bluuebunny/crossref_metadata_2025 huggingface dataset:
Benefits of Recent Clean Air Actions in China on Global Air Quality and Climate Change
Authors: Zhang Yuqiang , Shindell Drew , Seltzer Karl , Shen Lu , Zhang Qiang , Zheng Bo , Xing Jia , Jiang Zhe , Zhang Lei
Published: March 2020

Significant emission reductions have been observed in China recently, especially after the the ‘Air Pollution Prevention and Control Action Plan’ in 2013. Major air pollutants, such as NOx, CO, SO2, are found to reach their peak in 2012 or 2013. Few studies attempted to investigate how the recent emission reductions in China will affect global air quality and climate change. Here, by using global climate-chemistry models and health impact functions, we investigate how the contrasting emission changes in China from 2010 to 2017 will affect global air quality, mortality burden and climate change. We calculate that compared with the year 2010, 4800 deaths were avoided due to ozone reductions in 2017 globally, while 65% of the avoided deaths happen in China, and the other 35% worldwide. In 2017, 109,000 deaths were avoided due to PM2.5 reductions, while 92% of the avoided deaths happen in China, and the other 8% worldwide. We also find that the cooling effect from the emission reductions of SO2 in China has been compensated by the warming effect from the emission reductions of black carbon at the same time in China, which is the opposite trend as found in the developed countries in previous decades.
Shrub encroachment decreases soil inorganic carbon stocks in Mongolian grasslands
Authors: Liu Shangshi , Zhou Luhong , Li He , Zhao Xia , Zhu Yankun , Shen Haihua , Fang Jingyun
Published: March 2020

Widespread shrub encroachment in global drylands may increase plant biomass and change soil organic carbon stocks of grassland ecosystems. However, the response of soil inorganic carbon (SIC), which is a major component of dryland carbon pools, to this vegetation shift remains unknown. Here, we conducted a systematic field survey in 75 pairs of shrub-encroached grassland and control plots at 25 sites in the grasslands of the Inner Mongolia Plateau to evaluate how shrub encroachment affects SIC density (SICD) in these ecosystems. We found that shrub encroachment significantly reduced SICD in the upper 100 cm, especially in the subsurface soil (20-50 cm layer). The magnitude of SICD changes was related to the change in soil pH, shrub patch size, and initial SICD, reflecting that the reduction in SICD might be attributed to the shrub encroachment-related soil acidification. Our results also revealed that the lost SIC was mainly released into the atmosphere rather than redistributed into deeper soil layers. Overall, we provide the first evidence for the soil acidification-induced SIC loss caused by shrub encroachment. Our findings highlight the non-negligible role of SIC dynamics in the C budget of shrub-encroached grassland ecosystems and the need to consider these dynamics in terrestrial C cycle research.
The role of mineral composition regulating the turnover of organic matter in 13 forest soils from Hungary
Authors: Zacháry Dóra , Jakab Gergely , Filep Tibor , Balázs Réka , Szalai Zoltán
Published: March 2020

The organic matter stability is regulated by the different protection mechanisms of the soil matrix and soil minerals. In spite of that, beyond the determination of the amount of fine fractions, relatively little research studied the mineralogical composition of these fractions and their organic matter stabilizing effects. Therefore, the aim of my work was to investigate the influence of the soil mineral phases on the decomposition of soil organic carbon pools of soils under forest vegetation.

Maize residues were added to the 13 soil samples (depth of 0−20 cm) collected from Hungary. The samples were incubated at 20°C and 70% field capacity during 163 days. The soil respiration was measured at specified intervals (on day 3, 8, 15, 30, 51, 79, 107, 135 and 163) and trapped in 2M NaOH and quantified by titration with 1M HCl. Another aliquot of NaOH was mixed with 2MSrCl2 to get SrCO3 for δ13C analysis.

The samples were analysed with an X-ray diffractometer (Rigaku Miniflex 600), a microwave plasma-atomic emission spectrometer (4200, Agilent Technologies) and an isotope ratio mass spectrometer (Delta plus XP, Thermo Finnigan). Carbon mineralization kinetics was modelled by fitting a first-order two pools model.

The results showed that 1−6% and 2−18% of the organic carbon content of the soils was mineralized in the control and amended samples during the incubation, respectively. Carbon mineralization was mostly reduced by the illite content (R2=0,797; p<0,001), Al-oxide content (R2=0,708; p<0,001) and clay content (R2=0,475; p<0,05) of the soils. The decomposition rates of the two carbon pools were found to be influenced to the greatest extent by the illite and total Al-oxide content of the soils investigated. Whereas the decomposition rate constant of the slowly mineralizable C pool was only affected by the Al-oxide and illite content, the decomposition rate constant of the easily mineralizable carbon pool was also sensitive to the other soil parameters (aromaticity, Fe-oxide content, C/N ratio, pH and clay content).

The priming effect was found to be influenced to the greatest extent by the pH (R2=0,715; p<0,05), whereas weaker negative relationship with the content of non-swelling clay minerals (R2=0,396; p<0,05), illite content (R2=0,389; p<0,05) and the C/N ratio (R2=0,345; p<0,05) of the soils was also detected.

