bluuebunny/crossref_metadata_2025 huggingface dataset:
The new ice nucleation assay AU-Micro-INC
Authors: Wieber Corina , Madsen Sigurd Agerskov , Jeppesen Mads Rosenhøj , Voldbirk Frederik , Melvad Peter , Chuhutin Andrey , Vergeynst Leendert , Meire Lorenz , Finster Kai , Melvad Claus , Šantl-Temkiv Tina
Published: March 2022

The properties and formation of clouds are one of the largest sources of uncertainties in climate models. Hereby, ice nucleating particles (INPs) play a major role since they directly affect the ice formation in clouds. To better characterize the impact of INPs, measuring devices are necessary to reliably determine the freezing temperatures of various aerosols.

We have developed a new ice nucleation assay, AU-Micro-INC, to measure the freezing temperatures with high accuracy. 96-well and 384-well plates can be inserted into a gallium matrix which ensures good thermal contact to the underlying cooling system. A Peltier element in combination with a vapor chamber provide a homogeneous cooling of the system. The freezing temperatures are measured with an infrared thermal camera with high precision.

The setup is validated using well-studied samples such as Snomax® and Illite NX. Further, the new setup is applied to sea water, sea surface microlayer, and sea ice samples previously collected in Kobbefjord and Nuup Kangerluaand in proximity of Nuuk, Greenland and preliminary data will be shown. 
Fluvial bedrock gorges as markers for Late-Quaternary tectonic and climatic forcing in the French Southwestern Alps 
Authors: Cardinal Thibaut , Petit Carole , Rolland Yann , Audin Laurence , Zerathe Swann , Schwartz Stéphane , Valla Pierre , Braucher Régis , Team Aster
Published: March 2022

As one of the major erosive processes acting at Earth’s surface, fluvial incision is highly sensible to tectonic, isostatic and climatic variations. In order to better understand what is the timing and driving mechanism(s) for Late-Quaternary incision in the Southwestern Alps, we focused on bedrock gorges and measured in situ-produced 36Cl concentrations along several river-polished gorge walls in the external Southwestern French Alps. Unlike previously dated river gorges in the study area, these newly dated catchments lie out of the previously glaciated domains during the last glacial periods, which makes them suitable to quantify fluvial incision dynamics in a non-glacial environment.

Cosmic-ray exposure dating results (ranging from 1 to 85 ka), compared to previous literature results in nearby catchments with glacial imprint and combined with a morphometric analysis, allow us to highlight three catchment groups related to different incision dynamics: (i) Group A with very high (≈5 mm/yr) and recent (post-10 ka) incision rates that reflect recent topographic readjustment of glaciated catchments by fluvial and hillslope processes; (ii) Group B, including gorges that are directly or indirectly connected to the glacial processes, showing increased incision rates (1-3 mm/yr) during the paraglacial period after the Last Glacial Maximum (ca. 20 ka), possibly related to an increase in sediment yield and water runoff following glacier retreat; (iii) Group C with slow and steady incision rates (<1 mm/yr over the last ca. 30 kyr), which do not seem to reflect any impact of any climatic variations (except the humid Holocene phases) and that are comparable to previously estimated long-term denudation and rock-uplift rates in the area.

In catchments with glacial imprints, the climatic impact on fluvial incision is evidenced through high amplitudes changes that hinder the long-term (background) tectonic signal. Despite this, our results suggest the influence of long-term tectonic on geomorphic processes for sites disconnected from the glacial influence, showing that fluvial bedrock gorges can provide insightful constraints on both long-term tectonic and short-term climatic forcing.
How does the rise of atmospheric water demand affect flash drought development in Spain?
Authors: Noguera Iván , Domínguez-Castro Fernando , Vicente-Serrano Sergio M.
Published: March 2022

Flash droughts are distinguished by a rapid development and intensification, which increase the potential drought impacts on natural and socio-economic systems. In recent years, a great effort has been made to identify and quantify this type of events in different regions of the world using different metrics. We developed a methodology to analyze the flash droughts based on SPEI at short-time scale (1-month) and high-frequency data (weekly). Thus, we characterized the occurrence of flash drought in Spain over the period 1961-2018 and showed that flash drought is a frequent phenomenon (40% of all droughts were characterized by rapid development), which exhibit a great spatiotemporal variability. The northern regions, where a higher frequency of flash droughts was found, showed negative trends in the frequency of flash droughts, while the central and southern regions subject to fewer flash drought events showed generally positive trends. Usually, the flash drought is associated with severe precipitation deficits and/or anomalous increases in atmospheric evaporative demand (AED), but while the role of precipitation seems obvious and essential, the role played by AED in triggering or reinforcing flash drought episodes is much more complex and exhibits important spatial and temporal contrasts. In Spain, the effect of AED is mainly restricted to water-limited regions and the warm season, but its role is minimal in energy-limited regions and in cold periods in which precipitation deficits are the main cause of flash drought development. However, the contribution of the AED on the development of flash droughts has increased notably over the last six decades, thus becoming a decisive driver in explaining the occurrence of the latest flash droughts in some regions of Spain. These findings have strong implications for proper understanding of the recent spatiotemporal behavior of flash droughts in Spain and illustrate how this type of event can be related to global warming processes.
Properties of mesoscale eddies in the Arctic Icean from a very high-resolution model
Authors: Müller Vasco , Wang Qiang
Published: March 2022

