bluuebunny/crossref_metadata_2025 huggingface dataset:
Synoptic Circulation Patterns and Climate Regionalization of East Africa
Authors: Ware Markos , Mori Paolo , Warrach -Sagi Kisten , Jury Mark , Schiwtalla Thomas , Wulfmeyer Volker
Published: March 2020

Abstract. Climate regionalization is crucial for climate studies, especially in the case of heterogeneous regions like East Africa. This paper focuses on categorizing Ethiopia into homogeneous climatic sub-regions by applying a classiﬁcation of circulation patterns on precipitation. The sub-regions obtained will be applied on the verification of WRF-NOAHMP seasonal simulations performed over the Horn of Africa. We analyzed the occurrence of each circulation type per month and per year over the whole country. Then, trend analysis of temperature and precipitation over the respective sub-regions were performed. Principal Component Analysis (PCA) were applied to group daily mean Sea Level Pressure (SLP) into Circulation Types (CTs). Then, PCA coupled with k-means clustering employed to regionalize precipitation fields (distributed spatially) following CTs into homogeneous climatic sub-regions. Observational data were obtained from the National Center for Environmental Prediction (NCEP) reanalysis, Climate Hazards Group Infrared Precipitation with Stations (CHIRPS version 2), and National Meteorology Agency (NMA) of Ethiopia (gauge 1st and 2nd classes). Five principal components, which explain 98% of the total variance, were maintained using the Scree test technique. Ten CTs were obtained using positive and negative phases of each principal component scores following the extreme score values (> 2 and < −2) procedure. From ten CTs, we found that three (CT1, CT3, and CT8) were characterized by low pressure over the southwest corner of the domain, which consequently brings rainfall over the Ethiopian highlands. The number of days classified under different CTs shows different trends. CTs seasonal distribution agreed with the regional seasons. Long-term monthly mean rainfall ranges from 0-600 mm over the region. Ethiopia is clustered into four homogeneous sub-regions based on the spatial distribution of precipitation following CTs. Rainfall from CHIRPS and gauge did not have any specific trend over the sub-regions, however high standardized anomalies were observed compared to the long term mean. The temperature showed a 2 °C change for the past three decades. There was a negligible difference in the shape, size, and location of regions using data from different sources. The final decision on the optimal number of homogeneous climatic sub-regions depends upon the research objective, geographical domain size, and topographic features of the domain. This study provides an assessment and decision pathway.

 

Keywords: climatology, regionalization, Ethiopia, precipitation, k-means, circulation types
Evaluation and Projection of Extreme Precipitation over Northern China in CMIP5 Models
Authors: Lu Xi
Published: March 2020

This study evaluates 32 climate models from CMIP5 compared with a daily gridded
observation dataset of extreme precipitation indices including total extreme precipitation (R95p),
maximum consecutive five days of precipitation (RX5day) and wet days larger than 10 mm of
precipitation (R10mm) over Northern China during the historical period (1986–2005). Results show
the majority models have good performance on spatial distribution but overestimate the amplitude of
precipitation over Northern China. Most models can also capture interannual variation of R95p and
RX5d, but with poor simulations on R10mm. Considering both spatial and temporal factors, the best
multi-model ensemble (Group 1) has been selected and improved by 42%, 34%, and 37% for R95p,
RX5d, and R10mm, respectively. Projection of extreme precipitation indicates that the fastest-rising
region is in Northwest China due to the enhanced rainfall intensity. However, the uncertainty
analysis shows the increase of extreme rainfall over Northwest China has a low confidence level.
The projection of increasing extreme rainfall over Northeast China from Group 1 due to the longer
extreme rainfall days is more credible. The weak subtropical high and southwest winds from Arabian
Sea lead to the low wet biases from Group 1 and the cyclonic anomalies over Northeast China, which
result in more extreme precipitation.
Estimating real driving emissions from MAX-DOAS measurements at the A60 motorway near Mainz
Authors: Lauster Bianca , Dörner Steffen , Donner Sebastian , Uhlmannsiek Katharina , Gromov Sergey , Beirle Steffen , Wagner Thomas
Published: March 2020

Nitrogen oxides (NOx = NO + NO2) have a direct and indirect impact on human health. Therefore, the World Health Organization recommends limiting the concentration of nitrogen dioxide (NO2) in the atmosphere. Nevertheless, these limits are regularly exceeded. Especially, fossil fuel combustion from road traffic is a major contributor to the emission of NOx.

Multi Axis-Differential Optical Absorption Spectroscopy (MAX-DOAS) is able to measure trace gases in the lower troposphere. Here, this remote sensing method was used to measure NOx emissions at a highly frequented motorway. Two MAX-DOAS instruments were set up on both sides of the A60 motorway close to Mainz, Germany. The parallel viewing direction allows measuring the background signal at the upwind side and the background plus traffic emissions on the downwind side. Together with the effective wind speed perpendicular to the motorway, it is thus possible to retrieve the total traffic emissions. Compared to the expected emissions calculated from the European emission standards, the derived emissions of NOx are by a factor 7±4 higher.