This work was supported by the Development and Innovation Fund of Hungary [Nr. NKFIH 123953].
The reduction of the systematic RCM summertime warm bias in South-Eastern Europe by stochastic root depth variation
Authors: Breil Marcus
Published: March 2020

The intensity of latent heat fluxes strongly depends on the available amount of soil water for evapotranspiration, i.e. the water amount stored within the rooted soil depth. But the determination of the root depth itself, and consequently also of the water supply for evapotranspiration, is associated with large uncertainties. The latent heat fluxes are therefore in many cases spuriously simulated, leading to temperature biases especially in soil-moisture limited evapotranspiration regimes like Southern Europe.

To take these uncertainties into account, a new method is introduced, in which the root depths within the Regional Climate Model (RCM) COSMO-CLM are stochastically varied. For this, the root depths in each model grid box are perturbed by uniformly distributed random numbers. The results of this stochastic simulation are compared to the results of an unperturbed reference run. The study reveals that during the winter season, evapotranspiration is virtually not affected by the stochastic root depth perturbation. Changes in the simulated near-surface temperatures are caused by indirectly induced chaotic changes in the atmospheric circulation. But in summer, the latent heat fluxes are considerably increased all over Southern Europe, due to a stochastic increase of the available soil water amount for evapotranspiration. Soil warming is consequently reduced and lower near-surface temperatures are simulated for the whole Mediterranean region. These lower temperatures reduce the strong warm bias in South-Eastern Europe in the reference run, which is also consistently simulated in several other RCMs and General Circulation Models (GCMs). Therefore, stochastic root depth modelling constitutes a simple method that can be implemented in every modelling system, to mitigate systematically simulated warm biases and thus, potentially improving model performances in semi-arid regions.
Assessing the global risk of climate change to re/insurers using catastrophe models and hazard maps
Authors: Jones Sarah , Raven Emma , Toothill Jane
Published: March 2020

In 2018 worldwide natural catastrophe losses were estimated at around USD $155 billion, resulting in the fourth-highest insurance payout on sigma records, and in 2020 JBA Risk Management (JBA) estimate 2 billion people will be at risk to inland flooding. By 2100, under a 1.5°C warming scenario, the cost of coastal flooding alone as a result of sea level rise could reach USD $10.2 trillion per year, assuming no further adaptation. It is therefore imperative to understand the impact climate change may have on global flood risk and insured losses in the future.

The re/insurance industry has an important role to play in providing financial resilience in a changing climate. Although integrating climate science into financial business remains in its infancy, modelling companies like JBA are increasingly developing new data and services to help assess the potential impact of climate change on insurance exposure.

We will discuss several approaches to incorporating climate change projections with flood risk data using examples from research collaborations and commercial projects. Our case studies will include: (1) building a national-scale climate change flood model through the application of projected changes in river flow, rainfall and sea level to the stochastic event set in the model, and (2) using Global Climate Model data to adjust hydrological inputs driving 2D hydraulic models to develop climate change flood hazard maps.

These tools provide outputs to meet different needs, and results may sometimes invoke further questions. For example: how can an extreme climate scenario produce lower flood risk than a conservative one? Why may adjacent postcodes' flood risk differ? We will explore the challenges associated with interpreting these results and the potential implications for the re/insurance industry.
Investigation of Dynamic and Static Effects on Earthquake Triggering Using Different Rate and State Friction Laws and Marmara Simulation
Authors: Sopaci Eyup , Özacar Atilla Arda
Published: March 2020

The clock of an earthquake can be advanced due to dynamic and static changes when a triggering signal is applied to a stress-loading fault. While static effects decrease rapidly with distance, dynamic effects can reach thousands of kilometers away. Therefore, earthquake triggering is traditionally associated to static stress changes at local distances and to dynamic effects at greater scales. However, static and dynamic effects near the triggering signal are often nested, thus identifying which effect dominates, becomes unclear. So far, earthquake triggering has been tested using different rate-and-state friction (RSF) laws utilizing alternative views of friction without much comparison. In this study, the analogy of an earthquake is simulated using single degree of freedom spring-block systems governed with three different RSF laws, namely “Dieterich”, “Ruina” and “Perrin”. First, the fault systems are evolved until they reach a stable limit cycle and then static, dynamic and their combination are applied as triggering signals. During synthetic simulations, effects of the triggering signal parameters (onset time, size, duration and frequency) and the fault system parameters (fault stiffness, characteristic slip distance, direct velocity and time dependent state effects) are tested separately. Our results indicate that earthquake triggering is controlled mainly by the onset time, size and duration of the triggering signal but not much sensitive to the signal frequency. In terms of fault system parameters, the fault stiffness and the direct velocity effect are the critical parameters in triggering processes. Among the tested RSF laws, “Ruina” law is more sensitive than “Dieterich” law to both static and dynamic changes and “Perrin” is apparently the most sensitive law to dynamic changes. Especially, when the triggering onset time is close to an unperturbed failure time (future earthquake), dynamic changes result the largest clock advancement, otherwise, static stress changes are substantially more effective. In the next step, realistic models will be established to simulate the effect of the recent (26 September 2019) Marmara earthquake with Mw=5.7 on the locked Kumburgaz fault segment of the North Anatolian Fault Zone. The triggering earthquake will be simulated by combining the static stress change computed via Coulomb law and the dynamic effects using ground motions recorded at broadband seismic stations within similar distances. Outcomes will help us to better understand the effects of static and dynamic changes on the seismic cycle of the Kumburgaz fault segment, which is expected to break soon with a possibly big earthquake causing damage at the metropolitan area of Istanbul in Turkey.
Ocean-Atmosphere positive feedback in the Barents Sea region with reanalyses data
Authors: Kalavichchi Katrina , Bashmachnikov Igor
Published: March 2020

