bluuebunny/crossref_metadata_2025 huggingface dataset:
Using structural frames to integrate structural geology into implicit 3D modelling
Authors: Grose Lachlan , Laurent Gautier , Ailleres Laurent
Published: March 2020

Implicit geological modelling allows for observations of surface location and orientation to be interpolated into continuous 3D surfaces. These surfaces are usually built by finding a function that minimises the misfit between the surface and observations (gradient or value of the implicit function) combined with a regularisation constraint that controls how the surface develops between observations. When modelling complex terranes such as fold series, fault networks or intrusions it is usually necessary to use interpretive constraints for creating the expected geometries. These interpretations are problematic, as the constraints are usually not observations but realisations of the geologists’ subjective interpretation, and are therefore difficult to change and interrogate to better understand the geometry. Recent developments for implicit modelling of folds and faults have built new local coordinate systems using the structural geology of the object being modelled and are termed structural frames. For example, for folds, the structural frame is aligned to the axial surface of the fold and fold axis. For faults, the structural frame is aligned to the fault surface and slip direction. Using structural frames, conceptual models of the fold and fault geometries can be combined with the observations of the surfaces. This means that rather than using the geologists' subjective interpretation to constrain the model geometries, the conceptual model can guide the interpolation where observations are missing. Geological uncertainties in the resulting geometries can be assessed by framing the modelling as an inverse problem and varying the conceptual model parameters to fit the geological observations. In this contribution, we review the use of structural frames for constraining 3D geometry of structurally complex terranes and provide an example of a faulted fold series.
A Global Picture of the Depth and Origin of Soil Water Uptake by Vegetation
Authors: Miguez-Macho Gonzalo , Fan Ying
Published: March 2020

Plants play a fundamental role in the climate system, not only as important components of the global water and carbon cycles, but because they provide a key link between water stores in the deep soil and the atmosphere. Vegetation has evolved strategies to cope with droughts, such as the existence of deep roots allowing for the shifting of water uptake to deeper layers storing past precipitation, as water from more recent precipitation on top is depleted and not replenished. Here we ask the following question: To what extent is the soil water uptake source for vegetation the recent rain reaching shallow soils, or past wet-season rain stored in deep soils, or past rain that reached the water table, which sends the water back up through capillary flux, or past rain that flowed down the topographic gradient from ridges to valleys (i.e. upland to lowland subsidy)? We address this question through (a) a synthesis of 528 observations of stable isotopes of O/H in plant xylem and source waters, compiled from the literature, and (b) a dynamic high-resolution (1km) model representing the global soil-plant-atmosphere continuum at the global scale by explicitly coupling land surface-groundwater and root uptake, driven by reanalysis atmosphere and observed leaf area. Both model and isotope methods reveal that plant use of past precipitation is globally widespread and particularly significant in semi-arid or seasonally dry climates and lowland ecosystems. Seasonal shifting to deeper uptake tapping past precipitation in dry periods is common even in wetter climates. The model results allow us to further distinguish among past precipitation stored as deep soil water or from local or remote groundwater sources. Our findings shed critical lights on the depth and origin of the water supporting global photosynthesis, hence their resilience or vulnerability to seasonal-interannual droughts across the globe and vegetation response to climate change.
Tracking surface and subterranean water flow using continuous seismic tremor
Authors: Karbala Ali Haleh , Bean Chris , Craig David , Li Ka Lok , O’Brien Gareth , Hickey Caoimhe , O'Keeffe Billy
Published: March 2020

Water is a critical resource that can range from being either available in short supply or excess, causing floods. In many locations the majority of this supply is underground. In some geological terrains such as karst these underground systems transport water primarily through crack or conduit flow. Determining the subsurface locations of the dominant flowing structures and their flow rates in such karst systems is a significant challenge. The details of these complex flow networks can, for example, have a first-order control on water supply, surface floods and the locations of seasonal lakes. Current geophysical methods focus on active geophysical imaging of karst structures but usually fail in determining if such structures are flowing. In this work, we take a different approach locating flowing conduits in Irish karst via a multi-method analysis of ground vibrations from temporary deployments of passive seismic sensors. We start by testing the methodology on surface rivers.

 Hydrological processes including turbulent water flow and sediment transport create ground vibrations that can be detected on seismic stations. In the initial test, we deployed two small aperture arrays of 4 and 6 three-component (3C) short-period seismometers and a short linear array beside a river with a typical flow rate of 25 m3/second. We see clear spectral peaks associated with water flow at frequencies of 10 to 40 Hz. We locate the sources for these frequency bands using both conventional beamforming array analysis and an Amplitude Source Location Method (ASLM). Before ASLM, we constrain the velocity based on array analysis. Both methodologies perform well in determining the known locations of rapid flow in the river. We then move to a test karst location where the subsurface pathways of large conduits are known through cave dives. We deploy 3C short period seismometers for a few hours. Again we see clear peaks in the seismic spectra which, using ASLM and Frequency-Dependent Polarization Analysis (FDPA), located close to the known conduits. In the station close to a known conduit, we see sustained very high-frequency signals which are in agreement with numerical simulation of crack dominated flow for secondary short narrow cracks. This work is the prelude to a larger seismic nodal deployment that will take place in the winter/spring of 2020 in the same location. Initial results from that experiment will also be presented.
Learning Lyapunov stable Dynamical Embeddings of Geophysical Dynamics
Authors: Ouala Said , Drumetz Lucas , Chapron Bertrand , Pascual Ananda , Collard Fabrice , Gaultier Lucile , Fablet Ronan
Published: March 2020

Within the geosciences community, data-driven techniques have encountered a great success in the last few years. This is principally due to the success of machine learning techniques in several image and signal processing domains. However, when considering the data-driven simulation of ocean and atmospheric fields, the application of these methods is still an extremely challenging task due to the fact that the underlying dynamics usually depend on several complex hidden variables, which makes the learning and simulation process much more challenging.

