Controls on pristine aerosol over the Southern Ocean (SO) are critical for constraining the strength of global aerosol indirect forcing. Observations of summertime SO clouds and aerosols in synoptically varied conditions during the 2018 SOCRATES aircraft campaign reveal novel mechanisms influencing pristine aerosol-cloud interactions. The SO free troposphere (3-6 km) is characterized by widespread, frequent new particle formation events contributing to much larger concentrations (≥ 1000 mg-1) of condensation nuclei (diameters > 0.01 μm) than in typical sub-tropical regions. Synoptic-scale uplift in warm conveyor belts and sub-polar vortices lifts marine biogenic sulfur-containing gases to free-tropospheric environments favorable for generating Aitken-mode aerosol particles (0.01-0.1 μm). Free-tropospheric Aitken particles subside into the boundary layer, where they grow in size to dominate the sulfur-based cloud condensation nuclei (CCN) driving SO cloud droplet number concentrations (Nd ~ 60-100 cm-3). Evidence is presented for a hypothesized Aitken-buffering mechanism which maintains persistently high summertime SO Nd against precipitation removal through CCN replenishment from activation and growth of boundary layer Aitken particles. Nudged hindcasts from the Community Atmosphere Model (CAM6) are found to underpredict Aitken and accumulation mode aerosols and Nd, impacting summertime cloud brightness and aerosol-cloud interactions and indicating incomplete representations of aerosol mechanisms associated with ocean biology.

Solute transit or travel time distributions (TTDs) in catchments are relevant to both hydrochemical response and inference of hydrologic mechanisms. Long-tailed TTDs and fractal scaling behavior of stream concentration power spectra (~1/frequency, or 1/frequency to a power < 2) are widely observed in catchment studies. In several catchments, a significant fraction of streamflow is derived from groundwater in shallow fractured bedrock, where matrix diffusion significantly influences solute transport. I present frequency and time domain theoretical analyses of solute transport to quantify the influence of matrix diffusion on fractal scaling and long-tailed TTDs. The theoretical concentration power spectra exhibit fractal scaling, and the corresponding TTDs resemble a gamma distribution. The tails of the TTDs are influenced by accessible matrix width, exhibiting a sustained power-law (rather than exponential) decline for large matrix widths. Application to an experimental catchment shows that theoretical spectra match previously reported power spectral estimates derived from concentration measurements.

Antarctic ice sheets play an important role in global sea-levels and climate changes. Snowmelt information with high spatial resolution on the surface of ice sheets is of great significance to the study of global climate change. Currently, the spatial resolution of snowmelt detection results based on low-frequency data from microwave radiometers is low, and accurate freeze-thaw changes cannot be obtained. The spatial resolution of Advanced Microwave Scanning Radiometer-2(AMSR-2)89GHz data is at least twice that of other microwave channels, but vulnerable to atmospheric water vapour. This paper proposes a method to detect snowmelt on the Antarctic ice sheet based on 89GHz data. First, according to the stable relationship of the polarization ratio(PR)of 89GHz and 36GHz data under clear, cloudless weather, the affected 89GHz data were selected. Then, the functional relationship between 36 GHz data and the unaffected 89 GHz data was obtained. Finally, the modified 89 GHz data were applied to snowmelt detection on the Antarctic ice sheet. The average detection accuracy of this method in six automatic weather stations was 91%, while the average detection accuracy of the cross-polarized gradient ratio algorithm(XPGR)was 74%. The experimental results show that the modified 89GHz data have a high accuracy in detecting snowmelt in Antarctic ice sheets.

