bluuebunny/crossref_metadata_2025 huggingface dataset:
The greenhouse gas climate commitment and reversibility of peak warking from historical emissions
Authors: MacIsaac Alexander , Matthews H. Damon , Mengis Nadine , Zickfeld Kirsten
Published: March 2020

The warming caused by past CO2 emissions is known to persist for centuries to millennia, even in the absence of additional future emissions. Other non-CO2 greenhouse gas emission have caused additional historical warming, though the persistence of this non-CO2 warming varies among gases owing to their different atmospheric lifetimes. Under deep mitigation scenarios or in an idealized scenario of zero future greenhouse gas emissions, the past warming from shorter-lived non-CO2 gases has been shown to be considerably more reversible than that caused by CO2 emissions. Here we use an intermediate-complexity global climate model coupled to an atmospheric chemistry module to quantify the warming commitment and its reversibility for individual and groups of non-CO2 greenhouse gases. We show that warming caused by gases with short atmospheric lifetimes will decrease by more than half its peak value within 30 years following zeroed emissions at present day, with more 80 percent of peak temperature reversed by the end of this century. Despite the fast response of atmospheric temperature to the elimination of non-CO2 emissions, the ocean responds much more slowly: past ocean warming does not reverse, but rather continues for several centuries after zero emissions. Further consequences are shown for the land carbon pool, which decreases as an approximately linear function of historical non-CO2 greenhouse gas induced warming. Given that CO2 and non-CO2 greenhouse gas emissions share common emission sources, we also explore a set of scenarios where sets of emissions are zeroed according to two broad source categories: (1) fossil fuel combustion, and (2) land-use and agriculture. Using these additional mode runs, we investigate the temperature change that is avoided if all CO2 and non-CO2 greenhouse gas emissions from a particular source abruptly stops while others are allowed to continue. These results indicate the possibility of land-use change and agriculture activities continuing under deep mitigation scenarios and ambitious climate targets, without leading to exceedance of global climate targets. Though we analyze unlikely scenarios, our work provides baselines from which more realistic mitigation scenarios can be assessed. The reversibility of peak temperature caused by historical non-CO2 gases is a relevant measure for policy frameworks seeking to limit global warming to ambitious targets, such as the 1.5 oC target adopted by the Paris Agreement
A Diagnosis Analysis to inter-annual variation of air-sea Hg flux in global ocean and the “seesaw” effect in equatorial Pacific
Authors: huang Shaojian , Zhang Yanxu
Published: March 2020

The inter-annual variation of mercury(Hg) was spotted in monitoring stations, like the Alert and Mace Head. Nevertheless, the potential reason still lacks of studying. With periodic disturbance like ENSO, air-sea exchange flux, the largest flux between Earth system reservoirs, might greatly contribute to the inter-annual variation of Hg. Therefore, this study intended to explore the inter-annual variation of Hg0, a dominant evasion form of Hg, driven by MITgcm (ocean model). In general, the inter-annual variation of Hg evasion from global ocean was relatively stable in mid and high latitude, but a violent fluctuation was found in the tropical sea areas, especially equatorial Pacific. A distinct latitudinal difference was spotted that the fluctuation of Hg0 evasion was mainly attributed to wind speed in tropical sea areas, while in temperate zones were correlated with precipitation. Besides, air temperature variation seems to control the Hg0 evasion in the sea areas of South Temperate Zone (STZ) as well as South Frigid Zone (SFZ). Furthermore, an evident “seesaw” effect of Hg0 evasion anomaly was observed in equatorial Pacific, especially within Nino 3.4 and Nino 4, between El Niño(EN) and La Niña(LN) events. The increasing (decreasing) evasion anomaly in Nino 3.4 during the LN(EN) mainly attributed to the increase (decrease) of wind speed induced by stronger Walker circulation. While the increasing (decreasing) evasion anomaly in Nino 4 during EN(LN) was likely accounted for the rising (reducing) precipitation caused by the collapse of Walker circulation as well as the eastward shifting upward motion. Subsequently, the increasing anomaly of Hg0 evasion was simulated by GEOS-Chem model to further explore the potential impact. Results showed that countries, like American, China, India and Brazil. have occupied a large proportion of crops farming, but there spotted a relatively higher THg deposition anomalies, which might increase the human exposure to Hg. Finally, based on limited information, a hypothesis was put forward that there might be an indirect impact of ENSO-driven MeHg variation on the mass mortality of marine mammals.
Key Problems on Debris Flow Control Engineering after Wenchuan Earthquake in China
Authors: Gao Yanchao , Zhao Songjiang , Wang Jiazhu , Xu Wei
Published: March 2020

