bluuebunny/crossref_metadata_2025 huggingface dataset:
Seismic Tomography Using Variational Inference Methods
Authors: Zhang Xin , Curtis Andrew
Published: March 2020

In a variety of geoscientiﬁc applications we require maps of subsurface properties together with the corresponding maps of uncertainties to assess their reliability. Seismic tomography is a method that is widely used to generate those maps. Since tomography is significantly nonlinear, Monte Carlo sampling methods are often used for this purpose, but they are generally computationally intractable for large data sets and high-dimensionality parameter spaces. To extend uncertainty analysis to larger systems, we introduce variational inference methods to conduct seismic tomography. In contrast to Monte Carlo sampling, variational methods solve the Bayesian inference problem as an optimization problem yet still provide fully nonlinear, probabilistic results. This is achieved by minimizing the Kullback-Leibler (KL) divergence between approximate and target probability distributions within a predefined family of probability distributions.

We introduce two variational inference methods: automatic differential variational inference (ADVI) and Stein variational gradient descent (SVGD). In ADVI a Gaussian probability distribution is assumed and optimized to approximate the posterior probability distribution. In SVGD a smooth transform is iteratively applied to an initial probability distribution to obtain an approximation to the posterior probability distribution. At each iteration the transform is determined by seeking the steepest descent direction that minimizes the KL-divergence.

We apply the two variational inference methods to 2D travel time tomography using both synthetic and real data, and compare the results to those obtained from two different Monte Carlo sampling methods: Metropolis-Hastings Markov chain Monte Carlo (MH-McMC) and reversible jump Markov chain Monte Carlo (rj-McMC). The results show that ADVI provides a biased approximation because of its Gaussian approximation, whereas SVGD produces more accurate approximations to the results of MH-McMC. In comparison rj-McMC produces smoother mean velocity models and lower standard deviations because the parameterization used in rj-McMC (Voronoi cells) imposes prior restrictions on the pixelated form of models: all pixels within each Voronoi cell have identical velocities. This suggests that the results of rj-McMC need to be interpreted in the light of the specific prior information imposed by the parameterization. Both variational methods estimate the posterior distribution at significantly lower computational cost, provided that gradients of parameters with respect to data can be calculated efficiently. We therefore expect that the methods can be applied fruitfully to many other types of geophysical inverse problems.
Impact of the Pacific mean SST bias to the Atlantic-Pacific teleconnection
Authors: Li Chen , Dommenget Dietmar , McGregor Shayne
Published: March 2020

A robust eastern tropical Pacific surface temperature cooling trend along with the strengthening of Pacific trade wind is evident across different observations since late 1990s, which is considered as a pronounced contributor to the slowdown in global surface warming. However, most CMIP5 historical simulations failed to reproduce this La Niña-like change. Previous studies have attributed this discrepancy between the multi-model simulations and the observations to the underrepresentation of Pacific low-frequency variability together with the misrepresentation of inter-basin forcing response. The underlying reasons remain unclear. Here, we investigate a hypothesis that common Pacific mean SST bias may diminish the Pacific-Atlantic atmospheric teleconnection and further contribute to the underestimated eastern Pacific cooling. Model results suggest that the CMIP5-like Pacific bias acts to reduce the Atlantic heating response by strengthening the atmospheric stability over the Atlantic region and therefore weaken the trans-basin variability. In addition, the Pacific bias simulation with a strong SST cold tongue substantially undermined the positive zonal wind feedback, which also contributes to the underestimated Pacific cooling response. Future efforts aim at reducing the model mean state biases may significantly help to improve the simulation skills of the trans-basin teleconnection, Pacific decadal variability, and the associated Pacific dynamics.      
Dynamic Topography of Borborema Province and Surrounding Regions of Brazil
Authors: Santana Patricia , White Nicky
Published: March 2020

The Borborema Province is a Precambrian domain located in the northeastern corner of the Brazilian Shield. It has experienced a complex tectonic evolution that involves orogenic cycles during Precambrian times as well as continental break-up during Mesozoic times. Thermochronologic studies suggest that this region underwent Late Cretaceous-Cenozoic epeirogenic uplift, which is broadly coeval with basaltic volcanism. This uplift is manifest by marine Albian limestones, which crop out at 700 m altitude within the Araripe Basin, and by emergent Holocene marine terraces along the coastline. Despite its elevation, the Borborema Plateau is underlain by thin (30–35 km) crust and has a long-wavelength (> 700 km) positive free-air gravity anomaly. Both observations imply that some degree of sub-crustal support is required. Offshore, oceanic lithosphere adjacent to the Borborema Province has positive residual depth anomalies with amplitudes of hundreds of meters. We infer that sub-plate mantle convective processes have played a significant role in generating and maintaining plateau elevation. Here, a multi-disciplinary approach is used to analyze the causal relationship between surface topography, crustal thickness and crustal density with a view to constraining the residual topography of the Borborema province and surrounding regions. A combination of legacy active and passive source seismic experiments, comprising receiver function studies and deep seismic refraction profiles, were used to determine crustal velocity structure. The relationship between crustal velocity and density is investigated by analyzing a global compilation of rock physics measurements for a full range of crustal lithologies. In this way, the average density of Borborema crust is calculated and used to estimate residual topography by carrying out an isostatic balance between continental lithosphere and a typical mid-oceanic ridge. Positive residual topographic anomalies are obtained for the entire region that are consistent with the amplitude and sign of off-shore residual depth measurements. The aim of this project is to develop a quantitative understanding of the spatial and temporal evolution of the Borborema Plateau. Future work will focus on analyzing exhumed sedimentary basins that transect the plateau, on modeling the geochemistry of Neogene basalts, on inverting fluvial drainage networks, and on interrogating emergent marine terraces along the adjacent coastline.
Interaction between biomass-burning aerosol and clouds under different climate/weather regimes
Authors: Takeishi Azusa , Wang Chien
Published: March 2020

