bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamical-Chemical Feedbacks in General Circulation Models and Their Influence on Sudden Stratospheric Warming Events
Authors: Dimdore-Miles Oscar , Gray Lesley , Osprey Scott
Published: March 2020

Sudden Stratospheric Warming events (SSWs) are rapid disruptions of the Northern Hemisphere (NH) winter stratospheric polar vortex and represent the largest source of inter-annual variability in the NH winter stratosphere. They have been linked to winter surface climate anomalies such as cold snaps over North America and Eurasia. Representing these events accurately in large scale GCMs as well as developing a greater understanding of them is key to improving predictability of winter surface climate. A key component of a GCM is its representation of atmospheric chemistry. Chemical distributions are either prescribed or calculated interactively by coupling an atmospheric chemistry model to radiation and dynamical components, thus capturing any chemical dynamical feedback mechanisms but incurring significant running cost.

This work evaluates the impact of interactive chemistry when modelling SSW events and explores the feedback mechanisms between chemical distributions and stratospheric dynamical variability. Pre-industrial control runs from the MetOffice HadGEMGC3.1 model which prescribes chemical fields and UKESM1 which calculates trace gas concentration interactively are utilised. Over the whole season - The Earth System Model appears to suppress warmings while the model with prescribed physics overestimates their occurrence compared to reanalysis. The differing representation of the equatorial stratosphere appears to be partially responsible for this difference. Additionally we find that middle stratosphere equatorial ozone concentration in late NH summer is closely associated with SSW probability in the ensuing winter in UKESM1. Anomalously low ozone is generally associated with an elevated SSW rate. This implies a chemical-dynamical coupling between the equator and the vortex in this model which preliminary results suggest could be driven by chemical feedbacks influencing the state of the early winter Quasi Biennial Oscillation (QBO) and Semi-Annual Oscillation (SAO) in zonal winds which can alter the distribution of planetary wave propagation and breaking (the primary cause of SSWs). Further work will assess whether this phenomenon is observed in other GCMs and further explore the physical mechanisms responsible.
Recent Crustal Surface Deformation of the Alpine Region Derived from Geodetic Observations
Authors: Völksen Christof , Sánchez Laura , Sokolov Alexandr , Arenz Herbert , Seitz Florian
Published: March 2020

structure of the lithosphere has been considered in advance. in the boundary region between Switzerland, Austria and Italy.
Update on European Regional Air Quality Forecast in the Copernicus Atmosphere Monitoring Service (CAMS)
Authors: Colette Augustin , Collin Gaelle , Barré Jérôme
Published: March 2020

 

The Copernicus Atmosphere Monitoring Service (CAMS) delivers a wealth of information on atmospheric composition change over short to long timescales. One of the core products of CAMS regards short term air quality forecasts with a three days lead time as well as reanalyses over the past years for the European region.

This service is covered by the CAMS_50 project which is now operational since 2015. It relies on a distributed production of 9 individual air quality models, consolidated by a centralised regional production unit at Météo-France before delivery to the European Centre on Medium Range Meteorological Forecasts, which implements the CAMS service.

Each model is operated by its own development team across Europe, all of them deliver air quality forecasts covering the whole continent at 10km resolution. The modelling team currently operational are at present: CHIMERE (France), DEHM (Denmark), EMEP/MSC-W (Norway), EURAD-IM (Germany), GEM-AQ (Poland), LOTOS-EUROS (The Netherlands), MATCH (Sweden), MOCAGE (France), SILAM (Finland). Two additional models are now applying to join the ensemble: MINNI (Italy), and MONARCH (Spain).

Such an ensemble of different models offers excellent complementarity in model capabilities as demonstrated by the performances of the ENSEMBLE product. It also leads to substantial challenges in coordinated model development. We will present the main recent achievements, status, and future plans for the validation and development of models underlying the service.

 
Ignimbrite flare-ups in the Central Andes: Crustal sources and processes of magma generation
Authors: Wörner Gerhard , Belousova Elena , Turner Simon , Kemann Jelte , Schmitt Axel K , Gerdes Axel , de Silva Shan
Published: March 2020

Silicic magmatism in the Central Andes forms rhyolitic to dacitic volcanic deposits that range from large-volume ignimbrites (>1000 km3) to small local dome eruptions. The mass proportion between mantle-derived magmatic contributions to crustal melting was previously estimated to range from 20 to 70 % based on Sr-O isotope data obtained on separated feldspar and quartz contained as crystal cargo. New O-Hf isotope data from in-situ ion-probe and laser ablation measurements of U-Pb-dated zircons further constrain type, proportion, and processes of crustal input into silicic magmas. Variations in time and space of these geochemical parameters are documented here using representative samples that cover the entire Central Andes over 20 Ma and 800 km distance. Systematic covariations in isotope tracers relate to increasing crustal thickening through time during Andean orogenesis. Collectively, Sr-Nd-Pb-Hf-O isotopic signatures vary in space and time and temporally reflect increasing crustal input during ignimbrite flare-ups as the crust becomes thermally matures. Spatial variations derive from different crustal domains in the Central Andes and reflect the different age and composition of crustal components.

