bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring options for improving maize productivity for small farmers in the Loess Plateau
Authors: Wang Xiukang , Gao Yaguang , Xing Yingying
Published: March 2020

Millions of small farmers rely on maize (Zea mays L.) produced in the Loess Plateau of China. However, little has been reported on the effects of plastic mulch and maize cultivar on crop yield in the check dam environment. The objectives of this experiment were to determine the effects of maize cultivar and plastic mulch on photosynthetic characteristics and grain yield when grown in the check dam environment. Three maize cultivars were assessed with and without plastic mulch in 2016 and 2017 in Ansai County, Shaanxi Province, China. Results showed that mulch increased grain yield by 10.5% in 2016 and 11.3% in 2017 across all cultivars. Among all cultivars, ‘Xianyu335’ had the highest grain yield under both mulch and no mulch. Grain yield was significantly correlated with soil water content in the 0-20 cm layer. Soil temperature under mulch decreased with increasing soil depth. Averaged over soil depths, mulch increased soil temperature from 0.2 to 1.9 °C over the entire growing season. Maize cultivar directly determined photosynthetic characteristics. Grain yield was more closely related to photosynthetic rate in July than in August, and was significantly associated with stomatal conductance and transpiration rate. Our findings suggest that photosynthetic characteristics is an important index affecting maize grain yield for small farmers using check dams in the Loess Plateau.
Characteristics and sources of gravity waves in the summer stratosphere based on long-term and high-resolution radiosonde observations
Authors: Okui Haruka , Sato Kaoru
Published: March 2020

Using long-term high-resolution operational radiosonde observation data from nine stations in the subtropics and mid-latitudes of Japan, this study performed statistical analysis of the dynamical characteristics of gravity waves (GWs). Wave generation by shear instability in summer was a particular focus because orographic GWs cannot propagate deep into the middle atmosphere through their critical layer in the lower stratosphere. The kinetic energy of summer stratospheric GWs is markedly large south of 37°N. Hodograph analysis revealed that GWs propagating eastward relative to the ground are dominant in summer. The percentage of GWs propagating energy upward (downward) is large above (below) the height at which the mean occurrence frequency of shear instability is high. The time series of the kinetic energy of stratospheric GWs exhibited statistically significant positive correlation with the occurrence frequency of shear instability slightly below the tropopause. These findings strongly suggest the possibility of excitation of summer stratospheric GWs by shear instability above the jet. The shear instability condition is satisfied more frequently in the region 30°–35°N. This is probably related to two characteristics of the background fields slightly below the tropopause: larger vertical shear of zonal winds at higher latitudes and lower static stability at lower latitudes.
Higher temperatures enhance spatio-temporal rainfall concentration
Authors: Wang Dagang , Long Kaihao
Published: March 2020

Warming climate has significantly influenced the environment on the earth, which attracts wide attention in society. Previous studies show that precipitation extremes increase with warmer temperature. This phenomenon has been observed in the regions with various climates, with the theoretical support of the Clausius-Clapeyron relation. However, the effect of temperature on the spatio-temporal characteristics of precipitation extremes are less studied. In this study, we propose a new index to represent the temporal and spatial concentration of rainfall events, and study how temperature affect the rainfall concentration. It is found that precipitation events tend to have higher temporal and spatial concentration at higher temperatures, and rain events with shorter duration is more likely to be concentrated than those with longer duration in both time and space. The results indicate that rain events would be concentrated over smaller regions and during shorter periods under warming climate in the future, which leads to flood and drought occurring simultaneously.
A study on the improvement of seismic coefficients for pseudo static analysis of gravity type quay wall via dynamic centrifuge tests
Authors: Lee Moon-Gyo , Cho Hyung-Ik , Sun Chang-Guk , Kim Han-Saem
Published: March 2020

The pseudo-static approach has been conventionally applied for the design of gravity type quay walls. In this method, the seismic coefficient (kh), expressed in terms of acceleration due to gravity, is used to convert the real dynamic behavior to an equivalent pseudo-static inertial force for seismic analysis and design. The existing kh is simply defined as the expected peak ground acceleration (PGA) of the ground divided by the gravitational acceleration (g), which does not sufficiently reflect the real dynamic behavior. In order to improve the kh definition, a number of studies have been performed for reducing the differences between pseudo-static and true dynamic behavior. In this regard, questions regarding the need for considering the effect of frequency characteristics of input earthquake, natural period of the backfill soil and the subsoil underneath the wall, and wall height on the deformation of quay wall crown (Dh) have been explored. In this study, dynamic centrifuge tests were conducted using the gravity type quay wall models designed with a kh value of 0.13 to assess the behavior of the model wall during earthquakes. Three different variables: input earthquake motions, wall heights and the thickness of subsoil underneath the wall were considered, and the test results were compared and analyzed to assess the validity of the conventional kh concept under these conditions. In addition, some improvements that should be considered for the future revision of the kh definition are discussed.
Analysing and projecting spatial drought conditions of the Seine catchment based on ocean-atmosphere oscillations over interannual and decadal scales
Authors: Chun Kwok Pan , He Qing , Dieppois Bastien , Massei Nicolas , Fournier Matthieu
Published: March 2020

