bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Bayesian analysis of stellar occultation by small solar system bodies
Authors: Leiva Rodrigo
Published: September 2022

A stellar occultation occurs when an object (an asteroid, trans-Neptunian object, Centaur) passes in front of a distant star, blocking its light momentarily. The occultation technique allows deriving accurate positions, sizes, and shapes of small solar system objects. The accuracy of the predicted path of the occultation shadow has improved significantly in the last decade, increasing the number of viable targets for study via stellar occultations. The improvement is due mainly to the availability of an accurate astrometric catalog provided by the Gaia mission. In practice, the primary source of uncertainty in the predictions is the uncertainty in the occulting object ephemerides.

The analysis of stellar occultation measurements can be challenging in cases where there is photometry with a low signal-to-noise ratio, a short duration of the event, low temporal or spatial sampling, or a combination of those. Also, we need to account for cases with multiple occulting objects, and multiple occulted stars or combined detection of the same objects at different epochs. In these cases, we can have model parameters with significantly correlated uncertainties and where it is not trivial to discriminate between different models, requiring a rigorous quantitative approach. Last but not less, we need to account for the influence of the model a priori assumptions on the derived parameter values and uncertainties.

Bayesian statistics allow for analysis of these challenging cases, providing posterior probabilities for the object(s) size, shape, and orientation parameters and quantitative comparison of different possible models.

I have adopted a Bayesian approach for analyzing occultations measurements, including multi-epoch detections, single and multi-station detections, single and double objects, and occulting single and double stars.

I will present the application of the approach to the analysis of stellar occultation by Trans-Neptunian objects and Centaurs, exemplified by interesting cases from different projects and collaborations, both published or in the process of publication, including the ringed Centaur (10199) Chariklo, the extreme TNO (541132) Leleākūhonua, the small Centaurs 2014 YY49 and (591376) 2013 NL24, the binary TNO (523764) 2014 WC510, and the retrograde Centaur (342842) 2008 YB3 [1, 2, 3, 4].

 

References:

1. Strauss, Leiva, Buie et al. 2021. PSJ, 2, 1, 22.

2. Leiva, Buie, Keller et al. 2020. PSJ, 1, 2.

3. Buie, Leiva, Keller et al. 2020. AJ 159, 5.

4. Leiva, Sicardy, Camargo et al. 2017. AJ 154, 4.
Multi-instrument/Spacecraft observations of Mars upper Atmosphere Electron density
Authors: Karatekin Özgür , Krishnan Ananya , Verkercke Sebastien , Henry Gregoire , Sánchez-Cano Beatriz , Witasse Olivier
Published: September 2022

Electron density structure and its temporal/spatial variations is one of the critical quantities in understanding an upper atmosphere. Mars has currently several orbiters studying its upper atmosphere and in particular electron density profiles.  The Mars Express (MEX), in the orbit since 2003 has been measuring Mars upper atmosphere through remote measurements by the MARSIS (Sub-Surface Sounding Radar Altimeter) sounder and radio occultations by MaRS (Radio Science Experiment - sounding of the internal structure, atmosphere and environment). The Mars Atmosphere and Volatile EvolutioN,  MAVEN mission  whose science objectives include exploration of the interactions of the Sun and the solar wind with the Mars magnetosphere and upper atmosphere has  complete plasma package. Maven has been performing in-situ composition measurements since November 2014, in particular, the Langmuir Probe and Waves  (LPW) instrument onboard MAVEN provide electron density using current-voltage sweeps.

Here we  present the comparison of multi-instrument spacecraft measurements of Mars upper atmosphere for selected dates, using remote sensing (MEX) and in-situ measurements (MAVEN).  The mutual observations are selected from publicly available data on ESA Planetary Science Archive as well as MAVEN Science Data Center. The L2 level Radio Occultation data are analyzed to obtain the Mars upper Atmosphere Electron density profiles. The MARSIS and LPW provide top side electron profiles whereas Radio occultations provide the full electron density profile. We focuse on the photochemical equilibrium region of the Martian ionosphere–thermosphere  below 200 km. The analysis  also includesz the  Deep Dip  campaigns of MAVEN making in-situ measurements of the region near the ionospheric peak.

The comparison of independent measurements using different techniques will be presented and the differences and similarities between the observations will be discussed to help to validate our understanding of the physical and chemical processes occurring in the atmosphere.

Figure 1: Comparison of MEX Radio Occultations (RO) with the MAVEN Langmuir Probe and Waves (LPW) for 3 selected mutual observation in March 2015
Characterization of the Martian mesosphere with NOMAD/TGO observations and a Global Climate Model
Authors: González-Galindo Francisco , López-Valverde Miguel Ángel , Brines Adrián , Modak Ashimananda , Stolzenbach Aurélien , Funke Bernd , López-Moreno José Juan , Forget Francois , Millour Ehouarn , Lefèvre Franck , Vals Margaux , Montmessin Franck , Patel Manish , Bellucci Giancarlo , Vandaele Ann-Carine
Published: September 2022

The Martian mesosphere, and in particular the upper mesosphere, above about 80 km from the surface, remains poorly explored in comparison with the troposphere and the thermosphere/ionosphere. Observations by the NOMAD and ACS instruments on board the ExoMars Trace Gas Orbiter mission (TGO in what follows) are starting to fill this gap by providing measurements such as the abundance of mesospheric water and the effects of global dust storms (Vandaele et al., 2019; Belyaev et al., 2021; Brines et al., 2022), the CO variability (Modak et al., 2022) or the temperature and density structure (López-Valverde et al., 2022). For the first time we have a set of diverse atmospheric parameters derived simultaneously with good vertical resolution and from a single instrument, which is ideal for model validation purposes.

