bluuebunny/crossref_metadata_2025 huggingface dataset:
Parameterizing heat and freshwater exchanges driven by subglacial discharge in Greenland's proglacial fjords
Authors: Stanway Adam , Wells Andrew , Johnson Helen , Ridley Jeff
Published: March 2020

Freshwater flux from the melting of Greenland’s Ice Sheet is thought to account for 25% of the observed rise in global mean sea level between 1992 and 2011, with a significant proportion of this associated with increased freshwater flux from marine terminating glaciers within coastal fjords. It has been suggested that increased ocean temperatures have triggered the retreat of Greenland’s outlet glaciers, with the melting of submarine glacier termini leading to an acceleration of inland regions of the ice sheet. Global climate  models  currently  operate  at  resolutions  too  coarse  to resolve  ice-ocean  interaction  on  the length  scales  typical  of  coastal  fjords. Therefore, a parameterization scheme is required to incorporate the relevant physics into such models.

As a first step towards such a parameterisation scheme, we develop theoretical understanding of the first order controls on heat and freshwater exchanges in Greenland’s proglacial fjords, guided by computational simulations in MITgcm. Fjords are modelled with idealised geometries, considering cases with and without bathymetric sills. The model parameterises melting at the glacier terminus, and non-hydrostatic flow in one or more buoyant plumes that form from fresh subglacial discharge at the glacier grounding line. We systematically explore how the overturning circulation and heat transport through a fjord respond to varying subglacial discharge.

In a subglacial-discharge dominated regime with flat bathymetry, we find that the horizontally integrated vertical flow structure set by buoyant plumes at the ice face remains unmodified along the length of the fjord, and is independent of the fjord width. For cases with either single or multiple subglacial-discharge plumes, we derive scaling laws for the heat and freshwater exchanges using buoyant plume theory, finding that the water in contact with the ice face mirrors that outside the fjord. This picture is complicated in the presence of a bathymetric sill, which can inhibit the transportation of deep coastal waters into the fjord. We conclude by discussing how our scaling laws might be used as a simple parameterisation of proglacial fjord dynamics in regimes where subglacial discharge controls the flow strength. We discuss how these results might be extended to incorporate the competing effects of circulation driven by along-fjord and along-shelf winds.
Snow accumulation rate and atmospheric oxidation pathway proxies from nitrate isotopes in East Antarctica
Authors: Akers Pete , Savarino Joël , Caillon Nicolas
Published: March 2020

Nitrate is naturally deposited in Antarctic snow and is detectable at low concentrations throughout our deepest ice cores. However, nitrate is photoreactive under ultraviolet light and experiences significant post-depositional loss. This nitrate loss favors 14NO3- over 15NO3-, and the resulting isotopic fractionation can be used as a proxy for duration of sunlight exposure. Here, we present nitrate isotope data (δ15N, δ18O, Δ17O) sampled from shallow snow cores and pits across East Antarctica. Our >30 sampling sites extend from coastal Adélie Land onto the high East Antarctic Plateau at Dome C and beyond, covering annual snow mass balances that range from 240 mm/yr to less than 30 mm/yr (water equivalent). The δ15N of nitrate at these sites show an inverse relationship with snow accumulation rate, with δ15N ≈ 20‰ at the coastal sites with the highest accumulations and δ15N ≈ 150-250‰ at the driest inland sites. This relationship develops because newly deposited nitrate is buried below the level of light penetration by new snow relatively quickly at high accumulation sites, but nitrate at drier sites can be exposed to sunlight for several years. After burial below the reach of sunlight, the δ15N signature of nitrate is preserved and thus offers a new proxy for snow accumulation rate in East Antarctic ice cores. In contrast, the oxygen isotopes of nitrate isotopically exchange with surrounding ice after burial, which complicates their interpretation. However, our large sample set allows an estimation of the rate of isotopic exchange at various sites, and the original isotopic values at the time of deposition may be approximated after correcting for this rate of exchange. These oxygen isotope values likely reflect in part the atmospheric oxidation history of the nitrate and its nitrogen oxide progenitor, but further study is needed to fully understand nitrate oxygen isotope dynamics.
Mitigating the warming in urban areas: Experimental study of different roof materials in a subtropical monsoon climate
Authors: Chen Xing , Jeong Sujong
Published: March 2020

Different roof materials are deployed for mitigating the urban heat, which significantly affects
our life. However, the performance of specific roof materials could be influenced by the
background climate. To evaluate the effectiveness of roof materials on temperature reductions in
a subtropical monsoon climate region, this study performs field experiments using four different
roof materials (gray and white surfaces, solar panel, and grass surface) from December 2017 to
July 2018. The results show that the white surface reduced the average daily surface temperature
by 3.37 °C. This cooling effect increased with the increase in surface albedo and incoming solar
radiation. However, the average cooling effect of the grass surface was much lower (0.43 °C).
This is attributable to the low soil moisture, which was influenced by the monsoon, thereby
indicating that irrigation is required to improve the thermal performance of grass roofs even in
humid regions. The solar panel reduced the daily surface temperature by 0.59 °C but exerted
strong warming (7.36 °C) during midday and cooling effects (4.03 °C) during midnight because
of its low albedo, low emissivity, and low heat capacity. Our results suggest that, for the roof
treatments explored here, white roofs are more effective for mitigating urban heat in a
subtropical monsoon climate under the present climatic conditions and especially for drier
climates predicted for the future, while grass roofs are not a sustainable method as they require
irrigation to achieve a cooling effect and solar panels may heat the urban atmosphere.
Evaluating the anomalous palaeomagnetic field behaviour in the Ediacaran with new palaeointensity data from Laurentia and Baltica.
Authors: Thallner Daniele , Biggin Andy , Hill Mimi , Halls Henry , McCausland Phil J. A. , Shcherbakova Valentina V. , Shcherbakov Valeriy P. , Bakhmutov Vladimir G.
Published: March 2020

