bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of relativistic and environmental influences on laser signals used for gravity field recovery with spaceborne optical clocks
Authors: Wassermann Noa , Leipner Andreas , Philipp Dennis , Scheumann Jan , Bremer Stefanie , List Meike
Published: February 2023

One major objective of Geodesy is the observation of the Earth, its gravity field and climate. To study subtle but impactful changes in the gravitational field, novel paradigms and high-precision measurement schemes are emerging.According to Einstein’s Theory of General Relativity, the proper time of a clock is the four-dimensional length of its worldline through curved spacetime. Thus, the comparison of clocks always is a comparison of local spacetime geometries. Thereupon, clock comparison could be used as a new method, termed chronometry, for gravity field recovery (GFR) via high-precision timing and redshift measurements. With the fast development of new, better, and smaller time measurement devices, optical clocks are a promising tool for GFR. Such clocks can be compared using, e.g., a light signal propagating in free space. For the determination of all gravitational degrees of freedom, it is necessary to relocate at least one clock around the planet. This can be done via moving clocks on satellites. To interpret these precise measurements correctly, it is essential to consider all influences on the laser signal used.For this purpose, DLR and ZARM developed a simulation platform called XHPS in the scope of the DFG Collaborative Research Center 1464 TerraQ to model the environmental effects on satellites. It is used to study the influences on the laser signal between a ground station and satellites (or between two satellites). In particular, we want to simulate the signal loss caused by the Earth’s atmosphere, as well as other influences such as the relativistic redshift. It might also be interesting to compare the magnitude of redshift and atmospheric perturbations. This work will present the current state of our research.
Dynamic strain anomalies detection at Stromboli from 2007 eruptive phase using machine learning
Authors: Romano Pierdomenico , Di Lieto Bellina , Sangianantoni Agata , Scarpetta Silvia , Messuti Giovanni , Scarpa Roberto
Published: February 2023

The characterization of volcano state is not a simple task due the complexity of physics processes underway. Understanding their evolution prior to and during eruptions is a critical point for identifying transitions in volcanic state. Recent developments in the field of Machine Learning (ML) have proven to be very useful and efficient for automatic discrimination, decision, prediction, clustering and information extraction in many fields, including volcanology. In Romano et al. (2022) the use of ML algorithms led to classify strain VLP families related with changes in volcano dynamics prior of paroxysmal eruptions: algorithms have been able to discriminate little differences in VLPs shape and to find a correspondence among a higher number of families and volcanic phenomenologies. For paroxysmal events occurring outside any long-lasting eruption, the initial success of our approach, although applied only to the few available examples, could permit us to anticipate the time of alert to several days, instead of few minutes, by detecting medium-term strain anomalies: this could be crucial for risk mitigation for inhabitants and tourists. The neural network method used in previous analysis has been extended to a wider (2007-2022) period to verify that families found in the previous narrower time interval were still present. We tried, then, to associate families with volcanic activity, confirming the conceptual model previously introduced (Mattia et al., 2021 and   Romano et al., 2022), capable of explaining the changes found. Our innovative analysis of dynamic strain, systematically conducted on several years of available data, may be used to provide an early-warning system also on other open conduit active volcanoes.Valuable information is embedded in the data used in the current work, which could be used not only for scientific purposes but also by civil protection for monitoring reasons. Such a variety of possible usage needs the setting of principles and legal arrangements to be implemented in order to ensure that data will be properly and ethically managed and in turn can be used and accessed by the scientific community.
Semi-Automatic Active Subglacial Lake Detection in Antarctica
Authors: Malczyk George , Gourmelen Noel , Michael Carolyn , Krauss Oskar
Published: February 2023

Most of the ice in the Antarctic ice sheet drains from the continent to the ocean through fast-flowing ice streams and glaciers. The high velocity of these features is thought to be maintained by water at the ice sheet's base, which reduces friction. Subglacial water moving has been linked to transient glacier flow acceleration and enhanced melt at the grounding line. Therefore, the presence, location, and movement of water at the ice sheet's base are likely significant controls on the mass balance of Antarctica.The transport of subglacial water from the interior of Antarctica to the grounding line was once thought to be a steady-state process. It is now known that subglacial water collects in hydrological sinks, which store and release water in episodic events. These features can be detected and quantified by satellite altimetry. This behaviour is interpreted as water moving in and out of 'active' subglacial lakes.Detecting active subglacial lakes with satellite altimetry commonly involves searching for localized regions of surface elevation change over short temporal time frames. In practice, this can be incredibly cumbersome due to the large amounts of data that need to be processed and a high degree of guesswork regarding where potential lakes might be located.Here we present a semi-automatic active subglacial lake approach for detecting and classifying drainage and filling events across Antarctica from an entire archive of satellite altimetry. We first use CryoSat-2 altimetry to produce time-dependent rate of elevation change maps for the whole of the Antarctic continent. From these maps, we search for localized regions of elevation change indicative of subglacial lake activity. We then extract time series for these features and perform change point analysis to automatically detect subglacial lake activity and extract important parameters such as discharge volumes and recharge rates. This approach reveals several new lakes previously undetected.For example, five new lakes are found over the Thwaites glacier in addition to the four previously recorded. Here we present the approach and the resulting updated inventory of subglacial lake activity across Antarctica.
Assessment of the relationship of atmospheric blocking and heatwaves over the Mediterranean region
Authors: Koutsoupi Iliana , Cartalis Constantinos , Philippopoulos Kostas , Agathangelidis Ilias
Published: February 2023

