Marine Cold Air Outbreaks (MCAOs) have a profound influence on atmospheric conditions and the surface-atmosphere heat exchange in Fram Strait and Svalbard. Comparing the global reanalysis ERA5 to its novel Arctic counterpart CARRA for November-March 1991-2020, we investigate the surface turbulent heat fluxes and the spatial characteristics of MCAOs throughout the troposphere. We find that the sensible heat flux from the surface to the atmosphere is substantially higher in CARRA, while the latent heat flux is higher in ERA5. For sensible heat flux, the differences scale with the magnitude, leading to maximum disagreement over the ice-free ocean where the flux is high. Accounting for the varying magnitude over different surface types, we find the largest relative disagreement over sea ice. During MCAOs, negative anomalies in temperature and specific humidity are present throughout the entire troposphere in both reanalyses. Meanwhile, positive heat flux anomalies are found in northwestern Fram Strait, where the sensible heat flux from the ocean to the atmosphere is roughly doubled during MCAOs. Around much of Svalbard, sea ice decline has caused positive trends in the surface-atmosphere potential temperature difference forming the basis of the MCAO index, leading to higher heat fluxes. In Fram Strait however, both reanalyses show negative trends in the MCAO index and the heat fluxes in January, when the increase in potential temperature is larger at 850 hPa than at the surface.
A major tool for curtailing the spread of COVID-19 pandemic in China was a nationwide lockdown, which led to significant reductions in anthropogenic emissions and fine particulate matter (PM2.5). However, the lockdown measures did not prevent high PM2.5 pollution episodes (EPs). Three severe EPs were identified in the Beijing-Tianjin-Hebei (BTH) region during the lockdown. The integrated process rate (IPR) analysis tool in the Community Multiscale Air Quality (CMAQ) model was employed to quantify the contributions of individual atmospheric processes to PM2.5 formation during the lockdown in the BTH region. The IPR results showed that emissions and aerosol processes were the dominant sources of net surface PM2.5 in Beijing and Tianjin, constituting a total of 86.2% and 92.9%, respectively, while emissions, horizontal transport, and aerosol processes dominated the net surface PM2.5 in Shijiazhuang and Baoding. In addition, the EPs in Beijing and Tianjin were primarily driven by local emissions, while the EPs in Shijiazhuang and Baoding were attributed to combined local emissions and regional transport. The reductions in PM2.5 in Case 2 relative to Case 1 were attributed to the weaker PM2.5 formation from emissions and aerosol processes. However, the EPs were enhanced by low planetary boundary layer heights, low vertical export of PM2.5 from the boundary layer to the free troposphere, and substantial horizontal import, especially in Shijiazhuang and Baoding. This study improves the understanding of buildup of PM2.5 during the EPs, and the results provide insights for designing more effective emissions control strategies to mitigate future PM2.5 episodes.
Key Points: 10 • Ice flowing over a rough basal topography may spontaneously develop an inter-11 nal shear band on topographical highs. 12 • The shear strain rate localization and shear heating in the internal shear band is 13 amplified by a non-linear rheology. 14 • We identify two competing mechanisms that affect the energy balance near the 15 bedrock: vertical advective cooling and internal shear heating. Abstract 17 The dramatic acceleration of ice surface speed from upstream to downstream is a no-18 ticeable feature in many ice streams and glaciers. This speed-up is thought to be asso-19 ciated with a transition from internal, distributed deformation to highly localized defor-20 mation at the ice-bedrock interface, but the physical processes governing this transition 21 remain unclear. Here, we argue that basal topography amplifies the feedback between 22 shear heating and localization, leading to the spontaneous formation of an internal shear 23 band for a non-linear rheology. We model the thermo-mechanical ice flow over a simpli-24 fied basal topography using a high-resolution Stokes solver. To capture the interactions 25 between ice and rock, we implement an Immersed Boundary Method and use a level-set 26 approach to represent the free surface of the ice. Our results suggest that an internal shear 27 band can form on topographical highs, continuously heating the basal ice and may grad-28 ually enable a transition to basal sliding. This effect depends sensitively on rheology, with 29 the composite rheology by Goldsby and Kohlstedt (2001) amplifying shear heating no-30 tably. 31 Plain Language Summary 32 On its way towards the ocean, ice speeds up dramatically from less than one me-33 ter per year inland to up to a kilometer per year downstream. In this paper, we inves-34 tigate the physical processes controlling this speed-up. More specifically, we focus on the 35 role that the bedrock topography underneath the ice might play to facilitate this tran-36 sition. We use a two-dimensional numerical model to simulate the temperature distri-37 bution and deformation within a slab of ice flowing down a ramp over a simplified to-38 pography. We find that including basal topography could lead to the development of in-39 ternal shear band located on top of topographical highs. Around half of the total shear 40 deformation within the ice occurs within this band. We compare our model results to 41 borehole measurements from Greenland and find evidence that supports the existence 42 of a shear band. 43