In this work, we will compare the predictions of the LMD-Mars GCM (LMD-MGCM) in the mesosphere with the NOMAD results (abundances of CO2, CO, and H2O, as well as temperature) obtained by the retrieval scheme developed at the Instituto de Astrofisica de Andalucia-CSIC (IAA), in order to validate the model and to gain insight into the physical processes at the origin of the observed structures. In particular, we will focus on the comparison of the CO2 density and temperature structure observed below ~120 km (López-Valverde et al., 2022) during the second half of Mars Year 34, a period including the MY34 global dust storm. We will show that the model reproduces well the strong seasonal variations of the CO2 density observed by NOMAD. However, the model tends to overestimate the temperatures above ~50 km.

Acknowledgments

F.G-G. is funded by the Spanish Ministerio de Ciencia, Innovación y Universidades, the Agencia Estatal de Investigación and EC FEDER funds under project RTI2018-100920-J-I00. MALV, AB, AM, and AS were supported by grant PGC2018-101836-B-100 (MCIU/AEI/FEDER, EU). The IAA team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa" award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709)
MAVEN Observations of a State-Transition in Ion Escape from Mars
Authors: Ramstad Robin , Brain David , McFadden James , Mitchell David , Andersson Laila , Espley Jared , Halekas Jasper , Holmström Mats , Curry Shannon
Published: September 2022

Fundamentally, what limits the rate of atmospheric ion escape from non-magnetized planets? Previous orbit-based in situ measurements of escaping heavy ions (O+, O2+ and heavier species) at Mars have yielded conflicting estimates of the dependencies on upstream solar wind and solar extreme ultraviolet (EUV) conditions. We compile 7 years (2014-2021) of measured 0.1 eV – 30 keV ion distributions from the STATIC instrument on the MAVEN orbiter to globally map the phase-space ion flux distribution, from which we derive globally integrated outflow, inflow, and net ion fluxes. Through binning the measurements by upstream solar wind (measured simultaneously by the Mars Express orbiter) and EUV conditions, we separately quantify the O+ and O2+ escape dependencies on these external drivers. The found trends indicate that ion escape from Mars is a supply/source-limited process under low solar EUV conditions, however, the appearance and increase of gravitationally bound heavy ion return flows under moderate EUV conditions suggests that the escape process can transition to a Venus-like energy-limited state. The findings show that the state of the ion escape process does not only differ between planets, but the state and thus the drivers of ion escape can also differ under varying external conditions. We discuss the implications for ion observations at Mars during the upcoming solar activity maximum, for the evolution of the Martian atmosphere, and for our understanding of atmospheric ion escape as a general process in the solar system and beyond.
Onwards to Europa: Results from the final ground calibration of the MASPEX-Europa flight instrument
Authors: Miller Kelly , Miller Greg , Waite Hunter , Brockwell Tim , Franke Kurt , Hoeper Paul , Perryman Rebecca , Glein Christopher , Burch Jim ,   MASPEX science and engineering teams
Published: September 2022

The MAss Spectrometer for Planetary EXploration (MASPEX) instrument is a multi-bounce time-of-flight mass spectrometer designed for high mass resolution and sensitivity. MASPEX-Europa will launch as part of the Europa Clipper mission payload in October 2024 to characterize the composition of major, minor, and trace neutral gases in Europa’s exosphere and potential plumes. The instrument has been designed to optimize measurement of complex natural environments with:

Variable mass resolution to support compositional reconnaissance with simultaneous measurement of ions from 2 u to 500 u at separation of unit masses, as well as focused analysis with mass resolution capable of separating CHN- and CHO-bearing organics over a more narrow mass range

Nearly 100% duty cycle via storage of ions in the source between extraction pulses

Exact mass identification via measurement in flight of the FC-43 calibrant gas

Measurement of trace compounds via enhancement of abundance with the cryocooler

Automated switching triggered in flight between “regular” and “ice grain” measurement parameters for optimization of data collection

These adaptations make MASPEX especially well-suited for data collection in a dynamic environment where measurement speed is important. The capability to provide both general and highly specific data on the composition of volatile and organic mixtures makes MASPEX very powerful to quantify habitability via geochemical indicators, and to search for the first, perhaps tentative signs of life beyond Earth via measurements of agnostic biosignatures such as isotopic ratios.