In this study, first measurement results are presented and the method is evaluated with regard to the practicability and error margin.
The critical importance of multi-decadal groundwater level observations for informing robust climate change impact assessments: lessons from sub-Saharan Africa
Authors: Cuthbert Mark , Taylor Richard
Published: March 2020

Groundwater is of fundamental importance to strategies for poverty reduction in tropical Africa and understanding the sustainability of more widespread groundwater abstraction for improving water and food provision is a key challenge. However, the hydraulic processes governing groundwater recharge that sustain this resource, and their sensitivity to climatic variability and change, are poorly constrained. Here we present results from The Chronicles Consortium initiative, which has collated multi-decadal groundwater hydrographs and co-located rainfall records across tropical Africa to better understand climate controls, among others, on groundwater recharge.

We find that recharge in more arid environments is generally highly dependent on infrequent large rainfall events causing focused recharge through losses during ephemeral overland flows. This process is not included in any large scale hydrological or land surface models, and these events are often driven by synoptic climate controls, which are themselves poorly constrained in existing climate models. In more humid locations, we find surprisingly linear relationships between rainfall and recharge indicating an apparent lack of threshold behaviour that is embodied in most hydrological models and hypothesise this is due to prevalence of preferential flow processes in the soil zone. While aridity exerts a strong control on the predominant recharge process, geological variations can dominate the observed sensitivity of recharge to climate variability.

Our results reveal the critical importance of long-term observational records for understanding the sensitivity of recharge to climate processes with implications well beyond Africa. This especially true in dryland environments where interpretations of short records would miss fundamental, episodic climate-controls on recharge expressed in longer records. We conclude that without a sound long-term observational basis for groundwater-climate sensitivity, climate change forecasts cannot be confidently constrained.
Evaluating skill and robustness of seasonal meteorological and hydrological drought forecasts at the catchment scale – Case Catalonia (Spain)
Authors: Van Lanen Henny A.J. , Van Hateren Theresa C. , Sutanto Samuel J.
Published: March 2020

Robust sub-seasonal and seasonal drought forecasts are essential for water managers and stakeholders coping with water scarcity. Many studies have been conducted to evaluate the performance of hydrological forecasts, that is, streamflow. Nevertheless, only few studies evaluated the performance of hydrological drought forecasts, e.g. forecast of deficit volumes in river flow, or duration of deficits. The objective of this study, therefore, was to analyse the skill and robustness of meteorological and hydrological drought forecasts at the catchment scale (the Ter and Llobregat rivers in Catalonia, Spain), rather than at a continental or global scale. Meteorological droughts were forecasted using downscaled (5 km) probabilistic seasonal weather reforecasts (ECMWF-SEAS4). These downscaled data were also used to drive the hydrological model (EFAS-LISFLOOD) to produce hydrological drought forecasts, which were derived from time series of simulated streamflow data. This resulted in seasonal hydro-meteorological reforecasts with a lead time up to 7 months, for the time period 2002-2010. These monthly reforecasts were compared to two datasets: 1) droughts derived from a proxy for observed data, including gridded precipitation data and streamflow simulated by the LISFLOOD model; and 2) droughts derived from in situ observed precipitation and streamflow. Results show that the skill of hydrological drought forecasts is higher than the climatology, up to 3-4 months lead time. On the contrary, meteorological drought forecasts, analysed using the Standardized Precipitation Index (SPI), do not show added value for short accumulation times (SPI1 and SPI3). The robustness analysis show that using either a less extreme or a more extreme threshold leads to a large change in forecasting skill, which points at a rather low robustness of the hydrological drought forecasts. Because the skill found in hydrological drought forecasts is higher than the meteorological ones in this case study, the use of hydrological drought forecasts in Catalonia is highly recommended to improve drought risk management. The results of this study have already been implemented by the Catalonian Water Agency to forecast reservoir volumes of two big reservoirs located in the Ter and Llobregat catchments, which supply the majority of water to the Barcelona metropolitan area.
Contribution of Climate Change and Landuse / Landcover Change on Variations of Hydrological Processes in The Water Towers of Yangtze River, China
Authors: Ahmed Naveed , Wang Genxu , Xiangyang Sun , Nabi Ghulam , Hussain Fiaz , Huang Kewei , Shakoor Aamir , Munir Sarfraz
Published: March 2020

