bluuebunny/crossref_metadata_2025 huggingface dataset:
Using zenith observations for evaluation of an improved interferometric imaging spectrometer
Authors: Dolet Aneline , Picone Daniele , Gousset Silvère , Dalla Mura Mauro , Le Coarer Etienne , Voisin Didier
Published: March 2021

In the context of climate change, atmospheric gas monitoring is of major interest. Accurate measurements of the concentration of CO2, CH4, NO2, O3, etc. are necessary to control their emissions. Indeed, these gases have impacts on climate change as well as on people’s health.

Good control of such emissions requires gas concentration measurements with high spatial, spectral and temporal resolutions. These acquisitions are mostly done with conventional dispersive hyperspectral imaging systems. However, these instruments result from a compromise between price, resolutions and size which not always allows concentration evaluation that are accurate enough. The Imaging Spectrometer On Chip (ImSPOC) device is based on a ground-breaking concept to overcome the compromise size versus performances allowing snapshot acquisition. Indeed, it is an interferometric imaging spectrometer, sized like a matches’ box, allowing acquisition of an interferogram by pixel instead of a spectrum. In this way, a snapshot acquisition with high spectral resolutions can be acquired from Nano-satellites, drones or ground. The device is composed of a matrix of Fabry-Perot interferometers of different thickness combined with a matrix of photodetectors. ImSPOC is then a competitive device for real-time acquisitions of the atmosphere. However, despite these advantages, the acquisition of interferograms requires ad hoc signal processing techniques to reconstruct the corresponding spectra used for the estimation of the gas concentration. As the interferogram acquisitions are only on a range of thicknesses, some information are missing and need to be compensated with the signal processing methods that are specially developed to provide accurate spectra allowing to evaluate the concentration of gases. The development of these algorithms is then quite challenging.

To validate the most recent ImSPOC prototype in the UV-visible range and the corresponding developed methods, zenith observations were acquired with the ImSPOC device and a classical dispersive hyperspectral spectrometer. These acquisitions allow the validation of ImSPOC at two different levels: 1) the reconstructed spectra are qualitatively compared to the spectra acquired by the classical device and 2) using the Differential Optical Absorption Spectroscopy (DOAS) method on both devices spectra, the evaluated concentrations of the gases are quantitatively compared. These comparisons allow us to validate the usefulness of the ImSPOC device for the evaluation of the gas concentration using zenith observations.  
The measuring of compound dunes – when height becomes a matter of perspective
Authors: Scheiber Leon , Visscher Jan , Lojek Oliver , Schlurmann Torsten
Published: March 2021

Subaqueous bedforms are a fascinating morphological feature that concerns natural scientists and engineers alike. Under certain conditions, the different scales of these natural seafloor patterns merge into compound dunes consisting of large-scale primary and superimposing secondary bedforms. When it comes to the measuring of these composites, however, scholarly opinion varies depending on the investigator’s perspective. Specifically, compound dunes can either be interpreted as a superposition of their respective constituents, whose individual heights are measured independently after mathematical disintegration, or as one coherent bedform with readily measurable extents. Both methodologies, undoubtedly, have fully legitimate scopes of application, but little is written about the actual discrepancy that can result from signal pre-processing or differing geometric height definitions.

We experienced this problem when recently validating a method for the decomposition of compound dunes by comparison with three alternative approaches, of which two relied on detrending the bed elevation profiles before examination, whereas the third approach (similar to the newly proposed one) assessed unfiltered profiles. Although all tools were applied to the same bathymetric raw data, the statistical values of obtained dune dimensions diverged significantly. Even between approaches that generally showed comparable mean dune lengths, the corresponding height values differed by a factor of 2 or so. These results suggest that detrending or band-pass filtering of bed elevation profiles, as it is commonly applied before dune identification, leads to a systematic underestimation of profile amplitudes and thus dune heights. We therefore recommend refraining from these pre-processing steps in all cases where unambiguous absolute heights are needed. Dune identification from unfiltered bed elevation profiles, in return, necessitates that dune dimensions are calculated in consideration of the inherent inclinations. When analyzing the respective behavior of primary and secondary bedforms and their complex interplay, however, mathematical disintegration is the method of choice and, accordingly, dune height remains a matter of perspective.
The hydrological cycle of the Walker Cell
Authors: Döös Kristofer , Berglund Sara , Dey Dipanjan , Aldama Campino Aitor , Menkes Christophe
Published: March 2021

The hydrological cycle of the tropical Pacific Ocean is traced with Lagrangian water mass trajectories in the coupled ocean-atmosphere system.
The cycle consists of one half in the atmosphere and one half in the ocean, where the two halves are connected by the evaporation and precipitation regions at the sea surface.
The atmospheric part of the water cycle is traced backward from the precipitation at the sea surface of the Warm Pool to the evaporation regions in the eastern tropical Pacific.
Reversely, the ocean part of the cycle is also traced from the precipitation to the evaporation regions with water mass trajectories, with emphasis on the part that recirculates within the Tropical Pacific.
The air circulation of the Walker Cell is superimposed on the ocean-atmosphere water cell both in the zonal-vertical space as well as in the hydrothermohaline space. This reveals how the ocean and atmosphere are connected, which are, to some extent, governed by the Clausius-Clapeyron relationship in the evaporation regions. 