The increasing trends of extreme heat and record-high temperatures in Europe are linked to large-scale circulation. The aim of this work is to investigate the role of atmospheric blocking on heatwaves over the Mediterranean region and to assess the drivers of such anomalies. The study is focused on the summer period and on the omega block upper-level weather pattern (i.e., a low-high-low pattern that remains stationary and distorts the progression of weather systems). The identification of the omega block patterns is based on the 500 hPa geopotential anomalies from 1981 to 2020 for the European region, using the state-of-the-art ERA5 reanalysis product at a 0.25° x 0.25° horizontal resolution. A duration threshold was employed (5 days) and 75 omega blocks are identified in total. Their persistence was typically between 5 and 10 days, and in a few cases, the pattern was observed for more than 20 days. An omega block classification was developed based on the blocking intensity using the 500 hPa geopotential gradient, and the events are characterized as weak, moderate, or strong. The majority of the events were classified as omega blocks with moderate intensity and only 3 cases as strong. In addition, the effect of the North Atlantic Oscillation (NAO)was examined, and a positive correlation between the omega events and the NAO negative phase was found and the majority of these events (approximately 70%) were located in the western European region. A significant finding based on the omega block characteristics is that during the last decade, an increase is found in their duration and intensity. The identification of the heatwave events over the Mediterranean region was based on the Excess Heat Factor (EHF) which is used to further categorize heatwaves by their severity. The effect of omega blocks on the EHF distribution is illustrated over the examined sector and specific case studies are also discussed. The results of the study illustrate the impact of atmospheric blocking on the predictability of extreme heat.
The Hunga Tonga-Hunga Ha’apai stratospheric eruption of 15th January 2022: a global warming volcanic plume?
Authors: Sellitto Pasquale , Legras Bernard , Duchamp Clair , Belhadji Redha , Carboni Elisa , Siddans Richard , Kloss Corinna
Published: February 2023

The underwater Hunga Tonga-Hunga Ha’apai volcano erupted in the early hours of 15th January 2022 and injected volcanic gases and aerosols to over 50 km altitude. In this talk, we synthesise satellite, ground-based, in situ and radiosonde observations of the eruption to investigate the emissions, the horizontal and vertical dispersion, and the strength of the stratospheric aerosol and water vapour perturbations in the initial six months after the eruption. The aerosol plume was initially formed of two clouds at 30 and 28  km, mostly composed of submicron-sized sulfate particles, without ash, which is washed out within the first day following the eruption. The large amount of injected water vapour led to a fast conversion of SO2 to sulphate aerosols. We find that the Hunga Tonga-Hunga Ha’apai eruption produced the largest global perturbation of stratospheric aerosols since the Pinatubo eruption in 1991 and the largest perturbation of stratospheric water vapour observed in the satellite era. Then, using offline radiative transfer calculations driven by aerosol and water vapour observations, we quantify the net radiative impact across the two species. Immediately after the eruption, water vapour radiative cooling dominated the local stratospheric heating/cooling rates, producing a spectacular radiatively-driven plume descent of several kilometres. At the top-of-the-atmosphere and surface, volcanic aerosol cooling dominated the radiative forcing during this first dispersion phase. However, after two weeks, due to dilution, water vapour heating started to dominate the top-of-the-atmosphere radiative forcing, leading to a net warming of the climate system. On a longer timescale, sulphate particles, undergoing hygroscopic growth and coagulation, sediment and gradually separate from the moisture anomaly entrained in the ascending branch Brewer–Dobson circulation. This is the first time a warming effect on the climate system has been linked to volcanic eruptions, which usually produce a transient cooling.
Aerosol Optical Depth Retrieval by Machine Learning Methods from Geostationary Environmental Monitoring Spectrometer
Authors: Beatty Audrieauna , Choi Hyunyoung , Kim Miae , Im Jungho
Published: February 2023

