bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring probability distribution functions best-fitting the kinetic energy of coarse particles at above threshold flow conditions
Authors: Farhadi Hamed , Valyrakis Manousos
Published: March 2021

Applying an instrumented particle [1-3], the probability density functions of kinetic energy of a coarse particle (at different solid densities) mobilised over a range of above threshold flow conditions conditions corresponding to the intermittent transport regime, were explored. The experiments were conducted in the Water Engineering Lab at the University of Glasgow on a tilting recirculating flume with 800 (length) × 90 (width) cm dimension. Twelve different flow conditions corresponding to intermittent transport regime for the range of particle densities examined herein, have been implemented in this research. Ensuring fully developed flow conditions, the start of the test section was located at 3.2 meters upstream of the flume outlet. The bed surface of the flume is flat and made up of well-packed glass beads of 16.2 mm diameter, offering a uniform roughness over which the instrumented particle is transported. MEMS sensors are embedded within the instrumented particle with 3-axis gyroscope and 3-axis accelerometer. At the beginning of each experimental run, instrumented particle is placed at the upstream of the test section, fully exposed to the free stream flow. Its motion is recorded with top and side cameras to enable a deeper understanding of particle transport processes. Using results from sets of instrumented particle transport experiments with varying flow rates and particle densities, the probability distribution functions (PDFs) of the instrumented particles kinetic energy, were generated. The best-fitted PDFs were selected by applying the Kolmogorov-Smirnov test and the results were discussed considering the light of the recent literature of the particle velocity distributions.

[1] Valyrakis, M.; Alexakis, A. Development of a “smart-pebble” for tracking sediment transport. In Proceedings of the International Conference on Fluvial Hydraulics (River Flow 2016), St. Louis, MO, USA, 12–15 July 2016.

[2] Al-Obaidi, K., Xu, Y. & Valyrakis, M. 2020, The Design and Calibration of Instrumented Particles for Assessing Water Infrastructure Hazards, Journal of Sensors and Actuator Networks, vol. 9, no. 3, 36.

[3] Al-Obaidi, K. & Valyrakis, M. 2020, Asensory instrumented particle for environmental monitoring applications: development and calibration, IEEE sensors journal (accepted).
Practitioners can’t agree on what Nature Based Solutions for flood management is: Why this matters and how to respond
Authors: Wingfield Thea , Macdonald Neil , Peters Kimberley
Published: March 2021

Nature Based Solutions (NBS) is a practice based approach developed in response to the global challenge of on-going environmental degradation and biodiversity loss. Interventions that restore or mimic hydrological processes to slow water within a catchment come under an umbrella term of NBS for flood management. Proponents of the practice link its use as beneficial in reducing flood risk but also climate change adaptation, urban hazard management, sustainable agriculture and eco-hydrology. Despite promising an integrated and sustainable future and receiving policy support, catchment scale adoption is limited. Understanding, designing and delivering NBS flood management is complex, crossing multiple disciplinary divides and practitioner communities, each with its own history, background, methods and uncertainties. Barriers and intervention points within the delivery system has received little investigation from the view of environmental professional practice. This research addressed this gap through participatory case studies of projects delivering NBS in England. We found low agreement amongst practitioners on how NBS for flood management is distinguished, resulting in differing perspectives on its identity and contested boundaries between it and other land and water interventions. Our transdisciplinary research project sought and generated a context for delivery that breaks down disciplinary boundaries and in doing so a new system and intervention point emerged. The problem that practitioners used NBS for flood management to address is a homogenised water cycle: reduced infiltration and increased surface runoff. Therefore NBS for flood management aims to reverse this by restoring catchment hydrodiversity in harnessing hydrological processes for integrated sustainable urban and catchment management. The implications for academic thinking and land and water management practice created by the novel conceptualisation of a catchment possessing an attribute of hydrodiversity is far reaching. In relation to supporting NBS for flood management mainstream adoption: the conceptualisation draws together different land use systems and a shared goal to deliver catchment hydrodiversity emerges enabling coordinated flood management at multiple spatial scales and across professional practice and disciplinary groups.
A New Mathematical Framework for Atmospheric Blocking Events
Authors: Lucarini Valerio
Published: March 2021

We use a simple yet Earth-like atmospheric model to propose a new framework for understanding the mathematics of blocking events, which are associated with low frequency, large scale waves in the atmosphere. Analysing error growth rates along a very long model trajectory, we show that blockings are associated with conditions of anomalously high instability of the atmosphere. Additionally, the lifetime of a blocking is positively correlated with the intensity of such an anomaly, against intuition. In the case of Atlantic blockings, predictability is especially reduced at the onset and decay of the blocking, while a relative increase of predictability is found in the mature phase, while the opposite holds for Pacific blockings, for which predictability is lowest in the mature phase. We associate blockings to a specific class of unstable periodic orbits (UPOs), natural modes of variability that cover the attractor of the system. The UPOs differ substantially in terms of instability, which explains the diversity of the atmosphere in terms predictability. The UPOs associated to blockings are indeed anomalously unstable, which leads to them being rarely visited. The onset of a blocking takes place when the trajectory of the system hops into the neighbourhood of one of these special UPOs. The decay takes place when the trajectory hops back to the neighbourhood of usual, less unstable UPOs associated with zonal flow. This justifies the classical Markov chains-based analysis of transitions between weather regimes. The existence of UPOs differing in the dimensionality of their unstable manifold indicates a very strong violation of hyperbolicity in the model, which leads to a lack of structural stability. We propose that this is could be a generic feature of atmospheric models and might be a fundamental cause behind difficulties in representing blockings for the current climate and uncertainties in predicting how their statistics will change as a result of climate change.