The Lagrangian trajectories are computed with the trajectory code TRACMASS, where the atmospheric water parcels are advected with the 3D water mass fluxes based on a new water mass conservation method, which includes precipitation.
Using borehole gamma-ray spectroscopy to detect tephra layers in lacustrine deposits: An example from Lake Chalco, central Mexico 
Authors: Sardar Abadi Mehrdad , Zeeden Christian , Ulfers Arne , Hesse Katja , Wonik Thomas
Published: March 2021

Lacustrine sediments are archives of past environmental conditions. In recent decades, multinational ICDP efforts have conducted lake drilling projects to encode the potential of paleoclimate signals. Gamma-ray spectroscopy is a particularly useful tool as it is non-destructive, fast, and affordable even in cased boreholes. Gamma radiation can be used to identify elemental isotopes in the geological record, which is used for stratigraphic correlation and paleoclimatic investigations. 

However, some lake sediments contain tephra layers with specific gamma-ray signatures, presenting a challenge for extracting the primary signals caused by environmental and climatic agents. Here, we use the sediments of Lake Chalco in central Mexico to propose a protocol to identify tephra layers embedded in other sediments using high-resolution spectral gamma-ray spectroscopy. This facilitates dividing the overall sediment column into representative horizons of tephra and non-tephra.

Among the upper 300 m of the lake deposit, our index detected 363 tephra layers, while 388 total tephra layers (≥1 mm in thickness) were reported from the core description of the same borehole, predicting 92% of tephra layers documented in the lake deposits from core descriptions. We suggest that not only the strength of the gamma-ray signal but also the composition of its constituent energy channels can be used to detect embedded tephra layers.
Derivation of landslide triggering thresholds in Sicily through artificial neural networks
Authors: Distefano Pierpaolo , Peres David Johnny , Scandura Pietro , Cancelliere Antonino
Published: March 2021

Landslides are among the phenomena that can cause casualties among the population and provoke considerable damage to infrastructures, and public and private assets. Precipitation must be mentioned as the main natural driver of these phenomena.  Over the years, landslide early warning systems (LEWS), aiming at reducing the exposure of the population, have been developed based on rainfall thresholds derived mostly by empirical methods, i.e. on finding a statistical link between the characteristics of precipitation (e.g. intensity and duration) and the occurrence of landslide movements. Commonly, landslide early warning thresholds are derived in the form of a power-law between rainfall intensity (or event rainfall) and duration.

One of the limitations of this approach is that using a predetermined form of the law may reduce its performances. In this work we investigate the advantages of removing such constraint by using artificial neural networks, which impose very low restrictions on the functional form of the threshold. We investigate this issue with reference to Sicily, Italy, where several landslide events have been documented in the past decades. In particular, we use rainfall data from almost 300 rain gauges from different monitoring network as the Sicilian hydrological observatory (Osservatorio delle Acque), the SIAS (Sicilian Agro-meteorological Information Service), the Department of Civil Protection (DPC) and almost 250 landslide events from FraneItalia (Calvello and Pecoraro, 2018). We then apply the CTRL-T code (Melillo et al., 2018) to automatically reconstruct rainfall events, identify the most probably rainfall condition that leads to slope failures and derive the traditional power-law threshold.  Then, the pattern recognition skills of artificial neural networks (ANN) are exploited to search the possible empirical relationship between rainfall characteristics and slope failure. Several options for the ANN structure are investigated. Finally, we show a comparison between the results of the two approaches, based on Receiver Operating Characteristic (ROC) analysis. Results show some potential of the ANN-based approach in improving landslide forecasting, although some limitations may exist due to possible quality issues of landslide and rainfall data.

References

Calvello, M., & Pecoraro, G. (2018). FraneItalia: a catalog of recent Italian landslides. Geoenvironmental Disasters, 5(1), 1-16.

Melillo, M., Brunetti, M. T., Peruccacci, S., Gariano, S. L., Roccati, A., & Guzzetti, F. (2018). A tool for the automatic calculation of rainfall thresholds for landslide occurrence. Environmental Modelling & Software, 105, 230-243.
Lofted aerosol layers over the North Pole during the winter period 2019-2020 measured during MOSAiC 
Authors: Ohneiser Kevin , Engelmann Ronny , Ansmann Albert , Radenz Martin , Griesche Hannes , Hofer Julian , Althausen Dietrich , Bühl Johannes , Baars Holger , Seifert Patric , Haarig Moritz
Published: March 2021

The MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition, lasting from September 2019 to October 2020, was the largest Arctic research initiative in history. The goal of the expedition was to take the closest look ever at the Arctic as the epicenter of global warming and to gain fundamental insights that are key to better understand global climate change. We continuously operated a multiwavelength aerosol/cloud Raman lidar aboard the icebreaker Polarstern, drifting through the Arctic Ocean trapped in the ice from October to May, and monitored aerosol and cloud layers in the Central Arctic up to 30 km height at latitudes mostly > 85°N. The lidar was integrated in a complex remote sensing infrastructure aboard Polarstern. A polarization Raman lidar is designed to separate the main continental aerosol components (mineral dust, wildfire smoke, anthropogenic haze, volcanic aerosol). Furthermore, the Polarstern lidar enabled us to study the impact of these different basic aerosol types on the evolution of Arctic mixed-phase and ice clouds.  The most impressive and unprecedented observation was the detection of a persistent, 10 km deep aerosol layer of aged wildfire smoke over the North Pole region between 8 and 18 km height from October 2019 until the beginning of May 2020. The wildfire smoke layers originated from severe and huge fires in Siberia, Alaska, and western North America in 2019 and may have contained mineral dust injected into the atmosphere over the hot fire places together with the smoke. We will present the main MOSAiC findings including a study of a long-lasting mixed-phase cloud layer evolving in Arctic haze (at heights below 6 km) and the role of mineral dust in the Arctic haze mixture to trigger heterogeneous ice formation. Furthermore, we present a case study developing in the smoke-dominated layer around 10 km height.
Comparing the hydrological response of regulated vs. not regulated mountain torrents in the Mediterranean semi-arid environment: a case study in Southern Italy
Authors: Bombino Giuseppe , D'Agostino Daniela , Denisi Pietro , Labate Antonino , Perez Cutillas Pedro , Martinez Salvador Alberto , Zema Demetrio Antonio , Zimbone Santo Marcello , Conesa Garcia Carmelo
Published: March 2021

In the Mediterranean semi-arid environment (e.g., in Southern Italy and Spain), headwaters are characterized by local factors, such as steep slopes, low drainage areas and heavy and short-duration rainstorms, which make the torrents prone to flash floods, soil erosion and landslides. The construction of check dams has contributed to mitigate the runoff and erosion rates, but the effectiveness of these structures has been rarely assessed. In these contexts, the availability of studies monitoring the mitigation effect of check dams on the hydrological response of torrents at the watershed scale over a long time could help developing new management strategies. To this aim, this study proposes an assessment of the multi-decadal runoff and erosion rates in two headwaters of torrents in Southern Italy, using a modeling approach. The first torrent (Vacale, 12.5 sq. km) is regulated by check dams built in ‘1950-1960, while the second torrent (Serra, 13.7 sq. km) is not regulated. Both catchments experienced an increase in forest cover up to the 70%, while the agricultural land decreased by about 30% of the total area after the construction of the control works until now. The hydrological response of the two headwaters has been simulated using the widely applied Hydrologic Modeling System (HEC-HMS) model for runoff and peak flow, coupled with the Modified Universal Soil Loss Equation (MUSLE) to model sediment yield. To this purpose, 10 heavy rainfall-runoff events occurred between 1956 and 1971 were modeled. The peak flows and sediment yields of the regulated watershed were compared with the corresponding simulations at the undisturbed torrent. To summarize the results of this modeling experience, the changes in land cover resulted in a noticeable decrease in flood peak discharge (on average -53%) in both torrents, while the torrent with check dams showed a significant reduction of eroded sediment for each event (on average -9%) compared to the unregulated headwater. These findings help supporting a better understanding on the impact of control works and land use changes on the hydrological responses of Mediterranean torrents, indicating the most effective strategy to mitigate flash flood hazards and heavy erosion risks in similar environmental contexts.

Acknowledgement: This research was funded by ERDF/Spanish Ministry of Science, Innovation and Universities-State Research Agency (AEI) /Project CGL2017-84625-C2-1-R; State Program for Research, Development and Innovation Focused on the Challenges of Society.
94 GHz radar mapping of terrestrial snow cover
Authors: Harcourt William D. , Robertson Duncan , Macfarlane David , Rea Brice , James Michael , Fyffe Blair , Diggins Mark
Published: March 2021

