bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Surface Tensions of Nanobubbles in Plant Xylem: When are they Stable?
Authors: Ingram Stephen , Salmon Yann , Lintunen Anna , Hölttä Teemu , Vesala Timo , Vehkamaki Hanna
Published: February 2023

Xylem sap exists in a state some have described as “doubly” metastable[1]: liquid water is transported from root to leaf under negative pressure, and, in some climates, below its freezing point. Sub-100 nm nanobubbles may be injected into the xylem liquid through pit membranes[2], becoming coated with Phospho- and Glycolipids in the process. Their surface properties, and therefore fate within the tree hydraulic system, remain largely unexplored.In this work, we have used molecular dynamics simulations to produce surface tension – area isotherms of biologically relevant lipid monolayers, as a function of both temperature and negative pressure (i.e. dynamic surface tensions).We find that glycolipid monolayers resist expansion proportionally to the rate of expansion[3]. Their surface tension increases with the tension applied, stabilising the bubble with respect to embolism. In contrast, a typical phospholipid rapidly condenses into more dense lamellar-like phase, rendering it highly resistant to tensions as high as -3.5 MPa. Mixed monolayers of the two exhibit hybrid behavior, as the glycolipids' larger head group disrupts the more ordered phase of the phospholipid. Finally, it is observed that increasing temperature also increases surface tension, at a given surface area.[1] Lintunen, A., Hölttä, T., & Kulmala, M. (2013). Anatomical regulation of ice nucleation and cavitation helps trees to survive freezing and drought stress. Scientific Reports, 3, 1–7. https://doi.org/10.1038/srep02031[2] Schenk, H. J., Steppe, K., & Jansen, S. (2015). Nanobubbles: a new paradigm for air-seeding in xylem. Trends in Plant Science, 20(4), 199–205. https://doi.org/10.1016/j.tplants.2015.01.008[3] Ingram, S., Salmon, Y., Lintunen, A., Hölttä, T., Vesala, T., & Vehkamäki, H. (2021). Dynamic Surface Tension Enhances the Stability of Nanobubbles in Xylem Sap. Frontiers in Plant Science, 12. https://doi.org/10.3389/fpls.2021.7327
Interpretation of the push and pull tracer test data in heterogeneous aquifers
Authors: Zarlenga Antonio , Maggi Maria Rita
Published: February 2023

Heterogeneous aquifer characterization is a key step in both quantitative and qualitative groundwater studies. The high cost required in the flow field characterization and the small budget usually available make accurate and effective models for data analysis and information acquisition necessary.We present here a methodology for the interpretation of the tracer test data widely used in the aquifer characterization; in particular we focus on the push and pull test, the latter is commonly adopted for the investigation of the hydrogeological and chemical parameters of aquifers.Our stochastic methodology through the direct simulation of transport within a heterogeneous formation, allows to characterize the main geostatistical properties of the flow field and the main transport parameters. The model conceptualization is a stratified formation with isotropic log-hydraulic conductivity normally distributed; the integral scale in the vertical direction is IY,V while the horizontal integral scale is unbounded IY,H=∞ The flow field is assumed to be steady state and driven by the pumping rate. Transport is simulated by a Lagrangian procedure considering advection dispersion and equilibrium adsorption reaction. The results show that adopting different test setup many aquifer parameters can be obtained. The promising methodology was tested with field data from literature, showing encouraging results.
Vorticity budget of convectively coupled equatorial Rossby waves: propagation and growth mechanisms
Authors: Matthews Adrian
Published: February 2023

Convectively coupled equatorial Rossby waves (CCERWs) are an intrinsic part of the spectrum of tropical weather systems, and can bring extreme precipitation to tropical locations. They are usually interpreted as modified versions of the theoretical dry equatorial Rossby wave solutions of the shallow water equations. However, the structure and dynamics of CCERWs are rather different to their theoretical cousins. Here, a vorticity budget is presented for both theoretical equatorial Rossby waves and for CCERWs (based on reanalysis data). The different strengths of the vorticity budget terms between the theoretical waves and CCERWs gives insights into CCERW propagation and growth mechanisms, and provides a focus and testbed for future model and forecast improvements.
Climate-driven changes to the long-range fluctuations in vegetation production: Consequences for the global carbon cycle
Authors: Naidu Dilip , Seshadri Ashwin , Bagchi Sumanta
Published: February 2023

