bluuebunny/crossref_metadata_2025 huggingface dataset:
Combining asynchronous data sets in regional body-wave tomography
Authors: Maupin Valerie
Published: March 2020

Body-wave tomography with data from regional networks, also called ACH tomography, has provided a lot of information on the upper mantle structure, especially in continental settings. A key factor in this technique is the usage of relative residuals, not absolute ones. It is based on the assumption that travel times at stations in a regional network are affected in a similar way by errors in source location and origin time, as well as by large-scale heterogeneities in the lower mantle, and that demeaning the residuals strongly reduces the influence of these factors on the inverse regional model. This results in the well-known fact that the final velocity model is relative to an unknown vertically varying reference model. This also prevents combining data obtained with networks in the vicinity of each other but operating at different times, even though we may have stations, for example permanent stations, which are common to these networks. This is because the residuals at the two networks are measured with respect to different unknown averages and cannot be inverted together. This is very unfortunate as we have numerous examples of asynchronous network deployments which together would provide a much more useful station coverage and model than independently.

I will analyse how a simple change in the formulation of the direct problem allows to take into account that the residuals are demeaned, and, most importantly, how this can be used to remedy the limitations of regional body-wave tomographic methods in terms of asynchronous station deployment. I will first illustrate this with a very simple example and then present the results of a more realistic synthetic test combining data from two neighboring asynchronous networks in a single inversion.
Detection of irrigation events on maize plots using sentinel-1 soil moisture products
Authors: Le Page Michel , Jarlan Lionel , Boone Aaron , El Hajj Mohammad , Baghdadi Nicolas , Zribi Mehrez
Published: March 2020

An accurate knowledge of irrigation timing and rate is essential to compute the water balance of irrigated plots. However, at the plot scale irrigation is a data essentially known by the irrigator. These data do not go up to higher management scales, thus limiting both the management of water resources on a regional scale and the development of irrigation decision support tools at the farm scale. The study focuses on 6 experimental plots in the south-west of France. The new method consists in assessing surface soil moisture (SSM) change between observations and a water balance model. The approach was tested using both in situ measurements and surface soil moisture (SSM) maps derived from Sentinel-1 radar data. The score is obtained by assessing if the irrigation event is detected within +/- three days. The use of in situ SSM showed that: (1) the best revisit time between two SSM observations is 3 days; short gaps is subject to uncertainties while longer gap miss possible SSM variations; (2) in general, higher rates (>20mm) of irrigation are well identified while it is very difficult to identify irrigation event when it is raining or when irrigation rates are small (<10mm). When using the SSM microwave product, the performances are degraded but are still acceptable given the discontinuity of irrigation events: 34% of absolute error and a bias of 5% for the whole season. Although high vegetation cover degrades the SSM absolute estimates, the dynamic appeared to be in accordance with in-situ measurements.
Extreme precipitation events in the Mediterranean region: their characteristics and connection to large-scale atmospheric patterns
Authors: Mastrantonas Nikolaos , Magnusson Linus , Pappenberger Florian , Matschullat Jörg
Published: March 2020

The Mediterranean region is an area with half a billion population, about 10 percent contribution to the world’s GDP, and locations of global natural, historical and cultural significance. In this context, natural hazards in the area have the potential for severe negative impacts on society, economy, and environment. 

Some of the most frequent and devastating natural hazards that affect the Mediterranean relate to extreme precipitation events causing flash floods and landslides. Thus, given their adverse consequences, it is of immense importance to better understand their statistical characteristics and connection to large-scale atmospheric patterns. Such advances can substantially support the accurate and early identification of these extreme events, improve early warning systems, and contribute to mitigating related risks. 

This work focuses on the characteristics and spatiotemporal variability of extreme precipitation events of large spatial coverage across the Mediterranean region. The study uses the ERA5 dataset, the latest, state of the art, reanalysis dataset from Copernicus/ECMWF. Initially, exploratory analysis is performed to assess the different characteristics at various subdomains within the study area. Furthermore, composite analysis is used to understand the connection of extreme events with large-scale atmospheric patterns. Finally, the Empirical Orthogonal Function (EOF) analysis is implemented to quantify the importance of weather regimes with respect to the frequency of extreme precipitation events. 

Preliminary results indicate that there is a spatial division in the occurrence of identified events. Winter and autumn are the seasons of the highest frequency of extreme precipitation for the east and west Mediterranean respectively. Troughs and cut-off lows in the lower and middle-level troposphere have a strong association with such extreme events, and the effect is modulated by other parameters, such as local orography. Results of this work are in accordance with previous studies in the region and provide information that can be utilized by future research for improving the predictability of such events in the medium- and extended-range forecasts. 