Efthymios Balomenos1, Panagiotis Davris1, Dimitrios Panias1, Ioannis Paspaliaris1Laboratory of Metallurgy, National Technical University of Athens, Zografos Campus, GreeceEmail: firstname.lastname@example.orgBauxite Residue‘Bauxite Residue’ (BR) refers to the insoluble solid material, generated during the extraction of alumina (Al2O3) from Bauxite ore using the Bayer process. When bauxite ore is treated with caustic soda, the aluminium hydroxides/oxides contained within, are solubilized, with approximately 50% of the bauxite mass being transferred to the liquid phase, while the remaining solid fraction constitutes the -bauxite- residue.Active lime is usually added during digestion to control and reduce caustic soda and alumina losses from the formation of desilication products.. The solid-liquid separation after ore digestion takes place in thickeners and washers, resulting in the formation of a red-colored bauxite residue slurry (approx. 50% solids) which was previously termed ‘red mud’. Nowadays many plants use, as a final step of slurry treatment, high pressure filtration (the most efficient method of alkali recovery), in which the bauxite residue slurry is pressed to remove the maximum of remaining liquor and produce a compact filtercake with a relative humidity of 25-30%.It is estimated that for each ton of alumina produced 1.0- 1.5 tons of solid residue (on a dry basis) is generated depending on the initial bauxite ore grade and alumina extraction efficiency (Evans 2016). Bauxite residue consists of of various metal oxides of Fe, Al, Ti, Si, Ca, Na, V, Ga (depending on the initial chemical composition of the bauxite ore) along with inclusions of unwashed sodium aluminate solution.As the global demand for primary aluminium metal increases so will the BR production, currently in excess of 150 million tons per year worldwide (Power et al. 2011). This is generated at more than 100 active alumina refining plants worldwide. In addition, there are at least another 50 closed legacy sites, so the combined stockpile of bauxite residue at active and legacy sites is estimated at three thousand million tons. ( World Aluminium and the European Aluminium Association, 2015)The primary aluminium industry has always focused on discovering potential applications for BR utilization. The vast amount of research and studies on BR utilisation is justified by more than 734 patents since 1964. Possible applications can broadly be broken down into various categories, such as cement and building materials production, iron production, trace element (Ga, REE, V,etc.) recovery, use as soil amelioration, landfill capping, acid mine drainage treatment and others (Evans 2016). The recent REE crisis fueled significant research effort in recovering the REE that are found in some BRs in concentrations between 1 - 2 kg of total REE / t of BR. Given the large quantity of the annual BR production, the total amount of contained REE becomes significant and could cover part of the global REE demand (Balomenos et al., 2017a). Furthermore, while the treatment of BR for the recovery of REEs does not solve the BR deposition problem, as the volume of the waste remains practically unaffected, it does help in the economic viability of holistic processing flowsheet seeking to achieve near zero-waste through multiple processing steps (Balomenos et al., 2017b).Rare Earths in Bauxite ResidueThe bauxite ore is one of the factors that affect the concentration of REE in bauxite Residue. Bauxites are classified in three categories, lateritic bauxites (88%), karstic bauxites (11,5%) and Tikhvin type bauxites (0,5%) (Bardossy, 1982; Bárdossy and Aleva, 1990). Karstic bauxites are mainly found in Europe, Jamaica, Russia and China. The karstic bauxites contain higher concentrations of REE than the lateritic bauxites. REE are detected in bauxite ore as fluorcarbonate or phosphate minerals which are very similar to the main industrial minerals of REE (bastnaesite - monazite) (Li et al., 2013; Mouchos et al., 2017; Ochsenkühn-Petropulu 1995; Vind et al., 2018a). It has also been reported that in the Bayer process REE end up in the BR in 2:1 ratio, compared to the initial bauxite ore. (Derevyankin et al., 1981; Ochsenkühn-Petropulu et al., 1994; Wagh and Pinnock, 1987).The worldwide typical concentration of REE in BR is 800-2500 mg/kg and is related to the initial bauxite ore and the operating conditions of the Bayer