Globally, aerosols, emissions, and greenhouse gases have an impact on the environment. With the help of satellite data and field instruments we can understand and continue to study the atmosphere. Specifically, in terms of understanding air quality and aerosol optical depth (AOD), the radiative transfer model is traditionally used but can have unpredictability and is time consuming. With use of machine learning, one can improve accuracy and can be more time efficient. In this paper, we present machine learning methods to estimate AOD from the Geostationary Environmental Monitoring Spectrometer (GEMS). GEMS has a hyperspectral scanning spectrometer that monitors air pollutants over Asia by different observation nodes. Random Forest (RF), and Light Gradient Boosting Machine (LGBM) with auxiliary. meteorological, and ground-based observation data were used to estimate hourly AOD. Inclusion of meteorological data can support the model in performance and reflecting dynamic conditions in the atmosphere. The two machine learning models were evaluated by random, spatial, and temporal 10-fold cross validation to test the transferability and robustness. The results showed that random forest model performed lower than the light-gradient boosting model. LGBM produced R2 of 0.286 – 0.680 and RSME of 0.025-0.057. Random forest produced R2 of 0.283 – 0.643 and RSME of 0.028-0.057. Overall, the model was able to show that AOD can be retrieved from machine learning methods from the Geostationary Environmental Monitoring Spectrometer (GEMS).
An investigation of fog and low cloud life cycles and their interaction with biomass burning aerosols in the Namib
Authors: Mass Alexandre , Andersen Hendrik , Cermak Jan
Published: February 2023

This contribution presents early results on the effects of biomass burning aerosols (BBA) on fog and low clouds (FLC) in the Namib, using data from multiple satellite platforms and station measurements.Fog, which is the most relevant non-rainfall water source for plants and animals in the coastal parts of the Namib Desert, may become increasingly important for local ecosystems as regional climate simulations predict a warmer and drier climate for southern Africa in the future. Previous studies showed the role of BBA on cloud development over the ocean off the Namibian coast. The same processes are likely to influence Namib-region FLC formation and persistence as well. However, the potential effects of aerosols on FLC in the Namib Desert, a direct extension of the South-East Atlantic cloud system, have yet to be investigated.A clear seasonal cycle of FLC dissipation is found in a satellite-based product of FLC formation and dissipation times, with longer FLC persistence during the BBA season. Using a BBA reanalysis product in combination with the satellite data, it is found that during this season, FLC dissipation times are positively correlated to BBA loading (higher aerosol loading coinciding with later FLC dissipation). It is assumed that semi-direct and indirect BBA effects contribute to this pattern, with further analyses aimed at isolating aerosol effects from possible confounders.These findings are a first step in a better understanding of the Namib-region FLC system and will help in the development of a statistical model to quantify the sensitivities of FLC lifetime in the region in the next step of the project.
Teaching by doing or a field course in our backyard: the first geosensing of the environment course in this geography institute
Authors: Ceperley Natalie , Fässler Linus , Leiser Peter , Schaefli Bettina
Published: February 2023

The ubiquitous "field trips in geography" type courses often exclude students on the basis of mobility and flexibility, have a high travel footprint, and rely primarily on passive knowledge.  In the summer of 2022, we taught a master level geography course, Geosensing of the Environment for the first time at the Geography Institute at the University of Bern. The course was team taught by the institute field technician, the assistant and master student, and a researcher in hydrology. This course is unlike anything currently or previously taught at our institute. It put the students in charge of their own scientific trajectories, taking them on a full scientific cycle "journey" from idea and question, to device development and measurement, to analysis and communication. The main goal of the course was for all students to use raspberry pi micro controllers or similar devices and a variety of sensors however they wish to build a scientific measuring device, while maintaining this course's relevance and connection to all physical geography subjects.The pedagogical framework of the course was innovative in a number of ways, namely bringing together a self-learning module teaching the basics of programming microelectronic boards, a hands-on workshop where they got to build their own sensor device based on their own scientific questions, and a follow-up phase where they got to propose a bigger project using their progress in the workshop as a pilot. Students particularly appreciated the open-ended nature of the course that could be adapted to their interests. Although the students' backgrounds were not technical, by the end of the course, we had one group measuring CO2 over a freeway, one group analyzing temperature variation caused by balcony vegetation, and one group measuring water temperature profiles around Bern. In the end, one device was based on raspberry-pi pico and a second based on the sparkfun thing plus RP2040. In the future, we hope to put more emphasis on energy management and communication of sensor networks.  Improvements to this course must balance the goal to empower each student to "start from scratch" or to provide ready-to-go kits, leaving students to mainly choose which sensors they use.  Our main lessons learned concern teaching technical subjects in non-technical disciplines, focusing on instrumentation to transcend disciplines, transforming field courses to more accessible and lower-impact formats, and empowering students to build sensing devices starting with a blank sheet of paper (and a raspberry pi).
Towards a high-resolution speleothem fluid inclusion water isotope record for the Holocene from Milandre Cave, Switzerland
Authors: Affolter Stéphane , Hofmeister Elisa , Kipfer Timon , Cheng Hai , Fleitmann Dominik
Published: February 2023

