bluuebunny/crossref_metadata_2025 huggingface dataset:
Combining the FAO56 agrohydrological model and remote sensing data to assess water demand in a Sicilian irrigation district
Authors: Ippolito Matteo , Minacapilli Mario , Provenzano Giuseppe
Published: March 2020

Agricultural water use in irrigated areas plays a key role in the Mediterranean regions characterized by semi-arid climate and water shortage. In the face of optimizing irrigation water use, farmers must revise their irrigation practices to increase the drought resilience of agricultural systems and to avoid severe damages in agro-ecosystems. In this direction, during the last decades, the research has been focused on mathematical models to simulate the process of driving mass transport and energy exchanges in the Soil-Plant-Atmosphere system.

The objective of the paper was to test the suitability of the combination of FAO56 agro-hydrological model with remote sensing data retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) platform, to assess the spatiotemporal distributions of crop water requirement and to schedule irrigation in an irrigation district of the south-west of Sicily, Italy.

The proposed approach allowed obtaining the spatiotemporal distributions of soil and crop parameters used in the FAO56 model implemented in a GIS environment to simulate the water balance, as well as to assess the actual irrigation strategy. The GIS database was organized to include soil and crop parameters, as well as the irrigation volumes actually delivered to each farmer; the latter data can be used not only as input for water balance to evaluate the efficiency of the actual irrigation strategies but also to identify different irrigation scheduling scenario obtained by the FAO56 procedure.

The first application was carried out for the period 2014-2017, to identify a combination of irrigation scheduling parameters to be implemented in the model aimed at reproducing the ordinary strategy adopted by the farmers, based on the spatiotemporal variability of soil and climate forcings. When the model outputs were aggregated for single crop types, a fairly good agreement was found between simulated and actual seasonal irrigation volumes delivered either at the level of district and secondary units. Alternative scenarios of irrigation water distribution were then identified and analyzed, to provide irrigation technicians and policymakers a decision support tool to improve the efficiency of irrigation systems and to optimize the distribution based on the availability of water resources.
Holocene moisture variations in the Tianshan Mountains and their geographic coherency in the mid-latitude Eurasia: A synthesis of proxy records
Authors: Yang Yunpeng
Published: March 2020

Understanding the Holocene moisture variations in the Arid Central Asia (ACA) is of a large-scale climatic significance simply because the vast ACA is influenced by several different climate systems. However, the temporal and spatial patterns and the modulating mechanisms of the Holocene aridity (or moisture) variations in the ACA remain in the center of controversies for the past two decades. Firstly, we in this research depicted the spatial and temporal patterns of the Holocene aridity variations in the Tianshan Mountains based on thirteen already-published aridity sequences and two recently obtained aridity sequences. Our depiction shows that the regionally-averaged standardized aridity-index (RA-SAI) curve for the Eastern Tianshan Mountains exhibits a wetting trend. In contrast, the RA-SAI curve for the Western Tianshan Mountains exhibits a drying trend. Secondly, we further examined these two RA-SAI sequences (one for the Eastern Tianshan and another for the Western Tianshan) within a much larger geographic context for exploring the mechanisms modulating the Holocene patterns. Our examination shows that the summer precipitation-dominated northern middle-latitude Eurasia (i.e., MLEA-N) has experienced a wetting trend and the winter precipitation-dominated southern middle-latitude Eurasia (i.e., MLEA-S) has experienced a drying trend. The wetting trend in MLEA-N is proposed to have resulted from increasingly more positively-phased AMO activities that have increasingly enhanced cyclonic pressure anomalies over the Atlantic regions, directly or indirectly bringing more and more summer precipitation to MLEA-N stretching from West Europe to the Eastern Tianshan. And, the drying trend in MLEA-S is proposed to have resulted from increasingly more negatively-phased NAO activities. That is, the negatively-phased NAO activities weakened the strength of Western Disturbances, therefore resulting in decreased winter precipitations in MLEA-S stretching from the Eastern Mediterranean to the Western Tianshan.

 
Observational evidence of surface wave-generated strong ocean turbulence
Authors: Ma Hongyu , Dai Dejun , Guo Jingsong , Qiao Fangli
Published: March 2020

By using an Acoustic Doppler Velocimeter (ADV) mounted on the seabed of the continental shelf of the northern South China Sea, high frequency velocity fluctuations were measured for 4.5 days. The turbulent kinetic energy dissipation rate was estimated. During the observation, the strong ocean response to Typhoon Rammasun was recorded to compare the turbulent characteristics before and during the typhoon. The results show that the turbulence near the seabed is mainly generated by the tidal current shear and exhibits a quarter diurnal variation during the period before the typhoon. During the typhoon period, the dissipation rate dramatically increased from 1×10-6 m2 s-3 to 1×10-2 m2 s-3 within a short time, and the significant wave height and the surface wave orbital velocity showed the same tendency. This finding suggests that the turbulence is dominantly generated by the surface waves near the seabed.
Why Northeast China Has a Cooling Trend in 21st century?
Authors: Li Xiang , Gao Hui
Published: March 2020

