of northward propagating BSISO in CFS T382, even though the model shows substantial biases in simulating mean state and other BSISO modes.

Description: The microstructural stability of Y-Al oxides during the recrystallization of Fe-Cr-Al oxide dispersion strengthened alloy is studied in this work. The goal is to determine the specific distribution pattern of oxides depending where they are located: in the matrix or at the grain boundaries. It was concluded that those located at the grain boundaries yielded a faster coarsening than the ones in the matrix, although no significant differences in composition and/or crystal structure were observed. However, the recrystallization heat treatment leads to the dissolution of the Y 2 O 3 and its combination with Al to form the YAlO 3 perovskite oxide particles process, mainly located at the grain boundaries. Finally, atom probe tomography analysis revealed a significant Ti build-up at the grain boundaries that might affect subsequent migration during recrystallization.

Description: It is established that the eliminations of construction sand with the content of SiO 2 about 70 wt.% and particle size less than 60  μ m are suitable for the production of a foam-glass–crystal material on the basis of the low-temperature frit, which was synthesized at the temperature of 900°C. The obtained foam-glass–crystal material exceeds foam-glass (by 3.0 times) and clayite (by 1.5 times) by strength and is characterized by the low value of water absorption (0.1%).

Description: The TAO/TRITON array is the cornerstone of the tropical Pacific and ENSO observing system. Motivated by the recent rapid decline of the TAO/TRITON array, the potential utility of TAO/TRITON was assessed for ENSO monitoring and prediction. The analysis focused on the period when observations from Argo floats were also available. We coordinated observing system experiments (OSEs) using the global ocean data assimilation system (GODAS) from the National Centers for Environmental Prediction and the ensemble coupled data assimilation (ECDA) from the Geophysical Fluid Dynamics Laboratory for the period 2004–2011. Four OSE simulations were conducted with inclusion of different subsets of in situ profiles: all profiles (XBT, moorings, Argo), all except the moorings, all except the Argo and no profiles. For evaluation of the OSE simulations, we examined the mean bias, standard deviation difference, root-mean-square difference (RMSD) and anomaly correlation against observations and objective analyses. Without assimilation of in situ observations, both GODAS and ECDA had large mean biases and RMSD in all variables. Assimilation of all in situ data significantly reduced mean biases and RMSD in all variables except zonal current at the equator. For GODAS, the mooring data is critical in constraining temperature in the eastern and northwestern tropical Pacific, while for ECDA both the mooring and Argo data is needed in constraining temperature in the western tropical Pacific. The Argo data is critical in constraining temperature in off-equatorial regions for both GODAS and ECDA. For constraining salinity, sea surface height and surface current analysis, the influence of Argo data was more pronounced. In addition, the salinity data from the TRITON buoys played an important role in constraining salinity in the western Pacific. GODAS was more sensitive to withholding Argo data in off-equatorial regions than ECDA because it relied on local observations to correct model biases and there were few XBT profiles in those regions. The results suggest that multiple ocean data assimilation systems should be used to assess sensitivity of ocean analyses to changes in the distribution of ocean observations to get more robust results that can guide the design of future tropical Pacific observing systems.

Description: The tensile deformation mechanisms of an extruded Mg-1Mn (wt.%) alloy at 323 K (50°C) was investigated by a combination of in situ tensile testing and electron backscatter diffraction analysis. The strong basal texture of the material resulted in placing the c -axis of most of the grains under compression during tensile loading parallel to the extrusion axis. Basal, prismatic, and pyramidal 〈 c + a 〉 slip activity was observed along with \( \left\{ {10\overline{1}2} \right\} \) extension twinning. However, \( \left\{ {10\overline{1}1} \right\} \) contraction twinning dominated the deformation. Although contraction twinning and pyramidal 〈 c + a 〉 slip both allow for c-component deformation, contraction twinning was preferred over pyramidal 〈 c + a 〉 slip, and this was expected to be due to the lower critical resolved shear stress (CRSS) value for the former mechanism at ambient temperatures. The contraction twins evolved into \( \left\{ {10\overline{1}1} \right\} - \left\{ {10\overline{1}2} \right\} \) double twins with an increase in strain. The propensity of double twins to form shear bands due to shear localization within the double twinned region, which eventually resulted in cracks, led to the failure of the material. The shear localization in the double twins was expected to be due to the enhanced activity of basal slip in the twinned volume. The observations from the present study suggest that contraction twinning may play a critical role in the limited cold formability of magnesium and its alloys.

Description: In this work, we present a micro electro-mechanical systems (MEMS)-based in situ transmission electron microscope (TEM) experimental setup for high-temperature uniaxial tensile behavior of nanocrystalline thin films. This setup utilizes self-heating (Ohmic) to raise the temperature of thin films while applying uniaxial tensile loading using electro-thermal actuators. Self-heating is achieved by passing a high-density direct current through the specimen. We carried out a qualitative uniaxial tensile experiment on a 75-nm platinum thin film at 360 K. Temperature is estimated using COMSOL modeling. In this qualitative experiment, we observed initial grain growth followed by formation of edge serrations. We propose that grain boundary sliding coupled with grain growth is the underlying mechanism responsible for the observed behavior.