This work is part of the Climate Advanced Forecasting of sub-seasonal Extremes (CAFE) project. The project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 813844.
Anthropogenic land cover change impact on climate extremes during the 21st century
Authors: Quesada Benjamin , Sy Souleymane
Published: March 2020

Beyond global mean temperatures, anthropogenic land cover change (LCC) can have significant impacts at regional and seasonal scales but also on extreme weather events to which human, natural and economical systems are highly vulnerable. However, the effects of LCC on extreme events remain either largely unexplored at global and regional scale and/or without consensus. Here, using several Earth System Models under two different LCC scenarios (the RCP8.5 and RCP2.6 Representative Concentration Pathways) and analyzing 20 extreme weather indices, we find future LCC substantially modulates projected weather extremes particularly at regional level.

On average by the end of the 21st century, under RCP8.5 and RCP2.6 scenarios, future LCC robustly lessens global projections of high rainfall extremes. Accounting for LCC diminishes regional projections of heavy precipitation days or consecutive wet days by more than 50% in southern Africa or northeastern Brazil but intensifies projected dry days in eastern Africa by 30%. LCC do not substantially affect projections of global and regional temperature extremes projections (<5%), but it can impact global rainfall extremes 2.5 times more than global mean rainfall projections.

Under RCP2.6 scenario, global LCC impacts are similar but of lesser magnitude while at regional scale in Amazon or Asia, LCC enhances drought projections. We investigate the underlying biophysical drivers behind those projected changes.

We stress here that multi-coupled modelling frameworks incorporating all aspects of land use-land cover change and more model-data benchmarking are needed for reliable projections of extreme events.

 
Refined assessment of urban residents' exposure to extreme temperatures across the United States
Authors: Yang Jiachuan , Hu Leiqiu
Published: March 2020

Extreme temperatures during heat and cold waves are severe health hazards for humans. Residents’ exposure controls the susceptibility of the urban population to these hazards, yet the spatiotemporal population dynamics has been long overlooked in assessing the risk. In this study, we conducted comparative analysis over 16 major urban habitats under three massive heat waves and one cold wave across the contiguous United States. Incorporating WRF weather simulations with commute-adjusted population profiles, we found that the interaction between population dynamics and urban heat islands makes residents exposed to higher temperatures under extreme weather. After accounting for diurnal population movement, urban residents’ exposure to heat waves is intensified by 2.0 ± 0.8 oC (mean ± standard deviation among cities), and their exposure to cold wave is attenuated by 0.4 ± 0.8 oC. The aggravated exposure to extreme heat is more than half of the heat wave hazard (temperature anomaly 3.7 ± 1.5 oC). The underestimated exposure to extreme heat needs to be taken into serious consideration, especially in nighttime given the evident trend of observed nocturnal warming. Results suggest that the major driver for modified exposure to heat waves is the spatial temperature variability, i.e., residents’ exposure is more likely to be underestimated in a spread-out city. The current release of warnings for hazardous extreme weather is usually at the weather forecast zone level, and our analysis demonstrates that such service can be improved through considering spatiotemporal population dynamics. The essential role of population dynamics should also be emphasized in temperature-related climate adaptation strategies for effective and successful interventions.
Mapping evapotranspiration of a mountain area using a model without calibration
Authors: Gisolo Davide , Bevilacqua Ivan , Previati Maurizio , Canone Davide , Gentile Alessio , N'Sassila Mesmer , Ferraris Stefano
Published: March 2020

The mountains are known as the water towers of the World and they are also climate hot spots. Therefore, water availability studies are extremely useful. To this purpose, Evapotranspiration analyses are important because it plays an essential role in water balance. Its estimation is an important challenge in complex terrains because of few measurement sites and of models’ resolution. Research on both meteorological and hydrological models is still ongoing and there are multiple aims: better catch the physical processes in the atmosphere and in the soil and simulate the reaction of ecosystems to temperature changes, droughts and vegetation shifts towards higher altitudes.

It is therefore important to elaborate new tools for the monitoring of mountain environments and ecosystems from a meteo-hydrological and also climatological point of view.

We elaborated and used a high-resolution model to compute the evapotranspiration field of an Alpine domain located in Italy. The model includes a meteorological module and a hydrological module, which is based on a soil bucket approach. The model allowed us to estimate the local water balance and was validated using three eddy covariance quality-controlled data sets. Furthermore, it was also compared to satellite products. The first results indicate a rather good agreement between simulations of our model, observations, and satellite evapotranspiration estimates.

These are first, encouraging results and the model will be hopefully used in a climate change perspective by means of climate models' outputs, to simulate future scenarios in the Alps.
A Nine-year series of daily oxygen and hydrogen isotopic composition of precipitation at Concordia station, East Antarctica
Authors: Stenni Barbara , Dreossi Giuliano , Casado Mathieu , Scarchilli Claudio , Landais Amaelle , Del Guasta Massimo , Grigioni Paolo , Casasanta Giampietro , Werner Martin , Masiol Mauro , Cauquoin Alexandre , Ciardini Virginia
Published: March 2020

The atmospheric processes determining the isotopic composition of precipitation on the Antarctic plateau are yet to be fully understood, as well as the post-depositional processes altering the snow pristine isotopic signal. Improving the comprehension of these physical mechanisms is of crucial importance for interpreting the isotopic records from ice cores drilled in the low accumulation area of Antarctica, e.g., the upcoming Beyond EPICA drilling at Little Dome C.