Terrestrial snow cover is a perennial feature throughout the global cryosphere, taking the form of individual snow patches during summer and becoming more spatially continuous in winter. The characteristics and conditions of these snowpacks can be altered by rapid changes in temperature and precipitation, significantly impacting local ecosystems, upland hydrology and snow avalanche risks. In Scotland, for example, monitoring the hazards associated with snowpack alterations is a central focus of the Scottish Avalanche Information Service (SAIS) and is essential to ensuring the safety of local communities, hill walkers and mountaineers. In this context, the development of new remote sensing techniques for snow monitoring will help the SAIS develop avalanche forecasts and potentially without the need to undertake arduous and dangerous fieldwork. Here, we aim to develop the utility of millimetre-wave radar at 94 GHz as a new remote sensing tool for monitoring snowpacks. We use a ground-based 94 GHz, real-aperture system called AVTIS2 which mechanically scans across a scene of interest to generate radar backscatter images and 3D Digital Elevation Models (DEMs). AVTIS2 uses a narrow beamwidth of 0.35° (i.e. a spot size of 6 m per km) and has a maximum range of ~6 km, enabling kilometre-scale mapping at high angular resolution. This radar system has previously been successful in monitoring the topographic changes of volcanic lava domes, measuring the dynamics of active lava flows and quantifying 94 GHz radar backscatter from glacier ice. We aim to deploy the AVTIS2 millimetre-wave radar in the Cairngorms National Park, Scotland, in January/February 2021 and validate our measurements with a co-located Terrestrial Laser Scanner (TLS). Additionally, we will acquire in situ observations of snow properties to gain a better understanding of how 94 GHz radar signals interact with the snowpack. Overall, we will report on the following: (1) the radar backscatter characteristics from a variety of snow surface conditions at millimetre wavelengths; (2) point cloud and DEM differences between AVTIS2 and TLS measurements over snow-covered terrain; and (3) the effect of snowpack properties on radar backscatter and how this can be used to understand snow-associated hazards.
Urban water storage capacity inferred from observed evapotranspiration recession 
Authors: Jongen Harro , Steeneveld Gert-Jan , Beringer Jason , Fortuniak Krzysztof , Hong Jinkyu , Hong Je-Woo , Jacobs Cor , Järvi Leena , Meier Fred , Roth Matthias , Theeuwes Natalie , Velasco Erik , Teuling Ryan
Published: March 2021

The amount and dynamics of urban water storage play an important role in mitigating urban flooding and heat. Assessment of the capacity of cities to store water remains challenging due to the extreme heterogeneity of the urban surface. Evapotranspiration (ET) recession after rainfall events during the period without precipitation, over which the amount of stored water gradually decreases, can provide insight on the water storage capacity of urban surfaces. Assuming ET is the only outgoing flux, the water storage capacity can be estimated based on the timescale and intercept of its recession. In this paper, we test the proposed approach to estimate the water storage capacity at neighborhood scale with latent heat flux data collected by eddy covariance flux towers in eleven contrasting urban sites with different local climate zones, vegetation cover and characteristics and background climates (Amsterdam, Arnhem, Basel, Berlin, Helsinki, Łódź, Melbourne, Mexico City, Seoul, Singapore, Vancouver). Water storage capacities ranging between 1 and 12 mm were found. These values correspond to e-folding timescales lasting from 2 to 10 days, which translate to half-lives of 1.5 to 7 days. We find ET at the start of a drydown to be positively related to vegetation fraction, and long timescales and large storage capacities to be associated with higher vegetation fractions. According to our results, urban water storage capacity is at least one order of magnitude smaller than the known water storage capacity in natural forests and grassland.
Using the foods we love and need to enhance climate literacy
Authors: Hoffmann Michael
Published: March 2021

Climate change is affecting the foods we love and need—just about everything on the menu is changing. Plants, the basis of life, require the right temperatures, water, soil, air, and sunlight. All but sunlight are changing and having subtle and in many cases ominous impacts on our foods and beverages—from spices and herbs to pistachios. The flavors of teas, the protein and mineral content of wheat, vitamins in rice, and yields of many crops are undergoing change. This story needs to be told given the cultural, historical, and personal connections everyone has to food. The communication and outreach approaches taken to enhance climate literacy include a book – Our Changing Menu: Climate Change and the Foods we Love and Need and a companion website, which includes a searchable database of the hundreds of food ingredients that are changing. The changing menu may be a way to join forces—consumers, producers, chefs, restaurateurs, and food businesses—to find a common ground and draw more attention and action to address this grand challenge of climate change. We all eat.
Modulations in vertical stability trigger intraseasonal variations in phytoplankton bloom
Authors: Madhavan Girijakumari Keerthi , Levy Marina , Aumont Olivier
Published: March 2021

Seasonal surface chlorophyll (SChl) blooms are very chaotic in nature, but traditional bloom paradigms have climbed out of these intraseasonal/subseasonal variations. Here we quantify these intraseasonal fluctuations and explore the links between the surface bloom and vertical stability at intraseasonal timescales, along the spring bloom region of the northwestern Mediterranean Sea. We use 8-day merged ocean color SChl product distributed by the European Space Agency Ocean Color Climate Change Initiative (ESA OC-CCI), in situ data from the long-term time series BOUSSOLE, wind stress and heat flux from ERA-Interim reanalysis. The 8-day SChl product from ESA OC-CCI has excellent data coverage in the northwestern Mediterranean Sea. Comparison with the high frequency in situ data from the BOUSSOLE mooring shows that the satellite and in situ SChl products are reliable at the subseasonal timescale. Our results reveal that intraseasonal variability explains nearly half of the SChl variability in the bloom region and occur at smaller spatial scales (~100 km). We demonstrate that weekly SChl fluctuations are in phase with weekly changes in wind stress and net heat flux during the initial state of the bloom in winter and early spring, thus expanding the convection shutdown hypothesis of bloom onset to subseasonal timescales. We postulate that intermittency in vertical stability due to short-term episodes of calm weather in winter or to stormy conditions in early spring leads to short-term variations in light exposure or to events of vertical dilution, and to strong intermittency in phytoplankton bloom.
Efficacy of Seismic Interferometry in Removing Surface Waves from Active Seismic Records
Authors: Singla Varun Kumar , Lokmer Ivan
Published: March 2021