In this work, we aim to extract Ordinary Differential Equations (ODE) from partial observations of a system. We propose a novel neural network architecture guided by physical and mathematical considerations of the underlying dynamics. Specifically, our architecture is able to simulate the dynamics of the system from a single initial condition even if the initial condition does not lie in the attractor spanned by the training data. We show on different case studies the effectiveness of the proposed framework both in capturing long term asymptotic patterns of the dynamics of the system and in addressing data assimilation issues which relates to the short term forecasting performance of our model.
Meridional Distribution of Surface CO2 along 67°E of the Indian Ocean
Authors: Kang Dong-Jin , Choi Sang-Hwa , Kim Daeyeon , Lee Gyeong-Mok
Published: March 2020

Surface seawater carbon dioxide was observed from 3 °S to 27 °S along 67 °E of the Indian Ocean in April 2018 and 2019. Partial pressure of CO2(pCO2) in the surface seawater and the atmosphere were observed every two minutes using an underway CO2 measurement system (General Oceanics Model 8050) installed on R/V Isabu. Surface water temperature and salinity were measured as well. The pCO2 was measured using Li-7000 NDIR. Standard gases were measured every 8 hours in five classes with concentrations of 0 µatm, 202 µatm, 350 µatm, 447 µatm, and 359.87 µatm. The fCO2 of atmosphere remained nearly constant at 387 ± 2 µatm, but the surface seawater fCO2 peaked at about 3 °S and tended to decrease toward the north and south. The distribution of fCO2 in surface seawater according to latitude tends to be very similar to that of sea surface temperature. In order to investigate the factors that control the distribution of fCO2 in surface seawater, we analyzed the sea surface temperature, sea surface salinity, and other factors. The effects of salinity are insignificant, and the surface fCO2 distribution is mainly controlled by sea surface temperature and other factors that can be represented mainly by biological activity and mixing.
High-resolution geomorphological mapping of the Pico and Cisnes basins, Patagonia (44-45°S)
Authors: Cooper Emma , Thorndycraft Varyl , Davies Bethan , Palmer Adrian , García Juan
Published: March 2020

The drivers of latitudinal variations in glacier advance/retreat in Patagonia remain a fundamental question in palaeo-glacier studies. Broader climatic influences that underpin large-scale glacial fluctuations are mediated by topographic, calving, and process-related controls. A key step in understanding the relative importance of these factors in localised glacier response is a thorough investigation of geomorphological evolution.

In southern South America, large ice-lobes associated with the eastern flanks of the former Patagonian Ice Sheet terminated in the stepparian foothills. The geomorphological records accompanying these palaeo-glaciers represent an invaluable tool for reconstructing past glacier fluctuations. In the Pico and Cisnes valleys (44-45oS), ice-lobes underwent multiple advances, likely since the onset of the Great Patagonian Glaciation (~1.1 Myrs ago). The first account of Pico glacial geomorphology and the recognition of palaeo-lake existence was made by Caldenius (1932). Since then, only limited geomorphological investigations of the valley have been undertaken. 

Here we present a high-resolution geomorphological map of the Pico-Cisnes valleys based on mapping from satellite imagery at a 1:5000 scale, supported by ground-truthing in the field. Newly mapped ice limits, glaciolacustrine and glaciofluvial landforms are presented and include moraines, palaeo-shorelines, ice-contact fans, crag and tails, glacially-scoured bedrock, outwash plains and meltwater channels. These landforms provide new insights into landscape evolution essential in understanding the complex glacial/glaciolacustrine processes of the Cisnes and Pico valleys. Moreover, such data will underpin new geochronological frameworks, and allow fresh insights into the spatial and temporal response of these central Patagonian palaeo-glaciers to the onset of deglaciation.

 
Build seismic cycle balance deformation with InSAR in Northen Chile
Authors: Bayle Lauriane , Jolivet Romain , Cubas Nadaya , Le Pourhiet Laetitia
Published: March 2020

Lauriane Baylé (1), Romain Jolivet (2), Nadaya Cubas (1) and Laetitia Le

Pourhiet (1)

(1) Institut des Sciences de la Terre de Paris, UMR 7193, UPMC UniversitéParis 6, CNRS, Paris,

France

(2) Laboratoire de Géologie, Département de Géosciences, École Normale Supérieure, CNRS UMR 8538,

PSL ResearchUniversity, Paris, France

Recent studies have pointed out to a discrepancy between the short- and long-

term deformation of overriding plates in subduction zones. This led to debates

about when and how permanent deformation is acquired. This contradiction

has notably been observed along the Central Andes Subduction Zone, where

the coast subsides during and shortly after major earthquakes while a coastal

uplift with rates ranging between 0.1 and 0.3 mm/yr has been inferred the

last 4000 ky. For instance, during the 15th September 2015 Mw 8.3 Illapel

earthquake the geodetics (GPS and InSAR) data show a coastal subsidence

along the line-of-sight of 20 cm in InSAR.