The United Nations 2030 Agenda brings a holistic and multi-sectoral view on sustainability via the Sustainable Development Goals (SDGs). However, a successful implementation of this agenda is contingent on understanding the multiple, complex interactions among SDGs, including both synergies and trade-offs, for informing planning for sustainability at the local level. Using a case study in the Goulburn-Murray region in Victoria, Australia, we prioritised global goals and targets for the local context, characterised the interactions between them, analysed the main synergies and trade-offs, and identified potential policy solutions to achieve local sustainability. We identified the five highest priority SDGs for the region as clean water and sanitation (SDG 6), agricultural activities (SDG 2), economic growth (SDG 8), climate action (SDG 13), and life on land (SDG 15). Across these five priority SDGs and their 45 targets, we found 307 potential interactions, of which 126 (41%) were synergistic, 19 (6%) were trade-offs, and 162 (53%) were benign. We highlight the most salient trade-offs, particularly how unsustainable agricultural practices could negatively affect water resources, the environment, and sustainable economic growth. Also, critical ongoing uncertainties like climate change, local policies on environmental water recovery, international markets, and emerging new technologies could pose risks for the future of agriculture and the economy. Our results provide important insights for local and regional sustainability policy and planning across multiple sectors. Our methodology is also broadly applicable for prioritising SDGs and assessing their interactions at local scales, thereby supporting evidence-based policy-making for the SDGs.

Background: Combustion-related nitrogen dioxide (NO2) air pollution is associated with pediatric asthma incidence. We estimated global surface NO2 concentrations consistent with the Global Burden of Disease Study for 1990-2019 at 1km resolution, and concentrations and attributable pediatric asthma incidence trends in 13,189 cities from 2000-2019. Methods: We scaled an existing surface annual average NO2 concentrations dataset for 2010-2012 from a land use regression model (based on 5,220 NO2 monitors in 58 countries and land use variables) to other years using NO2 column densities from satellite and reanalysis datasets. We applied these concentrations to epidemiologically-derived concentration-response factors, population, and baseline asthma rates to estimate NO2-attributable pediatric asthma incidence. Findings: We estimated that 1.85 million (95% uncertainty interval: 0.93 – 2.8 million) new pediatric asthma cases were attributable to NO2 globally in 2019, two-thirds of which occurred in urban areas. The fraction of pediatric asthma incidence that is attributable to NO2 in urban areas declined from 20% in 2000 to 16% in 2019. Urban attributable fractions dropped in High-income (-41%), Latin America/Caribbean (-16%), Central Europe, Eastern Europe, and Central Asia (-13%), and Southeast Asia, East Asia, and Oceania (-6%), and rose in South Asia (+23%), Sub-Saharan Africa (+11%), and North Africa and Middle East (+5%) regions. The importance of NO2 concentrations, pediatric population size, and asthma incidence rates in driving these changes differs regionally. Interpretation: Despite improvements in some regions, combustion-related NO2 pollution continues to be an important contributor to pediatric asthma incidence globally, particularly in cities. Funding: Health Effects Institute, NASA

We developed a flexible finite-fault inversion method for teleseismic P waveforms to obtain a detailed rupture process of a complex multiple-fault earthquake. We estimate the distribution of potency-rate density tensors on an assumed model plane to clarify rupture evolution processes, including variations of fault geometry. We applied our method to the 23 January 2018 Gulf of Alaska earthquake by representing slip on a projected horizontal model plane at a depth of 33.6 km to fit the distribution of aftershocks occurring within one week of the mainshock. The obtained source model, which successfully explained the complex teleseismic P waveforms, shows that the 2018 earthquake ruptured a conjugate system of N-S and E-W faults. The spatiotemporal rupture evolution indicates irregular rupture behavior involving a multiple-shock sequence, which is likely associated with discontinuities in the fault geometry that originated from E-W sea-floor fracture zones and N-S plate-bending faults.

Identifying the main environmental drivers of SARS-CoV-2 transmissibility in the population is crucial for understanding current and potential future outbursts of COVID-19 and other infectious diseases. To address this problem, we concentrate on basic reproduction number R0, which is not sensitive to testing coverage and represents transmissibility in an absence of social distancing and in a completely susceptible population. While many variables may potentially influence R0, a high correlation between these variables may obscure the result interpretation. Consequently, we combine Principal Component Analysis with feature selection methods from several regression-based approaches to identify the main demographic and meteorological drivers behind R0. We robustly obtain that country’s wealth/development (GDP per capita or Human Development Index) is by far the most important R0 predictor, probably being a good proxy for the overall contact frequency in a population. This main effect is modulated by built-up area per capita (crowdedness in indoor space), onset of infection (likely related to increased awareness of infection risks), net migration, unhealthy living lifestyle/conditions including pollution, seasonality, and possibly BCG vaccination prevalence. Also, we show that several variables that significantly correlate with transmissibility do not directly influence R0 or affect it differently than suggested by naive analysis.