In this presentation, we will provide results from the final calibration and performance characterization of the MASPEX-Europa flight model instrument completed in summer 2022. We will also present the science that will be enabled for Europa Clipper, and how new scientific and technical innovations will allow MASPEX to open more windows into planetary evolution, cosmochemistry, and astrobiology for future missions.
Two-body interactions with surface integrals
Authors: Wold Margrethe , Ho Alex , Poursina Mohammad , Conway John
Published: September 2022

Two-body interactions between extended, non-spherical bodies can be challenging to compute.
In the most general case, a full three-dimensional treatment requires a sextuple integral
to be solved because a volume integration is carried out over both bodies
(a double volume integral). This is computationally intensive, and approximations and
simplifications are normally done at the cost of accuracy. Here, we are presenting a new model
for computing forces, torques and the mutual gravitational potential
between two bodies with ellipsoidal shapes. The model allows for an exact solution of the
full rigid two-body problem using surface integrals, and is therefore more efficient than
computing volume integrals, as the double volume integral is reduced to a double surface integral.
Compared to more commonly used methods where the mutual potential is expanded in a
series and truncated at e.g. the 2nd or 4th order and hence suffer from truncation errors,
our method is exact and can also be used for bodies in close proximity.

We argue that the model is particularly applicable for closely interacting
asteroids that can be approximated by ellipsoids, such as binary systems, or for studying the dynamical
evolution of asteroids directly after a rotational fission event.

In particular, we show results from some simulations of binary systems formed via rotationial fission of
contact binaries. Asteroid binaries among Near-Earth Objects are believed to have formed by
rotational fission, and we simulate several cases with varying initial conditions
where the components have different shapes and densities. More than 80 per cent
of the simulations end with the two bodies impacting, and collisions between the
bodies are more common when the density of the secondary is lower, or when it becomes more elongated.
When comparing with data on asteroid pairs from Pravec et al. (2019) we
find that variations in density and shape of the secondary can account for some of the spread
seen in the rotation period for observed pairs.

Since our model allows for accurate calculations of the force and torque between two rigid, ellipsoidal
bodies, we make a comparison with models from the literature that uses 2nd and 4th order
approximations of the mutual potential. This allows us to point out which configurations between two asteroids
that will result in significant errors both in the force and torque when using truncated potentials.
Features and Trends Identified in Observations at Mars and Comets
Authors: Andersson Laila , Madanian Hadi , Schwartz Steven , Andrews David
Published: September 2022

Mars has surface crustal fields but no intrinsic magnetic field. A dense ionosphere exists at Mars where the solar wind interaction can drive an induced magnetic field to develop. The atmosphere of Mars often extends far into the solar wind. Newly-ionized particles then mass load the solar wind. Comets instead have no intrinsic or surface magnetic field and the ionosphere is generally not thick enough to develop a significant induced magnetic field around the comet. However, it has a highly variable atmosphere reaching far out in to the solar wind suggesting the solar wind interaction should be similar in some respects to that at Mars. This presentation postulates some similarities in the details of the solar wind interaction with these two objects, and the consequences in the ionosphere of extended mass loading of the solar wind under varying driving conditions. The motivation for these ideas are from recent observations made by the NASA MAVEN and the ESA ROSETTA missions, both of which show periodic trains of large amplitude features in the magnetic field and corresponding kinetic plasma structures.
Closed Fluxtubes and Proton Conics in Jupiter’s Polar Cap
Authors: Szalay Jamey , Clark George , Livadiotis George , McComas David , Mitchell Don , Rankin Jamie , Sulaiman Ali , Allegrini Frederic , Bagenal Fran , Ebert Rob , Gladstone Randy , Kurth Bill , Mauk Barry , Valek Phil , Wilson Rob , Bolton Scott
Published: September 2022

We present a discrete observation of diverse plasma populations and evidence of closed magnetic topology at Jupiter’s polar cap. Two distinct populations of protons are observed over Jupiter’s southern polar cap: a ~1 keV core population and ~1-300 keV dispersive conic population at 6-7 Jovian radii planetocentric distance. We find the 1 keV core protons are likely the seed population for the higher-energy dispersive conics. Transient wave-particle heating in a “pressure-cooker” process is likely responsible for this proton acceleration. The plasma characteristics and composition during this period show Jupiter's polar-most field lines can be topologically closed, with conjugate magnetic footpoints connected to both hemispheres. Finally, these observations demonstrate energetic protons can be accelerated into Jupiter's magnetotail via wave-particle coupling.
An Angular Momentum Approach to the study of the Cassini States of large triaxial icy satellites in synchronous rotation 
Authors: Coyette Alexis , Baland Rose-Marie , Tim Van Hoolst
Published: September 2022

The large icy satellites are thought to be in a Cassini State, an equilibrium rotation state characterized by a synchronous rotation rate and a precession rate of the rotation axis equal to the precession rate of the normal to the orbit. In such states, the spin axis of the satellite, the normal to its orbit and the normal to the inertial plane remain coplanar and the angle between the spin axis and the normal to its orbit, also called the obliquity. For a rigid body, up to 4 Cassini States exist, characterized by an obliquity close to 0 (Cassini State I), π/2 (Cassini State II), π (Cassini State III) and -π/2 (Cassini State IV). However, only the Cassini States I and IV are stable.