Description: Recent numerical studies in stratospheric dynamics and its variability as well as climate, have highlighted the need of more observational analyses to improve simulation of the West African monsoon (WAM). In this paper, activity and spectral characteristics of short-scale vertical waves (wavelengths 〈4 km) are analysed in equatorial coastal and tropical lower stratosphere during the WAM. A first detailed description of such waves over West Africa is derived from high-resolution vertical profiles of temperature and horizontal wind obtained during Intensive Observation Period of the African Monsoon Multidisciplinary Analyses (AMMA) Campaign 2006. Monthly variation of wave energy density is revealed to trace the progression of the inter-tropical convergence zone (ITCZ) over West Africa. Mesoscale inertia gravity-waves structures with vertical and horizontal wavelengths of 1.5–2.5 and 400–1100 km respectively and intrinsic frequencies of 1.1–2.2 f or periods 〈2 days are observed in the tropical LS with intense activity during July and August when the WAM is installed over the tropical West Africa. Over equatorial region, gravity waves with intrinsic frequencies of 1.4–4 f or periods 〈5.2 days, vertical wavelength of 2.1 km and long horizontal wavelengths of 1300 km are intense during the WAM coastal phase. From July to October, gravity waves with intrinsic frequencies of 1.2–3.8 f or periods 〈6 days, vertical wavelength of 2.1 km and horizontal wavelengths of 1650 km are less intense during the WAM Sahelian phase of the WAM, March–June. Unlike potential energy density, kinetic energy density is observed to be a good proxy for the activity of short-scale vertical waves during the WAM because quasi-inertial waves are dominant. Long-term wave activity variation from January 2001 to December 2009, highlights strong year-to-year variation superimposed on convective activity and quasi-biennial oscillation-like variations especially above tropical stations.

Description: Satellite based top-of-atmosphere (TOA) and surface radiation budget observations are combined with mass corrected vertically integrated atmospheric energy divergence and tendency from reanalysis to infer the regional distribution of the TOA, atmospheric and surface energy budget terms over the globe. Hemispheric contrasts in the energy budget terms are used to determine the radiative and combined sensible and latent heat contributions to the cross-equatorial heat transports in the atmosphere (AHT EQ ) and ocean (OHT EQ ). The contrast in net atmospheric radiation implies an AHT EQ from the northern hemisphere (NH) to the southern hemisphere (SH) (0.75 PW), while the hemispheric difference in sensible and latent heat implies an AHT EQ in the opposite direction (0.51 PW), resulting in a net NH to SH AHT EQ (0.24 PW). At the surface, the hemispheric contrast in the radiative component (0.95 PW) dominates, implying a 0.44 PW SH to NH OHT EQ . Coupled model intercomparison project phase 5 (CMIP5) models with excessive net downward surface radiation and surface-to-atmosphere sensible and latent heat transport in the SH relative to the NH exhibit anomalous northward AHT EQ and overestimate SH tropical precipitation. The hemispheric bias in net surface radiative flux is due to too much longwave surface radiative cooling in the NH tropics in both clear and all-sky conditions and excessive shortwave surface radiation in the SH subtropics and extratropics due to an underestimation in reflection by clouds.

Description: Mineral dust aerosols are an essential component of climate over West Africa, however, little work has been performed to investigate their contributions to potential climate change. A set of regional climate model experiments with and without mineral dust processes and land cover changes is performed to evaluate their climatic effects under the Representative Concentration Pathway 8.5 for two global climate models. Results suggest surface warming to be in the range of 4–8 °C by the end of the century (2081–2100) over West Africa with respect to the present day (1981–2000). The presence of mineral dusts dampens the warming by 0.1–1 °C in all seasons. Accounting for changes in land cover enhances the warming over the north of Sahel and dampens it to the south in spring and summer; however, the magnitudes are smaller than those resulting from dusts. Overall dust loadings are projected to increase, with the greatest increase occurring over the Sahara and Sahel in summer. Accounting for land cover changes tends to reduce dust loadings over the southern Sahel. Future precipitation is projected to decrease by 5–40 % in the western Sahara and Sahel and increase by 10–150 % over the eastern Sahel and Guinea Coast in JJA. A dipole pattern of future precipitation changes is attributed to dust effects, with decrease in the north by 5–20 % and increase by 5–20 % in the south. Future changes in land cover result in a noisy non-significant response with a tendency for slight wetting in MAM, JJA, and SON and drying in DJF.

Description: Sheet-like precursors of NiO and Ag/NiO with different Ag contents were synthesized by a facile and easily controlled hydrothermal method. The NiO and Ag/NiO composite nanosheets were prepared by calcination of the corresponding precursors at 400°C for 3 h. The as-synthesized samples were characterized by thermogravimetric analysis, x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The antibacterial activity of NiO and Ag/NiO composites to several gram-positive and gram-negative bacteria was examined. Results showed that NiO nanosheets hardly exhibited antibacterial activity; however, Ag/NiO composites displayed higher activity even with low Ag content.

