bluuebunny/crossref_metadata_2025 huggingface dataset:
The glacier seismo-acoustic monitoring system in the Ukrainian Antarctic Station region
Authors: Liashchuk Liudmila , Liashchuk Oleksandr , Zhukovsky Vadym , Karyagin Yevheniy , Andrushchenko Yuriy , Dovbysh Serhiy
Published: March 2021

Continuous long-term monitoring of the glacier is not an easy task. For the Woozle Hill ice cap near the Vernadsky Research Station, which is located on Galindez Island (Argentine Islands Archipelago), the task was solved by periodic ice sampling, GNSS measurements, photometry, and the use of GPR in the summer season. Some meteorological parameters were also periodically measured inside the ice cave in the glacier when conditions were favorable. In the past few years, GPR measurements have become more constant, and now they are carried out monthly. For continuous monitoring of the internal stresses of the glacier, we proposed using a network of seismoacoustic mini-arrays located along the perimeter of the glacier. Each array consists of four seismoacoustic sensors arranged in a cross. The length of the line between the extreme sensors reaches 100 meters. Proprietary sensors use an optical system for recording the seismic and infrasonic vibrations. The built-in microcontroller of each sensor transmits the digitized data (16 bit, 100(300) Hz) to the main unit based on the LattePanda, where preprocessing is performed. GPS receiver is also connected here for data synchronization. There is a Wi-Fi module for transmitting data to the collection station. Also, data can be transmitted to the collection station by wires installed on the cable-growth. Power is supplied 220 V through an adapter and a 12V battery. The sensors are waterproof, the rest of the equipment is assembled in a sealed waterproof box. There are three such arrays, in their turn, they form a regular triangle with a side of 700 meters, inside which there is a glacier. The processing consists of detecting signals in each array by the STA / LTA method, followed by correlation processing of the selected data fragment and calculating the azimuth to the signal, wave velocity, period, and amplitude. Also, the isolation of the coherent part of the low-intensity signal at the noise level can be carried out without preliminary STA / LTA detection, using algorithm F-statistics. Correlated interference is clipped in azimuth. The intersection of two or three azimuths allows you to locate the signal source. All parameters of detections with time stamps are recorded in the database and can be further processed using station meteorological data. The system began to be deployed around the glacier in January 2021. The presentation will present the first results of the deployed monitoring system.
A Prototype IMERG Error Modeling Framework based on GPM DPR Observations and its Global Validation
Authors: Li Zhe , Wright Daniel , Hartke Samantha , Kirschbaum Dalia , Khan Sana , Maggioni Viviana , Kirstetter Pierre-Emmanuel
Published: March 2021

The potential of global high-resolution near-realtime multi-sensor merged satellite precipitation products such as NASA’s 30-minute, 0.1° Integrated Multi-satellitE Retrievals for Global Precipitation Mission (IMERG) to monitor, characterize and model the water cycle has been widely recognized. Despite continuing improvements in the coverage, accuracy, and resolution of these products, their usefulness in real-world applications is still limited by the lack of insight into errors in estimated precipitation and the ability to properly quantify errors in ways that benefit various end users. A fundamental limitation is the lack of reliable “ground truth” data (e.g., rain gauges or ground weather radars)—such reference observations are lacking in precisely the places (complex terrain, ungauged areas, and developing countries) that could benefit most from satellite products. Moreover, error characterization of satellite precipitation products poses a unique challenge due to the “mixed” discrete and continuous distribution of errors, a challenge that is increasingly important to address as satellite precipitation products advance to higher resolutions.

In this work, we propose to use the instantaneous swath-based data products from the Dual-frequency Precipitation Radar (DPR) aboard the GPM core observatory as an alternative reference to replace ground observations—which could facilitate IMERG global error estimation at its native resolution. We compare two DPR-based products, 2ADPR and 2BCMB, against the Multi-Radar/Multi-Sensor (MRMS) data over the contiguous United States (CONUS). We then select 2BCMB to train a mixed discrete-continuous error model based on the Censored Shifted Gamma Distribution (CSGD) to estimate IMERG errors. This error model is evaluated and compared against an alternative CSGD model trained on MRMS data in the CONUS during 2014-2019. Using NASA’s MERRA-2 reanalysis products, we also demonstrate how IMERG errors can be further constrained by including ancillary information as covariates within the error model. This error modeling framework will be further examined at several ground validation sites around the globe (e.g., WegenerNet, AMMA-CATCH among others) to evaluate its robustness under different climatic, land cover, and DPR sampling conditions.
Simulation and Projection of Global Mean Surface Temperature Using the Empirical Model of Global Climate and Comparison to CMIP6 GCMs
Authors: McBride Laura , Hope Austin , Canty Timothy , Tribett Walter , Bennett Brian , Salawitch Ross
Published: March 2021