Climate plays a vital role in the carbon (C) uptake through vegetation productivity (Gross Primary Production; GPP) that is crucial to the persistence of the land as a carbon sink, thereby resulting in negative land-climate feedbacks. Large uncertainties persist in understanding the role of climate variability on this C flux, which influence future projections using Earth System Models (ESMs). One important source of uncertainty arises from the temporal variability in the carbon influx, and this includes effects of autocorrelation—i.e., similarity in observations with time-lag due to temporal structuring (“memory”) in the underlying dynamics. Evidence of the presence of memory in C uptake through GPP arises from field-based measurements through eddy covariance flux towers, but these lack widespread spatial distribution across environmental conditions and ecosystems. Therefore, estimating memory in the C cycle and its drivers on the global scale is important to our understanding of the global C cycle. For this, we used remotely sensed long-term GPP data from MODIS over the past two decades (2001-2021), to estimate long-term memory in C cycling through C-uptake by vegetation. Additionally, we also examined how the climate variables – temperature and precipitation- that are known to drive C influx, influenced the memory in C-uptake. We find that memory occurs in satellite-based estimates of GPP, corroborating field-based measurements. Interestingly, the memory in the C cycle was not limited to either short- or long-term but consisted of both these characteristics across different timescales. Climate variability through temperature and precipitation influenced memory and their effects are heterogeneous across ecosystems. With climate variability predicted to increase in the near future, our results suggest that these effects are likely to be consequential for the memory in C-uptake and, ultimately on the dynamics of the global C cycle. Therefore, estimating the memory in C cycle and its variation, is crucial for understanding as well as predicting the C-influx, under present and future climate change scenarios. 
2D numerical simulation of the shallow magmatic body at Krafla
Authors: Girela Arjona Gabriel , Papale Paolo , Garg Deepak , Colucci Simone , Montagna Chiara
Published: February 2023

The Krafla caldera, located in the Northern Volcanic Zone of Iceland has become the most studied volcano in the country since its last eruption, the Krafla Fires, happened between 1975 and 1984. From that moment, an extensive monitoring system has been developed in the caldera, focused on both geothermal exploration and production, as well as scientific research. In 2009, the IDDP-1 exploratory well aiming to 4 km depth in search of supercritical hydrothermal fluids got stuck at 2.1 km, retrieving quenched glass cuttings. It was then understood that an unexpected and undetected rhyolitic magma body had been drilled. This body stood without apparent signs of crystallization at the rooftop, opposing the most common belief that magmatic bodies at shallow depths should present a mushy region adjacent to the body’s walls. We aim to simulate the dynamics of the magma encountered in Krafla. We perform 2D numerical simulations of the magma thermo-fluid dynamics, assuming thermodynamic equilibrium in a sill-like, disk-shaped body 1200 metres wide and 260 metres deep. We include a 100 metres thick aureola with fixed boundary temperature of 350 ºC and initial linear temperature gradient up to 900 ºC in the magmatic body. In order to simulate the magma dynamics we use the software GALES (Garg and Papale, Frontiers in Earth Sciences 2022), which solves the 4D dynamics of multi-component fluids in geometrically complex domains. Melt-solid-gas thermodynamic are computed with rhyoliteMELTS (Gualda et al., J. Petrol. 2012) using the alphaMELTS-2 front end (Smith & Asimow, GCubed 2005). The properties density, heat capacities, single-phase and multiphase non-Newtonian viscosity, thermal conductivity, and compressibility, are locally computed as a function of pressure, temperature, phase distribution, and phase composition. The results allow a first evaluation of the conditions under which a crystal mush can form and be stable close to the roof and margins of a shallow magmatic intrusion.
A Lagrangian view of seasonal overturning variability in the eastern North Atlantic subpolar gyre.
Authors: Tooth Oliver J. , Johnson Helen L. , Wilson Chris , Evans Dafydd G.
Published: February 2023

The Atlantic Meridional Overturning Circulation (AMOC) plays a critical role in the global climate system through the uptake and redistribution of heat, freshwater and carbon. At subpolar latitudes, recent observations show that the strength of the AMOC is dominated by water mass transformation in the eastern North Atlantic Subpolar Gyre (SPG). Both observations and ocean reanalyses show a pronounced seasonality of the AMOC within this region. However, the distribution of the strength and seasonality of overturning across the individual circulation pathways of the eastern SPG remains poorly understood. To investigate the nature of this seasonal overturning variability, we use Lagrangian water parcel trajectories evaluated within an eddy-permitting ocean sea-ice hindcast simulation.By introducing a novel Lagrangian measure of the density-space overturning, we show that water mass transformation along the circulation pathways of the eastern SPG accounts for 8.9 ± 2.2 Sv (55%) of the mean strength of AMOC in the eastern subpolar North Atlantic. Our analysis highlights the crucial role of water parcel recirculation times in determining the magnitude of the strength and seasonality of overturning. We find that upper limb water parcels flowing northwards into the eastern SPG participate in a recirculation race against time to avoid wintertime diapycnal transformation into the lower limb of the AMOC. Upper limb water parcels sourced from the central and southern branches of the North Atlantic Current typically recirculate on interannual timescales (1-5 years) and thus determine the mean strength of overturning within this region. The seasonality of Lagrangian overturning is explained by a small collection of water parcels, recirculating rapidly (≤ 8.5 months) in the upper Central Iceland and Irminger Basins, whose along-stream transformation is dependent on their month of arrival into the eastern SPG.
F30 is the most suitable solar activity proxies for foF2 at middle latitudes
Authors: Laštovička Jan
Published: February 2023