While there are seismic techniques which make use of surface waves in imaging the subsurface, there are also those where these types of waves are considered coherent noise. Important examples where the surface waves may significantly degrade the obtained images include different types of reflection seismic surveys (e.g., shallow surveys for engineering, environmental and groundwater investigations, and deep surveys for imaging hydrocarbon reservoirs). In a strongly heterogeneous medium (encountered typically in onshore surveys), the conventional methods for attenuating these waves (such as f-k "velocity" filtering) often do not give satisfactory results.

Seismic interferometry is a data-driven approach that offers a viable alternative for removal of surface waves from active seismic records. In this approach, the reflection data of several sources is considered and for each source, the seismic signals at a pair of receivers are cross-correlated to produce the surface wavefield between the receivers. The cross-correlated waveforms are then summed over all the sources to obtain the "interferometric" signal for the considered receiver pair. During this summation, the reflection and non-physical events cancel out due to the variable differences in the travel times to the considered receiver pair from different sources. The "interferometric" signal consequently contains predominantly the surface waves and this makes it conducive for adaptive subtraction (or filtering) from the original records. This study investigates the efficacy of the commonly used filtering techniques in interferometry to remove the surface waves from active seismic records. For this, the reflection data of a complex 2-D elastic medium is simulated and the filtering techniques are applied to this data. The limitations of these techniques inferred from the quality of the filtered data are discussed and possible remedies to overcome them are suggested.
Rivers on Ice: The Evolution of Supraglacial Channels on the Greenland Ice Sheet
Authors: Rawlins Lauren , Rippin David , Sole Andrew , Livingstone Stephen , Yang Kang
Published: March 2021

Throughout the satellite era, an increasingly positive trend in the extent and duration of seasonal surface melt has been observed across the Greenland Ice Sheet (GrIS). Surface melt, and meltwater runoff now accounts for over half of GrIS mass loss annually, signifying the importance of surface mass balance on the future contribution to global sea level rise. A vast expanse of supraglacial channel networks and lakes now dominate the ablation zone during the melt season, transporting, storing, and evacuating increasingly large volumes of meltwater from the ice surface. The interception of this water, either by moulins or through linked crevasses, can propagate through the ice column and flood the ice-bed interface, influencing ice velocity and, in turn ice discharge over the grounding line.

To date, much of the hydrological interest on the GrIS has centred around its western and south-western margins, often limited to short windows (days) during the melt season. This study expands surface hydrological mapping to other regions of the GrIS, specifically its northern sector, and explores network evolution across both seasonal (intra-) and inter-annual timescales.

This study utilises a satellite-derived Normalised Difference Water Index (NDWI) alongside an automatic river detection algorithm to effectively delineate active supraglacial channel networks and (hydrologically-connected) saturated slush zones using Sentinel-2 and Landsat optical imagery. This work reveals a transformation of the northern supraglacial channel network from a highly-fragmented system of short channels extending a maximum of ~40 km inland during the 1980’s, to one dominated by long, parallel channels extending ~80 km inland from 2016. The observations presented in this study have significant implications on both the speed and efficiency of supraglacial meltwater drainage of the GrIS, holding a great potential to impact the dynamic response of outlet glaciers, and ice sheet mass loss.
Waves in elastic material
Authors: Whitchelo Yiyi , Olsen Ingrid , Trulsen Karsten
Published: March 2021

Sea ice covers about 7% of the Earth's surface and 12% of the world's oceans. The presence of global warming and an increase in human activities in the polar region has resulted in significant interest in the behaviour of waves and ice interaction. In this study, the experimental investigation of waves-ice interaction is presented in the form of propagating waves in elastic materials. This investigation aims to study wave propagation, and energy transition as waves enter from open water to a water region covered with an elastic sheet. As the waves propagate in the elastic material, the waves immediately attenuate, suggesting a loss in energy. This loss in energy cannot be explained in the classical sense (breaking etc.) as the elastic sheet's existence prevents the breaking in waves of large amplitudes. The underlying mechanism as waves adapt to the elastic region is crucial for understanding the possibility of build-up in wave energy within the elastic sheet.