Remarkably, inherited zircon representing basement involved in crustal assimilation is exceedingly rare over the entire province. This most probably reflects high temperatures that exceed zircon saturation temperatures of crustal melts in ignimbrite-forming magmas. This observation distinguishes silicic ignimbrite-forming magmatism from typical granitoid-forming magmatism in orogenic settings where abundant older zircons inherited from the crust are commonly found.
Scaling of magnetic reconnection with a limited x-line extent
Authors: Huang Kai , Liu Yi-Hsin , Lu Quanming , Hesse Michael
Published: March 2020

Contrary to all the 2D models, where the reconnection x-line extent is infinitely long, we study magnetic reconnection in the opposite limit. The scaling of the average reconnection rate and outflow speed are modeled as a function of the x-line extent. An internal x-line asymmetry along the current direction develops because of the flux transport by electrons beneath the ion kinetic scale, and it plays an important role in suppressing reconnection in the short x-line limit; the average reconnection rate drops because of the limited active region, and the outflow speed reduction is associated with the reduction of the J×B force, that is caused by the phase shift between the J and B profiles, also as a consequence of this flux transport.
Desertification and Development: some broader contexts
Authors: Kirkby Mike
Published: March 2020

The dominant direct physical processes responsible for desertification are water erosion, wind erosion and salinization.  Other threats that degrade the soil  include loss of biodiversity, loss of soil organic matter, fire, changing water resources, soil compaction, soil sealing and contamination. Soil management inevitably combines  human and physical effects.  Climate, which is the most important driver of the physical systems, is now being rapidly modified by human action, and at a scale which is much coarser than any local remedial action. 

  

In a model of near-subsistence systems, productivity is limited by climate and available labour, with some options for additional inputs through improved seed, fertilizer or tillage equipment. Optimum solutions in a particular environment depend on both climate and access to markets.  Agricultural surpluses, if any, allow investment in infrastructure – some of it directly  supporting agriculture through irrigation and market systems, some less directly useful through, for example, warfare or pyramid building.

 

Today some traditional drivers of desertification may no longer be relevant, as land, particularly in the global South, is grabbed for intensive irrigated farming, and populations move into mega-cities. The dominant drivers may become soil sealing around cities and transfers of urban and irrigation water.  In semi-arid areas this will lead to competition for the best land – for urban expansion and agricultural land with irrigation potential.  Desertification then becomes an issue increasingly focussed on abandoned marginal land, maintaining biodiversity, managing regional water resources and controlling erosion in the face of global climate change.
Consistency of observed sea surface height changes, bottom pressure changes and temperature, salinity variations in a South Atlantic transect of the Antarctic Circumpolar Current
Authors: Yakhontova Alisa , Rietbroek Roelof , Schröter Jens , Jonas Nadja , Lück Christina , Uebbing Bernd
Published: March 2020

Improved estimates of temperature, salinity, and sea surface height changes are computed from radar altimetry, satellite gravimetry and Argo profiles, and validated by the in situ ocean bottom pressure measurements in a South Atlantic transect of the Antarctic Circumpolar current. Using satellite gravimetry and altimetry observations, separate contributions to the global sea level can be estimated, but a regional solution is more challenging. Furthermore, Argo derived steric sea level change suffers from spatio-temporal sampling problems, and some signals are not well captured, e.g. in the deeper ocean below 2000m, around the boundary currents, in the Arctic or in the shelf/coastal regions. Jointly processing radar altimetry, Argo and data from the Gravity Recovery and Climate Experiment (GRACE), would allow to correct the deficiencies of the individual datasets, and produce observation based estimates of consistent temperature, salinity and sea surface height changes. In order to pave the way for an advanced joint inversion scheme that additionally resolves for temperature and salinity, the observation equations are formulated which link the satellite observations to temperature and salinity at depth. Observations in the South Atlantic region are compared with simulations from the FESOM model in terms of variability and the model data is used to find the spatial coherence of the signals at the sites with the surrounding ocean. The experiment is performed in the Southern Atlantic Ocean, where the estimates can be validated using an array of in situ ocean bottom pressure observations.
The MacroSeismic-Sensor Network
Authors: Mertl Stefan , Brückl Ewald , Brückl Johanna , Carniel Peter , Filz Karl , Krieger Martin , Stickler Gerald
Published: March 2020

The MacroSeismic Sensor network (MSS network) is a dense layout of 46 custom-built seismic low-cost sensors in populated area in the southern part of the Vienna Basin, Austria. The recorded ground-motion is sent to a central server using the Internet, processed on the server and then visualized in a web application in near real-time. The MSS network has been started 2014 by a funding program dedicated to the participation of young people and “Citizen Science” (Sparkling Science - a program of Federal Ministry of Education, Science and Research Austria) and has been further developed and kept in operation by private and public funding, participation of public schools as well as voluntary contribution of individuals.