process (Deady et al., 2018). Recent research shows that REE in BR can be found in secondary mineral phases produced by the Bayer process, known as the desilication product (DSP). DSP is the result of the silicon removal from the aluminate solution during the leaching of the bauxite ore, as silicon is major pollutant for the final alumina product. Presence of REE in the DSP can be attributed to REE from the bauxite ore being dissolved in the Bayer process; these REE are incorporated into the newly formed DSP mineral matrix that contains a mixture of Fe, Ti, Si, Al Ca and Na ions (Vind et al., 2018a).Scandium (Sc) often differs from the other REE behavior. Especially in lateritic bauxites and their corresponding BR, it is often correlated with iron and titanium and zircon minerals (Vind et al., 2018a) (Liu et al., 2018; Zhang et al., 2017), which for the most part are unaffected by the Bayer process. This is also confirmed by the laterite deposits in Australia and the Greek BR (Chassé et al., 2016) where the main mineral, with high concentration of Sc is goethite (Vind et al., 2018b). However, there are cases of BR ,where Sc is found to be related to larger extent to the soluble Al-bearing minerals, as is reported by Russian researchers (Suss et al., 2018).Published chemical analysis and leaching studies of bauxite residue focus on the concentration of Sc, because Sc represents 95% of REE’s financial values found in BR (case of Greek Bauxite, reported by Ochsenkühn-Petropoulou et al., 2002). Table 1 presents the Sc concentration in different Bauxite Residues worldwide as reported in literature.Table 1 Concentration of Scandium in Different Bauxite Residues
Mesoscale eddies are found throughout the global ocean. Generally, they are referred to as “coherent” structures because they are organized rotating fluid elements that propagate within the ocean and have a long lifetime. Since in situ observations of the ocean are very rare, eddies have been characterized primarily from satellite observations or by relatively idealized approaches of geophysical fluid dynamics. Satellite observations provide access to only a limited number of surface features and exclusively for structures with a fingerprint on surface properties. Observations of the vertical sections of ocean eddies are rare. Therefore, important eddy properties, such as eddy transports or the characterization of eddy “coherence”, have typically been approximated by simple assumptions or by applying various criteria based on their velocity field or thermohaline properties. In this study, which is based on high-resolution in-situ data collection from the EUREC4A-OA field experiment, we show that Ertel potential vorticity is very appropriate to accurately identify the eddy core and its boundaries. This study provides evidence that the eddy boundaries are relatively intense and intimately related to both the presence of a different water mass in the eddy core from the background and to the isopycnal steepening caused by the volume of the eddy. We also provide a theoretical framework to examine their orders of magnitude and define an upper bound for the proposed definition of the eddy boundary. The results suggest that the eddy boundary is not a well-defined material boundary but rather a frontal region subject to instabilities.
To aid California's water sector to better manage future climate extremes, we present a method for creating a regional ensemble of plausible daily future climate and streamflow scenarios that represent natural climate variability captured in a network of tree-ring chronologies, and then embed anthropogenic climate change trends within those scenarios. We use 600 years of paleo-reconstructed weather regimes to force a stochastic weather generator, which we develop for five subbasins in the San Joaquin River in the Central Valley region of California. To assess the compound effects of climate change, we create temperature series that reflect scenarios of warming and precipitation series that are scaled to reflect thermodynamically driven shifts in the daily precipitation distribution. We then use these weather scenarios to force hydrologic models for each of the San Joaquin subbasins. The paleo-forced streamflow scenarios highlight periods in the region's past that produce flood and drought extremes that surpass those in the modern record and exhibit large non-stationarity through the reconstruction. Variance decomposition is employed to characterize the contribution of natural variability and climate change to variability in decision-relevant metrics related to floods and drought. Our results show that a large portion of variability in individual subbasin and spatially compounding extreme events can be attributed to natural variability, but that anthropogenic climate changes become more influential at longer planning horizons. The joint importance of climate change and natural variability in shaping extreme floods and droughts is critical to resilient water systems planning and management in the Central Valley region.