The impact assessment of landuse / landcover change (LULCC) and climate change (CC) on the runoff in a highly elevated watershed has key importance in terms of sustainable water resources and ecological developments. In this research, statistical technique was deployed with the addition of Soil and Water Assessment Tool (SWAT) in the Water Towers of Yangtze River (WTYZ). The coefficient of determination (R2) and Nash-Sutcliffe Efficiency (NSE) were used as a decision criterion to ensure the performance of model simulations. The model performed satisfactory with monthly R2 = 0.80 to 0.83 and NSE = 0.63 to 0.69 during calibration (1985 - 2000) and (2001 – 2016) periods. Major LULCC transformations were assessed from low grassland to medium grassland (2.017%) and wetlands (0.90%), bare land to medium grassland (0.23%) and glaciers to wetland (16.83%), high grassland to medium grassland (5.77%) during 1990s and 2005s. Impact of CC increased runoff by 97.97% and decreased evapotranspiration by -5.15% of total runoff and evapotranspiration respectively. It was also noteworthy that LULCC caused the increase in runoff and evapotranspiration by 2.02% and 105.15% relative to totals, respectively. Thus, the variations of runoff in the WTYZ are mainly impacted by landuse/landcover, while climate change have relatively least impacts.
Deep soil accumulation of organic carbon under cultivated Kazakh Steppe soils
Authors: Prays Aleksey , Banze Sonia , Jalowy Friedrich , Kaiser Klaus , Mikutta Robert
Published: March 2020

The decline in organic carbon (OC) stocks after conversion from grassland to cropland under conventional soil tillage practices was 24-32% for American prairie soils. The respective decreases in OC stocks ranged from 27% to more than 40% for steppe soils of the European part of Russia and was about 31% in semi-arid steppe soils of South Siberia. Here, we present results on the soil OC stocks in steppe soils of Northern Kazakhstan, which partly were converted to arable land over the last 60 to 90 years. We sampled soils by genetic horizons along a north-south transect, where precipitation increased towards north but negligible variation in temperature. Soil samples were analyzed for organic and inorganic carbon as well as bulk density.

Surprisingly, we found along the transect on average only 3.5% smaller OC stocks at 0-10 cm depth in arable than in natural soils. Even more astonishing, all arable soils tested had larger OC stocks in the layers beneath 10 cm depth than the natural steppe soils. On average, the OC stocks in 10-100 cm depth were 34% larger in soils under arable management than in natural steppe soils. We credit the enhanced deep soil accumulation of OC in arable soils of Northern Kazakhstan to colloidal translocation of OC-rich particles along vertical pores. The cause of the increased in colloidal transport under arable management is still under evaluation but appears connected to the clayey soil texture and the large abundance of expandable clay minerals. We conclude that despite of the intense land use and severe climatic conditions accumulation of subsoil carbon is possible even after many decades of cultivation history. Our findings stress the importance of considering whole soil profiles for analyzing the consequences of land use change on the net carbon balance of soils.
Influence of Sand-Dust on Solar Radiation in the Hinterland of Taklimakan Desert
Authors: Jin Lili , He Qing , Li Zhenjie , Mamtimin Ali , Miao Qilong
Published: March 2020

In order to reveal the essential feature of radiation in extreme arid region of Northwest China,using the global radiation，direct radiation,diffuse radiation and meteorological data in the Tazhong station( in Takli-makan desert hinterland,83°39'E,38°58'N),the characteristics of atmospheric transparency coefficient,influence of sand-dust on solar radiation were analyzed by the statistical methods.The results show that: The coefficient of atmosphere transparency is better from October to December than other months,but it's worse in spring and summer.The index of the atmosphere transparency P2 is the most ( least) in clear day ( sand storm day ) .The global radiation is more than 1000 W·m-2 in clear day,dust day and sand blowing day,while,it is up to 700 W·m-2 in sand storm day at most.The diffuse radiation is partly less than 400 W·m-2,mainly between 100 and 200 W·m-2in clear day.It is less than 600 W·m-2 in dusty day mostly. The direct radiation is reduced by dust aerosol.The probability are 41.2%,72.5%,78.1% and 100% when direct radiation is less than 200 W·m-2 during clear day,dust day,sand blowing day and sand storm day.The diffuse radiation is gradually concentration high value with the sand of the atmosphere is increased.The variation of every radiation is big in dusty day.The daily curve (value) of diffuse radiation is similar to the global radiation,which is reduced by dust aerosol is the same as the direct radiation.That suggests the atmosphere transparency is closely related to the global radiation,diffuse radiation and direct radiation.
Unconventional hydrocarbon resource plays in the North Sea Basin, Northwestern Europe
Authors: Schovsbo Niels , Ladage Stefan , Mathiesen Anders , Nelskamp Susanne , Stewart Margaret A. , Britze Peter
Published: March 2020

In 2017 the geological surveys contributed to the European wide project ‘EU Unconventional Oil and Gas Assessment’ (EUOGA). The goal of EUOGA was to assess all potentially prospective shale formations from the main onshore basins in Europe and included contributions of twenty-one European geological surveys and the assessment covered 82 geological formations from 38 basins (Zijp et al. 2017).

