bluuebunny/crossref_metadata_2025 huggingface dataset:
On the momentum-, heat-, and moisture-exchange on the ocean surface under strong wind conditions.
Authors: Savenkova Elena , Kudryavtsev Vladimir , Chapron Bertran
Published: March 2020

We present results of the model treatment of momentum-, heat-, and moisture-exchange on the ocean surface under strong wind conditions. Despite the large amount of experimental and theoretical efforts, the mechanism and physics of the air-sea interaction at high wind conditions is still poor known and many open questions are still remained. (see e.g. Donelan et.al. 2004, Powell 2003, Kudryavtsev 2006, Jarosz 2007, Troitskaya et.al. 2011).

The model is based on extension of wind-over-wave couple model suggested by Kudryavtsev, Chapron and Makin (2014, hereinafter KCM2014). This model confirmed crucial role of wave breaking on surface drag and heat-, moister-transfer coefficients. Description of wave breaking crest roughness in KCM2014 is treated as Kolmogorov-type spectra resulting from the energy flux from the largest energetic breaking disturbances toward shorter scales. To extend KCM2014 model on high wind conditions, we introduced  Kelvin- Helmholtz instability which is able to disrupt both the crests of short regular (non-breaking) waves, and the small-scale breaking crests roughness. It is suggested that at wind speed exceeding a critical value, spectral components of both regular wind waves and breaking crests roughness are subjected to Kelvin-Helmholtz instability and aerodynamically disrupted, and thus do not contribute to the total form drag. This effect results in decrease of the surface drag, that in turn, following KCM2014, leads to  enhancement of exchange at the sea surface heat and moister transfer. As a consequence, ratio of the enthalpy to the drag coefficient increases and at wind speed above 25 m/s exceeds critical level introduced by (Emanuel, 1995). Comparison of model predictions with available data at high winds is encouraging, and suggests that accounting for the Kelvin- Helmholtz instability in the wind-over-wave coupled model provides realistic description of air-sea interaction under strong wind condition.

The work was supported by Russian Science Foundation grant No 17-77-30019.
Improved ocean wind forcing products
Authors: Giesen Rianne , Trindade Ana , Portabella Marcos , Stoffelen Ad
Published: March 2020

The ocean surface wind plays an essential role in the exchange of heat, gases and momentum at the atmosphere-ocean interface. It is therefore crucial to accurately represent this wind forcing in physical ocean model simulations. Scatterometers provide high-resolution ocean surface wind observations, but have limited spatial and temporal coverage. On the other hand, numerical weather prediction (NWP) model wind fields have better coverage in time and space, but do not resolve the small-scale variability in the air-sea fluxes. In addition, Belmonte Rivas and Stoffelen (2019) documented substantial systematic error in global NWP fields on both small and large scales, using scatterometer observations as a reference.

Trindade et al. (2019) combined the strong points of scatterometer observations and atmospheric model wind fields into ERA*, a new ocean wind forcing product. ERA* uses temporally-averaged differences between geolocated scatterometer wind data and European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis fields to correct for persistent local NWP wind vector biases. Verified against independent observations, ERA* reduced the variance of differences by 20% with respect to the uncorrected NWP fields. As ERA* has a high potential for improving ocean model forcing in the CMEMS Model Forecasting Centre (MFC) products, it is a candidate for a future CMEMS Level 4 (L4) wind product. We present the ongoing work to further improve the ERA* product and invite potential users to discuss their L4 product requirements.

References:

Belmonte Rivas, M. and A. Stoffelen (2019): Characterizing ERA-Interim and ERA5 surface wind biases using ASCAT, Ocean Sci., 15, 831–852, doi: 10.5194/os-15-831-2019.

Trindade, A., M. Portabella, A. Stoffelen, W. Lin and A. Verhoef (2019), ERAstar: A High-Resolution Ocean Forcing Product, IEEE Trans. Geosci. Remote Sens., 1-11, doi: 10.1109/TGRS.2019.2946019.
Alternative Level 1A to 1B Processing of GRACE Follow-On LRI data
Authors: Misfeldt Malte , Müller Vitali , Heinzel Gerhard , Danzmann Karsten
Published: March 2020

The Laser Ranging Interferometer (LRI) on-board GRACE Follow-On, which was launched in May 2018, provides ranging data between two satellites with previously unknown precision. The low noise level of approximately 200 pm/rtHz at Fourier frequencies around 10 Hz allows us to investigate features, that have not been seen before in the ranging data.  

Due to this high sensitivity of the LRI, we are able to assess spurious linear non-gravitational accelerations in direction of the line-of-sight caused by attitude thruster activation, which should ideally produce only angular motion. This analysis may help to refine the models used in the Calibrated Accelerometer Data (ACT) product. The ACT product is derived from raw accelerometer data and corrects artefacts present in the raw accelerometer (ACC) product. However, linear non-gravitational accelerations can only be measured in narrow frequency ranges by the LRI, where the gravity ranging signal decayed below other contributors.