In the Cassini State, the obliquity remains almost constant over time. As the gravitational torque exerted on the satellite shows small periodic variations, the orientation of the rotation axis also varies with time, resulting in periodic nutations in obliquity.

Even if the Galilean Moons are thought to be characterized by an obliquity close to 0, it is possible that other satellites in synchronous rotation (in our Solar System or elsewhere in the Universe) occupy another Cassini State. We investigate the influence of the triaxiality and of the presence of a subsurface ocean on the obliquity (close to 0 or close to π)  of the Galilean Moons and of Titan.

In the early 30s, the ESA JUICE (Jupiter Icy moons Explorer) mission will measure the rotation of Ganymede and Callisto. We therefore focus on this period of time to determine if future observations of the obliquity of these satellites, and of their nutations, could constrain their interior structure.
 Impact-induced transformation of simple aromatic compounds in planetary atmospheres
Authors: Petera Lukáš , Knížek Antonín
Published: September 2022

Asteroids and comets are often rich in polyaromatic hydrocarbons (PAHs), which represent in general about 30 % of total carbon in space. The fate of these molecules in extraterrestrial delivery was investigated by experimentally simulating asteroid impacts – using laser induced breakdown (LIBD) – into rocky planetary atmospheres and surfaces. Experiments were performed with benzene, naphtalene and anthracene as simple members of PAHs. The effect of LIBD on chemistry of these compounds in various chemical environments, such as atmospheric composition and solid phase matrices, were also studied. The main gas phase products are acetylene and HCN, followed by CO and CO2, whose yields mainly depend on the content of water vapour in the atmosphere. A brownish solid product was also observed. Therefore, simple aromatic compounds, and likely also PAHs, can be a viable source of HCN – molecule with significant prebiotic importance– in planetary environments.

 
A 2-dimensional model of the Jovian circumplanetary disk
Authors: Schneeberger Antoine , Mousis Olivier , Cavalié Thibault , Lunine Jonathan
Published: September 2022

At the very end of its growth, Jupiter became surrounded by a circumplanetary disk (CPD) in which the Galilean moons formed.  How these moons formed remains an outstanding question. We aim to model the chemical evolution of this CPD to establish a connection between the moons’ surface compositions measured by the Juice and Europa-Clipper spacecrafts to disentangle between the existing formation scenarios. To do, so we develop a 2D circum-planetary disk model, designed to form the backbone of the chemical model that will follow the gas phase evolution of all species of interest. Our disk structure is based on the work Heller et al (2015) [1], with some key improvements at the level of the description of the opacity. Our disk’s parameters have also been scaled to those observed recently in the CPD around the exoplanet PDS70c.  Here we present the CPD structure and display some preliminary results regarding the chemical evolution of C- and N- dominated species in the gas phase of the CPD.

 

[1] Heller, R. & Pudritz, R. 2015, ApJ, 806, 181.
Enabling participation in exoplanet research with open source tools 
Authors: Tsiaras Angelos
Published: September 2022

The field of exoplanets is one of the most rapidly growing, with more than 5000 planets discovered to date. Follow-up observations of Exoplanets is one of the few fields of astronomy that small telescopes can still contribute to ongoing research. In fact, observations with small and medium scale telescopes are becoming more and more popular among amateur astronomers, students and early career scientists as they do not require sophisticated instrumentation. However, an important barrier between observing and producing scientifically valid results is the data analysis and modelling. To assist observers towards this aspect and make it possible for more people to contribute to scientific research I have developed a series of open-source pieces of software that support the work of inexperienced observers. In my presentation I will talk about the importance and the impact of open-source software and I will also present HOPS, a python-based package which includes a user interface and it is compatible with Linux, OS X and Windows. HOPS is designed to analyse data from small and medium class telescopes. HOPS is a user-friendly package where graphic representations, statistics and models are brought together into a single package. With these characteristics, HOPS can be used by amateur astronomers individually or as part of citizen science projects or as an educational for university or school students.
Minor species in the Venus mesosphere from SOIR on board Venus Express: detection and upper limit profiles of H2CO, O3, NH3, HCN, N2O, NO2, and HO2
Authors: Mahieux Arnaud , Robert Séverine , Mills Frank , Trompet Loïc , Aoki Shohei , Piccialli Arianna , Jessup Kandis Lea , Vandaele Ann Carine
Published: September 2022

We report on detection and upper-limit of H2CO, O3, NH3, HCN, N2O, NO2, and HO2 above the cloud deck using the SOIR instrument on-board Venus Express.

The SOIR instrument performs solar occultation measurements in the IR region (2.2 - 4.3 µm) at a resolution of 0.12 cm-1, the highest of all instruments on board Venus Express. It combines an echelle spectrometer and an AOTF (Acousto-Optical Tunable Filter) for the order selection. SOIR performed more than 1500 solar occultation measurements leading to about two millions spectra.