The Empirical Model of Global Climate (EM-GC) (Canty et al., ACP, 2013, McBride et al., ESDD, 2020) is a multiple linear regression, energy balance model that accounts for the natural influences on global mean surface temperature due to ENSO, the 11-year solar cycle, major volcanic eruptions, as well as the anthropogenic influence of greenhouse gases and aerosols and the efficiency of ocean heat uptake. First, we will analyze the human contribution of global warming from 1975-2014 based on the climate record, also known as the attributable anthropogenic warming rate (AAWR). We will compare the values of AAWR found using the EM-GC with values of AAWR from the CMIP6 multi-model ensemble. Preliminary analysis indicates that over the past three decades, the human component of global warming inferred from the CMIP6 GCMs is larger than the human component of warming from the climate record. Second, we will compare values of equilibrium climate sensitivity inferred from the historical climate record to those determined from CMIP6 GCMs using the Gregory et al., GRL, 2004 method. Third, we will use the future abundances of greenhouse gases and aerosols provided by the Shared Socioeconomic Pathways (SSPs) to project future global mean surface temperature change. We will compare the projections of future temperature anomalies from CMIP6 GCMs to those determined by the EM-GC. We will conclude by assessing the probability of the CMIP6 and EM-GC projections of achieving the Paris Agreement target (1.5°C) and upper limit (2.0°C) for several of the SSP scenarios.
New insights into the ~74 ka Toba eruption from sulfur isotopes of polar ice cores
Authors: Crick Laura , Burke Andrea , Hutchison William , Sparks Stephen , Mahony Sue , Wolff Eric W. , Doyle Emily A. , Rae James W. B. , Savarino Joel , Kohno Mika , Kipfstuhl Sepp , Wörner Gerhard
Published: March 2021

The ~74ka Toba eruption in Indonesia was one of the largest volcanic events of the Quaternary and loaded an estimated 100 million tonnes of H2SO4 into the atmosphere. Understanding the precise timing of this colossal eruption is vital to unravelling the climatic and environmental impacts of the largest volcanic events on Earth. Sulfur aerosols injected into the stratosphere following large volcanic events scatter incoming radiation and lead to global cooling, and in the case of Toba it has been suggested that it led to cooling of 1 – 5°C and extinctions of some local hominin populations. One of the most enigmatic features of the Toba eruption is that the S peak has yet to be identified in the ice core records, although numerous candidate sulfate peaks have been identified in both Arctic and Antarctic ice cores. To address this, we analysed the sulfur isotope fingerprint (δ34S and Δ33S) of 11 Toba candidates from two Antarctic ice cores by multi-collector inductively coupled plasma mass spectrometry. This approach allows us to evaluate injection altitudes and to distinguish large tropical eruptions from proximal eruptions because stratospheric sulfur aerosols undergo UV photochemical reactions that impart a sulfur mass-independent isotopic fractionation (S-MIF). In contrast, tropospheric sulfur aerosols do not exhibit S-MIF because they are shielded from the relevant UV radiation by the ozone layer.

We identify three stratospheric, tropical eruption candidates with two recording the largest Δ33S signals measured to date in the ice core archives. The largest of these Δ33S signals is >2 ‰ more negative than previous measurements of the 1257 Samalas eruption (the largest eruption of the last 2000 years), despite having a similar integrated sulfate flux for this event to the ice core. These three candidates are within uncertainly of the Ar40/Ar39 age estimates for the Toba eruption and when considered with other paleoclimate proxies place the event during the transition into Greenland Stadial 20.  Finally, we further analyse the relationship between the Toba eruption candidates and these proxies to determine the precise timing and potential climatic impacts of one of the largest eruptions of the Quaternary period.
Vegetation dynamics of the eastern Mediterranean region during the Holocene
Authors: Cruz-Silva Esmeralda , Harrison Sandy P. , Marinova Elena , Prentice I. Colin
Published: March 2021

The circum-Mediterranean region is characterized by high climatic diversity derived from its orographic heterogeneity and the influence of global marine and atmospheric circulation patterns. The region also has a long and dynamic history of human occupation dating back to ~ 8000 years BP.  The complexity of this area is a challenge for reconstructing the dynamics of the vegetation through the Holocene. Rule-based approaches to reconstructing changing vegetation patterns through time are insufficient as they require the imposition of subjective boundaries between biomes and can be affected by known biases in pollen representation.  We have developed and tested a new method that characterises biomes as a function of observed pollen assemblages based on a similarity index, conceptually related to the likelihood function, which takes account of within-biome variability in taxon abundances. We use 1181 modern pollen samples from the EMBSeCBIO database and assign these samples to biomes as represented in a map of potential natural vegetation that was developed using machine learning. The method was applied down-core to reconstruct past vegetation changes. Preliminary results show that this new methodology produces more accurate biome assignments under modern conditions (<80% accuracy) and more stable down-core reconstructions, apparently reducing the "flickering switch" problem found when using the traditional biomisation method for this purpose. Climate-induced vegetation changes are observable on a sub-regional scale in the Eastern Mediterranean through the Holocene. Most of the records show a change from humid to more arid biomes between 4000 and 3000 years BP. However, they are distinct subregional patterns in the expression and timing of wetter conditions during the Holocene. Mountain regions appear to show more muted changes during the Holocene, although there are biome shifts everywhere across the Pleistocene-Holocene transition.
Mapping river corridors at the network scale for integrating natural infrastructures into rural/urban spatial planning
Authors: Rousson Christophe , Piégay Hervé , Fantino Guillaume
Published: March 2021