The MSS uses 4.5 Hz geophones, 16bit analog-to-digital conversion (ADC) at a sampling rate of 100 samples per second and the Seedlink protocol for data transmission. A Raspberry Pi single board computer is used for controlling a custom-built ADC circuit board, data transmission and communication. Time synchronization is done using the Network Time Protocol.

For the visualization, the peak-ground-velocity is computed using 2 horizontal components at a sampling rate of 1 sample per second. An amplitude threshold algorithm using the Delaunay triangulation of the MSS network is used for the detection of seismic events and an amplitude-based localization method is used to compute the epicenter of the events.

The peak-ground-velocity and the detected events are presented on a map display by the web application with a focus of an intuitive presentation of the current state and the short-term history of the ground-motion within the area of the MSS network.

The output of the MSS network is used by public and private institutions. The the regional hazard warning center of Lower Austria (Landeswarnzentrale Niederösterreich) has integrated the MSS network visualization into their infrastructure to inform and warn the general public in case of a strong ground-motion in the area. A local quarry operator uses the data of the MSS network for a transparent monitoring and documentation of their blasting activity.
Assessment of Surface Exchange Coefficients in the Noah-MP Land Surface Model for Different Land Cover Types over China
Authors: Zhang Xia , Chen Liang , Ma Zhuguo , Gao Yanhong
Published: March 2020

The parameterization of surface exchange coefficients (Ch) representing land–atmosphere coupling strength plays a key role in land surface modeling. Previous studies have found that land–atmosphere coupling in land surface models (LSMs) is overestimated, which affects the predictability of weather and climate evolution. To improve the representation of land–atmosphere interactions in LSMs, this study investigated the dynamic canopy-height-dependent coupling strength in the offline Noah LSM with multiparameterization options (Noah-MP) when applied to China. Comparison with the default Noah-MP LSM showed the dynamic scheme significantly improved the Ch calculations and realistically reduced the biases of simulated surface energy and water components against observations. It is noteworthy that the improvements brought by the dynamic scheme differed across land cover types. The scheme was found superior in reproducing the observed Ch as well as surface energy and water variables for short vegetation (grass, crop, and shrub), while the improvement for tall canopy (forest) was found not significant, although the estimations were reasonable. The improved version benefits from the treatment of the roughness length for heat. Overall, the dynamic coupling scheme markedly affects the simulation of land–atmosphere interactions, and altering the dynamics of surface coupling has potential for improving the representation of land–atmosphere interactions and thus furthering LSM development.
Sundaland's subsidence requires revisiting its biogeography
Authors: Husson Laurent , Boucher Florian , Sarr Anta-Clarisse , Sepulchre Pierre , Cahyarini Sri Yudawati
Published: March 2020

It is widely accepted that sea level changes intermittently inun- dated the Sunda Shelf throughout the Pleistocene, separating Java, Sumatra and Borneo from the Malay Peninsula and from each other. On this basis, the dynamics of the biodiversity hotspot of Sundaland is consistently regarded as solely contingent on glacial sea level os- cillations, with interglacial highstands creating intermittent dispersal barriers between disjunct landmasses. However, recent findings on the geomorphology of the currently submerged Sunda shelf sug- gest that it subsided during the Pleistocene and that, over the Late Pliocene and Quaternary, is was never submerged prior to Marine Isotope Stage 11 (MIS 11, 400 ka). This would have enabled the dispersal of terrestrial organisms regardless of sea level variations until 400 ka and hampered movements thereafter, at least during interglacial periods. Existing phylogeographic data for terrestrial organisms conform to this scenario: available divergence time esti- mates reveal an 8‐ to 9‐fold increase in the rate of vicariance be- tween landmasses of Sundaland after 400 ka, corresponding to the onset of episodic flooding of the Sunda shelf. These results highlight how reconsidering the paleogeographic setting of Sundaland chal- lenges understanding the mechanisms generating Southeast Asian biodiversity.
Toward CO2 and CH4 measurements by ground based observations of surface-scattered sunlight: Radiative transfer modeling
Authors: Proß Christin , Hemmer Benedikt , Wellmann Constanze , Kostinek Julian , Butz André
Published: March 2020