 

For the experiments, a JONSWAP spectrum was used to generate wave fields. Ultrasonic probes were used to measure the surface elevation of the elastic layer and the open water free surface, and these two were compared. The attenuation rates are investigated as a function of distance. The spatio-temporal properties of the wave fields are investigated using 2D FFT to obtain the wavenumber-frequency spectrum. We find significant second-order nonlinear effects as the waves propagate with an elastic cover. Especially the occurrence of second-order difference interactions, sometimes called the group line, was found to be conspicuous in some of the wave fields.
Global observations of 3D mantle attenuation using normal modes 
Authors: Talavera-Soza Sujania , Deuss Arwen
Published: March 2021

Seismic tomographic models based solely on wave velocities are unable to distinguish between a temperature or compositional origin for Earth’s 3D structure variations, such as the Large Low Shear Velocity Provinces (LLSVPs) beneath the lower mantle of Africa and the Pacific. Seismic attenuation or damping is able able to provide additional information that may help to unravel the origin of the LLSVPs, which is fundamental to understand mantle convection evolution. For example, a thermal origin for the LLSVPs will point to them being short-lived anomalies, whereas a compositional origin will point to them being long-lived, forming mantle 'anchors' and influencing the pattern of mantle convection for a large part of Earth’s history. Seismic attenuation is able to make that distinction, because it is directly sensitive to temperature variations. So far, global 3D attenuation models have only been available for the upper mantle, with only two regional body waves studies exploring the lower mantle (Lawrence and Wysession, 2006; Hwang and Ritsema, 2011).
Here, we use normal mode data to measure elastic splitting functions (dependent on velocity and density) and anelastic splitting functions (dependent on attenuation). The advantage of normal modes is that they allow us to include focussing and scattering due to the velocity structure without the need for approximations, because we measure the elastic splitting function jointly with the anelastic splitting function. In our measurements for upper mantle sensi- tive modes, we find anti-correlation between the elastic and anelastic splitting functions, suggesting a thermal origin for low velocity spreading ridges, and agreeing with previous studies. On the other hand, for lower mantle sensitive modes, we find correlation, suggesting the averagely attenuating LLSVPs are surrounded by strongly attenuating regions potentially due to the presence of post-perovskite.
Equatorial belt vapour measurements in the upper TTL under superpressure balloon during STRATEOLE 2 pre-campaign: tape recorder effect, role of waves and deep convection.
Authors: Riviere Emmanuel , Ghysels Mélanie , Durry Georges , Burgalat Jérémie , Amarouche Nadir , Carbone Sullivan , Podglajen Aurélien , Capitaine Clément
Published: March 2021

STRATEOLE 2 is a French-American project based on superpressure balloon borne measurements to study dynamics and processes in the TTL and the lower stratosphere of equatorial regions. One single flight of these balloons (of a duration of about 80 days) can make several turns of the Earth.

Here we present water vapour measurements by the Pico-SDLA infrared laser spectrometer on-board the TTL 2 gondola. The float altitude was of about 19 km during the technical campaign of STRATEOLE 2, providing measurements at the top of the TTL or the lower stratosphere. In this presentation, we analyse the tape recorder signal at a constant altitude during the 80 days of flight. We compute an anomaly of the in situ water vapour measurements with respect to a regional/temporal satellite-borne mean climatology from Aura MLS. It allows to analyse the local measurements by Pico-SDLA with respect to what is expected at a given position and a given time. The obtained contrast allows the positioning of observations with respect to local climatology and therefore, the identification of singular events responsible for modulation of the local water vapour content. Our analysis shows that a long wet anomaly above the Pacific Ocean is explained by the balloon “surfing” on a warm perturbation of a Kelvin wave. Concurrently, a dry anomaly is put to the fore over the Indian Ocean, associated to a packet of gravity waves cold perturbations. The balloon has flown twice above the Maritime Continent. For each passage, a short scale succession of dry and wet anomalies is shown, indicating a possible influence of local deep convection. This influence is studied further using satellite borne cloud top data.
The importance of satellite soil moisture assimilation for low-level jet forecasts
Authors: Ferguson Craig R. , Agrawal Shubhi , Bosart Lance F.
Published: March 2021

The U.S. Great Plains low-level jet (LLJ) is active on 26% and 62% of May-September days in the northern and southern Plains, respectively. Characterized by a diurnally-oscillating low-level wind maximum below 700 hPa, large vertical wind shear, and enhanced atmospheric moisture convergence, LLJs have been shown to fuel extreme wind- and precipitation generating mesoscale convective systems. Overall, they explain 30-50% of May-September precipitation in the Plains. The considerable societal impacts of LLJs, which span agriculture, severe weather, and wind energy, have long motivated meteorologist-led investigations into their dynamics and predictability. The sensitivity of LLJs to regional soil moisture gradients was established over thirty years ago. However, it was only recently that our work provided the first estimates of the added-value of satellite soil moisture data assimilation (DA) to LLJ forecasts.

In this presentation, we review and expand upon our previous analysis of 75 NASA Unified WRF LLJ case studies simulated with- and without weakly-coupled NASA Soil Moisture Active Passive (SMAP) soil moisture DA. Of the 75-jet cases, 43 are uncoupled LLJs and 32 are coupled LLJs. Their dynamical classification corresponds with the probable efficacy of land data assimilation. Cyclone-induced coupled LLJs, found in the warm sector of frontal systems, are strongly driven by synoptics and less likely to be influenced by land forcing. Conversely, uncoupled LLJs that occur during quiescent conditions of an anticyclonic high pressure ridge system are likely to be more strongly affected by terrain and soil moisture gradient-induced circulations.