To study ionospheric climate and to study its long-term changes and trends we need solar activity proxies, because long and homogeneous data series of solar ionizing flux are not available. Also models like IRI are based on solar proxies. To select the optimum solar activity proxies, we use yearly average foF2 data of six ionospheric stations from middle latitudes of four continents over 1976-2014 and six solar activity proxies, F10.7, sunspot numbers, F30, Mg II, He II and solar Lyman-α flux. The highest percentage of total variance of yearly foF2 is described equally by F30 and Mg II. However, when we divide period 1976-2014 into two parts, 1976-1995 and 1996-2014, F30 is the only proxy which reveals the same dependence of foF2 on solar proxy. Moreover, F30 is available since March 1957 whereas Mg II only since November 1978. Thus for long-term studies of yearly foF2 at middle latitudes F30 is the most suitable solar activity proxy.Change of the dependence of foF2 on solar activity proxies from 1976-1995 to 1996-2014 appears to be of solar origin; it is related to changes of interdependences among solar proxies between the first and second periods.
How land use and land cover change affect the water retention of alpine landscapes in Austria
Authors: Stecher Gabriel , Hohensinner Severin , Herrnegger Mathew
Published: February 2023

Long-term land use and land cover changes (LULCC) are estimated to affect almost one third of the global land area (Winkler et al., 2021). This also alters hydrological processes and has implications on the ability of the landscape to retain water. In alpine areas of Austria, extensive LULCC have occurred since the mid-19th century, which also led to changes in flood hazard and an increase in flood risk, especially in the valley floors.This contribution analyses, how long-term LULCC from the 1820s until now affect the water retention potential of the Austrian catchments of the rivers Rhine, Salzach and Drava. The Water retention index (WRI) (Vandecasteele et al., 2017) was calculated at a high spatial resolution (100*100 m) for the past and present LULC situation. The WRI is a qualitative indicator and shows the water retention capacity on a relative scale (0-10) by a composition of the governing physical processes (e.g. interception, percolation) through proxy datasets.The resulting WRI maps of the historic and present state reveal that the general spatial features and characteristics exhibit similar WRI patterns. High values (WRI > 5) occur in valley floors and rather flat areas. Areas dominated by steep topography and alpine characteristics show low WRI values (< 3). The comparison of the two time periods shows a moderate to strong reduction (< -2) of the water retention potential especially in the alpine valleys and low elevations for the current state. This is largely explained by the expansion and development of settlement areas and soil sealing. Additionally, the draining of wetlands, river channelization and disconnection of flood plains and deforestation also strongly reduced the WRI values. In contrast, increasing WRI values occur primarily in areas at higher altitudes. Here, forest areas increased and wasteland transformed to grassland. In addition, new artificial water reservoirs have been constructed to produce hydropower, which have a positive effect on the retention potential. Generally, the spatial and altitudinal changes in the water retention capacity reflects the land and settlement development in the past 150 years. This development resulted in higher flood exposure but might have also reduced flood hazards due to higher water retention capacities.References: Vandecasteele, I., Marí i Rivero, I., Baranzelli, C., Becker, W., Dreoni, I., Lavalle, C., and Batelaan, O., 2017. The Water Retention Index: Using land use planning to manage water resources in Europe. Sustainable Development, 26 (2), 122–131. https://doi.org/10.1002/sd.1723Winkler, K., Fuchs, R., Rounsevell, M., and Herold, M., 2021. Global land use changes are four times greater than previously estimated. Nature Communications, 12 (1), 1–10. https://doi.org/10.1038/s41467-021-22702-2
DOAS applied to shipping emission monitoring: compliance assessment and comparison to satellite measurements
Authors: Prignon Maxime , Conde Vladimir , Timothy J. Smyth , Anu-Maija Sundström , Jasper van Vliet , Johan Mellqvist
Published: February 2023