Mesoscale eddies are believed to play a substantial role for the dynamics of the Arctic Ocean, influencing the interaction of the ocean with the atmosphere and sea-ice as well as the transport and mixing of water masses. Especially their effects on the thermohaline structure and stratification could be crucial for better understanding future changes in the Arctic and the ongoing ‘atlantification’ of the Arctic Ocean water masses. Better understanding of Arctic eddy dynamics also allows the improvement of parametrization of eddy processes in models, which is critical for a realistic representation of the Arctic in climate models and understanding the role of the Arctic Ocean in the global climate. However, simulating Arctic Ocean mesoscale eddies in ocean circulation models presents a great challenge due to their small size at high latitudes and adequately resolving mesoscale processes in the Arctic requires very high resolution, making simulations very computationally expensive.
Here, we use the new unstructured‐mesh Finite volumE Sea ice-Ocean Model (FESOM2) with 1-km horizontal resolution in the Arctic Ocean to evaluate properties of mesoscale eddies. This very high-resolution model setup can be considered eddy resolving in the Arctic Ocean and has recently been used to investigate the distribution of eddy kinetic energy in the Arctic. The analysis here is based on automatically identifying and tracking eddies using a vector geometry-based algorithm and focuses on the model’s representation of eddy properties and dynamics. In-situ observations from the year-long MOSAiC expedition give us the unique possibility to assess the model’s representation of eddy properties against direct observations, both in the Arctic summer and winter seasons.
Stomatal closure under drought is controlled by below-ground hydraulics 
Authors: Abdalla Mohanned , Ahmed Mutez , Cai Gaochao , Wankmüller Fabian , Schwartz Nimrod , Litig Or , Javaux Mathieu , Carminati Andrea
Published: March 2022

Stomatal closure allows plants to promptly respond to water shortage. Although the coordination between stomatal regulation, leaf and xylem hydraulics has been extensively investigated, the impact of below-ground hydraulics on stomatal regulation remains unknown.

We used a novel root pressure chamber to measure, during soil drying, the relation between transpiration rate (E) and leaf xylem water pressure (ψleaf-x) in tomato shoots grafted onto two contrasting rootstocks, a long and a short one. In parallel, we also measured the E(ψleaf-x) relation without pressurization. A soil–plant hydraulic model was used to reproduce the measurements. We hypothesize that (1) stomata close when the E(ψleaf-x) relation becomes non-linear and (2) non-linearity occurs at higher soil water contents and lower transpiration rates in short-rooted plants.

The E(ψleaf-x) relation was linear in wet conditions and became non-linear as the soil dried. Changing below-ground traits (i.e. root system) significantly affected the E(ψleaf-x) relation during soil drying. Plants with shorter root systems required larger gradients in soil water pressure to sustain the same transpiration rate and exhibited an earlier non-linearity and stomatal closure.

We conclude that, during soil drying, stomatal regulation is controlled by below-ground hydraulics in a predictable way. The model suggests that the loss of hydraulic conductivity occurred in soil. These results prove that stomatal regulation is intimately tied to root and soil hydraulic conductances.
Cloud Classification and Characteristics Analysis of Stratocumulus Clouds over Bucharest-Magurele, Romania
Authors: Saftoiu Golea Genica Liliana , Stefan Sabina , Antonescu Bogdan , Iorga Gabriela , Hriscan Tiberiu
Published: March 2022

Stratocumulus clouds represent one of the key components of the Earth's radiative balance because it generally reflects incident solar radiation. The aim of the study is to understand the cloud occurrence and characteristics of stratocumulus clouds using satellite data collected from Dec 2019 to Feb 2021. The time series for cloud characteristics contained 10944 hourly profiles of which 1513 were for Stratocumulus clouds. We used a statistical cloud classification model based on data on cloud optical depth and cloud pressure top. Of the total clouds measured, Cumulus clouds were the most frequently detected (25 %), followed by Altocumulus clouds (17.48 %), Cirrus clouds (17.01 %) and Stratocumulus clouds (13.82 %). We focused on the Stratocumulus clouds. They represent a higher percentage of the total number of clouds detected, especially, in the winter months. A series of macrophysical and microphysical stratocumulus cloud parameters (cloud cover fraction, cloud top temperature, cloud top pressure, cloud height, cloud optical depth, liquid water path) were extracted from the Clouds and the Earth's Radiant Energy System (CERES) database for Magurele, a region in south west Bucharest, Romania. The highest median value for liquid water path was observed in winter 2020–2021 (61.4 g m-2), reflecting the large number of Stratocumulus cloud observations during this period. The lowest median value for liquid water path was 35.14 g m-2 in summer 2020. The cloud water radius of the liquid particles has similar median values ​​(8.67 - 8.92 μm) during the study period except for the winter 2020–2021, when the median value of the radius had the maximum value (9.69 μm). We calculated cloud geometric depth of the stratocumulus clouds, whose median value varied between 141.7 m (summer) and 187.3 m (winter). All these characteristics help us better understand the climatology of stratocumulus clouds [1].