Strong earthquakes often induce a substantial rise in secondary geohazards. This problem has been studied more after the Great Kanto Earthquake in Japan and the Chichi Earthquake in Taiwan. In western China, after the 2008 Mw7.9 Wenchuan earthquake, large-scale regional debris flows occurred in 2008, 2009, 2010, 2011, 2013, 2014, and 2019 in the strong earthquake zone. Many control projects have been constructed, including more than 1,000 check dams. Part of the projects were damaged in the subsequent large debris flows. Debris flow after the earthquake is characterized by many loose sources, high frequency and large magnitude. Traditional design parameters and control engineering cannot meet disaster prevention requirements. In the 11 years after the Wenchuan earthquake, our research team continued to investigate the formation of the debris flow in the earthquake area, and summarized the reasons for the failure of the control projects, such as the low estimate of the loose sources and the insufficient design capacity of the check dam. In response to the above problems, we have proposed corresponding solutions, including the optimal combination of different control measures, the design of the dam site and storage capacity, and the structural form of the check dam. This optimization concept has been applied in debris flow prevention such as Qipan gully and Shaofang gully and has achieved good control results. The research provides a reference for subsequent disaster prevention and mitigation in similar earthquake areas.
Data products from the ESA CCI Sea Level Budget Closure project
Authors: Horwath Martin ,   Sea Level Budget Closure CCI Team
Published: March 2020

Studies of the sea-level budget are a means of assessing our ability to quantify and understand sea-level changes and their causes. ESA's Climate Change Initiative (CCI) projects include Sea Level CCI, Greenland Ice Sheet CCI, Antarctic Ice Sheet CCI, Glaciers CCI and the Sea Surface Temperature CCI, all addressing Essential Climate Variables (ECVs) related to sea level. The cross-ECV project CCI Sea Level Budget Closure used different products for the sea level and its components, based on the above CCI projects in conjunction with in situ data for ocean thermal expansion (e.g., Argo), GRACE-based assessments of ocean mass change, land water and land ice mass change, and model-based data for glaciers and land hydrology. The involvement of the authors of the individual data products facilitated consistency and enabled a unified treatment of uncertainties and their propagation to the overall budget closure. 

After conclusion of the project, the developed data products are now available for science users and the public. This poster summarizes the project results with a focus on presenting these data products. They include time series (for the periods 1993-2016 and 2003-2016) of global mean sea level changes and global mean sea level contributions from the steric component, from the ocean mass component and from the individual mass contributions by glaciers, the Greenland Ice Sheet, the Antarctic Ice Sheet and changes in land water storage. They are designed and documented in the consistent framework of ESA SLBC_cci and include uncertainty measures per datum. Additional more comprehensive information, such as geographic grids underlying the global means, are available for some components.

For the long-term trend, the budget is closed within uncertainties on the order of 0.3 mm/yr (1 sigma). Moreover, the budget is also closed within uncertainties for interannual variations.
Antarctic Ice Sheet mass balance over the past decade from 2005 to 2016
Authors: Lin Yijing
Published: March 2020

Global warming has become a world concerned issue which draws increasingly attention of the scientific community. Sea-level rise is an important indicator of Global warming as it integrates many factors of climate change including ice sheet melting.  The accurate assessment of the Antarctic ice sheet mass balance is applied to deeply explore the impact of minor change in Antarctic ice sheet on sea level rise. Based on multi-source remote sensing product, we finely estimated the mass balance of the Antarctic ice sheet and discussed dynamics and climatological causes of the fluctuations from 2005 to 2015 by IOM (Input-Output-Method).

In our study, the calculation method of ice flux on the grounding line is improved. We also precisely evaluate the ice flux as an output component. The result shows that: (1) The Antarctic ice sheet was continuously losing mass during the period of 2005-2016. (2) The mass loss of the Antarctic ice sheet was dominated by West Antarctica when East Antarctica was in a positive mass balance, but some basins also occurred significant mass loss. The Antarctic peninsula fluctuated in a state of zero balance. (3) The change in the mass balance of the ice sheet was dominated by the surface mass balance as a whole, and was mainly affected by the interannual variation of climatological factors. From a small-scale perspective, ice shelf thinning and glacier calving causes the change of ice flux on the grounding line. That change leads to the severe mass loss in the region it happened. Therefore the mass loss in the year of the disintegration event happened increases.
Laplacian structure, solution domain geometry and successive approximations in gravity field studies
Authors: Holota Petr , Nesvadba Otakar
Published: March 2020

When treating geodetic boundary value problems in gravity field studies, the geometry of the physical surface of the Earth may be seen in relation to the structure of the Laplace operator. Similarly as in other branches of engineering and mathematical physics a transformation of coordinates is used that offers a possibility to solve an alternative between the boundary complexity and the complexity of the coefficients of the partial differential equation governing the solution. The Laplace operator has a relatively simple structure in terms of spherical or ellipsoidal coordinates which are frequently used in geodesy. However, the physical surface of the Earth substantially differs from a sphere or an oblate ellipsoid of revolution, even if these are optimally fitted. The situation may be more convenient in a system of general curvilinear coordinates such that the physical surface of the Earth is imbedded in the family of coordinate surfaces. The structure of the Laplace operator, however, is more complicated in this case and in a sense it represents the topography of the physical surface of the Earth. The Green’s function method together with the method of successive approximations is used for the solution of geodetic boundary value problems expressed in terms of new coordinates. The structure of iteration steps is analyzed and if useful, it is modified by means of the integration by parts. Subsequently, the individual iteration steps are discussed and interpreted.
Molecular Dynamics simulations indicate solvation and stability of single-strand RNA at the air/ice interface, supporting a primordial RNA world on Ice
Authors: Neshyba Steven , Gladich Ivan , Rowe Penny , Berrens Maggie , Pereyra Rodolfo
Published: March 2020