Midlatitude droughts are affected by the tropical disturbances, which are linked to sea-surface temperature patterns in the Pacific and Atlantic Oceans. The combined effects of these two ocean basins manifest themselves in the variation of streamflows, from land surface filtering. In this study, we have developed a framework to explore the effects of global sea surface temperature variations along with atmospheric teleconnection patterns, on local hydroclimatic conditions related to droughts over the Seine catchment, a main waterway in northern France. Using the Standardized Runoff-discharge Index (SRI) to quantify hydrological drought conditions over the Seine, the North Atlantic Oscillation (NAO) index was found to be a significant driver for the upstream dryness between 2001 and 2015. The El Nino Southern Oscillation (ENSO) index was also found to be a significant forcing variable, but for the Seine downstream. The Atlantic Multidecadal Oscillation (AMO) and the West Mediterranean Sea (WMED) indices were significant over almost the whole Seine River basin. Results show that the drought spatial patterns of the Seine River vary differently with the atmospheric and oceanic oscillations from interannual to decadal scales. Over a small catchment with a drainage area around 78,700 square kilometres, the spatial drought variations in the Seine catchment appear to be usual, and they are likely to be related to regional conditions which drive local land surface mechanisms linked with microclimates or geological processes. In general, during the negative phase of AMO and the positive phase of ENSO, the sea surface temperature of the North Atlantic Ocean is low. The positive phase of NAO also lowers sea surface temperatures of the North Atlantic Ocean and the West Mediterranean Sea. Droughts are likely to occur at the Seine during the negative phase of AMO and the positive phase of NAO, because the cold North Atlantic Ocean has less evaporation and provides less moisture to France. Based on these results, a statistical downscaling model is developed to relate SRI to atmospheric and oceanic oscillation indices, which are derived from the Institut Pierre Simon Laplace climate model (IPSL-CM5) outputs. Using this statistical downscaling model and scenarios of Representative Concentration Pathways (RCP4.5 and RCP8.5), the drought conditions of the Seine are projected for the mid- and long-term future (2050s and 2080s). Diverse drought results are obtained. Based on relative importance of oscillation indices, the implications of diverse projections for general drought managements in midlatitude regions related to tropical sea surface temperature disturbances and atmospheric teleconnections are discussed.
Transient hyporheic exchange during rainfall events in a gaining stream: Field investigation, conceptual model, and numerical interpretation
Authors: Lu Chengpeng , Ji Keyan , Zhang Yong , Fleckenstein Jan , Zheng Chunmiao , Salsky Kate
Published: March 2020

Hyporheic exchange is transient in nature, considering the temporal fluctuations in hydrological and/or biogeochemical conditions in surface water and groundwater (SW/GW).  Efforts are needed to further identify the patterns and driving mechanisms of transient hyporheic exchange.  This study combined a reach-scale field survey and numerical modeling analysis to reveal the pattern of transient hyporheic exchange during rainfall events in the Zhongtian River, southeast of China. Field observations revealed hydrodynamic properties and temperature variations in SW/GW, suggesting that the regional groundwater recharged the study reach.  A one-dimensional heat transport solution was built and used to generate the planar and cross-sectional hyporheic flow fields. A two-step numerical modeling procedure, including a hydraulic surface flow model and a groundwater flow model, was then used to simulate the observed flow system. The hyporheic exchange exhibited strong temporal evolution, as indicated by the rainfall event-driven hyporheic exchange, the depth-dependent hysteretic response to rainfall, and the area of local downwelling flow increasing with rainfall. Dynamics of the hyporheic exchange in the study reach, therefore, significantly changed in space and time due to rainfall. The reversal of hydraulic gradient and transient hyporheic exchange were observed and validated using the numerical simulation. Anisotropic hydraulic conductivity is the key to generate transient hyporheic exchange. A revised conceptual model was used to interpret the observed temporal patterns in hyporheic exchange  The pattern of transient hyporheic exchange indicates that transient hyporheic exchange only appears after an increased phase of river stage but does not last for a long time. The temporal pattern of hyporheic exchange can significantly affect the evolution of biogeochemical processes in the hyporheic zone for a gaining stream by, for example, temporally facilitating special biogeochemical processes.
Lava flow risk assessment on Mount Etna through hazard and exposure modelling
Authors: Cappello Annalisa , Bilotta Giuseppe , Corradino Claudia , Ganci Gaetana , Hérault Alexis , Zago Vito , Del Negro Ciro
Published: March 2020