Precise knowledge of sources and sinks in the carbon cycle is desired to understand
its sensitivity to climate change and to account and verify man-made emissions. An
important role herein play extended sources like urban areas. While in-situ measure-
ments of carbon dioxide (CO2) and methane (CH4) are highly accurate but localized,
satellites measure column-integrated concentrations over an extended footprint. Our
innovative measurement technique aims at determining CO2 and CH4 concentrations
near to the ground on the scale of a few kilometers and therefore fills the sensitivity
gap between in-situ and satellite measurements.
Using a modified EM27/SUN Fourier transform spectrometer we are able to record
spectra of surface scattered sunlight in the range of 4000 − 11000 cm−1 . To accurately
retrieve CO2 and CH4 concentrations an advanced retrieval method is required that
includes the simultaneous estimation of atmospheric scattering properties.
Based on our radiative transfer and retrieval software RemoTeC, we built a simulation
environment that includes atmospheric scattering processes. With this tool we can
generate and retrieve synthetic scattered light observations. Here we present our
simulation environment, first results and ongoing developments.
Sea floor topography modeling by cumulating different types of gravity information
Authors: Seoane Lucia , Beirens Benjamin , Ramillien Guillaume
Published: March 2020

We propose to cumulate complementary gravity data, i.e. geoid height and (radial) free-air gravity anomalies, to evaluate the 3-D shape of the sea floor more precisely. For this purpose, an Extended Kalman Filtering (EKF) scheme has been developed to construct the topographic solution by injecting gravity information progressively. The main advantage of this sequential cumulation of data is the reduction of the dimensions of the inverse problem. Non linear Newtonian operators have been re-evaluated from their original forms and elastic compensation of the topography is also taken into account. The efficiency of the method is proved by inversion of simulated gravity observations to converge to a stable topographic solution with an accuracy of only a few meters. Real geoid and gravity data are also inverted to estimate bathymetry around the New England and Great Meteor seamount chains. Error analysis consists of comparing our topographic solutions to accurate single beam ship tracks for validation.
Daily monitoring of retrogressive thaw slumps in the Fosheim Peninsula, Ellesmere Island, Canada
Authors: Ward Jones Melissa , Jones Benjamin , Pollard Wayne
Published: March 2020

Retrogressive thaw slumps (RTS) occur from the mass wasting of ice-rich permafrost. These horseshoe-shaped features have an ablating or retreating ice-rich headwall with fluidized sediment that is transported along the RTS floor. RTS can remain active for up to decades and enlarge as the headwall retreats. With observed increases in RTS number, rates and sizes in recent decades, there is a need to understand these highly dynamic landforms, however there is a general lack of detailed field observations of RTSs. We monitored 3 RTS for over half of the 2017 thaw period by setting up and tracking survey transects on a near daily basis. We correlated mean daily and cumulative retreat to mean daily air temperature (MDAT), total daily precipitation (TDP) and thawing degree days (TDD) using various polynomial regressions and Pearson correlation techniques. Our results show that July retreat was highly variable and periods of increased RTS retreat did not always align with periods of increased air temperature. Also, multiple periods of increased retreat could occur within a single period of increased air temperature. These retreat trends were observed to be largely driven by sediment redistribution in the RTS floor. Retreat rates decreased suddenly in early August, indicating a threshold of either air temperature, solar radiation or a combination of both must be reached for increased retreat rates. There was a statistically significant correlation between daily mean and mean cumulative retreat with MDAT (p < 0.001) and TDD (p < 0.001 and < 0.0001) but not with TDP. Correlating mean cumulative retreat and cumulative TDD using polynomial regression (quadratic and cubic) generated R2 values greater than 0.99 for all 3 sites as these variables account for past and current conditions within the monitoring period, as well as lag responses of retreat. This suggests the potential of accurately modelling RTS retreat with minimal field data (air temperature and headwall position), however this is currently restricted to individual RTSs and only within short time scales. We tested this idea by modelling 2 weeks of cumulative retreat in 2018 for 2 of our sites we monitored using the 2017 regression equations. Percent prediction error was 8% at one site and 16% at the other. Monitoring RTS on a daily scale allows RTS behaviour and trends to be identified that may be obscured at annual time scales. With the widespread increased numbers of RTSs being observed around the Arctic, understanding their dynamics is critical as these landforms impact surrounding ecosystems and infrastructure which will be exacerbated with climate change.  
Parameters controlling the incorporation of Cu in calcite
Authors: Brazier Jean-Michel , Götschl Katja , Dietzel Martin , Mavromatis Vasileios
Published: March 2020

Carbonate minerals record, through their chemical and isotopic composition, the environmental conditions occurring at the time of their formation. Thus, the incorporation of traces/impurities in CaCO3 minerals calcite and aragonite, have been widely studied over the last five decades in order to provide the fundamental knowledge needed for the use of these traces in paleoenvironmental reconstructions. The processes controlling the uptake of traces in natural samples, however, are manifold and hard to distinguish from each other. Thus, experimental co-precipitation studies on synthetic material under strictly controlled abiotic conditions can provide fundamental understanding on the effect of each process involved in the chemical signatures of natural carbonates. In this study, we explore the incorporation of Cu in calcite and its potential as proxy of reactive fluid composition. This transition metal commonly occurs complexed with organic ligands in natural waters, however, it exhibits very high affinity for calcite. Our experiments were performed at pH 6.3 and 8.3, with varying growth rate ranging between 10-8.5 and 10-7.6 (mol/m2/s). Our first results highlight that the partitioning coefficient of Cu is positively correlated to the calcite growth rate at both pH conditions, indicating an increase of Cu entrapment at higher growth rate. These new preliminary findings could bring fundamental understanding of Cu incorporation in calcite and highlight the potential of Cu partitioning coefficient as a proxy of mineral growth rate.
The uncertainty of storage-based drought indices from GRACE
Authors: Saemian Peyman , Tourian Mohammad Javad , Sneeuw Nico
Published: March 2020