Outstanding questions about the RNA world hypothesis for the emergence of life on Earth concern the stability and self-replication of prebiotic aqueous RNA. Recent experimental work has suggested that solid substrates and low temperatures could help resolve these issues. Here, we use classical molecular dynamics simulations to explore the possibility that the substrate is ice itself. We find that at -20 C, a quasi-liquid layer at the air/ice interface partially solvates a short (8-nucleotide) RNA strand such that the phosphate backbone anchors to the underlying crystalline ice structure though long-lived hydrogen bonds. The hydrophobic bases, meanwhile, are seen to migrate toward the outermost layer, exposed to air. Our simulations also reveal two key kinetic differences with respect to aqueous RNA. First, hydrogen bonds between solvent water molecules and phosphate diester moieties, believed to shield the RNA from hydrolysis, are much longer-lived for RNA on ice, compared to aqueous RNA at the same temperature. Second, contact between solvent water and ribose 2-OH’ groups, considered a precursor to nucleophilic attack by deprotonated 2-OH’ on the phosphate diester, is significantly less frequent for RNA on ice. Both differences point to lower susceptibility to hydrolysis of RNA on ice, and therefore increased opportunities for polymerization and self-copying compared to aqueous RNA. Moreover, exposure of hydrophobic bases at the air/ice interface offers opportunities for reaction that are not readily available to aqueous RNA (e.g., base-pairing reaction with free nucleotides diffusing across the air/ice interface). These findings thus offer the possibility of a role for an ancient RNA world on ice distinct from that considered in extant elaborations of the RNA world hypothesis. This work is, to the best of our knowledge, the first molecular dynamics study of RNA on ice.
Non-iterative numerical model of soil freezing
Authors: Vogel Tomas , Dohnal Michal , Votrubova Jana , Dusek Jaromir
Published: March 2020

Increasingly, numerical models of varying complexity are used to simulate the thermal and water balance of soils exposed to freezing-thawing cycles. An important aspect of soil freezing modeling is the highly non-linear nature of the energy balance equation during phase transition. To handle the transformation between sensible and latent heat during freezing–thawing events, the majority of existing models employ the concept of apparent heat capacity. The main disadvantage of this approach is that the apparent heat capacity increases by several orders of magnitude at the freezing point, which complicates the numerical solution, possibly causing numerical oscillations and convergence problems.

An alternative approach was developed to facilitate the simulations of soil water flow and energy transport during sporadic freezing–thawing episodes, which are typical for the winter regime of humid temperate continental climate. The approach is based on an accurate non-iterative algorithm for solving highly non-linear energy balance equation during phase transitions. The suggested modeling approach abstracts from many complexities associated with the freezing phenomena in soils, yet preserves the principal physical mechanism of conserving the internal energy of the soil system during the phase transitions. When applied to simulate occasional freezing soil conditions, the model algorithm delivers the desired effect of slowing down the propagation of surface freezing temperatures into deeper soil horizons by converting water latent heat into sensible heat. The model also allows the evaluation of the extent and duration of frozen soil conditions – a crucial information for soil water flow modeling, as the frozen soil significantly reduces the soil hydraulic conductivity.

The proposed algorithm was successfully verified against analytical solutions for idealized freezing and thawing conditions and applied to both hypothetical and real field conditions.
Impacts of invasive fauna and wildfires on hydrological regimes in a tropical valley of New Caledonia (SW Pacific)
Authors: Tramier Caroline , Genthon Pierre , Delvienne Quentin , Sauvan Nicolas , Cassan Jean-Jérôme , Ebrard Etienne , Dumas Pascal , Queffelean Yann
Published: March 2020

In New Caledonia wildfires and invasive animal species (deers and wild pigs) constitute major agents of land surface degradation and an important threat to forests. As a result of land degradation the lagoon and the quality of drinking water are impacted by sediments transported by rivers. The study area, the Thiem watershed, is located on the northeast windward coast of New Caledonia and on micaschist basement. The landscape is constituted by a mosaic of savannahs and forests. Forests are restricted to highest remote areas or near talwegs and waterways. Savannahs are located on the crests and on the superior slopes of watersheds, near the villages. The hydrological regime of contrasted land surfaces is assessed using a 1 year record from three 100 m2 plots located in a healthy forest, in a forest degraded by invasive fauna and in a woody savannah regularly burned. Significant isolated rainy events (50-100 mm rainfall) were observed during the dry season (May-December), while the wet season presented only few isolated dry periods. Difference of monthly rainfall between the three plots were less than 10% as a general rule. However rainfall difference reach 30% at the scale of a rainy event. Moreover, 40% of rain occurs during small events with less than 50 mm cumulated rainfall, although events larger than 200 mm were observed. The healthy forest corresponds to an annual runoff coefficient of 0.04 which is commonly observed in tropical forests. The savannah corresponds to a 0.16 coefficient which is in the high range of those commonly observed in similar tropical areas. The degraded forest presents a 0.86 runoff, rising to more than 100% for many rainy events of the wet season. The maximum event-based runoff coefficient was observed in the three plots during the OMA cyclone, corresponding to 0.18, 0.71 and 2.7 at the healthy forest, savannah and degraded forest respectively. It is proposed that the extra runoff (ER) regularly observed at SCAR results from subsurface flow originating from the upstream area and focused toward the plot. A reservoir model is proposed and calibrated against available data. The model results indicate that ER accounts for 47% of the total observed runoff in this plot. Our study confirms the major role played by subsurface flow in the water regime of forested and savannah areas. It is emphasized that subsurface flow exfiltration in degraded land surfaces could enhance erosion and transport of harmful bacteria (leptospira). Moreover savannah, as a dominant high runoff surface in upper catchments of our study area, might control runoff at the scale of the watershed and might constitute a target for controlling downstream flooding and gullies erosion.
Effect of gravity data coverage on geoid determination: comparison between Stokes and Collocation techniques in Egypt and Austria
Authors: Abd-Elmotaal Hussein , Kühtreiber Norbert
Published: March 2020