The wavelength range probed by SOIR allows a detailed chemical inventory of the Venus atmosphere at the terminator in the mesosphere, with an emphasis on vertical distribution of the gases.

In this work, we report detections in the mesosphere, between 60 and 100 km.

Implications for the mesospheric chemistry will also be addressed.
The core flow induced by Mercury’s libration: density stratification and magnetic fields 
Authors: Seuren Fleur , Rekier Jérémy , Triana Santiago Andrés , Van Hoolst Tim
Published: September 2022

Since the era of Messenger, many observational constraints on Mercury’s thermal evolution and magnetic field have strengthened the idea that the outermost layer of Mercury’s fluid core is stably stratified. The presence of such a stably stratified zone can significantly alter the core flow compared to the flow in a completely homogeneous fluid core. This is on the one hand because stratified layers can impede fluid motions that are parallel to the density gradient, which in the case of Mercury would mean that radial flows are strongly suppressed. On the other hand this is because a stably stratified layer can support different types of waves that are affected by the buoyancy force.

In this study we have created a numerical model to investigate flow in Mercury’s fluid outer core that includes a radial background stratification. The exact structure of the density profile in the planet’s core is unknown, and we assume profiles based on recent findings of the interior evolution of the planet. We studied core flow that is excited by Mercury’s librations, oscillations of the mean rotation rate due to the solar gravitational torque acting on Mercury’s triaxial shape. Based on the work by Rekier et. al. (2019) we represent the librational forcing by the superposition of three different decoupled motions: a horizontal component, which represents the viscous drag of the core fluid by the librating mantle and spherical inner core, and two radial components that are representing the radial push that the core flow would experience due to the librating triaxial boundaries.

We show that especially the second component has a profound effect, inducing a large non-axisymmetric flow close to the core-mantle boundary. It turns out that even though the origin of said flow is radial, the horizontal component of the flow is far larger than it’s radial counterpart. This indicates that the stratified layer acts to convert radial motions into strong horizontal motions.

We show how the strength and existence of this flow depend on the strength of the stratification of the layer and discuss implications of this flow for the magnetic field.

References:

Rekier, J., Trinh, A., Triana, S. A., & Dehant, V. (2019). Internal energy dissipation in Enceladus's subsurface ocean from tides and libration and the role of inertial waves. Journal of Geophysical Research: Planets, 124, 2198–2212. https://doi.org/10.1029/2019JE005988
Exoplanet observations: amateur experience from the Europlanet Telescope network
Authors: Libotte Florence , Correa Mercè
Published: September 2022

I this talk I will present the process to get observations on a Europlanet network telescope for an exoplanet transit.  The steps of obtaining and also analysing the exoplanet transit light curve will be described. These data are used for the future Ariel space mission organised by ESA. Moreover,  the talk will describe the process of writing the proposal for the request of the observation and in the particular case to the Instituto de Astrofísica de Canarias. In parallel, I will explain the way to obtain the funding for the telescope cost by Europlanet organization. Then I will go through the observations themselves and the live decisions regarding signal to noise, exposure time and so on in order to maximize the success probability. Then a report regarding the progress of the observation(s) is written and sent to the organisers. After the part of obtaining the observation, I will describe he process of analysing the images with the ExoClock HOPS software. Details will be provided on how to work with it, how to choose comparison stars, how to get the best light curve and to determine the exact moments of the ingress of the transit and the egress of it. Once the light curve is produced, it is uploaded in the ExoClock website and after reviewing it gets published at the ExoClock database. I would like to highlight that main partners in this work are two women, what is not so common in this field.
A Low-Cost Sensor Network System for Reliable Small Stream Monitoring
Authors: Post Christopher , Mayyan Mohammad , Merritt Jackson , Cook Chuck , Sammeta Dharan , Isaac Angel , Modi Vandini , Minerva Paul , Mikhailova Elena
Published: September 2022

Resilient monitoring of streams with dense sense sensor networks requires a system that manages and monitors everything from sensor node deployment through data collection, deployed equipment health, data quality analysis, and visualization.  The Clemson University Intelligent River® project has developed a range of technologies to monitor water in small urban streams and beyond using internet-connected devices that can stream data in near real-time. By leveraging the latest Internet of Things (IoT) advances, these sensor systems can increase the density of water measurements in both the waterways and connected stormwater pipes to help monitor the storm and drought response of these streams to help understand their function. These Intelligent River® sensor nodes have the added advantage of being able to interface into the latest sensor technologies as they are developed and to the best-in-class commercial water sensors. Spatially-dense measurements of water quantity and quality utilizing newly developed Intelligent River® real-time monitoring technology includes integrated low-cost sensors, embedded computers, and metadata management and visualization system. These technologies have the potential to significantly improve how water can be monitored in a range of situations and environments (e.g., river water monitoring and modeling and well water level). The recent advances in cellular Internet-of-Things (IoT) and Low Power Wide Area Network (LPWAN) technologies have increased the communication range and optimized the operating time for the wireless sensor network nodes. We will discuss a low-cost IoT system with near real-time hydrologic reporting using a sensor network of power-optimized embedded computers linked to a cloud-based back end system that serves as a data repository and interfaces to commercial IoT platforms for machine-learning-based anomaly and event detection. The designed sensor network is an end-to-end power-efficient system capable of adaptive sensing, remote data-logging which uses either LoRaWAN or low-power LTE cellular networks to send observations to a cloud-based data repository. We will discuss the design installation, and data results for deployments that measure stream level, flow, and water quality.  Overall network and data reliability is examined through data analysis of over a year of system deployment.
An enhanced meteorological ensemble postprocessing scheme for improving the prediction of extreme rainfall events 
Authors: Zhang Yu , Ghazvinian Mohammadvaghef , Seo Dong-Jun
Published: September 2022