The maritime continent in Southeast Asia is characterized by the frequent convective activities on a wide range of scales, as well as by the seasonal emissions of biomass-burning particles. The emission of biomass-burning particles in this region typically peaks in September and October, whereas its intensity varies considerably from year to year. Since the atmospheric circulation over the region is heavily influenced by a range of meteorological and climatological variabilities, such as ENSO, it is important to quantitatively examine the impacts of biomass-burning particles on clouds while taking weather/climate regimes into account. We investigate the effects of biomass-burning particles on clouds, especially convective ones, with cloud-resolving simulations by the WRF-CHEM model. Instead of focusing on a particular case, our simulations cover an extended period of time in the month of September, allowing us to examine both individual convection and an ensemble of convective clouds developing under different weather/climate regimes and hence different aerosol abundance and distributions. Such long-term and high-resolution simulations over the region will give us an insight into the climate-regime dependent two-way interaction between aerosols and clouds.
Reducing filter effects in GRACE-derived polar motion excitations
Authors: Göttl Franziska , Murböck Michael , Schmidt Michael , Seitz Florian
Published: March 2020

Polar motion is caused by mass redistribution and motion within the Earth system. The GRACE satellite mission observed variations of the Earth’s gravity field which are caused by mass redistribution. Therefore GRACE time variable gravity field models are a valuable source to estimate individual geophysical mass-related excitations of polar motion. Since GRACE observations contain erroneous meridional stripes, filtering is essential in order to retrieve meaningful information about mass redistribution within the Earth system. However filtering reduces not only the noise but also smooths the signal and induces leakage of neighboring subsystems into each other.

We present a novel approach to reduce these filter effects in GRACE-derived equivalent water heights and polar motion excitation functions which is based on once and twice filtered gravity field solutions. The advantages of this method are that it is independent from geophysical model information, works on global grid point scale and can therefore be used for mass variation estimations of several subsystems of the Earth (e.g. continental hydrosphere, oceans, Antarctica and Greenland). In order to validate this new method, we perform a closed-loop simulation based on a realistic orbit scenario and error assumptions for instruments and background models, apply it to real GRACE data (GFZ RL06) and show comparisons with ocean model results from ECCO and MPIOM.
Effect of whistler precursor waves on energy dissipation in supercritical quasi-perpendicular collisionless shocks.
Authors: Lalti Ahmad , Khotyaintsev Yuri , Graham Daniel , Vaivads Andris , Johlander Andreas , Torbert Roy , Giles Barbara , Russell Chris , Burch Jim
Published: March 2020

The process of transforming the bulk kinetic energy of solar wind into the random motion of the plasma particles is still an open question. One of the proposed mechanisms for energy dissipation in such shocks is wave-particle interactions. Specifically reflected ions at the foot of the shock could interact with the solar wind plasma in an unstable way causing an increase in the temperature of the upstream plasma. Phase standing Whistler precursor waves upstream of the shock front could play a major role in enhancing energy dissipation. We analyze multiple shock crossing events encountered by the Magnetospheric Multiscale (MMS) multi-spacecraft Mission, with Alfvenic Mach numbers around 4 and a θBn around 80 degrees. We use these events to study the effect of such waves on energy dissipation at quasi perpendicular shocks.  Using spectral analysis and by calculating the poynting flux of the waves, we investigate the upstream shock energy transport by whistler waves, then we discuss the consequences of these results on the wave particle interaction as a mechanism for stabilizing such high Mach number shocks.
The WRF-SUEWS coupled system: development and evaluation in two UK cities
Authors: Omidvar Hamidreza , Sun Ting , Li Zhenkun , Zhang Ning , Huang Wenjuan , Kotthaus Simone , Ward Helen , Luo Zhiwen , Grimmond Sue
Published: March 2020

To capture complex physical processes in cities with high degree of heterogeneity, sophisticated urban land surface models (ULSMs) are used with various anthropogenic activities considered. These ULSMs can be used either offline, using atmospheric measurements as forcing inputs, or online, coupled with large-scale climate models. One downside of using ULSMs in offline mode is that most of atmospheric measurements in cities are spatially limited (e.g. a few points or sites) preventing the physical processes across extremely diverse or heterogeneous conditions in cities from being studied in their entire complexity. Coupling ULSMs with meso-scale models helps us study two-way interactions between the urban surface and atmosphere, and provides spatio-temporal information about the effect of urban climate on various city-related environmental issues such as the urban heat island and urban stormwater.