The coverage of the gravity data plays an important role in the geoid determination. This paper tries to answer whether different geoid determination techniques would be affected similarly by such gravity data coverage. The paper presents the determination of the gravimetric geoid in two different countries where the gravity coverage is quite different. Egypt has sparse gravity data coverage over relatively large area, while Austria has quite dense gravity coverage in a significantly smaller area. Two different geoid determination techniques are tested. They are Stokes’ integral with modified Stokes kernel, for better combination of the gravity field wavelengths, and the least-squares collocation technique. The geoid determination has been performed within the framework of the non-ambiguous window remove-restore technique (Abd-Elmotaal and Kühtreiber, 2003). For Stokes’ geoid determination technique, the Meissl (1971) modified kernel has been used with numerical tests to obtain the best cap size for both geoids in Egypt and Austria. For the least-squares collocation technique, a modelled covariance function is needed. The Tscherning-Rapp (Tscherning and Rapp, 1974) covariance function model has been used after being fitted to the empirically determined covariance function. The paper gives a smart method for such covariance function fitting. All geoid are fitted to GNSS/levelling geoids for both countries. For each country, the computed two geoids are compared and the correlation between their differences versus the gravity coverage is comprehensively discussed.
Korea Institute of Ocean Science & Technology Earth System Model and its simulation characteristics
Authors: Kim Young Ho , Pak Gyundo , Noh Yign , Lee Myong-In , Yeh Sang-Wook , Kim Daehyun , Kim Sang-Yeob , Lee Joon-Lee , Lee Ho Jin , Hyun Seung-Hwon , Lee Kwang-Yeon , Lee Jae-Hak
Published: March 2020

In our presentation, we will show the performance of a new earth system model developed at the Korea Institute of Ocean Science and Technology (KIOST), called the KIOST-ESM. The KIOST-ESM is based on a low-resolution version of the Geophysical Fluid Dynamics Laboratory Climate Model version 2.5. The main changes made to the base model include using new cumulus convection and ocean mixed layer parameterization schemes, which improve the model fidelity significantly. In addition, the KIOST-ESM adopts dynamic vegetation and new soil respiration schemes in its land model component. The performance of the KIOST-ESM was assessed in pre-industrial and historical simulations that are made as part of its participation into Climate Model Intercomparison Project phase 6. The response of the earth system to increases in greenhouse gas concentrations were analyzed in the ScenarioMIP simulations. The KIOST-ESM exhibited superior performance compared to the base model in terms of the mean sea surface temperature over the Southern Ocean and over the cold tongue in the tropical Pacific. The KIOST-ESM can also simulate the dominant tropical variability in the intraseasonal (Madden-Julian Oscillation) and interannual (El Niño-Southern Oscillation) timescales more realistically than the base model. On the other hand, like many other contemporary ESMs, the KIOST-ESM showed notable cold bias in the Northern Hemisphere, and the so-called double-Intertropical Convergence Zone bias remains. The ScenarioMIP results confirm the global average surface atmospheric temperature responds to the CO2 concentration.
Momentum flux across breaking air-water interface
Authors: Takagaki Naohisa , Suzuki Naoya , Matsuda Keigo , Komori Satoru , Troitskaya Yuliya
Published: March 2020

It is important to measure the momentum flux across the air–water interface in the droplet- and bubble-laden turbulent flow at extremely high-wind speeds. Generally, the momentum flux is measured by a profile method, eddy correlation method, or momentum budget (balance) method at normal wind speeds. We assessed the usage of three measurement method at extremely high wind speeds in three wind-wave tanks, Kyoto, Kindai, and Kyushu Universities, JAPAN. Here, the Kyoto tank is 15 m long, 0.8 m wide, 0.8 m high and the maximum wind speed is 68 m/s. The Kyushu tank is 64 m long and the max. speed is 40 m/s. Moreover, we will show the preliminary results for the effects of the fetch on the momentum flux.
A numerical study about the influence of channel-scale secondary circulation on mixing processes at Kama/Vishera confluence
Authors: Lyubimova Tatyana , Lepikhin Anatoly , Parshakova Yanina , Gualtieri Carlo , Roux Bernard , Lane Stuart
Published: March 2020

