bluuebunny/crossref_metadata_2025 huggingface dataset:
Mid-infrared spectroscopy tracing of sediment sources in highly erosive catchments on the Chinese Loess Plateau
Authors: Ni Lingshan
Published: March 2022

Identification of the sediment sources is the key to control soil erosion in the Chinese Loess Plateau (CLP), which is helpful to understand the process of erosion, transport and deposition, and is of great significance to formulate soil conservation measures according to the local conditions. The current research attempted to use the mid-infrared (MIR) spectroscopy fingerprinting method to trace sediment sources within nine small catchments in the hilly-gully region of the CLP. Two major categories of sediment sources were identified: gully and topsoil. Sediments trapped by check dams were collected as the final sediment transferred by soil erosion. The two types of sediment sources could be discriminated by MIR spectroscopy. The partial least squares regression (PLSR) analyses was applied to quantify the contributions of gully and topsoil to the total final sediment. The MIR-PLSR results showed that gully contributed 19% to 66% of the total sediment with an average of 33 ± 16% in the nine small catchments. A comparison between the MIR spectroscopy method and the geochemical fingerprinting method in one catchment revealed that although the two methods agreed well on the gully contributions, the two methods produced a significant difference (R2=0.4). The analyses further suggested that although gully accounted for relative large proportions of final sediment, topsoil erosion was the predominant process in small dam controlled catchments on the CLP.
Using the Dual Porosity Approach to Quantify Non-uniform Fluxes for the Estimation of Hydrological and Stability Performance of Sloped Covers over Coal
Authors: Baumgartl Thomas , Shao Qi , Filipović Vilim
Published: March 2022

Environmental impacts of open-pit coal mining include issues such as fire risk, large-scale slope instability and groundwater contamination. Because of the man-made landforms used to cover open-pit mines and the coal material itself, soil hydrology can be affected in a way that non-uniform fluxes and preferential flow may occur. The aim of this study was to evaluate soil hydraulic properties of open-pit mines and coal material and to implement dual porosity approach into numerical experiments to quantify non-uniform fluxes and slope stability. Water retention and hydraulic conductivity curves were estimated for both coal and clay (overlaying material) using the combination of Dewpoint potentiometer WP4C and HYPROP devices. Mechanical properties were determined additionally using the Unconfined Compressive Strength test. Numerical simulations have been performed using HYDRUS 2D/3D and associated SLOPE CUBE module to assess the hydrological and mechanical behavior of coal-cover slope models under different climatic scenarios. Results showed that coal has very different hydraulic properties from the soil, with three to four orders of magnitude smaller saturated hydraulic conductivity, two orders of magnitude larger air entry point, and larger material strength parameters. The effects of present cracks/fractures on hydraulic properties of both, soil cover and coal have been taken into account by the bimodal properties determined using an extended van Genuchten-Mualem (Durner) model. Comparison of hydraulic conductivity curves indicates that the identified cracks/macropores play an important role in increasing hydraulic conductivity when the material is close to saturation. Therefore, 5% and 10% crack-weighting factors were adopted in numerical simulations for coal and topsoil/cover, respectively. The underlying coal changes its pore size distribution dramatically, depending on the degree of drying, which was confirmed during evaporation experiments. Numerical experiments showed higher risk to slope stability during the wetter years, albeit still on an acceptable level. The challenge remains on how to adequately quantify water balance in coal material with present preferential flow, and with the additional complexity of changing pore size distribution properties over time.
Generation of Archean TTGs by slab melting during sluggish, drip-like subduction
Authors: Foley Bradford
Published: March 2022

The tectonic processes responsible for the formation of early Earth felsic crust (predominantly composed of tonalite-trondhjemite-granodiorite, or TTGs) inform the global regime of mantle convection that operated at this time. Many models have been proposed to explain the formation of Archean TTGs, including melting of downgoing crust in hot subduction zone settings, or melting of crust that is buried by lava flows and founders into the mantle. Formation in a subduction zone setting would imply at least some form of mobile-lid tectonics on the early Earth, while TTG formation via crustal burial and foundering does not require subduction or plate tectonics, and can thus occur in a stagnant-lid regime.  

Regardless of tectonic setting, TTGs can only form if hydrated basaltic protocrust melts before it experiences metamorphic dehydration. Previous work has argued that this constraint may preclude a subduction origin to TTGs. Regional scale numerical models have found that slabs sink quickly and steeply through the mantle at Archean mantle temperatures, such that they dehydrate before melting. However, these models do not consider evolution of grainsize in the mantle interior and in plate boundaries. Using numerical models of mantle convection with grain damage, a mechanism for generating mobile-lid convection via grain size reduction, I show that a sluggish, drip-like style of subduction emerges at early Earth conditions. This subduction style is a result of plate boundaries becoming effectively stronger with increasing mantle temperature, and leads to significant slab heating at shallow depths.