The conversion of LRI Level-1A to 1B is a complex task that comprises non-trivial removal of phase jumps, scaling, filtering and interpolation of data. In order to access the high-quality ranging data and have low post-fit residuals, the LRI instrument team at the Albert-Einstein Institute (AEI) in Hanover, Germany derived an alternative LRI Level-1B data product for January 2019 with some improvements compared to the official SDS RL04 data. The data can be downloaded at https://wolke7.aei.mpg.de/s/AYza4wrFjYBxHHQ.

In this poster we compare the AEI release with RL04 and explain the differences in the preprocessing of the data, which mainly originate from a more sophisticated estimation of the scale factor (i.e. the absolute laser frequency or wavelength), a continuous data stream without biases at day bounds and a light time correction with less noise from numerical inaccuracies.
Detecting drought effects on tree mortality in forests of Franconia (Germany)
Authors: Heisig Johannes , Samimi Cyrus
Published: March 2020

Central European forests face challenges with climate changing much faster than they can adapt. Extremely hot and dry summers like in 2018 deprive forests of soil moisture, leaving them with low ground water levels. While individuals with deep and well-established root systems survive, young individuals and shallow-rooted species perish.

In southern Germany, die-off of single trees or small groups got noticeable recently. Such effects of harsher conditions rarely occur over large areas, but more in a spotted, irregular manner. This makes the phenomenon difficult to detect and to estimate its extent. The share of trees lately deteriorated may be larger than expected and represent a considerable portion of forests. Therefore, we see the great need for monitoring. Remote sensing data is suitable to examine inaccessible areas at a large scale. To quantify mortality of individual trees among a majority of vital ones, sensor platforms and respective data have to fulfill certain criteria regarding spatial, temporal and spectral resolution. Dead trees can be distinguished from others due to discoloration and defoliation. This change in appearance affects the spectral response, even in pixels larger than the tree’s extent.

This study aims at recommending a suitable spatial scale for space-borne multispectral imagery products to achieve this task. We evaluate commercial and free remote sensing data products and their ability to estimate fractional cover of dead vegetation. Satellite data employed in this study comes from Landsat 8 (30 m), Sentinel-2 (10 m), RapidEye (6.5 m) and PlanetScope (3 m). Classification performance is tested against high-resolution multispectral aerial imagery (17 cm) acquired with a Micasense RedEdge-M camera.

High-resolution Micasense images are capable of detecting single dead trees, even after downgrading the resolution from 17 cm to 3 m. For all data products tested, fraction of dead trees per pixel did not differ significantly among land cover types (dead vegetation, vital vegetation, pavement, open soil). This indicates that individual dead trees may not be detectable in vital forest stands. The finding even seems to be valid for a resolution of 3 m (PlanetScope), which is identical to the downgraded Micasense data. In the near future the detection of this phenomenon might profit from technical developments towards even higher spatial detail of space-borne sensors. Alternatively, high resolution images from aerial campaigns, manned or unmanned, could bridge this gap when flight time and spatial coverage are increased significantly and facilitating policies are in place.
Back analysis numerical modelling of the 19/06/1996 Cardoso (Stazzema, LU - Italy) flood: from gravitational movements to their evolution in rapid flows
Authors: Amaddii Michele , D'Agostino Vincenzo , Disperati Leonardo , Fantozzi Pier Lorenzo
Published: March 2020

During the June 19th of 1996 a storm involved the Tyrrhenian sector of northern Tuscany (Italy), especially hitting the Versilia and Garfagnana areas. Major consequences and damages, due to the extremely intense precipitation (about 500 mm/13 h and 158 mm/h peak intensity), occurred in the surrounding of the Cardoso village (Versilia river basin, Stazzema, LU), with 14 casualties. At 1.20 p.m., the rainfall peak intensity coupled with the development of a large number of shallow landslides, triggered rapid flows and caused severe flooding in the Cardoso area, which was covered by hundred thousand of cubic meters of deposits.
The aim of this study was the characterization of the rapid flows occurred during the event and their back analysis numerical modelling by using a hydrological-hydraulic software. First of all, the amount of mobilized solid volume was assessed, differentiating between materials collapsed from the slopes and those eroded from the low-order drainage network. This goal was obtained by visual interpretation of post-event orthophotos and by morphometric analysis. Subsequently, starting from the rainfall data of the event, the hydrological modelling was performed by the Curve Number method, in order to define flood hydrographs along the drainage network of the Cardoso sub-basins. For the hydraulic modelling, the liquid discharge data were used to calculate debris-graphs of rapid flows, by implementing empirical correlations based on peak discharge, debris volume and channel slope. Different rheological parameters were tested to perform numerical modelling.
Back analysis results allow to infer that the mass movements initially started as hyperconcentrated flows in the upper parts of the sub-basins and after evolved into muddy debris flows, which caused flooding of the Cardoso valley. The results are in good agreement with the flooded area extent, as estimated by visual interpretation of both archive photos and aerial orthophotos acquired immediately after the event.
Unmeasured inflows determination in the context of the assessment of the water balance of irrigation reservoir
Authors: Cisty Milan , Soldanova Veronika , Cyprich Frantisek
Published: March 2020