Climate change and the growing demand for freshwater have raised the frequency and intensity of extreme events like drought. Satellite observations have improved our understanding of the temporal and spatial variability of droughts. Since March 2002, the Gravity Recovery and Climate Experiment (GRACE) and its successor GRACE Follow-On (GRACE-FO) have been observing variations in Earth's gravity field yielding valuable information about changes in terrestrial water storage anomaly (TWSA). The terrestrial water storage vertically integrates all forms of water on and beneath land surface including snow, surface water, soil moisture, and groundwater storage.

Drought indices help to monitor drought by characterizing it in terms of their severity, location, duration and timing. Several drought indices have been developed based on GRACE water storage anomaly from a GRACE-based climatology, most of which suffer from the short record of GRACE, about 15 years, for their climatology. The limited duration of the GRACE observations necessitates the use of external datasets of TWSA with a more extended period for climatology. Drought characterization comes with its own uncertainties due to the inherent uncertainty in the GRACE data, the various post-processing approaches of GRACE data, and different options for external datasets on the other hand.

This study offers a method to quantify uncertainties for the storage-based drought index. Moreover, we assess the sensitivity of major global river basins to the duration of the observations. The outcome of the study is invaluable in the sense that it allows for a more informative storage based drought, including uncertainty, thus enabling a more realistic risk assessment.
Influence of atmospheric winds and tides on the propagation direction of mesospheric gravity waves observed in OH airglow in the Alpine region
Authors: Hannawald Patrick , Wüst Sabine , Bittner Michael , Lilienthal Friederike , Jacobi Christoph
Published: March 2020

Atmospheric gravity waves transport energy and momentum trough the different atmospheric layers from the troposphere up to the mesosphere and above. On the one hand this transport has influence on atmospheric circulation patterns and drives for example the meridional circulation in the mesosphere. On the other hand the prevailing wind field selectively influences the vertical propagation conditions of gravity waves of different phase speed and horizontal propagation direction.

The OH-airglow layer at ca. 86 km altitude (upper mesosphere / lower thermosphere, UMLT) is well-suited for the investigation of atmospheric dynamics, allowing continuous observations of the night-sky throughout the year. Especially, atmospheric gravity waves are prominent features in the data of airglow imaging systems. Furthermore, this altitude region is known to be a region where wave breaking occurs quite often making it particular interesting for quantifying the amount of energy and momentum released due to gravity waves.

Five years of airglow observations with three FAIM (Fast Airglow Imager) systems in and around the Alpine region are analysed regarding high-frequency gravity waves. Prevailing wind fields and tides from meteor radar wind data and ERA5 data are compared with the propagation direction of these waves and show patterns with high correlation. On seasonal timescales, the gravity waves clearly propagate predominantly to the East in summer and to the West in winter regarding the zonal direction. The meridional direction varies between the different years. On diurnal timescales, we find that atmospheric tides significantly impact the main propagation directions of the gravity waves.

We further present a case study of a stereoscopic reconstruction using two synchronized airglow-imagers with overlapping field-of-views. This allows deriving the wave amplitude and a 3D visualization of gravity wave patterns within the airglow layer.

This work received funding from the Bavarian State Ministry of the Environment and Consumer Protection.
Assessing reliability of HRM sap-flow sensors under large range of vapor pressure deficit
Authors: Schoppach Rémy , Ekwalla Hangue Daniella , Klaus Julian
Published: March 2020