To test whether TTGs can form from this style of sluggish subduction, I use scaling laws developed from numerical models combined with a simple model of the evolution of the vertical temperature profile through a slab. Results show that the slower sinking speed of slabs caused by grain size evolution in plate boundaries allows for crustal melting for a much wider range of mantle temperatures and subducting plate thicknesses than if the effects of grain size evolution were ignored. Overriding plate thickness is also important, with thin overriding plates favored for TTG formation. These results have important implications for the settings where subduction could generate Archean TTGs, and for potential episodicity in TTG formation resulting from both short- and long-term episodicity in subduction.  
210Pbex records the historical sediments accumulation in the water-level fluctuation zone of the Three Gorges Reservoir, China
Authors: Li Jinlin , He Xiubin , Bao Yuhai , Zhang Xinbao , Wei Jie , Tang Qiang
Published: March 2022

Impoundment regulation of the Three Gorges Reservoir (TGR) has created a water-level fluctuation zone (WLFZ) with a vertical height of 30 m and a total area of 349 km2. This special zone received approximately 7% of the total sediment captured by the TGR. The present study aims to reveal the history of sediments accumulation since the WLFZ was formed in 2006. A sedimentary core was retrieved from a representative floodplain at the lower part of the WLFZ and subsequently sectioned with an interval of 5 cm. Particle composition, 137Cs and 210Pbex activities of sediment were measured after pretreatment. The result shows that the 210Pbex activity can be used as a proxy for the seasonal high-resolution dating of sediment in the WLFZ, due to the sediments deposited during the dry season have high 210Pbex activity, while the opposite is true for sediments deposited in the wet season. Then, the annual sequence of the sedimentary profile has been established based on the distribution pattern of 210Pbex activity. The inter-annual variation of the sedimentary rate is shown as ‘low-high-low-high’, and mutation years are 2008, 2014, and 2018, corresponding deposition rates in these four periods are 12.5, 45, 20, and 32.5 cm, respectively. In the early period of the formation of the WLFZ (2006-2007), the staged impoundment of the TGR was the key influencing factor of the sedimentary rate. Afterward, the annual sedimentary rate was consistent with the suspended sediment load supplied into the TGR. From 2014 to 2017, due to the interception of the cascade reservoirs in the lower reaches of the Jinsha River, the suspended sediment load dropped sharply, resulting in a decrease in the sedimentation rate. From 2018 to 2019, the sedimentation rate of the floodplain increased owing to the increase in the suspended sediment load caused by frequent extreme rains in the upper reaches of the Yangtze River basin.
Hydrological response to meteorological drought in Chirchik river basin of Western Tian-Shan
Authors: Umirzakov Gulomjon , Remesan Renji , Rakhmonov Komiljon , Mujumdar Sanskriti , Omonov Nurmukhammad
Published: March 2022

This study investigated the link between meteorological and hydrological droughts in two rivers with and without glaciers in Сhirchik river basin of Western Tian Shan. Observed monthly hydrometeorological data was used to estimate Standardized Precipitation Indexes (SPI) and Standardized Streamflow Indexes (SSI) to analyze the hydrological response of snow-glacier fed Pskem and snow-rain fed Ugam rivers in the region. The Pearson correlation coefficient has been used to estimate statistical relations between SPI and SSI indices for the selected rivers. The SPI-SSI correlation coefficient has shown a positive trend with an increase in timescales, and it was more evident in indexes between the 6-month to 12-month  timescales in both rivers. The statistical relationships between the meteorological and hydrological drought indexes showed that the SPI-SSI relationship varies with river flow generation and its dynamics, and it was more in the Ugam River than the Pskem River. That indicates snow-dominated Ugam River is more prone to meteorological droughts, whereas the glaciers in the Pskem River basin were buffering hydrological drought and its frequency and severity. Obtained results allow better-informed forecasting of hydrological droughts in the river basin and, consequently, enable efficient water management in agricultural and hydropower sectors.
Separating of Glacial Isostatic Adjustment (GIA) across Antarctica from GRACE/GRACE-FO observations via Independent Component Analysis (ICA)
Authors: Shi Tianyan , Fukuda Yoichi , Doi Koichiro , Okuno Jun’ichi
Published: March 2022

The redistribution of the near-surface solid Earth due to glacial isostatic adjustment (GIA), which is the ongoing response of the solid Earth due to changes in the ice-ocean load following the Last Glacial Maximum, has a direct impact on the inferred Antarctic Ice Sheet (AIS) mass balance from gravimetric data acquired during the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions.

However, sparse in-situ observation networks across Antarctica have led to the inability to effectively constrain the GIA effect. Here, we analyze the mass change patterns across Antarctica via independent component analysis (ICA), a statistics-based blind source separation method to extract signals from complex datasets, in an attempt to reduce uncertainties in the glacial isostatic adjustment (GIA) effects and improve understanding of AIS mass balance.