Irrigation reservoirs are used to retain water during periods of surplus and to control its subsequent use for irrigation in drought periods. While designing a reservoir, it is essential to evaluate its function and assess its ability to provide the required amount of water for irrigation. It means an evaluation of the reservoir for the quantitative balance of water. The input data used in such computations include the water inflow into the reservoir, demand for water abstraction from the reservoir, data on the required outflow of water below the reservoir, and the evaporation and other losses of water from the reservoir. Smaller streams often supply irrigation reservoirs at the margins of river catchments. It is crucial, from the point of view of this work, that such smaller streams often do not have systematic measurements of their flow. Therefore determination of this quantity is often the main problem of water balance evaluation. This work proposes a method for the acquisition of such data. While identifying unknown stream flows required for such a calculation, authors suppose that historical climatic data for the given area and flows in some of the nearby river catchments are available (measured). Description of the method of selecting river catchments such that their measured flows can be used in the calculation of an unknown flow of a different stream will be presented. A case study from the Small Carpathians in Western Slovakia is reported in the presentation. This study compares the conceptual hydrologic model, linear regression with LASSO regularization, and various machine learning methods (CATboost, Random Forest, Support Vector Machines). Authors will evaluate the precision of flows determination by various statistical indicators.

Acknowledgements. This work was supported by the Slovak Research and Development Agency under Contract No. APVV-15-0489 and by the Scientific Grant Agency of the Ministry of Education of the Slovak Republic and the Slovak Academy of Sciences, Grant No. 1/0662/19.
Evaluating the accuracy of equivalent-source predictions using cross-validation
Authors: Uieda Leonardo , Soler Santiago
Published: March 2020

We investigate the use of cross-validation (CV) techniques to estimate the accuracy of equivalent-source (also known as equivalent-layer) models for interpolation and processing of potential-field data. Our preliminary results indicate that some common CV algorithms (e.g., random permutations and k-folds) tend to overestimate the accuracy. We have found that blocked CV methods, where the data are split along spatial blocks instead of randomly, provide more conservative and realistic accuracy estimates. Beyond evaluating an equivalent-source model's performance, cross-validation can be used to automatically determine configuration parameters, like source depth and amount of regularization, that maximize prediction accuracy and avoid over-fitting.

Widely used in gravity and magnetic data processing, the equivalent-source technique consists of a linear model (usually point sources) used to predict the observed field at arbitrary locations. Upward-continuation, interpolation, gradient calculations, leveling, and reduction-to-the-pole can be performed simultaneously by using the model to make predictions (i.e., forward modelling). Likewise, the use of linear models to make predictions is the backbone of many machine learning (ML) applications. The predictive performance of ML models is usually evaluated through cross-validation, in which the data are split (usually randomly) into a training set and a validation set. Models are fit on the training set and their predictions are evaluated using the validation set using a goodness-of-fit metric, like the mean square error or the R² coefficient of determination. Many cross-validation methods exist in the literature, varying in how the data are split and how this process is repeated. Prior research from the statistical modelling of ecological data suggests that prediction accuracy is usually overestimated by traditional CV methods when the data are spatially auto-correlated. This issue can be mitigated by splitting the data along spatial blocks rather than randomly. We conducted experiments on synthetic gravity data to investigate the use of traditional and blocked CV methods in equivalent-source interpolation. We found that the overestimation problem also occurs and that more conservative accuracy estimates are obtained when applying blocked versions of random permutations and k-fold. Further studies need to be conducted to generalize these findings to upward-continuation, reduction-to-the-pole, and derivative calculation.

Open-source software implementations of the equivalent-source and blocked cross-validation (in progress) methods are available in the Python libraries Harmonica and Verde, which are part of the Fatiando a Terra project (www.fatiando.org).
Gradual transition from temperature to precipitation controlled regime in Rhone River discharges
Authors: Taricco Carla , Rubinetti Sara , Arnone Enrico , Zanchettin Davide , Rubino Angelo , Bizzarri Ilaria
Published: March 2020

River discharge series provide large-scale hydrological information over a broad range of timescales. Despite discharge records consist of punctual measurements, they integrate variations in snowmelting, precipitation and runoff processes over the catchment till the discharge measurement site.

Discharges of the Rhone River, one of the largest rivers in Europe, have been monitored accurately during the last century at different sites. Long discharge records from seven stations along the course reveal the spatial and temporal behaviour of discharges from the source of the river to its mouth.  An accurate spectral analysis of the records, performed using advanced spectral analysis methods, allow us to extract significant periodic variations in the records at different temporal scales. Then, we analyse the sensitivity of such periodic variations to evolving hydroclimate conditions, in particular focusing on the relationship between discharge and temperature and precipitation.