References:
V. Lucarini, A. Gritsun, A. A new mathematical framework for atmospheric blocking events. Climate Dynamics 54, 575–598 (2020). https://doi.org/10.1007/s00382-019-05018-2
M. Ghil, V. Lucarini, The Physics of Climate Variability and Climate, Rev. Modern Physics, 92, 035002 (2020). https://link.aps.org/doi/10.1103/RevModPhys.92.035002  
S. Schubert, V. Lucarini, Dynamical analysis of blocking events: spatial and temporal fluctuations of covariant Lyapunov vectors. Q. J. R. Meteorol. Soc. 142, 2143-2158 (2016). https://doi.org/10.1002/qj.2808
The role of multi-sensor remote sensing for drought characterization: challenges and opportunities
Authors: Wang Lixin , Jiao Wenzhe , McCabe Matthew
Published: March 2021

Satellite based remote sensing plays important role in studying regional to continental scale drought. One of the unique elements of remote sensing platforms is their multi-sensor capabilities, which enhance the capacity for characterizing drought from a variety of aspects. However, multi-sensor integrated drought evaluation is in its infancy. To advocate and encourage on-going exploration and integration of multi-sensor remote sensing for drought studies, we provide an overview of the role of multi-sensor remote sensing for addressing knowledge gaps and driving advances in drought studies. We first present a comprehensive summary of large-scale drought-related remote sensing datasets that can be used for multi-sensor drought studies. Then we provide a detailed review of how the integrated multi-sensor remote sensing could enhance our analysis in multiple important drought related phenomena and mechanisms such as drought-induced tree mortality, drought-related ecosystem fires, post-drought recovery and legacy effects, flash drought, and drought trends under climate change. We also provide a summary of recent modeling advances towards developing integrated multi-sensor remote sensing drought indices. We highlight that leveraging multi-sensor remote sensing provides unique benefits for regional to global drought studies, particularly in: 1) revealing the complex drought impact mechanisms on various ecosystem components; 2) providing continuous long-term drought related information at large scales; 3) presenting real-time drought information with high spatiotemporal resolution; 4) providing multiple lines of evidence of drought monitoring to improve modeling and prediction robustness; and 5) improving the accuracy of drought monitoring and assessment efforts.
Using fossilised pigments to understand cyanobacterial blooms in New Zealand lakes
Authors: Puddick Jonathan , Page Carrie , Romanazzi Donato , Gunning Katie , Howarth Jamie , Moody Adelaine , Dahl Jenny , Li Xun , Naeher Sebastian , Reyes Lizette , Shepherd Claire , Vandergoes Marcus , Wood Susie
Published: March 2021

Phytoplankton (including cyanobacteria) are a natural component of lake ecosystems and are the base of many food webs. However, changes in the lake catchment, the lake itself and the wider environment (e.g., climate change) can alter the composition of phytoplankton communities. Of recent concern is the increase in the abundance of cyanobacteria and the formation of blooms in many of New Zealand’s low-land lakes (>30% of those that are monitored). Because regular monitoring data does not stretch back more than 10-30 years and many lakes are not regularly monitored, it is difficult to ascertain whether the intensity of present-day blooms are a new phenomenon or are part of a pre-existing cycle. The pigments produced by cyanobacteria (and other phytoplankton) are deposited in lake sediment and can be extracted from sediment cores and surface sediment samples. Analysis of these pigments by high-performance liquid chromatography has allowed us to reconstruct the historical phytoplankton community from nine New Zealand lakes and to track the emergence of cyanobacteria in impacted lakes. We will present data on the performance of different cyanobacteria pigment indicators and several case studies to demonstrate how fossilised pigment data can be used to understand shifts in lake phytoplankton communities.
The evolution of complex Es observed by multi instruments over low-latitude China
Authors: Sun Wenjie , Ning Baiqi , Hu Lianhuan , Zhao Xiukuan , Li Guozhu
Published: March 2021

Early and recent observations suggested that E-region field aligned irregularities (FAIs) related closely to the sporadic E (Es) layer of the ionosphere. The Sanya (18.3 ºN, 109.6 ºE) very high frequency (VHF) radar can operate at ionospheric irregularities mode for the detection of 3-m scale FAIs. The development of a portable digital ionosonde (PDI) which is collocated with the Sanya VHF radar can operate with temporal periods down to 1 minute, facilitating the capability of capturing the fast evolution of Es structures. But the low spatial resolution of the two kinds of instruments makes it difficult to depict the horizontal morphology of the Es structures and E-region FAIs. Since the capability of ground-based GNSS in strong Es detection was presented, it serves as a perfect supplement for the investigation of E region of the ionosphere. So comprehensive observation with multi kinds of instruments makes it possible to reveal the relationship and mechanisms of Es and E-region FAIs.