To reconcile the seemingly contradictory observations, we here propose to

provide a seismic cycle uplift balance by constrainning inter-, co- and post-

seismic vertical velocities from InSAR time series. The study focuses on La

Serena peninsula (71.3°W, 30°S, Chile) along which the Illapel earthquake

occurred and for which long-term uplift rates have been provided by previous

geomorphological studies.

To build this seismic cycle balance, we use InSAR data (Sentinel-1) acqui-

red between the September 15, 2015 and January 19, 2019. The time series

for the ascendant orbite is calculated and the accumulated vertical displace-

ment extracted providing co- and post-seismic displacement. The co-seismic

displacement are similar to those previously obtain. To constrain the displa-

cement during the inter-seismic period, data on both sides of the peninsula

are used. In that respect, we aim determining when, during the seismic cycle,

and where, along the coast, the uplift occurs.

The deduced time series will then be confronted to numerical modelling

to provide the short- and long-term mechanics reproducing the short- and

long-term observations.
Characterisation Campaign at the Gobabeb RadCalNet Site in Support of Satellite Calibration and Validation Activities
Authors: Sinclair Morven , McLellan Chris , Bialek Agnieszka , Woolliams Emma R , Taylor Sarah , Fox Nigel P
Published: March 2020

With increasing use of satellite-derived data in climate and Earth monitoring, the importance of reliable and traceable radiometric and spectral information is key. Due to the difficulties of maintaining instrument calibration post-launch, vicarious calibration sites play a vital part in ensuring the stability and interoperability of satellite sensor data.

RadCalNet, the Radiometric Calibration Network established through the Committee on Earth Observation Satellites Working Group on Calibration and Validation (CEOS-WGCV), provides a network of, currently four, instrumented ground reference sites providing users with bottom and top-of-atmosphere (BOA and TOA) reflectance measurements every 30 minutes in 10 nm spectral intervals and for nadir view. (For all sites, more detailed spectral information and off-nadir reflectances can be obtained from site owners). It is a key aspect of RadCalNet that the sites document their traceability to the International System of Units (SI) and that they provide traceable uncertainties associated with individual observations. These documents and uncertainties are peer reviewed by the RadCalNet working group.  Each RadCalNet site provides ground reflectance observations that are propagated to TOA through a centralised processing system. RadCalNet has over 300 active users who value the available information.

Gobabeb, in Namibia, is one of these four sites, given the reference GONA. GONA was the first site that was established as a new RadCalNet site (the other sites were pre-existing) and the location was determined from a global survey to find suitable sites, primarily due to spatial uniformity and the probability of suitable atmospheric conditions, such as clear skies. With an automatic radiometric station, this site continuously collects atmospheric data and surface radiance measurements. These are then processed to ground spectral reflectance and provided with uncertainties to the RadCalNet processor which propagates values to TOA.

Due to the limitations of the instrument used for autonomous measurements, recent fieldwork has been carried out in this location to acquire additional hyperspectral data to maintain the quality of the site products. In addition, further site characterisation was conducted to prepare a best location for a new site nearby that is being developed under the HYPERNETS project. This paper presents both the RadCalNet site and the results of the recent fieldwork.
Advancing our understanding of novel nitrous oxide reducers
Authors: Shan Jun , Ooi Sean , Sanford Robert A , Chee-Sanford Joanne , Löffler Frank , Konstantinidis Kostas , Yang Wendy H.
Published: March 2020

Sources of N2O (nitrous oxide) are multiple in the biosphere, but the only known process consuming N2O is the microbial reduction of N2O to dinitrogen (N2), which has traditionally been attributed to denitrifying bacteria and archaea. Recently, N2O reductase genes (nosZ) clearly phylogenetically differentiated from “typical” NosZ (Clade I) were shown to be more abundant in many soil ecosystems than “typical” nosZ genes, suggesting that our understanding of the role of nosZ in controlling soil N2O emissions was incomplete. This more abundant group of nosZ genes was designated as “atypical NosZ” or Clade II.  Here, by synthesizing a meta-data of the 631 peer-reviewed papers published on NosZ in the six years since NosZ Clade II was first reported in the literature, we found that only 10% of studies evaluated Clade II NosZ and an additional 7% of papers merely mentioned Clade II NosZ showing little awareness of this novel gene. In addition, disciplinary silos also contribute to the slow spread of awareness about Clade II nosZ. A lack of consensus on the terminology used to refer to Clade I versus Clade II nosZ (more than 17 terminologies) may contribute to confusion about the two clades. Finally, we proposed several recommendations to accelerate progress in understanding the roles of Clade I versus Clade II N2O reducers in controlling soil N2O emissions.
Flexible Radio Array for Ionospheric and Atmospheric research (FRAIA)
Authors: Jorgensen Anders M. , Ngoc An , King Kyler , Lopez Willie , Mazarakis Alexander , Jungling Leviy , McHaley Wesley , Edick Delos , Sonnenfeld Richard
Published: March 2020