Here we couple and evaluate state-of-the-art surface urban energy and water scheme (SUEWS) with the weather research and forecasting (WRF) model. The coupled system (WRF-SUEWS) is evaluated in two UK cities: London (dense urban) and Swindon (suburban) for four two-week periods in each season. In general, WRF-SUEWS models the surface energy balance fluxes well in both cities across all periods. One strength of the coupled system is the ability to model the spatial and temporal distribution of anthropogenic heat in urban areas. We study how the difference between the anthropogenic heat flux of residential and commercial areas affects the energy balance as well as atmospheric variables over these areas.
The experience of Iberoamerican Meteorological Cooperation in the improvement of the provision of Weather and Climate Services
Authors: Tamayo Jorge
Published: March 2020

The cooperation between Iberoamerican National Meteorological and Hydrological Services (NMHS) it is coordinated through the Conference of Directors of Iberoamerican NMHS (CIMHET), who takes advantage of the unique framework that provides the cultural and idiomatic heritage in the region. It is constituted by all 21 NMHSs of Iberoamerica, including Spain and Portugal. CIMHET provides a forum for dialogue between Iberoamerican NMHSs, recognized by World Meteorological Organization (WMO) as an example of cooperation and operability.
The Conference approves, at its annual meetings from 2003, an action plan over three strategic lines: Institutional strengthening and resource mobilization; provision of meteorological, climatic and hydrological services; education and training
Among the activities carried out in the latest action plans related to a better provision of Weather and Climate Services (WCS) includes the support for the creation and operation of Virtual Regional Centers for the Prevention of Severe Events, the development of a free database management system, namely MCH, which has been donated to WMO for distribution among interested NMHS, the implementation of a regional lightning detection network in Central America, or the development of downscaling climate change scenarios for Central America, with access to information and view via web.
In order to carry out the proper provision of WCS, it is also necessary to have sufficient and properly trained NMHS staff. Therefore, this activity, both for technical and management personnel, has been one of the fundamental elements in the activities carried out by CIMHET, with more than 60 courses and workshops from 2004, most of which have been face-to-face, attended by more than 1500 students.
It is also important to have the appropriate infrastructure and human resources so that NMHS can provide their services to society in a reliable and timely manner. For this, several modernization projects have been developed, mainly considering the needs of the different user sectors and showing their potential of NMHS for the different national social and economic sectors in case of solving their shortcomings.
Finally, intersectoral coordination mechanisms have been established with other Iberomerican networks with common interests, such as the Iberoamerican Network of Climate Change Offices (RIOCC) and the Conference of Iberoamerican Directors of Water (CODIA). A number of priority activities related to climate change adaptation issues linked to extreme hydrometeorological phenomena have been identified and started its development.
Seismo-acoustic ground coupling: Wave types, transfer efficiency, and near-surface structure
Authors: Fuchs Florian , Novoselov Artemii , Bokelmann Götz
Published: March 2020

Pressure perturbations such as e.g. impulsive acoustic waves can couple into solid earth through the long-known phenomenom of seismo-acoustic coupling. Yet, the associated mechanisms are not always clear. Most studies investigate seismo-acoustic through low-frequency and high amplitude signals generated by e.g. natural or man-made explosions.

We conducted a small-scale field experiment with firecrackers as acoustic sources and hundred 3-component nodal geophones as receivers in a 20m diameter ring layout, some of them co-located with seismically decoupled Hyperion IFS-5111 infrasound sensors. This allowed us to investigate seismo-acousting coupling for higher frequencies and very small (meter scale) offsets.

The large receiver density enabled us to observe and distinguish different wave types induced by acoustic sources, including direct air waves, air-coupled Rayleigh waves, and possibly slow Biot waves. Having co-located seismic and pressure sensors additionally allowed us to investigate the coupling efficiency, which is in the order of 10-7 and thus similar to many of the low-frequency and large-offset studies. Furthermore, we can deduct soil properties such as rigidity, bulk modulus, and density from the co-located sensors, and efficiently infer near-surface (soil) properties using cheap acoustic sources.
A Seismic Event Relative Location Benchmark Case Study
Authors: Kvaerna Tormod , Gibbons Steven J. , Tiira Timo , Kozlovskaya Elena
Published: March 2020