A complex daytime sporadic E (Es) case with extremely high critical frequency (foEs) was observed over the low latitude of China on 19 May 2018. Simultaneous observational results from two very high frequency (VHF) radars, two ionosondes, and multiple Global Navigation Satellite System total electron content and scintillation receivers are analyzed to investigate the evolution of the complex Es occurrence, which consisted of a relatively weak ambient Es layer (foEs < 8 MHz) and band-like strong Es structures (foEs > 17 MHz) drifting from higher latitude. The strong Es structures elongated more than 500 km in the northwest-southeast direction, drifted southwestward at a speed of ~65 m/s. VHF radar backscatter echoes were generated when the strong Es structures passed the radar field of view, with different echo patterns due to different radar and antenna configurations. No VHF radar backscatter echo was associated with the ambient Es layer.
Comparison of climate response to marine cloud brightening and ocean albedo modification: A model study
Authors: Zhao Mengying , Cao Long , Duan Lei , Bala Govindasamy , Caldeira Ken
Published: March 2021

Solar radiation modification (SRM), an artificial intervention to reduce the amount of solar radiation reaching the surface, has been proposed as a potential option to ameliorate some undesired consequences of global warming. Marine cloud brightening (MCB) and ocean albedo modification (OAM) are two proposed SRM approaches. MCB aims to cool the planet by increasing marine cloud albedo that might be achieved by injecting sea salt into low marine cloud.  OAM aims to cool the planet by increasing surface ocean albedo that might be achieved by using highly reflective microbubbles over ocean. There is speculation that climate effect of OAM and MCB would be similar as forcing is applied only over ocean in both cases.

In this study, we use NCAR CESM model to compare climate response in  these two SRM approaches under the framework of “fast versus slow response”. The term “fast” refers to climate adjustment that is associated with rapid adjustment of the atmosphere and land surface, and “slow” refers to climate feedbacks that are associated with the slow evolution of sea surface temperature.

In our simulation we find that to offset global warming from a doubling of atmospheric CO2, OAM requires a stronger negative effective radiative forcing than that of MCB, indicating MCB is more effective in producing cooling per unit of radiative forcing. This is mainly associated with differing fast climate adjustment between OAM and MCB forcing. OAM increases upward shortwave radiation from surface and heats the lower atmosphere, causing low-level clouds to dissipate. A reduction in low cloudiness allows more solar radiation to reach the surface, partly offsetting the negative radiative forcing from increase in ocean albedo. At equilibrium state, however, OAM and MCB produces similar pattern of change in temperature and hydrological cycle, but prominent differences in climate response is observed over the tropical ocean where OAM produces larger reduction in precipitation and evaporation than that of MCB. Our results indicate that there is similarity between climate response to marine cloud brightening and ocean albedo increase, but caution should be exercised when using climate response from one to infer the other. 
Localized megathrust slip controlled by metasomatic reactions in subduction mélanges
Authors: Ujiie Kohtaro , Noro Kazuya , Shigematsu Norio , Fagereng Åke , Nishiyama Naoki , Tulley Christopher , Masuyama Haruna
Published: March 2021

Aseismic megathrust slip down-dip of the seismogenic zone is accommodated by either steady creep or episodic slow slip events (SSEs). However, the geological conditions defining the rheology of megathrust slip remain elusive. Here, we show that subduction mélanges deformed at ~370–500 °C in warm-slab environments record fluid release and viscous shear localization associated with metasomatic reactions between juxtaposed metapelitic and metabasaltic rocks. Metasomatic reactions induced albitization of metapelite, resulting in depth-dependent rheological behavior. In a mélange deformed at ~370 °C, near the down-dip limit of the seismogenic zone, very fine-grained metasomatic albite facilitated grain boundary diffusion creep at stresses less than those in the surrounding metapelite and metabasalt, contributing to an overall decreased megathrust strength. In a mélange deformed at ~500 °C, near the mantle wedge corner, metasomatic reactions led to brittle fracturing, albite grain growth, and incorporation of strengthened albitized metapelite blocks into a chlorite-actinolite matrix deforming at locally elevated strain rate of ~10-10 s-1. We suggest that metasomatic reactions facilitate localized changes in megathrust slip mode with depth, potentially providing a mechanism for change from viscous creep to SSEs with tremor.
Determining the height of Mount Everest using the shallow layer method
Authors: Xie Youchao , Shen Wenbin , Han Jiancheng , Deng Xiaole
Published: March 2021