We present the Flexible Radio Array for Ionospheric and Atmospheric
research (FRAIA). FRAIA consists of 18 relocatable RF receiver
stations with the capability to receive in the VLF band (0-50 kHz),
the HF/VHF band (3-85 MHz), as well as at discrete beacon satellite
frequencies 150, 400, and 1067 MHz. The antennas are monopole for the
VLF reception, all-sky broad-band crossed dipoles for the HF/VHF band,
and co-centric all-sky quadrifilar antennas for the beacon satellite
bands. Each station contains a 8-core CPU and a high-end
software-defined radio for real-time sampling and processing of the RF
signals. Each station include GPS timing to 50 ns, and three
synchronization devices allows for the 18 stations to be used together
in a single phased array or up to three phased arrays. FRAIA stations
can be used for observing VLF whistler waves, receiving standard
VHF/UHF beacon satellite signals for ionospheric tomography, for
riometry, for lightning observations and lightning interferometry, as
ionosonde receivers, HF radar receivers, over-the-horizon radar
receivers, and receivers for a future HF beacon satellite which we
propose, for ionospheric tomography.
Seismotectonic analysis of the 2014 seismic swarm at the Western Corinth Gulf (Greece)
Authors: Serpetsidaki Anna , Sokos Efthimios , Lambotte Sophie , Bernard Pascal , Lyon-Caen Helene
Published: March 2020

The Corinth Rift (Greece) is one of the most seismically active regions in Europe and has been studied extensively during the past decades. It is characterized by normal faulting and extension rates between 6 and 15 mm yr−1 in an approximately N10E° direction. The seismicity of the area is continuously monitored by the stations of the Corinth Rift Laboratory Network (CRL Net). The availability of a dense permanent seismological network allows the extensive analysis of the seismic swarms which occur frequently. In this study, the September 2014 swarm located at the western part of the Corinth Gulf is analyzed. Initially, more than 4000 automatically located events, of a two month period, were relocated using the HYPODD algorithm, incorporating both catalogue and cross-correlation differential traveltimes. Consequently, the initial seismic cloud was separated into several smaller, densely concentrated clusters. Double difference relocation was also applied to 707 manually located events in order to investigate the Vp/Vs ratio variation, due to its sensitivity in pore fluids. The swarm’s parameters such as seismicity distribution and moment tensors were combined with the seismotectonic data of the area. The results indicate an initial activation of the Psathopyrgos normal fault; afterwards the seismicity extended both towards East and West, while most events occurred at the western part of the study area. The seismicity distribution revealed a main activation of the North – dipping faults. The seismicity migration with respect to pore pressure changes due to fluid movements was investigated through diffusivity calculations. The diffusivity value was found to be 4.5m2s-1, which is consistent with results of previous studies in the area. The results of the investigation of the fault- zone hydraulic behavior provide evidence for the fluid – triggered earthquake swarms and the related rock physical properties.
Using Swarm to study ionosphere-thermosphere coupling
Authors: Burchill Johnathan
Published: March 2020

Properties and dynamics of ionosphere-thermosphere coupling may be investigated using observations from the Swarm electric field instruments (EFI). We illustrate this claim using measurements of vertical ion drift and electron temperature made by the EFIs, within the context of ambipolar diffusion parallel to the geomagnetic field. The associated ambipolar electric field is difficult to measure directly. Rather, under conditions where the ambipolar electric field is assumed to be specified, the ion-neutral momentum transfer collision frequency may be derived from the EFI measurements. In this talk, the theory, measurements and methodology of this approach are presented. Statistical analysis reveals highly-correlated ion upflow and electron temperature. Derived collision frequencies are found to be within an order of magnitude of empirical estimates at Swarm altitudes. We speculate on the feasibility of using this technique to examine the dynamics of ionosphere-thermosphere coupling using Swarm.
TROPOMI Aerosol Index: detailed aerosol plume tracking and plans for future development
Authors: Stein Zweers Deborah , Sneep Maarten , Kooreman Maurits , Stammes Piet , Tilstra Gijsbert , Loots Erwin , Wagner Thomas
Published: March 2020

