bluuebunny/crossref_metadata_2025 huggingface dataset:
A High-Resolution, Model-Based Lightning Risk Map for Turkey
Authors: Yılmaz Mustafa Yağız , Göktürk Ozan Mert , Fidan Güven
Published: March 2020

Lightning strikes from convective storms are a serious safety concern for public and businesses alike. Accurate assessment of local lightning risk is therefore crucial for various industries. However, it is usually not possible to obtain lightning climatologies with reasonable spatial detail, due to the scarcity of well distributed, long term observations. At this respect, meteorological models serve as a useful tool for creating lightning risk maps, provided that their output can be verified with available observations. In this study, a high resolution (3 km) lightning risk map has been constructed for Turkey, using output from Weather Research and Forecasting Model (WRF). The model was forced by the ECMWF’s ERA-5 reanalysis data, and run for the period of January 2014 – December 2018 (5 years). Simulations were conducted on high-performance computers offered by Amazon Web Services. Lightning flash rates were estimated from WRF output using the parameterization scheme proposed by McCaul et al. (2009). Model-derived lightning rates have been calibrated and validated by observed lightning data for the determined region. The spatial pattern and average rate of lightning flashes over the validation region have been found to agree reasonably well with available observations. The high resolution lightning risk map produced in this study is the first one for Turkey that is based on numerical modeling, and it will serve as an objective guidance for location-based lightning risk assessment in the country.
Oceanic δ13C, environmental changes and Carboniferous coral reef development: Records from Tianlin and Ziyun (southern China)
Authors: Maillet Marine , Samankassou Elias
Published: March 2020

Metazoan reef builders receded globally during the Carboniferous, after the Late Devonian extinction event, with only few exceptions of coral-bearing bioconstructions reported worldwide. Among the latter, two exceptional extended coral reefs, dated as Late Viséan–Serpukhovian and Kasimovian-Gzhelian in age, respectively, were recently reported from southern China. The scarcity of coral buildups worldwide suggests global unfavorable conditions, with specific settings considered to represent refugia. To constrain these environmental conditions, seawater composition is reconstructed using carbon and oxygen isotopes originating from five measured sections located in southern China.

The resulting δ13C data reveals several environmental changes throughout the Carboniferous attributed to climate changes, ocean current variations, and proliferation of terrestrial plants. During the Late Viséan-earliest Serpukhovian, the high δ13C values (˜3‰) are interpreted as recording short-lived glacial events, with the expansion of ice-sheets in South America and eastern Australia. The scarcity of coral reef growth suggests that the cooling acted as an inhibiting factor during this period. Conversely, the development of the exceptional coral reefs in southern China could be explained by the persistence of warm oceanic currents in the epicontinental sea, located in equatorial position. During the Kasimovian-Gzhelian, the gradual δ13C positive shift from -0.7 to +4.7‰ coincides with a short-lived warming, which should be suitable for the recovery of coral communities. However, in spite of the mild climate, the scarcity of Pennsylvanian coral reef leads to consider other inhibiting factors (e.g. biological competition and aragonite seas). Interestingly, the disappearance of coral reefs in southern China correlates with negative δ13C shifts (e.g. Mid-Viséan, Late Gzhelian), interpreted as related to intensified upwellings.

The reconstitution of the Carboniferous environmental conditions documents several factors contributing to the metazoan reef demise and recovery subsequent to the Late Devonian extinction events, and adds to our current knowledge of the longest reef recovery in the Phanerozoic.

 

 
Mid-late Holocene hydroclimate variation in the source region of the Yangtze River revealed by lake sediment records
Authors: Xiaohuan Hou , Lina Liu , Zhe Sun , Xianyong Cao , Juzhi Hou
Published: March 2020

The headwater region of the Yangtze River serves as major constituent of Chinese Water Tower and is critical in providing fresh water for hundreds of millions of people living downstream. Hydrological variation is mainly influenced by environmental changes. Therefore, a good understanding of climate changes in the source region of the Yangtze River (SRYR) is of great significance. Here, we provide a lacustrine sediment core from Saiyong Co in SRYR, northeastern Tibetan Plateau, China, to reconstruct hydrological variation and the main influencing factors based on the analysis of grain size, scanning XRF, loss on ignition (LOI), which cover the past 6 ka. It is remarkable that total organic matter (LOI-550℃) exhibits opposite patterns regarding to the PC1 of XRF, which represents the allochthonous input, indicating the majority of organic matter was mainly yielded within the lake. Clustering of palaeohydrological proxies, such as the reduced PC1 and increase in median grain size, seems coincide with the weakened strength of the Indian summer monsoon, which suggest a generally dry trend in the SRYR during the mid-late Holocene. However, short pulses of outrageous period occurred at 3.8-3.2 ka BP and 1.5-1.0 ka BP. The abrupt increase in PC1 and very coarse silt indicate the lake catchment became more humid with higher surface runoff, which is consistent with weaker lake productivity. The inferred hydrological change in SRYR since 6 ka BP not only have significant environmental influence, but also agree with other sequences from Tibetan Plateau and the adjacent regions This study provides long-term records of paleoenvironmental evolution which is particularly significant to understand recent and to predict future hydrological change in SRYR.
The forgotten drought of 1765-1768: Reconstructing and re-evaluating historical droughts in the British and Irish Isles
Authors: Murphy Conor , Wilby Robert , Matthews Tom , Horvath Csaba , Crampsie Arlene , Ludlow Francis , Noone Simon , Brannigan Jordan , Hannaford Jamie , MacLeman Robert , Jobbova Eva
Published: March 2020