The “green infrastructure” metaphor have put a new emphasis on river spatial planning as a mean to protect fluvial corridors on the long term (Kline and Cahoon, 2010) as they provide ecosystem benefits such as flood expansion zones or better functioning ecological networks. In order to provide support data for strategic planning at the regional or national scales, we have developed automated mapping tools of fluvial corridors and floodplains based on high-resolution DEM and landcover datasets. Our goal is to characterize the continuity of fluvial corridors in the longitudinal and lateral dimensions and produce indicators on their integrity.

Following the work done by Alber and Piégay (2011) and Roux et al. (2015), we produced high-resolution detrended DEM (height maps) that support the delineation of valley bottoms, can be used for 0D flood risk mapping or to identify potential wetlands. Based on the hypothesis that fluvial processes imprint the modern landscape, even in the presence of human-driven disturbance, we have also developed a novel landcover continuity analysis method. These continuity maps provide insights on the spatial scale of river processes and the amount of space, if not natural, that is still well connected to the river and is eventually available for floodplain restoration. Finally, we explored the possibility to disseminate our results through a web platform to share the database across scales for promoting participative approaches and land use planning.

At the intersection between fluvial risks mitigation, water resource preservation, and biodiversity and landscape conservation, this strategy is rooted in the concept of “freedom of space” and unifies the concepts of greenways, waterways and floodways in a common approach to making room for the river and working with natural processes, integrating the concept of natural infrastructures that has been proposed in the 1990s (Mermet, 1993). This holistic view insists on river corridors and floodplains as multifunctional spaces. It is expected that this spatial knowledge will in turn raise awareness and encourage local authorities to better protect river corridors as green infrastructures through land planning.

Further perspectives include studying how the intended recipients of our approach, such as local authorities or river practitioners, appropriate the produced maps and information, and to what extent they contribute to an effective protection of river corridors. This understanding should prove useful to integrate such data into regional observatories and communicate a more integrative view of the river.
Modeling the Interaction between Easterly Waves and Deep Convection in Costa Rica
Authors: Torri Giuseppe , Lintner Benjamin , Durán-Quesada Ana María , Serra Yolande
Published: March 2021

Easterly waves (EWs) are an important feature of the intertropical convergence zone, they often serve as precursors to tropical cyclones, and, during boreal summers, are one of the main contributors to rainfall in various countries in Central America. Given the land-sea configuration that features the region, a better understanding of the EWs impact on regional rainfall would leverage the comprehension of regional interactions processes. EWs were also one of the foci of OTREC (Organization of Tropical East Pacific Convection), an observational campaign that took place in Costa Rica and Colombia from 5 August to 9 October 2019. Here, we will present some results obtained with high-resolution numerical simulations conducted with the System for Atmospheric Modeling (SAM), which are based on data collected during OTREC. We will begin by presenting a series of simulations forced with high-frequency radiosonde data collected in Santa Cruz, Costa Rica, for a weeklong period during OTREC, highlighting model performance in reproducing the data. We will then discuss more idealized SAM simulations designed to investigate convective initiation and convective organization at various stages of EW passage. Finally, using sensitivity experiments with SAM in which we override soil moisture conditions, we will address the role of surface moisture in modulating the interaction between EWs and deep convection over land. This work aims to improve current knowledge on the role of EWs for regional rainfall, influence on the initiation of deep convection and further surface-atmosphere feedbacks.
Active faulting offshore the Maltese Islands revealed by geophysical and geochemical observations
Authors: Micallef Aaron , Spatola Daniele , Caracausi Antonio , Italiano Francesco , Barreca Giovanni , D'Amico Sebastiano , Petronio Lorenzo , Coren Franco , Facchin Lorenzo , Blanos Rita , Pavan Alessandro , Paganini Paolo , Taviani Marco , Baradello Luca , Gordini Emiliano
Published: March 2021