Palaeomagnetic investigations from the Ediacaran period (635-541 Ma) give anomalous results, which might indicate unusual behaviour of Earth’s magnetic field. In contrast to the conventional geomagnetic dipole field, geocentric and aligned with Earth’s rotational axis, records of the palaeomagnetic field from several locations in Laurentia and Baltica indicate that the Ediacaran geomagnetic field might have been exceptionally weak and spent extended periods of time with its poles close to the geographic equator. Multi-method palaeointensity determinations have been performed on rocks from the Grenville Dykes (Canada, 584-598 Ma), Skinner Cove volcanics (Newfoundland, 550.5 Ma) and the Volyn Traps (Ukraine, 560-580Ma), confirming that the field was exceptionally weak, with VDM values between 4 and 15 ZAm2. These values could correspond to considerably lower VDM strengths predicted by geodynamo simulations for fields with low dipolarity before the onset of nucleation of the solid inner core. In contrast, preliminary evaluation of published directional data indicates that palaeosecular variation in the Ediacaran might not be distinguishable from palaeosecular variation predicted from palaeomagnetic data of the last ten million years.

These new palaeointensity results contribute to the elimination of data gaps in the Neoproterozoic palaeomagnetic record and will be used in combination with qualitatively assessed published directional and intensity data to capture the behaviour of the geomagnetic field of this time period in statistical field models. Comparisons of time averaged palaeosecular variation and VDM distribution with predictions of the geomagnetic field from geodynamo simulations will help to verify and improve models of deep Earth structures and dynamics.
Constructing paleoclimate networks from annually laminated lake sediments – the VARDA database
Authors: Ramisch Arne , Brauser Alexander , Dorn Mario , Blanchet Cecile , Brademann Brian , Köppl Matthias , Mingram Jens , Neugebauer Ina , Nowaczyk Norbert , Ott Florian , Pinkerneil Sylvia , Plessen Birgit , Schwab Markus J. , Tjallingii Rik , Brauer Achim
Published: March 2020

Reconstructing global patterns of past climate change requires large-scale networks of paleoclimatic archives. Generating paleoclimatic networks relies on precise synchronization of individual records with robust age control. The detailed age constrains of continuous varved lake sediments and the good preservation of isochrones from supra-regional extreme events make these records ideal for constructing large scale continental paleoclimatic networks. Yet, a global synthesis of varved lake archives is missing.

Here we present the VARved sediments DAtabase 1.0 (VARDA 1.0), the first global data compilation for varve chronologies and associated palaeoclimatic proxy records. VARDA 1.0 uses a connected data model provided by a state-of-the-art graph database, enabling custom generations of synchronized paleoclimatic networks. We report on compilation strategies for the identification of varved lakes and assimilation of high-resolution chronologies. Existing chronologies have been re-assessed and harmonized using a novel approach that infers information on sedimentation rates enclosed in varve thickness records. This information provides detailed information on the priors required for Bayesian age-depth modelling and strongly improves these results. Additionally, a synthesis of tephra layers from volcanic eruptions provides supra-regional isochrones for synchronizing even distant varved lake records. The current version (VARDA 1.0) comprises 261 datasets from 95 varved lake archives, including chronological information from 14C dating and varve thickness measurements, but also palaeoclimatological proxy data. We further explore potential applications of such networks in paleoclimatic studies, such as identifying leads and lags of regional climate change, large-scale model-data comparisons or differentiated proxy responses between archives. The VARDA graph-database and user interface can be accessed online at https://varve.gfz-potsdam.de.
A new estimation of water and nutrients (N & P) discharge to the Mediterranean Sea from the LPJmL model: modelling the dynamics of the land-sea nutrient transfer
Authors: Ayache Mohamed , Bondeau Alberte , Pagès Rémi , Baklouti Melika
Published: March 2020

   Runoff from rivers and coastal plains delivers significant amounts of nutrients to the Mediterranean Sea from the agricultural activities and urban waste waters. Several recent studies show that variations in rivers inputs may play a significant role on the marine biogeochemical cycles and planktonic food web in the entire basin. The aim of this study is to estimate the release of nutrients (N & P) to the Mediterranean Sea from basin-wide agriculture and urbanization through the implementation of the biogeochemical land-sea nutrient transfer processes within the agro-ecosystem model LPJmL. This is a contribution to the LaSeR-Med project (Towards an integrated prediction of Land & Sea Responses to global change in the Mediterranean Basin).