While shipping is generally the most energy-efficient freight transportation mode (in terms of gCO2 t-1 km-1), its intensive use (80 % to 90 % of global merchandise trade volume), coupled with high pollutant emission factors, leads to serious impact on the environment and the human health. The primary pollutants emitted by ships, nitrogen oxides (NOx = NO2 + NO), sulphur oxides (SOx, mainly SO2) and particulate matter (PM), degrade the air quality and are involved in the formation of secondary pollutants as tropospheric ozone (O3). As 70 % of ship emissions occur within 400 km of coastlines, ship emissions have strong impact in harbour cities and coastal areas situated along high traffic shipping lanes.Compliance monitoring for fuel sulphur content (FSC) is usually done by the collection and the analysis of fuel samples by competent authorities from ships at berth. The complexity of the method results in very few ships being formally controlled. In consequence, various remote compliance monitoring techniques of FSC have been developed in the last years, mainly involving sniffer techniques (extractive methods coupled with analyser instruments) performed from fixed or moving (e.g., manned and unmanned aircrafts, ships) platforms. Optical remote sensing techniques such as differential optical absorption spectroscopy (DOAS) have also been applied to shipping emission monitoring in the past years.Here we present results of several ship-based campaigns conducted in the last years (in the Mediterranean Sea in 2019 and 2021, and in the English Channel in May 2022), with a focus on the DOAS technique. While the performed DOAS zenith measurements are not fully suitable to conduct a quantitative monitoring of the ship compliance to the FSC regulations, we propose a method to qualitatively identify potential non-compliant ships. Comparisons are made with state-of-the-art sniffer measurements. Despite the larger uncertainty yielded by this technique in comparison to sniffer systems, it may be applied for the guidance of formal controls (e. g., authorities at port).During the English Channel campaign in May 2022, we modified our DOAS setup in order to sequentially scan various elevation angles from the horizon to the zenith (i.e., multi axis DOAS, MAX-DOAS) and, thus, to retrieve vertical tropospheric columns of NO2. Here we compare our shipborne MAX-DOAS NO2 columns to the ones retrieved from TROPOMI (TROPOspheric Monitoring Instrument). TROPOMI could be further involved in the monitoring of shipping emissions as it has been recently used to identify the emission plumes of single (or group of) ships. Therefore, its validation with independent datasets at sea is needed to strengthen the monitoring of shipping emissions.
Global seasonal distribution of CH2Br2 and CHBr3 in the upper troposphere and lower stratosphere
Authors: Jesswein Markus , Fernandez Rafael P. , Berná Lucas , Saiz-Lopez Alfonso , Grooß Jens-Uwe , Hossaini Ryan , Apel Eric C. , Hornbrook Rebecca S. , Atlas Elliot L. , Blake Donald R. , Montzka Stephen , Keber Timo , Schuck Tanja , Wagenhäuser Thomas , Engel Andreas
Published: February 2023

Halogens from long-lived anthropogenic substances contribute to the depletion of stratospheric ozone. Besides these long-lived substances, chlorinated and brominated substances with lifetimes of less than 6 months are additional sources of stratospheric halogens. These substances, also known as very short-lived substances (VSLSs), have both natural and anthropogenic origins. The contribution of chlorinated VSLSs (Cl-VSLSs) to stratospheric chlorine is a few percent. In comparison, brominated VSLSs (Br-VSLS) contribute to about a quarter of the stratospheric bromine. The relative contribution of VSLSs to stratospheric halogen loading is expected to increase as the Montreal Protocol controlled substances progressively decrease. Due to their short lifetimes, VSLSs rapidly release their halogen content into the lowermost stratosphere, a region where changes in ozone have a relatively large impact on surface climate.
Here we present the global seasonal distribution of the two major Br-VSLSs CH2Br2 and CHBr3, which account for about 80 % of total organic Br-VSLS. Measurements from four High Altitude and Long Range Research Aircraft (HALO) missions, the HIAPER Pole-to-Pole Observations (HIPPO) mission, and the Atmospheric Tomography (ATom) mission were used for this purpose. Observational results show a similar seasonality of CH2Br2 in the free and upper troposphere of both hemispheres and less clear seasonality with larger variations for CHBr3. The distribution of CH2Br2 in the lowermost stratosphere suggests differences in hemispheric autumn, where the influx of tropospheric air seen in northern hemispheric summer to autumn is not evident in the Southern Hemisphere. However, the southern hemispheric database is insufficient to quantify this difference. The observed distributions were additionally compared to distributions based on model results of TOMCAT and CAM-Chem, both using the emission inventory of Ordóñez et al. (2012). Neither model was able to reproduce the seasonal distribution of CH2Br2 in the Southern Hemisphere. In contrast, both models show a pronounced seasonality of CHBr3 in both hemispheres, which is not confirmed by observations. The distributions of both substances in the lowermost stratosphere are overall well captured by the models, except for southern hemispheric autumn with considerably lower mixing ratios in the observations.
Tracing anomalies in moisture recycling and transport to two record-breaking droughts over the Mid-to-Lower Reaches of the Yangtze River
Authors: Guan Yansong , Gu Xihui
Published: February 2023

The influence of moisture recycling and transport on major drought events is poorly understood, but essential to enhance our knowledge of the atmospheric water cycle. Here, we investigate this for two record-breaking droughts over the Mid-to-Lower Reaches of the Yangtze River (MLRYR), the winter-spring (WS) drought of 2011 and summer-autumn (SA) drought of 2019. Using a land–atmosphere water balance framework, we find the precipitation recycling ratio (the percentage of precipitation in a region derived from the same region’s evaporation) increased during both droughts, especially for the SA drought (from 14.5% to 22.9%). The WS drought was characterized by a 27.8% reduction in external advected moisture, originating principally from the northeast China and Bohai Sea (reduced by 22.3%) and from the northwest Pacific and South China Sea (25.7%). The SA drought was driven by a 43.8% reduction in external advected moisture, originating mainly from a southwesterly path, i.e. the Bay of Bengal and the South China Sea (reduced by 26.8%). From a regional viewpoint, moisture transportation from the Pacific Ocean (and South China Sea) decreased during the WS (SA) droughts, mainly resulting in moisture deficit over the MLRYR. Analyses reveal that this reduction was driven by strong negative convergence, which was unfavorable for precipitation formation and enhanced air flow out of the MLRYR. The weakened moisture transport was principally driven by seasonal mean flow rather than transient eddies. Changes in wind (i.e. dynamic processes), rather than specific humidity (i.e. thermodynamic processes) were dominant in regulating the seasonal mean moisture transport. Our study helps understand the atmospheric water cycle anomalies driving extreme drought events, and advances knowledge on moisture transportation and its controlling processes.
The global freshwater availability and water use model WaterGAP 2.2e – features, evaluation and application within ISIMIP3
Authors: Müller Schmied Hannes , Rabanizada Ezatullah
Published: February 2023