The results reveal that GIA signal could be directly separated from GRACE/GRACE-FO observations without introducing any external model.  Although the GIA signal cannot be completely isolated, the correlation coefficients between ICA-separated GIA, and the ICE-5G and ICE-6G models are 0.692 and 0.691, respectively. The study demonstrates the possibility of extracting GIA effects directly from GRACE/GRACE-FO observations.
Diatoms in Ice Cores, a novel proxy for reconstructing past wind variability in the Pacific sector of the Southern Hemisphere Westerly Wind belt
Authors: Tetzner Dieter , Thomas Elizabeth , Allen Claire
Published: March 2022

The Southern Hemisphere Westerly Winds play a critical role in the global climate system by modulating the upwelling and the transfer of heat and carbon between the atmosphere and the ocean. Since observations started, the core of the westerly wind belt has increased in strength and has contracted towards Antarctica. It has been proposed that these deviations are among the main drivers of the observed widespread warming in West Antarctica, threatening the stability of ice shelves, and ultimately contributing to global sea level rise.

 Over the last decades, it has been widely believed these atmospheric changes have occurred in response to recently increased greenhouse gas concentrations and ozone depletion. However, the lack of long-term wind records in the Southern Hemisphere mid-latitudes hinders our ability to assess the wider context of the recently observed changes. This lack of a clear consistent timing limits our understanding of the causes of westerly wind changes and the roles they have played in driving recent environmental changes in Antarctica. Addressing these questions is crucial for future climate predictions.

 In this work, we present records of diatoms preserved in ice cores retrieved from the southern Antarctic Peninsula and the Ellsworth Land region. The diatom abundance and species assemblages from these ice cores prove to represent the regional variability in wind strength and circulation patterns that influence the onshore northerly winds. We use this novel proxy to produce an annual reconstruction of winds in the Pacific sector of the Southern Hemisphere Westerly Wind belt over the last 140 years. This wind reconstruction allows exploring the link between the recent increase in wind strength, greenhouse gases and ozone depletion in the atmosphere
Late Cenozoic sea-level indicators in west Luzon, Philippines
Authors: Maxwell Kathrine , Westphal Hildegard , Rovere Alessio , Garas Kevin
Published: March 2022

Using the framework of the World Atlas of Last Interglacial Shorelines (WALIS), we produced a standardized database of Last Interglacial (LIG) sea-level indicators in Southeast Asia after reviewing available studies on relative sea-level (RSL) proxies such as coral reef terraces and tidal notches in the Philippines; Sulawesi; and Sumba, Timor, and Alor regions. In total, we reviewed 43 unique RSL proxies in the region and highlighted sites for future studies. Following this work, we revisited a site in west Luzon, Philippines where LIG coral reef terraces were previously reported. In this paper, we present new geomorphic and stratigraphic data on the fossil coral reef terraces in Pangasinan, west Luzon which adds to the limited sea-level indicators in the region. The low-lying areas of western Pangasinan are underlain by sequences of calcareous sandstone-mudstone with minor pebbly conglomerate and tuffaceous sandstone units belonging to the Sta. Cruz Formation, with tentative age designation of Late Miocene to Early Pliocene. Unconformably overlying the tentatively assigned sandstone unit of Sta. Cruz Formation is the Plio-Pleistocene Bolinao Limestone, the youngest formational unit in the area. Based on previous literature, a sequence of coral reef terraces (possibly LIG) is cut onto the Bolinao Limestone. Rising to about 14 meters above mean sea level (m amsl) along the coast of western Pangasinan are previously dated Holocene coral reef terraces. While additional data is needed to shed more light on the RSL changes in the region, our work proves to be more challenging due to the difficulties of doing field surveys during a global pandemic. Nonetheless, we hope that data from this research will help us further understand the different drivers of past sea-level changes in SE Asia providing necessary geologic baseline data for projections of sea-level change in the future.
Exploring Weak Impulsive Narrowband Quiet Sun Emissions (WINQSEs): Clues to coronal heating
Authors: Oberoi Divya , Mondal Surajit , Sharma Rohit , Biswas Ayan , Bawaji Shabbir , Alam Ujjaini
Published: March 2022