We proposed an alternative method to determine the height of Mount Everest (HME) based on the shallow layer method (SLM), which was put forward by Shen (2006). We use the precise external global Earth gravity field model (i.e., EGM2008 and EIGEN-6C4 models) as input information, and the digital topographic model (i.e., DTM2006.0) and crust models (i.e., CRUST2.0 and CRUST1.0 models) to construct the shallow layer model. There are four combined strategies：(1) EGM2008 and CRUST1.0 models, (2) EGM2008 and CRUST2.0 models, (3) EIGEN-6C4 and CRUST1.0 models, and (4) EIGEN-6C4 and CRUST2.0 models, respectively. We calculate the HME by two approaches: first approach, the HME is directly calculated by combining the geoid undulation (N) and geodetic height (h); second approach, we calculate the HME by the segment summation approach (SSA) using the gravity field inside the shallow layer determined by the SLM. Numerical results show that for four combined strategies, the differences between our results and the authoritatively released value 8848.86 m by the Chinese and Nepalese governments on December 8, 2020 are 0.448 m, -0.009 m, -0.295 m, and -0.741 m using first approach and 0.539 m, 0.083 m, -0.214 m, and -0.647 m using second approach. The combined calculation of the HME by the terrain model and gravity field model is more accurate than that by the gravity field model alone. This study is supported by the National Natural Science Foundations of China (NSFC) under Grants 42030105, 41721003, 41804012, 41631072, 41874023, Space Station Project (2020)228.
Mn(II) carbonate authigenesis marks the benthic SMTZ and is fueled by Mn-driven anaerobic oxidation of methane: A Black Sea evidence
Authors: Sun Tiantian , Böttcher Michael E , Kallmeyer Jens , Treude Tina , Lipka Marko , Schmiedinger Iris , Eckert Sebastian , Wehausen Rolf , Jørgensen Bo B , Martinez-Ruiz Francisca
Published: March 2021

In the Black Sea, sediment cores covering the last brackish-limnic transition were recovered and investigated for anaerobic biogeochemical processes controlling sulfur, carbon, and metal cycling. The development of a sulfate-methane transition zone (SMTZ) is nowadays found below the brackish zone in the limnic part of the sediments that limits the upward migration of biogenic methane into surface sediments and the water column. The position of the SMTZ may have changed in the past due to dynamic fluxes of dissolved species in the pore water. Besides dissolved sulfate, metal-bearing minerals have been shown to serve as potential reactants, also converting CH4 into dissolved inorganic carbon (DIC). The pore water and sediment stable isotope (C, S, O) and geochemical composition were investigated, as well as in-situ microbial rates of sulfate reduction and total anaerobic oxidation of CH4 (AOM) obtained from sediment incubations for the identification of a potential contribution of manganese-bearing minerals to AOM in the limnic part of the sediments (Mn-AOM). In the limnic Black Sea sediments Mn-AOM is causes an upward flux of dissolved Mn whereas intense SO4-AOM located in shalower sediments leads to an increase in pH and a maximum in DIC concentrations in the SMTZ. The resulting change in saturation states leads to the precipitation of mixed MnCa-carbonate solid-solutions (‘rhodochrozitization front’) and the development of a zone enriched in excess sedimentary Mn(II). We further argue that these authigenic fronts may survive changes in pore water composition and are stable in the anoxic sedimentary record, marking the position of paleo-SMTZs. The persisting formation of this geochemical marker has advantage in application over the transient development of a sulfidization front of metastable mackinawite, that is fromed by the reaction of downard migrating sulfide with upward diffusing Fe(II), originating from SO4-AOM and Fe-AOM, respectively.
Late-Holocene climate variability of coastal East Asia reconstructed from the Yongneup fen in central Korea
Authors: Park Jinheum , Jin Qiuhong , Choi Jieun , Park Jungjae
Published: March 2021

This study presents a reconstruction of climate change in central Korea during the last 3,000 years, using a core from a montane peatland of Yongneup. Multiple proxies of pollen, macrocharcoal, and geochemistry were analysed to provide three findings as follows: First, abrupt climate events at ca. 2.8 and 2.3 ka BP possibly accompanied dry summer as well as cold and arid winter seasons on the Korean peninsula. The first macrocharcoal analysis on the peninsula indicates increased wildfire activities during these dry periods. Next, a weakening of summer monsoon during El Niño-like phases was clearly found during the late Holocene. This confirms previous findings of a dominant oceanic influence on hydroclimate variability on the Korean peninsula. Finally, changes in temperature were likely synchronous with a global trend, indicated by the total organic content (TOC) and arboreal pollen percentages. Due to its location at a high-altitude, the environment of Yongneup has possibly sensitively responded to fluctuations in temperature. Altogether, these findings suggest that temperature and precipitation changes on the Korean peninsula have been separately influenced by insolation and oceanic circulations, respectively.
Long-Range Predictability of the Length of Day and Extratropical Climate.
Authors: Scaife Adam , Hermanson Leon , van Niekerk Annelize , Baldwin Mark , Belcher Stephen , Bett Philip , Comer Ruth , Dunstone Nick , Geen Ruth , Hardiman Steven , Ineson Sarah , Knight Jeff , Nie Yu , Ren Hongli , Doug Smith
Published: March 2021