Description: In a previous study Pons et al. (Clim Res 54(3):197–207, 2010 . doi: 10.3354/cr01117g ) reported a significant decreasing trend of snowfall occurrence in the Northern Iberian Peninsula since the mid 70s. The study was based on observations of annual snowfall frequency (measured as the annual number of snowfall days NSD) from a network of 33 stations ranging from 60 to 1350 m. In the present work we analyze the skill of Regional Climate Models (RCMs) to reproduce this trend for the period 1961–2000 (using both reanalysis- and historical GCM-driven boundary conditions) and the trend and the associated uncertainty of the regional future projections obtained under the A1B scenario for the first half of the twenty-first century. In particular, we consider the regional simulation dataset from the EU-funded ENSEMBLES project, consisting of thirteen state-of-the-art RCMs run at 25 km resolution over Europe. While ERA40 severely underestimates both the mean NSD and its observed trend (−2.2 days/decade), the corresponding RCM simulations driven by the reanalysis appropriately capture the interannual variability and trends of the observed NSD (trends ranging from −3.4 to −0.7, −2.1 days/decade for the ensemble mean). The results driven by the GCM historical runs are quite variable, with trends ranging from −8.5 to 0.2 days/decade (−1.5 days/decade for the ensemble mean), and the greatest uncertainty by far being associated with the particular GCM used. Finally, the trends for the future 2011–2050 A1B runs are more consistent and significant, ranging in this case from −3.7 to −0.5 days/decade (−2.0 days/decade for the ensemble mean), indicating a future significant decreasing trend. These trends are mainly determined by the increasing temperatures, as indicated by the interannual correlation between temperature and NSD (−0.63 in the observations), which is preserved in both ERA40- and GCM-driven simulations.

Description: The interannual-decadal variability of the wintertime mixed layer depths (MLDs) over the North Pacific is investigated from an empirical orthogonal function (EOF) analysis of an ensemble of global ocean reanalyses. The first leading EOF mode represents the interannual MLD anomalies centered in the eastern part of the central mode water formation region in phase opposition with those in the eastern subtropics and the central Alaskan Gyre. This first EOF mode is highly correlated with the Pacific decadal oscillation index on both the interannual and decadal time scales. The second leading EOF mode represents the MLD variability in the subtropical mode water (STMW) formation region and has a good correlation with the wintertime West Pacific (WP) index with time lag of 3 years, suggesting the importance of the oceanic dynamical response to the change in the surface wind field associated with the meridional shifts of the Aleutian Low. The above MLD variabilities are in basic agreement with previous observational and modeling findings. Moreover the reanalysis ensemble provides uncertainty estimates. The interannual MLD anomalies in the first and second EOF modes are consistently represented by the individual reanalyses and the amplitudes of the variabilities generally exceed the ensemble spread of the reanalyses. Besides, the resulting MLD variability indices, spanning the 1948–2012 period, should be helpful for characterizing the North Pacific climate variability. In particular, a 6-year oscillation including the WP teleconnection pattern in the atmosphere and the oceanic MLD variability in the STMW formation region is first detected.

Description: In this paper, decadal variability of the Pacific-South America (PSA) mode is examined from year 1871 to 2008 based on the newly developed ocean and atmosphere reanalysis products. The PSA mode, mirroring the Pacific-North America mode in the Northern Hemisphere, emerges as the second EOF mode of 500 mb geopotential height anomalies. The mode displays substantial interannual-decadal variability with distinct timescales between 3–8 and 10–18 years, respectively. The decadal variability of the PSA mode is found to be associated with the coupled ocean–atmosphere interaction over the subtropical South and tropical Pacific. The subduction of the subtropical temperature anomalies in the South Pacific in conjunction with the tropical–subtropical atmospheric teleconnection plays important role in the decadal variability of the PSA mode.

Description: The National Center for Atmospheric Research Community Earth System Model is used to study the “spring predictability barrier” (SPB) problem for El Niño events from the perspective of initial error growth. By conducting perfect model predictability experiments, we obtain two types of initial sea temperature errors, which often exhibit obvious season-dependent evolution and cause a significant SPB when predicting the onset of El Niño events bestriding spring. One type of initial errors possesses a sea surface temperature anomaly (SSTA) pattern with negative anomalies in the central–eastern equatorial Pacific, plus a basin-wide dipolar subsurface temperature anomaly pattern with negative anomalies in the upper layers of the eastern equatorial Pacific and positive anomalies in the lower layers of the western equatorial Pacific. The other type consists of an SSTA component with positive anomalies over the southeastern equatorial Pacific, plus a large-scale zonal dipole pattern of the subsurface temperature anomaly with positive anomalies in the upper layers of the eastern equatorial Pacific and negative anomalies in the lower layers of the central–western equatorial Pacific. Both exhibit a La Niña-like evolving mode and cause an under-prediction for Niño-3 SSTA of El Niño events. For the former initial error type, the resultant prediction errors grow in a manner similar to the behavior of the growth phase of La Niña; while for the latter initial error type, they experience a process that is similar to El Niño decay and transition to a La Niña growth phase. Both two types of initial errors cause negative prediction errors of Niño-3 SSTA for El Niño events. The prediction errors for Niño-3 SSTA are mainly due to the contribution of initial sea temperature errors in the large-error-related regions in the upper layers of the eastern tropical Pacific and/or in the lower layers of the western tropical Pacific. These regions may represent ‘‘sensitive areas’’ for El Niño–Southern Oscillation (ENSO) predictions, thereby providing information for target observations to improve the forecasting skill of ENSO.