A compilation of a new input data set of fertilizer, manure and wastewater nutrients content [1961-2005] has been added to the LPJmL forcing data set, with a new land use patterns produced by an econometric model. The representation of the nutrient transfer from land to sea has been introduced into LPJmL by considering the following processes: mineralization, denitrification, adsorption, remineralization, nitrification, and phytoplankton dynamics.

First basin-wide LPJmL simulation at 1/12°, indicates that the model succeeds in simulating the temporal variations of water discharge for the main rivers flowing to the Mediterranean Sea, and shows a good consistency between the simulated nutrients concentration (NO3 and PO4) and available in-situ data. Preliminary results show that wastewater strongly contribute to the phosphorus fluxes (as PO4), while both agriculture and wastewater control the nitrogen fluxes (mainly as NO3). Alternative scenarios for land-use will allow to explore the future amounts of terrestrial nutrients that will reach the sea through rivers discharge and water runoffs and impact the marine ecosystems.
Active Noise Tomography in Medical Ultrasound
Authors: Ulrich Ines
Published: March 2020

We propose a translation of widely-used seismic ambient noise tomography to active noise tomography in medical ultrasound. This is intended to eliminate time-consuming transducer calibration and to improve illumination of the target.

Ultrasound computed tomography (USCT) is an emerging visualization modality in medical imaging and is especially apt to screen soft human tissue such as the breast. Currently, USCT applications are developed for breast cancer detection using a collection of ultrasound scans that measure the pressure wavefield emitted by individual transducers. To obtain good coverage, a large number of emitter-receiver pairs is required, as well as careful calibration of transducers using reference measurements in water at constant temperature. Standard acquisition and calibration are time consuming processes, placing major constraints on the integration of USCT for breast cancer detection in medical practice.

We present a novel approach to obtain traveltime measurements between transducer pairs in USCT by applying random field interferometry, as developed in seismic imaging. Since ambient noise sources are absent in the medical application, we generate random wavefields actively by firing sources in a random sequence. Cross-correlation of the recordings provides an approximation of Green’s functions between receivers, from which traveltime measurements can be extracted.

The proposed method has two major benefits: (1) Since cross-correlation eliminates time shifts caused by the a priori unknown source wavelet, the tedious calibration step can be avoided. (2) Coverage improves because the implicit use of reflections off the device boundary overcomes limited illumination caused by the small opening angle of typical ultrasound transducers.

The traveltimes extracted from the Green’s function approximations can be used as new data in a ray-based traveltime tomography. As a proof of concept, we test the algorithm on numerical breast phantoms, and we show that the latter can be reconstructed successfully from the cross-correlation traveltimes. In summary, random field interferometry opens new perspectives to shorten and facilitate the acquisition and tomographic inversion of USCT datasets.
Multivariate and spatially calibrated hydrological model for assessing climate change impacts on hydrological processes in West Africa
Authors: Dembélé Moctar , Zwart Sander , Ceperley Natalie , Mariéthoz Grégoire , Schaefli Bettina
Published: March 2020

Robust hydrological models are critical for the assessment of climate change impacts on hydrological processes. This study analysis the future evolution of the spatiotemporal dynamics of multiple hydrological processes (i.e. streamflow, soil moisture, evaporation and terrestrial water storage) with the fully distributed mesoscale hydrologic Model (mHM), which is constrained with a novel multivariate calibration approach based on the spatial patterns of satellite remote sensing data (Dembélé et al., 2020). The experiment is done in the large and transboundary Volta River Basin (VRB) in West Africa, which is a hotspot of climate vulnerability. Climate change and land use changes lead to recurrent floods and drought that impact agriculture and affect the lives of the inhabitants.

Based on data availability on the Earth System Grid Federation (ESGF) platform, nine Global Circulation Models (i.e. CanESM2, CNRM-CM5, CSIRO-Mk3-6-0, GFDL-ESM2M, HadGEM2-ES, IPSL-CM5A-MR, MIROC5, MPI-ESM-LR and NorESM1-M) available from the CORDEX-Africa initiative and dynamically downscaled with the latest version of the Rossby Centre's regional atmospheric model (RCA4) are selected for this study. Daily datasets of meteorological variables (i.e. precipitation and air temperature) for the medium and high emission scenarios (RCP4.5 and RCP8.5) are bias-corrected and used to force the mHM model for the reference period 1991-2020, and the near- and long-term future periods 2021-2050 and 2051-2080.

The results show contrasting trends among the hydrological processes as well as among the GCMs. The findings reveal uncertainties in the spatial patterns of hydrological processes (e.g. soil moisture and evaporation), which ultimately have implications for flood and drought predictions. This study highlights the importance of plausible spatial patterns for the assessment of climate change impacts on hydrological processes, and thereby provide valuable information with the potential to reduce the climate vulnerability of the local population.

 

Reference

Dembélé, M., Hrachowitz, M., Savenije, H., Mariéthoz, G., & Schaefli, B. (2020). Improving the predictive skill of a distributed hydrological model by calibration on spatial patterns with multiple satellite datasets. Water Resources Research.
Under pressure: How pressure affects magnetic remanence
Authors: Volk Michael , Fu Roger , Feinberg Josh
Published: March 2020

Rocks have complicated histories and form under various conditions. However, all rocks, terrestrial and extraterrestrial, have been subjected to some form of pressure during their genesis. The effect of pressure (strain) on the magnetic remanence is a largely unexplored problem, with most of the work being focused on the study of meteorites. 