To extend the assessment to offshore basins the geological surveys of Denmark (GEUS), Germany (BGR), the Northlands (TNO) and United Kingdom (BGS) are working together on the Geological Analysis and Resource Assessment of selected Hydrocarbon systems (GARAH) project that aims at assessing the conventional and unconventional hydrocarbon resource in the North Sea Basin. Within the basin more than 10 shale layers have been recognised as holding potential resources. These shales include the offshore equivalent of the Cambrian Alum Shale, The Carboniferous Bowland shale and the Jurassic Wealden and Kimmeridge shales that onshore have been a target for hydrocarbon exploration within the European Union member states. Each shale layer will be characterized using thirty systematic parameters such as areal distribution, structural setting, average net to gross ratio of the shale reservoir, average Total Organic Carbon content (TOC) and average mineralogical composition.

This is a part of an ongoing EU Horizon 2020 GeoERA project (The GARAH, H2020 grant #731166 lead by GEUS).

References

Zijp, M., Nelskamp, S., Schovsbo, N.H., Tougaard, L. & Bocin-Dumitriu, A. 2017: Resource estimation of eighty-two European shale formations. Proceedings of the 5th Unconventional Resources Technology Conference, Austin, Texas, USA, 24–26 July, 2017. https://doi.org/10.15530/urtec-2017-2686270
Evaluation of Grassland Carbon Pool Based on a TECO-R Model and a Climate-Driving Function: A Case Study in the Xilingol Typical Steppe Region of Inner Mongolia, China
Authors: Lyu Xin
Published: March 2020

While researchers worldwide have spent much effort on quantitatively evaluating organic carbon at the regional scale, few studies have examined organic carbon pools at different levels, or their driving factors. Comprehensive analysis in this field would facilitate a deeper understanding of carbon pool mechanisms and lay a foundation for future work. In this study, the improved Terrestrial Ecosystem Regional (TECO-R) model was modified and parameters were calibrated for local application. The vegetation, litter, soil, and ecosystem carbon pools in the Xilingol typical steppe region of Inner Mongolia, China were quantitatively modeled for the 2011–2018 period. The organic carbon pools at different levels were compared and analyzed in terms of their spatial distribution, inter-annual variation, and climate-driving factors. Overall, the modified TECO-R model accurately simulated carbon storage, revealing that the various organic carbon pools increased overall and were characterized by different degrees of clustering in their spatial distribution, inter-annual variation, and climate-driving factors. Clear formation mechanisms were observed in the soil, litter, and root carbon pools. As the soil depth increased, the carbon stock of the root carbon pool and the soil carbon pool decreased. Climate factors exerted different degrees of constraints on each carbon pool. Integrated studies, such as this, promote understanding of the compositional differences in grassland carbon pools and the driving mechanism for these carbon pools, which, taken together, can help shape the policy for carbon sink management in grasslands.
Hydrography and nutrient concentrations in years of contrasting sea ice conditions in the Atlantic inflow region north of Svalbard
Authors: Renner Angelika , Bailey Allison , Reigstad Marit , Sundfjord Arild , Øygarden Sigrid
Published: March 2020

The shelf break north of Svalbard represents a major gateway for the inflow of nutrient-rich Atlantic Water (AW) to the Arctic Ocean. In this region, AW leaves the surface and subducts below Polar Surface Water (PSW). The supply of nutrients to the euphotic layer therefore varies strongly by season but also interannually, depending on e.g. rates of advection of sea ice and PSW over the AW boundary current. Additionally, the presence of sea ice can limit light availability in spring and early summer. Here, we present results from repeat sampling of hydrography, macronutrients (nitrate/nitrite, phosphate and silicic acid), and chlorophyll a along a transect at 31 E, 81.5 N in the period 2012-2017. Such time series are scarce but invaluable for investigating the range of variability in hydrography and nutrient concentrations. Measurements were done in late summer/early autumn, giving an indication of the nutrient consumption by primary producers over summer. The different years were characterised by very distinct sea ice conditions, both during the productive season and during the field campaigns. This impacted hydrography and primary production and thus nutrient concentrations in the surface and AW layers at the end of summer.
Structural analysis of the Theistareykir Fissure Swarm (NE Iceland) using field survey integrated with UAV-based - Structure from Motion techniques
Authors: Corti Noemi , Tibaldi Alessandro
Published: March 2020

Due to its position at the boundary between American and European plates, Iceland represents an ideal natural laboratory to study active rifting processes, where rifting mechanisms are complicated by the superimposition of tectonic and magmatic stresses. In order to contribute to the study of such processes, we focused our attention on the southern sector of the Theistareykir Fissure Swarm (ThFS), an active volcanic rift belonging to the Northern Volcanic Zone of Iceland, affected by both volcanic and seismic hazard.

We studied an area which is about 22 km2-large, situated 12 km south of the intersection of the ThFS with the Husavik Flatey Fault (HFF), a dextral strike-slip lineament belonging to the Tjornes Fracture Zone (TFZ). The area is characterized by the presence of normal faults and a dense swarm of extension fractures, affecting prevalently post-glacial, Holocene lavas, dated 8-10 and 11-12 ka. Only in the western sector of the area a Late Quaternary interglacial lava crops out, while the northeastern sector is covered by a Weichselian subglacial hyaloclastite. The southern sector of the area has been investigated with classical field survey, whereas in the northern part a 3.87 km2-large area has been reconstructed using the Structure from Motion (SfM) techniques, combined with an Unmanned Aerial Vehicle (UAV), obtaining orthomosaics, DSMs and 3D models with a centimetric resolution through 4189 UAV photos, collected in 7 different missions during summer 2018.