    Under the global warming scenarios, the air temperatures (T2m) in China in boreal winter shows a remarkable increasing trend since the 1980s, which is quite similar with the change of the globe. But in Northeast China (NEC), the temperature displays an opposite characteristics with an obvious decreasing trend in recent two decades. Results of the empirical orthogonal functions (EOF) of T2m in China indicate that the first leading mode is a consistent positive or negative temperature departures in the whole country, but the variance of this mode show a weakening tendency. The second leading mode of T2m in China shows a seesaw temperature anomaly pattern in NEC and in other regions of eastern China. Different from the 1st EOF mode, variances of this mode show an intensifying tendency. Both statistical analysis and case studies of 20 winters during 2000 to 2019 indicate that this opposite change in NEC may be related to the decadal relationship between the Siberian high and the Arctic oscillation. Previous studies explored that there was a significant negative correlation between the two factors, but this relationship was significantly weakened in the past two decades, which led to the independent influences from the two circulation members on the temperature in NEC, and consequently resulted in an inconsistent variation in the region.
Study on dynamic strength of sandstone based on SHPB numerical experimentation
Authors: Zhang Wengang , Meng Fansheng , Wang Qi
Published: March 2020

It is unavoidable that in rock engineering practices such as mining and tunnel constructions rocks are subjected to dynamic loading impacts including blasting, seismic loading, rock burst, and so on. The mechanical parameters for rock strength obtained via traditional static tests are not capable of characterizing the dynamic strength of rock mass. Therefore, the conventionally adopted tests cannot be further applied to guide the design of rock engineering subjected to dynamic loadings. Therefore the determination of the dynamic strength is essential for practical engineering. In this study, sandstone is chosen as the experimental sample for Split Hopkinson Pressure Bar (SHPB) numerical simulation by FLAC3D. The validation demonstrated that rocks are prone to fail under dynamic loading impacts. Extensive simulations are also carried out to investigate the development of rock dynamic strength and evolution process of energy accumulation and release in rock mass for samples of various sizes subjected to different levels of dynamic loading and axial loading. The simulation results may provide design guidance for the safety protection of rock engineering subjected to dynamic impacts.
Estimating daily 1-km surface air temperature from satellite all-weather land surface temperature over the Tibetan Plateau
Authors: Wen Xin , Zhou Ji , Zhang Xiaodong , Ma Jin
Published: March 2020

Over the past several decades, global climate change, particularly the rising temperature has caused public concerns. In the context of climate warming, many environmental and water problems such as decreasing runoff, shrinking glaciers and permafrost, vegetation degradation and desertification can be attributed to rapid climate change. Surface air temperature (SAT) plays a key role in land-atmospheric interactions and is an important parameter for climate change studies. Traditional SAT data are collected by ground meteorological observation. Nevertheless, such traditional measurements at ground stations cannot capture the spatial variations of SAT, especially over complicated areas such as the Tibetan Plateau, where meteorological stations are with large elevation variability and unreasonable spatial distribution. In contrast, satellite remote sensing provides an direct observation of land surface temperature (LST) and, thus, also provides an possible way to obtain SAT since LST and SAT are generally closely related to each other. The scientific communities have developed various methods to estimate SAT from LST through statistical or physical models. The widely used satellite LST, however, is derived from satellite thermal infrared remote sensing and thus, significantly affected by the clouds.

In this study, we report an examination of the estimation of daily 1-km SAT from the all-weather satellite LST over the Tibetan Plateau. The estimation of SAT is based on a noval method that dynamicall integrates the newly published 1-km all-weather LST data by merging satellite thermal infrared and microwave remote sensing observations based on the random forest. The matchups of the ground measured SAT at stations and the corresponding all-weather LST were separated into the training set and valiation set. In addition, independent SAT measured at experimental ground sites were used to evaluate the SAT method. Results indicate that reasonably integrating multiple LST terms provides daily average all-weather SAT with satisfactory accuracies over the Tibetan Plateau. The estimated SAT based on the proposed method has ignorable systematic error and low root-mean squared error when validated with ground measured SAT under all-weather conditions. Further comparison demonstrates that the SAT estimate agree well with other SAT estimated from satellite thermal infrared LST under cloud-free condition. In addition, the SAT method has the potential to be generalized and extended to various complicated areas. With this method, the daily 1-km SAT for the entire Tibetan Plateau from 2003 to 2018 were produced. This dataset is of great value to examine recent climate warming trend and the land-atmospheirc interactions in the entire Tibetan Plateau.
Ice-mass survival for approximately 800 Myr in the tropical Kasei Valles region, Mars
Authors: Hepburn Adam , Ng Felix , Holt Tom , Hubbard Bryn
Published: March 2020