Description: In this study, the relationship between the El Niño-Southern Oscillation (ENSO) and precipitation variability over the Korean Peninsula is investigated. In contrast to the previously-known positive correlation between them during an El Niño developing summer and winter, we found a considerably significant negative correlation in September between Niño3 Sea Surface Temperature and Korean precipitation during ENSO developing phase. The northerly wind is only seen during El Nino developing phase and is part of the cyclonic flow over the subtropical North Pacific. The cyclonic flow over the subtropical North Pacific is induced by the subtropical diabatic heating, which is a peculiar feature during El Niño developing phase. In addition, it is demonstrated that the negative correlation is partly attributed to the tropical cyclone (TC), particularly during La Niña phase. That is, TC tends to pass through Korean Peninsula more frequently during La Niña years, which leads to more precipitation over the Korean Peninsula.

Description: Explosive cyclones are rapidly intensifying low pressure systems generating severe wind speeds and heavy precipitation primarily in coastal and marine environments. This study presents the first analysis on how explosive cyclones respond to climate change in the extratropics of the Northern Hemisphere. An objective-feature tracking algorithm is used to identify and track cyclones from 23 CMIP5 climate models for the recent past (1981–1999) and future (2081–2099). Explosive cyclones are projected to shift northwards by about \(2.2^\circ\) latitude on average in the northern Pacific, with fewer and weaker events south of \(45^\circ \hbox {N}\) , and more frequent and stronger events north of this latitude. This shift is correlated with a poleward shift of the jet stream in the inter-model spread ( \(R=0.56\) ). In the Atlantic, the total number of explosive cyclones is projected to decrease by about 17 % when averaging across models, with the largest changes occurring along North America’s East Coast. This reduction is correlated with a decline in the lower-tropospheric Eady growth rate ( \(R=0.51\) ), and is stronger for models with smaller frequency biases ( \(R=-0.65\) ). The same region is also projected to experience a small intensification of explosive cyclones, with larger vorticity values for models that predict stronger increases in the speed of the jet stream ( \(R=0.58\) ). This strengthening of the jet stream is correlated with an enhanced sea surface temperature gradient in the North Atlantic ( \(R=-0.63\) ). The inverse relationship between model bias and projection, and the role of model resolution are discussed.

Description: Compression behavior of the Al 0.5 CoCrCuFeNi high-entropy alloy (HEA) was studied at different temperatures from 673 K to 873 K at a low strain rate of 5 × 10 −5 /s to investigate the temperature effect on the mechanical properties and serration behavior. The face-centered-cubic (fcc) structure is confirmed at the lower temperature of 673 K and 773 K, and a structure of mixed fcc and body-centered cubic (bcc) is identified at a higher temperature of 873 K after compression tests using high-energy synchrotron x-ray diffraction. By comparing the stress–strain curves at different temperatures, two opposite directions of serrations types were found, named upward serrations appearing at 673 K and 773 K and downward serrations at 873 K, which may be due to dynamic strain aging.

Description: We identify the dynamical drivers of systematic changes in persistent quasi-stationary states (regimes) of the Southern Hemisphere troposphere and their secular trends. We apply a purely data-driven approach, whereby a multiscale approximation to nonstationary dynamical processes is achieved through optimal sequences of locally stationary fast vector autoregressive factor processes, to examine a high resolution atmospheric reanalysis over the period encompassing 1958–2013. This approach identifies regimes and their secular trends in terms of the predictability of the flow and is Granger causal. A comprehensive set of diagnostics on both isentropic and isobaric surfaces is employed to examine teleconnections over the full hemisphere and for a set of regional domains. Composite states for the hemisphere obtained from nonstationary nonparametric cluster analysis reveal patterns consistent with a circumglobal wave 3 (polar)–wave 5 (subtropical) pattern, while regional composites reveal the Pacific South American pattern and blocking modes. The respective roles of potential vorticity sources, stationary Rossby waves and baroclinic instability on the dynamics of these circulation modes are shown to be reflected by the seasonal variations of the waveguides, where Rossby wave sources and baroclinic disturbances are largely contained within the waveguides and with little direct evidence of sustained remote tropical influences on persistent synoptic features. Warm surface temperature anomalies are strongly connected with regions of upper level divergence and anticyclonic Rossby wave sources. The persistent states identified reveal significant variability on interannual to decadal time scales with large secular trends identified in all sectors apart from a region close to South America.

Description: In this paper, aluminosilicate glass was prepared from blast furnace slag and quartz sand. Fourier transform infrared, differential scanning calorimetry and density measurements were carried out to investigate the effects of SiO 2 on the aluminosilicate glass network rigidity. The results indicate that glass structure would be enhanced if more SiO 2 was introduced into the glass system. Meanwhile, both the glass transition temperature ( T g ) and the glass crystallization temperature ( T c ) increase slightly; the increase in density of the glass being further evidence of the enhancement in glass network rigidity. Dielectric measurements show that the dielectric constant and dielectric loss decrease with more SiO 2 . The properties of the prepared aluminosilicate glasses are comparable to those of E glass, indicating that blast furnace slags are suitable for producing aluminosilicate glass with low dielectric constant and dielectric loss.