Lava flows represent the greatest threat to exposed population and infrastructure on Mt Etna volcano (Italy). The increasing exposure of a larger population, which has almost tripled in the area around Mt Etna during the last 150 years, has resulted from poor assessment of the volcanic hazard, allowing inappropriate land use in vulnerable areas. We present a new methodology to quantify the lava flow risk on Etna’s flanks using a GIS-based approach that integrates the hazard with the exposure of elements at stake. The hazard, showing the long-term probability related to lava flow inundation, is obtained by combining three different kinds of information: the spatiotemporal probability of the future opening of new flank eruptive vents, the event probability associated with classes of expected eruptions, and the overlapping of lava flow paths simulated by the MAGFLOW model. Data including all exposed elements have been gathered from institutional web portals and high-resolution satellite imagery, and organized in four thematic layers: population, buildings, service networks, and land use. The total exposure is given by a weighted linear combination of the four thematic layers, where weights are calculated using the Analytic Hierarchy Process (AHP). The resulting risk map shows the likely damage caused by a lava flow eruption, allowing rapid visualization of the areas subject to the greatest losses if a flank eruption were to occur on Etna.
Indicators for Environment Health Risk Assessment in the Jiangsu Province of China
Authors: jing zhang , shujie zhang
Published: March 2020

According to the framework of Pressure-State-Response, this study established an indicator system which can reflect comprehensive risk of environment and health for an area at large scale. This indicator system includes 17 specific indicators covering social and economic development, pollution emission intensity, air pollution exposure, population vulnerability, living standards, medical and public health, culture and education. A corresponding weight was given to each indicator through Analytical Hierarchy Process (AHP) method. Comprehensive risk assessment of the environment and health of 58 counties was conducted in the Jiangsu province, China, and the assessment result was divided into four types according to risk level. Higher-risk counties are all located in the economically developed southern region of Jiangsu province and relatively high-risk counties are located along the Yangtze River and Xuzhou County and its surrounding areas. The spatial distribution of relatively low-risk counties is dispersive, and lower-risk counties mainly located in the middle region where the economy is somewhat weaker in the province. The assessment results provide reasonable and scientific basis for Jiangsu province Government in formulating environment and health policy. Moreover, it also provides a method reference for the comprehensive risk assessment of environment and health within a large area (provinces, regions and countries).
Influences of point source and non-point source pollution of the Pearl River Basin on the Pearl River Estuary
Authors: Feng Xiao
Published: March 2020

Coastal waters around Hong Kong are affected by persistent and increasing eutrophication which to a certain extent is caused by the ecosystem’s responses to the nutrient discharge from the Pear River basin in South China. Large agricultural lands and high density of population contribute to both non-point source and point source pollution over the whole basin. It is important to identify dominant factors of water pollution in different watersheds and the major nutrient outputs to the estuary. In this study, SWAT (Soil and Water Assessment Tool) is selected to simulate the terrestrial processes in the Pearl River basin. Both point source (PS) and non-point source (NPS) pollution are considered and various forms of nitrogen (N) and phosphorus (P) are selected as pollution loads. The study would help to assess the primary source and type of water pollution in different watersheds and contribute to provide suggestions for local land use management and trends of eutrophication in the Pearl River estuary.
The substructure of extremely hot summers in the Northern Hemisphere
Authors: Röthlisberger Matthias , Sprenger Michael , Flaounas Emmanouil , Beyerle Urs , Wernli Heini
Published: March 2020

In the last decades, extremely hot summers (hereafter extreme summers) have challenged societies worldwide through their adverse ecological, economic and public health effects. In this study, extreme summers are identified at all grid points in the Northern Hemisphere in the upper tail of the July–August (JJA) seasonal mean 2-meter temperature (T2m) distribution, separately in ERA-Interim reanalyses and in 700 simulated years with the Community Earth System Model (CESM) large ensemble for present-day climate conditions. A novel approach is introduced to characterize the substructure of extreme summers, i.e., to elucidate whether an extreme summer is mainly the result of the warmest days being anomalously hot, or of the coldest days being anomalously mild, or of a general shift towards warmer temperatures on all days of the season. Such a statistical characterization can be obtained from considering so-called rank day anomalies for each extreme summer, that is, by sorting the 92 daily mean T2m values of an extreme summer and by calculating, for every rank, the deviation from the climatological mean rank value of T2m.  

Applying this method in the entire Northern Hemisphere reveals spatially strongly varying extreme summer substructures, which agree remarkably well in the reanalysis and climate model data sets. For example, in eastern India the hottest 30 days of an extreme summer contribute more than 70% to the total extreme summer T2m anomaly, while the colder days are close to climatology. In the high Arctic, however, extreme summers occur when the coldest 30 days are substantially warmer than climatology. Furthermore, in roughly half of the Northern Hemisphere land area, the coldest third of summer days contribute more to extreme summers than the hottest third, which highlights that milder than normal coldest summer days are a key ingredient of many extreme summers. In certain regions, e.g., over western Europe and western Russia, the substructure of different extreme summers shows large variability and no common characteristic substructure emerges. Furthermore, we show that the typical extreme summer substructure in a certain region is directly related to the region’s overall T2m rank day variability pattern. This indicates that in regions where the warmest summer days vary particularly strongly from one year to the other, these warmest days are also particularly anomalous in extreme summers (and analogously for regions where variability is largest for the coldest days). Finally, for three selected regions, thermodynamic and dynamical causes of extreme summer substructures are briefly discussed, indicating that, for instance, the onset of monsoons, physical boundaries like the sea ice edge, or the frequency of occurrence of Rossby wave breaking, strongly determine the substructure of extreme summers in certain regions.
The application of orthogonal experimental design to identify the interactive forces driving people’s perceptions of ecosystem services
Authors: Zhang Rui
Published: March 2020