Angular momentum is fundamental to the structure and variability of the atmosphere and hence regional weather and climate. Total atmospheric angular momentum (AAM) is also directly related to the rotation rate of the Earth and hence the length of day. However, the long-range predictability of fluctuations in the length of day, atmospheric angular momentum and the implications for climate prediction are unknown. Here we show that fluctuations in AAM and the length of day are predictable out to more than a year ahead and that this provides an atmospheric source of long-range predictability of surface climate. Using ensemble forecasts from a dynamical climate model we demonstrate predictable signals in the atmospheric angular momentum field that propagate slowly and coherently polewards into the northern and southern hemisphere due to wave-mean flow interaction within the atmosphere. These predictable signals are also shown to precede changes in extratropical surface climate via the North Atlantic Oscillation. These results provide a novel source of long-range predictability of climate from within the atmosphere, greatly extend the lead time for length of day predictions and link geodesy with climate variability.
Timescale-dependent stability of surface air temperature and the forced temperature response
Authors: Ellerhoff Beatrice , Rehfeld Kira
Published: March 2021

Earth's climate can be understood as a dynamical system that changes due to external forcing and internal couplings. It can be characterized from the evolution of essential climate variables, such as surface air temperature. Yet, the mechanisms, amplitudes, and spatiotemporal patterns of global and local temperature fluctuations around its mean, called temperature variability, are insufficiently understood. Discrepancies exist between temperature variability from model and paleoclimate data at the temporal scale of years to centuries and at the local scale, both of which are important socio-economic scales for long-term planning.
Here, we clarify whether global and local temperature signals from the last millennia show a stationary variance on these timescales and thus behave in a stable manner or not. Therefore, we contrast power spectral densities and their scaling behaviors using simulated, observed, and reconstructed temperatures on periods between 10 and 200 years. Despite careful consideration of possible spectral biases, we find that local temperatures from paleoclimate data tend to show unstable behavior, while simulated temperatures almost exclusively show stable behavior. Conversely, the global mean temperature tends to be stable. We explain this by introducing the gain as a powerful tool to analyze the forced temperature response, based on a novel estimate of the joint power spectrum of radiative forcing.
Our analysis identifies main deficiencies in the properties of temperature variability and offers new insights into the linkage between raditative forcing and temperature response, relevant to the understanding of Earth’s dynamics and the assessment of climate risks.
Particle-size distribution of transported sediment in the Pisha sandstone slope under the influence of complex erosion
Authors: Zhang Pan , Xiao pingqing
Published: March 2021

Coarse sediment of the Yellow River in the complex erosion area of the Pisha sandstone region of the Ordos Plateau is deposited on the downstream riverbed, posing a threat to the flood control safety of the river. The study of sediment particles in this erosion process can deepen the understanding of the erosion process, provide a theoretical basis for the establishment of an erosion prediction model, reveal the internal law of composite erosion, and guide the planning and design of soil and water conservation and the allocation of soil and water conservation measures. In this study, complex erosion indoor tests were carried out through the artificial rainfall-wind-freezing-thawing cycle solid model. The enrichment rate (ER), fractal dimension, and median diameter (d50) of soil particles were used to quantify the size distribution characteristics of sediment particles under different erosion dynamics. The coarse sediment was first transported in the process of soil erosion because of the special texture and terrain characteristics of Pisha sandstone soil. Moreover, the degree of heterogeneity of sediment under complex erosion was larger than that under water erosion. The effect of wind could aggravate the instability of the erosion dynamic system. Under the combined action of freezing-thawing, wind, and water, the particle size composition changed greatly, and the erosion energy was extremely unstable. The effect of complex erosion created conditions for the coarse sediment transportation. Under the freezing-thawing-wind-water combined action, the particle size of eroded sediment was the coarsest, and that of water erosion was the smallest. We concluded that the reason why the Pisha sandstone area has become the core area of the concentrated source of coarse sediment in the Yellow River is related not only to the special nature of the Pisha sandstone soil itself but also to the effect of complex erosion.
Novel method for determining 234U-238U ages of Devils Hole 2 cave calcite (Nevada)
Authors: Li Xianglei , Wendt Kathleen A. , Dublyansky Yuri , Moseley Gina E. , Spötl Christoph , Edwards R. Lawrence
Published: March 2021