Little is known about Antarctic subglacial hydrology, but based on modeling, theory and indirect observations it is thought that subglacial runoff enhances submarine melt locally through buoyancy effects. However, no studies to date have examined effects of runoff on sea ice and circulation on the continental shelf. Here we use modeled and observational estimates of runoff to force a regional model of the Amundsen Sea Embayment. We find that runoff enhances melt locally (i.e. within the ice-shelf cavity), increasing melt at Thwaites ice shelf by up to 15 Gt/a given estimates of steady runoff, and up to 25 Gt/a if runoff is episodic as remote sensing measurements suggest. However runoff also has smaller nonlocal effects through freshwater influence on flow and stratification. We further find that runoff reduces summer sea-ice volume over the continental shelf (by up to 10\% with steady runoff but over 30\% with episodic runoff). Furthermore runoff is much more effective at reducing sea ice than an equivalent volume of ice-shelf meltwater – due in part to the latent heat loss associated with submarine melting. Results suggest that runoff may play an important role in continental shelf dynamics, despite runoff flux being small relative to ice-shelf melting – and that runoff-driven melt and circulation may be an important process missing from regional Antarctic ocean models.
Rising temperatures amplify biogenic volatile organic compound (VOC) emissions from arctic vegetation, causing feedbacks to the climate system. Changes in climate also alter plant physiology and vegetation composition, all of which can influence VOC emissions. Moreover, leaf development and biotic stresses cause highly variable emissions during the growing season. Therefore, linking VOC emissions with plant traits and tracking responses to climate change might provide better understanding of VOC emission regulation under future conditions. We measured VOC emissions and other plant traits in dwarf birch (Betula glandulosa) at two elevations in Narsarsuaq, South Greenland. The measurements were performed in warming experiments that have run since 2016. We collected VOCs using the branch enclosure method from early June until late July 2019 (n = 200). Emissions of green leaf volatiles (GLVs), oxygenated monoterpenes (oMTs), and homoterpenes followed a seasonal trend. VOC emission rates and the diversity of the VOC blend decreased at the end of the measurement period. Differences in VOC emission rates between elevations were most pronounced early in the season. Most traits did not explain the variation in VOC emissions. We show strong seasonal variability in VOC emissions within the growing season, which are likely driven by leaf phenology. While the diversity of VOCs was greater at the milder low-elevation site, VOC emission rates were higher or similar at the harsher high-elevation site, showing stronger VOC emission potentials than previously assumed. Seasonal variations in the VOCs are crucial for accurate predictions of current and future VOC emissions from arctic ecosystems.
California's arid Central Valley relies on groundwater pumped from deep aquifers and surface water transported from the Sierra Nevada to produce a quarter of the United States' food demand. The natural recharge to deep aquifers is thought to be regulated by the adjacent high Sierra Nevada mountains, but the underlying mechanisms remain elusive. We investigate large sets of geodetic remote sensing, hydrologic, and climate data and employ process-based models at annual time scales to investigate possible recharge mechanism. Peak annual groundwater storage in the Central Valley lags several months behind that of groundwater levels, which suggests a longer transmission time for water flow than pressure propagation. We further find that peak groundwater levels lag the Sierra Nevada snowmelt by about one month, consistent with an ideal fluid pressure diffusion time in the Sierra's fractured crystalline body. This suggests that Sierra Nevada snowpack changes likely impact freshwater availability in the Central Valley aquifers. Our datasets, analysis and process-based models link the current precipitation and meltwater in the high mountain Sierra to deep Central Valley aquifers through the mountain block recharge process. We call for new hydroclimate models to account for the role of the Sierra in California's water cycle and for revision of the current management and drought resiliency plans.
Urban water utilities are increasingly exploring cooperative regional water supply investment and management strategies due to climate change and growing demands. Theoretically, regional cooperative agreements promise improved resource efficiency by realizing economies of scale, adding flexibility for achieving improved supply reliability, and, ideally, limiting individual and collective financial risks. However, there has been little research exploring how implementation uncertainties in the partners’ cooperative actions shape infrastructure investment and management pathways’ robustness and drive counterparty risks. Counterparty risks potentially exacerbate collaborating partners’ vulnerability to the supply and financial challenges they initially sought to mitigate through cooperation. To address these concerns, we introduce the Safe Operating Spaces for Deeply Uncertain Water Supply Pathways (DUSOS Pathways) framework. The framework, demonstrated on the multi-city Sedento Valley benchmarking test case, facilitates the formal characterization of the effects of implementation uncertainty within cooperative regional water supply investment and management policy pathways. Results demonstrate the path-dependent effects of implementation uncertainties in short-term operational drought mitigation instruments and long-term infrastructure investments. Our analysis further reveals the potential for increased regional conflict due to asymmetries between partners’ vulnerabilities to the actions of cooperating partners that can be exacerbated by other deeply uncertain factors that reduce their robustness (e.g., demand growth rates). The study finally delineates safe operating spaces, beyond which utilities experience robustness degradation and increased vulnerabilities to future uncertainties to guide implementation of cooperative policy pathways. Overall, this framework is broadly applicable to regional systems seeking to navigate complex cooperative regional water supply investment and management policy pathways.