It is shown that SMAP DA is generally more effective in uncoupled LLJ cases. However, significant SMAP DA-induced wind speed differences are noted for both LLJ types at their core and exit regions. Notably, the range of SMAP DA-induced wind speed differences between LLJs of the same class (i.e., uncoupled LLJs) is comparable to the range of differences between LLJs of different classes (i.e., coupled vs. uncoupled). Follow-on analyses presented here address the question of what differs between LLJs with small and large SMAP DA effects. Specifically, we explore attribution of event-scale differences in the added-value of SMAP DA to factors including SMAP spatial coverage, antecedent soil moisture, and the strength of synoptic forcing. Finally, a closer look is given to the verification of jet exit region SMAP DA-induced wind speed shifts using Rapid Refresh.
Water level changes in Swedish lake systems using pixel-specific Sentinel-1 phase change
Authors: Aminjafari Saeid , Jaramillo Fernando
Published: March 2021

Sweden has approximately 100,000 lakes covering roughly nine percent of the country’s surface area. These lakes are one of the important sources of fresh water for urban, industrial, and agricultural use, further providing a wide range of ecosystem services. In order to conserve and protect the lakes from the impacts of climate change, hydrologic monitoring should ideally be conducted in all of these lakes. However, it is almost impossible to gauge all of these lakes on a regular basis, due to economical and logistic constraints. Radar altimetry has been successfully used to obtain water levels from specific lakes; however, the technology can only be used in large lakes that are located precisely under the orbit of the satellite, thus excluding most Swedish lakes. We here develop a new procedure based on the application of differential interferometric synthetic aperture radar (DInSAR) on sequential image pairs with short temporal baseline to measure the water level of 36 lakes. We processed Sentinel-1 twin satellite data with 6-day revisiting intervals, pair by pair, from March 2019 to November 2019. In total, we constructed 41 interferograms considering only the pixels with coherence values greater than 0.2 in all interferograms to ensure consistent scattering and good coherence in all images. We found that the pixels located near tree trunks in flat areas or near steep cliffs in mountainous areas showed a steady phase change in all interferograms that could be converted to water level change. In some of these lakes, the water level changes derived from this methodology correlated well with the in-situ water level of the gauge stations provided by the Swedish Meteorological and Hydrological Institute. We believe that this methodology has good potential for monitoring water level data in small lakes that cannot be monitored by radar altimetry, and serves as evidence of the unknown potential of DInSAR to track hydrological changes in open water surfaces.
Is it possible to embed the ecosystem impacts of solar parks into industry practice?
Authors: Treasure Lucy , Armstrong Dr Alona , Sharp Dr Stuart , Smart Dr Simon , Parker Dr Guy
Published: March 2021

The energy sector is the largest contributor to global greenhouse gas emissions. Therefore it is imperative that we take steps to de-carbonise energy supplies if we are to meet the 2°C goal of the Paris Agreement.  Of the existing renewable energy technologies, Photovoltaic (PV) capacity has seen exponential growth in the past decade, with 508.1 GW of PV currently installed globally and predictions that it will become the dominant renewable energy source by 2050. A large proportion of this capacity is deployed as ground-mounted solar parks. Despite the rapid growth of solar parks, little research has been conducted into the ecosystem impacts. Here we use a systematic literature review of the available evidence to show that the main ecosystem impacts of solar parks can be grouped into five themes: microclimate, land-use change, soil and vegetation, wildlife impacts and pollution. Impacts can be positive or negative, and vary according to site location, former land use and management practices throughout the construction, operational and decommissioning phases of the solar park life cycle. The most widely reported impacts associated with the construction phase were habitat loss and fragmentation, with subsequent effects on fauna, flora, and soil. Commonly reported operational impacts included changes to local microclimate, pollution, mortality of wildlife and disturbance due to site maintenance. Decommissioning impacts depended largely on the site management objectives; sites continued to be managed to deliver ecosystem service co-benefits or returned to their original state prior to construction. The review also revealed significant knowledge gaps. Understanding the ecosystem impacts of solar parks is pivotal, both for informing site management that maximises ecosystem co-benefits and avoids detrimental impacts, and for quantifying the potential ecosystem costs and gains as required by policy, for example the upcoming mandatory biodiversity net gain requirement for UK planning applications.
Mapping and analyzing land subsidence for Tehran using Sentinel-1 SAR and GPS and geological data
Authors: Rajabi Baniani Soheil , Chang Ling , Maghsoudi Yasser
Published: March 2021

Tehran, as a megacity in Iran, is exposed to a high rate of land deformation. Recent research shows average land deformation speed is up to 39.9 mm/year in southeast plain (from 2014 to 2017) and groundwater extraction in Tehran plain for agricultural and industrial demands is the most probable driving mechanism. It is undisputed that infrastructure and structure in Tehran are continuously under threat by such rapid land subsidence, and this subsidence may also lead to significant economic losses such as structural damage and high maintenance costs for roads, railways, dikes, pipelines, and buildings. Therefore, when, where and why the subsidence did/does occur has to be closely monitored and analysed considering future planning and the importance of infrastructure and structure damage, which has a profound effect on human activities. This study attempts to use Sentinel 1 SAR data to map land subsidence in Tehran and validate the results by using GPS data.