The confluence of the data from the Murchison Widefield Array (MWA) and an imaging pipeline tailored for spectroscopic snapshot images of the Sun at low radio frequencies have led to enormous improvements in the imaging quality of the Sun. Among other science advances, these developments have lowered the detection threshold for weak nonthermal emissions by up to two orders of magnitude as compared to earlier studies, and have enabled our discovery of Weak Impulsive Narrowband Quiet Sun Emissions (WINQSEs). Their typical flux densities lie in the range of a few mSFU (1 SFU = 10,000 Jy) and they are found to occur in large numbers all over the quiet Sun regions. In the solar radio images, they appear as compact sources and our estimate of their median duration is limited by the instrumental resolution of 0.5 s. Their spatial distribution and various other properties are consistent with being the radio signatures of coronal nanoflares hypothesized by Parker (1988) to explain coronal heating in the quiet Sun emissions. As steps towards exploring this tantalising possibility of making progress on the coronal heating problem, we have been pursuing multiple projects to improve our ability to detect and characterise WINQSEs. These include attempts to look for WINQSEs in multiple independent datasets; using different independent detection techniques; attempting to characterise their morphologies in radio maps using Artificial Intelligence/Machine Learning based approaches; looking for their counter parts in EUV wavelengths; estimating the energy associated with groups of WINQSEs; and investigation of the spectro-temporal structure of WINQSEs. Here we present the current status of these projects and summarise our learnings from them.
Air Quality Measurement Analysis in the Antarctic
Authors: Kahya Ceyhan , Kucuk Furkan Ali
Published: March 2022

The sources that cause air pollution are evaluated in two main groups; natural and anthropogenic sources, respectively. One of the anthropogenic sources; particulate matter has direct effect on climate change and air pollution.  Particulate matter exists in the atmosphere as solids or liquids. In terms of their diameters, they are classified into two main groups; PM10 and PM2.5. The transport of atmospheric particles to the polar regions is a result of the prevailing winds, mainly. The prevailing wind direction in the Antarctic Region was observed to be Northeast and Southwest. The main purpose of this study is to compare PM10 and PM2.5 data and to determine the scope, level and effects of regional and long-distance PM2.5 and PM10 transport around Horseshoe Island, Antarctic. The data of the Copernicus Atmosphere Monitoring Service (CAMS) for the period 2018-2021 will be used.  And as another result it is aimed to investigate the Covid-19 pandemic impact over the region by means of particulate matter, as well.
Climatological distributions of mid-latitude trough region irregularities based on Swarm in situ measurements
Authors: Liu Yiwen , Xie Wenhao , Xiong Chao , Ye Ting , Wang Yuhao , Wan Xin , Cao Yueyan
Published: March 2022

A large number of studies have confirmed the frequent occurrence of plasma irregularities in the mid-latitude ionospheric trough (MIT), but their distribution characteristics have not been fully understood. Based on the Swarm in situ plasma density measurements from 2014 to 2020, the diurnal, seasonal, solar activity and geomagnetic activity variations of the occurrence rate of MIT region irregularities are analyzed. The results show that for the irregularities with scale size of 7.5-75 km: (1) the geomagnetic activity has an obvious inhibitory effect on the formation of irregularities inside the MIT region, regardless of dayside or nightside. (2) The occurrence rate of irregularities inside MIT region during the day is significantly higher than that at night, and the difference between day and night is greater than the difference between the two walls at the same local time sector. (3) On the dayside, the highest and lowest occurrence rate appears in winter and summer, respectively; but on the nightside, the highest and lowest occurrence rate appears in equinoxes and winter, respectively. (4) On the nightside, it shows lower occurrence rate under high solar activity conditions, but no obvious solar activity effect is shown on the dayside occurrence rate. The above results of the seasonal dependence, geomagnetic activity inhibitory effect, and solar activity influnce are newly and important for understanding the behaviors of the plasma irregularities at MIT region.
Update on IAGOS greenhouse gas observations from commercial airliners
Authors: Gerbig Christoph , Schultz Uwe , Seifert Thomas , Franke Harald , Stosius Ralf , Nedelec Philippe
Published: March 2022

Within European Research Infrastructure IAGOS (In-service Aircraft for a Global Observing System) regular observations of atmospheric greenhouse gases have started in 2018 onboard a Lufthansa Airbus A330. The aircraft is based in Frankfurt with service to destinations in central Africa, the Middle East, and North America. During the initial deployment periods, each lasting from several months to more than a year, various lessons have been learned related to the robustness and resilience of the autonomous operation of the IAGOS-core system, its maintenance in the laboratory, as well as the data transmission and regular automated processing of near-real-time (NRT) data with provision to users through the IAGOS data centre. Equipped with a two-standard in-flight calibration system, trace gas measurements could be made fully traceable to WMO calibration scales. The Covid-19 Pandemic had a significant impact on aviation, and thus on the IAGOS operation, but the aircraft carrying the IAGOS GHG equipment was flying throughout, with services to China and South Korea for medical supplies during the initial phase of the pandemic, allowing for frequent profile observations in the Far East. We present an overview of the observations collected so far, and an outlook on the future expansion of the IAGOS-core GHG measurements
Multiple techniques for calibration and validation of SWAT model in an ungauged catchment in Inner Himalayan Ranges.
Authors: Anand Vicky , Oinam Bakimchandra , Wieprecht Silke
Published: March 2022