People’s perception of ecosystem services is usually affected by a variety of interacting factors, making it difficult to identify the actual driving factors. An orthogonal experimental design can effectively identify interactions and has the potential for use in social perception studies. Based on 20,642 questionnaires on the topic of WTP (willingness to pay), the interactive forces driving people’s perceptions of ecosystem services on the Tibetan Plateau were identified using an orthogonal experimental design. The results show that 1) when interactions are not considered, management attitudes have the strongest influence on WTP, the second most influential factors are subjective cognitions, and objective indicators are ranked last. 2) The interactions has a stronger impact on WTP than some of individual factor: when interactions and observed variables are compared simultaneously, the interaction between the “importance of the Tibetan Plateau” and the “WTP for residents” has a stronger influence on WTP (451 Chinese yuan/year) than any of the individual variables except “WTP for residents” (666 CNY/year) and “knowledge of the Tibetan Plateau” (484 CNY/year). Among the interactions between pairs of variables, that between education (212 CNY/year) and income (260 CNY/year) has a greater impact on WTP (266 CNY/year) than either variable alone. 3) When the interactions are considered, subjective cognitions are the most important indicators for WTP, and management attitudes are the second most important indicators. This study provides a feasible method for the identification of interactive driving forces in analyses involving questionnaires, and the conclusions can provide guidance from the public for ecosystem management on the Tibetan Plateau.
Variation of glacial dynamics in Peru: from valley glaciers to mountain glaciers in a context of climate change
Authors: Loarte Edwin , Medina Katy , Curo Yadira , Leon Hairo , Quiñonez Fiorella , Castillo Francisco , Huggel Christian
Published: March 2020

One of the effects of climate change on tropical glaciers is the accelerated reduction of their glacial tongue, reflected in a morphometric variation. Many glaciers that had pronounced tongues and that extended through a valley (Valley glacier) now have reduced their fronts located in the upper parts of the valleys (Mountain glacier).

This has been studied with glaciers of Peru located in 18 mountain ranges located from S 8°20'56" to 15°53'26" and W 77°56'10" to 69°05'14", which are an important solid water reserve that directly supplies the population of 11 departments.

The study focused on the "digit 1" (primary classification) of the Global Land Ice Measurement from Space (GLIMS), which classifies the glaciers mainly in: valley glaciers and mountain glaciers. The processing of raster and vector data through the use of geographic information system and remote sensing tools allowed to analyze the changes and variations affecting glaciers with respect to their morphometry. For this, a comparison was made between glacier coverage in 2016 (using images Sentinel 2), produced by INAIGEM, and the baseline of the glacier coverage of 1955 and 1970 (using aerial photography), from the first inventory of glaciers in Peru, produced by Hidrandina S.A.

The results show a significant morphometric variation of 83.7%, where valley glaciers (from Hidrandina inventory) became mainly mountain glaciers. Nowadays only four mountain ranges have mountain glaciers inside whereas in the past it were nine. When we analyze the results for watersheds, the most morphometric changes were 89% in the Atlantic watershed, followed by 57% in the Pacific watershed; in the Amazon watershed there was not any registration of any mountain glaciers since the first inventory in Peru. The surface changes do not show specific any predominant aspect, and average slopes are between 25° and 50°.

The glacial tongues that are considered valley glacier area located in ablation zones, where the mass balance is negative and there is more susceptibility to reducing their mass and, consequently, to variations in shape and size in a short period. This change has been accentuated in recent decades.
Study on the variation of energetic particle pitch angle caused by NWC VLF transmitter
Authors: Chu Wei , Xu Song , Zhang ZhenXia , Huang Jianping , Zeren Zhima , Shen Xuhui
Published: March 2020

Based on the observation data collected by the Energetic Particles Detector Package(HEPP) on board CSES satellite during the period of 2018 and 2019.We analyzed the characterizes of pitch angle spectrum of energetic electron precipitated caused by NWC. Our analysis revealed in details the transient properties of the space electrons induced by the man-made VLF wave emitted by the transmitter at NWC.The center location of the NWC electron flux locates in the north hemisphere other than in the south hemisphere during both quiet and disturbance period which is surprising.And the central location of NWC electron belt move westwards during the geomagnetic storm.The pitch angle distributions of the precipitation electron have the maximum flux at about 60-70 degree other than at 90 degree.The pitch angle distributions presented here are examined for evidence of the transportation mechanism especially for the electron loss mechanism.