Up to now, few records of the isotopic composition of precipitation in Antarctica are available, most of them limited in time or sampling frequency. Here we present a 9-year long δ18O and δD record (2008-2016) of precipitation at Concordia base, East Antarctica. The snow is collected daily on a raised platform (1 m), positioned in the clean area of the station; the precipitation collection is still being carried out each year by the winter over personnel.

A significant positive correlation between isotopes in precipitation and 2-m air temperature is observed at both seasonal and interannual scale; the lowest temperature and isotopic values are usually recorded during winters characterized by a strongly positive Southern Annular Mode index.

To improve the understanding of the mechanisms governing the isotopic composition of precipitation, we compare the isotopic data of Concordia samples with on-site observations, meteorological data from the Dome C AWS of the University of Wisconsin-Madison, as well as with high-resolution simulation results from the isotope-enabled atmospheric general circulation models ECHAM5-wiso and ECHAM6-wiso, nudged with the ERA-Interim and ERA5 reanalyses respectively.
Aggravated water deficit in the Loess Plateau of China as indicated by the soil available water content
Authors: Zhang Xiao , Zhao Wenwu , Pereira Paulo
Published: March 2020

The soil available water content (AWC) has a strong ability to indicate the soil water conditions under different land cover types. Although the AWC has long been calculated, soil water characteristic curve estimation models and the distribution of AWC, as well as the impact factors, have rarely been evaluated in the Loess Plateau of China. In this study, four typical land cover types were selected: introduced shrubland, introduced grassland, natural restored shrubland and natural restored grassland. Four widely used models were compared with the van Genuchten (VG) model, including the Arya and Paris (AP) model, Mohammadi and Vanclooster (MV) model, Tyler and Wheatcraft (TW) model, and linear fitting (LF) model to estimate the wilting point. The distribution of AWC and the relationships with environmental factors were measured and analyzed. The results showed the following: (1) the MV model was the most suitable model to estimate the soil water characteristic curve in the Loess Plateau; (2) the factors impacting the AWC varied under different precipitation gradients, and the area with a mean annual precipitation of 440-510 mm was the most sensitive zone to environmental and vegetation factors; and (3) the soil water deficit was more severe when considering AWC than when considering soil water content (SWC), and the water deficits were different under introduced grassland and introduced shrubland. Consequently, the construction of vegetation restoration should be more cautious and consider the trade-off between soil conservation and water conservation. During restoration, policy makers should focus on the AWC in addition to the SWC to better assess the soil moisture status.
Ocean reporting of the Copernicus Marine Environment Monitoring Service
Authors: von Schuckmann Karina , Le Traon Pierre-Yves
Published: March 2020

The Copernicus Marine Environment Monitoring Service (CMEMS) ocean state-of-the-art ocean reporting for the global ocean and European seas is part of the production center service elements in order to establish a unique reference of value-added expert information at a regular frequency. This is achieved through two principal activities:

Annual release of the peer-reviewed CMEMS Ocean State Report containing a state-of-the-art value-added synthesis of the ocean state, variability and change from the past to present

Ocean Monitoring Indicators and related operational framework on the CMEMS web portal. In particular, CMEMS has developed several indicators based on global or regional ocean reanalyses. For a series of indicators, consistency estimates are available, based on a multiproduct approach inherited from CLIVAR/GODAEIV-TT ORA IP.

This activity is aiming to reach a wide audience from the scientific community, over climate and environmental service and agencies, environmental reporting bodies, decision maker to the general public. Currently, the ocean state report activity is in its 5th cycle, and a huge number of indicators have been made freely available via the CMEMS web portal, including numerical data, scientific and quality context and product documentation. We will give here an overview on the CMEMS ocean reporting activity, highlight main outcomes, and introduce future plans and developments.
Assessment of maximum flow and emplacement temperatures reached by PDCs using charred wood fragments
Authors: Pensa Alessandra , Corrado Sveva , Giordano Guido
Published: March 2020

Temperature evaluation of PDCs has been recently performed using optical analysis of charred wood (Reflectance analysis - Ro%) embedded within the pyroclastic deposits.

The validity of this proxy for the emplacement temperature assessment, has been established in different case studies (Fogo Volcano, Laacher See volcano, Merapi Volcano, Colima Volcano, Doña Juana Volcano, Ercolano-Vesuvius Volcano), resulting comparable with the already well know paleomagnetic analysis (pTRM).

Due to its not retrograde nature, the process of carbonification records over time the maximum temperatures experienced by the wood fragment/tree trunk/furniture. This peculiarity has great importance in terms of timing of charring events, as the charred wood can record the possible temperature fluctuations in case of multiple pulse events. This allows us to reconstruct the thermal and dynamic of PDCs history at different steps.