Acknowledgment

GLSG work was supported by the Romanian Nucleu Programme - Project PN 19 06 03 03. GLSG work was also supported by the University of Bucharest, PhD research grant. SS, GI and TH acknowledge the support from NO Grants 2014-2021, under Project EEA-RO-NO-2019-0423, contract no 31/01.09.2020.  BA work was supported by a grant of the Romanian Ministry of Education and Research, CNCS-UEFISCDI (Project No. PN-III-P1-1.1-TE-2019-0649) within PNCDI III. BA work was also supported by the Romanian National Core Program (Contract No. 18N/2019). Present research [1] was accepted for publication and is currently in press at Romanian Reports in Physics (http://www.rrp.infim.ro/IP/AP601.pdf).
Validation of a CDF-t bias correction method using palaeo-data for the Mid-Holocene and the Last Glacial Maximum
Authors: Zapolska Anhelina , Vrac Mathieu , Quiquet Aurélien , Arthur Frank , Renssen Hans , François Louis , Roche Didier M.
Published: March 2022

The main objective of this study is to develop and test a method of bias correction for paleoclimate model simulations using the “Cumulative Distribution Functions – transform” (CDF-t) method. The CDF-t is a quantile-mapping based method, extended to account for climate change signal. Here we apply the CDF-t to climate model outputs for the Mid-Holocene and the Last Glacial Maximum, simulated by the climate model of intermediate complexity iLOVECLIM at 5.625° resolution. Additionally, we test the proposed methodology on iLOVECLIM model outputs dynamically downscaled on a  0.25° resolution.

The results are validated through inverse and forward modelling approaches. The inverse approach implies comparing the obtained results with proxy-based reconstructed climatic variables. Here we use temperature and precipitation reconstructions, obtained with inverse modelling methods from pollen data. In this study, both gridded and point-based multi-proxy reconstruction datasets were used for the analysis.

The forward approach includes a further step of vegetation modelling, using the climatologies derived from bias-corrected outputs of the iLOVECLIM model in CARAIB (CARbon Assimilation In the Biosphere) global dynamic vegetation model. The modelled biomes are evaluated in comparison with pollen-based biome reconstructions BIOME6000.

The findings of this study indicate that the use of the proposed methodology results in significant improvements in climate and vegetation modelling and suggest that the CDF-t method is an valuable approach to reduce biases in paleoclimate modelling.
Interacting Influence of Log Jams and Branching Channels on Stream-Groundwater Exchange
Authors: Sawyer` Audrey H. , Wilhelmsen Karl , Marshall Anna , Zhang Xiaolang , Roumelis Christian , Singha Kamini , Wohl Ellen
Published: March 2022

Log jams restructure the hyporheic zone, or region where stream water and groundwater mix, by storing sediment, widening the stream in backwater areas, forcing new channel branches, and altering hydraulic gradients that drive hyporheic exchange. Here, we use flume and numerical experiments to quantify the effects of interacting jam structures and channel branches on hyporheic exchange at three stream flow rates. The presence of multiple jams increased wetted streambed area (the area available for hyporheic exchange) by 9-38% and increased hyporheic fluxes across the bed by roughly an order of magnitude, leading to an order-of-magnitude decrease in the turnover length that stream water travels before interacting with the hyporheic zone. Decreased turnover lengths corresponded with greater reaction significance per km, a measure of the potential for the hyporheic zone to influence stream water chemistry. For low-flow conditions, log jams increased reaction significance per km five-fold, from 0.07 to 0.35. Jams with larger volumes led to longer hyporheic residence times and path lengths that exhibited multiple scales of exchange. Additionally, the longest flow paths connecting multiple jams occurred in the reach with multiple channel branches. These findings suggest that large gains in hydrologic connectivity can be achieved by promoting in-stream wood accumulation and the natural formation of both jams and branching channels. More studies are needed at field scales to understand relationships between jams, wetted channel area, and hyporheic fluxes under natural and more complex conditions. 
Mapping glacial lakes and their changes using cloud processing of optical satellite images
Authors: Bazilova Varvara , Kääb Andreas Max
Published: March 2022

Glacial lakes are an important component of terrestrial meltwater storage and respond to climate change and glacier retreat. Although there is evidence of rapid worldwide growth of glacial lakes, changes in frequency and magnitude of glacier lake outburst floods (GLOFs) under climatic changes are not yet understood. We refine existing methods of water mapping, based on optical remote sensing images, that can be applicable for the mapping of glacial lakes. We propose and discuss methods for regional-scale glacial lake mapping and GLOF detection using large time series of optical satellite images and the cloud processing tool Google Earth Engine in a semi-automatic way. The methods are presented for various temporal scales, from the 2-week Landsat revisit period to annual resolution. The proposed methods show how constructing an annual composite of pixel values such as minimum or maximum values can help to overcome traditional problems associated with water mapping from optical satellite data like clouds, or terrain and cloud shadows. For annual-resolution glacial lake mapping, our method set only involves two different band ratios based on multispectral satellite images. The elevation range, computed from a digital elevation model is used on the postprocessing step to filter out noise associated with image quality and misclassifications. The study demonstrates various examples of how the proposed methods can be applied to detect GLOFs and to produce a complete regional-scale glacial lake inventory, using the Greater Caucasus as an example. We also discuss limitations of the approaches, finding that for applications where reliable detailed maps are required, visual revision of the results is still recommended owing to the often small size of glacial lakes, combined with their large variability in, for example, topographic setting, turbidity, depth, or temporal occurrence.
Changes in Terrace Structures and Soil Properties in Hani Paddy Terraces after Conversion to Upland Terraces
Authors: Li Yanbo , Wang Ming , Jiao Yuanmei , Rong Li , Huang Jiangcheng
Published: March 2022