"Precision seismology'' encompasses a set of methods which use differential measurements of time-delays to estimate the relative locations of earthquakes and explosions.  Delay-times estimated from signal correlations often allow far more accurate estimates of one event location relative to another than is possible using classical hypocenter determination techniques.  Many different algorithms and software implementations have been developed and different assumptions and procedures can often result in significant variability between different relative event location estimates.  We present a Ground Truth (GT) database of 55 military surface explosions in northern Finland in 2007 that all took place within 300 meters of each other.  The explosions were recorded with a high signal-to-noise ratio to distances of about 2 degrees, and the exceptional waveform similarity between the signals from the different explosions allows for accurate correlation-based time-delay measurements.  With exact coordinates for the explosions, we can assess the fidelity of relative location estimates made using any location algorithm or implementation.  Applying double-difference calculations using two different 1-d velocity models for the region results in hypocenter-to-hypocenter distances which are too short and the wavefield leaving the source region is more complicated than predicted by the models.  Using the GT event coordinates, we can measure the slowness vectors associated with each outgoing ray from the source region. We demonstrate that, had such corrections been available, a significant improvement in the relative location estimates would have resulted.  In practice we would of course need to solve for event hypocenters and slowness corrections simultaneously, and significant work will be needed to upgrade relative location algorithms to accommodate uncertainty in the form of the outgoing wavefield.  We present this dataset, together with GT coordinates, raw waveforms for all events on six regional stations, and tables of time-delay measurements, as a reference benchmark by which relative location algorithms and software can be evaluated.
Ocean productivity and bottom water oxygenation across the onset of the Cenozoic cooling trend
Authors: Alexander Sophie M. , Sexton Philip F. , Anand Pallavi , Bohaty Steven M.
Published: March 2020

The onset of the Cenozoic global cooling trend represents a major transition in Earth’s climate from the extremely warm early Eocene ‘greenhouse’ towards much colder unipolar glaciation by the end of the Eocene. Data across this interval of profound climatic change have long suggested contemporaneous changes to marine biological productivity and the carbon cycle. Modern observations, conceptual models from the last glacial cycle and models documenting change at Cenozoic timescales, all predict heterogeneous biological productivity responses between high and low latitudes. We test for this heterogeneity between latitudes across the onset of the Cenozoic global cooling trend. Here we utilise bulk sediment elemental compositions, and concentration of benthic foraminifera and ichthyoliths to reconstruct changes in palaeoproductivity, export and preservation of CaCO3 across the early-to-middle Eocene interval (~42 to 50 Ma) at multiple deep-sea sites in the Atlantic basin. We also present evidence of changes in bottom-water oxygenation across the Southern Atlantic sites. We find opposing trends in Biogenic barium (BioBa) versus benthic foraminifera accumulation rates (BFAR) and Ichythyolith Accumulation Rates (IAR) for many of our sites across the high southern latitudes. These trends could be explained by increased organic carbon flux to the sediment, which would have increased the BFAR and IAR while at the same time potentially causing oxygen depletion and reductive barite dissolution in the sediments driving our observed synchronous decreases in BioBa and Mn/Al. This trend of synchronous decreases in BioBa and Mn/Al is evident within the Atlantic Sector of the Sub-Antarctic Zone. Within the Antarctic zone, an opposing trend of decreasing BioBa coincides with increasing Mn/Al and BFAR, suggesting a differing mode of production, export and fate of marine CaCO3. Ongoing work seeks to determine the nature of biological productivity responses across the high and low latitude oceans during the Eocene ‘greenhouse’ to ‘icehouse’ transition.
Inorganic and organic bromine measurements around the extra-tropical tropopause: Insights into total stratospheric bromine
Authors: Rotermund Meike , Schreiner Ben , Kluge Flora , Hüneke Tilman , Engel Andreas , Schuck Tanja , Kerber Timo , Grooß Jens-Uwe , Zahn Andreas , Pfeilsticker Klaus
Published: March 2020

Bromine greatly influences the UT/LS ozone concentrations, however the transport of bromine across the tropical tropopause layer and in particular across the extratropical tropopause is not well quantified. Air-borne measurements of atmospheric trace gases such as organic and inorganic bromine along the tropopause are studied during the WISE (Wave-driven ISentropic Exchange) research campaign over the northern Atlantic and western Europe from September 13 - October 21, 2017. The remote sensing instrument mini-DOAS (Differential Optical Absorption Spectroscopy) is mounted on the HALO (High Altitude and LOng range) aircraft and measures BrO (O3, NO2 among other trace gases). The novel scaling method is applied to infer the target gas BrO mixing ratios from slant column densities using in-situ O3 measurements from the FAIRO instrument (operated by KIT) as the scaling gas. For each flight, the inferred mixing ratios are directly compared with CLaMS (Chemical Lagrangian Model of the Stratosphere) simulated curtains of the trace gases along the flight path. The partitioning coefficient of inorganic bromine from CLaMS and all relevant organic halogen species and air mass ages (SF6, CO2) from the GhOST-MS instrument (operated by UFra) are used to determine the total bromine budget along the UT/LS. A climatology of organic, inorganic and total bromine is constructed with respect to the extratropical tropopause as well as the air mass ages. This indicates the interplay of bromine transport across the extratropical tropopause and of the transport of air via the lower branch from the tropics as well as potential losses of inorganic bromine by uptake onto and sedimentation of ice particles.
PICASSO: a PICo-satellite for Atmospheric and Space Science Observations
Authors: Baker Noel , Anciaux Michel , Dekemper Emmanuel , Demoulin Philippe , Fussen Didier , Pieroux Didier , Ranvier Sylvain
Published: March 2020