Reliability of hydrological model simulation plays an important role in better understanding of hydrological processes, eco-hydrologic and eco-hydraulic condition of a data scarce catchment with limited baseline data. Due to the lack of baseline hydrological dataset, precise simulation of hydrological output from a hydrological model becomes essential. There has been several studies carried out to calibrate a data scarce catchment using river discharge solely on remote sensing data but they have been limited to the rivers with large width. The current study was carried out in Manipur River basin where the widths of the streams are narrow due to which direct application of remotely sensed data possesses serious challenge. This study attempts to calibrate and validate a comprehensive physically semi-distributed Soil and Water Assessment Tool (SWAT) model in Manipur River basin. The SWAT hydrological model was set-up using elevation, soil, weather, and land use land cover (LULC) dataset. For the calibration and validation of model two different approaches has been applied. In the first approach, river streamflow was generated by using stage data based on stage-discharge curve through the technique of spatial proximity, whereas in the second approach, Moderate Resolution Imaging Spectroradiometer (MODIS) evapotranspiration dataset was used at sub-basin scale to calibrate and validate the SWAT model. In the calibration period, the model returned R2 and Kling-Gupta Efficiency (KGE) of 0.78 and 0.73, whereas in the validation period R2, KGE was found to be 0.75, 0.71 while using the stage-discharge curve approach. The model performance of R2, KGE equals 0.67, 0.41, respectively during calibration and R2, KGE equals 0.79, 0.53 respectively was obtained during validation when MODIS evapotranspiration dataset was used. From the modelling result it was observed that the model performance was found to be better when streamflow dataset derived from stage-discharge curve used as compared to the MODIS evapotranspiration dataset. The main reason behind the under performance of the model while using MODIS evapotranspiration dataset was due to the underestimation of evapotranspiration by the SWAT model in the cold-dry season from December to February.

 
Reconstructing fire regimes using micro-charcoal in modern marine sediments off Africa
Authors: Haliuc Aritina , Daniau Anne-Laure , Mouillot Florent , Chen Wentao , David Valérie , Hanquiez Vincent , Dennielou Bernard , Schefuß Enno , Bayon Germain , Crosta Xavier
Published: March 2022

Fire is a pervasive component of almost every terrestrial ecosystem, but the African continent is rather unique, holding the most vulnerable ecosystems to fire which account for most of the global burned area and for more than half of fire-carbon emissions. Fire has a significant role in ecosystem functioning though our understanding of this complex process is still limited which hinders our ability to model and predict fire.

Paleofire records go beyond the short instrumental records of the last decades and can provide long-term information about fire, but only at a descriptive scale and with difficulties in relating it to the fire regime. To address these limitations, we attempt to develop a quantitative calibration model based on the examination of micro-charcoal from 137 surface sediment samples collected offshore the African continent in conjunction with a set of fire parameters (burnt perimeter, fire radiative power, fire spread) derived from satellite data, environmental information (hydrographic basins, vegetation cover, climatic parameters) and a wind dispersal particle model. Our results show that changes in charcoal concentration and morphometry are linked with fire regime and the type of burnt vegetation on the adjacent continent. In (sub)tropical settings, elongated micro-charcoal particles in high concentrations relate to rare but intense fires spreading in graminoid-mixed ecosystems whereas squared particles in low concentrations are typical for frequent but low intensity fires, characteristic for tree-dominated ecosystems.

This work provides the first calibration model of micro-charcoal in marine sediments which can be applied to long marine charcoal records to help reconstruct past fire regimes. This investigation addresses a key issue in unlocking specific methodological and theoretical problems related to fire research; it provides a better understanding of the local to regional processes that govern the fire signal and contextualize current and past environmental changes.
PIXL’s Micro Context Camera performance on the surface of Mars
Authors: Pedersen David , Henneke Jesper , Jørgensen John Leif , Benn Mathias , Denver Troelz , Timmermann Lars , Liebe Carl Christian , Denise Robert , Elam Tim , Wade Lawrence , Foote Marc , Hurowitz Joel , Allwood Abigail
Published: March 2022

The Micro Context Camera (MCC) of PIXL onboard Perseverance has successfully completed commissioning. It meets all requirements and has led to the first proximity science using the PIXL instrument. This abstract presents the inflight system performance.

The pre-launch calibration of the MCC system has been verified on the surface of Mars. Distance measurements to Martian Rock surfaces are performed at with an accuracy better than 100 µm. This is accomplished utilizing Structured Light over the full diurnal thermal environment on the surface of Mars. The PIXL sensor unit is mounted on the turret of the Mars Perseverance rover arm. This autonomous navigation capability has enabled safe approaches of rugged surfaces, without ground intervention or interaction with e.g. a touch plate. It has also enabled proximity science of the Martian surface at unprecedented accuracy. The autonomy further enables PIXL to capture high resolution XRF scans while continuously maintaining optimal distance and focus of the X-ray beam. The system’s performance is robust enough for PIXL to navigate relative to both abraded and natural surfaces.

The MCC also has the capability of multispectral imaging. This has provided information for the interpretation of surface lithology and it also provides additional information for the XRF measurements interpretation due to its high resolution.