Evapotranspiration (ET) is a major water flux of ecosystems and represents globally 60-80% of the incoming precipitation lost by terrestrial environments. In forested lands, tree transpiration (TR) is the dominant component of ET, yet remains challenging to measure. Over the years, sap-flow sensors have become the standard tool for quantifying tree TR and different methods based on thermal approaches have been developed. Heat ratio methods (HRM) are considered as the most reliable and accurate method to quantify absolute flows. Leading commercial brands ensure an accurate measurement of positive flows up to 100 cm hr-1 but different studies have highlighted a saturation effect at high flows with threshold for accuracy remaining elusive[RS1] . Due to climate change, the occurrence, the severity and the duration of extreme events like heat waves and dry periods are expected to increase in future, so the potential for high TR rate periods will also increase. Therefore, it is crucial to determine the species-specific environmental conditions allowing a reliable measurement of TR in order to improve or understanding of eco-hydrological and physiological processes during high potential TR periods that can be crucial for vegetation survival. In this study, we tested the accuracy of HRM sap-flow sensors for beech (Fagus sylvatica) and oak (Quercus robur) tree species under extreme vapor pressure deficit (VPD) conditions in order to determine threshold for reliable measurements. In greenhouse conditions, we collected a complete and dense series of TR response to VPD between 0.7 to 8.3 kPa for potted beech and oak trees using three different methods: infrared gas analyser, gravimetric method, and HRM sap-flow sensors. Responses shown a linear trend at the low-canopy leaf level (41.5 and 45.1 mg H2O m-2 s-1 kPa-1 respectively for beech and oak) but a bi-linear conformation at the whole plant level (1st slope = 12.04 ± 0.7 mg H2O m-2 s-1 kPa-1 and break-point at 3.9 ± 0.07 kPa for beech trees). Sap-flow sensors using the HRM method displayed a clear inability to reliably measure flows under high VPD conditions. Thresholds of 2.25 ± 0.04 and 2.87 ± 0.14 kPa were identified as the maximum limit of method reliability for beech and oak respectively. In highly demanding environments, we suggest a bi-linear extrapolation beyond VPD threshold for better quantifying tree TR. Further experiments aiming at characterizing TR responses to VPD for a broad range of species and in different water deficit conditions are certainly needed for better understanding tree transpiration at the whole stand level.
Analyzing trends of changes in fire regimes on a global scale
Authors: Nolde Michael , Plank Simon , Friedemann Monika , Riedlinger Torsten
Published: March 2020

Analyzing trends of changes in fire regimes on a global scale

Wildfire is a dominant factor for shaping the landscape ecology in many parts of the world. It also poses an enormous threat to human lives and property. Climate change is expected to influence historical fire patterns, e.g., to intensify the occurrence of fire in already fire-prone ecosystems. This work is an attempt to investigate trends of changes in fire regimes on a global scale, regarding seasonality, intensity, and distribution of fire activity.

Thermal remote sensing allows the monitoring of wildfire activity worldwide. Data from several satellite sensors featuring varying spatial/temporal resolutions and radiometric sensitivities have been used towards that purpose, allowing for a combined temporal resolution of only a few hours between satellite overpasses (in the case of geostationary satellites, such as MSG or GOES, data is even gathered every 15 minutes). The combination of the acquired data therefore allows a fairly seamless monitoring timespan of several decades.

Due to the differences in utilized systems and methodologies, however, these data collections are highly heterogeneous regarding spatial/temporal resolution, utilized data formats, naming conventions, data types and comprised information. In preparation for this work, available datasets have been collected and harmonized, e.g. fire radiative power (FRP) has been corrected to account for the respective spatial resolution. By that, a comprehensive, decade-scale data basis was generated, which is used to derive fire related trends.

This study uses data from AQUA/TERRA MODIS, SUOMI-NPP VIIRS, MSG SEVIRI (covering Europe, South America and Africa), ENVISAT AATSR as well as ERS-2 ATSR-2. The generated data basis covers the time span from June 1995 to October 2019 and contains a collection of several billion active fire locations together with radiated power. The data was transferred into a uniform grid of 1x1 degrees, which was then analyzed regarding year-to-year developments.

 
Stochastic optimal scheduling of hydropower compensation for wind and photovoltaic power output considering multiple uncertainties
Authors: Liu Weifeng , Wang Chao , Lei Xiaohui , Zhong Ping-an , Lu Qingwen
Published: March 2020

Multiple uncertainties, including from the uncertainty of a single power (wind power or photovoltaic power) output forecasting to the uncertainty of the combined power output of wind and photovoltaic forecasting to the power shortage after hydropower compensation for wind and photovoltaic power output, exist in the wind-photovoltaic-hydropower system. Furthermore, as the forecast is updated, the above uncertainty will evolve accordingly. Revealing the evolution of multiple uncertainties is of great significance for the hydropower compensation for the combined power output of wind and photovoltaic. We use a generalized martingale model of forecast evolution to describe the uncertainty of a single power output. We then superimpose the single power output to obtain the combined power output of wind and photovoltaic. we establish a stochastic programming with recourse model for optimal scheduling of the hydropower compensation for wind and photovoltaic power output. The results indicate that the uncertainty of the combined power output of wind and photovoltaic forecasting is less than that of wind power output forecasting, and greater than that of photovoltaic power output forecasting. After hydropower compensates for combined power output of wind and photovoltaic, compared with the uncertainty of combined wind and photovoltaic power output forecasting, the uncertainty of power shortage is greatly reduced by 90%, which has significant benefits. And with the dynamic update of the forecast, the uncertainty of the single power output forecast, the uncertainty of the combined power output forecast, and the uncertainty of the power shortage will decrease accordingly.
Can Radiocarbon Records lead to Quantitative Estimates of Deep-Ocean Ventilation Rates with Error Estimates in the Geologic Past?
Authors: Marchal Olivier , Zhao Ning , Duffy Faith
Published: March 2020