Suppression of large precipitation amounts in the forecasts of  heavy-to-extreme events has been a critical limitation of contemporary postprocessing schemes. To tackle this limitation, we investigate a statistical postprocessing scheme that explicitly accounts for the Type-II conditional bias in establishing the predictand-predictor relationship.  This scheme is a variant of Mixed-type Meta-Gaussian Distribution (MMGD) that relies on Conditional Bias Penalizing Regression (CBPR), rather than simple linear regression to relate precipitation forecast and observations.  To assess the effectiveness of this scheme, we perform a set of hindcast experiments wherein both CBPR and MMGD are applied to the Global Ensemble Forecast System (GEFS) to create probabilistic quantitative precipitation forecasts (PQPFs) over subbasins of three major river basins in California, namely the American, Russian, and Elk River Basins. These experiments broadly confirm that CBPR scheme is capable of producing PQPFs that are both better calibrated and less biased (in Type-II sense) than the baseline from MMGD.  Potential regionalization approach for determining the weight parameter a priori is discussed.
Impact of bias-corrected RCM lateral boundary conditions on precipitation extremes
Authors: Kim Youngil , Evans Jason , Sharma Ashish
Published: September 2022

Hydro-climatological applications often require global climate models (GCMs) outputs to assess the impacts of climate change. However, it is well known that the direct use of GCM simulations is limited as their spatial and temporal resolution are insufficient to provide output at the regional scale required in assessing changes in extreme rainfall. Although regional climate models (RCMs) forced with GCM data are widely used to resolve finer resolutions, their application is hindered by systematic biases contained in large-scale circulation patterns from driving GCM data. To deal with these considerable biases, recent studies have suggested the bias correction of the input boundary conditions of RCM.

This study focuses on the impact of bias corrections in the input boundary conditions of RCM on extreme rainfall events. Three bias correction methods are used: mean, mean and variance, and nested bias correction (NBC) that corrects lag-1 autocorrelations. RCM used here is the Weather Research and Forecasting model (WRF), and the European Center for Medium-Range Weather Forecast’s (ECMWF) ERA-Interim (ERA-I) reanalysis model is used as an “observational” reference for bias correction. The downscaling is performed over the Australasian Coordinated Regional Climate Downscaling Experiment (CORDEX) domain.

Two quantitative measures are used to evaluate the impact of bias correction on the RCM output: root-mean-square errors (RMSE) and bias. Indices from the World Meteorological Organization (WMO) Expert Team on Climate Risk and Sectoral Climate Indicators (ET-CRSCI) are used to evaluate bias correction performance on extreme rainfall.

It is clear from the statistics used here that bias correction on the input boundary condition produces a noticeable improvement in daily precipitation percentile indices. The results also show that the sophisticated method representing rainfall variability and long-term persistence corrects details in simulating extreme rainfall.
Statistical model for compound flood hazard to separate local and upstream flow inputs on the Niger River at Niamey
Authors: Sauzedde Elisa , Vischel Théo , Panthou Geremy , Tarchiani Vieri , Massazza Giovanni
Published: September 2022

In recent years, West Africa has experienced an increasing number of flood disasters, urging governments and decision makers to take adaptation measures, particularly in cities where the population is growing very fast.

The present study focuses on the hydrological hazard of the city of Niamey (capital of Niger) along the Niger River. The regime of the Niger river at Niamey is marked by two successive floods: a first flood (July-August) resulting from the contributions of local Sahelian catchment (Sahelian red flood) and a second flood (February-March) resulting from the contribution of upstream catchments (Guinean black flood). Past studies have shown how the 1st flood, which was almost non-existent in the 1950s and 1960s, has predominated since the 1980s causing the most damaging floods due to a combined effect of climate and land use/cover changes. However, there is no in-depth study on statistical flood modelling, which is an essential step in any flood management strategy. The aim of the study is to evaluate how Niger discharge regime has changed since the 1950s with a specific focus on floods with the aim of deciphering the impact of Guinean and local flows in a statistical model.