The Maltese Islands (central Mediterranean Sea) are intersected by two normal fault systems associated with continental rifting to the south. Because of a lack of evidence for offshore displacement and insignificant historical seismicity, the systems have been considered to be inactive. Here we integrate aerial and marine geological, geophysical and geochemical data to demonstrate that: (i) the majority of faults offshore the Maltese Islands underwent extensional to transtensional deformation during the last 20 ka, (ii) active degassing of CH4 and CO2 occurs via these faults. The gases migrate through Miocene carbonate bedrock and the overlying Plio-Pleistocene sedimentary layers to generate pockmarks at the muddy seafloor and rise through the water column into the atmosphere. We infer that the offshore faults systems are permeable and that they were active recently and simultaneously. The latter can be explained by a transtensional system involving two right-stepping, right-lateral NW-SE trending faults, either binding a pull-apart basin between the islands of Malta and Gozo or associated with minor connecting antitethic structures. Such a configuration may be responsible for the generation or reactivation of faults onshore and offshore the Maltese Islands, and fits into the modern divergent strain-stress regime inferred from geodetic data.
Impacts of Climate Change on Groundwater Recharge & Discharge in Water Scarce Region: A Case Study of the Ubar/ Shisr Agricultural Region of Oman.
Authors: Boluwade Alaba , Al-Mamani Asma , Alruheili Amna , Al-Maktoumi Ali
Published: March 2021

 

*Correspondence: alaba@squ.edu.om

Abstract: The primary objective of this study was to quantify the impacts of climate change on groundwater recharge using the 3D numerical-based HydroGeoSphere (HGS) model in the Ubar/ Shisr Agricultural region in South of Oman. This region has multi-million US dollar irrigated agriculture project purposely developed for the food security of the country. Excessive abstraction of groundwater for irrigation use (using the center pivot irrigation system) has contributed to the “drying-up” of several groundwater wells located in this area. Therefore, there is an urgent need to characterize the long-term sustainability of this agricultural project under a changing climate. HGS model was calibrated on both steady and transient states using selected monitoring wells located within the study area (approximately 980-km2). The coefficient of determination (R2) for the steady-state performance was 0.93 while the transient state performances correctly reproduced the seasonality for each monitoring well. A transient-based calibrated version of the HGS model, using 30-year historical observations (1980-2018) was termed “Reference” while model configurations were developed for the immediate climatic projection (period: 2020 – 2039) based on two Representative Concentration Pathways (RCP): - RPC4.5 and RCP8.5 extracted from the World Bank Knowledge portal. These two configured models (scenarios) were evaluated for monthly transient simulations (2020-2039). From the total hydraulic head (THH) fluctuations standpoint, there were reductions when compared with “Reference” for all the scenarios with up to 20% THH reductions for groundwater well levels under persistent seasonal agricultural activities. This study is very important in quantifying the trade-offs and synergies involved between sustainable water management and food security initiatives, especially for an arid climate.

Keywords: groundwater recharge; climate change, hydrogeologic modeling; Sultanate of Oman
Development of new pathogen surrogates and synthetic DNA tracers for water applications
Authors: Pang Liping
Published: March 2021

In recent years, we have conducted research into developing new pathogen surrogates and synthetic DNA tracers for water applications. Biomolecule-modified particles have been used to mimic Cryptosporidium, rotavirus and adenovirus with respect to their filtration removal and transport in porous media. Additionally, we have developed new DNA tracers as free DNA molecules or DNA-encapsulated biopolymer microparticles to track water contamination. DNA markers are also used to label some surrogates to facilitate their sensitive detection by using qPCR.

The surrogates have been validated in laboratory conditions alongside the actual pathogens. The Cryptosporidium surrogates have been satisfactorily validated in alluvial sand, in limestone sand, in coagulation and rapid sand filtration studies. The rotavirus surrogates have been successfully validated in coastal sand aquifer media, in unmodified and hydrophobically modified quartz sand, and in stony alluvial soils under on-site wastewater applications. The research findings have demonstrated that these new surrogates significantly outperform the most commonly used existing surrogates, namely, unmodified microspheres for Cryptosporidium oocysts and MS2 phage for viruses. Working with the water industry, we have applied the Cryptosporidium surrogate to pilot-scale rapid sand filters and point-of-use domestic filters and determined its removal efficiencies in water filtration systems commonly used in New Zealand. The artificial DNA tracers have been validated in surface water, groundwater and soils, and they were readily trackable in a surface stream for up to 1 km.

Our proof-of-concept studies suggest that the new pathogen surrogates and synthetic DNA tracers we have developed show great promise as new tools for water applications. The ‘micro mimics’ approach has opened up a new avenue for assessing pathogen removal and transport in water systems without the risk and expense that accompany work with actual pathogens. With further validation, the new surrogates could be used to study pathogen removal and transport in subsurface media after the disposal of effluent and biosolids to land, and to assess the performance of filtration processes in water and wastewater treatment. With future up-scaling validation of the new synthetic DNA tracers, these tracers could be useful for concurrently tracking multiple pollution sources and pathways in freshwater environments.
Variability of various nightglow emissions from about 100,000 VLT/X-shooter spectra
Authors: Noll Stefan , Kausch Wolfgang
Published: March 2021