Description: The effect of inverting the Mo/Si ratio on the oxidation of two boron-containing alloys has been studied in air for temperatures 700–1400°C. The compositions of the alloys in atomic percent are Nb-25Cr-20Mo-15Si-15B, Nb-25Cr-20Mo-15Si-10B, Nb-25Cr-15Mo-20Si-10B, and Nb-25Cr-15Mo-20Si-15B hereafter referred to as 10B, 15B, 2010, and 2015 alloys, respectively. The as-cast microstructure of the alloys contains a mixture of NbCr 2 Laves phase, Nb 5 Si 3 silicide, and additionally Nb 3 Si silicide for the Mo/Si modified alloys. Primary oxides developed for all alloys are CrNbO 4 , Nb 2 O 5 , and SiO 2 . Improvements in high-temperature oxidation have been seen for the Mo/Si-modified 15B containing alloy under cyclic testing. Samples have shown similar oxidation responses in both long-term static and cyclic oxidation for 168-h exposures up to 1300°C. Characterization of oxide products was done by x-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy.

Description: The measurement of mechanical properties at the microscale is of interest across a wide range of engineering applications. Much recent work has demonstrated that micropillar compression can be used to measure changes in flow properties at temperatures up to 600°C. In this work, we demonstrate that an alternative microscale bend testing geometry can be used to measure elastic, plastic, and fracture behavior up to 770°C in silicon. We measure a Young’s modulus value of 130 GPa at room temperature, which is seen to drop with increasing temperature to ≈125 GPa. Below 500°C, no failure is seen up to elastic strains of 3%. At 530°C, the microcantilever fractures in a brittle fashion. At temperatures of 600°C and above plastic deformation is seen before brittle fracture. The yield stresses at these temperatures are in good agreement with literature values measured using micropillar compression.

Description: The microthermomechanical behavior of a precipitation-hardenable Ni-48Ti-25Pd (at.%) shape memory alloy has been investigated as a function of temperature. Micropillars were fabricated within a large 〈145〉-oriented grain and compressed in situ in the SEM at elevated temperatures corresponding to the martensite and austenite phase transformation temperatures. The precipitation-strengthened alloys exhibited stable pseudoelastic behavior with little or no residual strains when near the transformation temperatures. In the plastic regime, slip was observed to occur via pencil glide, circumventing the fine scale precipitates along multiple slip planes.

Description: The mean and variability of the Atlantic meridional overturning circulation (AMOC), as represented in six ocean reanalysis products, are analyzed over the period 1960–2007. Particular focus is on multi-decadal trends and interannual variability at 26.5°N and 45°N. For four of the six reanalysis products, corresponding reference simulations obtained from the same models and forcing datasets but without the imposition of subsurface data constraints are included for comparison. An emphasis is placed on identifying general characteristics of the reanalysis representation of AMOC relative to their reference simulations without subsurface data constraints. The AMOC as simulated in these two sets are presented in the context of results from the Coordinated Ocean-ice Reference Experiments phase II (CORE-II) effort, wherein a common interannually varying atmospheric forcing data set was used to force a large and diverse set of global ocean-ice models. Relative to the reference simulations and CORE-II forced model simulations it is shown that (1) the reanalysis products tend to have greater AMOC mean strength and enhanced variance and (2) the reanalysis products are less consistent in their year-to-year AMOC changes. We also find that relative to the reference simulations (but not the CORE-II forced model simulations) the reanalysis products tend to have enhanced multi-decadal trends (from 1975–1995 to 1995–2007) in the mid to high latitudes of the northern hemisphere.

Description: This study applies WACCM, a stratosphere-resolving model to dissect the stratospheric responses in the northern winter extratropics to the imposed ENSO-related SST anomalies in the tropics. It is found that the anomalously warmer and weaker stratospheric polar vortex during warm ENSO is basically a balance of the opposite effects between the SST anomalies in the tropical Pacific (TPO) and that over the tropical Indian Ocean basin (TIO). Specifically, the ENSO-related SST anomalies over the TIO are to induce an anomalously colder and stronger stratospheric polar vortex during warm ENSO, which acts to partially cancel out the much stronger warmer and weaker polar vortex response to the SST anomalies over the TPO. Further analysis indicates that, while the SST forcing from the TPO contributes to the anomalously positive Pacific North America (PNA) pattern in the troposphere and the enhancement of the stationary wavenumber (WN)-1 in the stratosphere during warm ENSO, the TIO SST forcing is to induce an anomalously negative PNA and a reduction of both WN-1 and WN-2 in the stratosphere. Diagnosis of E–P flux confirms that, the anomalously upward propagation of stationary waves in the extratropics mainly lies over the western coast of North America during warm ENSO, which is mainly associated with the TPO-induced positive PNA response and is partially suppressed by the effect of the accompanying TIO SST forcing.