This study investigates the mechanism of positive feedback in the Barents Sea region, using the results of reanalyses from 1993 to 2014. Vertical heat fluxes, wind and pressure fields are obtained from OAFlux and ERA-Interim databases, the water temperature and currents from the ARMOR-3D database.

Oceanic heat transport was computed through three sections-at the entrance to the Barents Sea (BSO), in the southern part of the Norwegian sea and in the west of Spitsbergen. The results show that, during the study period, the oceanic heat flux through BSO was rapidly increasing, significantly faster than in the northwards heat transport in the Norwegian Sea. west of Spitsbergen, a negative linear trend was observed, indicating a redistribution of the increasing transport of the Atlantic Water into the Nordic Seas.

Based on reanalyses data, we show the tight relationship between the current velocities through the BSO and the change in the gradient of the zonal component of wind velocity. The variability of the atmospheric circulation and the variability of the convergence of atmospheric heat fluxes for the studied region was also assessed.

The results also show that, in winter, with increasing oceanic heat flux through the BSO, the turbulent heat fluxes in the southwestern part of the sea decreased, and the northern part of the sea and west of Novaya Zemlya increased. In the annual means, the increasing heat flux from the ocean to the atmosphere is due to a retreat of the ice edge and an increase in the ice-free area of the sea. The sea-surface atmospheric pressure also increased over the water area, with a maximum changes in the south-east of the sea.

For the years with the maximum oceanic winter heat fluxes into the Barents Sea, the atmospheric heat flux across the southern boundary increased, while it across the northern border weakened. The convergence of the atmospheric heat fluxes increased only at the sea surface (1000-975 hPa), whereas above (975-100 hPa) the convergence decreased, and the total atmospheric heat convergence varies out of phase with that of the ocean.

This study was supported by the Russian Science Foun- dation, project no. 17-17-01151.
Impacts of the PMIP4 ice-sheets on Northern Hemisphere climate during the last glacial period
Authors: Izumi Kenji , Paul Valdes Paul , Ivanovic Ruza , Gregoire Lauren
Published: March 2020

The Last Glacial Maximum (LGM; 21,000 yr before present) is a target period of the paleoclimate simulations in the Coupled Model Intercomparison Project Phase 6 – the Paleoclimate Modeling Intercomparison Project Phase 4 (CMIP6-PMIP4) because of abundant paleoenvironmental data in continental, ice, and marine indicators. The LGM was a period of low atmospheric trace gases when large ice sheets covered over North America and Scandinavia. Paleoclimate reconstructions and modeling studies suggest that the Northern Hemisphere climate differed from today.

In this study, we used the coupled atmosphere and ocean model HadCM3B-M1 in order to investigate the impacts of the main LGM boundary condition changes, in particular, the ICE-6G_C, GLAC-1D, and PMIP3 ice-sheet reconstructions following the PMIP4 protocol, on the mean state of the climate over the Northern Hemisphere. First, we check the surface albedo forcing and feedback with a simplified partial derivative method and assess the surface temperature changes and their composition using a simple surface energy balance equation. Then, we investigate how patterns of stationary waves, westerly jet precipitation over the Northern Hemisphere change in response to the LGM ice-sheet configuration. Finally, we implement a paleo data-model comparison for validation of the large-scale climate changes over the Northern Hemisphere at the LGM. The wintertime stationary waves have the largest amplitude and different responses among the experiments, while stationary waves in summer are weak and similar responses. The LGM simulation with the ICE-6G_C better captures features of the LGM climate, but compared to the reconstructions, the climate model tends to overestimate cooling in summer and underestimate cooling in winter and simulate wetter conditions over the Northern Hemisphere.  
14C Ventilation ages suggest a brief reversal of ocean Meridional Overturning Circulation during deglacial ‘Heinrich Stadial 1’
Authors: Sarnthein Michael , Grootes Pieter M.
Published: March 2020