Chemiluminescent emission from the mesopause region between 75 and 105 km dominates the Earth's low-to-mid-latitude nocturnal radiation in the wavelength domain from the near-UV to the near-IR. This nightglow consists of various roto-vibrational bands of molecules such as hydroxyl and molecular oxygen as well as individual lines from atoms such as oxygen and sodium. In principle, each line shows an individual vertical emission profile with a characteristic mean peak height and a typical full width at half maximum of less than 10 km. The total emission rate, peak height, and shape of the different profiles depend on the temperature, density, and the concentrations of different chemical species, especially of atomic oxygen. As the state of the mesopause region is strongly affected by the solar activity (especially via the rate of hard UV photons that produce highly reactive radicals) and different kinds of passing waves such as tides and gravity waves that mainly originate in the lower atmosphere, nightglow is also highly variable and can, thus, be used to trace the different processes. Various ground- and space-based observing strategies have already been applied. However, recording the variations of many different (and especially weak) emission lines in parallel with good temporal coverage for perturbations with time scales from minutes to years is challenging. 

In this context, we have now achieved to process about 100,000 medium-resolution spectra with a wavelength coverage from 0.3 to 2.5 µm that were taken with the astronomical X-shooter spectrograph at the Very Large Telescope of the European Southern Observatory at Cerro Paranal in Chile between 2009 and 2019. This promising data set allows us to study the variability of hundreds of nightglow lines and mutual correlations on time scales from those related to gravity waves to those related to the solar activity cycle. We will show first results. The goal of the project will be a better understanding of the nightglow layering and the sensitivity of the different emissions to different kinds of changes in the atmospheric conditions. 
Impact of latent and dry-static atmospheric energy transport on the Arctic sea ice variability
Authors: Hofsteenge Marte G. , Graversen Rune G. , Rydsaa Johanne H.
Published: March 2021

Superimposed on a strong observed decline in Arctic sea ice extent there is large inter-annual variability. Recent research indicates that atmospheric temperature fluctuations are the main drivers for this variability. They can result both from local ocean heat release and from poleward atmospheric energy transport. Previous studies have emphasised a significant warming effect associated with latent energy transport into the Arctic region. In particular this is due to enhanced greenhouse effect associated with the convergence of the humidity transport over the Arctic. While previously some sea ice minima events have been linked to anomalous moist air convergence, a systematic study of this linkage between energy transport and sea ice variability was missing. Through a regression analysis we here investigate the coupling between transport anomalies of both latent and dry-static energy and sea ice anomalies. From the state-of-the-art ERA5 reanalysis product the latent and dry-static transport over the Arctic boundary (70°N) is calculated. The transport is then split into transport by planetary and synoptic-scale waves using a Fourier decomposition. Lagged regression analysis of sea ice concentration anomalies on the transport anomalies reveal the statistical linkage between the occurrence of sea ice anomalies after transport events. The results show that latent energy transport as compared to that of dry-static energy induces a much stronger decrease in sea ice concentration. One day after maximum of the latent transport event by planetary waves, sea-ice concentration shows a significant decrease lasting up to at least 45 days. In addition, the energy transport by planetary waves shows a greater effect on the sea ice concentration than transport by synoptic-scale waves. Hence, this study emphasizes the important impact of latent energy transport by planetary waves on the sea ice variability.
A comprehensive database of the optical properties of mineral dust aerosol particles for spaceborne remote sensing applications
Authors: Saito Masanori , Yang Ping
Published: March 2021

Airborne atmospheric aerosol impacts the Earth’s energy budget through their radiative effects and interactions with clouds. Among various aerosol species, mineral dust particles are the most dominant aerosols over desert areas.Continuous monitoring of the global distributions of the mineral dust aerosol is essential to the assessment of their local and climatic impacts. Satellite observations in conjunction with remote sensing techniques have been playing an essential role in the understanding of the global distribution of dust aerosol properties. However, the satellite-based retrievals of mineral dust aerosol properties may involve systematic biases and large uncertainty partly because their optical properties that are fundamentally determined by particle sizes, chemical compositions, and complex morphologies of aerosol particles are not adequately modeled. This presentation will introduce a recently developed comprehensive database for the single-scattering properties of irregular aerosol particles (so-called TAMUdust2020 database) for various remote sensing applications including both passive and active-sensor observations. The TAMUdust2020 database was developed based on an ensemble of various irregular particle shape models that mimic realistic mineral dust particle shapes and their diversity, and was developed with the state-of-the-art light scattering computational capabilities including the physical-geometric optics method (PGOM) and the invariant-imbedding T-matrix (II-TM) method. Comparisons of the scattering properties between laboratory measurements and the present simulations based on TAMUdust2020 database show reasonable consistency. Furthermore, we apply the dust aerosol scattering properties to simulate various spaceborne satellite observations, including multiangle polarimetric observations, thermal infrared observations, and lidar observations. In this presentation, we will demonstrate the capability of current satellite observations with the scattering property database to infer aerosol optical depth and particle effective radius.
Flash Drought and Heat Waves: An Overview of Cascading and Compound Events
Authors: Grace Taylor , Christian Jordan , Basara Jeffery
Published: March 2021