The strong annual oscillation recorded at stations close to the source is almost entirely due to snow melting on alpine glaciers, closely resembling the temperature annual cycle. This remarkable agreement allows to consider the upstream discharges as a thermometer on the glacier region during the melting season. On the contrary, the decrease of the annual cycle going towards the mouth of the river and the contemporary growth of interannual components demonstrates the transition from a temperature to a precipitation controlled discharge regime.

We will finally discuss the impact of large-scale variability patterns on the detected discharge variations and associated implications for their near-term predictability.
Characterization of sub-ionospheric VLF/LF waveguides for seismic event studies during solar minimum
Authors: Eichelberger Hans , Schwingenschuh Konrad , Boudjada Mohammed Y. , Besser Bruno P. , Wolbang Daniel , Rozhnoi Alexander , Solovieva Maria , Biagi Pier Francesco , Stachel Manfred , Aydogar Özer , Muck Cosima , Grill Claudia , Jernej Irmgard
Published: March 2020

In this study we present measurements and simulations of mid-latitude sub-ionospheric propagation paths between several VLF/LF transmitters and the Graz seismo-electromagnetic receiver facility (Schwingenschuh etal, 2011) during the current solar minimum condition. The upper D/E-region boundary of the waveguide is stable during the low solar activity in the years 2018 and 2019, i.e. measured VLF/LF amplitude and phase variations are mainly due to natural excitations from the lithosphere, atmosphere, and man-made disturbances. In particular, this period gives a baseline to characterize VLF amplitude and phase modulations in the waveguide cavity related to seismic activity over Europe. In addition, this opportunity let us probe the signal threshold and feed-back into waveguide simulation models. We conclude, proven long-term VLF/LF measurements, the continuous monitoring of the cavity, could be valuable in the assessment of seismic hazard scenarios.

Ref:

Schwingenschuh, K., Prattes, G., Besser, B. P., Mocnik, K., Stachel, M., Aydogar, Ö., Jernej, I., Boudjada, M. Y., Stangl, G., Rozhnoi, A., Solovieva, M., Biagi, P. F., Hayakawa, M., and Eichelberger, H. U.: The Graz seismo-electromagnetic VLF facility, Nat. Hazards Earth Syst. Sci., 11, 1121–1127, https://doi.org/10.5194/nhess-11-1121-2011, 2011.
Deriving a Physically-Based Calving Rate Law for Marine Ice-Cliff Instability
Authors: Crawford Anna , Todd Joe , Benn Doug , Åström Jan , Zwinger Thomas
Published: March 2020

Rapid grounding line retreat at marine-terminating glaciers could expose ice cliffs with heights greater than those on observational record. However, the finite strength of ice places a limit on the height of subareal cliffs. It is proposed that marine ice-cliff instability (MICI) will begin once a stable height threshold is exceeded. If a glacier is situated over a retrograde slope, as is the case for Thwaites Glacier and much of the West Antarctic Ice Sheet, MICI can be expected to accelerate as retreat progresses and increasingly tall and unstable ice cliffs are formed. This is consequential for global sea level rise, yet large uncertainties remain in the prediction of MICI retreat rates.

We investigate MICI by pairing the full Stokes continuum model Elmer/Ice and the Helsinki Discrete Element Model (HiDEM). Viscous flow, simulated in Elmer/Ice, is found to be a necessary pre-condition for MICI collapse. Forward advance and bulging lead to ice-front instability and pervasive crevassing in HiDEM. This culminates in full-thickness calving events. We do not observe calving at ice faces prior to viscous deformation. HiDEM simulations that implement viscous flow (HiDEM-ve) also show forward advance and waterline bulging, similar to the Elmer/Ice simulations. However, the importance of granular shear is highlighted by pronounced shear bands and patterns of surface lowering in HiDEM-ve output. These results emphasize the importance and complexity of viscous and brittle process interaction during MICI.

A simulation matrix of grounded termini shows that calving frequency and magnitude increase with the thickness of the calving front. The time required for viscous flow to recreate unstable conditions is influenced by thickness as well as ice temperature and basal friction. Simulations of buoyant termini are seen to calve through basal-crevassing and block-rotation, as opposed to incising surface-crevasses. Lastly, we observe that buttressing mélange can suppress retreat rate if a sufficient resistive force is delivered to the calving front. A physically-based law for MICI retreat rate is derived from our simulation matrix; this calving rate law can be incorporated into large-scale ice sheet models to constrain projections of Antarctic retreat and associated global sea level rise. Our results will also be used to investigate the future retreat of Thwaites Glacier, which is vulnerable to MICI due to a retreating grounding line, fragile floating ice shelf, and precarious positioning above an overdeepening basin.
New evidences of seasonal deep ocean current variability in the north-eastern tropical Pacific Ocean impacted by remote gap winds
Authors: Purkiani Kaveh , Paul André , Vink Annemiek , Walter Maren , Schulz Michael
Published: March 2020

There has been a steady increase of interest in mining of deep-sea mineral in the Clarion-Clipperton Zone in the eastern Pacific Ocean during the last decade. This region is known as one of the most eddy-rich regions, typically at the mesoscale, which are mainly generated by the intense wind burst channelled through gaps in the Sierra Madre mountains in Central America. Here we use a combination of satellite and in situ observations to evaluate the relationship between deep-sea current variability at the region of potential future mining and Eddy Kinetic Energy (EKE) at the vicinity of gap winds.