The aerosol index (AER_AI) as calculated using data from the Tropospheric Monitoring Instrument (TROPOMI) onboard the ESA Sentinel 5 Precursor (S5P) platform was publically released in July 2018. The operational AER_AI dataset is available from May 2018 through the present. It is a useful data product not only for tracking ultraviolet (UV) absorbing aerosol plumes of desert dust, volcanic ash, and smoke from biomass burning but also for monitoring the quality of the TROPOMI Level 1b (L1b) data since the AER_AI calculation is very sensitive to the absolute calibration of irradiance and radiance. The aim of this work is first to highlight the new level of detail seen in aerosol plume events based on the recent switch to a reduced pixel size of 3.5 x 5.5 km. Such high spatial resolution also presents specific challenges as non-Lambertian cloud features and 3-D effects of clouds are now visible in the TROPOMI AER_AI data. Plans for an approach to flag and correct these features in future AER_AI updates will be given. Secondly this work will include an overview of the impacts on AER_AI due to observed degradation in the TROPOMI measured irradiance and wavelength-dependent features in the radiance. As a result of these L1b effects, there is a steadily increasing negative bias in the global mean AER_AI value. Examples are given how the new version of the L1b data (2.0.0) will be used to correct for this degradation-driven bias. Recommendations are also given to guide data users looking to perform trend analysis or those using AER_AI as a filter for aerosol removal or detection in other L2 data products.  
Thermal modeling of the binary asteroid Didymos
Authors: Karatekin Özgür , Henry Gregoire , Gloesener Elodie , van Hove Bart
Published: March 2020

The target of the ESA’s HERA mission is asteroid 65803 Didymos (1996 GT), an Apollo-type near-Earth object (NEO). Didymos is a binary asteroid; the primary body has a diameter of around 775 m and a rotation period of 2.26 hours, whereas the secondary body (informally called Didymoon) has a diameter of around 165 m and rotates around the primary at a distance of around 1.2 km in around 12 hours.

Thermophysical properties of the uppermost surface govern the exchange of radiative energy between the asteroid and its environment, hence determine surface and subsurface temperatures.  These thermophysical properties are characterized by grain size, porosity, or packing of the surface materials.  Diurnal change in surface temperature show large variations in fine soils like sand and highly porous rock with low thermal inertia, and much smaller variations in in dense rock with high thermal inertia. Here we present a thermophysical model of Didymoon based on known, assumed and derived range of physical properties.  A parameter study has been carried out for surface temperatures assuming possible thermal inertia ranges.  

Results from this study are used to investigate performance for Thermal Infrared instrument TIRA onboard HERA spacecraft. Hera is the European contribution to an international double-spacecraft collaboration. Due to launch in 2024, Hera would travel to the binary asteroid system. TIRA onboard HERA will be operating in the 8-14 µm wavelength range. It will be used for scientific analysis and to demonstrate the feasibility of using a TIR camera for GNC (Guidance, navigation and control). The main scientific output for TIRA is to determine the thermal inertia and thus the properties of the surface material.
Impact of the regional runoff Nitrogen Flux using the GFDL-TOPAZ simulation on the Arctic Ocean phytoplankton.
Authors: Park Jung hyun , Kim Baek-min
Published: March 2020

Phytoplankton is closely related to the Arctic Amplification in a future caused by the biogeophysical feedback. In particular, the increase in nutrients, which is one of the limiting factors of phytoplankton, affected by the increased inflow of rivers due to the Arctic warming in the Arctic region. Since Arctic region is sensitive to the feedback, the biological feedback is still difficult to expect an accurate simulate in the modeling simulation. This study used the GFDL-TOPAZ model by prescribing a runoff nitrogen flux in the contemporary level to simulate the phytoplankton, then prescribing the nitrogen flux over the East Siberian-Chukchi Sea. The model results underestimate chlorophyll A concentration and nutrient compared to the ARAON ship observation. But, We showed that the experiment of prescribing a regional runoff nitrogen flux by the river is well simulatinges the chlorophyll A concentration and nutrients than the CTRL experiment. Also, a  model result showed that the sea ice concentration in the Chukchi-East Siberian Sea and Kara-Barents Sea decreased, and it suggests that the regional change of the nutrient could, directly and indirectly, affect that Arctic sea ice concentrations
Environmental parameters affecting composition of modern Mediterranean planktonic foraminifera assemblages
Authors: Azibeiro Lucía A. , Kucera Michal , Jonkers Lukas , Sierro Francisco J. , Cloke-Hayes Angela
Published: March 2020

La reconstrucción de la temperatura de la superficie del mar (TSM) ha estado durante mucho tiempo en el centro de la investigación paleoceanográfica. Los estudios en el Mediterráneo no han sido una excepción, ya que la reconstrucción cuantitativa de TSM en esta cuenca semicerrada es crucial para comprender el cambio climático pasado en la región. Muchos de estos métodos se basaron en foraminíferos planctónicos, tanto en su geoquímica de caparazón como en la composición de los ensamblajes (por ejemplo, funciones de transferencia). Comprender y modelar las relaciones entre el censo actual y las variables ambientales es la base para transformar los datos fósiles en estimaciones cuantitativas de estas variables. Aunque globalmente, los conjuntos de foraminíferos parecen estar determinados principalmente por la temperatura, en cuencas marginales como el Mediterráneo, 

In this study we attempt to determine which environmental parameters may control the variability of planktonic foraminifer assemblages in the modern Mediterranean. For this purpose, census counts of planktonic foraminifera assemblages from Mediterranean coretops (ForCenS data base) have been integrated with monthly estimates of SST, chlorophyll concentration, and vertical gradients of various parameters as proxies for water column stratification/mixing (WOA 1998).  Redundancy Analysis (RDA) was used to evaluating the explanatory power and the collinearity among tested environmental parameters and a forward selection of variables was carried out to identify those explaining independently the largest share of the variance in the composition of planktonic foraminifera assemblages.