Historical precipitation records are fundamental for the management of water resources, yet rainfall observations typically span 100 – 150 years at most, with considerable uncertainties surrounding earlier records. Here, we analyse some of the longest available precipitation records globally, for England and Wales, Scotland and Ireland. To assess the credibility of these records and extend them further back in time, we statistically reconstruct (using independent predictors) monthly precipitation series representing these regions for the period 1748-2000. By applying the Standardised Precipitation Index at 12-month accumulations (SPI-12) to the observed and our reconstructed series we re-evaluate historical meteorological droughts. We find strong agreement between observed and reconstructed drought chronologies in post-1870 records, but divergence in earlier series due to biases in early precipitation observations. Hence, the 1800s decade was less drought prone in our reconstructions relative to observations. Overall, the drought of 1834-1836 was the most intense SPI-12 event in our reconstruction for England and Wales. Newspaper accounts and documentary sources confirm the extent of impacts across England in particular. We also identify a major, ‘forgotten’ drought in 1765-1768 that affected the British-Irish Isles. This was the most intense event in our reconstructions for Ireland and Scotland, and ranks first for accumulated deficits across all three regional series. Moreover, the 1765-1768 event was also the most extreme multi-year drought across all regional series when considering 36-month accumulations (SPI-36). Newspaper and other sources confirm the occurrence and major socio-economic impact of this drought, such as major rivers like the Shannon being fordable by foot. Our results provide new insights into historical droughts across the British Irish Isles. Given the importance of historical droughts for stress-testing the resilience of water resources, drought plans and supply systems, the forgotten drought of 1765-1768 offers perhaps the most extreme benchmark scenario in more than 250-years.
Geomorphological controls on seismic recordings in volcanic areas
Authors: Gabrielli Simona , De Siena Luca , Spagnolo Matteo
Published: March 2020

In volcanoes, topography, shallow heterogeneity, and even shallow morphology can substantially modify seismic coda signals. Coda waves are an essential tool to monitor eruption dynamics and model volcanic structures jointly and independently from velocity anomalies: it is thus fundamental to test their spatial sensitivity to seismic path effects. Here, we apply the Multiple Lapse Time Window Analysis (MLTWA) to measure the relative importance of scattering attenuation vs absorption at Mount St. Helens volcano (MSH) before its 2004 eruption. The results show the typical dominance of scattering attenuation in volcanoes at lower frequencies (3 - 6 Hz), while absorption is the primary attenuation mechanism at 12 Hz and 18 Hz. Still, the seismic albedo (measuring the ratio between seismic energy emitted and received from the area) is anomalously-high (0.95) at 3 Hz.

A radiative-transfer forward model of far- and near-field envelopes confirms this is due to strong near-receiver scattering enhancing anomalous phases in the intermediate and late coda across the 1980 debris avalanche and central crater. Only above this frequency and in the far-field, diffusion onsets at late lapse times.  We also implemented a layered model with a shallower layer with increased scattering properties to model late coda envelopes. While the broadening of late coda phases improves, this model cannot explain the phases of the intermediate coda with higher amplitude than the direct waves.

The scattering and absorption parameters derived from MLTWA are used as inputs to construct 2D frequency-dependent bulk sensitivity kernels for the S-wave coda in the multiple-scattering (using the Energy Transport Equations - ETE) and diffusive (AD, independent of MLTWA results) regimes. At 12 Hz, high coda-attenuation anomalies characterise the eastern side of the volcano using both kernels, in spatial correlation with low-velocity anomalies from literature. At 3 Hz, the anomalous albedo, the forward modelling, and the results of the tomographic imaging confirm that shallow heterogeneity beneath the extended 1980 debris-avalanche and crater enhance anomalous intermediate and late coda phases, mapping shallow geological contrasts.

The geomorphological map of MSH highlights extremely rough landforms (hummocky structures) of the already complex morphology of the debris avalanche. The comparison with the attenuation tomography reveals several matches, not only with the debris avalanche itself but also with other areas in the south flank of MSH, like the volcanoclastic plane, affected by intense eruptions in the past (e.g. Cougar stage, 28-18 ka).