Confluences are common components of all riverine systems, and are characterized by converging flow streamlines and mixing of separate flows, which can take some significant distance to be complete. Whilst turbulent diffusion and Taylor dispersion are expected to affect mixing in any open channel flow, the analysis of mixing at river confluences should also consider some peculiar processes, which could be divided between near-field processes and far-field processes. The former, which have been well studied, are those operating at the junction itself and lead to rapid mixing only if some form of asymmetry (geometry, discordance, momentum, density difference) between the tributaries exists. The latter are advective processes, such as secondary circulation, that can enhance mixing to degrees greater than those associated with turbulent diffusion or Taylor dispersion combined. These processes, which have received less attention, were investigated using a three-dimensional computation of the Reynolds averaged Navier-Stokes equations combined with a Reynolds stress turbulence model for the confluence of the Kama river and Vishera rivers in the Russian Urals. To test the hypothesis that far-field mixing can be both enhanced and reduced by the type of secondary circulation that develops, numerical simulations on an idealized configuration (rectangular channel with no curvature) and on the real configuration with the natural planform and/or bathymetry were carried out to isolate the relative impacts of real planform and bathymetry on secondary circulation and mixing for different combinations of momentum/discharge ratio. Results show that if the rivers are represented as an idealized junction, the initial vortices that form due to channel-scale pressure gradients decline rapidly with distance downstream. Mixing is slow and incomplete at more than 10 multiples of channel width downstream from the junction corner. On the other side, if the real configuration is introduced, rates of mixing increase dramatically. This is related to both increase intensity of secondary circulation at the junction and the formation of a single channel-scale vortex downstream of the junction. The latter appears to be aided by curvature of the post-junction channel. This effect is strongest when the discharge of the tributary that has the same direction of curvature as the post junction channel is greatest.

The study was performed under financial support of the Government of Perm Krai (grant C 26/788) and Russian Foundation for Basic Research (grant 19-41-590013).
Changes in hydrological behaviour: case studies of the Unica and Rižana karst springs, Slovenia
Authors: Ravbar Natasa , Kovačič Gregor , Petrič Metka
Published: March 2020

Environmental changes, such as alterations in precipitation and evapotranspiration regimes, changes in vegetation type, etc. are triggering direct impact on hydrological cycle through modified amounts and patterns of recharge conditions, as well as occurrence of more frequent and severe hydrometeorological events. Karst aquifers are particularly vulnerable to these effects due to highly dynamic hydrological processes. In this study, we were interested in studying the possibilities to observe changed hydrological behaviour of karst springs on a human timescale. Therefore, we focused on two examples in Slovenia, both regionally important for freshwater supply, agriculture and hydropower. The Unica spring mostly drains areas under moderate continental climate. Its catchment has been repeatedly and severely hit by natural disasters (e.g., ice break, bark beetle attack, windthrow) after 2014 causing large-scale forest disturbances. The catchment of Rižana spring, on the other hand, belongs to the moderate Submediterranean climate. There these types of disturbance did not occur in recent years (excluding some wildfires), but the catchment has been liable to substantial land use changes in the past six decades. For assessment of vegetation cover changes and large-scale disturbances in forests, historical digital orthophotos of the Surveying and Mapping Authority of the Republic of Slovenia since 1957 have been compared with the recent land use data provided by Ministry of Agriculture, Economy and Food and forest state database of Slovenian Forest Service. At the same time, hydrological data of the Unica (Hasberg gauging station) in the period 1962-2018 and Rižana springs (Kubed gauging station) in the period 1966-2018 and precipitation data from Postojna (period 1962-2018) and Podgrad (period 1966-2018) meteorological stations have been processed. Individual flood pulse events over the 57 years for Unica and 53 years for Rižana have been separated. For each flood pulse various information about precipitation amount and intensity, duration of discharge increase, its intensity and amplitude have been specified. We compared these findings with the calculated trends of meteorological and hydrological variables and also changes in land use. The impact of particular environmental change on discharge values of both springs has been evaluated, showing that both, climate and land-use changes, have considerable impact on hydrological regime of studied karst springs. In particular, altered duration of flood pulses increase, their amplitude and intensity have been observed, meaning that the most important issues of water availability that are crucial for water-dependant economic sectors are under threat.
From experimental granular collapses to a three-dimensional numerical solver for landslides
Authors: Wyser Emmanuel , Podladchikov Yury , Derron Marc-Henri , Jayboyedoff Michel
Published: March 2020

A granular collapse can be regarded as an idealized case of slumping, e.g., landslides. It consists in a sudden release, by the mean of an apparatus, of a dry granular mass initially contained which elasto-plastically collapses under its self weight and flows upon it reaches a new equilibrium.