To do so, an original method is first proposed to isolate local flows from Guinean flows in the Niamey discharge data series. This separation allows us to distinguish three typologies of maximum annual floods according to whether they are generated by Guinean flows only, local flows only or a mix of the two. This observation leads us to propose different models of extreme discharge in Niamey based on the non-stationary extreme value theory able to consider both the typology of the floods and their temporal evolution.
Influence of risk perception on the impacts of multiple hydrological extremes
Authors: Mazzoleni Maurizio , Mondino Elena , Barendrecht Marlies , Matanó Alessia , Van Loon Anne
Published: September 2022

A variety of socio-hydrological models have been proposed to represent the complex dynamics generated by the interplays between the society and hydroclimatic extremes. Yet, it is still unclear how different adaptation actions and risk perceptions can influence the impacts of multiple extremes over time. Here we present a new system-dynamics model to simulate the interplay between water management, droughts, floods, and society. The model accounts for four stylized types of societies based on idealized scenarios of risk perception and management responses: risk neglecting, risk controlling, risk downplaying, and risk monitoring. We perform two synthetic experiments to investigate the importance of risk-aversion, drought and flood awareness, and the co-existence of communities with different risk behaviors on the drought and flood losses. Our findings show that participatory approaches aimed at increasing societal awareness and preparedness can trigger adaptation actions for specific hydrological extremes, which in turn can exacerbate the impact of opposite natural hazards. Higher drought and flood losses are found when considering multiple co-existing risk behaviors. Our study emphasizes the importance of including the interplays between different risk perception behaviors and the occurrence of multiple hydroclimatic extremes in current modeling frameworks for improving water risk management strategies.
Performance-based weighting of CORDEX projections of hydrological climate change impacts over Europe
Authors: Sperna Weiland Frederiek , Visser Robrecht , Greve Peter , Bisselink Berny , Brunner Lukas , Weerts Albrecht
Published: September 2022

Climate change will influence the severity and intensity of floods and droughts throughout Europe. Ensemble projections of future changes in discharge show large variation. Several methods for performance-based weighting exist that have the potential to increase the robustness of the change signal. Here we use future projections of an ensemble of three hydrological models forced with climate datasets from the Coordinated Downscaling Experiment - European Domain (EURO-CORDEX). The experiment is set-up for nine river basins spread over Europe that hold different climate and catchment characteristics. We evaluate the ensemble consistency and apply two weighting approaches; (1) the Climate model Weighting by Independence and Performance (ClimWIP) that focuses on meteorological variables and (2) the Reliability Ensemble Averaging (REA) that is in our study applied to discharge statistics per basin. For droughts we focus on the change in discharge during low flow periods of 7-days.

For basins with a strong climate signal, in Southern and Northern Europe, the consistency in the set of projections is large. For rivers in Central Europe the differences between models become more pronounced. Both weighting methods favor projections from similar GCMs and assign high weights to a single or few best performing GCMs. The ClimWIP method results in ensemble mean weighted changes that differ only slightly from the non-weighted mean. The REA method influences the weighted mean more. The weights assigned to the CORDEX model simulations based on basin specific discharges highly vary from basin to basin.
A process-based multisite multivariate stochastic weather generator for water resources management
Authors: Výleta Roman , Valent Peter , Szolgay Ján
Published: September 2022

When solving practical water resources management problems, situations when the amount of data is insufficient both terms of length and representativeness occur. Even the most extended observed series are short for reliable estimation and assessment long-term variability and extremes. A combination of stochastic weather generators, allowing the generation of arbitrarily long synthetic series of precipitation and air temperatures, and rainfall-runoff models, which transform them into an equally long synthetic series of river discharges, represent a feasible solution. This study aimed to develop a robust, practically oriented stochastic weather generator for rainfall-runoff modelling allowing the simulation of synthetic daily precipitation and air temperature series at multiple stations in catchments, considering seasonality, temporal dependency and spatial correlation. The design was based partly on the established methodological practices. In addition, it implements innovative components of temporal ad spatial multiscale disaggregation based process-oriented analysis of the processes involved and allows to consider the possibility of climate change. The ability of the weather generator to correctly reproduce characteristics of the observed rainfall and air temperature records was evaluated by both (temporal and spatial) statistical and hydrological process characteristics at each and across all stations.

Several case study results proved that the proposed concept of the generator is robust and practically applicable. It allows to reliably generate synthetic series of precipitation totals and air temperatures at individual stations in catchments and around simultaneously. Using a combined stochastic-deterministic rainfall-runoff modelling approach provides an infinite number of combinations of flow, including the extreme and the unobserved ones. It can be used to estimate extreme flood characteristics, determine hydrologic metrics of ecological flows, and detect changes in flow variability caused by land use and climate change.

Acknowledgements: This work was supported by the Slovak Research and Development Agency under Contract No. APVV-19-0340 and the VEGA Grant Agency No. 1/0632/19.
Assessing trade-offs and vulnerabilities to global changes in the Senegal River basin.
Authors: Guilpart Étienne , Tilmant Amaury , Bourgault Marc-André , Roy René
Published: September 2022

West Africa is one of the regions of the globe that is expected to face massive global changes in the coming decades due to sustain population growth rates and climate change. Pressures exerted on water resources are likely to rise as water demands will increase to meet the water, food and energy demands from an ever-increasing, mostly urban, population, while supplies dwindle.