We remark the effect those may have on coda-dependent source inversion and tomography, currently used across the world to image and monitor volcanoes.
Estimation of Soil Loss at Tehri Dam Catchment in Uttarakhand, India.
Authors: Nain Gourav
Published: March 2020

The soil erosion is the most serious environmental problem in watershed areas in Bhagirathi River. The main factors affecting the amount of soil erosion include vegetation cover, topography, soil, and climate. In order to describe the areas with high soil erosion risks and to develop adequate erosion prevention measures in the watersheds of dams, erosion risk maps should be generated considering these factors. “Reduction in the capacity and life of Tehri dam Reservoir was became a major concern. Remote Sensing (RS) and Geographic Information System (GIS) technologies were used for erosion risk mapping in the catchment area of Bhagirathi River. The principal aim of this paper is to utilize spatial-based soil erosion information to assess land suitability at a watershed level. The model integrated with RS and GIS technologies has great potential for producing accurate and inexpensive erosion risk maps.

Data on Climate (Total precipitation and its frequency and intensity), Geomorphology (Land form, Physiography, Slope and Drainage Characteristics), Soil characteristics (Texture, structure), Land Use/ Land cover (Density of forest or grassland, plant residue, crops etc.) and Soil management were calculated using standard reported methods (Naqvi et al., 2015). Total 6 parameters were calculated i.e. Slope, Slope length, Soil texture, Drainage density, landuse/landcover and Rainfall erosivity. Weightage of each parameters on the basis of value and classes were assign. At last SYI value were calculated using weightage map, Delivery ratio, area of watershed. The sub-watersheds 10, 11 were identified as being very high risk. Intense rainfall and reservoir area of dam coupled with poor soil structure and steep slopes are the main drivers of soil erosion in this area. Therefore, the proper designing of integrated watershed management and conservation strategies is a crucial element to reduce the current rate of environmental degradation and boost up agricultural production in the sub-watersheds.
The chemical and physical stability soil organic carbon in the top 1 m of the soil profile under different land uses in the UK
Authors: Antony Dedy , Clark Jo , Collins Chris , Sizmur Tom
Published: March 2020

Soils are the largest terrestrial pool of organic carbon and it is now known that as much as 50% of soil organic carbon (SOC) can be stored below 30 cm. Therefore, knowledge of the mechanisms by which soil organic carbon is stabilised at depth and how land use affects this is important.

This study aimed to characterise topsoil and subsoil SOC and other soil properties under different land uses to determine the SOC stabilisation mechanisms and the degree to which SOC is vulnerable to decomposition. Samples were collected under three different land uses: arable, grassland and deciduous woodland on a silty-clay loam soil and analysed for TOC, pH, C/N ratio and texture down the first one metre of the soil profile. Soil organic matter (SOM) physical fractionation and the extent of fresh mineral surfaces were also analysed to elucidate SOM stabilisation processes.

Results showed that soil texture was similar among land uses and tended to become more fine down the soil profile, but pH did not significantly change with soil depth. Total C, total N and C/N ratio decreased down the soil profile and were affected by land use in the order woodland > grassland > arable. SOM fractionation revealed that the free particulate organic matter (fPOM) fraction was significantly greater in both the topsoil and subsoil under woodland than under grassland or arable. The mineral associated OC (MinOC) fraction was proportionally greater in the subsoil compared to topsoil under all land uses: arable > grassland > woodland. Clay, Fe and Mn availability play a significant role (R2=0.87) in organic carbon storage in the top 1 m of the soil profile.

It is evidently clear from the findings that land use change has a significant effect on the dynamics of the SOC pool at depth, related to litter inputs to the system.
Stochastic generator of earthquakes in French territories
Authors: Gouache Corentin , Tinard Pierre , Bonneau François , Montel Jean-Marc
Published: March 2020

Both French mainland and Lesser Antilles are characterized by sparse earthquake catalogues respectively due to the low-to-moderate seismic activity and the low recording historical depth. However, it is known that major earthquakes could strike French mainland (e.g. Ligure in 1887 or Basel in 1356) and even more French Lesser Antilles (e.g. Guadeloupe 1943 or Martinique 1839). Assessing seismic hazard in these territories is necessary to support building codes and prevention actions to population. One approach to estimate seismic hazard despite lack of data is to generate a set of plausible seismic scenarios over a large time span. A generator of earthquakes is thus presented in this paper. Its first step is to generate only main shocks. The second step consists of trigger aftershocks related to main shocks.
To draw the time occurrence of main shocks, original draw of frequencies and year-by-year summation of it is proceeded. The frequencies are drawn, for each magnitude step, in probability density functions computed through the inter event time method (Hainzl et al. 2006). By propagating magnitude uncertainties contained in the initial catalogue through a Monte Carlo Markov Chain, each magnitude step has not only one main shock frequency but a distribution of it. Once a main shock is temporally drawn, its 2D location is drawn thanks to the cumulative seismic moment recorded on each 5x5 km cell in the French territories. A seismotectonic zoning is used to limit both the spatial distribution and magnitude of large earthquakes. Finally, the other parameters (strike, dip, rake and depth) are drawn in ranges of values depending on the seismotectonic zone where the main shock is located. 
For purpose of trigger aftershocks from the main shocks, an approximation of the Bath law (Richter 1958; Båth 1965) is proceeded during the computation of the frequency – magnitude distributions. Thus, for each magnitude step, an α–value distribution is obtained in which, for each main shock an α–value is drawn. In this way, the maximal magnitude of triggered aftershocks is known.
A New Process for Producing First Guess TAFs
Authors: Lanyon Andre , Standen Jessica , Buchanan Piers
Published: March 2020