 
Observed canopy evapotranspiration enhancement of green patches in Chinese metropolis
Authors: Zhao Jiacheng , Zhao Xiang
Published: March 2020

With the acceleration of urbanization, the canopy evapotranspiration (ET) of vegetation plays an increasingly important role in urban surface energy and water budget [1-2]. A reasonable assessment of urban vegetation ET requires not only the estimation of high-resolution ET but long-term monitoring due to high heterogeneity of city, especially that of metropolis, and changeable land management policy. The study takes advantages of Google Earth Engine (GEE) platform to investigate how canopy ET of green patches in Chinese metropolis, represented by Beijing, changes from 1984 to 2018. Typical green patches including city park, community green belt, large area lawns etc. in study area were manually vectored on GEE based on a thorough examination of historic high-resolution google earth images and thermal images. Using a simple Taylor skill fusion method by Yao et al. [3], 853 cloudless Landsat 5/8 surface reflectance images were used to retrieve long-time series ET for each green patch identified with 30 m spatial resolution. Time series analysis combined with robust regression were employed for trend detection. Results indicated that the ET of green patches in Beijing significantly increased from 1984 at a mean rate of 18.05 ± 4.21 W/m2/10 year (r2 = 0.42, p < 0.001). However, such enhancement varied in different green patch type. This talk will graphically depict the spatial pattern of enhanced green patch ET, explore their changes over long-term urbanization and the potential cooling capacity for urban heat island alleviation.

 

References:

[1] Grimmond, C. S. B. and Oke, T. R., 1991. An evapotranspiration‐interception model for urban areas. Water Resources Research, 27(7): 1739-1755.

[2] Chen, X., et al., 2019. Canopy transpiration and its cooling effect of three urban tree species in a subtropical city- Guangzhou, China. Urban Forestry & Urban Greening (43): 126368.

[3] Yao, Y. J. et al., 2017. Estimation of high-resolution terrestrial evapotranspiration from Landsat data using a simple Taylor skill fusion method. Journal of Hydrology (553): 508-526.
The influence of the eddy in north pacific on ocean internal mixing based on the finescale parameterization
Authors: Chen Juan , Li Shaofeng , Cao Anzhou , Song Jinbao
Published: March 2020

Based on the Vector Geometry method, the eddy identification is carried out by using the altimeter data in 2016-2018, and the ocean internal diapycnal mixing diffusivity near the eddy is calculated by using the finescale parameterization method and the Argo data. The influence of the eddy in the North Pacific on the internal mixing of the ocean is analyzed. The results show that the average diffusivity of the study region under the influence of eddies is 6% greater than that without the influence of the eddy. The cyclonic eddy enhances the mixing of 600-1200m depth, and the effect on the mixing at the depth of 600-900m is the maximal and can be up to 18%. The anticyclonic eddy significantly enhances the mixing at the depth of 300-900m, but the effect on the mixing at the depth of 900-1200m is not obvious. As the distance from the center of the eddy increases, the diffusivity outside the eddy slowly decreases and that inside the eddy does not change significantly, the result is consistent with the one of a single case analysis of the region (24°N-36°N and 132°E-152°E) from March to October 2014. Moreover, as the intensity of the eddy increases, the diapycnal mixing is significantly enhanced. The statistical result in the study region shows that the diffusivity value of 90 percent is within the range of 10-5.5-10-4 m2/s.
Tomographic images of Avacha and Koryaksky volcanoes in Kamchatka
Authors: Bushenkova Natalia , Koulakov Ivan , Senyukov Sergey , Gordeev Evgeny I. , Huang Hsin-Hua , El Khrepy Sami , Al Arifi Nassir
Published: March 2020

In this study, we have mapped for the first time robustly the 3D structure of two upper-crustal magmatic reservoirs beneath the active volcanoes Avacha and Koryaksky, which are called “home volcanoes” for Petropavlovsk-Kamchatsky, the main city of Kamchatka (~200,000 inhabitants). These volcanoes represent a serious potential hazard for the city, because they are located at a distance of 25–30 km from the populated areas. A new tomographic model (VP, VS, VP/VS ratio) was built, for which we used the arrival times of seismic P- and S-waves from almost 5,000 local events, recorded by a permanent network of seismic stations during 2009–2018.The resolution of the derived models was carefully tested by a series of synthetic simulations. Prominent anomalies with extremely high VP/VS ratios (up to 2.4) were retrieved directly beneath both volcanoes and interpreted as magma reservoirs containing high degrees of partial melt and/or fluids. Beneath Avacha, the upper limit of the anomaly is located at the depth of ~2 km below the surface. The reservoir appears to be connected to the surface by a neck-shaped anomaly of high VP/VS ratio associated with active seismicity, which is interpreted as a magma and fluid conduit. Beneath Koryaksky, the magma related anomaly is deeper: its upper limit is located at a depth of ~ 7 km below the surface. This anomaly is connected with the volcanic coneby a vertical seismicity cluster, which possibly marks the pathway of fluid ascent and degassing. Between the volcanoes, a 2–3 km thick layer of very low VP and VS is interpreted as deposits of volcanoclastic sediments. Generally low Vp/Vs ratios in the area between the volcanoes show that the magma reservoirs in the upper crust are not interconnected.