We investigated such process by, i) performing numerical simulations and observing experimental evidences thanks to a newly designed apparatus that minimizes initial influences of the retaining walls over the collapse dynamic and, ii) developing an analytical formulation for the run-out distance of the granular mass in agreement with both experimental evidences and numerical solutions obtained by a home-made Material Point Method (MPM) implementation in Matlab based on the Generalized Interpolation Material Point (GIMP) variant. Finally, we further iii) showcase the suitability of the MPM solver to study strain localization problems and associated deformations considering homogeneous or inhomogeneous material properties for dry slumping processes.

We report an excellent agreement of the analytical solution with the experimental data. However, numerical solutions are in a similar range of validity but tend to overestimate the runout distance of the collapse. Nevertheless, large deformations induced by the elasto-plastic collapse are well captured by the solver. In addition, we report similar runout distances regardless for elasto-plastic constitutive relation. We finally demonstrate the importance of heterogeneities over the strain localization and the role of initial geometry in the non-linear behavior of the slumps. Moreover, this also establishes MPM as a relevant numerical framework to address fundamental issues for the geomechanics of slumping.
Evapotranspiration estimation with MODIS land surface temperature after correction of the angle effect with two MODIS BRDF related products
Authors: Jiang Yazhen , Tang Ronglin , Jiang Xiaoguang , Li Zhao_Liang
Published: March 2020

Land surface temperature (LST) from remote sensing has been widely used to estimate regional and local scale evapotranspiration (ET). However, remotely sensed LST viewed by the same sensor from different angles would lead to different LST retrievals and this would lead to the deviation in ET estimations with LST as input. The terrestrial surface bidirectional reflectance distribution function (BRDF) are commonly inverted against multiple cloud-free, atmospherically-corrected directional reflectance values that sufficiently sample the anisotropy caused by different view angles. The MODerate-resolution Imaging Spectroradiometer (MODIS) product MCD43A1 contains three-dimensional (3D) data sets and can provide weighting parameters for the models used to derive the Albedo. The MODIS MCD43A4 is reflectance product providing reflectance data adjusted using a bidirectional reflectance distribution function (BRDF) to model the values as if they were taken from nadir view and solar zenith. Here we intend to operate the correction of the angle effect in LST with these two MODIS BRDF related products in ET estimation. The two products are used to provide reflectance with consistent view angle and with solar zenith of satellite sensor and 0° solar zenith, respectively, and then corresponding fractional vegetation cover (FVC) are calculated with two kinds of corrected reflectance, respectively. Combining the soil temperature (Ts) and vegetation temperature (Tv) components which are separated from MODIS LST and have no directional effects with the corrected FVC, the nadir LST (with solar zenith of satellite sensor and 0°solar zenith, respectively) were obtained. Finally, ET were estimated with the surface energy balance system (SEBS) model using the remote sensed LST and the two kinds of corrected LST as input, respectively. The results showed that compared to ET measurements, the ET estimations with two kinds of corrected LST as input performed much better than that with uncorrected LST as input, and ET estimation with corrected LST in which FVC are calculated from MCD43A1 had highest accuracy.
Investigating quasi-resonant Rossby waves with an idealized general circulation model
Authors: Mooring Todd , Linz Marianna
Published: March 2020

Petoukhov et al.’s (2013, PNAS) hypothesis of quasi-resonant Rossby waves as a mechanism for destructive weather extremes—both heat- and rain-related, observed and projected—has received a great deal of attention in recent years.  Most notably, it has been used for diagnostic studies of reanalysis products and full-physics atmospheric or coupled general circulation models. However, studies of this sort essentially assume (rather than test) the validity of the underlying theory.

Since the quasi-resonance theoretical arguments do not explicitly involve the full complexity of atmospheric physics, it ought to be possible to test them within the much simpler framework of an idealized general circulation model. By carefully constructing the forcing fields for such a model, we will achieve control of its zonal mean state and thus the waveguide properties of the zonal jet. We will explore the properties of the quasi-stationary Rossby waves in such simulations to test whether they have the properties predicted by Petoukhov et al. By testing this dynamical mechanism in a simplified model, we can better understand its applicability and limitations for investigations of future climate.
Combined analysis of polarimetric SAR data and optical imagery for rapid landslide mapping in vegetated areas
Authors: Plank Simon , Martinis Sandro
Published: March 2020

Rapid mapping of the extent of the affected area as well as type and grade of damage after a landslide event is crucial to enable fast crisis response, i.e., to support rescue and humanitarian operations. Change detection between pre- and post-event very high resolution (VHR) optical imagery is the state-of-the-art in operational rapid mapping of landslides. However, the suitability of optical data relies on clear sky conditions, which is not often the case after landslides events, as heavy rain is one of the most frequent triggers of landslides. In contrast to this, the acquisition of synthetic aperture radar (SAR) imagery is independent of atmospheric conditions. SAR data-based landslide detection approaches reported in the literature use change detection techniques, requiring VHR SAR imagery acquired shortly before the landslide event, which is commonly not available. Modern VHR SAR missions, e.g., Radarsat-2, TerraSAR-X, or COSMO-SkyMed, do not systematically cover the entire world, due to limitations in onboard disk space and downlink transmission rates. Here, we present a fast and transferable procedure for mapping of landslides in vegetated areas, based on change detection between pre-event optical imagery and the polarimetric entropy derived from post-event VHR polarimetric SAR data. Pre-event information is derived from high resolution optical imagery of Landsat-8 or Sentinel-2, which are freely available and systematically acquired over the entire Earth’s landmass. The landslide mapping is refined by slope information from a digital elevation model generated from bi-static TanDEM-X imagery. The methodology was successfully applied to two landslide events of different characteristics: A rotational slide near Charleston, West Virginia, USA and a mining waste earthflow near Bolshaya Talda, Russia.
Changes in the hydrodynamic intensity of Bosten Lake and its impact on early human settlement in the northeastern Tarim Basin, eastern Arid Central Asia
Authors: Xie Haichao
Published: March 2020