Reflectance analysis (Ro%) results display samples with homogeneous charring temperature (same Ro% values) from rim to core and others with different charring temperatures throughout the sample. Ro% of the latter usually infer higher temperature on the edge of the fragment/tree trunk than in the inner part. This bimodal reflectance distribution can be attributable to multiple temperature exposure, occurred during diachronous events of flow and deposition. Therefore, within the same fragment/tree trunk we can extrapolate PDCs temperature information related not only to equilibrium (emplacement) condition but, more importantly, to dynamic (flow) regime.

This study constitutes a pioneering attempt for the indirect estimation of the temperature of the PDCs not only for volcanic hazard estimation, but also in the archaeological field. In fact, the numerous remains of charred wooden artefacts found in the archaeological sites of Pompeii, Herculaneum and in the Meurin quarry (Eiffel-Germany), allowed the reconstruction of temperature variation based on the vent distance and the presence of buildings which may have interacted with the depositional processes of pyroclastic flows. This study opens a promising new frontier to evaluate the maximum temperature of the PDCs, based on the degree of carbonization of the organic matter incorporated during volcanic events. Estimating the temperature of the dynamic temperature of the PDC has important implications in terms of volcanic risk assessment.
An investigation on possibilty of creep on the Makran subduction zone based on deformation data
Authors: Ghadimi Moghaddam Homa , Khodaverdian Alireza , Zafarani Hamid
Published: March 2020

Long term crustal flow of the Makran subduction zone is computed with a kinematic finite element model based on iterated weighted least squares fits to data. Data include 91 fault traces, 56 fault offset rates, 76 geodetic velocities, 1962 principal stress azimuths, and velocity boundary conditions. Model provides long-term fault slip rates, velocity, and distributed permanent strain rates between faults in the Makran region from all available kinematic data. Due to low seismicity of western Makran compared to its eastern part we defined two models to evaluate the possibility of creep in the Iranian Makran subduction. One model assumes that geodetic velocities measured adjacent to the Makran subduction zone reflect a temporarily locked subduction zone will be referred to as the “seismic deformation model”. In contrast, another model called the “half creeping deformation model” assumes that the western part of Makran may creep smoothly without any locking. In order to verify the models, the estimates of fault slip rates are compared to slip rates from merely analysing geodetic benchmark velocities or paleoseismological studies or published geological rates which have not been used in the model. Our estimated rates are all in the range of geodetic rates and are even more consistent with geological rates than previous GPS-based estimates. Another verification for the model is comparison of the computed interseismic velocities at GPS benchmarks to GPS measurements. While neither model accurately predicts these interseismic velocities at benchmarks, the half creeping deformation model is more accurate for Chabahar station than the seismic deformation model. These results have important earthquake and tsunami hazard implications. For example, Fault slip rates are the main component of time-dependent seismic hazard studies and can be used to estimate activity rates for more sophisticated earthquake models.
Tracing recent carbon from photosynthesis to stem and soil respiration in an experimental tropical rainforest in response to drought
Authors: Ingrisch Johannes , Meeran Kathiravan , Kübert Angelika , Ladd Nemiah , van Haren Joost , Werner Christiane , Meredith Laura , Bahn Michael
Published: March 2020

Tropical rainforests play a major role in the terrestrial carbon (C) cycle. However, to date little is known about the mechanisms and processes controlling C fluxes in tropical forests. Within the C cycle of a forest, trees allocate a substantial amount of photoassimilates belowground, and fuel respiration by stems, roots and microorganisms. This link between assimilation and respiration represents a significant pathway by which assimilated C is quickly returned to the atmosphere. However, the nature of this coupling, including the speed of above- to below-ground C allocation and the proportion of rapidly metabolized assimilates is yet unknown for mature tropical rainforest systems. Furthermore, the role of tree species and size and the relative roles of canopy versus understory plants are still unresolved.

Drought spells can exert a major control on the C balance of tropical forest ecosystems by altering C uptake, the partitioning of C and the dynamics of C allocation and belowground utilization. As such responses are difficult to measure in tropical rainforest, the consequences of drought for the dynamics of recent C in stem and soil respiration in this biome remain unclear.

To assess and quantify these processes, we made use of the Tropical Rain Forest at the Biosphere 2 research complex in Arizona, US. This infrastructure provides unique opportunities to study drought effects on the C dynamics in a controlled environment. We simulated a drought spell for eight weeks and continuously measured stem and soil CO2 fluxes using isotope laser spectroscopy before and during the drought as well as during the subsequent rewetting period. Our study is part of a large-scale experiment that aims to disentangle C- and water-cycle processes underpinning ecosystem responses to drought from a molecular to an ecosystem-scale level, with particular focus on plant-soil and plant-atmosphere interfaces.