The MCC’s Terrain Relative Navigation (TRN) autonomous functionality has also been demonstrated in the Martian environment. This capability is essential for PIXL to maintain the planned scan trajectory relative to the rock surface – as PIXL’s longer duration scans (up to 10 hours) is relying on stability and capability to compensate for the diurnal thermal environment causing position drift relative to the Martian rock surface. We present the measured performance on Mars. This show that the system performs reliably on both high and low topography rock surfaces with and without dust coverage. This has enabled PIXL to autonomously track and self-correct for any drift away from the planned scan trajectory.
High-frequency ensemble wind speed forecasting using deep learning
Authors: Schicker Irene , Papazek Petrina , DeWit Rosmarie
Published: March 2022

In this study, we present a deep learning-based method to provide seamless high-frequency wind speed forecasts for up to 30 hours ahead. For each selected site, our method generates an ensemble forecast with an update frequency of 10 to 15 minutes(depending on the observation site’s update-frequency). The main objective in this machine learning based post-processing method is to optimally exploit highly resolved NWP models and particularly utilize their multi-level meteorological parameters to integrate the three-dimensionality of weather processes. Further key objectives of this research are to consider different spatial and temporal resolutions and different topographic characteristics of the selected sites. We evaluate the best praxis for efficiently post-processing both the 10-meter wind speed at selected Austrian meteorological observation sites and wind speed on hub height of wind turbines in wind farms.

The method is based on an artificial neural network (ANN), particularly a long-short-term-memory (LSTM) adopted to process several differently structured inputs simultaneously (i.e., different gridded inputs along with observed time-series) and generate ensemble output. An LSTM layer models recurrent steps in the ANN and is, thus, useful for time-series, such as meteorological observations.

Our ensemble forecast method is evaluated for a case study in 2021 using several years of training, including extreme weather event for the selection of sites. The utilized data includes the meteorological observations, gridded nowcasting data as well as NWP data from ECMWF IFS and AROME at several pressure/altitude levels. Hourly runs for 12 test locations (selected TAWES sites covering different topographic situations in Austria) and two wind turbine sites in different seasons are conducted. The obtained results indicate that the model succeeds in learning from inputs while remaining computationally efficient. In most cases the ANN method yields high forecast-skills and is compared to available methods such as the raw NWP model output, climatology, and persistence.
Contrasting responses of forest growth and carbon sequestration to heat and drought in the Alps
Authors: Galvagno Marta , Migliavacca Mirco , Cremonese Edoardo , Filippa Gianluca , Vacchiano Giorgio , Siniscalco Consolata , Oggioni Silvio , Morra di Cella Umberto , Oddi Ludovica
Published: March 2022

Projections of future climate change indicate that extreme events will be larger in frequency and intensity, with an increased risk of ecosystem transition from carbon sinks to carbon sources. In particular, warming is occurring at a higher rate in the Alps, with important impacts for tree species acclimated to a strong climate seasonality and a short growing season.

In this study, we investigated the ecosystem responses to heatwave and drought at a high-altitude Larix decidua (Mill.) forest in the western Italian Alps (IT-Trf, 2050 m asl), by coupling direct measurements of ecosystem-scale surface-atmosphere fluxes and tree-based observations. Ecosystem fluxes were monitored by means of the eddy covariance technique, measuring water and carbon fluxes (i.e., gross primary production, net ecosystem exchange, and evapotranspiration). From 2015 to 2017 additional observations were carried out at tree level, including stem growth and its duration, direct phenological observations, sap flow, and tree water deficit.

Results showed that the warm spells observed in 2015 and 2017, caused the advance of the larch phenological development and, thus, of the seasonal trajectories of many processes. However, we did not observe significant quantitative changes in the C sequestration at the ecosystem level, whereas in 2017 we found a reduction of 18% in larch stem growth and a contraction of 45% of the stem growth period. The growing season in 2017 was indeed characterized by different drought events and by the highest water deficit during the study years. By combining tree- and ecosystem-based observations, we demonstrated that larch growth decrease was not driven by a reduction of the photosynthetic activity.

We formulate two contrasting hypotheses to explain our results: i) a shift in C allocation within the plants towards the prioritization of NSC storage within leaves and roots over growth processes, which question the C-source limitation hypothesis, usually applied in vegetation modeling; ii) the ‘Insurance Hypothesis’, which can be used to explain the stability of the whole ecosystem gas exchanges, where the negative effects of climatic fluctuations on larch growth might have been buffered by the asynchrony responses of the understory species that can benefit from the higher temperatures.
Potential impacts of climate change on groundwater recharge in South Africa using stable isotopes of water
Authors: Ramudzuli Khahuliswe Edson
Published: March 2022

Potential impacts of climate change on groundwater recharge in South Africa using stable isotopes of water

KE Ramudzuli, JA Miller, T. Vennmann, A Watson and JD van Rooyen

Department of Earth Sciences, Stellenbosch University.