A geometry-based eddy detection algorithm has been applied to altimetry sea surface height data for a period of 24 years from 1993 to 2016 in order to study the main characteristic parameters and the spatio-temporal variability of mesoscale eddies in the north-eastern tropical Pacific Ocean. Significant differences between the characteristics of eddies with different polarity (cyclonic vs. anti-cyclonic) were found. For eddies with lifetimes longer than 7 days, the total number of cyclonic eddies exceeds that of anticyclonic eddies by about 16%. However, anticyclonic eddies are larger in size and greater in vorticity, and survive longer in the ocean than cyclonic eddies (often 90 days or more). Besides the polarity of eddies, the location of eddy formation should be taken into consideration for investigating the variability of current velocity at deep ocean region as we found eddies originated by Tehuantepec (TT) gap wind lasting longer in the ocean and travel farther distances in different direction compare to eddies emanated from Papagayo gap wind. Long-lived anticyclonic eddies generated at the vicinity of the TT gap wind are observed to travel long distances up to 4500 km far offshore west of 110° W.

EKE anomalies observed in the surface of the interior ocean at a distance of ca. 2500 km from the coast correlate with the seasonal variability of EKE in the region of the TT gap winds with a time lag of 5-6 months. This is consistent with the required time for an anticyclone eddy with the average translation speed of 12 cm/s to reach the ocean interior. Significant seasonal variability of deep ocean current velocity recorded by ocean-bottom moorings at depth of 4100 m likely reflecting the energy transfer of surface EKE generated by the gap winds to the deep ocean is also found. On an interannual scale, a significant relationship between cyclonic eddy characteristics and El-Niño Southern Oscillation was found, whereas no robust correlation was detected for anticyclonic eddies.
Investigating geological processes and their links with geological structures through geomanifestations
Authors: Barros Renata , Piessens Kris , Ferket Helga , Rman Nina , Kun Éva
Published: March 2020

GeoConnect³d introduced the concept of geomanifestations to define any distinct local expression of ongoing or past geological processes. These manifestations, or anomalies, often point to specific geologic conditions and, therefore, can be important sources of information to improve geological understanding of an area. Examples include seismicity, gas seeps, local compositional differences in groundwater and springs, thermal anomalies, mineral occurrences, jumps in hydraulic head, overpressured zones and geomorphological features. Geomanifestations are an addition to the structural framework model also being developed in GeoConnect³d, aiming to show where and how processes and structures may be linked.

Data on geomanifestations are being collected in three areas: the Roer-to-Rhine area of interest in northwest Europe, and the Mura-Zala Basin and Battonya High within the Pannonian Basin area of interest in Eastern Europe. A first assessment of available data showed that groundwater-related geomanifestations in the form of anomalies in chemical composition (enrichment in elements such as Fe, or hydrocarbon gases and CO2,) or temperature (thermal water springs, geothermal anomaly in wells) are mappable in all areas. These geomanifestations point to special geological features in each area, such as proximity to magmatic reservoirs, presence of deep-rooted faults and considerable differences in the subsurface relief (trough–high system of the basement) among others. These anomalies at times define spatial patterns, which might or not be represented in the structural framework model, thus demonstrating whether they can be explained by the current geological understanding embedded in the structural framework. With this first test, we conclude that data on groundwater-related geomanifestations add to the robustness of the structural framework model. Further investigations with other types of geomanifestations are foreseen.

This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 731166.
Numerical modeling towards the sub-kilometer scale: The potential for regional reanalysis
Authors: Valmassoi Arianna , Keller Jan , Friederichs Petra , Hense Andreas
Published: March 2020

In recent years convection-permitting models are increasingly often used for retrospective climate studies. Besides the better reproduction of atmospheric processes, the increase in resolution allows for a more accurate representation of land-surface heterogeneities and thus a more realistic depiction of smaller scale characteristics. The work presented here investigates the potential benefits of higher model resolutions on the atmospheric state estimates in possible future regional reanalysis data sets.

Specifically, we employ the ICOsahedral Non-hydrostatic model ICON (the current operational NWP model of the German Meteorological Service DWD) in its Limited Area Mode (ICON-LAM) with a LETKF data assimilation framework.
Simulations are conducted for a free run (dynamical downscaling) and a data assimilation (DA) one for various horizontal resolutions from the operational 2.1 kilometers towards finer resolutions of 1 kilometer and below. In addition, different land surface data sets are used as lower boundary conditions in order to explore their impact under the chosen horizontal resolutions. These experiments are conducted for Central Europe and Germany for the month of June 2019 which includes several extreme events, e.g., heatwave, heavy precipitation.