Terraces are important practice to conserve soil and water in farming systems in mountain areas. Since the mid- 20th century, marginalization of farmland occurred worldwide in mountainous areas. Farmers reduced investment in terraced fields or even abandoned the fields, and induced negative ecological consequences that are widely concerned. Current studies about marginalization of terraces mainly focus on upland terraces. The understandings of the process of marginalization of paddy terraces and their impacts are limited. Hani Paddy Terraces are one of the Globally Important Agriculture Heritage Systems. However, many of the paddy terraces have changed into upland terraces due to lack of water, labor out-migration ect, which hindered the conservation of the heritage. Taking Amengkong River Basin in Yuanyang County in Southwestern China as the case study area, we explored the changes in terrace structure, productivity of top soil (0~20 cm ) and the water holding capacity soil in 0~70 cm depth in Hani Paddy Terraces since conversion to upland terraces fields by 2~14 years. We found that (1) most ridges disappeared after conversion, the surface of fields were generally maintained in flat conditions, risers of terraces collapsed in varying degrees in more than 70% filed parcels. The degree of damages in terraces structures showed a U-shape curve along with time, as the pattern of drained by 2 years> drained by 3~4 years> drained by 10~14 years > drained by 5~9 years;（2）the soil productivity index increased after converted to upland terraces, and showed a trend of decreasing first and then increasing along with increasing years of conversion. (3) The water holding capacity of 0~70 cm soil dramatically decreased after conversion, and increasingly decreased along with increasing years of conversion. The maximum water holding capacity decreased by 9.16%~21.70% and the capillary volume decreased by 12.09%~24.20%，the decreasing of maximum water holding capacity and capillary volume were most serious in soils of 0~30 cm depth. Our study revealed the impacts of draining on structure of terraces and soil property in Hani Paddy terraces. The findings could enhance the understanding of the biophysical changes in soil during the marginalization in paddy terraces, which would benefit to the conservation and restoration of paddy terraces. 
Fire aerosols slow down the global water cycle
Authors: Li Fang , Lawrence David , Jiang Yiquan , Liu Xiaohong
Published: March 2022

Fire is an important Earth system process and the largest source of global primary carbonaceous aerosols. Earlier studies have focused on the influence of fire aerosols on radiation, surface climate, air quality, and biogeochemical cycle. The impact of fire aerosols on the global water cycle has not been quantified and related mechanisms remain largely unclear. This study provides the first quantitative assessment and understanding of the influence of fire aerosols on the global water cycle. This is done by quantifying the difference between simulations with and without fire aerosols using the fully-coupled Community Earth System Model (CESM). Results show that presentday fire aerosols weaken the global water cycle significantly. They decrease the continental precipitation, evapotranspiration, and runoff by 4.1±1.8, 2.5±0.5, and 1.5±1.4 ×103 km3 yr-1 as well as ocean evaporation, precipitation, and water vapor transport from ocean to land by 8.1±1.9, 6.6±2.3, and 1.5±1.4 ×103 km3 yr-1. The impacts of fire aerosols are most clearly seen in the tropics and the Arctic-boreal zone. Fire aerosols affect the global water cycle mainly by cooling the surface which reduces ocean evaporation, land soil evaporation and plant transpiration. The decreased water vapor load in the atmosphere leads to a decrease in precipitation, which contributes to reduced surface runoff and sub-surface drainage.
Using Earth system model output to simulate DCF variability in speleothems: Implications for atmospheric 14C calibration
Authors: Hubig Alexander , Therre Steffen , Kleinen Thomas , Frank Norbert
Published: March 2022

Speleothems have become a cornerstone in atmospheric 14C reconstruction. In particular, the part of the IntCal20 calibration curve before 34 ka BP (Reimer et al., 2020) heavily relies on a set of speleothems from Hulu Cave in China (Cheng et al., 2018). The interpretation of speleothem 14C archives, however, is often exacerbated by the so-called dead carbon fraction (DCF) in speleothem carbonate. It quantifies the percentage of old, 14C-free carbon from dissolved bedrock carbonate or aged soil organic matter, and is controlled by various parameters. Modelling efforts to disentangle these parameters have already been made by previous studies.