Changes in the geometry of ocean Meridional Overturning Circulation (MOC) are crucial in controlling changes of climate and the carbon inventory of the atmosphere. However, the accurate timing and global correlation of short-term glacial-to-deglacial changes in the MOC of different ocean basins still present a major challenge. The suite of jumps and plateaus in the record of past atmospheric radiocarbon (14C) concentrations offers a unique opportunity of age control and global correlation. The upper and lower boundaries of atmospheric 14C plateaus in the 14C records of both tree rings and Lake Suigetsu (age calibrated on the basis of Hulu U/Th model ages)­ provide a detailed stratigraphic ’rung ladder’ of ~30 age tie points from 29 to 10 ka that can be used for dating of planktic 14C records and an age correlation, by now employed to ~20 sediment cores obtained from key locations of MOC all over the global ocean. The age difference between paired planktic and benthic 14C ages provides an estimate of the ventilation age of deep waters since their last contact with the atmosphere. 14C ventilation ages of Last Glacial Maximum (LGM) deep waters reveal coeval opposed geometries of Atlantic and Pacific MOC. Similar to today, LGM Atlantic deep-water formation went along with an estuarine inflow of old abyssal waters from the Southern Ocean up to the northern North Pacific and an outflow of upper deep waters. Vice versa, low 14C ventilation ages of N.E. Pacific deep waters suggest a reversed, anti-estuarine MOC during early Heinrich Stadial 1 with a ~1500 year-long flushing of the deep North Pacific up to the South China Sea, when the North Atlantic was marked by an estuarine circulation geometry, gradually starting near 19 ka. Elevated 14C ventilation ages of LGM deep waters reflect a major drawdown of atmospheric carbon. Subsequent massive age drops accompanying changes in MOC reflect major events of carbon release to the atmosphere as recorded in Antarctic ice cores. These contemporaneous features of the MOC and the carbon cycle offer a great test case for comparison with model simulation.
The chemical interaction of biochar with iron and phosphate might explain the effects of biochar in alkaline and calcareous soils
Authors: Baigorri Roberto , Urrutia Óscar , San Francisco Sara , García-Mina José María
Published: March 2020

Due to the low consistency of the results obtained in field, the use of biochar as soil amendment is controversial. Thus, in general in acidic soils results are positive while in alkaline soils they are non-significant or even negative. The results regarding biochar action in acidic soils have been related to a lime-like effect due to its alkaline pH and the high doses normally used. However, the causes of biochar effects in alkaline soils remain unknown. We have used a well characterized biochar as a component of two complex N and PK granulated fertilizers at two different doses (1 and 5%). These fertilizers have been applied to wheat cultivated in pots containing an alkaline and calcareous soil and grown for 60 days. No effect was shown for the N-biochar fertilizer application. However, the PK-biochar fertilizer application caused a decrease in crop yield. Complementary, the absorption isotherms of Iron (Fe), Molybdenum (Mo), Manganese (Mn) and Phosphate (Pi) in biochar were also studied. The results showed that Fe was rapidly adsorbed in biochar, while Pi was only absorbed on the Fe-Biochar complex. Desorption experiments showed that P and Fe were no desorbed from the P-Fe-biochar complex by water or the Olsen reactant, while a partial desorption was observed when HCl 0.1 M was used. This blockage of Fe and P through Fe bridges in biochar could partially explain the negative effects in alkaline soils.
Contributions from extratropical North Pacific to Arctic summer atmospheric temperature and circulation
Authors: He Shengping , Furevik Tore
Published: March 2020

A fascinating character of the Arctic summer atmospheric circulation is the anomalous anticyclone circulation centered over the Arctic Ocean. Previous studies have related the underlying mechanisms to the atmospheric internal variability, the earlier spring Eurasian snowmelt, and the tropical Pacific forcing. Here we show that the Arctic summer anomalous anticyclone circulation is strongly associated with positive sea surface temperature anomalies (SSTAs) at midlatitudes of the extratropical North Pacific which are surrounded by significant negative SSTAs, resembling the negative phase of the Pacific Decadal Oscillation (PDO) but without significant signals in the tropics. The numerical experiments from the Whole Atmosphere Community Climate Model, prescribed with negative PDO-like SSTAs from May to August with the influence of El Niño-Southern Oscillation being reduced in advance, have simulated the observed positive air temperature and geopotential height anomalies over the Arctic and the circumpolar easterly anomaly at high latitudes in summer. The observational and simulated results strongly suggest that the extratropical SSTAs can influence the Arctic atmospheric temperature and circulation in summer.
An idealized Testbed for Radar Data Assimilation
Authors: Zeng Yuefei , Janjic Tijana , de Lozar Alberto , Blahak Ulrich , Seifert Axel
Published: March 2020

 

Data assimilation on the convective scale uses high-resolution numerical models of the atmosphere
that resolve highly nonlinear dynamics and physics. These non-hydrostatic, convection
permitting models are in short runs very sensitive to proper initial conditions.
However, the estimation of initial conditions is hampered by assumptions made in data assimilation algorithms
and in their models of the observation error and model error uncertainty. Within this work, an idealized testbed
for Radar Data Assimilation has been developed, which uses Kilometre-scale ENsemble Data Assimilation (KENDA) system
of the (Deutscher Wetterdienst) DWD. A series of data assimilation experiments for a supercell storm are conducted.
The sensitivity to the configurations of the radar forward operator and specification of the observation error
is investigated. Moreover, impacts of different observations (radial wind, reflectivity or both)
on the performance of data assimilation cycles and 6-h forecasts are shown, for instance,
the preservation of divergence, vorticity and mass of hydrometeors, compared to the nature run is of special interest.