The availability of freshwater resources is of essential importance for humans, freshwater biota, and ecosystem functions. In this scope, global hydrological models (GHMs) are developed to improve the understanding of the global freshwater situation in a globalized world, by filling gaps in observational coverage and assessing scenarios of the future under consideration of different socioeconomic developments and climate change. The Water Global Assessment and Prognosis (WaterGAP) model calculates water use and availability and is in development since 25 years. It consists of five water use models (for irrigation, domestic, cooling of thermal power plants, manufacturing, and livestock sectors) and the WaterGAP Global Hydrology Model (WGHM). Recently, the latest model version, WaterGAP 2.2e, was finalized, containing a number of enhancements and revisions such as integrating new reservoirs, improving naturalized simulations and updating the calibration data base. Furthermore, WaterGAP2.2e is applied in the Inter-Sectoral Impact Model Intercomparison Project ISIMIP3.This presentation provides an overview of the WaterGAP 2.2e scheme and features, assesses streamflow and total water storage anomalies against reference data, shows water balance components, and provides examples of application within ISIMIP3 with a focus on climate forcing uncertainty and selected indicators of climate change hazards. 
Impact of interplay of perceived environmental and socio-political uncertainties on adaptation decisions
Authors: Höllermann Britta
Published: February 2023

Accelerated climate, environmental and societal change and its dynamics challenge the resilience of complex socio-ecological systems and require constant adaptation. It also requires to better integrate uncertainties into the decision-making process. By comparing two case studies in Tanzania and Germany with different foci in human-water interaction and socio-political backgrounds, patterns of decision-making under uncertainty are identified. Using a (semi)participatory qualitative system analysis approach helps identifying the heterogeneity of actors and their specific ways of reasoning. For example, in the case studies the perception of change and uncertainty differed between the stakeholders and were identified as important drivers for different decision rationales and hence different preferred adaptation strategies. While research in reducing environmental uncertainty through e.g. improved physical understanding and models is important, it is only on side of the equation in complex socio-ecological systems. Especially, the interplay of environmental and socio-economic uncertainty and how this uncertainty loop creates different rooms of action and agency is worth considering. The comparison shows that acknowledging heterogeneity is important across regions and water management issues and supports in developing tailor-made adaptation strategies targeting the environmental issue. Additionally, the approach empowers and enables actors to increase their room of action and adaptation capacity by acknowledging their uncertainty perception.
The role of terrestrial productivity and hydrology in regulating aquatic dissolved organic carbon concentrations in boreal catchments
Authors: Zhu Xudan , Berninger Frank
Published: February 2023

The past decades have witnessed an increase in dissolved organic carbon (DOC) concentrations in the catchments of the Northern Hemisphere. Increasing terrestrial productivity and changing hydrology may be reasons for the increases in DOC concentration. The aim of this study is to investigate the impacts of increased terrestrial productivity and changed hydrology following climate change on DOC concentrations. We tested and quantified the effects of gross primary production (GPP), ecosystem respiration (RE) and discharge on DOC concentrations in boreal catchments over 3 years. As catchment characteristics can regulate the extent of rising DOC concentrations caused by the regional or global environmental changes, we selected four catchments with different sizes (small, medium and large) and landscapes (forest, mire and forest- mire mixed). We applied multiple models: Wavelet coherence analysis detected the delay-effects of terrestrial productivity and discharge on aquatic DOC variations of boreal catchments; thereafter, the distributed- lag linear models quantified the contributions of each factor on DOC variations. Our results showed that the combined impacts of terrestrial productivity and discharge explained 62% of aquatic DOC variations on average across all sites, whereas discharge, gross primary production (GPP) and RE accounted for 26%, 22% and 3%, respectively. The impact of GPP and discharge on DOC changes was directly related to catchment size: GPP dominated DOC fluctuations in small catchments (<1 km2), whereas discharge controlled DOC variations in big catchments (>1 km2). The direction of the relation between GPP and discharge on DOC varied. Increasing RE always made a positive contribution to DOC concentration. This study reveals that climate change-induced terrestrial greening and shifting hydrology change the DOC export from terrestrial to aquatic ecosystems. The work improves our mechanistic understanding of surface water DOC regulation in boreal catchments and confirms the importance of DOC fluxes in regulating ecosystem C budgets.
Hot weather amplifies the urban dry island effect, especially in wetter climates
Authors: Luo Sijia , Gu Xihui
Published: February 2023