Here, we present forward-modelled DCF time series obtained by coupling CaveCalc, a numerical model for speleothem chemistry and isotopes (Owen et al., 2018), with IntCal20 and results from paleoclimate modelling. To compare our coupled model with an extensive DCF measurement record from Sofular Cave in Northern Turkey, we convert time-dependent soil respiration output from the Max Planck Institute Earth System Model version 1.2 (MPI-ESM1.2) to soil pCO2 via a simplistic soil respiration model and use it as input for CaveCalc. The resulting forward-modelled DCF is in very good agreement with the long-term trends of the measurement record and demonstrates that soil respiration has been the main driver of DCF variability in the Last Glacial Maximum and the Early Holocene at Sofular Cave.

Further, we show that, holding soil respiration and all other climate parameters constant, adding only 10 % of 1000 year old carbon to the soil CO2 can cause variations of up to 200 years in the DCF. This finding suggests that the DCF variability of only 50 years, which is assumed for Hulu Cave by Reimer et al. (2020), might be significantly higher, and underlines the importance of including additional records, like the one from Sofular Cave, to the next generation of calibration curves.

 

References:

Reimer, P. J., Austin, W. E. N., Bard, E., Bayliss, A., et al.: The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0–55 cal kBP), Radiocarbon, 62(4), 725-757, doi:10.1017/RDC.2020.41, 2020.

Cheng, H., Lawrence Edwards, R., Southon, J., et al.: Atmospheric 14C/12C changes during the last glacial period from Hulu Cave, Science, 362(6420), 1293–1297, doi:10.1126/science.aau0747, 2018.

Owen, R., Day, C. C., and Henderson, G. M.: CaveCalc: A new model for speleothem chemistry & isotopes, Computers & Geosciences, 119, 115–122, doi:10.1016/j.cageo.2018.06.011, 2018.
Review of earthquake location quality since 2020 for Austria
Authors: Apoloner Maria-Theresia , Horn Niko , Hausmann Helmut
Published: March 2022

When monitoring seismicity, detection thresholds for magnitude and location accuracy for epicentres are basic quality factors used. However, these factors can be estimated in numerous ways, depending on available data, the tasks the network is built for and customer/legal guidelines.

In this work, we focus on location quality. We analyse location quality for the area of Austria and a smaller project within. For this purpose, we calculate location errors with NLLoc (Lomax, et al. 2009) for Austria and compare them with location errors automatically computed for each earthquake located by the Austrian Seismological Servicewithin the last 2 years. Additionally, we use the quality parameters given in Bondar, et al. (2004) for further analysis.
Models of Duricrust Formation in Tropical and Subtropical Areas
Authors: Fenske Caroline , Braun Jean , Guillocheau François , Robin Cécile
Published: March 2022

Ferruginous duricrust formation takes place by dissolution and accumulation of iron during the wet season and precipitation during the dry season. However, the formation of iron duricrusts has always been the centre of much debate. They commonly form as hard iron layers in tropical and subtropical environments with strong climatic seasonality. They were first described in Africa, Australia and India in the 1950’s. They often cap landscapes, which can be explained by their extremely high iron content making them more resistant to mechanical weathering. However, in recent years, iron duricrusts were also described at depth in the regolith, like in South America.

This has led to 2 distinct formation hypotheses: the first one relies on the vertical beating of the water table most likely in a stable environment combined to lateral hydraulic transport of iron. In this scenario, iron hydroxides accumulate in one specific region after being transported from surrounding source areas through the water table, and precipitate as Fe3+ during the dry season. Through time, this leads to duricrusts forming within the water table beating range. This model is compatible with duricrusts forming at depth within the regolith. The second hypothesis relies on the vertical, in situ leaching of elements and resulting compaction and surface lowering. During weathering, iron nodules accumulate with the progressive leaching of soluble elements from the parent rock, leaving only the iron oxides, ultimately forming a duricrust. It implies a genetic link between the duricrust, the lateritic profile and the underlying parent rock. This model explains why duricrusts are mostly observed near the surface. Nevertheless, there is no consensus on the conditions under which either of these hypotheses prevail.

 

To address this issue, we developed two separate first-order numerical models representing the two hypotheses for duricrust formation. We used the models to demonstrate that the hypotheses lead to different scenarios of duricrust formation by running a large number of simulations. Especially, we show that the stability of a landform is a discerning element between the 2 models. In the first case, quiescent periods of time in between uplifting periods are crucial, while in the second case, constant dynamic uplift is needed to enable the accumulation of enough elements by compaction. 
Is there still a case for Carbon Takeback or Carbon Removal Obligations in a world of low renewable energy costs?
Authors: Allen Myles , Jenkins Stuart , Ives Matthew , Kuijper Margriet
Published: March 2022

Upstream regulatory measures to require fossil fuel producers and importers to pay for carbon dioxide capture and disposal, such as the Carbon Removal Obligation (CRO, Bednar et al, 2021) or Carbon Takeback Obligation (CTBO, Jenkins et al, 2021), provide a potentially valuable "backstop" mitigation policy if demand-side measures fail to reduce emissions fast enough to meet climate goals. But what if renewable energy costs fall much faster than envisaged in the current generation of integrated assessment models? Would these upstream measures then result in a substantial investment in carbon capture and storage (CCS, encompassing both direct-air and point-source capture) that is subsequently stranded because it is not needed? We explore the implications of ultra-low renewable energy costs under an idealised global CTBO regime and argue that over-building mitigation capacity is unlikely given current trends and in any case would represent a sensible precautionary investment. The risk of stranding of CCS capacity is directly linked to the long-term cost of both CCS and the extraction costs of fossil fuels, reinforcing the case for delivering CCS through obligations on the fossil fuel extraction industry in order to align incentives and ensure that those who benefit most from continued use of fossil fuels also shoulder the risks associated with the transition.
LEO-based solution of GPS PCOs and impact on terrestrial scale 
Authors: Huang Wen , Männel Benjamin , Brack Andreas , Schuh Harald
Published: March 2022