 
Responses of arbuscular mycorrhizal fungi to nitrogen addition: a meta-analysis
Authors: Han Yunfeng , Zhu Biao
Published: March 2020

Arbuscular mycorrhizal (AM) fungi play many important roles in terrestrial ecosystems. The effects of increasing nitrogen (N) deposition on AM fungi will inevitably affect many important ecosystem processes. However, our quantitative understanding on the generalizable patterns of how N deposition affects AM fungi at the global scale remains unclear.

We conducted a meta-analysis of 431 observations from 111 publications to investigate the responses of AM fungi to N addition, including abundance, richness and diversity, and explored the mechanisms of N addition affecting AM fungi by trait-based guilds method.

Results showed that N addition had strong negative effects on AM fungal abundance and richness, and different AM fungal guilds showed different responses to N addition: the rhizophilic guild significantly decreased under N addition, while the edaphophilic guild increased (but with much variability) under N addition. Further analysis showed that N addition affects AM fungi mainly by causing soil acidification and increasing soil available N. Specifically, soil acidification had a negative effect on both the rhizophilic and edaphophilic AM fungi and increased soil available N mainly negatively affect the edaphophilic AM fungi. Moreover, the response of AM fungi to N addition was also affected by the shifts in plant carbon (C) allocation caused by soil phosphorus (P) availability.

This synthesis highlights that trait-based AM fungal guilds as well as taking soil P and C from host plants into consideration can improve our understanding of dynamics of AM fungal communities under increasing N deposition. This would further enable better predictions of the functional consequences of changes in AM fungal communities such as impacts on soil organic C dynamics, plant P uptake and plant diversity.
Interacting tipping elements increase risk of climate domino effects
Authors: Wunderling Nico , Donges Jonathan , Kurths Jürgen , Winkelmann Ricarda
Published: March 2020

The Greenland Ice Sheet, West Antarctic Ice Sheet, Atlantic Meridional Overturning Circulation (AMOC), El-Nino Southern Oscillation (ENSO) and the Amazon rainforest have been identified as potential tipping elements in the Earth system, exhibiting threshold behavior. While their individual tipping thresholds are fairly well understood, it is of yet unclear how their interactions might impact the overall stability of the Earth’s climate system. Here, we explicitly study the effects of known physical interactions using a paradigmatic network approach which is not yet possible with more complex global circulation models or process-based models in a comprehensive way.

We analyze the risk of domino effects being triggered by each of the individual tipping elements under global warming in equilibrium experiments, propagating uncertainties in critical temperature thresholds and interaction strengths via a Monte-Carlo approach.

Overall, we find that the interactions tend to destabilize the network, with cascading failures occurring in 41% of cases in warming scenarios up to 2°C. More specifically, we uncover that:

(i) With increasing coupling strength, the temperature thresholds for inducing critical transitions are lowered significantly for West Antarctica, AMOC, ENSO and the Amazon rainforest. The dampening feedback loop between the Greenland Ice Sheet and the AMOC due to increased freshwater flux on the one hand and relative cooling around Greenland on the other, leads to an enhanced ambivalency whether the Greenland Ice Sheet tips or not.

(ii) Furthermore, our analysis reveals the role of each of the five tipping elements showing that the polar ice sheets on Greenland and West Antarctica are oftentimes the initiators of tipping cascades (in up to 40% of ensemble members for Greenland), while the AMOC acts as a mediator, transmitting cascades.

This implies that the ice sheets, which are already at risk of transgressing their temperature thresholds within the Paris range of 1.5 to 2°C, are of particular importance for the stability of the climate system as a whole.
Can we use regional runoff models for correcting time series of absolute gravimetry?
Authors: Bramanto Brian , Ophaug Vegard , Gerlach Christian , Breili Kristian
Published: March 2020

Absolute gravity time series are available at various stations in Norway. The data have mainly been used for investigation of secular variations due to glacial isostatic adjustment. Previous work indicates that some of the estimated gravity trends suffer from unmodeled geophysical effects, like hydrological mass variations. Here we try to correct for hydrological effects by employing a combination of global and regional hydrological models. We use gravity data at two locations in the Norwegian network (NMBU and TRYC) which have frequently been observed with the absolute gravimeter FG5-226. 

For computing the gravity corrections, we test various Global Hydrological Models (GHMs) and combine them with a Regional Runoff Model (RRM) for Norway, run by the Norwegian Water Resources and Energy Directorate (NVE). We distinguish between an outer and an inner zone. In the outer zone, Newtonian attraction and loading effects are derived from the GHMs, while the RRM is used in the inner zone. Both types of models provide information on soil moisture and snow layers. The RRM provides groundwater variations in addition. Furthermore, we try to consider the ‘umbrella effect’ that accounts for local disturbances in subsurface water flow caused by the existence of the building in which the gravity site is located.  