This study was partially supported by the RFBR project # 18-55-52003.
Small contribution of conventionally-defined formation of secondary particulate matter to severe PM2.5 pollution in today’s northern China
Authors: Yao Xiaohong , Zhu Yujiao , Meng He
Published: March 2020

Benefited from the tightening emissions of air pollutants, a large annual decrease in mixing ratio of SO2 and a moderate decrease in PM2.5 can be identified in northern China since 2014. However, a few extreme PM2.5 pollution events still occur for sometimes during heating seasons, e.g., the 99th percentile value of PM2.5 concentrations during the heating season in 2018 had exceeded 200 µg m-3 therein. One unit of percentile value corresponds to approximately 30 hours. To reveal real causes of these extreme PM2.5 pollution events, we define two technical terms in this study, i.e., 1) secondary particulate species formed in ambient air (conventionally-defined FSPM); 2) formation of secondary particulate matter in the fresh plumes during the initial several minutes (plume-processed FSPM). We also introduce a metric, i.e., PM2.5/CO in unit of µg m-3 / ppm. With these technical terms in mind, we then struggle to dissect real mechanisms causing the severe PM2.5 pollution event in 11-14 January 2019 across norther China. A staircase function of ratios of PM2.5/CO against PM2.5 rather than a linear increase or decrease with PM2.5 generally occurred through the event. However, in general, larger ratios of PM2.5/CO were indeed observed with larger concentration of PM2.5. Regarding frequently observed invariant ratios accompanying with large variations in PM2.5, larger ratios are, however, probably not caused by conventionally-defined FSPM in PM2.5. Alternatively, our further multiple-technical analysis results confirm plume-processed FSPM, followed by accumulation under poor meteorological conditions, dominatingly resulting in the severe event. 
Real-world laboratories for studying anthropogenic aerosol impacts on clouds and Earth’s climate
Authors: Toll Velle , Trofimov Heido , Rahu Jorma
Published: March 2020

The cooling of the Earth’s climate through the effects of anthropogenic aerosols on clouds offsets an unknown fraction of greenhouse gas warming. We discuss how causal relationship between aerosols and clouds can be derived from contrast between clouds polluted by anthropogenic aerosols and nearby unpolluted clouds. Ship tracks have been long considered to be real-world laboratories of aerosol-cloud interactions. More recently, polluted cloud tracks induced by aerosols emitted from volcanoes and wildfires and various industrial sources - such as oil refineries, smelters, coal-fired power plants, and cities have been analysed (Toll et al. 2019; Nature, https://doi.org/10.1038/s41586-019-1423-9). In this research, we extend satellite observations of polluted cloud tracks from Toll et al. (2019) with analysis of smaller and larger scale polluted cloud areas detected in satellite images.

 

Polluted clouds are detected in MODIS and SEVIRI satellite images as areas with strongly increased cloud droplet number concentrations. Polluted cloud tracks can be utilized to study frequency and magnitude of anthropogenic cloud droplet number perturbations and subsequent cloud adjustments. Anthropogenic aerosol perturbations on liquid-water clouds are detected in various major global industrial areas. Both tens of kilometres wide ship-track-like polluted cloud tracks and hundreds by hundreds of kilometres wide polluted cloud areas show that cloud water can both increase and decrease in response to aerosols depending on meteorological conditions. On average, there is relatively weak decrease in cloud water. Polluted cloud tracks also show that cloud fraction can both increase and decrease compared to nearby less polluted clouds. Applicability of pollution tracks to study impact of absorbing aerosols situated above clouds on below-lying clouds is discussed. We expect that utilization of real-world laboratories of aerosol impacts on clouds will lead to improved physical parameterizations in global climate models and more reliable projections of the future climate.
Mapping urban changes of 31 global-mega cities using VIIRS nighttime light time series
Authors: Zheng Qiming , Wang Ke , Weng Qihao
Published: March 2020

The unprecedented urbanization process is bringing extremely complicated changes to global urban areas. The changes in urban land cover and land use have caused a succession of impact on global climate, ecology and local environment. Obtaining a comprehensive understanding on the diverse changes has a profound significance to urban environment and urban residents.

Nighttime light remote sensing data distinguished itself from other traditional remotely sensed data sets by its capability in providing both information on the physical property of the underlining earth surface and a good indication of human activities intensity. In this study we utilized dense nighttime light time series from Suomi-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) to characterize urban changes since 2012. Specifically, we (1) developed a non-linear  model to describe the trend and seasonal variation of VIIRS nighttime light time series; (2) incorporated temporal features to disentangle different urban change types; and (3) revealed urban change patterns of 31 global mega-cities.

Our results demonstrate that non-linear model has robust and satisfying performance in fitting diverse VIIRS trajectories. The proposed classification scheme based on temporal information noticeable improves classification accuracy, consistency and efficiency, compared to traditional year-by-year classification scheme. Unlike previous studies mainly focus on land cover change, we find that mega-cities comprise various change patterns of which land use intensification is the dominated change type in both urban cores and urban outskirts. Amongst all mega-cities, cities of developing countries demonstrate a wider extent and higher magnitude of change, as well as a larger proportion of land use intensification. Our study brings tangible benefit to achieve the goal of sustainable urban development by offering information about how urban changes over time, including urban change types and their spatial extent, intensity and trajectory trend.
Climate change effects on hydrometeorological compound events over southern Norway
Authors: Poschlod Benjamin , Zscheischler Jakob , Sillmann Jana , Wood Raul R. , Ludwig Ralf
Published: March 2020

Compound events are characterized as a combination of multiple drivers and/or hazards which contributes to societal, economical or environmental risk. In southern Norway, hydrometeorological compound events can trigger severe floods, for instance the joint occurrence of rainfall and snowmelt in south-eastern Norway in 1995 and 2013.  