The deviations of phase center offsets (PCOs) of GPS satellites were and still are significant bias sources for GPS-based terrestrial reference frames (TRF). Because of the strong correlation between the scale of the TRF and the satellite PCOs in the z-direction (z-PCOs), a no-net-scale (NNT) condition relative to, for instance, the International Terrestrial Reference Frame (ITRF) is commonly applied. Based on the released Galileo metadata, the GPS z-PCOs have been calibrated without introducing a scale determined by other techniques in the third re-processing of the International GNSS Service (IGS). Another approach purely based on GNSS is by integrating low Earth orbiters (LEOs) into the estimation of the GPS z-PCOs and the realization of the scale. Within this study, we estimated the GPS z-PCOs based on zero-difference ionosphere-free observations from six low LEOs and ground networks with different numbers of stations in 2019 and 2020. Besides the study based on six LEOs in two years, a twelve-year-based estimation of GPS z-PCOs and scale realization is done by using the two satellites of the GRACE mission.

We jointly estimate orbits (GPS and LEOs), station coordinates, z-PCOs of GPS satellites, and some other parameters in an integrated processing. The NNT condition on the ground network is not applied in the processing. By adding six LEOs, the correlation coefficients between the GPS z-PCOs and the scale is reduced significantly (from about 0.85 to 0.30). It means that the GPS z-PCOs and the scale have been decorrelated efficiently, and consequently the precision of the estimation is improved. For GPS satellites operated in 2019 and 2020, excluding GPS III, their estimated z-PCOs have an average difference of -231 mm compared to the values in igs14_2134.atx and the corresponding scale to the IGS14 reference frame is +1.89 part per billion. These results agree well with the solutions based on the metadata of Galileo. The improvement due to different numbers of LEOs and the impact of LEO z-PCO errors on the estimation is studied, where more LEOs decorrelate the GPS z-PCOs and the scale more efficiently. The accuracy of the LEO z-PCOs is critical to the solution. A one-millimeter accuracy of the z-PCOs of the LEOs is required to achieve a one-millimeter scale on the surface of the Earth. Thanks to the long-term available data of LEO missions in the last decade and even longer, the LEO-based method has an advantage on the real-data-based estimation of PCOs of former GPS satellites over the Galileo-based method. The z-PCOs of satellites of GPS blocks IIA, IIR, IIRM, and IIF are estimated by integrating the two GRACE satellites from 2004 to 2015. A twelve-year scale relative to the ITRF is realized simultaneously. The performance of the LEO-based method is shown by the long-time series.  
Possibility for strong northern hemisphere high-latitude cooling under zero and negative emissions.
Authors: Schwinger Jörg , Asaadi Ali , Goris Nadine , Lee Hanna
Published: March 2022

The Atlantic meridional overturning circulation (AMOC) transports large amount of heat northwards, where this heat contributes to warm the atmosphere. It is well established that an AMOC collapse, or strong reduction would substantially cool the northern high latitudes. New Earth system model (ESM) simulations indicate the possibility that such cooling, due to the large inertia of the climate system, could also happen when CO2 emissions are phased out after AMOC has been weakened by preceding climate change. Our simulations show a temporally and spatially strongly variable zero emission commitment (ZEC), which is first negative (up to -0.4K) and then turns positive (up to 0.5K) as AMOC recovers. Regionally, the strongest cooling-warming pattern is found in the northern high latitudes north of 40°N, where the amplitude of this cycle can exceed several degrees. The mechanism of this cooling can be understood by the fact that the radiative forcing of CO2 is reduced when emissions become zero while the Earth system is in a state of reduced northward heat transport. We further show that this northern high-latitude cooling could be amplified under deliberate CO2 removal and result in a temporary undershoot of a targeted temperature level. Such “stronger than intended” cooling north of 40°N under net negative emissions is a robust feature of Earth system models that show a strong AMOC decline in response to warming, both in idealized simulations but also in an overshoot scenario created for CMIP6 by an integrated assessment model. The future fate of ocean circulation is highly uncertain in ESM projections, and the amplified northern high latitude cooling under zero or net negative emissions is a feature of ESMs with a high sensitivity of AMOC to warming. Nevertheless, or results underscore (i) the importance of understanding the physical climate system’s response to phasing out emissions to avoid surprises, (ii) the importance of coordinated experimentation with ESMs such as CMIP6 ZECMIP and CDRMIP, and finally (iii) the importance of assessing zero and net negative emissions beyond simple metrics like global mean surface temperature. 
Storm surges and meteotsunamis of the Adriatic Sea: interplay and quantification of hazard level 
Authors: Ruić Krešimir , Šepić Jadranka , Mlinar Marko , Međugorac Iva
Published: March 2022

Sea level time series of up to 19 years length, recorded with one-minute sampling interval at 18 tide gauges, evenly distributed along the eastern and western coast of the Adriatic Sea, were analysed in an attempt to quantify hazard related to the Adriatic Sea level extremes.  Prior to analysis, quality control and pre-processing were done: all unphysical spikes and outliers were removed; shorter gaps were interpolated, and time series were de-tided.