Long-term seismicity is an effective tool to infer fault properties at depth, but the catalog construction is challenging because of the large data volume. We propose a new deep learning-based workflow that follows a “Train-Detect-Pick” procedure, which solves the generalization problem in AI pickers. We apply the new workflow on the preseismic phase (2008-2019) of Ridgecrest-Coso region. Results show that the new workflow realizes efficient and stable detection, and well substitutes matched filter. Our new catalog helps characterize the preseismic fault behavior: (1) the Ridgecrest area has a distributed deformation, and the 2019-ruptured segment has a persistent asperity; (2) the central Garlock fault is unfavorable for rupture propagation, because of its discontinuous geometry and low coupling ratio; (3) the Coso geothermal field generates intense and shallow seismicity, which has a high b-value that does not correlate with seismicity rate and industrial production, thus suggest a low stress level.
The inversion of remote sensing signatures of internal solitary waves (ISWs) can retrieve dynamic characteristics in the ocean interior. The ubiquitous large-amplitude ISWs limit the weakly nonlinear methods commonly used to retrieve wave parameters. We establish the relationship between surface features and internal characteristics of ISWs in laboratory experiments through the correspondence of the remote sensing signatures and the surface velocities of ISWs. The results show that the strong nonlinearity makes the solution of wave-induced velocity inseparable, and ISW theories under the weakly nonlinear assumption are inappropriate to describe strongly nonlinear ISWs from the surface. Therefore, the fully nonlinear model Dubreil–Jacotin–Long equation is used in the retrievals and has been well verified in both the laboratory and oceans. Mooring observations and the model show that stratification conditions differentiate the relationship between remote sensing signatures and ISW parameters in deep and shallow seas.
We examine the role of aerosol hygroscopicity (κ) affects clouds and precipitation formation over the Western Ghats (WG) in India using various numerical model simulations (i.e., particle-by-particle based small-scale, high resolution mesoscale model). For the diffusional growth of cloud droplets, the size dependent hygroscopicity is used in κ- Köhler equation of direct numerical simulation. The results of the small-scale model reveal that the distribution of cloud drop size varies from the initial mixing state to well mix state due to variation in κ. The value of κ is obtained from HTDMA instruments at High Altitude Cloud Physics Laboratory, India. The idealized and real simulations using WRF model with aerosol-aware Thompson microphysics scheme are conducted by changing κ values. Depending on the type of clouds (shallow or deep), different κ values determine the mass, number and precipitation of cloud and rain droplets. Low hygroscopicity (organics) simulates more and smaller drops, as well as uplifts below freezing level, resulting in more ice phase hydrometeors. Organic aerosols have a significant impact on the formation of more snow and graupel hydrometeors. As compared to high κ, low hygroscopicity weakens updrafts at the intermediate level and strengthens them at the upper level in the deep cloud region. The intensity of precipitation varies due to low and high κ. The findings indicate that aerosol composition has a significant impact on the activation of cloud condensation nuclei. This study suggests that aerosol hygroscopicity is essential in weather prediction models in order to integrate aerosol chemical compositions.
We compare the radiative feedbacks resulting from a uniform warming and cooling of sea surface temperatures by 4 K in an ensemble of global climate models. The global-mean net feedback is less stabilising in response to warming in all nine models. This is primarily due to a stronger tropical water vapour feedback, with a smaller contribution from the shortwave cloud feedback. The zonal-mean feedbacks are similarly robust across the ensemble. In the extra-tropics, more positive shortwave cloud feedback under warming is associated with further poleward migration of the mean Southern Hemisphere jet latitude in some models. However, additional experiments with an aquaplanet version of the HadGEM3 model suggest that the asymmetry of the jet shift is not driving that in the cloud feedbacks at these latitudes. In the tropics, stronger water vapour feedback under warming is offset by a weaker shortwave cloud feedback. The result is that the ensemble spread in the differences between the global feedbacks under warming and cooling is mainly determined by their differences in the tropics. The spatial distribution of the feedbacks largely reflects the zonal mean behaviour, although there is considerable intermodel variation in the regional cloud feedbacks, particularly in the tropical shortwave cloud feedback. Comparison with CO2- and solar-forced coupled experiments suggests that the global-mean longwave cloud feedback is nearly invariant to warming and cooling, regardless of the nature of the forcing. The shortwave cloud feedback is generally more positive under warming in the coupled models, consistent with the uniform SST perturbation experiments.