Terminal Aerodrome Forecasts (TAFs) are a widely accepted international form of aviation forecast used for flight planning procedures at all major airports. TAF production in the UK is currently a time-consuming, manual process carried out by Operational Meteorologists. It has long been speculated that providing a numerical weather prediction (NWP) model-derived first guess solution could bring large improvements in the efficiency of TAF production. Research into first guess TAFs has a long history but making progress has been challenging. However, significant progress has been made at the Met Office in recent months. A practical approach has been adopted that draws on experience of manually producing TAFs. Although NWP model data is utilised as much as possible, steps have been taken to ensure the first guess TAFs are kept as simple and readable as possible whilst retaining information important to the customer. By taking this approach, it is hoped that the first guess TAFs will require minimal intervention from Operational Meteorologists in the majority of weather situations. Development of first guess TAFs is still in the preliminary stages and not all weather parameters are currently included. However, they are produced in such a way that they can be verified using standard Met Office methods, allowing objective comparison with operationally issued TAFs. Verification scores analysed over a 3 year period are encouraging and suggest that forecast performance of first guess TAFs is generally similar to that of operationally issued TAFs. Occasionally, some large differences become apparent when comparing forecasts of rare events such as mist, fog and very low cloud bases, and this is likely to be an area of future research. With further development, it is speculated that the use of first guess TAFs could significantly reduce TAF production time, allowing Operational Meteorologists to make better use of their expertise, perhaps by adding value to model output or by providing valuable consultation services to aviation customers.
Vegetation and ocean feedbacks on the Asian climate response to the uplift of the Tibetan Plateau
Authors: Zhang Ran , Jiang Dabang , Zhang Zhongshi
Published: March 2020

The growth of the Tibetan Plateau (TP) is one of the important forcings acting on the evolution of the Asian climate during the Cenozoic. However, whether vegetation and ocean feedbacks play a specific role in the Asian climate response to TP uplift remains unclear. Here we investigate this issue through a set of numerical experiments with the Community Earth System Model. The results indicate that vegetation and ocean feedbacks have important but different effects on the Asian climate change in association with TP uplift, which are intrinsically related to the adjustment of thermal structure. The vegetation feedback leads to excess annual precipitation in East China and South Asia and a weakening of the Asian winter monsoon winds. By comparison, the ocean feedback induces a deficit of annual precipitation particularly in most areas of the Bay of Bengal and the South China Sea and a weakening of the Asian summer and winter monsoon winds. These results highlight the importance of vegetation and ocean feedbacks and further facilitate a better understanding of the paleoclimatic response to the uplift of the TP.
Global soil water estimates as landslide predictor: the effectiveness of observations, simulations and data assimilation results
Authors: Felsberg Anne , De Lannoy Gabriëlle , Girotto Manuela , Poesen Jean , Reichle Rolf , Stanley Thomas
Published: March 2020

Hydrological triggering of landslides is strongly connected to the water content of the soil. Previous local studies showed that the inclusion of predisposing soil hydrological conditions, such as soil moisture, improved the landslide prediction abilities over using rainfall only as predictor variable. Existing global models that predict landslides however still mostly rely on antecedent rainfall indices as a proxy for soil moisture conditions, because global precipitation data has been more readily available than soil moisture data. Soil moisture data are now available from satellite observations or modeling, or combinations thereof (data assimilation). Our research seeks to quantify to which extent global landslide prediction can benefit from these data products.

To tackle this question, we examined soil hydrological conditions at the times and locations of known landslide occurrences (Global Landslide Catalog, Kirschbaum et al. 2015). More specifically, we investigated soil moisture estimates retrieved from the Soil Moisture Ocean Salinity (SMOS) mission, simulated by the Catchment Land Surface Model (CLSM), or resulting from assimilation of SMOS or Gravity Recovery And Climate Experiment (GRACE) data into CLSM.