The recent surge in the development of small satellite platforms could offer the opportunity to significantly decrease the overall cost of science missions, if suitable instruments can be operated from such platforms. PICASSO is a CubeSat demonstration mission initiated by the Belgian Institute for Space Aeronomy and implemented by the European Space Agency (ESA). Its objective is to assess the ability of very low-cost satellites to carry out atmospheric measurements. PICASSO focuses on retrieving the ozone distribution in the stratosphere, the temperature profile up to the mesosphere, and the electronic density and temperature in the ionosphere.

Following its launch on a VEGA rocket in March 2020, PICASSO will fly for two years. The overall demonstration mission includes the end-to-end development of the satellite, launch, operation, and analysis of the scientific data. PICASSO follows a polar orbit at an altitude ranging from 475 to 500 km and an inclination of 98°. Its payload consists of a miniaturised hyper-spectral imager (VISION) and a four needle-like Sweeping Langmuir Probe (SLP). It utilizes four deployable solar panels with an average power generation of 8.7W, two on-board computers (OBC and PLC), and a high-performance ADCS with a pointing accuracy of around 1°.

The scientific objectives of VISION are to demonstrate the retrieval of polar and mid-latitude stratospheric ozone vertical profiles from multispectral transmittances observed in solar occultations. For SLP, the main goals are to study the ionosphere-plasmasphere coupling and aurora structures, and to monitor the density irregularities in the polar cap ionosphere.
Seasonal composition and source apportionment of nitrated aromatic compounds in atmospheric fine particulate matter in northern China over one year
Authors: Yuan Wei , Huang Rujin , Yang Lu
Published: March 2020

Nitrated aromatic compounds (NACs) are an important chromophore component of atmospheric brown carbon (BrC) and can affect both the urban air quality and global climate. However, the compositions, sources of NACs in atmospheric particulate matter and its impact on the optical properties of BrC are still of very limited understood. In this study, the concentrations of 10 NACs and their light absorption contributions to BrC were investigated based on daily aerosol fine particle filter samples collected in Xi’an, Northwest China from 2015 to 2016. Both the concentrations and constitutions of NACs show distinct seasonal differences with average concentration of 2.05, 1.06, 12.90 and 56.32 ng m-3 in spring, summer, fall and winter, respectively, which could be ascribed to the differences in emission sources and formation processes. The contributions of NACs to light absorption of BrC at wavelength between 300 to 500 nm was wavelength dependent and varied greatly over different seasons, with high contribution even at wavelength > 350 nm in fall and winter and contribution mainly at wavelength < 350 nm in spring and summer, which could be related to the differences in the composition of NACs and the specific light absorbing properties of each NAC. The mean contributions of NACs to the light absorption of BrC at wavelength of 365 nm were 0.14, 0.09, 0.36 and 0.91% during spring, summer, fall and winter, respectively, about 3-5 times higher than their corresponding mass fraction in total organic carbon. Further, the sources of NACs were achieved by positive matrix factorization (PMF) receptor model. The results show that the sources of NACs varies among different seasons. Specifically, vehicular emission and secondary formation are dominant sources in summer (~80%), while biomass burning and coal combustion are major sources in winter (~75%).
Coupling subglacial hydrology to basal friction in an Antarctic ice sheet model
Authors: Kazmierczak Elise , Zipf Lars , Pattyn Frank
Published: March 2020

Due to the lack of direct observations, subglacial hydrology is still marginally considered in Antarctic ice sheet modelling studies, albeit that several approaches exist (e.g., LeBrocq, Bueler and Van Pelt). Subglacial hydrology impacts basal friction through a reduction in effective pressure and through changing properties of subglacial sediments, both factors influencing the lubrication at the bottom of the ice sheet. Several approaches exist to represent subglacial hydrology in ice sheet models (Bueler and Brown, 2009, Goeller et al., 2013) and are generally coupled to either a Coulomb or a Weertman friction law. However, the type of subglacial process determines to a large extent the sensitivity of Antarctic mass change (Sun et al, submitted).