The Senegal River basin is a mostly underdeveloped river basin with a significant hydroelectric and agricultural potential. Policy makers are facing a challenging decision-making problem to identify climate-relevant investments because: (i) the strong divergence of the climate models and the associated uncertainties about future water availability, (ii) conflicting visions regarding the future of the basin: the first emphasizes modern uses such as energy production and irrigated agriculture; the second focuses on traditional uses such as flood recession agriculture and fisheries.

We propose a modeling framework to assess trade-offs and vulnerabilities to both climate and policy factors. First, we generate 1210 GCM-based hydrologic projections for the Senegal River basin from the CORDEX-Africa ensemble and the GR2M hydrological model. The projections are then clustered based on their hydrologic properties, using hydrologic attributes describing the flow regime of the Senegal River. For each cluster, the projection closest to the centroid is selected as the representative one. The next step involves the construction of alternative development and management scenarios of the river basin for the horizons 2050 and 2080. The development scenarios essentially assume different sets of dams and irrigation schemes. Management scenarios, on the other hand, assumed different priorities attached to the operating objectives (water uses).

For each triple projection-development-management scenarios, a stochastic hydroeconomic model determines the optimal operating policies, which are then used in simulation over all GCM-based hydrologic projections belonging to the same cluster. The analysis of simulation results reveals three categories of water uses: (i) high climate-sensitive sectors (hydropower production and navigation), (ii) high allocation policy sensitive sectors (flood recession agriculture and fisheries), and (iii) fairly robust sectors (irrigated agriculture).
Investigating the clustering mechanisms of hydroclimatic extremes: from identification to modelling strategies
Authors: Iliopoulou Theano , Dimitriadis Panayiotis , Koutsoyiannis Demetris
Published: September 2022

The understanding of the temporal properties of hydroclimatic extremes is critical to the mitigation of related risk as well as to society’s perception of risk. While the marginal properties of extremes have been extensively studied in the literature, their temporal behaviours have been rather overlooked, or approached via deterministic reasoning. We focus on the temporal variability and clustering mechanisms of extremes as seen in long-term hydroclimatic records, highlighting their links to the inherent stochastic properties of the parent hydrological process. To this aim, we apply a new simulation algorithm (Koutsoyiannis and Dimitriadis, 2021) capable of simultaneously reproducing the time dependence structure of a stochastic process, from short-term dependence to persistence (i.e. Hurst-Kolmogorov dynamics), its time directionality as well as its marginal distribution, irrespective of its type. The performance of the methdology in reproducing the observed extremal patterns is evaluated and the practical implications of the findings are discussed.

Reference: D. Koutsoyiannis, and P. Dimitriadis, Towards generic simulation for demanding stochastic processes, Sci, 3, 34, doi:10.3390/sci3030034, 2021.

 
Combining residence time and isotopic tracers for a better understanding of the fresh and marine water recharge and groundwater flux of a karstic thermal aquifer
Authors: Ranchoux Coralie , Ladouche Bernard , De Montety Véronique , Seidel Jean-Luc , Batiot-Guilhe Christelle
Published: September 2022

Karst hydrosystems are complex systems where the use of water resources is often shared by many actors. The addition of thermal and/or marine components in these systems makes classical methods of investigation difficult to apply. The combined use of geochemical tracers can allow a better understanding of the complex hydrogeological system and application of integrated water resources management. The thermal karst aquifer of Thau (South of France) illustrates the complexity of karst hydrosystems since it is a zone of convergence of young and shallow karst water, hot and mineralized thermal water and marine water (Thau Lagoon and/or seawater). Moreover, recurring phenomena of saltwater intrusion from the Thau Lagoon (i.e. inversac) into the freshwater aquifer can occur, modifying the type of circulation. It is proposed in this study, supported by the Dem'Eaux Thau project (2017-2022), to combine, with classical geochemical tools, tracers of water-rock interaction processes (Sr, Li) and residence time tracers (CFC, SF6, 3H, 4He, 14C, 36Cl) to better understand the origin of fluxes and to characterize the mixing that takes place in the system. 
Isotopic tools (Sr, Li) allowed to better constrain the thermal reservoir: thermal water flows mainly in a carbonate aquifer (87Sr/86Sr), fed by deeper flows from bed-rock ([Li]). The residence time of this water estimated by the different tracers (4He, 14C, 36Cl) is consistent and indicates ages of several thousands of years (10 000 to 50 000 years). This water subsequently feed a shallow reservoir (100-300m) through local fractures and mix with variable proportions of recent karst flows. These flows are mixtures of regional flows of about 30 years affected by thermonuclear tests (CFC, SF6, 3H, 14C, 36Cl) and more recent local flows contaminated by local anthropic activity (SF6, NO3-). During the inversac phenomenon, fluxes and mixtures are modified bringing a saltwater component to the system. Geochemical tools allow us to quantify the impact of the inversac and to characterize the spatial impact of such contamination by highlighting the connections between the intrusion zone and the different monitoring points. 