Se identificaron nueve variables significativas. Tres de ellos corresponden a TSM, mientras que los otros seis se distribuyen entre las concentraciones de clorofila superficial (2) y los gradientes térmicos verticales (4). Las variables más explicativas son la TSM de junio (R 2 0.43) y el gradiente térmico vertical de diciembre (R 2 0.15).
Simulations of large climate transition occurring at high and low latitudes during the late Pliocene (3.3 Ma) and the Plio/Pleistocene (3-2.5 Ma) boundary
Authors: Tan Ning , Yule Emma , Ramstein Gilles , Barboni Doris , Raj Rani , Dumas Christophe
Published: March 2020

The late Pliocene corresponds to a large cooling over Northern Hemisphere associated with sporadic occurrences of glaciations. The most important event occurred during the marine isotope stage M2 (MIS M2, 3.312–3.264 Ma) when a large glaciation took place with a sea level drop from 20 to 60 m, but its duration is short and the summer insolation forcing change at 65°N is weak. De Schepper et al (2013) invoked to explain the onset and termination of this glaciation with the opening and closing of the Central American Seaway (shallow CAS). Based on their hypothesis, we have intensively studied the onset mechanism of  MIS M2 through a series of sensitivity experiments using the IPSL AOGCM and the asynchronous coupling with an Ice sheet model (GRISLI). Our results demonstrate that the shallow CAS helps to precondition the low-latitude oceanic circulation and affects the related northward energy transport, but cannot alone explain the onset of the M2 glaciation, the most important contribution on MIS M2 are from the large change of pCO2 as well as the internal feedbacks of vegetation and ice sheet. Moreover, we have also investigated the period from the late Pliocene to the early Pleistocene (3-2.5 Ma) through a transient-like simulation using the same AOGCM and ISM. This enables to simulate the Greenland Ice Sheet (GRIS) onset and development using the pCO2 reconstructions from different proxies. All these simulations were analyzed with emphasis on cryosphere and focused on the Northern Hemisphere (mid-to-high latitudes). Here we used the same modeling simulations but with a focus over the tropical Africa. We first depict the large changes of temperatures and hydrological cycle produced over this area during these two periods and compare our data to reconstructions. Moreover, by prescribing our climate results as inputs for the vegetation model (Biome4), we compare more directly the simulated plant functional types (PFTs) with that constructed by the pollen data. In addition, we further quantify the respective impact of various driving factors on these PFTs variations.
Climate displacement, humanitarian needs and Forecast-based financing
Authors: Thalheimer Lisa , Li Sihan , Simperingham Ezekiel , Jjemba Eddie , Otto Friederike
Published: March 2020

The forced displacement of individuals and communities as a result of extreme weather events and the impact of anthropogenic climate change has been described as one of the greatest humanitarian challenges of the 21st Century. A multi-sectoral approach is required to address the humanitarian dimensions of climate displacement. Approaches span initiatives to prevent or reduce the conditions that lead to displacement (for example, resilience and adaptation strategies); response to displacement (including access to essential humanitarian assistance); recovery initiatives that increase resilience and support for the attainment of sustainable solutions (return, local integration and resettlement). Within the discussions on the humanitarian dimension of climate displacement, there has been increasing recognition of the specific importance of preparedness initiatives. Practitioners like the Red Cross Red Crescent Climate Centre (RCCC), for instance, have been starting to apply tests of forecast-based financing (FbF) to inform short-term humanitarian assistance based on disaster warnings from scientific forecasts. This paper serves as an innovative contribution towards understanding how FbF can be used as an effective approach to prepare for or prevent climate-related forced displacement. Using a panel econometric analysis, this paper models climate-related forced migration movements and humanitarian needs in Somalia during recent compound drought events. The model results support the improvement of early warning systems in the region and more broadly, the inclusive development and provision of time-effective humanitarian aid to those displaced globally.
Boundary layer height determination from lidar for improving air pollution episode modeling: development of new algorithm and evaluation
Authors: Yang Ting , wang zifa , zhang wei , Gbaguidi Alex , Sugimoto Nobuo
Published: March 2020

Predicting air pollution events in the low atmosphere over megacities requires a thorough understanding of the tropospheric dynamics and chemical processes, involving, notably, continuous and accurate determination of the boundary layer height (BLH). Through intensive observations experimented over Beijing (China) and an exhaustive evaluation of existing algorithms applied to the BLH determination, persistent critical limitations are noticed, in particular during polluted episodes. Basically, under weak thermal convection with high aerosol loading, none of the retrieval algorithms is able to fully capture the diurnal cycle of the BLH due to insufficient vertical mixing of pollutants in the boundary layer associated with the impact of gravity waves on the tropospheric structure. Consequently, a new approach based on gravity wave theory (the cubic root gradient method: CRGM) is developed to overcome such weakness and accurately reproduce the fluctuations of the BLH under various atmospheric pollution conditions. Comprehensive evaluation of CRGM highlights its high performance in determining BLH from lidar. In comparison with the existing retrieval algorithms, CRGM potentially reduces related computational uncertainties and errors from BLH determination (strong increase of correlation coefficient from 0.44 to 0.91 and significant decreases of the root mean square error from 643 to 142 m). Such a newly developed technique is undoubtedly expected to contribute to improving the accuracy of air quality modeling and forecasting systems.
Flooding sedimentation at the Yellow River mouth, China
Authors: Yonggui Yu , Xuefa Shi , Bin Wu , Shuqing Qiao
Published: March 2020