 

In this study we investigate the sensitivity of subglacial dynamics on the behaviour of the Antarctic ice sheet on centennial time scales. For this purpose we employ a subglacial hydrology model for subglacial water routing (Lebrocq et al., 2009) coupled to a thermomechanical ice-sheet model (f.ETISh; Pattyn, 2017). We consider different parametrizations and representations of effective pressure and till water content at the base.  We also consider the combination of different friction laws and hydrological models (sheet flow, till deformation) depending on estimates of the subglacial conditions of the Antarctic ice sheet. Results show that the way of coupling subglacial hydrology influences the sensitivity of the ice-sheet system on centennial time scales. However, the type and power of the friction law (Coulomb versus Weertman)  has the most dominant impact on ice sheet sensitivity.
Unraveling the AD 1755 Lisbon tsunami through 2DV modelling
Authors: Bosnic Ivana , Costa Pedro
Published: March 2020

Understanding past tsunami events is key to assess tsunami hazard and numerical modelling is a powerful tool to better understand these events. A rising number of studies focusing on palaeotsunami numerical modelling reinforce the potential of this tool to unravel unknown features of past tsunami events. The AD 1755 Lisbon is the largest historical tsunami registered on Western Europe and despite its relevance there are still uncertainties regarding its source, magnitude and wave characteristics.   

This work contributes to a better understanding of the AD 1755 tsunami through the evaluation of the wave characteristics and of the onshore and offshore sedimentary dynamic using Delft3D software (Flow module).  

The study site, Almargem lowland, is located on the Portuguese southern coast (central Algarve) where a two-dimensional vertical (2DV) morphodynamic modelling approach was carried out along 10 vertical layers. Bathymetry is represented by a across-shelf profile with 7 kilometers long thus, extending from the coast up to 50 m deep. Bottom sediments and roughness vary along the profile according to the sediment characteristics of each coastal sector (shelf, beach, dune and lowland area). Boundary conditions were imposed according to three scenarios represented by offshore sinusoidal tsunami waves of 3, 4- and 5-meters height. Tsunami-induced sedimentary dynamics results show that the 3 m wave scenario (50 m depth) present the most compatible scenario with the observed onshore deposit, in particular its 600 m inland extension. Moreover, the dune was singled-out as the main sediment source of the deposit. This source-to-sink relationship confirms previous field and sedimentary results (Costa et al., 2012, Sed Geol).  

A 3D morphodynamic modelling approach carried out by Dourado et al. (in press) on an adjacent study area (Salgados, central Algarve) also pointed to a 3-meter tsunami wave height (at 50 meters deep) and further corroborates the results of this work. Despite good initial results, with harmonization and validation of modelling results, further efforts are necessary to incorporate backwash influence on the onshore sediment dynamics as well as a detailed analysis on the vertical sediment distribution. 

The authors would like to acknowledge the financial support from FCT through projects UIDB/50019/2020 – IDL and PTDC/CTA-GEO/28941/2017 - OnOff. 
Using a long-term climate simulation to address future changes in Western Europe precipitation regimes due to global warming
Authors: Sousa Pedro M. , Ramos Alexandre M. , Trigo Ricardo M. , Raible Christoph C. , Messmer Martina , Pinto Joaquim G. , Tomé Ricardo
Published: March 2020

Moisture transport and Atmospheric Rivers (ARs) over the Northeastern Atlantic are a very relevant process for the inter-annual variability of precipitation over Western Europe. Based on a long-term transient simulation (850-2100CE) from the CESM model, we have showed that moisture transport towards Western Europe (using the vertically integrated horizontal water vapor transport, IVT) has been increasing significantly since pre-industrial period, in a clear association with the global warming trend. Both current and projected changes (using RCP 8.5) significantly exceed the range given by inter-annual to inter-decadal internal/external variability observed during the last millennium.

We have checked the emergence of the temperature, IVT and precipitation signals in Iberia and the UK, showing that while the first two have now clearly emerged from the pre-warming state, precipitation series are still slightly below that threshold. Nevertheless, projections clearly show an increase in rainfall at higher latitudes (i in phase with a warmer and moister atmosphere); and a decrease at lower latitudes decoupled from the overall increase in moisture availability. Additionally we have explored the role played by large-scale circulation and atmospheric dynamics for these contrasting projections. Overall, results show that a poleward migration of moisture corridors and ARs explain a significant fraction of these projected trends. Based on the Clausius–Clapeyron relation we have separated the thermodynamical from dynamical changes. We also show how that a significant increase in subtropical anticyclonic activity over Iberia is responsible for: i) dynamical circulation changes; ii) a shortening of the wet season; iii) to less efficient precipitation regimes in the region. These results highlight the urge to adapt to a drying trend in Mediterranean-type climates, as a consequence of Global Warming.

 

The financial support for this work was possible through the following FCT project: HOLMODRIVE - North Atlantic Atmospheric Patterns influence on Western Iberia Climate: From the Lateglacial to the Present [PTDC/CTA-GEO/29029/2017]
HydroSOS: a pilot global Hydrological Status and Outlook System integrating national to global scale hydrological services for increased resilience to hydro-climatic risks
Authors: Smith Katie , Silva Vara Luis Roberto , Dixon Harry , Barlow Victoria , Jenkins Alan , Berod Dominique , Kim Hwirin , Wang Guoqing , Wolock David , Tuteja Narendra , Paudyal Guna , Kanyike Tom , Blyth Eleanor , Wood Andy
Published: March 2020

Consistent hydrological status and outlook information across transboundary basins or regions of shared hydrological interest are not often available. Furthermore, whilst large-scale modelling capabilities are continually improving, there is an information and confidence gap between locally informed hydrological status information products and those developed globally.