In the whole area, we recognized and mapped a total of 624 structures (comprising 583 extension fractures and 41 normal faults), and we took various measurements at 626 structural stations along extension fractures, and 132 along normal faults. Regarding extension fractures, we collected the strike and, in 441 cases where it was possible, the opening direction and the amount of opening; along normal faults we measured the strike, dip and vertical offset.

Our approach allowed to calculate stretch values across the rift comprised between 1.002 and 1.013, and an average opening direction value of 104.4°N, normal to the average extension fracture strike measured at the structural stations (14°N), suggesting a pure extensional opening in the studied area. Actually, in 281 cases out of our 441 stations along extension fractures we noticed a lateral component > 5°. Furthermore, 49% of data is not consistent with tectonics, neither with regard to the extensional fracture strike, nor with regard to opening directions. This suggests that stresses linked to regional tectonics are not the only cause of deformation, which could have been affected by different processes like dyke intrusion, deglaciation, and inflation/deflation of the Theistareykir volcano magma chamber.
Very rare heat extremes: how anomalous could they get?
Authors: Gessner Claudia , Fischer Erich , Beyerle Urs , Knutti Reto
Published: March 2020

Extreme heat waves as in 2003 and 2010 can have severe consequences for the economy and society. This raises the question how anomalous they could have gotten. Addressing this question is challenging given the lack of long coherent reliably daily data. Multi-millennial GCM simulations and single-model initial condition large ensembles offer a new opportunity to investigate the very upper tail of temperature distribution. Here, we use a nearly 5,000-year long pre-industrial control run and a 84-member large initial condition ensemble performed with CESM1.2. Evaluations show that the simulated climate variability and temperature response to circulation anomalies agree well with the ERA5 reanalysis over large parts of the global land regions.

We show that highest temperature extremes in the long pre-industrial control simulation exceed the temperature records of 2003 by several degrees in the related hotspot region over Western Europe. The anomalies are caused by large anticyclonic circulation anomalies and very dry land surface conditions, leading to amplifying feedbacks in the surface energy budget. Moreover, the simulation results reveal that summer temperature maxima as a function of return period have an asymptotic , suggesting an upper temperature limit.

In a next step, we use a novel method of ensemble boosting to generate even more extreme temperatures. To that end, 100-member ensembles are reinitialized with perturbed atmospheric conditions weeks before the most intense events. Thereby, we gain insight into short-term mechanisms that underly these hot extremes. The result of the ensemble calculation shows that using this method even more extreme event anomalies can be generated, substantially exceeding highest values in the long pre-industrial control simulations. We investigate how the physical mechanisms of these rare and unseen simulated events differ from more moderate events. We further compare the simulated very rare events with maximum anomalies estimated based on statistical methods.
Electric-current Neutralization and Eruptive Activity of Solar Active Regions
Authors: Torok Tibor , Liu Yang , Leake James E. , Sun Xudong , Titov Viacheslav S.
Published: March 2020

The physical conditions that determine the eruptive activity of solar active regions (ARs) are still not well understood. Various proxies for predicting eruptive activity have been suggested, with relatively limited success. Moreover, it is presently unclear under which conditions an eruption will remain confined to the low corona or produce a coronal mass ejection (CME).

Using vector magnetogram data from SDO/HMI, we investigate the association between electric-current neutralization and eruptive activity for a sample of ARs. We find that the vast majority of CME-producing ARs are characterized by a strongly non-neutralized total current, while the total current in ARs that do not produce CMEs is almost perfectly neutralized, even if those ARs produce strong (X-class) confined flares. This suggests that the degree of current neutralization can serve as a good proxy for assessing the ability of ARs to produce CMEs. 

 
Managing conflicting objectives in hydro-economic models: A viability approach
Authors: pereau jean christophe
Published: March 2020

In aquifers managed with quotas, water agencies are facing conflicting objectives between ensuring minimum environmental flows for the preservation of groundwater-dependent ecosystems and satisfying the water claims of the farmers to irrigate their crops. Handling the potential conflict between economic and environmental objectives is a major concern to achieve sustainability. This paper analyses the existing trade-off between these objectives as a problem of constraints fulfillment and uses the viability method to adress this conflict.

Hydroeconomic models are generally developed as constraint optimization problems with environmental constraints represented by minimum flow requirements. At each period, the dynamics of an aquifer depend on the balance between the natural recharge, the natural discharge and the amount of extracted water. The natural discharge consists in water flows which sustain groundwater dependent-ecosystems. This natural discharge is assumed to be an affine function of the water table. It allows to defined a critical boundary value of the water table for which the natural discharge is nil. A first requirement of a sustainable management is then to keep the water table above this critical value.