Flash droughts and heat waves have substantial impacts on agriculture, socioeconomics, and human health. The combined influence of these two events exacerbate the damage to several sectors. The positive feedback between drought and heat waves has been previously studied, but the connection between flash drought and heat waves (or record temperatures) has only been investigated to occur roughly at the same temporal period. Further understanding the compound and cascading impacts of flash droughts and heat waves could potentially enhance monitoring and/or predictability of flash drought events benefiting subseasonal-to-seasonal forecasts, minimize human mortality, and prevent agricultural yield loss. We present a novel approach to analyzing compound and cascading impacts from the flash drought-heat wave relationship by investigating multiple case studies (e.g., 1950s drought event, 2011-2012 U.S. flash drought, and 2019 U.S. flash drought). Several reanalysis datasets were utilized to examine the intensity, temporal duration, and spatial extent relationships between flash drought and heat wave conditions during the case study events. We define heat waves using the following framework which incorporates classifications employed in previous studies; one classification is dependent on a relative threshold (i.e., 95th percentile) applied to daily maximum and minimum temperatures, whereas the second part of the definition utilizes heat index under the same relative threshold. In order for a heat wave event to begin, this definition must hold true for three or more consecutive days for a specified spatial method. Our flash drought analysis incorporated a percentile methodology based on standardized evapotranspiration stress ratio (SESR). Comparison between intensity, spatial extent, and temporal duration relationships for compound and cascading events were of particular focus for this study. A mixture of compound and cascading events were found within one flash drought study (i.e., 2011-2012 flash drought). As such, we further hypothesize that the intensity and temporal duration will differ between compound and cascading events. Yet, we expect the spatial extent to remain positively correlated as shown from previous studies.
 Spectral nudging in an hourly 4DVar framework: Status and Plans
Authors: Milan Marco , Clayton Adam , Lorenc Andrew , Dow Gareth , Tubbs Roberts , Macpherson Bruce
Published: March 2021

The Met Office hourly 4D-Var was introduced operationally to its convective-scale limited area model (UKV) in summer 2017, improving forecast skill for nowcasting and short-range purposes. However, in recent tests a downscaler run from a global analysis tends to be better than hourly 4D-Var, especially for some variables (e.g. screen temperature). This is probably due to a poor representation of large-scale dynamics in the LAM DA system, which is now integrated on an extended domain, whilst the global model has improved to a 10km resolution and with better DA (hybrid 4D-Var). Therefore, the MO recognises the necessity of coupling large scale dynamics with convective systems using the better estimation of these motions from the global model.
We opted for a solution similar to spectral nudging, which uses large scale increments derived from a model with a better representation of these scales. At the same time, the short scales from UKV are maintained. We call this method ‘Background Increments’ (BGInc), as it updates the UKV background fields using a spectrally filtered increment derived from a different (global) model. This update is calculated just prior to computing the analysis increments from the hourly DA cycle. We investigated different set-ups for the implementation, changing the cut-off wavelength, the vertical weights, the frequency of updates of BGInc and other set-up features.
This novel system is now in a testing phase for operational purposes. From preliminary results, the forecast is improved for about the first 12 hours for different variables. We also notice a reduction in the gravity wave activity generated when new lateral boundary conditions are introduced to the LAM from the latest global forecast. This research shows the benefits of a better representation of large-scale motions for LAM forecasts.
In the short term, future development involves the computation of new static covariances using a better representation of the large-scale error. In the longer term, this technique could be useful in a hybrid 4D-Var scheme while enabling the use of large-scale ensemble perturbations in the analysis without causing large adjustments at the lateral boundaries.
Probabilistic seismic hazard maps for California do not perform better relative to historical shaking data when site-specific VS30 is considered
Authors: Gallahue Molly , Salditch Leah , Lucas Madeleine , Neely James , Hough Susan , Stein Seth , Abrahamson Norman , Williams Tessa
Published: March 2021

Probabilistic seismic hazard assessments forecast levels of earthquake shaking that should be exceeded with only a certain probability over a given period of time are important for earthquake hazard mitigation. These rely on assumptions about when and where earthquakes will occur, their size, and the resulting shaking as a function of distance as described by ground-motion models (GMMs) that cover broad geologic regions. Seismic hazard maps are used to develop building codes.

To explore the robustness of maps’ shaking forecasts, we consider how maps hindcast past shaking. We have compiled the California Historical Intensity Mapping Project (CHIMP) dataset of the maximum observed seismic intensity of shaking from the largest Californian earthquakes over the past 162 years. Previous comparisons between the maps for a constant VS30 (shear-wave velcoity in the top 30 m of soil) of 760 m/s and CHIMP based on several metrics suggested that current maps overpredict shaking.