The climate of eastern arid central Asia (ACA) is extremely dry and early human settlement and civilization in the region were dependent upon a potentially unstable water supply. Thus, knowledge of the history of hydrological fluctuations is essential for understanding the relationship between humans and the environment in the region. Here we present a record of variation in lake hydrodynamic intensity based on the grain size of suspended lacustrine silt isolated from the sediments of Bosten Lake, which feeds a river flowing to the northeastern Tarim Basin. The results show that lake hydrodynamic intensity was very weak, and/or that the lake dried-out completely, during the early Holocene (12.0–8.2 ka). Then it increased with two distinct centennial-millennial-scale intervals of weak intensity occurring during 4.7–3.5 ka and 1.2–0.5 ka. Notably, increases in lake hydrodynamic intensity occurred some 2.2 kyr prior to an increase in local precipitation and effective moisture. We speculate that this was a consequence of relatively high early summer temperatures during 8.2–6.0 ka that resulted in an increased water supply from melting snow and ice in mountainous areas of the catchment. Thus, we conclude that changes in the hydrodynamic intensity of Bosten Lake during the Holocene were affected by changes in both temperature and precipitation. The variations in the hydrodynamic intensity of Bosten Lake since the middle Holocene also influenced water availability for the human population that occupied the downstream area of the northeastern Tarim Basin. A persistent increase in hydrodynamic intensity during 2123–1450 B.C. may have been responsible for human occupation of the region that contains the noted archaeological sites of Xiaohe and Gumugou Cemetery. In addition, a drastic decrease in hydrodynamic intensity at around 400 A.D. likely caused the emigration of the inhabitants of Loulan.
Green Sahara periods and climate-human interactions during the Last Glacial Period: Evidence from Northwest African speleothems
Authors: Ait Brahim Yassine , Sha Lijuan , Wassenburg Jasper A. , Cruz Francisco W. , Cheng Hai
Published: March 2020

North Africa is a key region to study the interactions between low-latitude African monsoon systems and high-latitude millennial-scale climate change. Here, we present new high‐resolution δ18O records and preliminary Δ17O data (deviation of triple oxygen isotope data between δ17O and δ18O) from four Southwest Moroccan speleothems (⁓31°N) spanning the last glacial period. Our δ18O records provide evidence of humid conditions during the Marine Isotope Stage (MIS) 5 and the early to mid‐Holocene. The apparent increase in moisture during these Green Sahara periods is linked to the increase of summer insolation and the resulting expansion of the West African monsoon fringe, which could reach 31°N in NW Africa. Furthermore, the preliminary Δ17O results support our interpretation of δ18O data and reveal substantial changes in moisture sources and climate regimes between glacial and interglacial cycles.

Additionally, the Green Sahara periods are good examples to illustrate how dramatic climate change could shape human life in Africa – the original home of anatomically modern humans (AMH). Archaeological evidence shows that the human populations in North Africa during MIS5 were geographically well placed to disperse after the “Green Sahara” faded. Our climate record shows an abrupt deterioration of climate conditions during the MIS5-MIS4 transition, which has been proposed as one of the main factors that pushed AMH to move into Eurasia. Interestingly, the MIS5-MIS4 transition is characterized by a decrease of summer insolation and the occurrence of the Heinrich events 7a and 7b, which possibly induced a southern shift of the Intertropical Convergence Zone (ITCZ) and, therefore, a retreat of the African monsoon during this period.
Predictability of the Wintertime 500 hPa Geopotential Height over Ural-Siberia in the NCEP Climate Forecast System
Authors: Zou Meng
Published: March 2020

Using hindcast and forecastdata from the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2)for the period 1982-2017, we comprehensively assess the predictability of the climatology, interannual variability, and dominant modes of the wintertime 500 hPa geopotential height over Ural-Siberia (40-80°Nand 30-100°E). Although the climatic mean 500 hPa heightover Ural-Siberia simulated by NCEP CFSv2has a negative bias, especially over the eastern part of the region, NCEP CFSv2 well predicts the spatial distribution of the two major modes(EOF1 and EOF2) over this region 2 months in advance.The forecasting skill of the principal component (PC) of the two major modes,PC1 (PC2), is highest1 (0) month in advance, where the linear correlation coefficient between the predicted and observed time series reaches +0.36 (+0.67), exceeding the 95% confidence level. Conversely, the forecasting skill of PC1 (PC2) is very low 0 (1) month in advance. The main reason for the poorer(better) prediction of PC1 0 (1) month in advance is associated with a less (more) accurate response of the Eurasian teleconnection to SST anomalies over the southwestern Atlantic. For PC2, the better (poorer) prediction of PC2 0 (1) month in advance may be due to more (less) accurate responses of the stratospheric polar vortex and the Scandinavian teleconnection to the dipole SST anomalies over the North Pacific. These results are useful for evaluating the predictability of the East Asian winter climate.
Synoptic climatological analysis on the rather abrupt seasonal transition to mid-winter situation around Germany with intermittent appearance of extremely low temperature events.
Authors: Miyake Chihiro , Kato Kuranoshin
Published: March 2020