Chinese Huanghe (Yellow River) provides an extreme case of human controlled large river system. Since 2002, a unique Water-Sediment Regulation （WSR） regime was implemented annually through Xiaolangdi Dam to buffer pool infilling and scour the hanging riverbed. This involves transfers of large-volume of water and sediment between reservoirs, becoming a human-made flooding event. 37 surface sediments 8 box cores sampled during the 2018 WSR were analyzed for grain-size, C/N, 13C, radionuclides, etc. Satellite images together with high-resolution bathymetric data were incorporated to depict the flooding sedimentation at the river mouth. The results show that 7Be and 210Pb activity is pretty low, implying its incapability of tracing flood sediments at the Huanghe River mouth. The results also uncover that a majority of the sediment was deposited in the vicinity of the river mouth where the water depth is less than 15 m. Two depocenters with a maximum thickness of 9 m were formed expanding within a very restricted area, which was largely controlled by tidal currents.
Uncertainty quantification during seismic oceanography inversion with start Temperature-Salinity models of different lateral resolutions
Authors: Xiao Wuxin , Sheen Katy , Tang Qunshu , Hobbs Richard , Shutler Jamie , Browse Jo
Published: March 2020

Seismic oceanography (SO) has been widely used on the inversion of physical oceanographic properties due to its higher lateral resolution up to 10m, compared to conventional oceanographic measurement methods. Normally, the inversion process requires seismic data and in-situ hydrographic data, and the latter is acquired by deploying XBTs/XCTDs. Recently, due to the advantage of providing quantifiable uncertainties of the inverted parameters, a Markov chain Monte Carlo (MCMC) algorithm has been used for the temperature and salinity inversion from SO data. Based on the MCMC inversion method, this study investigates the effect of the lateral density of XBT deployments on the resultant uncertainties of inverted temperature and salinity. We analysed the seismic data acquired in the Gulf of Cadiz (SW Iberia) in 2007 in the framework of the Geophysical Oceanography project. A nonlinear Temperature-Salinity relation is modelled using a Genetic Algorithm from CTD casts collected in the research area. Combining the temperature data from XBTs with the T-S relation, smoothed temperature and salinity prior distributions are derived. Then the posterior distributions of temperature and salinity are estimated using the prior information and the field reflectivity data. In this study, priors are changed by controlling the amount of XBTs used, after which the corresponding uncertainties of the inverted temperature and salinity are calculated. The result quantifies the impact of the prior models with different XBT deployment densities on the uncertainties of inverted results. It is proposed that the acquisition of a reasonable temperature starting model is the prior consideration when deciding the XBT deployment strategy along the seismic oceanography survey.
Determination of Snow Water Equivalent with only one Global Navigation Satellite System receiver and a Virtual Reference Station
Authors: Henkel Patrick , Lamm Markus , Koch Franziska
Published: March 2020

The snow water equivalent (SWE) is a key parameter in hydrology. In the past years, the signals of Global Navigation Satellite System (GNSS) receivers were discovered to be very attractive for SWE monitoring. The set-up of GNSS-based SWE monitoring typically consists of two GNSS receivers, whereas one is placed on the ground to sense the signal attenuation and time delay being caused by the snow pack. A second receiver is placed above the snow and serves as reference receiver. The measurements of both receivers are differenced to eliminate the common effect of errors in the satellite orbits and clocks, satellite phase and code biases and atmospheric errors, while the information on the snow is kept.

In this talk, we discuss the replacement of the reference receiver by a virtual reference station (VRS). The VRS is a virtual GNSS reference station, whose corrections are obtained by interpolation of the corrections from multiple surrounding reference stations to achieve a higher accuracy at the user location. The concept of VRS was first developed by Trimble and is widely used in today's real-time kinematic (RTK) positioning receivers. The concept of VRS is also attractive for snow monitoring, since the GNSS reference receiver could be avoided resulting in a lower power consumption and less costs. Moreover, this could be a big advantage for applications in slopes, which are, e.g., potentially avalanche prone. Within the hardware setup of our GNSS SWE sensors, an internet communication link for the reception of the corrections from the VRS corrections at the SWE monitoring site is already available.

However, there are also two challenges: First, the SWE monitoring stations in Alpine areas are typically at a significantly different altitude than the geodetic reference receivers. The differential tropospheric zenith delay is not negligible for altitudinal differences of more than 100 m. Therefore, the differential tropospheric delay needs to be considered either in the determination of VRS corrections or alternatively in the SWE determination. For altitudinal differences of less than 1000 m, the differential tropospheric zenith delay could be approximated by a model with sufficient accuracy. The residual modelling error is projected to the SWE estimate. Second, the use of a VRS instead of a conventional GNSS reference station requires a stronger data link, since the GNSS raw data (pseudoranges, carrier phases and carrier-to-noise power ratio measurements from all tracked satellites) need to be transmitted besides the final SWE results. However, an LTE link is totally sufficient.