The differences between the VS30 at the CHIMP sites and the reference value of 760 m/s could amplify or deamplify the ground motions relative to the mapped values. We evaluate whether the VS30 at the CHIMP sites could cause a possible bias in the models. By comparison with the intensity data in CHIMP, we find that using site-specific VS30 does not improve map performance, because the site corrections cause only minor differences from the original 2018 USGS hazard maps at the short periods (high frequencies) relevant to peak ground acceleration and hence MMI. The minimal differences reflect the fact that the nonlinear deamplification due to increased soil damping largely offsets the linear amplification due to low VS30. The net effects will be larger for longer periods relevant to tall buildings, where net amplification occurs. 

Possible reasons for this discrepancy include limitations of the dataset, a bias in the hazard models, an over-estimation of the aleatory variability of the ground motion or that seismicity throughout the historical period has been lower than the long-term average, perhaps by chance due to the variability of earthquake recurrence. Resolving this discrepancy, which is also observed in Italy and Japan, could improve the performance of seismic hazard maps and thus earthquake safety for California and, by extension, worldwide. We also explore whether new nonergodic GMMs, with reduced aleatory variability, perform better than presently used ergodic GMMs compared to historical data.
GPS-based dynamic orbit determination for low Earth orbit satellites
Authors: Mao Xinyuan , Arnold Daniel , Kobel Cyril , Villiger Arturo , Jäggi Adrian
Published: March 2021

A classical reduced-dynamic GPS-based Precise Orbit Determination (POD) strategy for Low Earth Orbit (LEO) satellites is often based on a limited explicit modelling of satellite dynamics and modelling deficiencies are compensated by numerous empirical parameters. With better gravitational models and the advances in satellite surface force modeling, uncertainties in the satellite dynamics are significantly reduced. Furthermore, single-receiver ambiguity resolution allows for more robust POD as well. Therefore, a dynamic POD strategy using  significantly fewer estimated empirical parameters can be implemented to generate dynamic orbits, which allow for force modeling sensitivity analyses and evaluating potential errors in the adopted GPS antenna reference points or phase center offsets, etc.

 

This presentation outlines the recent dynamic POD methodology developments at the Astronomical Institute of the University of Bern (AIUB) and investigates the POD performances for a few dedicated space geodesy satellite missions (Swarm, GRACE-FO, Sentinel-1, Sentinel-2, Sentinel-3 and Jason-3) that are operated at altitudes ranging from 430 to 1350 km. The focuses will be on satellite gravitational and non-gravitational force modeling, satellite dynamics parametrization, and orbit validations for different types of satellites. Results reveal that the dynamic POD strategy is flexible and robust to generate high-quality orbits for those satellites, showing reliable agreements with the independent ambiguity-fixed kinematic orbits and the external Satellite Laser Ranging (SLR) measurements.
Long-lasting impacts of winds on Arctic sea ice through the ocean’s memory
Authors: Wang Qiang , Danilov Sergey , Mu Longjiang , Sidorenko Dmitry , Wekerle Claudia
Published: March 2021

This modelling study reveals that the changes in the ocean state induced by wind perturbations can significantly influence the Arctic sea ice drift, thickness, concentration and deformation rates even after the wind perturbations have been eliminated for years. Wind perturbations can change the Arctic Ocean liquid freshwater content locally or basin-wide, thus changing the sea surface height and ocean surface geostrophic current accordingly. Such changes in the ocean can last for many years, which enforces long-lasting and strong imprint on sea ice. Both the changes in sea surface height gradient force (due to changes in sea surface height) and ocean-ice stress (due to changes in ocean geostrophic velocity) are found to be important in determining the overall impacts on sea ice. Depending on the preceding atmospheric mode driving the ocean, the ocean’s memory of wind forcing can lead to changes in Arctic sea ice characteristics with very different spatial patterns. We identified these spatial patterns associated with Arctic Oscillation, Arctic Dipole Anomaly and Beaufort High modes through dedicated numerical simulations in this study. Our results suggest the importance of initial ocean state in sea ice prediction on subseasonal to decadal time scales.
Water scarcity footprint of renewable electricity generation in the context of regional impacts from mining activities
Authors: Schomberg Anna , Flörke Martina , Bringezu Stefan
Published: March 2021