We performed two canopy-scale 13CO2 pulse labeling campaigns under ambient environmental conditions and towards the end of the experimental drought. We traced the allocation dynamics of recently assimilated C to soil respiration and to stem respiration of dominant tree species. First results show that the allocation of assimilates from the canopy to soil-respired CO2 took several days and was affected by tree size and species identity. Under drought, tracer efflux from stems and soils was  slowed down, with strong species-specific differences. Our results will allow novel insights into the combined effects of tree size, species identity and drought on the allocation dynamics and respiratory utilization of photoassimilates in tropical rainforest.
Glaciotectonics and tunnel valleys in the southeastern North Sea imaged by high-resolution multi-channel seismics
Authors: Lohrberg Arne , Krastel Sebastian , Unverricht Daniel , Schwarzer Klaus
Published: March 2020

Glaciotectonic disturbance of sediments and tunnel valleys are often found near the margin of former ice sheets. Hence, these landforms can be used to reconstruct the dynamics of former ice sheet margins. The direction of thrusts usually points perpendicular to the ice front. Considering heterogeneity due to local ice advances, this relation can be used to infer the regional forward direction of large ice lobes. Here, we present a dense grid of high-resolution 2D multi-channel reflection seismic data from the German sector of the southeastern North Sea imaging a buried glaciotectonic complex and tunnel valleys in unprecedented detail.

We have identified individual thrust sheets in an area of approx. 650 km² (combined with recent results of Winsemann et al. (2020)). All thrust sheets are buried and partly eroded at their top. Two major phases of thrusting with two corresponding detachment surfaces have been identified in the subsurface, of which the younger phase led to the deformation of sediments several kilometers further into the foreland. The thickness of individual thrust sheets differs between 180 and 240 m. Some thrust sheets have been cut by the subsequent formation of tunnel valleys with an overall incision direction ranging from east-west to northeast-southwest. The glaciotectonic complex is limited to its southeast by an updipping reflector, which represents the margin of a source depression.

The restauration of cross-sections shows that the thrust sheets transported sediments over more than a kilometer towards the northwest to west, which relates the formation of the thrust sheets and the source depression. The landforms are very similar to a hill-hole pair that led to the foreland thrust sheets, probably as a result of combined bulldozing and gravity spreading in the foreland of the ice margin. Their occurrence and the adjacent tunnel valleys leads us to assume that we identified the marginal position of an Elsterian ice lobe in the southeastern North Sea.

Reference:
Winsemann, J., Koopmann, H., Tanner, D.C., Lutz, R., Lang, J., Brandes, C., Gaedicke, C., 2020. Seismic interpretation and structural restoration of the Heligoland glaciotectonic thrust-fault complex: Implications for multiple deformation during (pre-)Elsterian to Warthian ice advances into the southern North Sea Basin. Quat. Sci. Rev. 227, 1–15. https://doi.org/10.1016/j.quascirev.2019.106068
Himalaya mass-wasting: impacts of the monsoon, extreme tectonic and climatic forcing, and road construction
Authors: Jones Joshua , Boulton Sarah , Bennett Georgina , Whitworth Michael , Stokes Martin
Published: March 2020

In mountainous regions, mass-wasting processes dominate landscape evolution and pose serious risk to life and socioeconomic development. In the Nepal Himalayas, annual rates of mass-wasting are primarily driven by the Asia Summer Monsoon (ASM), the strength of which is highly sensitive to changing global climate.  However, whilst relationships between precipitation intensity and suspended fluvial sediment flux in the Himalaya are well described, a longer-term empirical relationship between ASM strength and total mass-wasting volume has remained elusive. Here, we use a new 30-year landslide inventory for central-eastern Nepal to quantify an empirical relationship between ASM strength and total mass-wasting volume. As well as providing insight into how Himalaya hillslope denudation rates might change under possible future ASM strength scenarios, these data allow a quantification of how background rates of ASM-triggered mass-wasting have been perturbed by extreme climatic and tectonic forcing (e.g. earthquakes, storms) and anthropogenic activity (e.g. road building).

We find a strong exponential relationship (R2 = 0.66 – 0.88) between total ASM precipitation and total ASM-triggered mass-wasting volume, suggesting that relatively small changes in ASM strength can lead to significant increases in mass-wasting.  This relationship also allows the calculation of a climate normalised annual rate of mass-wasting for the study region between 1988 and 2018. This normalised rate reveals several years (1993, 2002, 2015 – 2018) with mass-wasting rates perturbed significantly above the rates expected given the ASM strength. We find that the perturbations in 1993 and 2002 correlate with the occurrence of extreme cloud outburst or flood events, resulting in above-expected mass-wasting equivalent to that caused by 3.5 average ASM seasons. By contrast, the 2015 – 2018 perturbation is more complex. We interpret the perturbation in 2015 as being caused by landscape preconditioning associated with the Mw 7.9 Gorkha earthquake, which caused above-expected ASM-triggered mass-wasting equivalent to that caused by 2.0 average ASM seasons. However, the increased mass wasting across the period 2016 – 2018 is actually found to be the result of a sudden increase in road-construction, with mass-wasting due to road-tipping in this period equivalent to that caused by 2.6 average ASM seasons. These results show that, in the Himalayas, extreme events and human activity can cause significant hillslope denudation above that expected from background ASM-driven mass-wasting.
Analysis of microseismicity in the Hengill Geothermal Area, SW Iceland
Authors: Rossi Camilla , Grigoli Francesco , Cesca Simone , Heimann Sebastian , Gasperini Paolo , Hjörleifsdóttir Vala , Dahm Torsten , Bean Christopher J. , Wiemer Stefan
Published: March 2020