In the absence of a magnetic field, subjecting a rock to pressure can demagnetize the natural remanent magnetization (NRM). This loss of magnetic remanence can lead to an underestimation of paleointensities. On the other hand, in the presence of a magnetic field, magnetic minerals can record a pressure remanent magnetization (PRM). The superposition of the remaining NRM and a newly acquired PRM can influence the remanence direction as well as the paleointensity. Since the reconstruction of the temporal changes of Earths’ magnetic relies on robust estimations of direction and intensity, the effects of pressure on the remanence should be taken into account.

Here we present a series of experiments that aim to explore the acquisition process of PRMs and their net contribution with respect to the rock’s original magnetization. Stoichiometric magnetites of four different grain sizes (65 nm, 440 nm, 16.9 µm, and 18.3 µm) and magnetic domain states were subjected to crustal pressures (226, 301, and 376 MPa) in the presence of a magnetic field. Surprisingly, the PRM intensity showed no detectable dependence on grain size. However, because the acquisition of a thermal remanence (TRM) is strongly dependent on particle size,  populations of large multidomain particles can acquire a PRM, which may represent up to 30% of a TRM acquired in the same field.

Finally, we will show how the influence of pressure on the magnetic remanence can be visualized by modern magnetic imaging techniques like the quantum diamond microscope (QDM). The QDM has a  ~1 µm maximum spatial resolution that is able to resolve the magnetic fields of individual mineral assemblages with ~10 µm diameter. The high spatial resolution and sensitivity enables us to visualize the changes in magnetic remanence due to pressure cycling and can help to better understand the possible implications for paleomagnetism.
The influence of orbital configurations on Northern Hemisphere ice sheet evolution during MIS 13 with a coupled climate-ice sheet model
Authors: Niu Lu , Gierz Paul , J. Gowan Evan , Lohmann Gerrit
Published: March 2020

Antarctic ice core and deep ocean sediment core records imply that the interglacial climate during Marine Isotope Stage 13 (MIS 13) was relatively cold, and ice sheets were likely larger than today. We model the MIS 13 climate with a coupled climate-ice sheet model AWI-ESM1.2-LR under different orbital configurations at 495, 506 and 517 kyr BP. Summer insolation at 65 °N at 495 kyr BP is similar to the preindustrial, but the lower greenhouse gas values lead to an ice sheet buildup relative to today. Boreal summer at perihelion at 506 kyr BP causes a warmer summer over Northern Hemisphere continents, inhibiting the development of Northern Hemisphere ice sheets. Lower obliquity induces cooling over the polar regions and is favorable for the ice sheet buildup. Aside from the polar regions, mountains with high elevation also have favorable conditions for ice sheet buildup. The Cordilleran Ice Sheet is more sensitive and has a faster response to boreal summer insolation change than the other large scale Northern Hemisphere ice sheets. This indicates that different ice sheets might have different development processes. In addition, ice sheets do not build up over northeastern North America and Eurasia in our simulations. In our final set of simulations, we address the multi-stability of the ice sheets which could be a reason for causing this phenomenon.
Volatile organic compounds in barite-hosted fluid inclusions from the 3.5 Ga old Dresser Formation, Western Australia
Authors: Thiel Volker , Duda Jan-Peter , van den Kerkhof Alfons M. , Reitner Joachim , Mißbach Helge
Published: March 2020

The c. 3.5 Ga Dresser Formation of the East Pilbara Craton (Western Australia) contains large amounts of blackish barite. These rocks produce an intense sulfidic odor when crushed, resulting from abundant primary fluid inclusions. In part, the black barites are interbedded with sulfidic stromatolites. Using Raman spectroscopy, microthermometry, and two different online GC–MS approaches, we characterized in detail the chemical composition of the barite-hosted fluid inclusions. Our GC–MS techniques were based on (i) thermodecrepitation at 150-250°C and (ii) solid phase microextraction (SPME)–GC–MS at reduced temperature (50°C), thereby minimizing external contamination and artefact formation. Major fluid inclusion classes yielded mainly H2O, CO2, and H2S in varying abundance, along with minor amounts of COS and  CS2, N2, and CH4 (< 1%). Notably, we also detected a wide range of volatile organic compounds, including short–chain ketones and aldehydes, thiophenes, and various organic (poly)sulfides. Some of these compounds (CH3SH, acetic acid) have previously been invoked as initials agents for carbon fixation under primordial conditions, but up to now their presence had not been observed in Precambrian materials. Based on our findings, we hypothesize that hydrothermal seepage of organic and inorganic compounds during Dresser times provided both, catabolic and anabolic substrates for early microbial metabolisms.
Quantification of water vapour transport from the Asian monsoon to the stratosphere
Authors: Nützel Matthias , Podglajen Aurélien , Garny Hella , Ploeger Felix
Published: March 2020

We use multiannual simulations with the chemistry-transport model CLaMS (Chemical Lagrangian Model of the Stratosphere) to analyze water vapour transport from the Asian monsoon region to the stratosphere. Further, we make comparisons of the transport characteristics from the Asian monsoon to the stratosphere with those of other source regions (e.g. from the tropics). In addition, we characterize the transport efficiency of the monsoon region compared to other source regions and bring our results into context with previous studies, which have focused on water vapour transport from the Asian monsoon to the stratosphere. These analyses are complementing the previously published work by Ploeger et al. (2017), who have analyzed mass transport from the Asian monsoon anticyclone to the stratosphere.