Besides the methodology, we will also focus on specific hardware implementations.
Study on the Structural Characteristics of Martian Regolith by Ambient Noise Data from SEIS Observation
Authors: Xiao Wanbo , Wang Yanbin
Published: March 2020

For Earth and Moon, the seismic observation data is the most direct and effective means to detect their internal structure. However, due to the long distance between Mars and Earth and the harsh observation conditions on Mars, the exploration of Martian velocity structure model is a very challenging task. The InSight lander deployed the first seismic observation instrument SEIS (Seismic Experiment for Internal Structure) on the Mars’ surface after its successful landing on Mars on November 26, 2018. In this study, we performed horizontal-to-vertical spectral ratio (HVSR) and polarization analysis of three component VBB seismic waveforms recorded by the SEIS station released on the IRIS website. We are trying to constrain the thickness of the Martian regolith at the landing site of InSight from the SEIS data. The VBB ambient noise data we used are in HHV/HHU/HHW channels of ELYSE station in 30 Martian days. These data are predominantly ambient noise data caused by wind effects and do not contain any known marsquake data. We found that the HVSR curves from nearly all released data show two distinct peaks at 11.9 Hz and 24.5 Hz, respectively. Furthermore, we conducted particle motion and polarization analysis on these data in various frequency bands, which indicate that the ground motion at the highest peak show linearly polarized and vertically incident motion with a fixed azimuth. This could be explained by the S-wave resonance of the Martian regolith at the InSight landing site caused by the wave motion source from the wind induced motion of the lander. Using the possible S-wave velocity of the Martian regolith proposed by previous studies and the peak frequencies of the HVSR results in this study, thickness of the Martian regolith at the InSight landing site was obtained that is smaller than the pre-evaluated thickness (3~5 m) for the InSight mission.
Improving Stoneley-mode constraints on the structures near the core-mantle boundary
Authors: Matchette-Downes Harry , van der Hilst Robert D. , Ye Jingchen , Shi Jia , Han Jiayuan , de Hoop Maarten V.
Published: March 2020

Although observations of seismic normal modes provide constraints on the structure of the entire Earth, the core-mantle boundary region remains poorly understood. Stoneley modes should offer better constraints, because they are confined near to the fluid-solid interface, but this property also makes them difficult to detect. In this study, we use recently-developed finite-element approach to show that Stoneley modes can be excited and detected, but only in certain special cases. We first investigate the physical explanation for these cases. Next, we describe how they could be detected in seismic data, and the sensitivity of these data to the material properties. We illustrate this sensitivity by calculating the modes of a three-dimensional Earth model containing a large low-shear-velocity province (LLSVP). Finally, we present some preliminary observations. We hope that this new understanding will lead to new constraints on the material properties and morphology of the core-mantle boundary region. In turn, this information, especially the constraints on density, should help to answer questions about the Earth, for example in mantle convection (are LLSVPs thermally or chemically buoyant? Primordial or slab graveyards? Passive or active?) and core convection (does the outermost core have a stable stratification?).
Determation of the ionospheric observable and short-term variations of receiver DCBs using modified carrier‑to‑code leveling method with multi-frequency and multi-GNSS data
Authors: Li Min , Zhang Baocheng , Zhang Xiao
Published: March 2020

When sensing the Earth’s ionosphere using pseudorange observations of global navigation satellite systems (GNSS), the satellite and receiver Differential Code Biases (DCBs) account for one of the main sources of error. For the sake of convenience, Receiver DCBs (DCBs) are commonly assumed as constants over a period of one day in the traditional carrier-to-code leveling (CCL) method. Thus, remarkable intraday variability in the receiver DCBs have been ignored in the commonly-used assumption and may seriously restrict the accuracy of ionospheric observable retrieval. The Modified CCL (MCCL) method can eliminate the adverse impact of the short-term variations of RDCBs on the retrieval of ionospheric TEC. With the rapid development of the GPS, GLONASS, Galileo and BeiDou systems, there is a strong demand of precise ionospheric TEC products for multiple constellations and frequencies. Considering the existed MCCL method can only be used for dual-frequency GNSS data, in this study, we extend the two-frequency MCCL method to the multi-frequency and multi-GNSS case and further carry out a series of investigations. In our proposed method, a newly full-rank multi-frequency (more than triple frequency) model with raw observations are established to synchronously estimate both the slant ionospheric delays and the RCB offset with respect to the reference epoch at each individual frequency. Based on the test results, compared to the traditional CCL-method, the accuracy of the ionospheric TEC retrieved using our proposed method can be improved from 5.12 TECu to 0.95 TECu in the case that significant short-term variations existed in receiver DCBs. In addition, the between-epoch fluctuations experienced by receiver code biases at all frequencies tracked by a single receiver can be detected by our the proposed method, and the dependence of multi-GNSS and multi-frequency RDCB offsets upon ambient temperature further are verified in this study. Compared to Galileo system, the RDCB in BDS show higher correlation with temperature. We also found that the RDCB at different frequencies of the same system show various characteristics.