Geothermal systems in the vicinity of the Hengill volcano, SW Iceland, started to be exploited for electrical power and heat production since the late 1960s, and today the two largest operating geothermal power plants are located at the Nesjavellir and the Hellisheidi. This area is a complex tectonic and geothermal site, being located at the triple junction between the Reykjanes Peninsula (RP), the Western Volcanic Zone (WVZ), and the South Iceland Seismic Zone (SISZ). The region is seismically highly active with several thousand earthquakes located yearly. The origin of such earthquakes may be either natural or anthropogenic. The analysis of microseismicity can provide useful information on natural active processes in tectonic, geothermal and volcanic environments as well as on physical mechanisms governing induced events. Here, we investigate the microseismicity occurring in Hengill area to understand physical source mechanisms and the origin of these microseismic events. We use a very dense broadband monitoring network deployed since November 2018 with support of the GEOTHERMICA project COSEISMIQ and apply robust and full-waveform based methods for earthquake location, clustering analysis and source mechanism determination. Our dataset consists of about 637 events with ML ranging between 0.8 and 4.7 from December 2018 to January 2019. We use this rich and large dataset for testing a workflow for automated processing. Earthquake location and clustering analysis show that seismicity is spatially clustered, with shallower events at the center of geothermal site in proximity to geothermal plants, and deeper earthquakes in the southern part of the study area. Most of our moment tensors can suggest the influence of geothermal activity and geothermal energy exploitation operations on the subsurface. This work is supported by the COSEISMIQ project of the EU GEOTHERMICA program .
Controls of alluvial aquifers on continental drainage
Authors: Kollet Stefan , Sharples Wendy , Naz Bibi
Published: March 2020

Continental-scale hydrological research is becoming more important as climate variability and change, and anthropogenic impacts on groundwater, are increasing over large spatial and temporal scales. Groundwater quantities and flows are usually difficult to observe due to sparse or spatially limited monitoring networks.  Thus, large-scale hydrological models are needed to provide continuous predictions of hydrological states and fluxes for water resource management. A large part of groundwater consumed comes from alluvial aquifers, which constitute valley fills of continental catchments. While the role of alluvial aquifers as a significant water store has been subject of many previous studies, the importance of the spatial extent and continuity of alluvial aquifers in the drainage characteristics of freshwater from the continental interior to the oceans is unclear. We present a high resolution (3km) hydrological model of continental Europe using ParFlow, a 3D, parallel groundwater and surface water flow model, which uses detailed hydrofacies information as input. We discuss the effect of spatial continuity and extent of alluvial aquifers on continental lateral groundwater flow and discharge to the oceans, water table depth, streamflow, and surface and subsurface storage. The results suggest that the alluvial valleys act as conduits that manage the drainage and retention of continental freshwater in sync with the atmospheric forcing. This dynamic equilibrium may be significantly disturbed by human interventions such as pumping and irrigation leading to a new equilibrium in terms of continental water quantity and also quality.
The thermal field across the Alpine orogen and its forelands and the relation to seismicity
Authors: Spooner Cameron , Scheck-Wenderoth Magdalena , Cacace Mauro , Götze Hans-Jürgen , Luijendijk Elco
Published: March 2020

The Alpine orogen and its forelands comprise a multitude of crustal blocks from different tectonic providences and different physical properties. This implies that the thermal configuration of the lithosphere would also be expected to vary significantly throughout the region. Temperature is a key controlling factor for rock strength via thermally activated creep and it exerts a first order influence on the depth of the brittle-ductile transition zone, the lower bound to the seismogenic zone and the spatial distribution of seismicity. Here we present new results from INTEGRATE, a project in the DFG priority program Mountain Building in 4 Dimensions, as part of the AlpArray initiative, which aims to gain a better understanding of the structure, temperature and rheology of the crust and the uppermost mantle beneath the Alps and their forelands using multiple 3D modelling techniques. The overall goal is to test different hypotheses on the configuration of the lithosphere and its relation to the distribution of deformation and related seismicity in the Alpine region. We build on previous work of a 3D density differentiated structural model of the region that is consistent with deep seismic data and gravity, to calculate the 3D conductive steady state thermal field of the Alps and their forelands. The model is unique in using different thermal parameters for different tectonic domains and is validated with a dataset of wellbore temperatures from across the region. Comparing recorded seismicity to the calculated thermal field we find a systematic clustering of the deep seismic activity that correlates with different isotherms within individual crustal blocks, reflecting the presence of different dominant lithologies. These inferred lithologies in conjunction with the calculated temperatures and the previous 3D density-structural model of the region, can be used to shed light on the lateral changes in crustal strength within the Alps and their forelands, helping to explain the observed patterns of deformation.  
Observations of Plasma Waves in the Multiple X-line Reconnection at the Magnetopause
Authors: Zhong Zhihong , Graham Daniel B. , Khotyaintsev Yuri V. , Zhou Meng , Tang Rongxin , Deng Xiaohua
Published: March 2020