Speleothem fluid inclusions contain relics of past precipitation water, which constitute a powerful tool for studying the past hydrological cycle. Analyses of hydrogen and oxygen isotopes of the water stored in fluid inclusions allow the reconstruction of paleoclimate information such as temperature. A previous study has shown the potential of speleothems from Milandre Cave to address temperature-related issues such as the so-called “Holocene temperature conundrum”. It additionally shows the main Holocene climate feature such as the cooling occurring at the Younger Dryas or the 8.2 ka event. The mean temporal resolution achieved for the samples is relatively high, with sampling intervals ranging between 10 years for the most recent times and 50-70 years for the early Holocene. Using our new analytical line at the Department of Environmental Sciences at the University of Basel, we aim to increase the temporal resolution of the record by a factor two to four in order to provide highly-resolved water isotope and inferred temperature records for the entire Holocene. The revised Milandre Cave Fluid Inclusion temperature (MC-FIT) allows us to gain more detailed information on shorter scale events such as the 8.2 ka cooling and other prominent Holocene climatic events. The new MC-FIT record, supported by additional speleothems from neighboring caves, allows a better understanding of the central European annual temperature variability during the Holocene.
Monitoring phenology as part of university education
Authors: Bartošová Lenka , Dížková Petra , Fischer Milan , Sedláček Filip , Trnka Miroslav , Žalud Zdeněk
Published: February 2023

Systematic and regular monitoring phenology over a larger area is often based on cooperation with volunteers or workers who monitor the onset of phenophases and are thus part of phenological societies or national phenological networks. As part of our work and teaching at Mendel University in Brno (Bioclimatology courses) we have been cooperating with students since 2015 till now and one of the parts of their required semester work is the observation of the phenological development of selected species. At the beginning of the semester, students are thoroughly familiarized with the observation methodology and choose the plant species they will observe at regular visits during the semester (field crops, trees, shrubs or vineyards). Each student observes at least two trees or shrubs and one field crop and needs to visit the localities every three days (or more frequently if possible) and record the phenological development with cameras (using personal smartphones). During the semester or at the end of the semester, students upload pictures and terms of phenophases through the website www.fenofaze.cz. On this website, students' results and observations are displayed in real-time and are open to the general public. Student observations are strictly controlled and unusable data are taken out. We cooperate with c. 200 students each semester (i. e. 600 observations) and the first outputs showed that 50% of all observations are usable. Terms of phenophases are observed at the cadastre level and are aggregated to the district level to evaluate the long-term changes. In most cases, students approach vegetation phenological monitoring responsibly and with enthusiasm, and we consider it a reliable way of recording phenological changes and dates.Acknowledgment: This research was funded by the Ministry of Education, Youth and Sports of the Czech Republic the project SustES—Adaptation strategies for the sustainability of ecosystem services and food security in adverse natural conditions (CZ.02.1.01/0.0/0.0/16_019/0000797).  
Assessing the climate impacts of land cover change under present and future environmental conditions
Authors: Cescatti Alessandro
Published: February 2023

Changes in land cover deeply affect the surface properties and therefore the direction and magnitude of the energy, water and carbon fluxes between the atmosphere and the land, ultimately impacting the local and global climate. The processes underlying biophysical and biogeochemical vegetation properties are themselves strongly influenced by the background climate and therefore affected by climate change in a complex and circular manner. For these reasons, deepening our understanding and prediction capacity of the ongoing changes in the land-climate nexus is of paramount importance to developing land-based climate mitigation strategies and policies that are robust and achievable.The high complexity of the land-based climate interaction is driven by its bi-directional nature that involves multiple positive and negative feedbacks, and by the co-occurrence of processes with opposite climate impacts (i.e. climate cooling and warming) both for biophysical and biogeochemical processes (e.g. radiative vs. non-radiative effects, respiration versus photosynthesis). These specific features of the land system lead to an extremely high sensitivity of the net climate impact of land cover change to management practices and environmental drivers.Because of the inherent complexities of the land-climate systems, simulations performed with land-atmosphere coupled models proved to be rather uncertain and strongly affected by knowledge gaps, weak assumptions and oversimplistic parameterization. On the other hand, disentangling the signals of the different processes from Earth observations is particularly complex and leads to uncertain attribution of causality. Even more challenging is using experimental signals derived under present climate conditions to project the future direction and magnitude of biophysical and biogeochemical impacts of land cover change on climate. To this scope, among the key limitations of the widely used “space for time” substitution we can list the role played by unaccounted factors (e.g CO2 fertilization), the speed and span of ecosystem adaptation, the assumption of steady state and the temporal and spatial dependence of the processes. Given the importance of this research topic in the current fight to mitigate climate warming, new approaches and methodological advances are required to benefit from the increasing computational capacity and by the expanding observation of the Earth system. To address the issue, in this presentation I will review the most recent progress of data-driven and hybrid analyses, and report on a recent attempt to investigate the impact of land transformation on the climate trajectory under future climatic conditions. Additional discussion points will deal with the emerging research needs related to non-linearity in the system and tipping points (e.g. related to plant mortality rates), and the possible way forward on the ingestion of knowledge derived from Earth observation in process-oriented modelling frameworks.
Groundwater transpiration of a salt steppic oak forest in the extreme dryness of 2022
Authors: Kele Zsombor , Kiss Csaba László , Gribovszki Zoltán , Pinke Zsolt , Ács Tamás , Kozma Zsolt , Kalicz Péter
Published: February 2023