The allocation of water quotas to farmers is also a problem of constraint. The use of market-based instruments such as tradable permits has been proposed as a promising way to replenish an aquifer or to efficiently manage groundwater aquifers for irrigated agriculture. Tradable permits ensure that water will be used by farmers with maximum efficiency. However like all "cap and trade" systems, the way the "cap" which consists in the available amount of water for users is set, remains a difficult issue. A second requirement of a sustainable management is then to implement relevant strategies in the allocation of water quotas for every farmer by a regulating agency.

To deal with these two requirements which take the form of constraints, the use of the viability approach has shown to be well-adapted. This paper developped a dynamic hydro-economic model in discrete-time using the viability approach. The viability kernel that defines the states of the resource yielding intertemporal feasible paths able to satisfy the set of constraints over time is analytically identified. The associated set of viable quota policies and the trade-off between food production and ecosystem conservation objectives are characterized.

The theoretical results of the paper are illustrated with numerical simulations based on the Western La Mancha aquifer in Spain.
Linear response theory for macroscopic observables in high-dimensional systems: when is it valid and when not?
Authors: Gottwald Georg , Wormell Caroline
Published: March 2020

The long-term average response of observables of chaotic systems to dynamical perturbations can often be predicted using linear response theory, but not all chaotic systems possess a linear response. Macroscopic observables of complex dissipative chaotic systems, however, are widely assumed to have a linear response even if the microscopic variables do not, but the mechanism for this is not well-understood.

We present a comprehensive picture for the linear response of macroscopic observables in high-dimensional coupled deterministic dynamical systems, where the coupling is via a mean field and the microscopic subsystems may or may not obey linear response theory. We derive stochastic reductions of the dynamics of these observables from statistics of the microscopic system, and provide conditions for linear response theory to hold in finite dimensional systems and in the thermodynamic limit. In particular, we show that for large systems of finite size, linear response is induced via self-generated noise.

We present examples in the thermodynamic limit where the macroscopic observable satisfies LRT, although the microscopic subsystems individually violate LRT, as well a converse example where the macroscopic observable does not satisfy LRT despite all microscopic subsystems satisfying LRT when uncoupled. This latter, maybe surprising, example is associated with emergent non-trivial dynamics of the macroscopic observable. We provide numerical evidence for our results on linear response as well as some analytical intuition.
The Topography Meter: a measurement system applicable for gravity-erosion experiments using a novel 3D surface measuring technique
Authors: Xu Xiangzhou , Xu Feilong Xu , Guo Wenzhao , Zhao Chao
Published: March 2020

Gravity erosion is one of the most remarkable natural hazards in mountainous regions, especially on the Loess Plateau of China. Nevertheless, the measurement of failure mass is very difficult because gravity erosion usually occurs randomly and it combines with hydraulic erosion. Here we present a novel testing technique that could quantitatively measure time-variable gravity erosion on the steep loess slopes. A structured light 3D surface measuring apparatus, the Topography Meter, was designed and manufactured in our laboratory. Dynamic variation of the steep slope relief was monitored under rainfall simulation and the slope deforming process was recorded by a computer video technology. With the help of laser marking, plane figures were vectorially transformed into 3D graphs, thus the shape of target surface was accurately computed. By comparing the slope geometries in the moments before and after the erosion incident on the snapshot images at a particular time, we could obtain the volume of gravity erosion and many other erosion data, including the volume of slide mass, the amount of soil loss eroded by overland flow, etc. A series of calibration tests were conducted and the results showed that the accuracy of this technique was high and sufficient for exploring the mechanism of slope erosion. More than 120 rainfall simulation events were subsequently tested with the apparatus, further confirming its feasibility and reliability.
Observation and thermodynamic modeling of the influence of snow cover on landfast sea ice thickness in Prydz Bay, East Antarctica
Authors: Zhao Jiechen , Cheng Bin , Vihma Timo , Yang Qinghua , Hui Fengming , Zhao Biao , Hao Guanghua , Shen Hui , Zhang Lin
Published: March 2020

The observed snow depth and ice thickness on landfast sea ice in Prydz Bay, East Antarctica, were used to determine the role of snow in (a) the annual cycle of sea ice thickness at a fixed location (SIP) where snow usually blows away after snowfall and (b) early summer sea ice thickness within the transportation route surveys (TRS) domain farther from coast, where annual snow accumulation is substantial. The annual mean snow depth and maximum ice thickness had a negative relationship (r = −0.58, p < 0.05) at SIP, indicating a primary insulation effect of snow on ice thickness. However, in the TRS domain, this effect was negligible because snow contributes to ice thickness. A one-dimensional thermodynamic sea ice model, forced by local weather observations, reproduced the annual cycle of ice thickness at SIP well. During the freeze season, the modeled maximum difference of ice thickness using different snowfall scenarios ranged from 0.53–0.61 m. Snow cover delayed ice surface and ice bottom melting by 45 and 24 days, respectively. The modeled snow ice and superimposed ice accounted for 4–23% and 5–8% of the total maximum ice thickness on an annual basis in the case of initial ice thickness ranging from 0.05–2 m, respectively.
Characteristics of blown sand activities in sandy land on the eastern shore of the Qinghai Lake
Authors: Zhang Dengshan , Wang Haijiao , Tian Lihui
Published: March 2020