Plasma waves are one of the important products of the magnetic reconnection process.  Plasma waves can produce particle heating, diffusion, and anomalous effects, which can potentially affect magnetic reconnection. We investigate the evolution and properties of plasma waves during a multiple X-line reconnection event at the magnetopause using measurements from the Magnetospheric Multiscale (MMS) mission. Both whistler waves and large-amplitude electrostatic waves were observed around the reconnecting current sheet. In these regions, the electron velocity distribution functions consist of a combination of a cold beam at low energies with an anisotropic population or a loss-cone at high energies. The electrostatic waves corresponded to regions where the cold beams are accelerated, while the whistlers corresponded to regions with significant anisotropies or loss cones. When the cold beams were accelerated to higher energies, the whistlers disappeared since the anisotropy or loss-cone distributions became less apparent. These results present the detailed evolution of the plasma waves reflecting the electron dynamics during magnetic reconnection.
Laboratory investigation of the effect of sea foam on the scattering of microwave radiation
Authors: Baydakov Georgy , Olga Ermakova , Maxim Vdovin , Daniil Sergeev , Yuliya Troitskaya
Published: March 2020

This paper models the impact of the presence of foam on the short-wave component of surface waves and momentum exchange in the atmospheric boundary layer at high winds. First, physical experiments were carried out in a wind-wave flume in which foam can be artificially produced at the water surface. Tests were conducted under high wind-speed conditions where equivalent 10-m wind speed, U10, ranged 12–38 m/s, with measurements made of the airflow parameters, the frequency-wavenumber spectra of the surface waves, the foam coverage of the water surface, and the distribution of the foam bubbles.

Microwave measurements were performed using a coherent Doppler X-band scatterometer with a wavelength of 3.2 cm and a sequential reception of linearly polarized radiation. It was shown that the presence of foam reduces the NRCS of the agitated water surface. Foam formations are concentrated mainly on the ridges and front slopes of wind waves, which make the main contribution to the scattering of radio waves. This may explain the effect of reducing the total NRCS: foam, which has less reflective properties, masks the main diffusers on the water surface. The second mechanism is associated with the effect of foam on short waves, by analogy with surfactant films.

The effect of foam on the shape of the Doppler spectrum of a microwave signal scattered by the water surface was investigated. In the case of weak wind, the presence of foam on the surface leads to a decrease in the short-wave part of the spectrum of surface waves and, as a result, to a decrease in the scattered signal. In addition, a mirror component appears in the Doppler spectrum corresponding to the fundamental frequency of the wave. In the case of a stronger wind, the grouping of additional scatterers (foam) on the crests of the waves leads to a shift of the Doppler spectra to the high-frequency region.

The work was supported by the RFBR (grants 18-35-20068, 19-05-00366, 19-05-00249) and the RF President’s Grant for Young Scientists (MK-144.2019.5).
Analysis of the Dominant Spatial Patterns of Summer Precipitation and Circulation Characteristics in Northwest China
Authors: liu liwei , lu guoyang , wei dong , li danhua , wang xing , wang fan
Published: March 2020

In recent years, the summer rainfall shows an increasing trend in Northwest China. Based on the NCEP/NCAR reanalysis data, the RESST data from NOAA and the precipitation data from 351 meteorological observation stations in Northwest China from 1981-2018, the dominant modes of summer precipitation anomalies, the corresponded circulation characteristic and the main influence systems were analyzed by diagnostic methods. There were three dominant EOF modes about summer rainfall, the first one showed the same anomaly in whole region, the second showed a inverse pattern between the east and west, and the third showed the opposite anomaly between the south and north. The variance contribution of the first mode accounted for 20% and the first mode was represented as the primary mode in the subsequent analysis. The high impact region of circulation which affected the precipitation in Northwest China was the middle and high latitudes area of Eurasia and the subtropical area: for the first mode’s positive phase, the 500hPa height field showed a "+ - +" distribution in the middle latitude of Eurasia, while on the 200hPa wind field, there was an anticyclone near the Ural and a cyclone near Lake Baikal, it also has an anticyclone on the Chinese mainland, this configuration will facilitates the strengthening of westerly jets. The tropical Pacific and the North Atlantic are the main external forcing signals of the circulation pattern: SST characteristics showed that the negative phase of the North Atlantic SST Tripole in spring, from winter of the previous year to summer of the current year, SST of the equatorial Middle East Pacific developed from warm to cold. The distribution of 500 hPa height field corresponding to the main mode of summer precipitation in Northwest China is similar to that of EU remote correlation type. An index(IHgt) was defined to reflect circulation patterns in mid-latitude and subtropical regions, when the index is positive/negative, most of the precipitation in northwest China is more/less. After 2000, the correlation between the two increased significantly. Given the performance of the IHgt index in describing the summer precipitation, it could be used as a good indicator in the monitoring and prediction of the summer precipitation in Northwest China.
Carbon dioxide and nitrous oxide fluxes from a legume-based grassland during contrasting seasons in eastern Finland
Authors: Li Yuan , Korhonen Panu , Virkajärvi Perttu , Shurpali Narasinha J.
Published: March 2020