For each tide gauge, two types of sea level extremes were defined and extracted from residual time series: (1) extremes related to storm surges, i.e. extremes that dominate the total residual signal; (2) extremes related to meteotsunamis, i.e. extremes that dominate the high-frequency signal (T < 2 h). The two types of extremes were analysed in detail and following conclusions were reached: (1) on average, extremes related to storm surges are stronger than those related to meteotsunamis; (2) nonetheless, there are stations at which two types of extremes are of almost comparable strength (e.g. Vela Luka, Stari Grad); (3) high-frequency oscillations can contribute significantly (up to 30% of residual signal) to the storm surge related extremes  at most areas; (4) extremes related to storm surges mostly happen from October to January while the second type of extremes happen more throughout the year, with peak appearances of the strongest ones from May to September. 

Conclusively, for both types of episodes, it has been shown that the high-frequency signal contributes significantly to total extremes and that analysis of sea level time series sampled at a one-minute time interval is a prerequisite for proper analysis of hazards related to sea level extremes.
Assessing modelled hydrological responses to afforestation using hectometre-scale cosmic-ray neutron soil moisture
Authors: Andreasen Mie , Christiansen Jesper R. , Sonnenborg Torben O. , Stisen Simon , Looms Majken C.
Published: March 2022

Since the 1990´s, and in particular during the last decade, afforestation has become a common water management practice. Afforestation improves the quality of the groundwater resource by reducing the leaching of nutrients and pesticides in the soil. Furthermore, planting of trees is also used to capture carbon from the atmosphere as an integral element of carbon emission mitigation, for biodiversity restoration and for biofuel. With the more extensive implementation of afforestation, it is important to understand the hydrological responses and to predict and quantify these adequately using hydrological modelling.

The hydrology of the forest system is characterized by high spatial variability. The forest vegetation intercepts and redistribute a considerable fraction of the precipitation resulting in an uneven input of water at the forest floor. The transpiration and soil evaporation vary in space according to the tree root distribution and soil texture. All these factors influence the soil moisture in the unsaturated zone, the percolation, and the groundwater recharge. Hydrological models are often used to estimate the groundwater recharge rate and to obtain information of the timing of the recharge to ensure sustainable groundwater exploitation and sufficient streamflow. The high spatial variability makes it difficult to predict forest hydrology and it is important that the observations are representative of the forest plot to assess the performance of the hydrological model.

In this study, we predict the water balance for bare ground conditions and for a coniferous forest to examine the hydrological responses to afforestation. We use a physically based and spatially distributed hydrological model with an energy-based description of evapotranspiration processes (MIKE SHE SVAT). The forest model was calibrated against timeseries of throughfall and point-scale soil moisture. Simulated soil moisture is evaluated against forest plot cosmic-ray neutron and point-scale estimates. Further assessment of the model is obtained through comparison to time-series of forest plot eddy-covariance evapotranspiration estimates and observation-based and predicted interception loss. We find that the forest plot and point-scale soil moisture estimates differ which in turn affects the assessment of the reliability of the model performance. The hydrological responses of afforestation are significant, influencing the total evapotranspiration, the soil moisture and the groundwater recharge.  
Machine-learned actual Evapotranspiration for an Irrigated Pecan Orchard in Northwest Mexico
Authors: Stoffer Robin , Rodríguez Julio César , van Heerwaarden Chiel , Hartogensis Oscar
Published: March 2022

Agriculture in semi-arid regions like Northwest Mexico, is typically characterized by heavily irrigated fields surrounded by a desert environment. The strong contrast in surface conditions increases the non-linear and non-local character of the evapotranspiration dynamics at the irrigated fields, in particular through the oasis effect: strong local evaporative cooling, associated with evapotranspiration enhanced by advection of warm and dry air from the surroundings. To estimate evapotranspiration for individual fields, the agricultural practice relies on traditional empirical models (e.g. Makkink, Priestley-Taylor, FAO-Penman-Monteith) that only make use of standard weather station data. The aforementioned empirical models typically rely on arbitrary, manual tuning (e.g. adjusted constants or the application of a locally determined crop factor) to work reliably.

The goal of this study is to explore whether a physics-informed machine learning approach can be used to improve the estimated evapotranspiration for irrigated fields located in a desert environment, without arbitrary tuning after training and only using regionally available data as input. To this end we will focus on a typical irrigated pecan orchard in Northwest Mexico. At this orchard we have obtained a rich multi-year dataset that encompasses eddy-covariance measurements, irrigation data, soil moisture measurements, and meteorological station data (e.g. air temperature, specific humidity, wind speed and direction) at a half-hourly time scale. In addition, we obtained complementary vegetation indices at the scale of the pecan orchard (~100m-1km) from operationally available remote sensing products.