Atmospheric humidity is usually drier in cities than the surrounding rural areas, a phenomenon known as the urban dry island (UDI) effect. However, the response of atmospheric humidity to hot weather in urban versus rural settings remains unknown. Using long-term summer (June-August) observations at 1658 stations over 1961-2020, we find that China is dominated by drying trends in atmospheric humidity (i.e., increasing vapor pressure deficit [VPD]). These drying trends are aggravated on hot days and amplified by urbanization, i.e., the UDI effect is stronger in hot weather. This amplification of the UDI effect on hot days is more prominent in humid than in arid regions. Attributions show that the stronger VPD-based UDI effect on hot days is explained by increased contribution of air temperature in southeastern China, and specific humidity in North China. We suggest that adaptations are required to mitigate adverse combined effects of urban heatwaves and UDIs.
Arctic extreme winter warming events lead to microbial N immobilization and evergreen shrub N limitation
Authors: Rasmussen Laura Helene , Danielsen Birgitte Kortegaard , Elberling Bo , Kurczy Michael , Ranjbari Elias , Andresen Louise
Published: February 2023

In Arctic soils, wintertime usually means subzero ground temperatures and only little unfrozen water available below a snow cover. While this period has less active nutrient cycling by microbes, some activity means that winter mineralization of e.g., nitrogen (N) can release a pulse of mineral N (ammonium, nitrate) into the soil solution, which can become biological available upon spring thaw. In springtime, plants may compete with microbes for the N pulse, but if thaw happens during winter, the N pulse could be immobilized by active microbes, which can decrease the size of the springtime N pulse, and therefore decrease the growing season N addition to the ecosystem.Many parts of the Arctic have with climate change seen an increase in the frequency of extreme winter warming events (WW events), which are periods of positive temperatures lasting 5-7 days and causing snow to melt and the upper soil layer to thaw. In a field scale experiment, we quantified the amount of mineral N released into solution upon soil thaw during a simulated WW event in Disko island, Western Greenland (69.28ᵒN, 53.48ᵒW). We used 15N tracing to determine which parts of the ecosystem that benefited from this N during the WW event. We further returned the following summer to test whether vegetation was more N limited the summer after a WW event.Our results show that after 6 days of thaw, 50-60 % of WW-released N was found either in active microbial biomass or stored in the soil, whereas none had been assimilated by the plants. The following summer, we saw that evergreen shrubs subject to the WW event had acquired less N than if they had experienced a stable winter. This indicates that evergreen shrubs are especially sensitive to a smaller spring N pulse, which is in line with studies showing that evergreen shrubs rely more on springtime N uptake. As evergreen shrubs are an important functional plant type in the tundra, increased frequency of WW events could therefore change tundra plant community composition. Our results also indicate that N immobilization during WW events could be a mechanism linking WW events to Arctic browning and decrease in photosynthetic C uptake rates.Our research sheds light on the little studied impact of climate change-related WW events on the nutrient cycling of Arctic soils and the plant-root competition for N in the future, and we develop methods for studying this phenomenon in the broader Arctic.
Geostatistical estimates of groundwater nitrate-N with spatial auxiliary information on DRASTIC-LU-based aquifer vulnerability
Authors: Jang Cheng-Shin
Published: February 2023

Groundwater nitrate-N contamination typically involves several natural and anthropogenic factors, such as hydrology, hydrogeology, topography, and land uses. DRASTIC-LU-based aquifer vulnerability can be adopted to explore pollution potentials of groundwater nitrate-N. Furthermore, groundwater nitrate-N pollution frequently has high levels of spatial variability because of various pollution sources and hydrogeological and hydrochemical conditions. Estimates are typically uncertain owing to limited in-situ data. Geostatistics is a commonly used technique of spatial estimates with limited data. To reduce the underestimation and overestimation of ordinary kriging (OK), this study employed regression kriging (RK) with environmental auxiliary information on DRASTIC-LU-based aquifer vulnerability to characterize groundwater nitrate-N pollution in the Pingtung Plain, Taiwan. First, the relationship between groundwater nitrate-N pollution and aquifer vulnerability assessment was determined using stepwise multivariate linear regression (MLR). Then, simple kriging was adopted to estimate residuals acquired from gaps between nitrate-N observations and MLR predictions. The sum of the estimated residuals and MLR predictions was the RK estimates for groundwater nitrate-N. Finally, groundwater nitrate-N distributions were spatially analyzed using RK, OK, and MLR. To reduce groundwater nitrate-N pollution, feasible environmental management strategies were discussed according to the study results. The study results revealed that the orchard land-use types and medium- and coarse-sand fractions of vadose zone were related to groundwater nitrate-N. Moreover, the fertilizer application in orchards was the major source of groundwater nitrate-N pollution. The RK estimates could characterize the characteristics of the pollution source of the orchard land uses, and exhibited higher spatial variability and accuracy via the correction of the residuals than MLR predictions and OK estimates. In addition, feasible management strategies of orchards at the eastern and western regions with high areal ratios of orchard land uses should be implemented to reduce nitrate-N leaching, such as organic fertilizer uses, ground covers, and irrigation with low intensity and high frequency.
Exploring the sensitivity of mineral dust aging to parameters of aerosol size distribution in the ICON-ART model
Authors: Octaviani Mega , Tian Rong , Hoshyaripour Gholamali , Rhunke Roland , Kirner Oliver , Scharun Christian , Klose Martina
Published: February 2023