Legumes facilitate soil carbon (C) sequestration and mitigation of nitrous oxide (N2O) emissions. They have an important role in improving model predictions of future feedbacks from the high-latitude carbon dioxide (CO2) and N2O fluxes and climate driving the response of northern ecosystems to warming. Legume based grasslands are an important part of the economy as high protein fodder for the cattle and thus, they are crucial for meat and dairy industries in Europe. However, there is a lack of regionally based, ecosystem scale field experimental data on legume based grasslands. Therefore, using the eddy covariance technique, we measured CO2 and N2O fluxes from a grassland site, growing timothy (Phleum pratense L.) and red clover (Trifolium pratense L.), treated with mineral nitrogen (MinN) or with digestate residue (OrgN) in eastern Finland during two growing seasons (May – Sep 2017 and 2018). Results showed that higher mean seasonal temperature (2018) increased net ecosystem CO2 exchange (NEE) and total dry matter (DM) and decreased N2O emissions. Specifically, NEE was 8.3 and 12.1 Mg ha-1 in 2017 and 2018, respectively with no differences between treatments over the two years. The DM yield was 5.9 and 4.9 Mg ha-1 for MinN and OrgN, respectively, in 2017, while it was 6.3 and 6.8 Mg ha-1 in 2018. Cumulative N2O fluxes were 0.01 (100-year global warming potential CO2-equivalent) and -0.6 Mg CO2 ha-1 in 2017 and 2018, respectively. Summing up the seasonal NEE, N2O flux and DM yield, the seasonal C balance was 2.1 and -1.3 Mg ha-1 for MinN and OrgN treatments in 2017, and it was -2.5 and -3.5 Mg ha-1, respectively, in 2018. Our observations from two climatically contrasting seasons suggest that the legume based grasslands in the boreal region have a strong C sequestration potential and the addition of organic fertilizer turns the systems to a larger sink in in the warmer year.
Lidar Observations of Seasonal Variability of Gravity-Waves
Authors: Strelnikova Irina , Baumgarten Gerd , Lübken Franz-Josef
Published: March 2020

In order to understand the generation, propagation and climatology of gravity waves (GWs)observations with high temporal and vertical resolution are required. The observation of gravity waves is important to understand the vertical coupling in the atmosphere.

Recent developments in lidar technology give us new possibilities to study GWs experimentally on a more or less regular basis and resolve spatial sales of 150 meters in the vertical and temporal scales of about 10 minutes. In particular, the capability to operate the lidar during daytime allows for long duration GW observations. The Doppler Rayleigh Iodine Spectrometer (DoRIS) in additionto the established hydrostatic temperature measurement technique yields simultaneous and common volume measurements of winds.

At the ALOMAR observatory in northern Norway (69°N, 16°E) the gravity wave potential energy density (GWPED) in the stratosphere is shown to have a large seasonal variation with a maximum in winter and a minimum in summer.

In this work we use the phase relation between both zonal and meridional wind components and temperature. We study gravity waves sorted for up- and downward propagating waves under summer and winter conditions to investigate different wave propagation and generation scenarios. We discuss the winter/summer difference not only in terms of total GWPED, but in terms of wave characteristics obtained from our extended analysis technique. We demonstrate, for example, that amount of downward propagating waves is larger in winter than in summer. Also, other wave characteristics like phase speed and mean intrinsic period will be discussed.
A method for retrieving the spatial distribution of trace gases using measurements of three ground-based MAX-DOAS instruments
Authors: Revesz Michael , Schreier Stefan F. , Weihs Philipp , Bösch Tim , Lange Kezia , Richter Andreas , Vrekoussis Mihalis , Schmalwieser Alois W.
Published: March 2020

Within the project VINDOBONA (VIenna horizontal aNd vertical Distribution OBservations Of Nitrogen dioxide and Aerosols), a method was developed to retrieve the spatial distribution of trace gases using data from three ground based MAX-DOAS instruments and was applied on the example of NO2. At three different locations in Vienna (Austria) MAX-DOAS instruments were installed performing measurements in the visible and UV spectral range. Currently, each instrument is set up to determine the column densities in different azimuthal directions and low elevation angles within approximately a horizontal plane. The different lines of sight of the three instruments intersect horizontally and can be used to estimate the horizontal spatial distribution of trace gases. With the knowledge of vertical profiles, even the vertical distribution can be estimated using this method. 

The intersections of the different lines of sight define segments along the slant columns for which the mass concentrations can be estimated. Knowledge about the vertical profiles for a chosen trace gas can be used to correct the retrieved trace gas concentration to specific altitudes above ground. Such corrections are also required since the three instruments were set up at different heights above ground, at different altitudes relative to sea level and with different elevation angles of the lowest viewing direction. One open issue for the retrieval process is the terrain in Vienna in combination with the prevailing wind condition that impacts the horizontal and vertical trace gas distribution and make the retrieval challenging. 