A first coarse-scale, univariate global analysis for the years 2011 through mid-2016 indicates that soil moisture and total water storage estimates are adequate alternatives for antecedent rainfall indices to predict landslides. In particular, the assimilation of SMOS or GRACE data into CLSM improves root-zone soil moisture and preferentially increases root-zone soil moisture at landslide events. Whereas both assimilation schemes help to predict landslides based on an increased landslide probability with increased water content, the SMOS or GRACE satellite observations alone (that is, without data assimilation) are too sparse, noisy or coarse to clearly distinguish the different hydrological conditions between landslide and non-landslide events.
Helio4Cast - a real time test environment to enhance space weather prediction at Earth
Authors: Möstl Christian , Bailey Rachel L. , Amerstorfer Ute V. , Amerstorfer Tanja , Weiss Andreas J. , Reiss Martin A. , Hinterreiter Jürgen , Bauer Maike
Published: March 2020

We introduce Helio4cast, an open source python package to provide real time solar wind predictions at the Sun-Earth L1 point, and to directly couple them to forecasts of the aurora oval, geomagnetically induced currents and further geomagnetic indices. We present its current status, using a combination of our PREDSTORM solar wind forecast and the real time modeling of the aurora with the OVATION model. The solar wind prediction is driven by data from either STEREO-A, a recurrence model, an empirical background solar wind model or a future L5 mission. For coronal mass ejections (CMEs), we plan to use our semi-empirical 3DCORE model to produce in situ magnetic flux rope signatures constrained by real-time solar observations, or a machine learning approach based on many previous observations of in situ CMEs. We are particularly interested in how the errors in the solar wind prediction propagate to ground-based observations. Challenges and future plans of the real-time implementation are discussed.
Comparison of Holocene and Last Interglacial sapropels in the Gulf of Sirte (eastern Mediterranean)
Authors: Tachikawa Kazuyo , Vidal Laurence , Pérez-Asensio José N. , Garcia Marta , Pratiwi Adnya , Schulz Hartmut
Published: March 2020

The Mediterranean thermohaline circulation is sensitive to ongoing climate change and generally stagnant circulation is expected by the end of the 21st century. In the past, the eastern Mediterranean Sea has experienced slower ventilation as demonstrated by rhythmic occurrence of organic-rich sediments “sapropels”. The two sapropels S1 (Holocene) and S5 (Last Interglacial) were formed under conditions of excess fresh water inputs via Nile river in relation to insolation-driven African monsoon intensification and deglacial meltwater inputs from the North Atlantic. In addition to the Nile river discharge, the paleodrainage toward Gulf of Sirte off Libya has been proposed although its contribution could be significantly different between S1 and S5 because of distinct monsoon intensification. Since the response of circulation to freshwater forcing could vary with the region of perturbation, comparison of S1 and S5 deposited in the Gulf of Sirte will provide key information on the Mediterranean ventilation sensitivity.

We applied a multi-proxy approach (bulk elemental composition by XRF scanning, redox sensitive elemental concentration, planktonic foraminiferal δ18O and benthic foraminiferal faunal assemblages) to core SL95 (32º46.46N, 19º11.46E; 1390 m water depth) from the eastern side of the Gulf of Sirte. Both S1 and S5 are marked by prominent peaks of Ba/Al and Ba/Ti with more pronounced Ba enrichment for S5. Redox sensitive elements such as U and Mo present enrichment prior to the Ba peaks that can be interpreted as reduced ventilation before sapropel deposition. However, expected reduced oxygenation is not synchronous with benthic foraminiferal faunal changes, suggesting possible remobilisation of the trace elements during sapropel interruption and/or post-sapropel oxygenation. Acquisition of high-temporal resolution data of Globigerinoides ruber δ18O and benthic foraminiferal assemblages is in progress. We will discuss potential influence of (partial) ventilation at intermediate water depths during sapropel interruption in association with 8.2 event and possible different freshwater inputs at S1 and S5 depositions.
Radial Miscible Viscous Fingering of the Icelandic Plume
Authors: Galbraith-Olive Patricia Hannah , White Nicky , Woods Andy
Published: March 2020

The Saffman-Taylor instability, a fluid dynamical phenomenon, occurs when a less viscous
fluid is injected into a more viscous fluid, leading to the development of radial miscible viscous
fingers. Approximately five horizontal fingers radiate away from the Icelandic plume at a
depth range of 100 km–200 km. These fingers are manifest as shear wave velocity anomalies in
full-waveform tomographic models. The best resolved fingers lie beneath the British Isles and
beneath western Norway, extending ∼1,000 km away from the Icelandic plume conduit. The
number and wavelength of miscible viscous fingers are controlled by Péclet number (i.e. the
ratio of advective and diffusive transport rates), mobility ratio (i.e. the ratio of fluid viscosities)
and thickness of the horizontal layer into which the fluid is injected. Observational estimates
for the Icelandic plume suggest the Péclet number is O(104), the mobility ratio is at least 20–
50 and the asthenospheric channel thickness is 100 ± 20 km. Appropriately scaled laboratory
experiments play a key role in developing a quantitative understanding of the spatial and
temporal evolution of the Icelandic plume planform. During laboratory experiments, Péclet
number is varied primarily by changing the flow rate as well as the altering the thickness of
the horizontal layer. Viscosity contrasts are generated by using glycerol and water mixtures
which are miscible, like plume material with ambient mantle. However there is no temperature
contrast in the experiments, which is probably significant in the mantle. Comparison between
scaled analogue experiments and observed values suggests the fluid dynamics may be more
complex than the Saffman-Taylor instability alone. Additional processes including influence
of temperature, interaction with the base of the lithospheric plate or small-scale convection,
along with the Saffman-Taylor instabillity, may be the origin of the fingers imaged by seismic
tomography.
Multi-GNSS PPP instantaneous ambiguity resolution with precise atmospheric corrections augmentation
Authors: Huang Jiaxin , Li Xin , Lv Hongbo , Xiong Yun
Published: March 2020