The presented findings have been recently published in Atmospheric Chemistry and Physics (Nützel et al., 2019).

 

References:

Ploeger, F., Konopka, P., Walker, K., and Riese, M.: Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere, Atmos. Chem. Phys., 17, 7055-7066, https://doi.org/10.5194/acp-17-7055-2017, 2017.

Nützel, M., Podglajen, A., Garny, H., and Ploeger, F.: Quantification of water vapour transport from the Asian monsoon to the stratosphere, Atmos. Chem. Phys., 19, 8947–8966, https://doi.org/10.5194/acp-19-8947-2019, 2019.

 

 

 
Relative importance of three climate factors on dust emissions over North Africa
Authors: Shi Lamei , Zhang Jiahua , Yao Fengmei , Zhang Da
Published: March 2020

The breakdown of nocturnal low-level jets (NLLJs), West African heat low (WAHL), and Harmattan Surges (HS) have been proved to be important meteorological drivers of the seasonal variation of dust emissions over North Africa. This study further investigated their relative contributions to the interannual variation of dust emissions from 1980 to 2018. Dust emissions from the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), precipitation data from TerraClimate, and wind speed, temperature, and geopotential from the European Centre for Medium-Range Weather Forecasts (ECMWF) were used to examine the roles of precipitation and wind speed in the dust emission trend as well as the spatiotemporal characteristics of the contributions of those three meteorological factors to the interannual variation of dust emissions. Results indicated that the dust emissions over Sahel and the southern coast of Mediterranean were more sensitive to precipitation rather than wind speed, while areas that were not influenced by rainfall were highly correlated with the cube of the wind speed at 10 m above surface with p < 0.001. The regional difference in the contribution of the three meteorological factors was significant. HS was the main contributor for dust emissions over the northern North Africa primarily in winter and spring. NLLJs primarily controlled the southern part (south of 20°N) in almost all seasons especially in winter and spring, while they contributed more to dust emissions north of 20° N from June to August. The contribution of WAHL started from the south of the Hoggar-Tibesti channel and the lee of Ethiopian Highlands in winter, then it moved northwestward in spring and reached their strongest states in summer.
Imaging magma storage in the Main Ethiopian Rift with 3-D Magnetotellurics
Authors: Huebert Juliane , Whaler Kathy , Fisseha Shimeles , Iddon Fiona , Hogg Colin
Published: March 2020

The Main Ethiopian Rift (MER) as part of the large East African continental break-up zone is characterized by lateral extension and active volcanism. Rifting in the MER is magma assisted, with surface expressions of magmatism concentrated at en echelon Quaternary magmatic segments and off-axis linear features, but questions still remain about their respective roles in rifting.

The storage and pathways of magma ascent are of great interest for the assessment of both geohazard and geothermal energy potential. Imaging magma storage throughout the crust and in the upper mantle can be achieved by geophysical deep sounding techniques such as magnetotellurics (MT). Through MT measurements it is possible to access the electrical conductivity of the subsurface, a parameter that is greatly sensitive to the melt and water content. We present new MT data from the Central MER and a three-dimensional model of conductivity of the crust, imaging across-rift magma storage not only under the well-developed central-axis silicic volcanic complex Aluto, but also under several off-axis basaltic monogenetic volcanic fields. The conductivity model supports the idea of bi-modal magma storage in the CMER and helps constrain the melt and water content in the crust through the use of petrological melt-mixing models. Integrating our findings with the results from seismic tomography and receiver functions as well as Bouguer gravity data and petrological observations allows a comprehensive picture of magma storage and pathways in the MER.
Occurrence of Freak Waves in near-coast regions of the North Sea and their potential relationship with objective weather types
Authors: Möller Jens , Teutsch Ina , Weisse Ralf
Published: March 2020

Rogue waves are a potential threat for both shipping and offshore structures like wind power stations or oil platforms. While individual Rogue waves are short-lived and almost unpredictable, there is a chance to predict the probability of the occurrence of freak waves in conjunction with different weather types. The German Ministry of Transport and digital Infrastructure has tasked its Network of Experts to investigate the possible evolutions of extreme threats for shipping and offshore wind energy plants in the German Bight, the south-eastern part of the North Sea near the German coast.

In this study, we present an analysis from the co-occurrence of freak waves with different weather types in the German Bight in the past (from observations). In addition, we investigate potential changes of the occurrence of freak waves in the future due to a changing climate and changing appearance of the relevant weather types (by use of a coupled Regional Ocean-Atmosphere Climate Model, MPI-OM).