Over the past two decades, an impressive amount of radiocarbon age measurements on samples of fossil benthic foraminifera and deep-sea corals have been published in the literature. These measurements are commonly used to draw inferences about changes in the ventilation of deep oceanic basins during the last deglacial period. Lacking in most previous studies, however, are quantitative estimates of deep-ocean paleo-ventilation rates and quantitative estimates of their errors, leading to potential over-interpretation and sterile debate. Moreover, most previous studies were concerned with the interpretation of individual records with low or no regard for other records available for the same time interval.

Here we present an effort to go beyond the qualitative interpretation of single radiocarbon records by analyzing an updated compilation of 14C age data using recursive least-squares (RLS) methods (a Kalman filter and a related smoother). In stark contrast with other methods of data analysis, RLS methods can provide an estimate of the history of the state of the physical system of interest and an estimate of the error in this history, which are consistent (in the least-squares sense) with times series of data and with a dynamical model, given estimates of the statistics of the errors in the data and in the model. Our current compilation includes 1,698 deep water 14C age data for the past 40 kyr based on fossil samples of benthic foraminifera, deep‐sea corals, deep‐dwelling planktonic foraminifera, bivalves, and spiral shells. The geographic distribution of the samples is very irregular, with most of them originating from near the margins and with large regions devoid of any data. The depths of the samples vary from about 250 m to about 5,000 m. In our study, the potential of RLS methods to estimate the history of deep-ocean ventilation rates and their errors from deep water 14C age data is explored for a number of abyssal layers in the Atlantic Ocean during the deglacial interval from 20 to 10 kyr BP. The approach used to apply the powerful but computationally expensive RLS methods to the analysis of geologic time series is described, the least-squares estimates of ventilation rate history in different layers are reported, and their significance in the light of their error estimates is discussed.
Continuous monitoring of ground deformational scenario of Veneto region (Italy) through Sentinel-1 data
Authors: Confuorto Pierluigi , Bianchini Silvia , Festa Davide , Raspini Federico , Casagli Nicola
Published: March 2020

Continuous monitoring of the Earth surface is fundamental for the development and the evolution of the society, to reduce the risks posed by major geo-hazards like landslides, subsidence and sinkholes, which have a large impact on urban areas and can cause direct and indirect socio-economic losses. The start of spaceborne Synthetic Aperture Radar systems represented a milestone for the control of the territory, since SAR-based monitoring enables accurate measurement of the surface deformation over large areas, with a frequency dependent on the revisit time of the satellites. In this sense, the launch of the European Space Agency Sentinel-1 mission, characterized by a 6-days repeat pass, portrayed a great innovation and a step towards near-real-time monitoring. In this work, we present the first results of the continuous monitoring of the Veneto region (Northeastern Italy) performed by means of Sentinel-1 data, in the framework of an operational monitoring service. The procedure applied is based on a systematic processing chain made of four steps: i) Continuous generation of Sentinel-1 ground deformation maps, providing Measurement Points (MP) characterized by annual average velocity (mm/yr) and displacement Time Series (TS); ii) TS screening and classification, applied after each new satellite acquisition, to identify any change in the deformation pattern, according to a selected threshold; iii) constant update of the “anomalies” and their classification, according to the type of deformation; iv) warning to local authorities, in case of persistent and significant anomalous trends which require further investigations and field surveys. Its first application on the Veneto region shows promising outcomes, evidencing those areas characterized by movements that can be detected by SAR satellites. A few examples of this operational procedure are here shown, such as the cases of Lamosano, where a translational slide involves the local village, or of Recoaro Terme, where the Mt. Rotolon landslide is constantly studied. Moreover, subsidence is also a major threat in Veneto region, testified by the long-term phenomena of the NE plain (Verona and Vicenza provinces) and by the city of Venice, where the interaction of tides and subsidence causes the periodical flooding (“acqua alta”) of the renowned UNESCO site. The presented results want to demonstrate that the constant and continuous monitoring of the territory through Sentinel-1 data represents a best practice for the detection of ground deformation events, aiming at the natural risk mitigation for the development of the human environment.
The Barreme Basin and the Gevaudan diapir - an example of the interplay between compressional tectonics and salt diapirism
Authors: Graham Rod , Csicsek Adam
Published: March 2020

The Barreme Basin and the Gevaudan diapir - an example of the interplay between compressional tectonics and salt diapirism

 

Adam Csicsek and Rod Graham

Imperial College London

 

Our understanding of the role of salt diapirism in determining the finite geometry of fold and thrust belts has grown apace in the last few years, but the interplay between the two remains a significant problem for structural interpretation. The Gevaudan diapir in the fold and thrust belt of the sub-Alpine chain of Haute Provence is well known and has been documented by numerous eminent alpine structural geologists. Graciansky, Dardot, Mascle, Gidon and Lickorish and Ford have all described and illustrated the geometry and evolution of the structure, and Lickorish and Ford’s interpretation is figured as an example of  diapirism  in a compressional setting by Jackson and Hudec in their text on salt tectonics. We review these various interpretations and present another.