High obliquity excursions on Mars are hypothesised to have redistributed water from the poles to nourish mid-latitude glaciers. Evidence of this process is provided by a variety of viscous flow features—ice-rich deposits buried beneath sediment mantle—located there today, including ‘lobate debris aprons’, or LDAs. During high obliquity extremes, ice may have persisted even nearer the equator, as indicated by numerous enigmatic moat-like depressions in the tropical Kasei Valles region. Numerous depressions surround isolated mesas and demarcate the past interaction between flowing lava and what were presumably ice-rich radial flows resembling today’s LDAs, but which have long since disappeared. Little is known about ‘ghost lobate debris aprons’ (ghost LDAs), besides their spatial extent as recorded by these depressions. This collection of ghost LDAs implies tropical ice loss over an area ~100,000 km2. To constrain their history in Kasei Valles we derive model ages of different terrain types from crater counts. To constrain the volume of ice loss, we use a 2D perfect-plasticity model of ice flow to reconstruct the ghost LDA surfaces. Parametrised by the present surface topography and the range of yield stresses derived from radar interrogation of mid-latitude ice masses, the model reconstructs former ice surfaces along multiple flowlines orientated normal to ghost LDA boundaries. This reconstruction indicates between 1,300–3,300 km3 of ice—similar to that present in Iceland on Earth—was lost since lava emplacement ~1.4 Ga. Dating of these depressions shows that the ghost LDAs survived for ~800 million years following lava emplacement in the Kasei Valles region before their final demise.
Soil Organic Carbon Accumulation under Different Forms of Organo-Mineral Fertilizers and Methods of Their Application on Ukrainian Black Soil
Authors: Hetmanenko Viktoriia , Skrylnyk Ievgen , Kutova Anzhela
Published: March 2020

Soil organic carbon management is a key element in solving such urgent global-scale challenges as overcoming degradation of soils and mitigating climate change. Organic fertilizers application has a significant potential for sequestering C in soils, but their efficiency depends on decomposition characteristics. Firstly, it noted the dependence of resynthesis of humic compounds in a soil on a quality of organic inputs, secondly - a need for zonal approach to fertilizers production based on amphiphile properties of macromolecules.

The present study was conducted in long-term field experiment on black soil in Forrest-Steppe zone of Ukraine. The technology of production of organo-mineral fertilizers (OMFs) was based on the regulated processing of livestock waste with mineral components to stabilize it with hydrophobic bonds. OMFs in amorphous and granular form were compared in case of broadcast and band method of incorporation. The dose of OMF input was equivalent 350 C kg ha-1 and 80 N, 80 P, 80 K kg ha-1. Organic carbon content in soil was determined by Turin method. Different organic matter fractions were isolated: humic acids (HA), fulvic acids (FA), and humin.

The soil C accumulation rates in OMF treatment was by 15 % higher than in manure treatment and up to 70 % higher than in chemical fertilizer treatment, respectively. The soil C accumulation was strongly influenced by the form of OMF and method of their application. The highest TOC level was found over band application of amorphous OMF, accumulating 6.2 t C ha–1 yr–1 in 0-20 cm soil layer. Lower efficiency of broadcast incorporation OMFs could be explained by more intensive mineralization due to higher aeration. Taking into account the effect of OMFs on C stock an advantage of amorphous form versus granulated OMF with similar composition was proven. Black soil on control plot (without fertilization) had almost equal ratio between HA, FA and humin in humus composition. The content of humic compound increased in all treatments. Applying OMF significantly increased HA content in black soil compared to applying mineral fertilizer. OMFs application promoted the increase of the degree of condensation of organic matter. The highest HA/FA was found under the effect of broadcast incorporation OMF. That means that low molecular weight compounds were rapidly degraded while more resistant to mineralization HA were formed in soil. There was no significant difference in humus composition between amorphous and granulated OMF.
Evaluating the effect of tropical and extratropical Pacific initial errors on two types of El Niño prediction using particle filter approach
Authors: Hou Meiyi , Zhi Xiefei
Published: March 2020

Different types of El Niño-Southern Oscillation (ENSO) predictions are sensitive to the initial errors in different key areas in the Pacific Ocean. And it is known that the prediction can be improved by removing the initial errors by using assimilation methods. However yet, few studies have quantified to what extent can different types of ENSO predictions be improved by assimilating variable in different key areas. In Hou et.al (2019), 4 types of ocean temperature initial error patterns were classified for two types of El Niño prediction. It was indicated that initial errors in the north Pacific, covering the Victoria Mode region, along with south Pacific, covering the South Pacific Meridional Mode region, and subsurface layer of western equatorial Pacific have strong influence on the ENSO prediction. Following the data analysis method and the initial error patterns they proposed, we assimilate ocean temperature in these three key areas of Pacific Ocean by using CMIP5 pi-control dataset and particle filter method. Most EP- and CP-El Niño predictions in December are improved after assimilating the ocean temperature in southeast Pacific, north Pacific and western equatorial Pacific from January to March. Specially, for the prediction ensemble which contains EP(CP)-type-1 initial errors, the EP(CP)-El Niño prediction skill raises the most after assimilating the Tropical Pacific temperature, comparing with the result of assimilating the south Pacific and north Pacific. As for the prediction ensemble which contains EP-type-2 initial errors, which present similar pattern to EP-type-1 but with opposite sign, the EP-El Niño prediction skill increases the most by assimilating the north Pacific temperature. The results verify that the initial errors in the north Pacific exert contrary influences on the ENSO prediction with that in the southeast Pacific and western tropical Pacific. In addition, the initial errors in the north Pacific is more of concern for the SST prediction in the central tropical Pacific in December, while those in the southeast Pacific and tropical western Pacific is more related to the SST prediction in the central-eastern tropical Pacific. In conclusion, to better predict the types of El Niño, attentions should be paid to the initial ocean temperature accuracy not only in the tropical Pacific but also in the north and south Pacific. 