Groundwater use of a lowland forest is especially important from the point of view forest ecosystem survival as drought periods become more severe, and the groundwater is going deeper in the Great Hungarian Plain. Diurnal methods using high frequency water table data are more and more popular nowadays to quantify groundwater consumption of groundwater dependent ecosystems. Riparian forest ecosystems were typical natural vegetation form alongside Great Hungarian Plain Rivers. These ecosystems were supplied by the river inundation of the river. Nowadays these forests are very rare and generally groundwater dependent. A representative of the rest of this ecosystem is a salt steppic oak forest in Ohat, on the edge of Hortobágy. Maps from the 18. century proof, that this area was continuously covered by forests before the great levee-building and water-regulation of Hungary, which drained the significant part of the Hungarian Great Plain.The hydrological year of 2021-2022 is particularly interesting in terms of water uptake analysis because of its extreme dryness and heat.Two groundwater wells settled in this research area and were instrumented by pressure transducers. The groundwater time series shows strong diurnal water table fluctuations, which we used for the calculation of oak forest groundwater transpiration. We found significant relationshipForest groundwater transpiration was significant at the first part of the growing season despite the relatively deep water table. When the water table sank to a depth of 4.7-4.8 m transpiration from the groundwater reduced very significantly. The relationship between water table depth and groundwater transpiration is significantly different when comparing the years 2021 and 2022. Results showed that drought caused lowering of the water table poses a threat to the groundwater dependent forest ecosystem.This article was made in frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.
The Future of Thwaites Glacier, West Antarctica.
Authors: Gudmundsson G. Hilmar , De Rydt Jan , Rosier Sebastian , Barnes Jowan , Goldberg Daniel , Morlighem Mathieu
Published: February 2023

We use numerical modelling to address several questions related to the future evolution of Thwaites Glacier over the next 50 years. The importance of Thwaites Ice Shelf for upstream grounded flow is investigated by quantifying the buttressing stresses along the grounding line. Removing the ice shelf changes the stress regime along the grounding line by less than 20%. This change is small compared to many, if not most, grounding lines of the Antarctic Ice Sheet, and much smaller than corresponding changes for the neighboring Pine Island and Pope, Smith and Kohler glaciers.  Transient ice-flow modelling experiments show that mass loss from Thwaites Glacier over the next 50 years is insignificantly affected by removal of the ice shelf. We then explore the consequences of the proposed marine ice-cliff instability for Thwaites Glacier. For recently proposed calving laws, where the calving rate increases sharply with cliff height, we do not observe an onset of an unstable calving front retreat. Further numerical modelling experiments for future climatic forcing scenarios will be presented, including uncertainty quantification. Interactions between the ice and the ocean are studied using a coupled ice+ocean modelling framework. As shown before in several studies, we find when simulating its future evolution, that Thwaites Glacier can enter unstable periods of self-enhancing retreat. This appears to be a very robust result, and this behavior is found in all model runs, including coupled ice+ocean simulations.
Drivers of speleothem carbon isotope and radiocarbon variability explored using Earth System Model output as input of a dripwater and speleothem chemistry model
Authors: Seubert Pauline , Frank Norbert , Hubig Alexander , Kleinen Thomas , Warken Sophie
Published: February 2023

Interpreting carbon isotopes in speleothems is challenging due to the multiple interacting in-soil and in-cave chemical processes. The degree of free soil CO2, the relative abundance of aged soil organic matter (SOM) and bedrock dead carbon modifies the carbon isotopic composition in speleothems in addition to fractionation during speleothem formation or prior calcite precipitation. Knowledge of the relevant drivers of DCF and stable C isotope variability may help deciphering the climate impact imprinted on speleothem carbon isotopes. Here, we combine Earth System Model output (Max Planck Institute Earth System Model version 1.2, Kleinen et al. 2020), a simplistic soil model, IntCal20, and the speleothem chemistry and isotope equilibrium model CaveCalc (Owen et al., 2018) to produce 25'000 yearlong DCF and d13C time series for numerous speleothems and several cave environments.The modelling results are tuned to reasonable agreement with the respective DCF and d13C mean measurement values at each cave location for intermediate openness values of 5-120 L/kg. However, all model tuning attempts fail to reproduce fast (centennial) isotope and DCF variability. To overcome this limitation, we explore possibilities to include climate driven changes in vegetation, aged SOM, and how water availability drives the openness of the dissolution system. Extending the modelling framework to include vegetation changes produces d13C time series with more small-scale variability. Interestingly, accounting for aged SOM not only results in higher modelled DCF values, but also adds small-scale variability, assuming 20% higher fractions of aged SOM with mean soil ages for each cave location from Shi et al. (2020). Thus, our modelling efforts permit exploring the role of climate and Karst chemical processes to investigate DCF and d13C variability in speleothems over millennial time scales.References:Kleinen, T., Mikolajewicz, U., and Brovkin, V.: Terrestrial methane emissions from the Last Glacial Maximum to the preindustrial period, Clim. Past, 16, 575–595, doi:10.5194/cp-16-575-2020, 2020.Owen, R., Day, C. C., and Henderson, G. M.: CaveCalc: A new model for speleothem chemistry & isotopes, Computers & Geosciences, 119, 115–122, doi:10.1016/j.cageo.2018.06.011, 2018.Shi, Z., Allison, S.D., He, Y. et al.: The age distribution of global soil carbon inferred from radiocarbon measurements, Nature Geoscience, 13, 555–559, doi:10.1038/s41561-020-0596-z, 2020.
Wave groups signature in small scale wave height variability from cfosat
Authors: De Carlo Marine , Ardhuin Fabrice , Ollivier Annabelle
Published: February 2023