The presentation evaluates the simulations against non-assimilated observations for the free and DA experiments. The impact of the land-surface heterogeneity and resolution are quantified on both atmospheric and soil variables to account for possible feedback processes. Particular attention is given to the effects on the vertical atmospheric structure and precipitation generation.
Anomalous Vp/Vs in highly pressurized rocks: Evidence for anisotropy or mafic composition?
Authors: Pimienta Lucas , Schubnel Alexandre , Fortin Jerome , Guéguen Yves , Lyon-Caen Helene , Violay Marie
Published: March 2020

         Anomalously high seismic P- to S-wave velocity ratios (Vp/Vs) have been observed in subduction zones, in locations where varieties of earthquakes and slips are expected to occur. From qualitative laboratory knowledge of rocks Poisson’s ratio, these results were interpreted as evidence of near-lithostatic pore fluid pressure. Because most laboratory data did not document such high Vp/Vs values, these were further linked to additional constrains of anisotropy or the dominance of minerals of very high intrinsic Vp/Vs, e.g. mafic rocks.However, does high Vp/Vs necessarily imply anisotropy and/or mafic composition?

         Recently, the measuring frequency (f) was shown to play a major role on rocks’ resulting Poisson’s ratio, so that usual laboratory results (at f = 1 MHz) might not directly transfer to field ones (at f = 1 Hz). From this consideration, we investigate Vp/Vs of a variety of crustal rocks in the elastic regime relevant at the field scale, the undrained elastic regime.Accounting for rocks dispersive properties, this work aims to show that:

In the laboratory, in isotropic rocks, one might attain Vp/Vs values as high as the anomalous ones observed in subduction zones.

No mineralogical control is needed for such high Vp/Vs values, which could be consistent with the inherent mineral variability in different settings across the globe.

High pore fluid pressure is a major parameter, but not alone: such high values cannot be achieved without very high degree of micro-fracturing of the rock, opened by high fluid pressures, an information of potential importance to understand those seismogenic zones.
Evaluation of near-surface temperature forecasts against super-site observations
Authors: Schmederer Polly , Sandu Irina , Haiden Thomas , Beljaars Anton , Leutbecher Martin , Becker Claudia
Published: March 2020

ECMWF’s medium-range forecasts of near-surface weather parameters, such as 2 m temperature, humidity and 10 m wind speed, have become more skilful over the years, following the trend of improvements in the forecast skill of upper-air fields. However, they are still affected by systematic errors which have proved difficult to eliminate. Systematic forecast errors in temperature and humidity near the surface can be better understood by also examining errors higher up in the atmospheric boundary layer and in the soil. Meteorological observatories, also known as super-sites, provide long-term observational records of such vertical profiles. ECMWF started to use data from super-sites more systematically to evaluate the quality of forecasts in the lowest part of the atmosphere (up to 100m) and in the soil, in an attempt to disentangle sources of forecast error in near-surface weather parameters. Findings for 2-metre temperature errors in ECMWF forecasts at European super-sites suggest that the errors are partly the result of the model exchanging too much energy between the atmosphere and the land. However, the influence of other factors, such as errors resulting from the representation of vegetation in semi-arid areas and from small-scale variations in vegetation and soil type near measurement stations, mean that it is difficult to adjust the energy exchange in a way which leads to an overall error reduction on the European scale.
Simulation of mineral dust transport to the East China Sea with FLEXPART 10.4
Authors: Hilboll Andreas , Kalisz Hedegaard Anna Beata , Adam Lia , Kaiser Katharina , Schneider Johannes , Vrekoussis Mihalis
Published: March 2020

Particulate matter is of special interest in atmospheric studies because it has important effects on both the Earth's climate and on human health.  Currently, aerosols contribute largest to the overall uncertainty of the net radiative effects in studies of climate change.  At the same time, aerosols are responsible for a large fraction of the overall impact of air quality on human health.  Mineral dust is an important aerosol constituent and makes up a significant part of the total aerosol load.  After its emission, mineral dust can be transported over very large distances in the atmosphere, and in extreme cases influence air quality far away from its source region.

The project Effect of Megacities on the Transport and Transformation of Pollutants on the Regional to Global Scales (EMeRGe) consisted of two measurement campaigns with the research aircraft HALO.  HALO operated for two four-week periods in Europe (based close to Munich) and East Asia (based in Taiwan) in July 2017 and March 2018, respectively.  The aircraft was fully equipped with extensive measurement instrumentation to sample atmospheric composition with a focus on the air pollution outflow from major population centers.