Description: The study evaluated for the first time the ability of meteorological models of TIGGE to forecast the main features of the West African monsoon rainfall. Seven numerical models were retained over the 2008–2012 period and compared to satellite rainfall estimates. We focused on the seasonal cycle and in particular on the onset of the rainy season and on the intra-seasonal variability that are both of high importance for agriculture, water management and health sectors. We found that the seasonal latitudinal shift of the ITCZ is rather well predicted in terms of amplitude and timing by the different models although there is a systematic northward drift in the ITCZ latitude from the lead-times 1- to 10-day. Although the onset date of rainfall varies a lot according to the different definition in the literature, we also found good performance of TIGGE forecasts in predicting the onset date of the monsoon. The analysis of intra-seasonal variability revealed that the skill of TIGGE forecasts is decreasing with the lead-time from 1- to 15-day and the performance of the ensemble mean of all models overcomes the one of any individual models. Overall criteria used in this study (intra-seasonal fluctuations, onset and seasonal cycles), the skill of UKMO and ECMWF models is better than any other model. Based on such analysis it is likely than an ensemble mean based only on these two models would be more skillful than the ensemble mean based on the seven models. TIGGE forecasts represent a promising step towards the delivery of useful climate information to end-users of key sectors such as agriculture, water management, health and public safety.

Description: The link between interannual variability of seasonal rainfall over the Cape south coast of South Africa and different synoptic types as well as selected teleconnections is explored. Synoptic circulation over the region is classified into different synoptic types by employing a clustering technique, the self-organizing map (SOM), on daily circulation data for the 33-year period from 1979 to 2011. Daily rainfall data are used to investigate interannual variability of seasonal rainfall within the context of the identified synoptic types. The anomalous frequency of occurrence of the different synoptic types for wet and for dry seasons differs significantly within the SOM space, except for austral spring. The main rainfall-producing synoptic types are to a large extent consistent for wet and dry seasons. The main rainfall-producing synoptic types have a notable larger contribution to seasonal rainfall totals during wet seasons than during dry seasons, consistent with a higher frequency of occurrence of the main rainfall-producing synoptic types during wet seasons compared to dry seasons. Dry seasons are characterized by a smaller contribution to seasonal rainfall totals by all the different synoptic types, but with the largest negative anomalies associated with low frequencies of the main rainfall-producing synoptic types. The frequencies of occurrence of specific configurations of ridging high pressure systems, cut-off lows and tropical-temperate troughs associated with rainfall are positively linked to interannual variability of seasonal rainfall. It is also shown that the distribution of synoptic types within the SOM space is linked to the Southern Annular Mode and El Niño Southern Oscillation, implying some predictability of intraseasonal variability at the seasonal time scale.

Description: In order to study the interactions between the atmospheric circulations at the middle-high and low latitudes from the global perspective, the authors proposed the mathematical definition of three-pattern circulations, i.e., horizontal, meridional and zonal circulations with which the actual atmospheric circulation is expanded. This novel decomposition method is proved to accurately describe the actual atmospheric circulation dynamics. The authors used the NCEP/NCAR reanalysis data to calculate the climate characteristics of those three-pattern circulations, and found that the decomposition model agreed with the observed results. Further dynamical analysis indicates that the decomposition model is more accurate to capture the major features of global three dimensional atmospheric motions, compared to the traditional definitions of Rossby wave, Hadley circulation and Walker circulation. The decomposition model for the first time realized the decomposition of global atmospheric circulation using three orthogonal circulations within the horizontal, meridional and zonal planes, offering new opportunities to study the large-scale interactions between the middle-high latitudes and low latitudes circulations.

Description: We examined how coupled general circulation models (CGCMs) simulate changes in the jet stream differently under greenhouse warming, and how this inter-model diversity is related to the simulated Arctic climate changes by analyzing the simulation of the Coupled Model Intercomparison Project Phase 5. Although the jet stream in the multi-model ensemble mean shifts poleward, a considerable diversity exists among the 34 CGCMs. We found that inter-model differences in zonal wind responses, especially in terms of meridional shift of the midlatitude jet, are highly dependent on Arctic surface warming and lower stratospheric cooling. Specifically, the midlatitude jet tends to shift relatively equatorward (poleward) in the models with stronger (weaker) Arctic surface warming, whereas the jet tends to shift relatively poleward (equatorward) in the models with stronger (weaker) Arctic lower stratospheric cooling.

Description: This paper investigates the potential impact of “idealized-but-realistic” land cover degradation on the late twentieth century Sahel drought using a regional climate model (RCM) driven with lateral boundary conditions (LBCs) from three different sources, including one re-analysis data and two global climate models (GCMs). The impact of land cover degradation is quantified based on a large number of control-and-experiment pairs of simulations, where the experiment features a degraded land cover relative to the control. Two different approaches of experimental design are tested: in the 1st approach, the RCM land cover degradation experiment shares the same LBCs as the corresponding RCM control, which can be derived from either reanalysis data or a GCM; with the 2nd approach, the LBCs for the RCM control are derived from a GCM control, and the LBCs for the RCM land cover degradation experiment are derived from a corresponding GCM land cover degradation experiment. When the 1st approach is used, results from the RCM driven with the three different sources of LBCs are generally consistent with each other, indicating robustness of the model response against LBCs; when the 2nd approach is used, the RCM results show strong sensitivity to the source of LBCs and the response in the RCM is dominated by the response of the driving GCMs. The spatiotemporal pattern of the precipitation response to land cover degradation as simulated by RCM using the 1st approach closely resembles that of the observed historical changes, while results from the GCMs and the RCM using the 2nd approach bear less similarity to observations. Compared with the 1st approach, the 2nd approach has the advantage of capturing the impact on large scale circulation, but has the disadvantage of being influenced by the GCMs’ internal variability and any potential erroneous response of the driving GCMs to land degradation. The 2nd approach therefore requires a large ensemble to reduce the uncertainties derived from the driving GCMs. All RCM experiments based on the 1st approach produce a predominantly dry signal in West Africa throughout the year, with a dipole pattern found in the peak monsoon season that features a slight increase of precipitation over the Guinea Coast and strong decrease in the north; a similar spatiotemporal distribution is found for temperature changes, with warming (cooling) coinciding with precipitation decrease (increase). The model precipitation changes in West Africa are dominated by evapotranspiration changes in the north and by atmospheric moisture convergence changes in the south; in temperature changes, surface warming due to the decrease of evaporative cooling dominates over the albedo-induced radiative cooling.