Recent altimeter retracking (e.g. Tourain et al. 2021) and filtering methods (Quilfen et al. 2019) have considerably reduced the noise level in estimates of the significant wave height (Hs), allowing to study smaller scale processes. Previous studies on the along-track variations of wave height have shown that wave-current interactions may explain most of the variability at scales 20 to 100 km (Ardhuin et al. 2017, Quilfen and Chapron 2019). Here we take advantage of the very low noise level of SWIM nadir beam to explore scales under 10 km, looking at the accuracy of Hs measurements in storms.From theory, we expect that part of the short-scale variability of the estimated Hs is related to wave groups which lead to random variations in wave height at scales of a few kilometers, depending on the sea state. Theory on signal envelopes links the spatial distribution of wave heights to the convolution of the wave spectrum (Rice 1944) thus allowing to estimate the variability linked to wave groups.Here, we use the fact that ocean waves spectra are routinely measured by CFOSAT’s SWIM instrument to evaluate the theoretical contribution of wave groups to the wave height variability within the 80 km² SWIM boxes, using the CFOSAT L2 and L2S products. In this study, we show that, in average, around half the Hs variance at the scale of SWIM boxes can be associated to wave groups. 
Denitrification rates measured in streams and inundated meadows
Authors: Hasselholt Anne , Henriksen Emil Skole , Kronvang Brian , Thodsen Hans , Carstensen Mette V. , Audet Joachim
Published: February 2023

Denitrification rates measured in streams and inundated meadows Anne Hasselholt*, Emil S. Henriksen*, Brian Kronvang, Hans Thodsen, Mette V. Carstensen, Joachim AudetDepartment of Ecoscience, Aarhus University, Aarhus C, Denmark.*Shared first authorship Nitrogen (N) pollution in aquatic environments is a major concern worldwide due its negative effect on water quality and biodiversity. Part of the N applied as fertilizer and manure on agricultural fields is leached to streams and further exported to the sea. To mitigate N losses from agriculture, several mitigation strategies have been implemented in Denmark including field-level measures, constructed wetlands, and restoration of wetlands.Most of the previous research have therefore focused on investigating the retention and turnover potential of these measures. However, streams and temporarily inundated riparian area also play an important role in retaining and removing N from surface waters but the overall effect at a larger scale such as Denmark (43,100 km2) is yet poorly investigated.To estimate the significance of N turnover in streams and temporarily flooded riparian areas, we are conducting an in situ investigation of denitrification rates spanning four seasons during 2022-2023. The denitrification rates are measured using the N isotope pairing technique in six replicate measuring chambers in 15 streams and ditches. The study will also include in situ measurements of temporarily inundated riparian areas three times a year at three locations along typical Danish streams.The results of the present study will contribute to a new update of an existing Danish N model consisting of three sub-models (leaching model, groundwater hydrological model and several surface water sub-models; Højbjerg et al., 2020). Each sub model deals with either calculation of N-leaching from arable fields, hydrological N-transport, and N-turnover in the groundwater zone and lastly N-turnover in surface waters such as streams and temporarily inundated meadows. The model complex has been used to develop national N-retention maps for groundwater and surface waters at a scale of app. 15 km2. The new updated N-model is intended to deliver new N-retention maps on a finer scale. ReferencesHøjberg, A.L., Thodsen, H., Børgesen, C.D., Tornbjerg, H., Nordstrøm, B.O., Troldborg, L., Hoffmann, C.C., Kjeldgaard, A., Holm, H., Audet, j., Ellermann, T., Christensen, J.H., Bach, E.O. & Pedersen, B.F. 2021. National kvælstofmodel – version 2020, Metode rapport. De Nationale Geologiske Undersøgelser for Danmark og Grønland. GEUS Specialrapport. 
New Aerosol-sensitive Heterogeneous Ice Nucleation Parameterization in the EC-Earth3 Earth System Model: evaluation and climate response
Authors: Costa-Surós Montserrat , Gonçalves Maria , Chatziparaschos Marios , Georgakaki Paraskevi , Ilić Luka , Montane Gilbert , Myriokefalitakis Stelios , van Noije Twan , Le Sager Pilippe , Kanakidou Maria , Nenes Athanasios , Pérez García-Pando Carlos
Published: February 2023