Neglecting the GIA trend, both NMBU and TRYC gravity time series show different amplitude and pattern. NMBU shows a lower amplitude, and with no prominent periodic pattern in the data, while TRYC shows the opposite. Significant discrepancies occurring in the NMBU gravity dataset between 2014 and 2015 are likely due to an instrumental effect, such as maintenance. The total modelled hydrological signal ranges from -4 and 4 µGal. Application of the correction reduces the standard deviation in the gravity time series, at its best, by about 33% or 0.8 µGal for NMBU, and by about 43% or two µGal for TRYC. Secular gravity rates have been derived from both, the uncorrected and the corrected time series. We find that application of the hydrological correction improves the fit of the computed secular gravity rates as compared to rates derived from the state-of-the-art Fennoscandian land uplift model NKG2016LU_abs. The uncorrected trends are 75% and 50% of the expected trend (0.77 and 1.12 µGal/year), while the hydrological corrections improve the fit to 82% and 93% for NMBU and TRYC, respectively.
Analysis of the Miage Glacier Lake GLOFs (Aosta Valley - Italy).
Authors: Troilo Fabrizio , Segor Valerio , Perret Paolo , Bertholin Manuel , Mondardini Luca , Gottardelli Simone
Published: March 2020

Miage Glacier Lake is a glacial marginal lake that forms on the right snout of Miage Glacier, located in the Val Veny Valley (Aosta Valley – Italy). The lake has been experiencing seasonal drainages at least since the 1930’s and 15 events have been documented from 1930 to 1990. The lake position has been almost unvaried since the first existing maps of late 1700, but lake morphology experienced major changes after the drainage event of September 2004, after which the water level could not reach again a sufficient height to fill the 3 depressions that used to form a bigger lake until 2003 (36.000 m2). The lake having decreased its volume and surface, it did not seem by that time that GLOF from Miage Lake could cause any risk downstream (Deline et Al. 2004), but recent observation of Sentinel 2B satellite images  led to the individuation of unusual lake expansion towards its north shore. Thus, an UAV survey was performed to assess the actual lake area in July 2019, and the integration of satellite images and UAV surveys demonstrated a consistent lake area expansion since 2015. Moreover an emptying occurred in late August 2019 so that another UAV survey could be performed, and water volume estimation could be performed by means of DEM differencing. An important water volume was individuated, reaching 196.000 m3 and an estimation of maximum subglacial GLOF debit has been performed. Global evolution trend of the glacier mass has been evaluated by analyzing different airborne Lidar surveys (1991-2008). A cumulated geodetic mass balance could be thus inferred and found good matching with remote sensed analysis (2003-2012) performed by means of stereo satellite imagery by Berthier et Al. in 2014. Average surface lowering of the glacier surface could be analyzed and average values of -1.12 m/yr could be observed around lake Miage. The strong elevation loss of Miage Glacier lower snout is probably the cause of the lowering of the piezometric level in intra-glacial water limiting maximum altitude that water level can reach in the lake, so that the bigger basin of 2004 cannot be filled anymore. Moreover, an analysis of recent GLOFs of Miage Lake gave an insight about the possible dynamics of lake subglacial drainage, suggesting the existence of 2 different mechanisms of emptying as some events occur with lower water debits, earlier in the season, and other events occur later in the summer season with major water debits. Similar GLOF behavior has been described at Plaine Morte Glacier Lake in the Canton of Bern-Switzerland (Fahrni 2018). Field surveys of 2018 showed very likely evidence of hydrostatic uplift of the ice dam, so multi temporal UAV surveys and GNSS field surveys are planned for 2020 to possibly highlight evidences of hydrostatic uplift of the glacier prior to GLOFs.
Holocene biomarker- and microfossil-based sea-ice reconstructions off the eastern North Greenland continental shelf (western Fram Strait)
Authors: Syring Nicole , Stein Ruediger , Llyod Jeremy M. , Fahl Kirsten , Vahlenkamp Maximilian , Zehnich Marc , Spielhagen Robert , Niessen Frank
Published: March 2020

Understanding the processes controlling the natural variability of sea ice in the Arctic, one of the most dynamic components of the climate system, can help to constrain the effects of future climate change in this highly sensitive area. For the first time, a detailed multi-proxy study was carried out to reconstruct past sea-ice variability off eastern North Greenland. This area is strongly influenced by cold surface waters and drift ice transported via East Greenland Current, meltwater pulses from the outlet glaciers of the Northeast Greenland Ice Stream, the build-up of landfast ice, and the formation of the Northeast Water Polynya. For our study, we have used well-dated sedimentary sections of Kastenlot Core PS93/025 and Gravity Core PS100/270. These sites are ideally suited to identify and disentangle the driving mechanisms of sea-ice distribution in the western Fram Strait. As proxies for the reconstruction of sea-ice cover we have used the sea-ice proxy IP25, a highly branched isoprenoid (HBI) monoene with 25 carbon atoms, in combination with specific open-water phytoplankton and terrestrial higher land plant biomarkers as well as specific microfossils (e.g., diatoms). Based on these high-resolution data sets we are able to reconstruct sea-ice variability, primary productivity, terrigenous input and seasonal formation of the NEW Polynya that evolved during the Holocene at the eastern North Greenland shelf.