Due to this high impact, the investigation of compound events is important, but is hampered by some limiting factors. The multivariate character and the associated very rare occurrence of these events require a large database in order to conduct statistically robust investigations, whereas the available meteorological observations are too scarce in space and time.
With this current study, we present a quantile-based framework to define and examine compound events within a single model initial condition large ensemble (SMILE). To overcome the limitation of data scarcity, we use 50 high-resolution climate simulations from the SMILE CRCM5-LE to investigate two hydrometeorological compound event types in southern Norway:

(1) Heavy rainfall on saturated soil during the summer months (June, July, August, September),

(2) Concurrent heavy rainfall and snowmelt (also often referred to as rain-on-snow).

Furthermore, the application of climate model data enables us to quantify the impact of climate change on the frequency and spatial distribution of both types of compound events. Thereby, we compare current climate conditions (1980-2009) with future conditions (2070-2099) under the high-emission scenario RCP 8.5. We find that the frequency of heavy rainfall on saturated soil increases by 38% until 2070-2099 on average. In contrast, the occurrence probability of rain-on-snow is projected to decrease by 48% over the whole study area, largely driven by decreases in snowfall. The spatial patterns of both events are found to shift. Additionally, we assess the range of the natural variability of the drivers and of the compound event probability within the 50 members of the CRCM5-LE. The univariate spread of the meteorological drivers is found to be relatively small, whereas the occurrence probability of both compound events shows a high inter-member variability. Hence, we conclude that the frequency of the joint occurrence of the contributing drivers is highly variable, which is why a SMILE is needed to assess this probability.

Our current work shows the limitations of regional climate models, stressing the need for even higher-resolution setups to resolve the complex topography of Norway. However, it also highlights the benefits of SMILE simulations for the analysis of compound events.
Estimation of global vegetation productivity from 1981 to 2018 With remote sensing data
Authors: Sun Rui , Wang Juanmin , Xiao Zhiqiang , Zhu Anran , Wang Mengjia , Yu Tao
Published: March 2020

ly during 1981 and 2018, which was in great agreement with the other similar products. The global NPP has shown a significant increase trend, with an annual growth rate of 0.10 PgC/yr (R2=0.4684)
Biascorrected projections of snow cover fraction from EURO-CORDEX regional climate models with MODIS remote sensing observations for the European Alps
Authors: Matiu Michael , Petitta Marcello , Notarnicola Claudia , Zebisch Marc
Published: March 2020

Snow is a key environmental parameter in mountains, and in this changing climate reductions in snow are expected. Traditionally, future estimates of snow are based on dedicated snow/hydrological models forced by climate projections, which, however, are computationally intensive and which decouple hydrology from climate forcing. Recently, regional climate models (RCM) have been used as an alternative, although snow is only an auxiliary parameter in RCMs and not as accurately represented as compared to dedicated snow models. Nonetheless, RCMs encompass the climate-hydrology feedbacks, cover large areas, and have recently become available in moderate horizontal resolutions.

Here, we skip the need to biascorrect the input variables to the snow/hydrological models (i.e. temperature, precipitation, …) and use observations to directly biascorrect the target variable, i.e. snow cover. Quantile delta mapping (QDM), a trend preserving bias correction method, is used to correct biases in EURO-CORDEX RCMs that provide snow cover fraction as output (CCLM4-8-17, ALADIN63, WRF331F, WRF381P, RACMO22E, RCA4) using remote sensing observations of snow cover from MODIS for the European Alps. As such, snow cover biases were accounted for, which originated mostly from orographic mismatches as well as temperature and precipitation biases. Model ensemble means were calculated for two emission scenarios (rcp26 and rcp85; with 6 and 21 GCM-RCM combinations available). The biascorrected projections can be used to put the climate model projections into context of current observations thus facilitating interpretations.