Unimodal wet season precipitation plays a significant role in ensuring sustainable and continuous replenishment of groundwater resources, especially in arid to semi-arid climates that only recharge during heavy rainfall events. For this reason, changes in precipitation patterns (i.e., the frequency, intensity, duration and seasonality of precipitation events) may impact the reliability and sustainability of groundwater resources. This study investigates the relationship between the stable water isotope precipitation vs groundwater composition from across different climatic zones in South Africa. The analysis was done to examine the record of evaporation recorded in the stable water isotopes of precipitation before groundwater recharge, in order to extrapolate how variable changes in climatic conditions would translate to groundwater recharge (e.g., induced evaporative loss of rainfall). Both precipitation and groundwater samples showed a strong alignment with the Global Meteoric Water Line (GMWL) and respective LMWLs with a dispersion that increased from the O- and H- isotope depleted sections towards the enriched areas. Groundwater samples generally recorded the same characteristics as wet season precipitation irrespective of whether this was winter or summer rainfall regions, and plotting with the same regionality for Local Meteoric Water Lines (LWMLs). Secondary evaporation of precipitation, noted by the deviation of groundwater samples from the GMWL and respective LMWLs, increased from the south-eastern and east coasts, which receive relatively higher precipitation amounts, towards the interior along with south and west coast of the country, which are somewhat dryer. This analysis will assist in the forecasting of future groundwater recharge patterns in response to climate change and represents an important step in assessing the impact of climate variability on groundwater sustainability.
The topographic signature of relative sea level in numerical and real landscapes.
Authors: Malatesta Luca C. , Huppert Kimberly L.
Published: March 2022

Crustal deformation along active coastline can be constrained with age and elevation of marine terraces. These are essentially the product of an erosive process (waves eroding bedrock) and a preservation process (rock uplift moving terraces up and away from subsequent wave erosion). The morphology that results from this combination depends nonlinearly on the characteristics of the two processes. In particular, variations in rock uplift rate can promote or hinder the creation of marine terraces at specific age and elevations (e.g., past sea level high stands).  While widespread and well-outlined in some coastal settings, marine terraces can be rare or absent from other areas despite the coexistence of the two driving processes. If they do not produce discrete terraces, wave erosion and rock uplift still contribute to shaping the coastal landscape in conjunction with subaerial processes, and their history is somehow encoded in the topography. Using the logic of a “sea level occupation map” that we introduced to describe the cumulative effect of wave erosion during the eustatic seesaw (Malatesta et al., 2022), we inspect the hypsometry of numerical and real landscapes whether or not they hold terraces. Hypsometry allows for a continuous representation, and inspection, of parameters in numerical models. In real landscapes, a hyspsometric survey does not require very high resolution digital elevation models, and produces tractable information from the entire topography. In this contribution we 1) explain our approach to create a metric that can be equally applied to numerical and real landscapes; 2) highlight threshold effects in numerical outputs that were difficult to identify previously; and 3) present preliminary results extracting valuable information about rock uplift rate and sea level occupation from coastal landscapes with limited or no marine terraces.
Role of Moist Static Energy Advection in Evolution of Convective Aggregation in Observations
Authors: Maithel Vijit , Back Larissa
Published: March 2022

Organization of convection in tropics exhibits a wide range of spatial and temporal scales on account of a complex maze of interactions between clouds, circulation, radiation, and moisture. Somewhere in that maze are also present the mechanisms responsible for the phenomenon of convective self-aggregation in idealized simulations. However, the exact role played by these self-aggregation mechanisms on organization of convection in the real world remains unclear including understanding when convection will aggregate further and when convection will disaggregate. Cloud radiative feedbacks have been found to be important for initiation and maintenance of self-aggregation in idealized modelling studies. In observations too, it has been shown that radiation varies linearly with convection across different regions in the tropics. This implies that radiative feedbacks add moist static energy (MSE) to the already moist columns (that is it favors aggregation). However, the question comes up then, why does convection disaggregate in observations despite the support from radiative feedbacks? We hypothesize that advection of moisture and moist static energy (MSE) instead is important for determining when convection aggregates or disaggregates in the real world.