Clouds are large contributors to uncertainty in climate projections, with aerosol-cloud interactions playing a key role. To better reproduce heterogeneous ice clouds and, ultimately, the Earth’s changing energy budget in EC-Earth3 (one of the CMIP6 Earth System Models), its heterogeneous ice nucleation scheme has been updated. Specifically, the temperature-based parameterization has been substituted by a combination of aerosol-and-temperature-sensitive ice nucleating parameterizations. In particular, the model now considers a dust-and-soot-sensitive deposition nucleation scheme for cirrus clouds and aerosol-sensitive immersion freezing schemes for mixed-phase clouds. The latter is sensitive to the mineralogical composition of dust, specifically to the content of K-feldspar and quartz, and to marine organic aerosols, which are explicitly traced in EC-Earth3. Moreover, a secondary ice production parameterization based on a random forest regressor enhances the ice formed by the primary processes.We evaluate the model against an extended observational dataset of INP concentrations and analyze the effect of modelled aerosols upon heterogeneous ice nucleation in mixed-phase clouds and cirrus clouds produced with the new parameterizations. We also investigate the sensitivity of the simulated liquid and ice water content and the atmospheric radiative fluxes to the two different soil mineralogy atlases. Additionally, we use this updated model version to study in more detail a severe dust intrusion event that produced dust-infused clouds that affected Europe in March 2022.The results with the new ice nucleation parameterizations show a clear association of the simulated ice crystal number concentrations with the aerosol sources and transported regions. We also show that replacing the temperature-dependent ice nucleation parameterization with an aerosol-sensitive parameterization in EC-Earth3 significantly impacts surface temperature at high latitudes.
Coupled surface and subsurface flows for earthen embankments using finite-volume methods
Authors: Delpierre Nathan , Rattez Hadrien , Soares-Frazao Sandra
Published: February 2023

The majority of breaching of earthen embankments is triggered by overtopping flows or waves. These phenomena are usually simulated using the shallow-water equations complemented by the Exner equation to reproduce the progressive erosion of the embankment and the growth of the breached area. Such an approach neglects the degree of water saturation in the embankment as well as the flow through the embankment that can alter the stability of this structure by reducing the soil’s mechanical strength. This is enhanced in case of severe droughts, as observed during the summer 2022, when desiccation cracks were observed in several embankments, leading to preferential paths for the water to infiltrate the soil during subsequent rainfalls.In this paper, we present a combined approach in which the degree of saturation and the flow through the embankment are solved using the Richards equation that is coupled to the system of shallow-water equations for the flow over the embankment. The groundwater flow is simulated by solving the 2D Richards’s equation on an unstructured triangular mesh with an implicit finite volume scheme, based on a direct gradient evaluation. The shallow-water equations are solved in one dimension on a structured mesh using an explicit scheme with Roe’s formulation for the fluxes.Several tests were performed to demonstrate the capacity of the proposed Richards’s solver to reproduce transient groundwater flows and compared to results from the literature obtained with different numerical approaches. In the same way, the shallow-water’s equation solver was validated by comparison with previous experimental results from the literature.Then, by coupling both models using a source term, a mass-conservative coupled model was obtained. It became possible to simulate the evolution of the pore water content inside a dike subjected to overtopping for different initial conditions. Further work will focus on the interaction of dike’s related flows with erosion and mechanical failure processes, and on the validation of the model by comparisons with experimental data that will be obtained with medium-scale tests.
Long-term trend of ozone pollution in China during 2014-2020: distinct seasonal and spatial characteristics and ozone sensitivity
Authors: Wang Wenjie , Su Hang , Cheng Yafang , Parrish David D. , Wang Siwen , Bao Fengxia , Ni Ruijing , Li Xin
Published: February 2023