We implemented the standard persistent scatterer interferometry (PSI) approach with the customized parameter configuration, for Tehran with an area of ​​about 1600 km2. 52 Sentinel 1A (C-band) dataset acquired between 2018 and 2019 were collected. There were 1,746,317 PS measurement points generated. The PSI results illustrate that the maximum loss of elevation over the time period did amount to 11.7 cm/year.  

We used the GPS observations between 1/1/2018 and 27/10/2019, from the two GPS stations GPS-m318 (35.64 N, 51.29 E), GPS-m020 (35.58 N, 51.42 E) to evaluate the PSI deformation results. We found that the maximum and minimum double difference between GPSs and PSs were 0.0536 m, 0.0015 m respectively; moreover, the corresponding histogram shows that most of the double-difference values are in the interval of [-0.01 0.01] m, and the RMSE is 0.011 m. Besides, we also applied the velocity comparison of double-differenced GPS and PS, which shows that the PS measurements matched well with the GPS observations.

By comparing the water table variations and PSI-derived land deformation, we found that the groundwater withdraw could be a major driving mechanism but the variation in soil type also plays an important role. For instance, although the groundwater levels (Xutm = 503498, Yutm = 3948916) has decreased by approximately 13m from 2012 to 2017 at the place of Andisheh-Jadid, no subsidence was detected possibly due to the presence of well grade layers at that location.
Ocean Shelf Exchange, NW European Shelf Seas: measurements, estimates and comparisons.
Authors: Huthnance John M. , Hopkins Joanne E. , Inall Mark , Holt Jason , team FASTNEt
Published: March 2021

We describe estimates of overall transport across three contrasted sectors of the north-west European shelf edge: the Celtic Sea south-west of Britain, the Malin-Hebrides shelf west of Scotland and the West Shetland shelf north of Scotland.  The estimates derive from a variety of measurements in the project FASTNEt (Fluxes across sloping topography of the North East Atlantic): drifters and moored current meters, effective “diffusivity” from drifter dispersion and salinity surveys, other estimates of velocity variance contributing to exchange.  Process contributions include transport by along-slope flow, internal waves and their Stokes drift, tidal pumping, eddies and Ekman transports, in a wind-driven surface layer and in a bottom boundary layer.   

Estimated overall exchange across the shelf edge is several m2/s (Sverdrups per 1000 km) and thereby large compared with many other locations, large compared with oceanic transports if extrapolated globally and potentially important to the shelf-sea and adjacent oceanic budgets.  However, the large majority of this is in tides and other motion with periods of order one day or less; such exchange is only effective for water properties that evolve on time-scales of a day or less.  Nevertheless, cross-slope fluxes, and exchange due to motion with periods exceeding two days, are large by global standards and also very variable.  Flux values nearest the shelf break were in the range 0.3 – 3 m2/s, and exchanges were 0.8 – 4 m2/s.  Deeper longer-term moorings and drifters crossing the 500 m depth contour gave much larger fluxes and exchanges up to 20 m2/s.  Significance of these transports depends on distinctive properties of the water, or its contents, and on internal shelf-sea circulation affecting the further progress of these transports.  For the NW European shelf, transports across the shelf edge enable its disproportionately strong CO2 “pump”.

The small scales of numerous processes enabling cross-slope transports, and the complex context, imply a need for models.  Measurements remain limited in extent and duration, but a wide variety of contexts, particular conditions, events and behaviours is now available for model validation, especially around the north-west European continental shelf edge.  Variability continues to render observations insufficient for stable estimates of transports and exchanges, especially if partitioned by sector and season; indeed, there may be significant inter-annual differences.   Validated fine-resolution models give the best prospect of coverage and of estimating shelf-sea sensitivities to the adjacent ocean.
Supercell Pre-convective Environments in Spain: a dynamic downscaling of ERA-5 Reanalysis
Authors: Calvo-Sancho Carlos , Martín Yago
Published: March 2021

Supercell thunderstorms are often associated with severe weather conditions, such as tornadoes, hail, strong wind gusts, heavy rainfall, and flash-floods, producing damage to populations and assets. The goal of the study is to analyze and improve our understanding of pre-convective environments conducive for supercell development in the different regions of Spain. We use 2014-2020 data from the Spanish Supercell Database (Martin et al., 2020), ERA-5 reanalysis, and a dynamical downscaling with WRF-ARW model to a 9 km spatial resolution to be able to generate sounding-derived parameters at the moment of formation of each supercell. Results indicate that supercells are more common in high values of CAPE and Shear 0-6 Km, but in the south-western of Spain predominates supercells of HSLC (High Shear-Low CAPE) in the cold season.