The presence of IP25 throughout the core PS93/025 confirms that there has been seasonal sea ice in the area during the entire Holocene time interval. Our biomarker proxies indicate relatively rapid changes in sea-ice conditions at ~9 ka and ~1 ka, i.e., sea-ice conditions progressed through three major stages over the course of the Holocene. During the early Holocene we recorded a reduced, but variable sea-ice cover. Between about 9.3 and 5.5 ka, sea-ice coverage increased towards seasonal conditions. Based on terrigenous biomarkers and IRD we assume a stronger regional than local sea-ice signal at core site PS93/025, due to the high influence of drift ice transported from the central Arctic Ocean along the eastern North Greenland shelf. During the late Holocene, especially during the last 1 ka, our records reflect the seasonal formation of the NEW Polynya leading to stable sea-ice edge conditions and a fully developed polynya situation. Probably, cyclic changes in the solar activity acted as trigger for the short-term variability in sea-ice cover during Holocene times.
The Water Mass Transformation Framework for Ocean Physics and Biogeochemistry
Authors: Groeskamp Sjoerd
Published: March 2020

To understand the role of the ocean in the climate system, it is no longer sufficient to study either physics or biogeochemistry. Future efforts need to combine these disciplines to truly understand our future climate. The water mass transformation (WMT) weaves together circulation, thermodynamics, and biogeochemistry into a description of the ocean that complements traditional Eulerian and Lagrangian methods. Here we present a derivation of a WMT framework that offers an analysis that renders novel insights and predictive capabilities for studies of ocean physics and biogeochemistry that determine ocean tracer uptake, circulation and storage. We will discuss application for this framework for biogeochemical studies and its potential for inferring unmeasurable biogeochemical processes from estimates of the measurable physical processes.
Disentangling turbulent and non-diffusive fluxes in the boundary layer
Authors: Kowalski Andrew , Fratini Gerardo , Miranda Gabriela , Serrano-Ortiz Penélope , Burba George
Published: March 2020

Arithmetic averaging procedures are traditionally used in many applications in the field of micrometeorology, but these neglect Osborne Reynolds's specification of turbulence, and thus, strictly speaking, violate the momentum conservation law. Recently, it has been shown  that applying linear momentum conservation to surface exchanges defines an average motion in the surface-normal direction (i.e., a Stefan flow), and thereby describes a non-diffusive transport that is distinct from turbulent transport. Here we examine data from a nearly ideal micrometeorological field site (extensive, flat, and mono specific-reed wetland) to show that traditional flux-tower calculations, including but not limited to the Webb corrections,  generally provide an inadequate approximation of turbulent  fluxes and yet still adequately characterize the net fluxes in most traditional cases. The importance of such conflation of diffusive and non-diffusive transport is greatest for situations with relatively large non-diffusive fluxes, as occurs during particular times of day in general and particularly when considering fluxes in the stream-wise direction. An examination of fluxes calculated using the traditional arithmetic averaging procedure, versus the proposed, more theoretically appropriate calculations that fully obey conservation law, illustrates important implications for the characterization of gas-exchange processes and more generally the discipline of micrometeorology. These implications may become particularly critical in near future as gas flux measurements enter an era of automated operation on massive network scales, including automated gas flux calculations. At the same time, such measurements strive to adequately represent gas exchange of newer species with extremely low fluxes (vs traditionally measured larger fluxes of H2O and CO2). Multiple assumptions, and neglected terms and processes historically deployed for evaluating larger fluxes, may no longer work well when much smaller fluxes are considered, especially when measured by a non-expert using a fully automated flux station. These no-longer-negligible aspects include fundamentals of adequately handling the diffusive and non-diffusive transport mechanisms addressed in this presentation.
Applying seismic ring-fault models to real case scenarios
Authors: Contreras Arratia Rodrigo , Neuberg Jurgen
Published: March 2020

 Previous studies have found discrepancies concerning the seismic radiation between planar and curved faults; moment tensor (MT) interpretations, seismic moment estimation and waveforms change dramatically when the rupture is not planar. Therefore, assuming a point source on a planar fault for earthquakes in volcanic environments can be an oversimplification that needs to be addressed if we observe some seismological clues. First, we study waveforms for LP events at Etna. To explain these waveforms we propose a full-ring rupture with an inner net movement of magma, in in contrast to the planar fault approach that returns a pulsating rupture. Second, we study MT inversions for the biggest earthquakes during the 2014-2015 collapse of the Bardarbunga caldera, which show non-double couple solutions, with vertical compression axis. We calculate synthetic seismograms for partial-ring ruptures using an “ideal” seismic network, and one emulating the existing monitoring network at Bardarbunga. Observations using distal stations can return a better-constrained seismic moment, but they fail to characterise the dynamics involved. On the other hand, using proximal stations we obtain a reliable representation of the forces involved; however, the seismic moment is systematically overestimated due to the proximity to the curved source and the corresponding focussing effects. Finally, we correct the area of rupture due to fault shape to estimate the real cumulative seismic moment during the caldera collapse. The result shows a closer relationship between seismic and geodetic moment.
The brittle-to-viscous transition and its potential relationship to seismic deformation
Authors: Stunitz Holger , Marti Sina , Mansard Nicolas , Pec Matej , Raimbourg Hugues , Précigout Jacques , Heilbronner Renée
Published: March 2020

Strength profiles through the crust and upper mantle typically show the brittle to viscous transition as a change in deformation mechanism from frictional sliding to crystal plastic (dislocation creep) mechanisms. Even though such a change may conceivably take place, experimental evidence and natural observations indicate that a transition from semi-brittle to diffusion creep mechanisms rather than dislocation creep is more common.