 

 
Seismic detection of the low-velocity anomaly at the crust and uppermost mantle beneath the central Tien Shan
Authors: Cui Ran , Zhou Yuanze
Published: March 2020

As one of the most active intracontinental orogenic belts in the world, the Tien Shan orogenic belt originated in the Paleozoic and then experienced tectonic activities such as plate subduction and closure of the Paleo-Asian Ocean. Previous seismological and geodynamic studies have shown the observed the low-velocity anomaly (LVA) beneath the central Tien Shan at the uppermost mantle, which has a significant influence on the formation and modification of the crust and mantle lithosphere ( Lei et al, 2007). However, the distribution, morphology and physical property of the LVA are highly debatable.

We conduct 2-D forward waveform modeling based on spectral-element method (SEM) to investigate waveform distortions that were generated by the velocity contrast boundary of the LAV. The broadband P- and S- waves from three intermediate-depth earthquakes at Hindu Kush-Pamir were recorded by the Chinese Digital Seismograph Network (Zheng et al., 2010). We use these records to confirm the location, shape and velocity decrement of the LVA by fitting the observed records with the synthetics through SEM based on the 1D velocity structures (TSTB-B) of the central Tien Shan and northern Tarim basin (Gao et al., 2017). We find the LVA at 10~100 km beneath the eastern part of the central Tien Shan. And the northward under-thrusting of the Tarim Basin may trigger some mantle upwelling, contributing to the observed LVA.

Lei, J., Zhao, D. (2007). Teleseismic P-wave tomography and the upper mantle structure of the central Tien Shan orogenic belt. Physics of the Earth and Planetary Interiors, 162, 165-185, doi: 10.1016/j.pepi.200704010.

Zheng, X., Jiao, W., Zhang, C., et al. (2010). Short-Period Rayleigh-Wave Group Velocity Tomography through Ambient Noise Cross-Correlation in Xinjiang, Northwest China. Bulletin of the Seismological Society of America, 100(3): 1350-1355, doi: 10.1785/0120090225.

Gao, Y., Cui, Q., Zhou, Y. (2017). Seismic detection of P-wave velocity structure atop MTZ beneath the Central Tian Shan and Tarim Basin. Chinese Journal of Geophysics ( in Chinese with English Abstract ), 60 (1) : 98-111, doi: 10.6038 /cjg20170109.
The analysis of heterogeneity and frequency of extreme storms under urban settings: A case study in Shanghai City
Authors: Zhou Zhengzheng , Zhuang Qi , Liu Shuguang
Published: March 2020

Cities are increasingly vulnerable to extreme hydro-meteorological disasters, like rainfall-generated flooding. The urban floods lead to devastating damage to property and loss of human life. Extreme storms, which is the major trigger of urban flooding, thus need to be carefully examined. Our previous studies have found an increase of large rainfall intensity and variability in Shanghai City, China. In this study, we will further explore: 1) the change of spatio-temporal heterogeneity and frequency of extreme storms over decades; 2) the association between urbanization and these changes. We first extract the extreme storm catalogs for various time scales. The characteristics of space-time structure of storms in these storm catalogs are examined by using spatial analysis methods. The interannual variation of rainfall space-time structure are investigated. By using the strategy of Stochastic Storm Transposition (SST), extreme storm frequencies are generated. Various storm frequencies with different storms catalogs are then compared to show the change of magnitude of extreme storms frequencies. The correlation between the process of urbanization and the change of extreme storms is analyzed from the statistical perspective. From these results, we will have a clearer understanding of urban extreme storms and provide important implementations for assessment of flood risks in urban areas.
Ground and Dead Ice in Alpine Proglacial Areas – Sensitivity towards Climate Change since 1850, Recent Dynamics and Future Trends
Authors: Bernsteiner Heidi , Götz Joachim , Haas Florian , Heckmann Tobias , Sass Oliver , Becht Michael
Published: March 2020

As the climate warms, the earths’ cryosphere melts. Among the regions with the highest sensitivity to recent climate change are the high altitudes of the European Alps. This can be seen most clearly in the melting of glacier ice. Most glaciers show a strong receding trend since the last maximum extent during the little ice age (LIA) around AD 1850. When glaciers retreat, they leave behind a characteristic paraglacial landscape in a transient state from glacial to non-glacial conditions. Dominated by large amounts of unconsolidated glacial sediments they show an extremely high geomorphic activity.