Renewable energies play a key role in avoiding carbon dioxide emissions from fossil electricity generation. However, support for certain renewable energy technologies focused only on greenhouse gas reduction can reinforce other environmental impacts and thus shift the problems. The authors therefore compare three forms of renewable electricity generation, namely concentrated solar power, run-of-river hydropower and sugarcane bagasse burning, to classical electricity generation from hard coal combustion with respect to their contribution to regional water scarcity. In a comparative life cycle impact assessment the quantitative and qualitative demand for water is assessed in a comprehensive conceptual framework against the background of regional water availability. A spatially explicit analysis reveals hotspots of water use along the case studies’ supply chains with a strong focus on mining activities. For this purpose, the global supply chains of nine mineral resources (aluminium, clay, coal, copper, gypsum, iron, lime, lithium and phosphate) were regionalised at mine site level in advance, so that contributions to environmental impacts can be assigned to single mine clusters. Next to the locations of the case studies itself, about 40 % of all contributions are associated with mining activities. Hard coal mining in Russian and Chinese mines as well as in South Africa as part of the supply chains of all case studies makes up the largest share of this. Further contributions are from mining of iron ore in Australian mines and copper extraction in Chinese, North American and Peruvian mines. However, up to 65 % of the life cycle impacts cannot be spatially analysed due to limited data availability. These findings indicate that a detailed investigation of mining supply chains is necessary to compare power generation technologies in a meaningful way. Results also show that sugarcane bagasse burning, if used as by-product and not as waste, is responsible for the largest contributions to all indicators, suggesting that targeted use of biomass for electricity generation is not is not very effective in reducing global environmental impacts, such as contribution to water scarcity.
Evaluation of Shrinkage and Desiccation Crack Propagation Patterns in Clays for the assessment of their suitability in landform rehabilitation
Authors: Yaghoubi Mohammadjavad , Baumgartl Thomas
Published: March 2021

The variation of water content has a significant effect on the engineering behaviour of clayey soils. This is in particular of high importance to infrastructure projects such as open pit mine rehabilitation. During the construction of open pit mines, the natural ground water level needs to be lowered for the feasibility of mining activities. This dewatering causes significant shrinkage and development of cracks amongst the deposits of cohesive soils. In order to design a rehabilitation plan, it is critical to investigate the shrinkage and desiccation cracks occurred within and around open pit mines as the result of dewatering. This study aims at identifying the shrinkage and crack development patterns using an experimental approach and utilizing image analysis. Three different types of clays were studied to this end. Physical properties including liquid limit, plastic limit and linear shrinkage of clays were determined. Soil samples were put in circular moulds of 150 mm diameter and 5 to 25 mm thickness. The variation of water content, while desiccating, was monitored. In addition, a digital camera was used to capture the initiation and propagation of desiccation cracks. Crack and shrinkage intensity factors were determined and analysed against various soil properties. The results obtained in this study could potentially lead to developing models to predict crack propagation patterns in various soils. This will ultimately result in more realistic and reliable future designs of infrastructures, such as mine rehabilitation.
Simulating the Effects of Lower-Energy (<30 keV) Electrons on the Inner Magnetosphere Satellite Surface Charging Environment
Authors: Yu Yiqun , Su Shengjun , Cao Jinbin , Denton Michael , Jordanova Vania
Published: March 2021

Satellite surface charging often occurs in the inner magnetosphere from the pre-midnight to the dawn sector when electron fluxes of  hundreds of eV to tens of keV are largely enhanced. Inner magnetosphere ring current models can be used to simulate/predict the satellite surface charging environment, with their flux outer boundary conditions specified either based on observations or provided by other models, such as MHD models. In the latter approach, the flux spectrum at the outer boundary is usually assumed to follow a Kappa or Maxwellian distribution, which however often departs greatly from, or underestimates, the realistic distribution below tens of keV, the energy range that is crucial in the spacecraft surface charging anomaly. This study aims to optimize the electron flux boundary condition of the inner magnetosphere ring current model to achieve a better representation of the surface charging environment. The MHD-parameterized flux spectrum is combined with an empirical electron flux model that specifies the < 40 keV electron flux spectrum. New simulation results indicate that the surface charging environment, monitored by an integrated electron flux between 10<E<50 keV, is significantly enhanced by 1-2 orders of magnitude as opposed to the case in which Kappa/Maxwellian distribution is used at the outer boundary. The new results therefore show better agreement with Van Allen Probes measurements. The improved boundary condition also impacts the auroral precipitation, which may change the conductivity and circulated dynamics. 
Solar and Energy Storage Based Microgrids:  Data-Driven Optimization and Economic Analysis to Examine Energy Savings from a Microgrid within a School Campus
Authors: Narayan Yash
Published: March 2021

Solar and storage based microgrids offer a unique opportunity for both climate change mitigation by reducing CO2 emissions and for climate change adaptation by increasing infrastructure resiliency. In this work, we design a time-of-use (ToU) optimization algorithm to determine whether it would be economically viable to install microgrids within two school campuses in the Bay Area, California that have unique load profiles. Our algorithm, which combines machine learning for accurate site-level net load forecasts, examines three years of electricity consumption data to compute the school’s savings from peak demand charges, energy charges, and demand response revenue generated by providing ancillary services to the grid. Given the school’s unique load profile combined with SGIP and MACRS incentives available in the state of California, we determine that a 15-year battery installed at these two campuses with a cost of $600/kWh provides a net positive internal rate of return (IRR) of 11.9% and 18.3% respectively year-over-year. In addition, the battery provides backup power in case of a power outage and improves grid resilience by providing peak shaving when the power grid is stressed. We hope that our computational analysis can motivate other schools to examine the huge economic and climate benefits that a microgrid poses at their campus. 