Description: Clouds are an important regulator of climate due to their connection to the water balance of the atmosphere and their interaction with solar and infrared radiation. In this study, monthly total cloud cover (TCC) records from different sources have been inter-compared on annual and seasonal basis for the Mediterranean region and the period 1984–2005. Specifically, gridded databases from satellite projects (ISCCP, CLARA, PATMOS-x), from reanalysis products (ERA-Interim, MERRA), and from surface observations over land (EECRA) and ocean (ICOADS) have been examined. Then, simulations from 44 climate runs of the Coupled Model Intercomparison Project phase 5 corresponding to the historical scenario have been compared against the observations. Overall, we find good agreement between the mean values of TCC estimated from the three satellite products and from surface observations, while reanalysis products show much lower values across the region. Nevertheless, all datasets show similar behavior regarding the annual cycle of TCC. In addition, our results indicate an underestimation of TCC from climate model simulations as compared to the satellite products, especially during summertime, although the annual cycle is well simulated by most models. This result is quite general and apparently independent of the cloud parameterizations included in each particular model. Equally, similar results are obtained if the ISCCP simulator included in the Cloud Feedback Model Intercomparison Project Observation Simulator Package is considered, despite only few models provide the post-processed results. Finally, GCM projections of TCC over the Mediterranean are presented. These projections predict a reduction of TCC during the 21st century in the Mediterranean. Specifically, for an extreme emission scenario (RCP8.5) the projected relative rate of TCC decrease is larger than 10 % by the end of the century.

Description: Numerous reconstructions of tropical hydroclimate in the Pleistocene display substantial variability on precessional timescales. Precessionally-induced insolation variations, with a mean period of \({\sim }21{,}000\) years, affect the strength of the seasonal cycle, but not annual mean insolation. The existence of variations in annual mean climate on precessional timescales therefore hints at the existence of nonlinear mechanisms that rectify the zero annual mean forcing into a non-zero annual mean response. The aim of this study is to identify these nonlinear rectification mechanisms. The traditional view of precessionally-forced precipitation changes is that tropical precipitation increases with summer insolation. By comparing two simulations with an earth system model (CESM1.0.3) we find that this paradigm is true for continental but not for oceanic changes in precipitation. Focusing on the Atlantic intertropical convergence zone (ITCZ), we find that the continental temperature and precipitation response to precessional forcing are key rectifiers of annual mean precipitation over the ocean. A boundary layer response to temperature changes over northern Africa affects the meridional position of the ITCZ over the North Atlantic in boreal spring and summer, but not in fall and winter. Over the equatorial and South Atlantic, the intensity of precipitation is strongly impacted by diabatic forcing from the continents through an adjustment of the full troposphere. Although the top of atmosphere insolation forcing is seasonally symmetric, continental precipitation changes are largest in boreal summer, thus skewing the annual mean response. These results show that it is important to take into account the seasonality of climatic forcings, even when studying annual mean climate change.

Description: Numerous global warming studies show the anticipated increase in mean precipitation with the rising levels of carbon dioxide concentration. However, apart from the changes in mean precipitation, the finer details of daily precipitation distribution, such as its intensity and frequency (so called daily rainfall extremes), need to be accounted for while determining the impacts of climate changes in future precipitation regimes. Here we examine the climate model projections from a large set of Coupled Model Inter-comparison Project 5 models, to assess these future aspects of rainfall distribution over Asian summer monsoon (ASM) region. Our assessment unravels a north–south rainfall dipole pattern, with increased rainfall over Indian subcontinent extending into the western Pacific region (north ASM region, NASM) and decreased rainfall over equatorial oceanic convergence zone over eastern Indian Ocean region (south ASM region, SASM). This robust future pattern is well conspicuous at both seasonal and sub-seasonal time scales. Subsequent analysis, using daily rainfall events defined using percentile thresholds, demonstrates that mean rainfall changes over NASM region are mainly associated with more intense and more frequent extreme rainfall events (i.e. above 95th percentile). The inference is that there are significant future changes in rainfall probability distributions and not only a uniform shift in the mean rainfall over the NASM region. Rainfall suppression over SASM seems to be associated with changes involving multiple rainfall events and shows a larger model spread, thus making its interpretation more complex compared to NASM. Moisture budget diagnostics generally show that the low-level moisture convergence, due to stronger increase of water vapour in the atmosphere, acts positively to future rainfall changes, especially for heaviest rainfall events. However, it seems that the dynamic component of moisture convergence, associated with vertical motion, shows a strong spatial and rainfall category dependency, sometimes offsetting the effect of the water vapour increase. Additionally, we found that the moisture convergence is mainly dominated by the climatological vertical motion acting on the humidity changes and the interplay between all these processes proves to play a pivotal role for regulating the intensities of various rainfall events in the two domains.