Uranium-uranium (234U-238U) disequilibrium dating can determine the age of secondary carbonates over greater time intervals than the well-established 230Th-234U dating method. Yet it is rarely applied due to unknowns in the initial d234U (d234Ui) value, which result in significant age uncertainties. In order to understand the d234Ui in Devils Hole 2 cave, Nevada, we have determined 110 d234Ui values from phreatic calcite using 230Th-234U disequilibrium dating. The sampled calcite was deposited in Devils Hole 2 between 4 and 590 ka, providing a long-term look at d234Ui variability over time. We then performed multi-linear regression among the d234Ui values and correlative d18O and d13C values. The regression can be used to estimate the d234Ui value of Devils Hole calcite based upon its measured d18O and d13C values. Using this approach and the measured present-day d234U values of Devils Hole 2 calcite, we calculated 110 independent 234U-238U ages. In addition, we used newly measured d18O, d13C, and present-day d234U values to calculate 10 234U-238U ages that range between 676 and 731 ka, thus allowing us to extend the Devils Hole chronology beyond the 230Th-234U-dated chronology while maintaining an age precision of ~2 %. Our results indicate that calcite deposition at Devils Hole 2 cave began no later than 736 ± 11 kyr ago. The novel method presented here may be applied to future speleothem studies in similar hydrogeological settings, given appropriate calibration studies.
Projecting Global Mean Sea-Level Change Using CMIP6 Models
Authors: Hermans Tim , Gregory Jonathan , Palmer Matthew , Ringer Mark , Katsman Caroline , Slangen Aimée
Published: March 2021

The effective climate sensitivity (EffCS) of models in the Coupled Model Intercomparison Project 6 (CMIP6) has increased relative to CMIP5. Consequently, using CMIP6 models tends to lead to larger projections of global mean surface air temperature (GSAT) increase for a given emissions scenario. The effect of increased EffCS on projections of global mean sea-level (GMSL) change however, has so far only been studied using a reduced complexity model. Here, we explore the implications of increased EffCS in CMIP6 models for GMSL change projections in 2100 for three emissions scenarios: SSP5-8.5, SSP2-4.5 and SSP1-2.6.

Whereas CMIP6 projections of GSAT change are substantially higher than in CMIP5, projections of global mean thermal expansion (GTE) are only slightly higher. We use these projections as input to construct projections of GMSL change, using the Monte Carlo approach of IPCC AR5. Isolating the impact of the CMIP6 simulations using consistent methods is an important step to ensure traceability to past IPCC projections of global and regional sea-level change. The resulting 95th percentile of projected GMSL change at 2100 is only 3-7 cm higher for CMIP6 than for CMIP5, depending on the emissions scenario. Projected rates of GMSL rise around 2100 increase more strongly from CMIP5 to CMIP6, though, implying more pronounced differences beyond 2100 and greater committed sea-level rise. GMSL change in 2100 is accurately predicted by time-integrated temperature change and therefore mitigation requires early reduction of emissions.

We also find that the 95th percentile projections based on individual CMIP6 models can differ as much as 51 cm and that the 5-95% range of projected GMSL change for individual CMIP6 models can be substantially outside of the 5-95% range of the CMIP6 multi-model ensemble. Thus, through subsetting the CMIP6 ensemble using EffCS, a choice can be made between characterizing the central part of the probability distribution and more comprehensively sampling the high end of the GMSL projection space, which is relevant to risk-averse stakeholders. Our results show this may substantially alter ensemble projections, underlining the need to constrain EffCS in global climate models in order to reduce uncertainty in sea-level projections.
Suitable geochemical markers to determine tsunami impact - an approach on coastal areas in Northern Japan
Authors: Frenken Mike , Bellanova Piero , Nishimura Yuichi , Reicherter Klaus , Schwarzbauer Jan
Published: March 2021

The 2011 Tohoku-oki tsunami had a destructive effect and impact on the coast of Japan. Coinciding with the inundation of vast coastal areas, the catastrophic event released many pollutants from damaged facilities but also remobilized sediment-bound residues. These environmental and depositional variations left a distinct signature in the sediment, both sedimentologically and geochemically.

A wide variety of organic geochemical substances were detected in the sampled sediment profiles in Northern Japan (Misawa harbor, Futakawame and Oirase). Some compounds reflect the 2011 tsunami’s impact and may serve as possible indicators for further investigation of the inundation and backwash, sediment and pollutant distribution, and the preservation. For comparability, the tsunami samples and the respective over- and underlying layers (topsoil & soil) were analyzed.

The selected compound groups differentiated the tsunami layer from the non-affected layers. Natural compounds, relocated by the tsunami, revealed an enrichment of short-chained n-alkanes as expressed by the terrigenous/aquatic ratio (TAR) and locally accumulated n-aldehydes pointing to an intensive mixing of marine and terrestrial material. Petrogenic pollutants, for instance hopanes, steranes, and polycyclic aromatic hydrocarbons (PAHs), illustrate a higher load in tsunami sediments as the result of damage of harbor facilities. Sewage-related compounds, such as linear alkylbenzene (LABs) and diisopropylnaphthalene (DIPN), were also enriched in the tsunami samples in contrast to the surrounding sites. Another compound group enriched in the tsunami deposits, are chlorinated pollution burdens by the backwash, such as DDX and polychlorinated biphenyls (PCBs), remobilized by erosion dominantly.