Using this dataset, we first identify and visualize the main non-linear physical processes (including amongst others the oasis effect) that drive the actual evapotranspiration at the irrigated pecan orchard, both on seasonal and daily time scales. Subsequently, we explore to what extent the effect of the previously identified non-linear processes on the actual evapotranspiration, can be captured with two different machine learning techniques (i.e. gradient boosting decision trees and multi-layer perceptrons) that only receive input variables from a regional meteorological station network and the aforementioned remote sensing products. We trained and tested the machine learning techniques on the evapotranspiration flux measured by an eddy-covariance station located at the orchard, where the estimates provided by the physics-inspired FAO-PM method were used as a starting point for the machine learning models. We find that the machine learning techniques primarily show promise in improving the representation of the seasonal dynamics.
The search for low-abundant species in the coma of comet 67P/Churyumov-Gerasimenko
Authors: Dhooghe Frederik , De Keyser Johan , Hänni Nora , Altwegg Kathrin , Cessateur Gaël , Jehin Emmanuel , Maggiolo Romain , Rubin Martin , Wurz Peter
Published: March 2022

During the ESA/Rosetta mission more than 1.5 million individual mass spectra have been obtained in the coma of 67P/Churyumov-Gerasimenko with the ROSINA/DFMS mass spectrometer. A single spectrum at a specific mass represents the accumulation of 3000 scans with an integration time of 6.6 ms, for a 19.8 s total measuring time.

DFMS data has been a source of information on coma composition and even on refractories. Although DFMS has a high sensitivity and high dynamic range, there may still be species hidden in the spectra. One approach to improve the signal-to-noise ratio is the summation of spectra. This way, species with a low abundance, close to the limit of detection of DFMS, should become more pronounced, however, at the cost of the loss of possible time variability information.  Unfortunately, the creation of sum spectra is not straightforward. Sum spectra need a clean dataset, where all erroneous and non-cometary data have been removed. Also, instrumental effects (e.g. detector aging, changes in settings in the course of the mission) need to be taken into account.

This contribution will present the methodology and some first results for sum spectra from DFMS. It is shown how this approach can provide inputs in the search for Fe and Ni in comet 67P.
Localised Drought Early Warning using In-situ Groundwater Sensors
Authors: Veness Will , Buytaert Wouter , Butler Adrian
Published: March 2022

Drought Early Warning Systems (DEWSs) require data on spatial drought intensity and exposure to highlight the most-affected areas for early interventions. This data also provides evidence of drought severity to trigger early financing mechanisms. However, existing DEWSs are dependent on satellite-based parameters, which have a course spatial resolution and high measurement uncertainty. As a result, these indicators do not provide a reliable proxy for local groundwater availability during hydrological drought. This research explores groundwater monitoring for providing an alternative, direct index of groundwater availability for DEWSs, considering the increasing affordability and feasibility of monitoring due to advancements in modern sensors. Using in-situ observations collected from abstraction wells in Maroodi Jeex, Somaliland, a lumped parameter groundwater model has been calibrated that can forecast local groundwater levels during drought, by inputting seasonal and mid-range weather forecasts. The model can also simulate well water levels if the sensor is removed after 1 year, enabling an ongoing, locally calibrated groundwater index without the need for sensor maintenance. This suggests that national-scale groundwater monitoring in Somaliland is technically feasible, and it raises further research questions regarding how such a system can be funded, governed and maintained, as well as how this groundwater information would be practically used in the drought early warning early action process to inform management and financing decisions.
The Randolph Glacier Inventory (RGI) version 7
Authors: Maussion Fabien , Hock Regine , Paul Frank , Rastner Philipp , Raup Bruce , Zemp Michael , Consortium the RGI
Published: March 2022

The Randolph Glacier Inventory (RGI) is a globally complete collection of digital glacier outlines, excluding the two ice sheets. It has become a pillar of glaciological research at global and regional scales for estimates of recent and future glacier changes, glacier mass balance, glacier contribution to sea-level rise, among others. The latest RGI version (V6) was released in July 2017.

Here, we present a new version of the RGI (version 7.0), which is our best estimate of global glacier outlines around the year 2000. Unlike previous versions which were compiled by an ad-hoc manual process using different sources, RGI7.0 is generated directly from the Global Land Ice Measurements from Space (GLIMS) glacier database, ensuring full traceability of single outlines to their original authors. The dataset is generated automatically with Python scripts parsing the GLIMS database and selecting outlines according to community decisions (based on data availability, quality and closeness to the year 2000). Prior to its release, the dataset was available for open review from the scientific community, and further refined as necessary.

About 70% of the outlines (30% of the total area) in RGI7.0 are obtained from new inventories that were submitted to GLIMS since the last release of RGI6.0 by different groups around the world. This led to considerable quality improvements especially in High Mountain Asia, Northern Canada, northern Greenland, Caucasus and Middle East, South America and New Zealand. RGI7.0 includes updated topographical and geometrical glacier attributes generated with a new community software. The new RGI generation process is open-source, fully reproducible and easily adaptable, making future updates straightforward to generate.