The investigation indicates a connection between the probability of the occurrence of freak waves at different stations and certain weather types. Potentially, this relationship could be used for warning crews of ships or offshore constructions. In a coupled Regional Ocean-Atmosphere Climate Model (MPI-OM) under scenario RCP8.5 we detect an increase of just such weather types, which are correlated with high waves, for the future.
Spatio-temporal global patterns of 70 years of daily temperature using Fisher-Shannon complexity measures
Authors: Amato Federico , Guignard Fabian , Kanevski Mikhail
Published: March 2020

Global climate has been the focus of an increasing number of researches over the last decades. The ratification of the Paris Agreement imposes to undertake the necessary actions to limit the increase in global average temperature below 1.5oC to ensure a reduction of the risks and impacts of climate change.

Despite the importance of its spatial and temporal distribution, warming has often been investigated only in terms of global and hemispheric means. Moreover, although it is known that climate is characterised by strong nonlinearity and chaotic behaviour, most of the studies in climate science adopt statistical methods valid only for stationary or linear systems. Nevertheless, it has already been shown that warming trends are characterised by strong nonlinearities, with an acceleration in the increase of temperatures since 1980.

In this work, we investigate the complex nature of global temperature trends. We study the maximum temperature at two meters above ground using the NCEP CDAS1 daily reanalysis data, with a spatial resolution of 2.5o by 2.5o and covering the time period from 1 of January 1948 to 30 of November 2018. For each spatial location, we characterize the corresponding temperature time series using methods from Information Theory. Specifically, we analysed the temperature by computing the Fisher Information Measure [1] (FIM) and the Shannon Entropy Power [2] (SEP) in a temporal sliding window, which allows to follow the temporal evolution of the two parameters. We find a significant change in the spatial patterns of the dynamic behaviour of temperatures starting from the early eighties. Specifically, two different patterns are recognizable. In the period from 1948 to the early eighties the latitudes higher than 60oN and lower than 60oS show high levels of SEP and low levels of FIM. The situation completely revers starting from 1980s, and in a faster way for the latitudes higher than 60oN, so that tropical and temperate zones are now characterized by high levels of entropy. The stronger growth of SEP is measured in the northern mid-latitudes. These regions are also known to have been characterized by higher warming trends. Finally, a drastic difference between oceans and land surfaces is detectable, with the former generally interested by significant increases of SEP since the eighties.

[1] Fisher, R.  A Theory of statistical estimation. Math. Proc. Camb. Philos. Soc.22, 700–725, DOI:  10.1017/S0305004100009580 (1925).

[2] Shannon, C. E.  A mathematical theory of communication. Bell Syst. Tech. J.27, 379–423, DOI: 10.1002/j.1538-7305.1948.tb01338.x (1948).
The differing impact of air stagnation on near-surface ozone across Europe
Authors: Garrido-Pérez José M. , Ordóñez Carlos , García-Herrera Ricardo , Schnell Jordan L.
Published: March 2020

Daily maximum temperature is known to be the meteorological variable that mostly controls the afternoon near-surface ozone concentrations during summer. Air stagnation situations, characterised by stable weather conditions and poor ventilation, also lead to the accumulation of pollutants and regional ozone production close to the surface. This work evaluates the joint effect of daily maximum temperature and a simplified air stagnation index on surface ozone observations in eight regions of Europe during summer 1998-2015.

As expected, the correlations of MDA8 O3 (maximum daily 8-h running average ozone) with temperature are higher than with stagnation for most regions. Nevertheless, stagnation can also be considered as a good predictor of ozone, especially in the regions of central/southern Europe, where the correlation coefficients between MDA8 O3 and the percentage of stagnant area are within the range 0.50–0.70. MDA8 O3 consistently increases over central/southern Europe under stagnant conditions, but this is not always the case in the north. Under non-stagnant conditions and daily maximum temperatures within 20-25 ºC (typical temperatures of fair weather conditions that allow photochemical production), northern Europe is affected by southerly advection that often brings aged air masses from more polluted areas, increasing the MDA8 O3 mixing ratios.

We have also found that the ozone diurnal cycles in the central/southern regions exhibit large amplitudes, with above-average daytime and below-average night-time concentrations, when stagnation occurs. Stagnant nights are often associated with stable shallow planetary boundary layer and, presumably, enhanced dry deposition and chemical destruction of ozone. After sunrise, mixing with air from air from the residual layer, accumulation of ozone and precursors, and photochemical production seem to be the main mechanisms involved in the build-up of daytime ozone.

According to previous studies, some of the central/southern European regions where stagnation has a clear impact on ozone have undergone significant upward trends in air stagnation in the past and are also likely to experience increases in the future. However, our study has identified other regions with unclear responses of summer ozone to the occurrence of stagnation. This indicates that climate model projections of increases in stagnation should not directly be translated into enhanced summer ozone pollution if the sensitivity of this pollutant to stagnation has not been proved for a particular region.
Reconstructing the pre–Variscan puzzle of Cambro–Ordovician basement rocks in the western Mediterranean region of Gondwana
Authors: Quesada Cecilio , Álvaro José Javier , Casas Josep Maria
Published: March 2020