However, these proglacial areas can still hold ice even decades after the glacier has left. In a simplified manner, this can be conceptually described by two main mechanisms: i) When glaciers retreat parts of the glacier front are often decoupled from the main glacier. These so-called dead ice bodies can remain for years, especially when they are buried by a thick debris cover and thus protected from atmospheric conditions. ii) Particularly in high-elevated glacier forefields, the thermal regime can be suitable for the direct transition from a glacial to a periglacial environment, compassing the aggradation of permafrost ice in areas that have been released from the glacier.

Climate warming speeds up in recent times, related with an enhanced receding of glaciers and growing alpine proglacial areas. Ground and dead ice are among the most important drivers of geomorphic activity in these regions, though in the long-term it is most likely, that it will melt out as well. How fast this will happen and in what stage it may play a role in stabilizing these environments is not yet fully clarified. Therefore, a better knowledge on ice distribution and dynamics in alpine proglacial regions is needed. Additionally, the quantification of ice and water contents is crucial in terms of potential hazardous processes, regarding the supply of (drinking) water and hydropower.

Here we present a new (PhD-) project in close cooperation with the DFG-funded research unit SEHAG, which is at the beginning of its implementation. Focussing on ground and dead ice we aim i) to assess the current distribution, ii) to reconstruct dynamics since the LIA, iii) to reveal recent and future trends (aggradation, degradation and persistence), and iv) to quantify effects on sediment dynamics in three Central Alpine proglacial areas. We combine different geophysical techniques with a focus on electrical resistivity tomography, water isotope analysis and ground (surface) temperature measurements with high-resolution geomorphic change modelling.
Topological Waves in Astrophysical and Geophysical Flows
Authors: Venaille Antoine
Published: March 2020

Over the last decade, the concept of topological wave has spread over all fields of physics. These ideas were initially developed in condensed matter to describe peculiar electronic transport properties in exotic materials; it has now become clear that topological tools apply as well to classical systems, and thus to geophysical fluid dynamics.  Topology predicts the emergence of unidirectional modes trapped along interfaces or boundaries, depending on broken discrete symmetries, and on the twisting of bulk eigenmodes. It guarantees the robustness  of undirectional trapped modes against disorder, such as random topography or small scale turbulence. We will explain how to compute such topological features, discuss possible experimental realizations, and present three recent applications to geophysical flows :

The emergence of equatorially trapped topological modes in Laplace tidal equations as a consequence of  Coriolis force breaking time-reversal symmetry [1,2].

The  emergence of Lamb-like waves that connect acoustic wave bands to internal gravity waves bands in compressible-stratified fluids, as a consequence of gravity breaking miror symmetry, with potential applications in helioseismology [3] .

A new manifestation of these topological features in geophysical ray tracing : when computing first order corrections to ray tracing, we find that rays  or wave packets are deflected by an effective field corresponding to the so-called Berry curvature. To our knowledge, the effect of this Berry curvature had up to now been overlooked in geophysical context [4].

[1] P. Delplace, J.B. Marston, A. Venaille, Topological origin of equatorial waves, Science 2017 
[2] C. Tauber, P. Delplace, A. Venaille, A bulk-interface correspondence for equatorial waves, Journal of Fluid Mechanics 2019
[3] M. Perrot, P. Delplace, A. Venaille, Topological transition in stratified fluids, Nature Physics  2019
[4] N. Perez, P. Delplace, A. Venaille Manifestation of Berry curvature in geophysical ray tracing, in prep. 2020

 
Predicting the proximity to system-scale rupture using fracture networks
Authors: McBeck Jessica , Aiken John , Mathiesen Joachim , Ben-Zion Yehuda , Renard Francois
Published: March 2020

A fundamental challenge in geophysics is predicting the timing of large earthquakes. A key step in addressing this problem is constraining the factors that indicate the timing of the next large rupture. To isolate the factors that help predict the proximity of the next earthquake, we develop machine learning models to predict the stress distance to macroscopic failure in triaxial compression X-ray tomography experiments on rocks at the stress conditions of the upper crust. In these experiments, we apply increasing axial stress in steps, and acquire a 3D X-ray tomogram at each stress step while the rock is under constant load, revealing the 3D density distribution. Segmenting the density fields provide the locations of rock (voxels dominated by solid), and pores and fractures (voxels dominated by air). We train the machine learning models using the geometry and clustering properties of the fracture networks identified in the tomography scans. We develop extreme gradient boosting (XGBoost) models to predict the stress distance to failure. In experiments on Carrara marble, monzonite, and granite, the models predict the stress distance to failure with r2 values > 0.7. We examine the feature importance to identify the factors that provide the best predictive power of the distance to failure. Measurements of the fracture network clustering and the shape anisotropy of fractures tend to have the highest importance of the features, providing greater predictive information than the fracture volume, fracture length, fracture aperture, and fracture orientation relative to the maximum compression direction.
Contributions of tropical-extratropical oceans to the prediction skill of ENSO after 2000
Authors: Shi Liang , Ding Ruiqiang , Tseng Yu-heng
Published: March 2020