These are results from CliRSnow, a project that aims at providing bias corrected and downscaled projections of snow cover for the whole Alpine region until 2100. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 795310.
MMS observations of reconnection separatrix region in the magnetotail at different distances from the active neutral X-line
Authors: Sergeev Victor , Apatenkov Sergey , Nakamura Rumi , Wellenzohn Simon , Plaschke Ferdinand , Baumjohann Wolfgang , Khotyaintsev Yuri , Burch Jim , Torbert Roy , Russell Christopher , Giles Barbara
Published: March 2020

The region surrounding the reconnection separatrix consists of the multitude of particle and wave transient features (electron, cold and hot ion beams, Hall E&B fields, kinetic Alfven and LH waves, e-holes etc) whose pattern and intensities may vary depending on the stage of reconnection process as well as on the distance from the active neutral line (XNL), whose characterization from observations is not a trivial task. We explore quick MMS entries into the plasma sheet boundary layer from the lobe in 2017 and 2018 tail seasons which potentially could be the crossings of the active separatrix as suggested by energy dispersed beams and polar rain gap features. By combining  the observations of beam dispersion with the measured plasma convection and PSBL motion (obtained using the timing method) we attempt to separate  temporal and spatial (velocity filter) contributions  to the observed beam energy dispersion and evaluate the MMS distance from the XNL. In this report we discuss similarities and differences of separatrix manifestations  observed far from the XNL (at distances exceeding several tens Re) and those found close to it (where the outermost electron beam directed toward the XNL is seen).  One of surprizes was that we were often able to identify the intense Hall-like E&B field structures at very large distances from the XNL.  
High-impact winter weather in EURO-CORDEX climate models and their links to large-scale atmospheric circulation
Authors: Plavcová Eva , Lhotka Ondřej , Stryhal Jan
Published: March 2020

Regional Climate Models (RCMs) are powerful tools to study changes in the climate system on the regional scale. However, the reliability of their simulations has been considerably limited by the longstanding issue that climate models often fail to reproduce various aspects of the historical climate. In our study, we analyse how RCMs from the EURO-CORDEX project are able to reproduce high-impact winter weather. We analyse temporal and spatial characteristics of snowfalls, wind gust, extreme temperatures, late spring frosts, total precipitation, and winter storms. Model outputs are validated against observed data from the gridded European database (EOBS) and the novel ERA5 reanalysis. We focus on the Central European domain (defined roughly between 48–52°N and 10–20°E) over the 1979 – 2017 period. We investigate a set of 12 simulations of 4 different RCMs driven by 3 different global climate models which allow us to analyse the influence of driving data on the RCM’s performance. Since local climate elements are relatively tightly linked to a large-scale atmospheric circulation over Europe in winter, we also evaluate the ability of RCMs to reproduce the atmospheric circulation and its links to selected high-impact winter weather in detail. Investigation of these links can lead to better physical understanding of the climate and to the identification of inadequacies in simulated characteristics of the studied events. All of this is an important step forward in further improving the models and enhancing the credibility of climate change scenarios based on climate model simulations.
Eliminating Laser Induced Elemental U-Pb Fractionation using low sample volume multi-shot ablation protocols
Authors: Corbett Eoghan , Simonetti Antonio , Shaw Phil , Corcoran Loretta , Crowley Quentin , Hoare Brendan
Published: March 2020

The interaction of incident laser radiation and sample substrate is complex and difficult to predict. Natural zircons areoften both structurally and chemically heterogeneous in 3-dimensional space. Encountering growth-related, structural micro-heterogeneities, inclusions and chemical complexities is almost inevitable when employing ‘conventional’ static, high-frequency laser sampling protocols often lasting several tens of seconds at a time.

 

A multi-shot approach to laser ablation by contrast implements a minimal sample exposure time to incident laser radiation by applying multiple 1 Hz shots in delayed succession to a single sampling site. This process can be conceptualised as a “slowing down” of a high-frequency (10-20 Hz) static Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) analysis. Each laser pulse applied in this manner, produces signal peak which is distinct albeit transient. The ability to integrate and collate signal pulses for a small number of consecutive laser shots (10-30 shots), as opposed to continuously pulsing the laser, produces highly precise age determinations (<1% reproducibility, 2slevel) on small sample volumes (~695µm3 on 91500 zircon standard). The multi-shot LA-ICP-MS protocol employed here effectively eliminates ‘downhole’ fractionation as the resultant craters are extremely shallow (as shallow as ~553nm on 91500 zircon standard) and maintain an aspect ratio of <<1. Further benefits include a reduced probability of thermally induced effects (e.g., substrate melting), plasma loading, and the potential for signal mixing (with depth) in a heterogeneous sample.
Systemic risks emerging from global climate hotspots and their impacts on Europe
Authors: Gaupp Franziska , Sillmann Jana
Published: March 2020

In a globalized world, Europe is increasingly affected by climate change events beyond its borders that propagate through our interconnected systems impacting the socio-economic welfare in Europe. The REmote Climate Effects and their Impact on European sustainability, Policy and Trade (RECEIPT) project uses a novel stakeholder-driven storytelling approach that maps representative connections between remote climate hazards such as droughts or hurricanes and European socio-economic activities in the agricultural, finance, development, shipping and manufacturing sectors. As part of RECEIPT, this work focuses on systemic risks in global climate risk hotspots and their knock-on effects on the European economy. In five stakeholder workshops, expert elicitation methods are used to identify and map sector- and storyline-specific systemic risks: interlinkages between different events, hidden causes and consequences, potential feedback loops, uncertainties and other systemic risk characteristics will be investigated. A special focus lies on “gray rhino” events, “foreseeable random surprises” that follow clear warning signs but are only known to a smaller group of people. Results reveal sector-specific “topographies of risk” within the storylines identified by stakeholders.