The performance of precise point positioning (PPP) can be significantly improved with multi-GNSS observations, but it still needs more than ten minutes to obtain positioning results at centimeter-level accuracy. In order to shorten the initialization time and improve the positioning accuracy, we develop a multi-GNSS (GPS + GLONASS + Galileo + BDS) PPP method augmented by precise atmospheric corrections to achieve instantaneous ambiguity resolution (IAR). In the proposed method, regional augmentation corrections including precise atmospheric corrections and satellite uncalibrated phase delays (UPDs) are derived from PPP fixed solutions at reference network and provided to user stations for correcting the dual-frequency raw observations. Then the regional augmentation corrections from nearby reference stations are interpolated on the client through a modified linear combination method (MLCM). With the corrected observations, IAR can be achieved with centimeter-level accuracy. This method is validated experimentally with Hong Kong CORS network, and the results indicate that multi-GNSS fusion can improve the performance in terms of both positioning accuracy and reliability of AR. The percentage of IAR for multi-GNSS solutions is up to 99.7%, while the percentage of GPS-only solutions is 88.7% when the cut-off elevation angle is 10°. The benefit of multi-GNSS fusion is more significant with high cut-off elevation angle. The percentage of IAR can be still above 98.4% for multi-GNSS solutions while the result of GPS-only solutions is below 43.5% when the cut-off elevation angle reaches 30°.  The positioning accuracy of multi-GNSS solutions is improved by 30.0% on the horizontal direction (0.7 cm) and 17.1% on the vertical direction (2.9 cm) compared to GPS-only solutions.
The assembly of Pannotia: a thermal legacy for Pangaea?
Authors: Murphy J. Brendan , Nance R. Damian , Heron Philip J.
Published: March 2020

Controversy about the status of Pannotia (Laurentia + Baltica + Gondwana) as an Ediacaran supercontinent centers on palaeomagnetic data (which is permissive not conclusive) and geochronology (which implies breakup commenced before full assembly). But evidence of past supercontinent assembly is not limited to these two criteria and can be found in many other phenomena that accompany the process. Irrespective of whether Pannotia qualifies as a supercontinent, a key unanswered question is whether the legacy of its amalgamation influenced global mantle convection patterns because such patterns are generally ignored in models claiming the transition from Rodinia to Pangaea represents a single supercontinent cycle. We contend that the proxy signals of assembly and breakup in the Ediacaran are unmistakable and indicate profound changes in mantle circulation. These changes correlate with a wealth of geologic data for Pan-African collisional orogenesis, reflecting the amalgamation of the Gondwana, and for tectonothermal activity along the Gondwanan portion of Pannotia’s periphery.

 

Collisional orogenesis necessitates subduction of oceanic lithosphere between the converging continental blocks. By analogy with the amalgamation of Pangea, the subducted oceanic lithosphere should have congregated to form a “slab graveyard” along the core-mantle boundary that would have generated a superplume beneath the Gondwanan component of Pannotia, the effects of which can be seen along its margins. We suggest that such dramatic changes in mantle convection patterns can indeed be recognized, they provide insights into the processes responsible for the opening of the Iapetus and Rheic oceans, and a potential explanation for some of the enigmatic tectonothermal events that characterize the Late Neoproterozoic-Early Paleozoic tectonic evolution of the margin of Gondwana.
Cold pool driven convective initiation: How can we improve its representation in km-scale models?
Authors: Hirt Mirjam , Craig George
Published: March 2020

Cold pools are essential for organizing convection and play a particular role in convective initiation in the afternoon and evening. Both aspects are deficient in current convection-permitting models and a better representation of cold pools is likely necessary to overcome these deficiencies. In a recent investigation, we identified several sensitivities of cold pool driven convective initiation to model resolution within hectometer simulations. In particular, a causal graph analysis has revealed that the dominant impact of model resolution on convective initiation is due to too weak gust front vertical velocities. This implies that cold pool gust fronts in km-scale models are too weak to trigger sufficient new convection.