In experiments we have carried out on granitoid and mafic rock material we can distinguish 3 main processes for the brittle to viscous transition: (1) Grain size comminution by cracking produces a sufficiently small grain size (sub-micron) to cause a switch to diffusion creep. (2) Amorphous material forms (aseismically) from mechanical wear at high stresses (high dislocation densities or high work rate) without melting. The amorphous material is observed to be weak and deforms viscously. (3) Nucleation of new minerals as a consequence of metastability of existing minerals at given P,T, fluid-conditions produces fine-grained and well-mixed aggregates causing a switch to diffusion creep as in (1).

The viscously deforming part of the crust or upper mantle is not the region where most earthquakes occur, because low stresses commonly are associated with viscous deformation. However, the transitions observed in experiments described above are transformational processes the material progressively evolves over a period of time in terms of microstructure, grain size, and/or composition, i.e., they are deformation-history-dependent transitions. In other words, during the transformation, only parts of the material deform by viscous processes while others have not evolved and are still brittle (and stronger). The bulk material strength of partially transformed rock depends on the connectivity of the weaker transformed material. The weaker material causes stress concentrations at the tips of transformed zones. The coalescence of transformed zones and/or a sufficiently large amount of transformed material is expected to cause catastrophic failure and thus seismic rupture. In such a way, transformation to viscously deforming weaker material may cause seismic behavior rather than according to the conventional view, where material properties change as a result of seismic deformation first, leading to creep.
A Solar Cycle of Observations with the Interstellar Boundary Explorer (IBEX)
Authors: McComas David
Published: March 2020

The Interstellar Boundary Explorer (IBEX) was launched in 2008 and has now returned observations over a full 11-year solar cycle (Solar Cycle 24). IBEX remotely images global ion distributions via charge exchange Energetic Neutral Atoms (ENAs) propagating inward from the heliosheath – the region between the termination shock and heliopause – and beyond. These observations have led to numerous discoveries about the outer heliosphere and its interaction with the surrounding interstellar medium. Heliospheric ENAs arise largely from two sources: the IBEX Ribbon, which is likely generated beyond the heliopause, in the very local interstellar medium, and the globally distributed flux (GDF), which is primarily produced in the heliosheath. In this talk we summarize some of the critical advances driven by IBEX observations. We also examine how the heliosphere and its interstellar interaction have evolved over the past solar cycle. For most of IBEX’s 11 years of observations, there was an overall reduction and then flattening of the ENA fluxes at all energies, consistent with a generally deflating, or shrinking, heliosphere. Over the past few years, IBEX has been observing the progressive response of the heliosphere to a large persistent increase in the solar wind output that passed 1 AU in the second half of 2014. This enhancement arrived at the outer heliosphere as indicated by an increase in the ENAs returning from the closest region of the inner heliosheath, south of the upwind direction, starting in the second half of 2016. Since then, the region of enhanced ENA emissions has expanded progressively outward from there, exposing increasingly further away regions of the heliosheath. IBEX observations over the past 11-years have led to a true scientific revolution in our understanding of the outer heliosphere and its interstellar interaction.
Tropical cyclone induced gravity wave perturbations in the upper atmosphere: GITM-R simulations
Authors: Zhao Yuxin , Lin Cissi-Y. , Deng Yue , Wang Jing-Song , Zhang Shun-Rong , Mao Tian
Published: March 2020

The tropical cyclone induced concentric gravity waves (CGWs) are capable of propagating upward from convective sources in the troposphere to the upper atmosphere and creating concentric traveling ionosphere disturbances (CTIDs). To examine the CGWs propagation, we implement tropical cyclone induced CGWs into the lower boundary of Global Ionosphere–Thermosphere Model with local-grid refinement (GITM-R). GITM-R is a three-dimensional non-hydrostatic general circulation model for the upper atmosphere with the local-grid refinement module to enhance the resolution at the location of interest. In this study, we simulate CGWs induced by typhoon Meranti in 2016. Information of the TC shape and moving trails is obtained from the TC best-track dataset and the gravity wave patterns are specified at the lower boundary of GITM-R (100 km altitude). The horizontal wavelength and phase speed of wave perturbation at the lower boundary are specified to be consistent with the TEC observations. The simulation results reveal a clear evolution of CTIDs, which shows reasonable agreement with the GPS-TEC observations. To further examine the dependence of the CTIDs on the wavelength and frequency of the gravity wave perturbation at the lower boundary, different waveforms have been tested as well. The magnitude of CTIDs has a negative correlation with the period, but a positive correlation with the wavelength when the horizontal phase velocities are sufficiently fast against the critical- level absorption.