  To know the detailed seasonal cycle in various regions, confined only to the middle and higher latitudes, is the common basis for deeper understanding of the seasonal backgrounds of (1) extreme meteorological or climatological events and (2) cultural generation through the “seasonal feeling” leading to cultural understanding education. For example, our previous studies (e.g., Kato et al. 2017) pointed out that the “seasonal feeling” on the severe winter relating to the traditional event for driving the winter away (“Fasnacht”) around Germany might be due to the intermittent appearance of the extremely low temperature events, although the winter mean temperature there is lower only by about 3~5℃ than in southern Japan. Hamaki et al.(2018) suggested the appearance of such events to be controlled greatly by the intraseasonal behaviors of the Icelandic low. Furthermore, Kuwana et al. (EGU2018 and 2019) pointed out the asymmetric seasonal progression of the behaviors of the Icelandic low including its intraseasonal variation from the autumn to the next spring. However, it has not been clarified yet what kind of seasonal transition of the dominant large-scale daily fields was related to the increase in appearance frequency of such extremely low temperature events after mid-December. Thus the present study will further examine the detailed features on the above processes, mainly for the 2000/2001 winter based on the NCEP/NCAR reanalysis data.

  Appearance frequency of extremely low temperature events (e.g., below -5℃) rapidly increased around mid-December of 2000 with the large amplitude of its intraseasonal variation although the seasonal mean the Icelandic low appeared from mid-October. It is interesting that the daily mean temperature decreased gradually with shorter-period fluctuation until mid-December, even after the seasonal formation of the Icelandic low.

  As for the seasonal mean fields from mid-December to the next March, the northeastern portion of the Icelandic low area extended more closely to the northwestern Europe and the baroclinicity was enhanced especially to the south of ~55°N. Composite analyses suggest that the extremely low temperature events after mid-December around Germany was related not only to the weakening and westward retreat of the Icelandic low but also to the cold air advection by the low-level easterly wind along the southeastern edge of the intraseasonal-scale surface high to the north of Germany.
Estimation of snow water equivalent in a mountain range by using a dynamic regression approach
Authors: Collados-Lara Antonio-Juan , Pulido-Velazquez David , Pardo-Igúzquiza Eulogio , Alonso-González Esteban , López-Moreno Juan Ignacio
Published: March 2020

The snow dynamics in alpine systems governs the hydrological cycle in these regions. However, snow data are usually limited due to poor accessibility and limited funds. On the other hand, the majority of scientific studies about snow resources are carried out at mountain slope or basin scale. The main goal of this work is to propose a parsimonious methodology to estimate snow water equivalent (SWE) at mountain range scale. A regression model that includes non-steady explanatory variables is proposed to assess snow depth dynamic based on the information coming from snow depth point observations, a digital elevation model, snow cover area from satellite and a precipitation index representative of the area. The main advantages of the method are its applicability in cases with limited information and in mountain ranges scales. In the proposed methodology different regression model structures with different degrees of complexity are calibrated combining steady and non-steady explanatory variables (elevation, slope, longitude, latitude, eastness, northness, maximum upwind slope, radiation, curvature, accumulated snow cover area and precipitation in a temporal window) and four basic mathematical transformations of these variables (square, root square, inverse and logarithm). In the case of the temporal variables different time windows to define the accumulated values of the explanatory indices have been tested too. We have applied the methodology in a case study, the Sierra Nevada mountain range (Southern Spain), where the calibration has been performed by using the snow depth data observation provided by the ERHIN program which have a very low temporal frequency (2 or 3 measurement per year). When only non-steady explanatory variables are considered, the coefficient of determination of the global spatial estimation model is 0.55. When we also include non-steady variables we obtain an approach with a coefficient of determination of 0.62. We have also calibrated a new regression approach by using, in addition to the ERHIN program information, data coming from a detailed temporal series of snow depth in a new specific location, which has allow to obtain models with R² of 0.59 (for steady explanatory variables) and 0.64 (including also non-steady explanatory variables). The dynamic of the snow density in the mountain range has been estimated by means of a physically based simulation driven by WRF data. Combining the snow depth and the density approaches we have estimated the final SWE in Sierra Nevada. 

This research has been partially supported by the SIGLO-AN project (RTI2018-101397-B-I00) from the Spanish Ministry of Science, Innovation and Universities (Programa Estatal de I+D+I orientada a los Retos de la Sociedad).