Here, we present simulations of coarse-mode aerosol transport to the East China Sea, where EMeRGe-Asia flight E_AS_F#11 was flying from Taiwan to Japan and back on 30 Mar 2018.  During the flight, enhanced concentrations of aerosol in the 0.5-3µm diameter range were measured using an optical particle counter (OPC) in several different locations.  We used version 10.4 of the FLEXPART Lagrangian dispersion model to simulate sensitivity fields to emissions of dust, sea-sealt, and biomass burning aerosol.  Combined with emission data for the three aerosol species, we can estimate the contribution of the different species and source regions to the measured aerosol enhancements.

Among others, our simulations show that mineral dust from as far as the Sahara desert in North Africa can contribute significantly to the total aerosol concentration over the East China Sea.
Mineralogy sensitive ice nucleation parameterizations in Dust Regional Atmospheric Model (DREAM)
Authors: Ilić Luka , Jovanović Aleksandar , Kuzmanoski Maja , Madonna Fabio , Rosoldi Marco , Marinou Eleni , Ničković Slobodan
Published: March 2020

The Sahara Desert is the major source of mineral dust, which is a significant portion of atmospheric aerosol. Mineral dust particles play a role in radiative balance, with a direct effect and by influencing cloud formation and lifetime. They have been recognized as highly efficient ice nuclei, fostering the development of parameterizations for immersion and deposition freezing involving dust particles. Feldspar minerals have shown to be a significantly more efficient ice nucleating agents than other dust minerals which led to the development of a ‘mineralogy sensitive’ immersion freezing parameterization. The investigation of the relative efficiency of quartz compared to feldspars for the immersion ice nucleation, based upon literature data and new experiments, led to the development of a new parameterization to be applied to mineral dust concentrations. Within numerical models, explicit simulation of mineral dust fractions enables the use of ‘mineralogy sensitive’ immersion parameterizations.

The operational DREAM model calculates the number of ice nuclei,but does not take into consideration the mineral composition of dust. In this study, instead, we use DREAM model to simulate the atmospheric cycle of feldspar and quartz fractions of dust. Dust mineral composition is used to calculate ice nucleating particle concentrations based on mineral-specific immersion freezing parameterizations. A case study related to the observations of geometrical and microphysical characteristics of the clouds formed in the Mediterranean, in April 2016 is considered. We compare the model results with ice nucleating particle concentrations retrieved using lidar and radar ground-based remote sensing observations at Cyprus and Potenza. The analysis explores how the mineral composition of dust and the parameterization of its effects on ice initiation could further improve ice nucleation representation in numerical models.
MMS Observations of FTE-Type Structures with Internal Magnetic Reconnection
Authors: Kieokaew Rungployphan , Lavraud Benoit , Fargette Naïs
Published: March 2020

A bipolar magnetic variation Bn with enhanced core and total fields in spacecraft data are recognized as a Flux Transfer Event (FTE) signature, which corresponds to the passage of a magnetic flux rope structure. Recent literature reported Magnetospheric Multiscale (MMS) observations of FTE signatures with magnetic reconnection signatures at the central current sheet. Among reported cases, electron pitch angle distributions (ePAD) in the suprathermal energy range show different features on either side of the reconnecting current sheet, indicating different magnetic connectivities. This structure is interpreted as interlinked/interlaced flux tubes, possibly formed by converging jets toward the central current sheet that in turn enhance magnetic flux pile-up and facilitate reconnection at the current sheet separating the two flux tubes. By surveying similar events using MMS data, we found some FTE-type structures with reconnection signatures at the central current sheet but with homogeneous ePAD of suprathermal electrons across the structures. Thus, these structures are inconsistent with interlinked flux tubes, but rather a regular flux rope. This leads to a question of how reconnection can occur in those single flux ropes, and their relation with interlinked flux tubes. In this work, we investigate properties of these structures and their related upstream solar-wind conditions. Formation mechanisms of such structures and how reconnection can occur will be discussed.
Airborne measurements of trace gas emissions from African biomass burning during the MOYA Campaign
Authors: Barker Patrick , Allen Grant , Bannan Thomas , Pitt Joseph , Bauguitte Stephane , Nisbet Euan , Lee James
Published: March 2020

Biomass burning (BB) is known to contribute significantly to the global budgets of atmospheric trace gases and aerosols.  Approximately 1.6–4.1 Pg of CO2, 11–53 Tg CH4 and 0.1–0.3 Tg of N2O is emitted to the atmosphere per year as a result of biomass burning on a global scale (Crutzen and Andreae, 2016). The contribution of BB to global GHG budgets is likely to increase over time due to climate feedback of warming and more widespread drought conditions increasing the likelihood and spread of wildfire events (Liu et al., 2014).

It is estimated that Africa accounts for approximately 52% of all BB carbon emissions, with the Northern Sub-Saharan African region alone accounting for 20-25% of global BB carbon emissions (van der Werf et al. 2010; Ichoku et al. 2016). Many of these fires are anthropogenic in origin, and occur for reasons such as clearing land for agricultural use, management of natural savannah vegetation, or as pest control (Andreae, 1991).  Despite the African contribution to global BB emissions, there are limited in situ studies of African wildfire emissions.