We utilize a moist static energy (MSE) variance budget-based phase plane as a process oriented diagnostic tool to test our hypothesis. The phase plane is formed by taking the variance of MSE on the x-axis and time tendency of variance of MSE on the y-axis. Then, cycles of aggregation and disaggregation show up as elliptical orbits on this plane. Contributions to the MSE variance tendency from the advective terms and radiative terms can be explicitly analyzed on this phase plane. Data from idealized simulations is used to understand how self-aggregation mechanisms show up on the phase plane. The results are compared with reanalysis data to understand the differences between self-aggregation mechanisms in models and mechanisms that favor aggregation in the real world. Data from different regions is also analyzed to determine whether it’s the variations in advective terms or the radiative term that govern when convection aggregates or disaggregates in observations.
Layer geometry as a constraint on the physics of sliding onset
Authors: Mantelli Elisa , Bryant Marnie , Seroussi Helene , Raess Ludovic , Castelletti Davide , Schroeder Dustin , Suckale Jenny , Siegert Martin
Published: March 2022

Transitions from basal no slip to basal sliding are a common feature of ice sheets, yet one that has remained difficult to observe. In this study we leverage recent advances in the processing of radar sounding data to study these transitions through their signature in englacial layers. Englacial layers encode information about strain and velocity, and the relation between their geometry and the onset of basal sliding has been demonstrated in ice flow models (the so-called "Weertman effect"). Here we leverage this relation to test the long-standing hypothesis that sliding onset takes the form of an abrupt no slip/sliding transition. By comparing the modeled signature of an abrupt sliding onset in englacial layer slopes against slope observations from the onset region of a West Antarctic ice stream (Institute Ice Stream), we conclude that observed layer geometry does not support an abrupt no slip/sliding transition. Our findings instead suggest a much smoother sliding onset, as would be consistent with temperature-dependent friction between ice and bed. Direct measurements of basal temperature at the catchment scale would allow us to confirm this hypothesis.
Risks of converting coniferous forests to broadleaved species
Authors: Lewis Caitlin , Lukac Martin , Vanguelova Elena , Ascott Matthew
Published: March 2022

Non-native coniferous plantations in the UK have long been associated with potentially negative impacts on surface water and groundwater quality due to high levels of nitrogen accumulation in their soils. Recent changes in UK forestry policy and targets and in attitudes towards biodiversity triggered a shift towards restocking conifer forests with broadleaved species. Broadleaved species are typically associated with lower rates of nitrogen deposition, scavenging and nitrate leaching, so it is often assumed that this change in management will enhance water quality. However, the conversion of coniferous woodland to broadleaved woodland typically stimulates the breakdown of organic matter, leading to a pulse release of nutrients which cannot be taken up rapidly enough by the nascent broadleaved forest.

 

To assess the significance of this process we conducted a study at Thetford Forest, Norfolk, a forest exposed to elevated levels of nitrogen deposition.  We measured throughfall and soil solution chemistry, soil C/N ratios, pH and net nitrification in a chronosequence of stands (0-72 years old) in the conversion process. Observed changes in organic soil C/N ratios indicate the potential for elevated nitrate leaching fluxes within the first decade post-conversion. Results also show an increase in net nitrification in the summer five to eight years post-conversion, followed by an accumulation of nitrogen in the deep mineral soils (30-90 cm depth) ten years post-conversion. Our ongoing analysis of deep soil solution and throughfall chemistry will confirm whether these observations are linked to elevated leaching fluxes in the first decade after conversion. Mature broadleaf stands were unexpectedly associated with greater concentrations of throughfall nitrate from August-October, and lower rates of soil nitrification in the summer than coniferous stands. Further analyses from winter-spring 2022 will explore seasonal variations in throughfall chemistry between broadleaf and coniferous stands in the context of elevated nitrogen deposition.

 

Our observations highlight the need to consider interactions between the effect of land management, seasonality and elevated deposition on nitrogen cycling processes to understand the impact of intensive nitrogen use on terrestrial nitrogen fluxes.    
Characterising the vertical structure of buildings for use in atmospheric models
Authors: Stretton Megan , Hogan Robin , Grimmond Sue
Published: March 2022

Urban schemes in weather and climate models often characterise urban structures in a grid cell using the mean building height and street width. This does not capture the sub-grid vertical variability that impacts fluxes. The vertical distribution of wall area and building heights are ideally required but are often unavailable in cities globally. In this work, building footprint and height data from six cities are used to parameterise the geometry with varying levels of detail of input data.

We conclude the vertical distribution of buildings can be parameterised using a function of mean building height and surface building plan area. Comparisons of the parameterised building plan area fraction with height to ‘true’ data (2 km x 2 km resolution) show 90% of the profiles have bias errors (BE) of < 0.03 (‘true’ values are: 0.05 – 0.55).

Building horizontal size (or effective building diameter, D) has a six-city mean of ~21 m. As D is impacted by normalised building edge length and building plan area, we use it to parameterise building edge length. The derived D parameterisations have normalised BE (nBE) < 16%, but without total wall area as an input the nBE increases to 26%.

The combined parameterisations are used with the radiative transfer model SPARTACUS-Urban to simulate total absorption of shortwave (SW) radiation and effective SW albedo. The latter is impacted 2-10% (cf. simulations using ‘true’ data). Larger errors occur when simulating  within-canyon absorption fluxes. Larger errors also occur when fewer morphology inputs are used, with total wall area having the most benefit.

We conclude urban vertical variability can be acceptably characterised for numerical weather prediction using three parameters: surface building plan area, mean building height, and effective building diameter.