Wind regime, sand drift potential and sand transport amount are important indicators to evaluate regional blown sand activities. This paper took Ketu sandy land on the eastern shore of Qinghai Lake as study area. The sand transport amount data were collected monthly in 2013-2014 and 2016-2017 with 16-azimuth sand collector, and data of local wind velocity and direction were used to compare and analyze the typical blown sand activities. The results were as follows: (1) In 2013-2014, the mean wind velocity in the study area was 2.79m/s and the frequency of sand-driving wind was 6.76%. While they were 2.63m/s and 6.13% in 2016-2017, respectively. (2) The directions of the sand-driving wind in two years were similar, clearly from WSW-WNW and ESE-SSE. The frequency of western wind increased whereas the frequency of southeastern wind decreased. (3) The seasonal variation of sand drift potential in two years were similar with the largest in spring and the smallest in summer. According to the annual variation trend of sand drift potential, the study area was belonging to low wind energy environment. (4) There is a significant difference in sand transport amount between the two years. The amount in 2016-2017 was 77.18kg less than that in 2013-2014, while the distribution of sand transport amount was similar. The increase of vegetation coverage in this area is the main reason for the decrease of sand transport amount.
Error structure of MSG rainfall operational product in Italy
Authors: Campo Lorenzo
Published: March 2020

The operational use of observation products of rainfall for forecasting/nowcasting purposes is nowadays wide spread in several regions in the world. While the applications for such data are numerous (flood early warning systems, agriculture, urban flood, etc.) the dealing with the uncertainty of the data when they come from different sources is still an open question. In fact, due to the extreme spatial variability of the rainfall fields also when limited (but intense) rain events occur, even a quite dense ground raingauges network can be not sufficient to effectively describe the precipitation. Thus, there is the need to employ multi-sources observation systems by exploiting, when available, meteo-radar and satellite products that provide spatially continuous maps, without neglecting their limits. With specific reference to the satellite products, there are several issues about the accuracy of the reconstruction of the actual rainfall fields in terms of intensity, timing and even presence of rainfall. In this work the EUMETSAT operational rainfall product based on MSG (Meteosat Second Generation) is evaluated by comparison with the observed time series of the ground network of raingauges in the Italy territory. The focus of the comparison is to investigate on the properties of the MSG product error, in particular on how it varies  with the spatial and temporal scales of aggregation, in different regions and different seasonal periods. The analysis was conducted on the whole Italian territory, in the period 2009-2013.
Collapses on the riverbank: what happened to the Lower Yellow River?
Authors: Gao Lu , Xu Xiangzhou
Published: March 2020

Riverbank collapses frequently occur in the lower reaches of the Yellow River, China, which result in a great loss of farmland and significant hydro-morphological evolution in the channel. A combination of field investigation and remote sensing analysis was conducted to understand the current status of riverbank collapse in the Shandong Reaches of the lower Yellow River. The results show that the planar failure and upward-concave collapse were the main types of river failures in these reaches. Taking the Jiyang section as an example, the average lateral dynamic displacements in the Jiyang section were 2.8 and 11.4 m, the retreat areas were 248.8 and 835.0 m2 and the maximum lateral dynamic displacement were 7.4 and 26.0 m during the periods 3/31/2016-4/18/2017 and 04/18/2017-5/10/2018, respectively. Factors such as the soil properties, upstream river-control works, and channel bends may change the probability of downstream riverbank collapse. Building materials that are effective, low-cost and environmental friendly, and easy to use, are anticipated in the river management projects to protect the riverbanks and improve the ecological environment in the study area.
Lightning super-bolts in Eastern Mediterranean winter thunderstorms
Authors: Yair Yoav , Lynn Barry , Ziv Baruch , Yaffe Mordecai
Published: March 2020

Superbolts are defined as lightning flashes that are a thousand times stronger than normal ones, and their occurrence is estimated to be less than 0.001% of total number of lightning on earth. The global distribution of these extremely powerful lightning flashes is remarkably different than that of regular lightning, which are concentrated in the well-known convective "chimneys" in tropical Africa, South-America and the maritime continent in South-East Asia. The physical mechanisms producing these powerful flashes remain unknown, and the puzzle is exacerbated by the fact that they are discovered mostly over oceans, in maritime winter storms.

The Mediterranean Sea is one of the most prolific regions where super-bolts occur, especially in the months November-January (Holzworth et al., 2019). We analyzed 8 years of lightning data obtained from the Israeli Lightning Detection Network (ILDN), defining a 200kA peak current threshold for superbolts. We mapped the spatial and temporal distribution of superbolts and their monthly frequency in winter season thunderstorms (DJF) in the eastern Mediterranean, and identified the meteorological and microphysical circumstances in such storms.