The different environmental- and pollution-related compounds illustrate the suitability of geochemical markers as indicators to assess tsunami impact in 2011 Tohoku-oki tsunami affected sediments of Misawa harbor, Futakawame and Oirase in Northern Japan.
Impact of urban emission on local and regional air-quality: investigating the role of the urban canopy meteorological forcing
Authors: Huszar Peter , Karlicky Jan , Markova Jana , Novakova Tereza , Liaskoni Marina , Bartik Lukas , Belda Michal
Published: March 2021

Urban canopies impact the meteorological conditions in the planetary boundary layer (PBL) and above in many ways: apart from urban heat island effect, the urban breeze circulation can form. Further, the enhanced drag causes intensification of the turbulent diffusion leading to elevated PBL height and this drag, at the same time causes lower windspeeds. These changes together act as a 'meteorological forcing' for the chemical processes involing transport, diffusion and chemical transformation of urban pollutants in the urban canopy and over larger scales, therefor we use the term urban canopy meteorological forcing (UCMF). Using regional scale coupled chemistry-climate models over central Europe (involving models RegCM, CAMx and WRF-Chem),  we investigate here how the UCMF influences the urban emissions and their dispersion into regional scales. The analysis covers key pollutants as O3, NO2 and PM2.5 and the 2015-2016 period.

While urban emissions contribute by about 60-80% to the total NO2 and PM2.5 concentrations in cities, for ozone, they cause decrease in the urban cores and slight increase over sourrounding rural areas. More importantly, we found that if UCMF is considered, the impacts on all three pollutants are reduced, by about 20-30%. This is caused by the fact that vertical turbulence is greatly enhanced in urban areas leading to reduced fingerprint of the urban emissions (the case of NO2 and PM2.5) while in case of O3, reduction of the NO2 impact means smaller first-order titraltion therefor higher ozone concentrations - i.e. the ozone fingerprint of urban emissions is smaller. Our analysis showed that for evaluating the impact of urban emissions over regional scales, the meterological effects caused by the urban canopy have to be considered in modeling studies.
Connecting velocity changes with complementary observations (fast and slow strain perturbations, temperature etc.): Insights from long-term (decades) monitoring in several Italian regions
Authors: Poli Piero
Published: March 2021

We present a set of studies on velocity variations (dv/v) measured from seismic noise correlation in the Italian region. By exploring the evolution of the dv/v as function of coda lapse time, and comparing with independent observations (e.g. dynamic and quasi-static strain, temperature induced strain, rain etc.) we are able to get new insights into the causes of velocity variations as function of space (depth). Out of our results we recognized depth dependence of coseismic velocity drop and recovery in the region of l’Aquila, and depth and spatial dependence of sensitivity to long period (years) small strain variation (~10e-6) induced by hydrological processes. In a similar way to dynamic acoustic-elastic testing in laboratory, we extract non-linear parameters of the crustal rocks. These measures are compared with laboratory results to get insights about the physical state of the rocks in the crust, in regions hosting seismogenic faults. A summary of frequency and strain dependent dv/v and sensitivity further permits to compare our results to laboratory experiments.
Crustal seismic structure of Red-River shear zone and surrounding area
Authors: Long Ha Vinh , Huang Hsin-Hua , Nguyen Le Minh , Nguyen Van Duong , Le Quang Khoi , Ha Thi Giang , Van Dinh Quoc , Huang Bor-Shouh , Le Tu Son
Published: March 2021

The collision between the Eurasian and Indian plates since about 65 Ma caused extensive deformation in the Tibetan Plateau and surrounding areas. Northern Vietnam located in the southeastern Himalayan syntaxis is directly influenced by the collision and extrusion through the Red River shear zone that runs from southeastern Tibet to the South China Sea. Knowledge of crustal structure characteristics in northern Vietnam and across the Red River shear zone is crucial to improve our understanding not only of seismic hazards in the region but also of the regional Himalayan tectonic evolution as a whole. Seismic tomography is one of few methods that allows to study the subsurface structures effectively. In this study, we perform a joint tomographic inversion for northern Vietnam integrating the P- and S-direct waves traveling in the crust and the head waves along the Moho waves arrival time from more than 1000 earthquakes observed by Vietnamese networks. The obtained velocity model shows a good correlation with shallow geological features but also some complexity at crustal-scale. Several velocity anomalies bounded by and across the fault zones are revealed and discussed

 

Keyword: Traveltime tomography, Northern Vietnam, VpVs ratio, crustal structure, Vietnam seismic network
Characterization of near-surface turbulence in the stable atmosphere of the Alpine Inn Valley
Authors: Lehner Manuela , Rotach Mathias W.
Published: March 2021