Mineral dust is known to play an important role in weather and climate through its interactions with clouds, radiation, and nutrient cycles. Dust aerosols are emitted as water-insoluble particles which experience chemical aging (conversion to water-soluble mixtures) through the accumulation of soluble materials like sulfate and nitrate. This aging process affects the chemical composition and size distribution of the dust particles as well as their optical properties. Within the context of the dust aging mechanism, different approaches are applied in atmospheric models regarding the representation of the aerosol size distribution (bin or modal representation) and the number of microphysical processes included. The ICOsahedral Nonhydrostatic model with Aerosols and Reactive Trace gases (ICON-ART) and the new AERODYN aerosol dynamic module consider the nucleation and condensation of sulfuric acid gas, coagulation and aging of aerosols, size-dependent wet and dry deposition, and sedimentation. The aerosol size distribution in the model is represented by eight unimodal lognormal distributions (also called modes) with constant width. These modes describe four different size groups, two in the submicron range (typically <1 μm) and two in the coarse range (>1 μm), and two hygroscopic classes in a homogeneous or core-shell mixture (insoluble, soluble, and mixed). This approach is a common technique in global aerosol simulations yet implies simplifications of complex aerosol size distributions. It may cause uncertainties in simulating the aging processes of dust aerosols and inaccuracies in representing their observed size distributions. We conduct global simulations using ICON-ART to analyze the sensitivity of simulated dust to parameters representing properties of the modes, namely initial geometric median diameter and standard deviations, and threshold diameters for shifting between modes. We also aim to explore the impact of the mineral dust aging process on the range of dust direct radiative feedback.  This study will show the importance of aerosol size distribution parameter combinations for representing the chemical aging of mineral dust and its climate impacts.
Hotspots and impacts of present and future compound hot and dry summers in Europe
Authors: Böhnisch Andrea , Felsche Elizaveta , Mittermeier Magdalena , Poschlod Benjamin , Ludwig Ralf
Published: February 2023

Compound hot and dry events (such as recent summers of 2015, 2018 and 2022 in Europe) have an impact on a wide range of sectors, including health, transport, energy production, ecology, agriculture and forestry. The co-occurrence of extreme heat and drought poses a risk to water security in particular, since heat exacerbates moisture shortages during dry periods through increased evapotranspiration while at the same time water demand increases (e.g., for drinking water, cooling, irrigation). Current research suggests that climate change will increase the intensity, frequency, and duration of joint hot and dry extreme events in Europe. However, most studies focus on the drivers applying coarse-resolution global climate models.This study exploits a 50-member single-model initial condition large ensemble (SMILE) of the Canadian Regional Climate Model, version 5, at 12 km resolution (CRCM5-LE, RCP 8.5 from 2006 onwards, driven by the Canadian Earth System Model Version 2 large ensemble, CanESM2-LE). The application of a regional SMILE provides an extensive database of compound events and, subsequently, robust estimations of their occurrence changes across Europe, from current to future states and in high geographical detail.We define compound hot and dry summers based on joint exceedances of temperature and (negative) precipitation thresholds (2001-2020 JJA 95th percentiles). By considering low soil moisture (below regional 2001-2020 JJA 10th percentile) as an impact indicator, we further show the spatially varying connection between compound hot and dry summers and low water availability in Europe. Compound event occurrences are investigated in a current climate (2001-2020) and future 20-year slices at global warming levels (GWL, derived from the CanESM2-LE) of +2 °C and +3 °C, with each period represented by 1000 model years. Last, we investigate the underlying processes (e.g., heat budget terms) of changing event occurrences and their spatial distribution, and discuss the land use-specific (e.g., urban, agricultural, natural) exposure to impacts on water availability during compound hot and dry summers.We identify areas in the Mediterranean and northern France as hotspots with a fivefold occurrence frequency of compound hot and dry summers for +2 °C GWL. With +3 °C GWL, the Mediterranean, France, Belgium, southern Germany, Switzerland, and the south of UK and Ireland are affected by a tenfold occurrence frequency with respect to current climate.This study is an important boundary condition to the development of adaptation strategies for the affected regions.  At the same time, it quantifies the reduction of event occurrence in a +2°C world compared to the higher GWL of +3°C, highlighting the importance of climate mitigation strategies and policies.
Double resonance before earthquakes
Authors: Chen Chieh-Hung , Lin Kai , Zhang Xuemin , Gao Yongxin
Published: February 2023