In today’s western Mediterranean region, Variscan and Alpine thrusts and shear zones combine to hamper a correct identification and palinspastic reconstruction of Cambro-Ordovician sequences. However, gap-related stratigraphic, climatically sensitive facies associations, sedimentary, volcanosedimentary, biogeographic, biodiversity and detrital zircon data mainly made available during the last two decades allow envisaging a new palaeogeographic scenario by linking proximal-to-distal transects across the western and eastern branches of the Ibero-Armorican Arc. Variscan parautochthonous and autochthonous domains are represented palaeogeographically by, from SW to NE: (i) the Central Iberian, West Asturian-Leonese and Cantabrian zones of the Iberian Massif and their laterally correlative Central Armorican Domain, fringed marginally by the Ossa-Morena and North Armorican thinned outer margin of Gondwana, reminiscent of the rift axis during the Cambrian; and (ii) the southeastern Pyrenees, Occitan and SW Sardinia domains, fringed marginally by the slope-to-basinal South Armorican, Thiviers-Payzac, Albigeois and northeastern Pyrenees domains. These proximal-to distal transects of West Gondwana record a diachronous SW-to-NE migration of evaporites, phosphorites and maximum peak of trilobite diversity, related to the counter-clockwise migration of the Gondwana supercontinent, supported by a gradual modification of detrital zircon provenance. Both branches of the Ibero-Armorican Arc also display a diachronous migration of Cambro-Ordovician rift-to-drift conditions associated with distinct igneous manifestations (volcanosedimentary and plutonic). This migration is related to the development of the Furongian (Toledanian) to Mid-Late Ordovician (Sardic) geodynamic events, in response to gap-related thermal doming, subaerial denudation and magmatic activity evolving from calc-alkaline to tholeiitic affinity.
Impulse concept in formulating a unified approach to bedload transport
Authors: Diplas Panayiotis , Shih WuRong
Published: March 2020

Due to their stochastic and fluctuating nature, the entrainment and transport of sediment particles present great challenges to scientists and engineers who endeavor to formulate a universal framework for quantifying sediment dynamics and transport behaviors. The application of impulse theory represents one of such efforts and has received increased attention over the past decade. Practically, the impulse concept helps to remove the inactive periods of transporting process from the entire transport history, such that the underlying driving mechanism of particle movements can be better identified. This approach not only proves to be useful in characterizing the threshold of motion conditions, as tested against experimental data from an increased body of literature, but also provides a new perspective in formulating the constitutive relation of bedload transport. In this study, we employ a similar criterion, yet based on the pertinent amounts of energy imparted upon sediment particles, to reproduce the stress-transport relations. These post-conditioned stress-transport relations are almost devoid of the inactive periods and, thus, better represent the physics of transport of sediment particles. It is noted that a consistent 1.5th power law has been recovered from a wide range of transport flow conditions, which can be deemed as a constitutive relation for bedload transport. Further examination of these data sets indicates that, in essence, the obtained 1.5th power relation accounts for a constant energy transfer efficiency of fluid flow applied upon the sediment particles. These efforts, based on the impulse concept, lead to a unified approach to sediment transport problems.
Analysis of N2O emissions and isotopomers to understand nitrogen cycling associated with multispecies grassland swards at a lysimeter scale
Authors: Bracken Conor , Lanigan Gary , Richards Karl , Tracy Saoirse , Müller Christoph , Murphy Paul
Published: March 2020

Nitrous oxide (N2O) is a potent greenhouse gas associated with nitrogen fertiliser inputs to agricultural production systems. Minimising N2O emissions is important to improving the efficiency and sustainability of grassland agriculture. Multispecies grassland swards composed of plants from different functional groups (grasses, legumes, herbs) have been considered as a management strategy to achieve this goal. Numerous soil nitrogen transformation pathways can lead to the production of N2O emissions. These transformation pathways are regulated by soil microbial communities and the environmental conditions and management practices that impact on them. Much research has been carried out on N cycling and N2O emissions from predominantly grass monoculture systems. However, there is a lot yet to understand about how agricultural grasslands with diverse plant communities influence soil N cycling and N2O emissions. A lysimeter experiment was set up as a completely randomised block design and carried out over a full year to investigate N2O production, and nitrogen cycling associated with four sward types. The swards four swards were: perennial ryegrass (PRG, Lolium perenne); PRG and low white clover (PRG + LWC, Trifolium repens); PRG and high white clover (PRG + HWC); PRG, WC and ribwort plantain (PRG + WC + PLAN, Plantago lanceolata) managed at 250, 90, 0, and 45 kg N ha-1yr-1, respectively. Fertiliser N was applied by syringe as urea in splits at suitable timings to meet grass growth demands. N2O fluxes were measured using a static chamber technique and additional samples were taken after the final flux sample to measure the associated N2O isotopomers using a novel Cavity Ring Down Spectroscopy technique. Leachate volumes were measured on a weekly basis and composite monthly samples were used to determine the total amount of N leached from each treatment over the full year. Herbage was harvested on a monthly basis to measure DM yield (kg DM ha-1), total N (%) and N yield (kg N ha-1).This work reports on the N2O emissions and N leaching associated with the four sward treatments and related these N losses to the treatments DM yields and N uptake as an estimation of the efficiency of these differing grassland management strategies. N2O isotopomer measurements were used to indicate N transformation pathways driving N loss over the growing season particularly around periods of peak N2O emissions.
Polyalthia longifolia (False Ashoka) is an ideal choice for better air quality at kerbside locations
Authors: Parkar Vidit , Datta Savita , Hakkim Haseeb , Kumar Ashish , Shabin Muhammed , Sinha Vinayak , Sinha Baerbel
Published: March 2020