In situ measurements of CH4, CO2 and N2O and CO in biomass burning plumes were carried out in Senegal in February 2017 and in Uganda in January 2019 during the Methane Observations and Yearly Assessments (MOYA) project. These observations were carried out using the Facility for Airborne Atmospheric Measurements BAe-146 Atmospheric Research Aircraft (ARA), which is fitted with a range of specialist instrumentation for in situ trace gas sampling. Emission factors for these species were calculated for both near-field and far-field biomass burning plumes. A notable difference in the linear trend between methane emission factors and completeness-of-combustion was identified between Senegalese and Ugandan fires.
Building amorphous calcium carbonate into geochemical biomineralisation models
Authors: Evans David , Gray William , Rae James , Greenop Rosanna , Webb Paul , Penkman Kirsty , Kröger Roland , Allison Nicola
Published: March 2020

Amorphous calcium carbonate (ACC) has been observed, or inferred to exist, in the majority of the major phyla of marine calcifying organisms. The CaCO3 produced by these organisms represents one of the largest long-term carbon sinks on Earth’s surface, such that identifying how calcification will respond to anthropogenic climate change is an urgent priority. A substantial portion of our knowledge of the biomineralisation process of these organisms is derived from inferences based on skeletal geochemical data, yet such models typically do not include an ACC component because little is known about trace element and isotope fractionation into ACC. In order to address this, we present, to our knowledge, the first structural and geochemical data of ACC precipitated from seawater under varying carbonate system conditions, seawater Mg/Ca ratios, and in the presence of three of the most common intracrystalline amino acids (aspartic acid, glutamic acid, and glycine). Based on these data we identify the carbonate system conditions necessary to produce ACC from seawater [Evans et al., 2019], and identify the dominant controls on ACC geochemistry. As an example, we utilise these data to build a simple biomineralisation model for the low-Mg (e.g. planktonic) foraminifera, based on precipitation of low-Mg calcite through an ACC precursor phase in a semi-enclosed pool. This exercise demonstrates that the observed shell geochemistry of this group of organisms can be fully reconciled with a model that includes an ACC component, and moreover that constraints can be placed on the degree of ACC utilisation and the ACC-calcite transformation process. More broadly, the exercise demonstrates that knowledge of the characteristics and geochemistry of ACC is important in the development of a process-based understanding of marine calcification.

Evans, D., Webb, P., Penkman, K. Kröger, R., & Allison, N. [2019] The Characteristics and Biological Relevance of Inorganic Amorphous Calcium Carbonate (ACC) Precipitated from Seawater. Crystal Growth & Design 19: 4300.
Application of polarimetric radar to infer ice fabric anisotropy
Authors: Ershadi Mohammadreza , Drews Reinhard , Martín Carlos , Eisen Olaf
Published: March 2020

Understanding ice flow of ice sheets is not only important to predict their future evolution, but is also required for finding future ice-core sites with an intact stratigraphy and a constrained age-depth relationship of the corresponding climate record. Anisotropic ice flow, induced through the formation of aligned Crystal Orientation Fabric (COF), is in this context important as it may cause ice overturning and folding at larger depths. Here, we use a synthetic radar forward model to explore the feasibility of detecting the crystal orientation fabric orientation and strength using coherent, polarimetric ice-penetrating radar data (ApRES). We compare our results, with ApRES data collected in Antarctica. Some of the sites are located near deep drill ice-core sites (e.g., Dome C), and we validate our approach with ice-core data.

In multilayer models, we distinguish between birefringence (caused by ray propagation through anisotropic COF with unknown strength and orientation) and anisotropic scattering (caused by an unknown depth variability of anisotropic COF). We show analytically that the scattering ratio is determined by the angular dependence of co-polarization extinction nodes. Building on previous work, we infer COF orientation using the depolarization component, and COF strength from the gradient of polarimetric coherence, respectively.

We apply this approach to polarimetric ApRES datasets. We show COF orientation can often reliably be inferred as long as it does not change significantly with depth. Rotation of principal axis with depth, on the other hand, causes a complicated radar response that is not straightforwardly interpreted. At dome positions, where the ice anisotropy develops more gently compared to flank-flow settings, the degree of anisotropy can be estimated with the phase gradient method. This becomes increasingly more difficult for flank-flow settings where phase unwrapping is required. We delineate a number of anisotropic scattering zones which likely correspond to COF patterns changing abruptly. In some cases, boundaries between anisotropic scattering zones coincide with climate transitions within the ice.

We provide our model code in the form of a user-friendly GUI, enabling to quickly explore a wide range of possible COF patterns and their corresponding imprint in the radar data. This is useful both for scientific and educational purposes. Our analysis underlines the potential of coherent, polarimetric radars to infer the COF orientation of ice sheets also away from ice core sites. This will provide important data for the inclusion of ice anisotropy in ice-flow models in the future.