In the past decade, ozone (O3) pollution has become a severe environmental problem in major cities in China. Here, based on available observational records, we investigated the long-term trend of ozone pollution in China during 2014–2020. Ozone concentrations were slightly higher in urban areas than in non-urban areas. During these seven years, the highest ozone concentrations primarily occurred in summer in northern China, and in autumn or spring in southern China. Although ozone precursors, including nitrogen oxides (NOX) and carbon monoxide (CO), continuously decreased, ozone concentrations generally increased throughout the seven years with a slower increasing rate after 2017. The long-term trend of ozone concentrations differed across seasons; especially from 2019 to 2020 when ozone concentrations decreased in summer and increased in winter. To analyze the causes of this observed trend, a photochemical box model was used to investigate the change in ozone sensitivity regime in two representative cities – Beijing and Shanghai. Our model simulations suggest that the summertime ozone sensitivity regime in urban areas of China has changed from a VOC-limited regime to a transition regime during 2014–2020; by 2020, the urban photochemistry is in a transition regime in summer but in a VOC-limited regime in winter. This study helps to understand the distinct trends of ozone in China and provides insights into efficient future ozone control strategies in different regions and seasons.
Prospects of Space Geodesy to Monitor Atmospheric Moisture and Atmospheric Net-Water Fluxes
Authors: Balidakis Kyriakos , Dobslaw Henryk , Zus Florian , Eicker Annette , Dill Robert , Wickert Jens
Published: February 2023

Accurate representation of the time-variable atmospheric state is achieved by assimilating numerous and disparse observations into numerical weather models (NWM). The four-dimensional atmospheric density distribution, a derivative of essential meteorological variables, affect among else how electromagnetic signals propagate through Earth’s atmosphere and how satellites orbit through Earth’s gravity field. Atmospheric refraction to which microwave signals are subjected as they traverse the electrically neutral atmosphere is quantified e.g., during the GNSS data analysis, and holds valuable information about the water vapor distribution in the vicinity of the ground stations. Satellite gravimetry as realized by the GRACE and GRACE-FO missions is sensitive to mass redistribution within Earth’s fluid envelope, including but not limited to the atmosphere and the terrestrail water storage, and also to high-frequency variations stemming from the time-integrated effect of precipitation and evapotranspiration. In this contribution we employ two state-of-the-art meso-beta scale NWM (ECMWF’s latest reanalysis ERA5 and DWD’s operational model ICON-global) as well as ERA5‘s ensemble members to demonstrate that tropospheric mosture distribution and net atmospheric freshwater fluxes are quite uncertain in modern NWM in comparison to other quantities such as hydrostatic atmospheric mass and that certain space geodetic observing systems such as GNSS and GRACE-FO are appropriate tools to monitor them, thus enhancing the accuracy of weather prediction.
Sea ice, wind waves and coastal erosion in Hornsund, Svalbard
Authors: Swirad Zuzanna , Moskalik Mateusz , Herman Agnieszka , Johansson Malin , Rees Gareth
Published: February 2023

Increasing water levels at the shore can cause coastal erosion, wave overtopping and flooding that threaten communities and infrastructure. More frequent, longer and more severe storm events observed in the North Atlantic sector of the Arctic bring more energetic waves to beaches of western Svalbard. Decreasing extent and duration of the sea ice cover increases potential fetch which makes the waves higher and longer. At the shore, the number of ice-free days per year has increased and coasts that were protected from waves by ice are becoming exposed perennially or over longer time. Modelling suggests that in future the sea ice will continue to decrease while the storminess will further increase. Better understanding the role of sea ice conditions and nearshore wave transformations on wave energy at the Arctic shores is needed to predict coastal hazards under changing climate.In this study we focus on wave energy delivery to the shores of Hornsund, a ~300 km2 fjord of south-western Spitsbergen, Svalbard, and particularly to Isbjornhamna bay in northern Hornsund, where the Polish Polar Station infrastructure is located. We monitor continuously nearshore wind wave conditions and the state of the shore ice, and seasonally the wave run-up and beach morphology. We use three nested SWAN (Simulating WAves Nearshore) models that take low-resolution global wind and wave models and nearshore bathymetry to reconstruct wind wave conditions in the nearshore (~15 m depth) Isbjornhamna. Finally, we use Sentinel-1 SAR data to reconstruct sea ice conditions in Hornsund area which need be incorporated into the wave model. Here we show how our monitoring and modelling scheme facilitates the comprehensive understanding of the nearshore and coastal processes in Isbjornhamna.
Seasonal velocity variations in Greece associated with aquifers
Authors: Delouche Estelle , Stehly Laurent
Published: February 2023

Velocity variations related to water movements in aquifers are relatively unknown, thus, we propose to study the temporal changes of velocity variations of several aquifers in Greece. To this end, the stretching method is applied to the early coda of the autocorrelation functions of 90 permanent stations. These results, complemented by GPS and precipitation studies, indicate that the record of seasonal variations on seismic velocities may originate from two mechanisms: 1) a natural mechanism associated with the filling of the aquifer by precipitation and 2) an anthropogenic mechanism related to groundwater pumping.Between 1-3s of period, velocity variations can either vary as a function of water supply to the aquifer: increased water leads to a decrease in wave velocity; or record contraction/relaxation of the rocks beneath the aquifer that vary as a function of its recharge. Thus, the investigation conducted in this study allows us to explain all the seasonal variations observed on the dv/vs in Greece between 1-3s of period.  