Description: Using a novel Lagrangian approach, we assess the relative roles of the atmosphere and ocean in setting interannual variability in western European wintertime temperatures. We compute sensible and latent heat fluxes along atmospheric particle trajectories backtracked in time from four western European cities, using a Lagrangian atmospheric dispersion model driven with meteorological reanalysis data. The material time rate of change in potential temperature and the surface turbulent fluxes computed along the trajectory show a high degree of correlation, revealing a dominant control of ocean–atmosphere heat and moisture exchange in setting heat flux variability for atmospheric particles en route to western Europe. We conduct six idealised simulations in which one or more aspects of the climate system is held constant at climatological values and these idealised simulations are compared with a control simulation, in which all components of the climate system vary realistically. The results from these idealised simulations suggest that knowledge of atmospheric pathways is essential for reconstructing the interannual variability in heat flux and western European wintertime temperature, and that variability in these trajectories alone is sufficient to explain at least half of the internannual flux variability. Our idealised simulations also expose an important role for sea surface temperature in setting decadal scale variability of air–sea heat fluxes along the Lagrangian pathways. These results are consistent with previous studies showing that air–sea heat flux variability is driven by the atmosphere on interannual time scales over much of the North Atlantic, whereas the SST plays a leading role on longer time scales. Of particular interest is that the atmospheric control holds for the integrated fluxes along 10-day back trajectories from western Europe on an interannual time scale, despite that many of these trajectories pass over the Gulf Stream and its North Atlantic Current extension, regions where ocean dynamics influence air–sea heat exchange even on a very short time scale.

Description: Atmospheric model uncertainties at a seasonal time scale can be addressed by introducing stochastic perturbations in the model formulation. In this paper the stochastically perturbed parameterization tendencies (SPPT) technique is activated in the atmospheric component of the EC-Earth global coupled model and the impact on seasonal forecast quality is assessed, both at a global scale and focusing on the Tropical Pacific region. Re-forecasts for winter and summer seasons using two different settings for the perturbation patterns are evaluated and compared to a reference experiment without stochastic perturbations. We find that SPPT tends to increase the systematic error of the model sea-surface temperature over most regions of the globe, whereas the impact on precipitation and sea-level pressure is less clear. In terms of ensemble spread, larger-scale perturbation patterns lead to a greater increase in spread and in the model spread-skill ratio in a system that is overconfident. Over the Tropical Pacific, improvements in the representation of key processes associated with ENSO are highlighted. The evaluation of probabilistic re-forecasts shows that SPPT improves their reliability. Finally, we discuss the limitations to this study and future prospects with EC-Earth.

Description: Teleconnections originated by anomalous heat sources over the tropical Indo-Pacific oceans are investigated in this paper comparing observational results with numerical simulations run as part of the re-forecast set for the latest ECMWF seasonal forecasting system (System 4). We show that the traditional methodology of linearly relating circulation anomalies to SST anomalies, while appropriate for signals originated in central and east Pacific, fails to adequately identify the response to anomalous heating over the west Pacific and most of the Indian Ocean, because of the relatively weak (or even negative) correlation between SST and rainfall anomalies in these regions. Instead, if teleconnections are computed from covariances with rainfall anomalies, a stronger consistency is found between observed and modelled patterns, as well as between diagnostics derived from seasonal and intra-seasonal time scales. The main mode of inter-annual variability in Indo-Pacific rainfall associated with planetary-scale teleconnections is a tri-polar structure with two positively correlated centres in the western Indian Ocean and the central Pacific, and a third centre around the maritime continents which is anti-correlated with the other two. In the extratropical response, positive rainfall anomalies over the western and central Indian Ocean (WCIO) are connected with a negative height anomaly centred over Alaska and a positive North Atlantic oscillation (NAO) signal, in a way reminiscent of the Cold-Ocean–Warm-Land pattern. This teleconnection cannot be explained by the ENSO-forced component of Indian Ocean rainfall, and is in phase with signals associated with the Madden–Julian oscillation. Results from the System-4 re-forecasts show that the ECMWF coupled model reproduces the broad features of tropical and extratropical teleconnections with a good degree of fidelity. However, the model significantly over-estimates the correlation between rainfall anomalies in the WCIO with those over the western and central Pacific. The impact of this deficiency on the extratropical flow is to weaken the relationship between the NAO and Indian Ocean rainfall on the seasonal scale, and to affect the projection of the ENSO response on the NAO. Finally, we argue that reproducing the correct relationship between SST and rainfall anomalies in different part of the Indo-Pacific basin is also crucial for the correct simulation of inter-decadal variability. Particular care should be taken in interpreting results of AGCM simulations with prescribed SST, where the absence of feedbacks between convection and SST over the warm pool region affects the simulation of rainfall anomalies.