To address this deficiency, we develop a parameterization for the convection-permitting COSMO model to improve the representation of cold pool gust fronts. We use the potential temperature gradient to identify cold pool gust fronts and enhance vertical wind tendencies within these gust front regions.  Also, we perturb horizontal wind tendencies to yield 3d non-divergent perturbations.  This parameterization strengthens gust front circulations and thereby enhances cold pool driven convective initiation. Consequently, precipitation is amplified and becomes more organized in the afternoon and evening. This improves the diurnal cycle of precipitation and also has some positive impact on the spatial distribution as quantified by the fraction skill score. Furthermore, cold pools themselves are strengthened, which can further enhance the gust front circulations, giving rise to a feedback loop. 
TROPOMI's potential for ocean applications
Authors: Oelker Julia , Losa Svetlana , Altenburg Soppa Mariana , Richter Andreas , Bracher Astrid
Published: March 2020

The backscattered light from within the ocean carries information about surface ocean optical constituents, e.g., phytoplankton and the amount of light in the ocean. Global quantified insight in these parameters is important for estimating primary productivity and heat budget, and for a better understanding and modeling of biogeochemical cycles. Atmospheric sensors such as SCIAMACHY and GOME-2 have proven to yield valuable information on phytoplankton diversity, sun-induced marine fluorescence, and the underwater light field. As commonly used for the retrieval of atmospheric trace gases, the oceanic parameters are inferred from differential optical absorption spectroscopy combined with radiative transfer modeling. Within the ESA Sentinel-5p+ Innovation themes, we explore TROPOMI's potential for deriving the diffuse attenuation coefficient, quantification of different phytoplankton groups and the fluorescence signal of phytoplankton. Here we present results on deriving the diffuse attenuation coefficient from the vibrational Raman scattering signal in backscattered radiances measured by TROPOMI. The diffuse attenuation coefficient describes how fast the incoming radiation in the ocean is diminished with depth. Retrieval results in three spectral regions covering the ultraviolet and blue region of the solar spectrum are presented and intercompared. In future, we will explore if information on sources of colored dissolved organic matter and ultraviolet-absorbing phytoplankton pigments can be inferred from these data sets.
Rare Earth Elements and Nd isotopes as tracers of modern ocean circulation in the central Mediterranean Sea
Authors: Garcia-Solsona Ester , Pena Leopoldo D. , Paredes Eduardo , Pérez-Asensio José Noel , Quirós-Collazos Lucía , Lirer Fabrizio , Cacho Isa
Published: March 2020

Seawater Rare Earth Element (REE) concentrations and Nd isotopic composition (εNd) are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater. However, their measurements are basically lacking in the Mediterranean Sea water column. This study analyzes 9 seawater stations around the central Mediterranean Sea to clarify the relative importance of external sources, vertical (biogeochemical) processes and lateral water mass transport in controlling REE and εNd distributions. Concentrations of REE do not show nutrient-like profiles with depth, likely indicative of relatively young waters with limited accumulation of remineralized REE. Light REE (LREE) present a non-conservative behavior, which largely peak at surface waters and rapidly decrease with depth. The negative correlation of surface LREE enrichment with offshore distance highlights the influence of continental input from the western Italian coast to the Tyrrhenian surface waters. In contrast to other regions with reported boundary exchange, this process does not modify the εNd values here. On the other side, distributions of dissolved heavy REE (HREE) and εNd display a conservative behavior that can be explained by mixing of western- (MAW and WMDW) and eastern- (LIW and EMDW) originated waters. We test this hypothesis with an Optimum Multi-Parameter Analysis (OMPA) including HREE and εNd parameters. Even though the limited data set, consistent results of water mass fractions are obtained for the four main water masses although with some particularities. While LIW take on major importance when considering HREE in the model, EMDW fractions are preferentially detected with εNd. This latter finding implies a noticeable deep water flux across the Sicily Strait into the Western Mediterranean that was not clearly evidenced before.
Bathymetric mapping in turbid braided mountain streams using SfM-MVS photogrammetry and statistical approaches
Authors: Mancini Davide , Antoniazza Gilles , Lane Stuart
Published: March 2020

River bathymetric investigation has a long tradition as river-bed morphology is a crucial geomorphological variable that also has implications for river ecology and sediment management. In one sense, this is becoming more straightforward with the development of UAV platforms and SfM-MVS photogrammetry. Mapping inundated and exposed areas simultaneously has proved possible either by adopting two media refraction correction or by using some form of the Beer-Lambert Law. However, both of these approaches rely upon the bed being visible which becomes restricted to progressively shallower zones as stream turbidity increases. Traditional survey techniques to collect bathymetric data for inundated zones (e.g. total station or differential GPS systems) are time consuming and require a trade-off between point density and the spatial extent of survey. In this study we test a simple hypothesis: it is possible to generalize the likely depth of water in a shallow braided stream from basic planimetric information and use such statistical relationships to reconstruct the bathymetry of inundated zones. This is based upon the principle that a suite of planimetric variables (e.g. distance from stream banks, river channel width, local curvature magnitude and direction, streamline convergence and divergence) can be used to model the spatial distribution of water depths. We attempt to do this for a shallow braided river with high suspended sediment concentrations using orthoimages and DEMs derived from application of SfM-MVS photogrammetry to UAV-based imagery. We develop separate calibration and validation relationships to train and to assess the statistical models developed. These are then applied to the stream to produce bathymetric maps of flow depth for integration with SfM-MVS derived data from exposed areas. The method produces a point specific measure of uncertainty and tests suggest that the associated uncertainties are sufficiently low that after propagation into DEMs of difference reliable data on braided river dynamics and erosion and deposition volumes can be obtained.
A database for the seismic properties of slow spreading mid-ocean ridges gabbros
Authors: Morales Luiz F. G. , Allard Maël , Ildefonse Benoit
Published: March 2020