HydroSOS is World Meteorological Organisation initiative that aims to increase global resilience to hydro-climatic risks through the production of hydrological status and outlooks assessments at different scales around the world. Currently in a pilot phase, HydroSOS is being developed through a collaboration between National Hydrometeorological Services, transboundary basin organisations, global modelling centres and the research community. The system will provide an appraisal of where current hydrological status is different from “normal”, as well as sub-seasonal to seasonal outlooks indicating whether this is likely to get better or worse over the coming weeks and months.

The HydroSOS programme consists of five main activity streams:

Increasing the interoperability of hydrological status and outlook products through Common Technical Specifications.

Increasing national capabilities to generate hydrological status and sub-seasonal to seasonal outlook products through Guidance on Methods and Tools.

Increasing the utility of large-scale hydrological status and outlook modelling through Co-design of Global Products, with international partners working from local to global scale.

Increasing shared production of transboundary hydrological status and outlook products through Regional Pilots, initially in South Asia and the Lake Victoria Basin.

Integration of hydrological status and outlook products for national, regional and global users through a Demonstration Portal.

This PICO contribution will present progress in the pilot project to date, including a hands-on demonstration of the web portal.
Innovation in Satellite Sensors for Ocean Observations : An OceanObs19 overview
Authors: Morrow Rosemary ,   OceanObs19 Satellite Innovation team
Published: March 2020

Over the next decade, new satellite sensors are being developed or proposed to enhance our global observations of ocean surface parameters, many aiming at finer scale processes. These sensors include the new generation of satellite altimeters with finer resolution in alongtrack SAR mode or with swath SAR-interferometry; missions to observe total surface currents and wind-wave interactions; high resolution sea surface temperature and salinity; and ocean color, polarimetry and lidar missions for biogeochemistry, among others. Key observational challenges are to have finer-resolution across open ocean fronts, to observe the surface dynamical interactions over multiple scales, and to extend our satellite observing systems into the coastal and polar regions. Understanding smaller-scale variability will have benefits for climate, ocean operations and ocean health.

This presentation will give an overview of the OceanObs19 discussions on the opportunities and priorities for new satellite ocean sensors for the upcoming decade.
Exploring the biomineral morphology of crossed-lamellar bivalve shells as a water temperature proxy
Authors: Höche Nils , Peharda Melita , Thébault Julien , Schöne Bernd R.
Published: March 2020

Bivalve shells serve as excellent high-resolution archives of marine paleoclimate. Recently, ultrastructural features of the shells were investigated as potential temperature proxies that can overcome the limitations of the stable oxygen isotope method (i.e., missing data on past seawater oxygen isotope signature and diagenetic overprint). According to previous studies, the size of individual biomineral units of prismatic, nacreous and crossed-lamellar ultrastructures in cross-sections along the axis of maximum growth was solely related to water temperature. Despite being present in 90% of all mollusks, the crossed-lamellar ultrastructure was only studied for environmental relationships in one species (Glycymeris bimaculata) until now. To determine whether this new proxy can be applied to other bivalves with crossed-lamellar ultrastructure, further studies are needed.

We analyzed the shells of other Glycymerididae collected at near-shore and shelf environments (G. nummaria and G. pilosa: Adriatic Sea, Croatia; G. glycymeris: Iroise Sea, France; Glycymeris sp: Southern Pacific, New Zealand) by means of SEM, using a previously developed automatic image analysis procedure. Morphological changes of the biomineral units of the shells were assessed for relationships with temperature, salinity and food availability. Additionally, the crossed-lamellar architectures of phylogenetically more distantly related taxa (Venus verrucosa and Callista chione: Adriatic Sea, Croatia) were assessed.

Our results show that all studied Glycymerididae species, irrespective of environmental setting and locality, formed larger biomineral units in warmer waters. However, biomineral properties of ontogenetically old shell portions are more difficult to interpret, because declining growth rates condense the shell record and aggravate ultrastructural analyses. The crossed-lamellar shell layers of V. verrucosa and C. chione exhibited hierarchical organizations very similar to those of the Glycymerididae. The ultrastructural temperature proxy can therefore be applied to crossed-lamellar shells of bivalves from a wide range of coastal settings, preferably in ontogenetically young shell portions.
Selection of Reliable Machine Learning Algorithms for Geophysical Applications
Authors: Dumitru Octavian , Schwarz Gottfried , Ao Dongyang , Dax Gabriel , Andrei Vlad , Karmakar Chandra , Datcu Mihai
Published: March 2020

During the last years, one could see a broad use of machine learning tools and applications. However, when we use these techniques for geophysical analyses, we must be sure that the obtained results are scientifically valid and allow us to derive quantitative outcomes that can be directly compared with other measurements.