The skills of most ENSO prediction models have declined significantly since 2000. This decline may be due to a weakening of the correlation between tropical predictors and ENSO. Moreover, the effects of extratropical ocean variability on ENSO have increased during this period. To improve ENSO predictability, we investigate the influence of the tropical-extratropical Atlantic and Pacific sea surface temperature(SST) on ENSO during the periods of pre-2000 and post-2000. We find that the influence of the northern tropical Atlantic(NTA) SST on ENSO has significantly increase since 2000. Meanwhile, there is a much earlier and stronger SST responses between NTA SST and ENSO over the central-eastern Pacific during June–July–August in the post-2000 period compared with the pre-2000 period. Furthermore, the extratropical Pacific SST predictors for ENSO still retain a ~10-month lead time after 2000. We use SST signals in the extratropical Atlantic and Pacific to predict ENSO using a statistical prediction model. These results reveal a significant improvement in ENSO prediction skills. These results indicate that the Atlantic and Pacific SSTAs can make substantial contributions to ENSO prediction, and can be further used to enhance ENSO predictability after 2000.
One year of MAX-DOAS measurements of tropospheric trace gases and aerosols in the suburban area of London
Authors: Donner Sebastian , Dörner Steffen , Buxmann Joelle , Beirle Steffen , Campbell David , Müller Detlef , Remmers Julia , Rolfe Samantha M. , Wagner Thomas
Published: March 2020

Multi-AXis (MAX)-DOAS instruments record spectra of scattered sun light under different elevation angles. From such measurements tropospheric vertical column densities (VCDs) and vertical profiles of different atmospheric trace gases and aerosols can be determined for the lower troposphere. These measurements allow a simultaneous observation of multiple trace gases (e.g. HCHO, CHOCHO, NO2, etc.) with the same measurement setup. Since November 2018, a MAX-DOAS instrument is operated at the Bayfordbury Observatory, which is located approximately 30 km north of London. This measurement site is operated by the University of Hertfordshire and equipped with an AERONET station, a LIDAR and multiple instruments to measure meteorological quantities and solar radiation. Depending on the prevailing wind direction the air masses at the measurement site can be dominated by the pollution of London (SE to SW winds) or rather pristine air (northerly winds). Therefore, this measurement site is well suited to study the influence of anthropogenic pollution on the atmospheric composition and chemistry at a rather pristine location in the vicinity of London, a major European capital with 9.8 million inhabitants and 4 major international airports.

In this study, trace gas and aerosol profiles are retrieved using the MAinz Profile Algorithm MAPA (Beirle et al., 2018) with a focus on tropospheric formaldehyde (HCHO) which plays an important role in tropospheric chemistry. The HCHO results are combined with the results of other trace species such as NO2, CHOCHO and aerosols in order to identify different chemical regimes and pollution levels.
An experimental investigation of microplastic transport in fluvial systems
Authors: Boos Jan-Pascal , Gilfedder Benjamin-Silas , Elagami Hassan , Frei Sven
Published: March 2020

Although a major part of marine microplastic (MP) pollution originates from rivers and streams, the mechanistic behavior of MP in fluvial systems is only poorly understood. MP enter fluvial systems from e.g. waste water treatment plant (WWTP) effluents, sewer overflows during heavy rain events, agricultural runoff, aerial input/atmospheric fallout, road runoff or via fragmentation of plastic litter. As part of this project we want to investigate the hydrodynamic transport mechanisms that control the behavior and re-distribution of MP in open channel flow and the streambed sediments. Hydrodynamic conditions in open channel flow are represented in an experimental flume environment.  Different porous media materials (e.g. aqua beads, glass beads and sand) are used in the flume experiments to shape typical bed form structures such as riffle-pool sequences, ripples and dunes. The aim of this experimental setup is to create hydrodynamic flow conditions such as hydraulic jumps, low and high flow velocity environments for which the transport and sedimentation behavior of MP can be investigated under realistic conditions. Hydrodynamic flow conditions in the flume are characterized using a Laser-Doppler-Anemometry (LDA) and Particle Image Velocimetry (PIV). Detection and tracking of fluorescent MP-particles in open channel flow and in porous media will be achieved with a fluorescence-camera-system.
Modification of the magnetosheath due to the high-speed jets propagation.
Authors: Goncharov Oleksandr , Gunell Herbert , Hamrin Maria , Norenius Linus , Gutynska Olga
Published: March 2020

Plasmoids, defined as plasma entities with a higher anti-sunward velocity component than the surrounding plasma, have been observed in the magnetosheath in recent years. Among other denominations, plasmoids are also called “magnetosheath jets” and can be classified by transient localized enhancements in dynamic pressure. Propagating through the magnetosheath, jets do not only affect the magnetopause and magnetosphere. Jets pushed slower ambient magnetosheath plasma out of their way. As a result, plasma moves around the jets, and it is slowed down or could even be pushed in the sunward direction. Consequently, jets may create anomalous flows and be a source of additional turbulence. Using the magnetosheath measurements by the Magnetospheric Multiscale (MMS) and THEMIS spacecraft, and comparing several criteria, we have identified several thousand events in the wide range of bow shock distances. Previous statistical studies have shown that jet occurrence is almost exclusively controlled by the angle between the IMF and the Earth–Sun line (cone angle), and jets are predominantly observed when this cone angle is small. However, high-speed jets downstream of the quasi-perpendicular bow shock are very common. Our statistical analysis shows differences of jets evolution in the quasi-parallel and quasi-perpendicular magnetosheath regions. We discuss their properties, nature and relation to anomalies regions in the magnetosheath.
Marine organic matter in the remote environment of the Cape Verde Islands – An introduction and overview to the MarParCloud campaign
Authors: van Pinxteren Manuela , Fomba Khanneh Wadinga , Triesch Nadja , Wex Heike , Gong Xianda , Vogtländer Jens , Barthel Stefan , Stolle Christian , Bahlmann Enno , Rixen Tim , Schulz-Bull Detlef , Robinson Tiera-Brandy , Wurl Oliver , Stratmann Frank , Herrmann Hartmut
Published: March 2020