The stable boundary layer is typically characterized by weak and sometimes intermittent turbulence, particularly under very stable conditions. In mountain valleys, nocturnal temperature inversions and cold-air pools form frequently under synoptically undisturbed and clear-sky conditions, which will dampen turbulence. On the other hand, thermally driven slope and valley winds form under the same conditions, which interact with each other and are both characterized by jet-like wind profiles, thus resulting in both horizontal and vertical wind shear, which creates a persistent source for turbulence production. Data will be presented from six flux towers in the Austrian Inn Valley, which are part of the i-Box measurement platform, designed to study near-surface turbulence in complex, mountainous terrain. The six sites are located within an approximately 6.5-km long section of the 2-3-km wide valley approximately 20 km east of Innsbruck. The data are analyzed to characterize the strength and intermittency of turbulence kinetic energy and turbulent fluxes across the valley and to determine whether the persistent wind shear associated with thermally driven flows is sufficient to generate continuous turbulence.
Comparison of Arctic cloud properties over sea ice and open ocean based on airborne spectral solar remote sensing
Authors: Klingebiel Marcus , Ehrlich André , Ruiz-Donoso Elena , Wendisch Manfred
Published: March 2021

Over the last decades, the Arctic has experienced an enhanced warming, which is known as Arctic amplification. This process leads to a decrease in the amount of Arctic sea ice, which is linked by different feedback mechanisms to clouds and the related radiative properties. To analyze how the properties of these Arctic clouds could change in a future sea ice free Arctic, we completed three airborne campaigns in the marginal sea ice zone between 2017 and 2020 covering summer and winter conditions. During these campaigns we performed in-situ and remote sensing measurements to study cloud micro- and macrophysical properties and analyzed how these clouds affect the radiation budget. In this study we use the passive remote sensing measurements from these airborne observations to retrieve cloud top effective radius, liquid water path and cloud optical thickness. We found that these cloud properties differ between a sea ice surface and over open water. The airborne observations are supported by an analysis of the cloud product from the MODIS satellite. The systematic differences of clouds over sea ice and the open ocean suggests that clouds may change in a future warming Arctic environment.
Evaluation of stratigraphic effects on seismic site response over large areas: the case study of Italy
Authors: Falcone Gaetano , Acunzo Gianluca , Mendicelli Amerigo , Mori Federico , Naso Giuseppe , Peronace Edoardo , Porchia Attilio , Romagnoli Gino , Tarquini Emanuele , Moscatelli Massimiliano
Published: March 2021

Estimation of site effects over large areas is a key-issue for land management and emergency system planning in a risk mitigation perspective. In general, site-conditions are retrieved from available global datasets and the ground-shaking estimation is based on ground motion prediction equations.

An advanced procedure to estimate site effects over large areas is here proposed with reference to the Italian territory. Site-condition were defined for homogenous morpho-geological areas in accordance to the borehole logs and the geophysical data archived in the Italian database for seismic microzonation (https://www.webms.it/). Ground motion modifications were determined by means of about 30 milion of one-dimensional numerical simulations of local seismic site response. Correlations between amplification factors (i.e. the ratio between free-field and outcrop response spectra), AF, and site-condition (i.e. harmonic mean of the shear wave velocity in the upper 30 m of the deposit, VS30) were determined for each morpho-geological homogeneous area depending on the reference seismic intensity (i.e. referred to the outcropping stiff rock characterised by VS30 ≥ 800 m/s). The AF-VS30 correlations were proved to satisfactory forecast the site effects when compared with the results of site specific estimation of local seismic site response.
Early-Warning Signals for a Critical Transition in the Coupled Amazon Rainforest-South American Monsoon System
Authors: Bochow Nils
Published: March 2021

The Amazon rainforest is widely recognised as a potential tipping element in the Earth's climate system. While several studies suggest a sudden dieback of the rainforest ecosystem after partial deforestation [e.g., 1, 2], there is still a lack of understanding where to search for early-warning signals that might precede such a dieback. In this work we employ a non-linear model of the moisture transport across the Amazon Basin to propose several statistical and physical early warning signals for a critical transition in the coupled dynamics of the Amazon rainforest and the atmospheric circulation of the South American monsoon. 

Widespread deforestation and its effects on evapotranspiration and radiation have been shown to potentially trigger a collapse of the positive feedback related to latent heat release over the rainforest [3], resulting in substantially reduced rainfall amounts. The model includes a nonlinear contribution representing the acceleration of low-level moisture flow caused by condensational latent heating.  

Guided by our modelling results, we associate characteristic changes in the hydrological cycle as well as statistical indicators in observed data with deforestation-induced circulation changes that are consistent with the identified early-warning signals. Our findings indicate that in response to deforestation, the coupled atmosphere-vegetation system is destabilising and that further deforestation could trigger a transition of the Amazon rainforest to a savanna state. 

[1] Nobre, C. A., & Borma, L. D. S. (2009). “Tipping points” for the Amazon forest. Current Opinion in Environmental Sustainability. https://doi.org/10.1016/j.cosust.2009.07.003

[2] Hirota, M., Holmgren, M., Van Nes, E. H., & Scheffer, M. (2011). Global resilience of tropical forest and savanna to critical transitions. Science, 334(6053), 232–235. https://doi.org/10.1126/science.1210657

[3] Boers, N., Marwan, N., Barbosa, H. M. J., & Kurths, J. (2017). A deforestation-induced tipping point for the South American monsoon system. Scientific Reports, 7. https://doi.org/10.1038/srep41489