Therefore, we set out to identify typical datasets that lend themselves well to geophysical data interpretation. To simplify this very general task, we concentrate in this contribution on multi-dimensional image data acquired by satellites with typical remote sensing instruments for Earth observation being used for the analysis for:

Atmospheric phenomena (cloud cover, cloud characteristics, smoke and plumes, strong winds, etc.)

Land cover and land use (open terrain, agriculture, forestry, settlements, buildings and streets, industrial and transportation facilities, mountains, etc.)

Sea and ocean surfaces (waves, currents, ships, icebergs, coastlines, etc.)

Ice and snow on land and water (ice fields, glaciers, etc.)

Image time series (dynamical phenomena, their occurrence and magnitude, mapping techniques)

Then we analyze important data characteristics for each type of instrument. One can see that most selected images are characterized by their type of imaging instrument (e.g., radar or optical images), their typical signal-to-noise figures, their preferred pixel sizes, their various spectral bands, etc.

As a third step, we select a number of established machine learning algorithms, available tools, software packages, required environments, published experiences, and specific caveats. The comparisons cover traditional “flat” as well as advanced “deep” techniques that have to be compared in detail before making any decision about their usefulness for geophysical applications. They range from simple thresholding to k-means, from multi-scale approaches to convolutional networks (with visible or hidden layers) and auto-encoders with sub-components from rectified linear units to adversarial networks.

Finally, we summarize our findings in several instrument / machine learning algorithm matrices (e.g., for active or passive instruments). These matrices also contain important features of the input data and their consequences, computational effort, attainable figures-of-merit, and necessary testing and verification steps (positive and negative examples). Typical examples are statistical similarities, characteristic scales, rotation invariance, target groupings, topic bagging and targeting (hashing) capabilities as well as local compression behavior.
Type III Radio Bursts and Langmuir Wave Excitation
Authors: Mann Gottfried , Vocks Christian , Bisi Mario , Carley Eoin , Dabrowski Bartosz , Fallows Richard , Gallagher Peter , Krankowski Andrzej , Magdalenic Jasmina , Marque Christophe , Morosan Diana , Rothkaehl Hanna , Zucca Pietro
Published: March 2020

Type III radio bursts are a common phenomenon the Sun’s nonthermal radio radiation. They appear as stripes of enhanced radio emission with a rapid drift from high to low frequencies in dynamic radio spectra. They are considered as the radio signatures of beams of energetic electrons travelling along magnetic field lines from the solar corona into the interplanetary space. With the ground based radio interferometer LOFAR and the instrument FIELDS onboard NASA’s “Parker Solar Probe” (PSP) , type III radio bursts can be observed simultaneously from high (10-240 MHz) to low frequencies (0.01-20 MHz) with LOFAR and PSP’s FIELDs, respectively. That allows to track these electron beams from the corona up to the interplanetary space. Assuming that a population of energetic electrons is initially injected, the velocity distribution function of these electrons evolves into a beam like one. Such distribution function leads to the excitation of Langmuir waves which convert into radio waves finally observed as type II radio bursts. Numerical calculations of the electron-beam-plasma interaction reveal that the Langmuir waves are excited by different parts of the energetic electrons at different distances in the corona and interplanetary space. This result is compared with special type III radio bursts observed with LOFAR and PSP’s FIELDS.
Estimation of soil moisture content using Citizen observatory data -lessons learnt from GROW Observatory project
Authors: Dobos Endre , Kovács Károly , Kibirige Daniel , Vadnai Péter
Published: March 2020

Soil moisture is a crucial factor for agricultural activity, but also an important factor for weather forecast and climate science. Despite of the technological development in soil moisture sensing, no full coverage global or continental or even national scale soil moisture monitoring system exist.  There is a new European initiative to demonstrate the feasibility of a citizen observatory based soil moisture monitoring system.  The aim of this study is to characterize this new monitoring approach and provide provisional results on the interpretation and system performance.

GROW Observatory is a project funded under the European Union’s Horizon 2020 research and innovation program. Its aim is to establish a large scale (>20,000 participants), resilient and integrated ‘Citizen Observatory’ (CO) and community for environmental monitoring that is self-sustaining beyond the life of the project. This article describes how the initial framework and tools were developed to evolve, bring together and train such a community; raising interest, engaging participants, and educating to support reliable observations, measurements and documentation, and considerations with a special focus on the reliability of the resulting dataset for scientific purposes. The scientific purposes of GROW observatory are to test the data quality and the spatial representativity of a citizen engagement driven spatial distribution as reliably inputs for soil moisture monitoring and   to create timely series of  gridded soil moisture products based on citizens’ observations using low cost soil moisture (SM) sensors, and to provide an extensive dataset of in-situ soil moisture observations which can serve as a reference to validate satellite-based SM products and support the Copernicus in-situ component. This article aims to showcase the design, tools and the digital soil mapping approaches of the final soil moisture product.