Gabbros are the main component of the oceanic crust and represent ~2/3 of the total magmatic crustal thickness. At the interface between magmatic, tectonic and hydrothermal processes, gabbros from slow spreading ridges may have a complex mineralogy and microstructural evolution. This includes structures that vary from purely magmatic fabrics, with layering and magmatic alignment of minerals, to rocks deformed from subsolidus temperatures to the lower-T brittle-ductile conditions. Such a variation is normally accompanied with changes in mineralogy, microstructures and crystallographic preferred orientations (CPO) of the main phases of these rocks, which in turn affect their seismic properties. Here we present a database of the CPO-derived seismic properties of 70 samples collected during the IODP Expedition 360 (site U1473). Initial results show that the dominant phases are plagioclase and clinopyroxene[MOU1] , and different samples may have different contents of olivine, enstatite, magnetite, ilmenite, chlorite and amphibole. Maximum velocities can be either parallel to the strongest concentration of (010) poles of plagioclase or olivine/clinopyroxene [001], depending on the proportions between these phases. Anisotropy of P waves vary from ~5% in the more isotropic gabbros with weak magmatic fabric to a maximum of ~10% in more mylonitic terms. A similar effect is observed for the S-waves. Destructive interference between plagioclase CPO vs. clinopyroxene/olivine reducing anisotropy is possibly observed. This is because the maximum Vp in a foliated gabbro is parallel to the maximum concentration of poles to (010), and perpendicular to olivine and clinopyroxene. As the lineation in our gabbros is generally marked by olivine and clinopyroxene [001] (instead of the fast direction [100]), this possibly cause anisotropy reduction. When present in the more mylonitized gabbros, amphibole has strong CPOs and help to increase the general anisotropy of P and S waves. The elastic constants calculated from these aggregates will be used as input for more physically robust calculations using differential effective medium approaches to better understand the effect of melt inclusions in these rocks by the time of their deformation in the lower crust.

 
Extremely low frequency detection of electrical discharges at Minamidake crater (Sakurajima volcano, Japan)
Authors: Vossen Caron E.J. , Cimarelli Corrado , Bennett Alec J. , Geisler André , Gaudin Damien , Miki Daisuke , Iguchi Masato , Dingwell Donald B.
Published: March 2020

Volcanoes are increasingly better monitored around the world. Nonetheless, the detection and monitoring of volcanic ash plumes remains difficult, especially in remote areas. Intense electrical activity and lightning in volcanic plumes suggests that electrical monitoring of active volcanoes can aid the detection of ash emissions in near real-time. Current very low frequency and wide-band thunderstorm networks have proven to be able to detect plumes of large magnitude. However, the time delay and the relatively high number of non-detected explosive episodes show that the applicability of these systems to the detection of smaller (and often more frequent) ash-rich explosive events is limited. Here we use a different type of thunderstorm detector to observe electrical discharges generated by the persistent Vulcanian activity of Minamidake crater at Sakurajima volcano in Japan. The sensors consist of two antennas that measure the induced current due to the change in electric field with time. In contrast to the current thunderstorm networks, these sensors measure within the extremely low frequency range (1-45 Hz) and can detect lightning up to 35 kilometres distance.

Two detectors were installed at a distance of 3 and 4 kilometres from Minamidake crater and recorded almost continuously since July 2018. Within this period, the ash plumes reached a maximum height of 5.5 kilometres above the crater rim. Using a volcanic lightning detection algorithm and the catalogue of volcanic explosions compiled by the Japan Meteorological Agency (JMA), the number of electrical discharges was determined for each individual explosive event. In addition, the start of electrical discharges was compared to the eruption onset estimated by the JMA.

Preliminary results show that the detector closest to the crater had the highest detection efficiency. It detected electrical discharges during 60% of the eruptions listed by the JMA. This is significantly higher than for the World Wide Lightning Location Network, which detected electrical discharges (in the very low frequency range) within 20 kilometres of Sakurajima for less than 0.005% of the eruptions. Furthermore, the results show that for 40% of the detected eruptions, electrical discharges were detected before the estimated JMA timing. Hence, electrical discharges can mark the inception of the explosion with a higher precision and are an indication of ash emission. This demonstrates the value of the cost-effective sensors used here as a monitoring tool at active volcanoes.