The project MarParCloud (marine biological production, organic aerosol particles and marine clouds: a process chain) aims at achieving a better understanding of the biological production of organic matter (OM)in the oceans, its export into marine aerosol particles and finally its ability to act as ice and cloud condensation nuclei (INP and CCN). The core of MarParCloud comprised a field campaign at the Cape Verde Atmosphere Observatory (CVAO) in autumn 2017, where a variety of chemical, physical, biological and meteorological approaches were applied. The investigations included concerted measurements of the bulk water, the Sea Surface Microlayer (SML), ambient aerosol particles on the ground (30 m a.s.l.) and in mountain heights (744 m) as well as cloud water. Important aspects of the ocean atmosphere Interactions focusing on marine OM have been addressed through detailed observation and modeling approaches.

Key variables comprised the chemical characterization of the atmospherically relevant OM components (e.g. lipids, proteins, sugars) in the ocean and the atmosphere as well as measurements of INP and CCN. Moreover, bacterial cell counts, mercury species and trace gases were analysed. To interpret the results, the measurements were accompanied by various auxiliary parameters such as air mass back trajectory analysis, vertical atmospheric profile analysis, cloud observations and pigment measurements in seawater. Additional modelling studies supported the experimental analysis.

Here we show the proof of concept of the connection between organic matter emission from the ocean to the atmosphere and up to the cloud level. A link between the ocean and the atmosphere was clearly observed as (i) the particles measured at the surface are well mixed within the marine boundary layer up to cloud level and (ii) ocean-derived compounds can be found in the aerosol particles at mountain height and in the cloud water. The organic measurements will be implemented in a new source function for the oceanic emission of OM. However, from a perspective of particle number concentrations, the marine contributions to both CCN and INP are rather limited.
The central importance of macrobenthos in benthic-pelagic coupling in coastal shelf seas
Authors: Zhang Wenyan , Neumann Andreas , Daewel Ute , Schrum Corinna
Published: March 2020

Benthic oxygen fluxes measured in the south-eastern North Sea indicate a prominent annual cycle characterized by a low level between mid-autumn (October) and early spring (March), a slow increase since mid-spring (April) till late summer (late August/early September), and a subsequent accelerated decrease in early autumn (September). A significant positive correlation between the benthic oxygen flux, total organic carbon (TOC) and macrobenthic biomass in surface sediments suggests their potential mutual dependence. To understand their interactions quantitatively, 3-D benthic-pelagic coupled modelling was used to reconstruct the benthic status. Simulation results based on a satisfactory agreement with field data reveal that the benthic oxygen flux is determined by not only pelagic drivers (hydrodynamics, temperature and primary production) but also internal dynamics associated with the interaction between organic carbon and benthic fauna, and bedform morphodynamics. The slow increase of benthic flux since mid-spring till late summer is a compound effect of several processes with dominant contribution by accumulation of labile OC and growth of macrobenthos in surface sediments. Bioturbation intensity peaks in late summer, resulting in highest oxygen flux into sediments and promoting remineralization of subsurface OC and release of nutrients. Shutdown of pelagic primary production in combination with enhanced wind-waves in early autumn cause a systematic shift of the benthic carbon pool from deposition to erosion within a few weeks, accounting for the accelerated decrease of benthic oxygen flux. Our results indicate a central role of macrobenthos in modulating the rate of both solute and solid fluxes across the sediment-water interface.
Fracture stratigraphy, fault architecture and DFN modeling of both diffuse and localized fracture networks
Authors: Agosta Fabrizio
Published: March 2020