The differences between the various interpretations say much about the complex interplay of salt diapirism and thin-skinned thrusting and have profound implications for the way we interpret the tectonic and sedimentary evolution of the Barreme basin which lies adjacent to the diapir

The Barreme basin is a thrust-top fragment of the Provencal foreland basin and has been described in detail from both sedimentological (e.g. Evans and Elliott, 1999) and structural (e.g. Antoni and Meckel, 1997) points of view. Here we make the case that it is also a salt related minibasin - a secondary minibasin developed on a now welded allochthonous Middle Cretaceous salt canopy.  We believe that within the basin it is possible to interpret successive depocentres which may record progressive salt withdrawal. We argue that though thrust loading must be the fundamental driving mechanism responsible for salt movement late in the tectonic history of the region, thrusting has not done much more than modify existing salt related geometry.    
Differential rotation of the solar corona and its importance for helioseismology
Authors: Obridko Vladimir , Badalyan Olga
Published: March 2020

It is shown that the solar corona rotates differentially at all heliocentric distances up to the source surface. As the distance increases, the differential rotation gradient decreases, and the rotation becomes more and more rigid. At small distances, the corona at latitudes above $\approx \pm 40^{\circ}$ rotates faster than the photosphere at the same latitudes. The type of the rotation depends also on the phase of the activity cycle. The differential rotation gradient is the largest in the vicinity of the cycle minimum. It is shown that time variations in the coronal rotation characteristics are associated with the tilt of the magnetic equator of the Sun. Based on the concept that the differential rotation of the corona reflects the rotation of deep subphotospheric layers, we compared the changes in the coronal rotation characteristics with distance with the helioseismic data and showed their satisfactory agreement. The results obtained allow us to suggest that the rotation of the solar corona can be used as indicator of the differential rotation of subphotospheric layers and calculate the nature of some current sheets in heliosphere/
Effects of local particle acceleration in the solar wind
Authors: Khabarova Olga , Zharkova Valentina , Xia Qian , Malandraki Olga
Published: March 2020

Recent observational and theoretical studies have shown that there is an unaccounted population of electrons and protons accelerated locally to suprathermal energies at reconnecting current sheets (RCSs) and 3-D dynamical plasmoids or 2-D magnetic islands (MIs) in the solar wind. The findings can be summarized as following: (i) RCSs are often subject to instabilities breaking those into 3D small-scale plasmoids/blobs or 2D magnetic islands (MIs) with multiple X- and O-nullpoints; (ii) RCSs and dynamical MIs can accelerate particles up to the MeV/nuc energies; (iii) accelerated particles may form clouds expanding far from a reconnecting region; and (iv) bi-directional(or counterstreaming) strahls observed in pitch-angle distributions (PADs) of suprathermal electrons may simply represent a signature of magnetic reconnection occurring at closed IMF structures (e.g., MIs), not necessarily connected to the Sun (Zharkova & Khabarova, 2012, 2015; Zank et al. 2014, 2015; Khabarova et al. 2015, 2016, 2017; 2018; le Roux 2016, 2017, 2018, 2019; Khabarova & Zank, 2017; Adhikari et al. 2019; Xia & Zharkova, 2018, 2020; Malandraki et al. 2019; Mingalev et al. 2019). We will briefly present an overview of the effects of local ion acceleration as observed at different heliocentric distances and focus on the impact of the locally-borne population of suprathermal electrons on typical patterns of PADs. 

Suprathermal electrons with energies of ~70eV and above are observed at 1 AU as dispersionless halo and magnetic field-aligned beams of strahls. For a long time, it has been thought that both populations originate only from the solar corona. This view has consequently impacted interpretation of typical patterns of suprathermal electron PADs observed in the solar wind. We present multi-spacecraft observations of counterstreaming strahls and dropouts in PADs within a previously reported region filled with plasmoids and RCSs, comparing observed PAD features with those predicted by PIC simulations extended to heliospheric conditions. We show typical features of PADs determined by acceleration of the ambient thermal electrons up to suprathermal energies in single RCSs and dynamical plasmoids. Our study suggests that locally-accelerated suprathermal electrons co-exist with those of solar origin. Therefore, some heat flux dropout and bi-directional strahl events observed in the heliosphere can be explained by local dynamical processes involving magnetic reconnection. Possible implications of the results for the interpretation of the strahl/halo relative density change with heliocentric distance and puzzling features of suprathermal electrons observed at crossings of the heliospheric current sheet and cometary comas are also discussed.