An instrumental array was established in southwest China for Monitoring Vibrations and Perturbations in the Lithosphere, Atmosphere and Ionosphere (MVP-LAI).  We retrieved multiple-geophysical data from the array to investigate common characteristics in LAI before earthquakes.  Broadband seismometers are utilized to monitor ground vibrations in the lithosphere.  Barometers record changes in air pressure near the Earth’s surface.  Magnetometers monitor variations in the ionospheric currents ~100 km above the Earth’s surface.  Instead of GPSTEC (Global Positioning System Total Electron Content), electromagnetic signals transmitted from the BDS (BeiDou navigation system) geostationary satellites are received by ground-based GNSS (Global Navigation Satellite System) receivers to compute TEC data.  The BDSTEC from the geostationary satellites continuously monitor changes in TECs ~350 km in altitude right over the array.  We transferred these data into the frequency domain and found that ground vibrations, air pressure, the magnetic field, and BDSTEC data share the frequency ~5×10-3 Hz before major earthquakes.  Ground vibrations exhibit frequency characteristics of ~5×10-3 Hz due to resonance of nature frequencies before failure of materials (i.e., dislocations of faults, and earthquakes).  Ground vibrations with frequency of ~5×10-3 Hz persistently hit the bottom of the atmosphere that can trigger atmospheric resonance before earthquakes.  Double resonance (i.e., crustal and atmospheric resonance) provides the new way to reveal the seismo-anomalies of multiple geophysical parameters in LAI.  Double resonance would shed a light in earthquake prediction in practice once we face the major issue for efficiently retrieving resonance signals from multiple observation data.  
Constraints on the IBEX Ribbon's Origin from its Evolution over a Solar Cycle
Authors: Zirnstein Eric , Swaczyna Pawel , Dayeh Maher , Heerikhuisen Jacob
Published: February 2023

The heliosphere surrounding our solar system is formed by the interaction between the solar wind and the local interstellar medium as the Sun moves through interstellar space. With dimensions on the order of hundreds to potentially thousands of au, it is difficult to determine the 3D structure of the heliosphere and the properties of the plasma surrounding it. However, observations of energetic neutral atoms (ENAs), which are created as a product of charge exchange between interstellar neutrals and energetic plasma ions, allow us to remotely discern the properties of the distant heliospheric boundaries.NASA's Interstellar Boundary Explorer (IBEX) mission, a small explorer spacecraft which has been measuring ENA fluxes at ~0.5-6 keV for more than a solar cycle, discovered a “ribbon” of enhanced ENA fluxes forming a narrow, circular band across the sky. While it is generally believed that the ribbon is formed from secondary ENAs from outside the heliopause, a source of ENAs that is separate from the globally distributed flux (GDF) across the sky, it is not clear exactly how the parent ions outside the heliopause evolve over time before they become ribbon ENAs. To help solve this issue, we present recent developments in modeling the evolution of the ribbon over a solar cycle, under different pitch angle scattering assumptions. We hypothesize that simulating the evolution of the ribbon under differing scattering rates may help discern the physical mechanisms responsible for creating the ribbon observed by IBEX. We compare our modeling results to IBEX data where the ribbon was separated from the GDF using spherical harmonic decomposition, analyzing the evolution of the ribbon’s intensity and geometry as a function of ENA energy.
The Evolution of the Snow Facies on the Greenland Ice Sheet Observed by the Last Decade of TanDEM-X Interferometric SAR Data
Authors: Becker Campos Alexandre , Rizzoli Paola , Gonzalez Carolina , Bueso-Bello José-Luis , Braun Matthias
Published: February 2023

Climate change and the resulting accelerating melt on the Greenland and Antarctic ice sheets are causing dramatic and irreversible changes at a global scale, significantly contributing to sea-level rise. In this scenario, monitoring the evolution of diagenetic snow facies can provide valuable insights to better comprehend climate-related variables and trends. Previous studies of the Greenland ice sheet led to the definition of four main snow facies, depending on the amount of snow melt and on the properties of the snow pack itself: the inner dry snow zone, where melt does not occur; the percolation zone, where a limited amount of melt per year occurs, leading to the generation of larger snow grains and the formation of small ice structures; the wet snow zone, where a substantial part of the snow melt drains off during summer and is characterized by the presence of multiple ice layers; and the outer ablation zone, where the previous year accumulation completely melts during summer, resulting in a surface of bare ice and surface moraine. By exploiting X-band TanDEM-X interferometric synthetic aperture radar (InSAR) acquisitions, previous works explored the idea of classifying different snow facies of the Greenland ice sheet utilizing an unsupervised machine learning clustering approach. The analysis was performed using data acquired in winter 2010/2011 only, under the assumption of stable climatic conditions and similar acquisition geometries. In this paper, we further investigate the evolution of the snow facies of Greenland throughout the last decade of TanDEM-X observations, proposing unsupervised machine learning strategies for snow facies characterization by using InSAR features such as backscatter, volume decorrelation, the incidence angle and height of ambiguity. We use TanDEM-X data acquired during the winter of 2010/2011, 2015/2016, 2016/2017, 2020/2021, and 2021/2022, where full or partial coverage of the Greenland ice sheet is available. The challenges and caveats of such approaches for different image acquisition geometries will be presented. Finally, the potential of TanDEM-X for investigating large-scale interannual changes in the dry snow zone over Greenland will be investigated as well.  