Our working hypothesis is that large amounts of desert dust aerosols, coming from the Sahara Desert, are ingested into maritime winter storms over the eastern Mediterranean. The large dust contributes to convective invigoration, enhanced freezing and efficient charge separation, implying that superbolts are more likely to occur in the presence of large dust. We will present the results of simulation conducted using the WRF-ELEC numerical model, and WRF with spectral bin microphysics coupled with Lynn et al.'s (2012) Dynamic Lightning Scheme (DLS) and the Lightning Potential Index (Yair et al., 2010; LPI), for selected case studies when an enhanced fraction of superbolts was observed.

 

Holzworth, R. H., McCarthy, M. P., Brundell, J. B., Jacobson, A. R., and Rodger, C. J. (2019). Global distribution of superbolts. J. Geophys. Res. Atmos., 124., doi:10.1029/2019JD030975.

Lynn, B., Y. Yair, C. Price, G. Kelman and A. J. Clark (2012). Predicting cloud-to-ground and intracloud lightning in weather forecast models. Weather and Forecasting, 27, 1470-1488, doi:10.1175/WAF-D-11-00144.1.

Yair, Y., B. Lynn, C. Price, V. Kotroni, K. Lagouvardos, E. Morin, A. Mugnai, and M. d. C. Llasat (2010). Predicting the potential for lightning activity in Mediterranean storms based on the Weather Research and Forecasting (WRF) model dynamic and microphysical fields, J. Geophys. Res., 115, D04205, doi:10.1029/2008JD010868
Strong ground motion simulation of the 2013 MS 7.0 Lushan, China, earthquake
Authors: Zhang Wenbo , Yu Xiangwei
Published: March 2020

The near source strong ground motions of the 2013 MS 7.0 Lushan, China, earthquake were simulated using empirical Green's function (EFG) method. At first, we estimated the amount and location of strong motion generation areas (SMGA) based on the character of both slip distributions from far-field seismic inversion and the envelopes of recorded acceleration from main shock, and determined the amount of subfaults on SMGAs referring to the scaling law introduced by Somerville et al.. Then, we implemented the genetic algorithm searching for the optimized source parameters. Based on the source models, we synthetized the waveforms for the 30 stations selected near the source region. Our results show that the comparison between the synthetic waveforms and the observed records agree very well with each other, especially for the part of high-frequency larger than 1.0 Hz. We found that there are two obvious SMGAs on the fault, which take the position that the asperities from far-field seismic inversion take. The combined strong motion generation areas we obtained were smaller than those values predicted by extension of the scaling law by Somerville et al..
An accurate relocation of the 2017 Ms 7.0 Sichuan Jiuzhaigou earthquake sequence and the seismicity analysis
Authors: Yu Xiangwei , Song Qian , Deng Shanquan
Published: March 2020

The 2017 Ms 7.0 Sichuan Jiuzhaigou earthquake occurred at the intersection of the Tazang, Minjiang, and Huya faults on the eastern margin of the Tibetan Plateau. Since it occurred on an unmarked blind fault, it is still a controversial issue whether the fault, which triggered the earthquake, was the extension of the East Kunlun fault or the northern branch of the Huya fault. Therefore, the accurate source location is of great significance for studying the deep distribution of seismogenic faults and seismicity analysis.

We have not only collected seismic phase arrival data recorded by 24 permanent stations and 6 temporary stations, but also picked up the seismic waveform data recorded by partial permanent stations in this study. Using absolute seismic location method and relative seismic location method, we relocated the earthquake events with magnitude greater than or equal to 1.0 occurred in the Jiuzhaigou area from August to December 2017. In order to ensure reliable data quality, we selected 23422 P-wave absolute arrival times, 24734 S-wave absolute arrival times and 124519 high quality P-waveform cross correlation data of 3449 earthquake events for relocation research.

The mean value of root mean square residuals of travel time of all earthquakes decrease from 0.21s to 0.08s after relocation. The average location errors in the E-W, N-S, and vertical directions are 0.11km, 0.12km, and 0.16km, respectively. Ninety-nine percent of the earthquake events are distributed in the depth range of 1-25 km, and the dominant distribution range is 5-15 km. The result shows that the earthquakes are distributed along the strike of northwest and southeast, and the Jiuzhaigou mainshock divided these events into two clusters: northwest and southeast. From the parallel strike section, we conclude that the depth of the northwest seismic cluster is shallow with the depth range of 2-15 km, and the depth of the southeast seismic cluster is deeper with the depth range of 6-18 km. Moreover, the number of aftershocks in the northwest cluster is greater than that in the southeast cluster, but after an M 4.9 aftershock occurred in the northwest cluster on the ninety-first day after the Jiuzhaigou mainshock, the number of aftershocks in the northwest cluster began to decrease. The result provides a basis for studying the seismogenic background and seismicity of the Jiuzhaigou earthquake.