Quantification of the geometry, distribution, and dimension of fracture networks is key to fully understand the petrophysical properties of outcrop-to-reservoir scales rock volumes. On these regards, Discrete Fracture Network (DFN) modeling is a very useful tool to compute the values of fracture porosity and equivalent permeability of geo-cellular volumes populated with stochastic or deterministic fracture networks. Independently of their size and cell dimensions, the single geocelullar volumes are populated by inputting the following parameters for each fracture set: (i) length; (ii) aspect ratio; (iii) mechanical and hydraulic apertures; (iv) fracture intensity, and (v) attitude. A sensitivity analysis is always carried out in order to test the seeding procedure of the employed software, and to check the validity of the fracture aperture values employed as input data. The latter values, in fact, are the most critical to assess from outcrop and laboratory analyses. The present contribution focuses on the results of recent works performed on the fractured limestone rocks of the Apulian Platform, which are widely exposed along the Italian peninsula. Outcrops are first introduced in order to define the fracture stratigraphy and fault architecture of the Meso-Cenozoic limestone rocks. Then, the criteria behind the construction of DFN models are illustrated. Methods employed for the build of individual fracture units and single fault damage zone domains are illustrated. Finally, the computed values of fracture porosity and equivalent horizontal permeability obtained for multiple DFN models are presented. Discussion of the data focuses on the fluid accumulation and migration properties of the fractured limestone rocks by considering their amount of exhumation experienced during Plio-Quaternary times. Results of DFN modeling could be helpful to optimize the appraisal and development operations of hydrocarbon reservoirs, and minimize the pollution of freshwater aquifer. In fact, the Apulian carbonates host in the underground significant amounts of freshwater of the Mediterranean Region, and the largest oil and gas reserves of continental Europe. Furthermore, the results could shed new lights into the role exerted by faults and fractures on subsurface CO2 storage in depleted carbonate reservoirs, a practice that envisioned to decrease the greenhouse gas concentration in the atmosphere in the next future.
Modeling the growth rates of cyanobacteria and diatoms in the Baltic Sea
Authors: Stramska Malgorzata , Stoń-Egiert Joanna , Ostrowska Miroslawa , Jakacki Jaromir
Published: March 2020

Potential influences of various environmental factors on phytoplankton growth rates in the Baltic Sea are discussed. Our focus is on quantitative comparisons of growth rates of two phytoplankton functional types, diatoms and cyanobacteria. Growth rates are calculated as a function of quanta absorbed by phytoplankton. This in turn depends on phytoplankton exposition to light, which was simulated to represent realistic conditions encountered in the Baltic Sea in summer. In addition, phytoplankton absorption capability was characterized by absorption coefficients derived from measurements on phytoplankton mono-cultures isolated from the Baltic Sea. Estimated exposition of phytoplankton to photosynthetically available radiation (PAR) in surface waters can change about five times in case of the same solar surface insolation and water turbidity, solely due to changes in the mixed layer depth from 2 to 20 meters. When additionally changes in water turbidity are considered, phytoplankton PAR exposition can change by one order of magnitude. Light exposition and absorption properties of phytoplankton determine the effectiveness of light absorption. In our simulations for the same species of phytoplankton, changes in light exposition resulted in differences of an order of magnitude of absorbed quanta. The importance of accounting for absorptive properties is underlined through comparisons of the number of quanta absorbed by different phytoplankton types in the same environmental conditions. The effectiveness of light absorption translates to different growth rates achieved by each phytoplankton type. Our results support the notion that knowledge about phytoplankton absorption properties and light exposition is crucial when modeling phytoplankton in the Baltic Sea. Further progress is currently hindered by a lack of systematic information about maximum phytoplankton growth rates and their responses to specific environmental conditions for different functional types. Such information should be inferred in the future in specially designed laboratory experiments, that encompass realistic ranges of phytoplankton exposition to light, nutrients, temperatures and other conditions.

This work has been funded by the National Science Centre (contract number: 2017/25/B/ST10/00159 entitled: “Numerical simulations of biological-physical interactions and phytoplankton cycles in the Baltic Sea”) and by the statutory funds of IOPAN.
Reconciling modelled and observed age of air through SF6 sinks
Authors: Loeffel Sheena , Eichinger Roland , Garny Hella , Reddmann Thomas , Versick Stefan , Fritsch Frauke , Stiller Gabriele , Haenel Florian
Published: March 2020

Mean age of air (AoA) is a common diagnostic for the stratospheric overturning circulation in both climate models and observations. Observations of AoA mostly base on measurements of SF6, which is an almost ideal AoA tracer because its emssions across the recent decades increased nearly linearly and it is fairly stable in the troposphere and stratosphere. Over the last ten years, however, researchers were puzzled as to why AoA climatologies and trends of model simulations and observational data do not coincide. AoA in climate models is generally much lower than in observations and models show a clear decrease of AoA over time while measurements show a non-significant increase.

What is commonly not considered in the models is that SF6 has chemical sinks in the mesosphere, and these lead to apparently older air in the stratosphere. In our experiment, we explicitely calculate SF6 sinks based on physical processes in simulations with the global chemistry-climate model EMAC (ECHAM MESSy Atmospheric Chemistry). We show that considering the SF6 removal reactions strongly increases stratospheric AoA and leads to much better agreement between the climatologies of EMAC and MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) satellite observations. Moreover, the stratospheric AoA trend over the recent decades reverses sign when we derive it from SF6 with sinks. This means that the trend can such be reconciled with the trend that has been derived from long-term balloon-borne measurements. Our specifically designed sensitivity studies moreover reveal that this positive trend results neither from circulation changes, nor from variations of the reactive species involved in mesospheric SF6 depletion. Instead, it is generated through the temporally growing influence of the SF6 sinks themselves, an effect that overcompensates the negative trend resulting from the accelerating stratospheric overturning circulation.