Tropospheric ozone is a major pollutant and it is harmful for humans at sustained exposures of 40 ppb or more in ambient air. In this study we calibrate the deposition of ozone for stomatal exchange (DO3SE) model for Polyalthia longifolia (False Ashoka), a tree that accounts for 5-20% of the urban plantations in Indian cities and subsequently use the model to estimate not only the stomatal O3 uptake by this tree but also its capability to sequester other criteria air pollutants. We discuss the impact of planting this tree on ozone precursors NOx and VOCs in a roadside plantation scenario for mitigating air pollution.

Stomatal conductance of Polyalthia longifolia was measured, using a SC-1 Leaf Porometer, at IISER Mohali-Punjab in the NW-IGP (Northwest Indo-Gangetic Plane) which has a sub-tropical dry climate. Stomatal conductance was measured during all the four (Summer, Monsoon, Post-Monsoon, Winter) seasons, while BVOC emission fluxes were quantified using a dynamic plant cuvette during post monsoon, winter and summer season. We use ambient mixing ratios of ozone, NO, NO2, SO2 and O3 in combination with the meteorological parameters such as temperature, RH, soil moisture and photosynthetically active radiation (PAR) from the IISER Mohali Atmospheric chemistry facility to quantify Polyalthia longifolia roadside plantations’ impact on urban air quality through stomatal uptake of air pollutants (primarily NO, NO2 and O3) and BVOC emissions. Polyalthia longifolia displays a number of very interesting characteristics that include being a low isoprene and monoterpene emitter, having an extremely high leaf area index thanks to its height, straight shape and dense canopy. It displays extreme resistance to drought and high vapour pressure deficits in summer allowing stomatal uptake of pollutants and evaporative cooling to continue even under unfavourable meteorological conditions.
Flood inundation mapping with multi-satellite soil moisture observations
Authors: Wang Jiao , Chen Otto , Chen Yiheng , Liu Ying , Zhuo Lu , Rico-Ramirez Miguel , Han Dawei
Published: March 2020

In recent decades, remote sensing has widely been used in mapping floods inundations, and many studies have explored the association between antecedent soil moisture and precipitation to assess or predict floods with quantity and intensity. However, capturing the specific flooding events is not always guaranteed because of the satellite poor revisit frequency. Moreover, little attention has been paid to retrieve historic flood inundation based on soil moisture dynamics, especially in the areas with the data scarcity both in terms of soil moisture observations and fine temporal resolution satellite data.

In this study we attempt to explore this issue in two contrasting areas: one arid and one humid, which are the Nile Delta and the Mississippi River Delta, respectively. Several flooding events are selected to conduct specific flood inundation analysis. Multiple satellite microwave soil moisture products are analysed, including European Space Agency Climate Change Initiative (ESA-CCI) Soil Moisture, Soil Moisture Active Passive (SMAP), Advanced Microwave Scanning Radiometer (AMSR-2) and ESA Sentinel satellite imagery.

Considering that the soil moisture decreases more slowly than the surface flooded water, the present study aims to retrieve historic flood inundation based on soil moisture dynamics from satellites, and the main objectives are: (1) to make a comparison on spatial and temporal dynamic patterns of the above-mentioned products in two study areas; (2) to investigate a method for distinguishing the flooded areas and the areas which are always fully saturated; (3) to develop an approach for detecting historic flood inundation based on soil moisture dynamics; and (4) to calibrate the soil moisture output from WRF-Hydro model using satellite soil moisture observations. Results are expected to be applicable for decision-making in flood disaster relief and flood prediction.
Analyzing the Impacts of Urbanization on Watershed Streamflow Characteristics
Authors: Shen Qining , Cong Zhentao
Published: March 2020

It is widely recognized that urbanization has a significant impact on streamflow characteristics. However, the influences of economic development, increasing population and positioning of urban development on streamflow regimes is still not fully understood. This study aims to clarify these influences by analyzing 134 catchments in China and 1064 catchments in the United State. Urbanization metrics were derived from gridded GDP dataset, gridded population dataset and land use/land cover datasets, while the streamflow characteristics were calculated using annual streamflow and mean daily discharge data. The statistical analysis indicated that the rate of change in rainfall-runoff ratio is positively related to the growth rate of GDP and urban area both in China and the U.S., but this relationship was not found in population growth rate. Increasing the extent of urbanized area increased high and low flow frequency in Kansas metropolitan region as well as San Antonio metropolitan region, while reduced low flow frequency in Atlanta metropolitan region. In addition, urban expansion also enhanced streamflow flashiness. Compared to down-stream development, up-stream development increased high flow volume in Atlanta metropolitan region and Kansas metropolitan region, while decreased high flow volume in San Antonio metropolitan region and low flow volume in all study metropolitan regions. The findings in this study provide a sight for future researches in hydrological variation due to urbanization.