The higher frequency and intensity of sustained heat events have increased the demand for cooling energy across the globe. Current estimates of summer-time energy demand are primarily based on Cooling Degree Days (CDD), representing the number of degrees a day’s average temperature exceeds a predetermined comfort zone temperature. Through a comprehensive analysis of the historical energy demand data across the USA, we show that the commonly used CDD estimates fall significantly short (±25%) of capturing regional thermal comfort levels. Moreover, given the increasingly compelling evidence that air temperature alone is not sufficient for characterizing human thermal comfort, we extend the widely-used CDD calculation to heat index, which accounts for both air temperature and humidity. Our results indicate significant mis-estimation of regional thermal comfort when humidity is ignored. Our findings have significant implications for the security, sustainability, and resilience of the grid under climate change.

Drilling and multi-stage hydraulic fracturing bring a large amount of water into the formation, and clay-bearing shale reservoirs interact with water, which may lead to reduction of gas production, attenuation of fracturing effects, and even wellbore instability. Because of the complex fabric of shale, a thorough understanding of changes in shale micromechanics and corresponding mechanisms when exposed to water remains unclear. In this work, representative terrestrial and marine shale samples were selected for experiments based on clay enrichment. Then, contact resonance (CR) technique was performed to characterize micromechanics of shale after exposure to water. Visual phenomena provided by environmental scanning electron microscopy (ESEM) assisted to explain the underlying mechanisms. It was found that the hydration effect lowered both the storage modulus and stiffness of samples, but with different contributions from brittle minerals and clay, as well as variations depending on bedding plane orientation. Owing to the difference in composition, terrestrial shale exhibited stronger water sensitivity and anisotropy, with a general 15%-25% decrease in modulus, while marine shale changed relatively little (-5%-15%). Moreover, microscopic observation experiments revealed that complex interaction mechanisms may have existed that produced the mechanical changes. The reduction of capillary force and the interlaminar swelling of clay particles after water adsorption weakened the strength-related behavior of shale. However, the swelling-caused confining effect or void space closure during the water imbibition process might have offset this weakening effect, and even increased mechanical properties. At mesoscale, excessive shrinkage caused the growth of micro-cracks, which significantly attenuated overall mechanical behavior.

The near-Earth plasma sheet becomes cold and dense under northward interplanetary magnetic field (IMF) condition, which suggests efficient solar wind plasma entry into the magnetosphere across the magnetopause for northward IMF and a possible contribution of ionospheric oxygen ion outflow. The cold and dense characteristics of the plasma sheet are more evident in the magnetotail flank regions that are the interface between cold solar wind plasma and hot magnetospheric plasma. Several physical mechanisms have been proposed to explain the solar wind plasma entry across the magnetopause and resultant formation of the cold-dense plasma sheet (CDPS) in the tail flank regions. However, the transport path of the cold-dense plasma inside the magnetotail has not been understood yet. Here we present a case study of the CDPS in the dusk magnetotail by Magnetospheric Multiscale (MMS) spacecraft under strongly northward IMF and high-density solar wind conditions. The ion distribution function consists of high- and low-energy components, and the low-energy one intermittently shows energy dispersion in the directions parallel and anti-parallel to the local magnetic field. The time-of-flight analysis of the energy-dispersed low-energy ions suggests that these ions originate in the region farther down the tail, move along the magnetic field toward the ionosphere and then come back to the magnetotail by the mirror reflection. The pitch-angle dispersion analysis gives consistent results on the traveling time and path length of the energy-dispersed ions. Based on these observations, we discuss possible generation mechanisms of the energy-dispersed structure of the low-energy ions during the northward IMF.

Several objectives of the PROVIDE project depend on a set of scenarios that can be modelled through either a ‘classical’ forward-looking approach or by a novel approach that ‘reverses the impact chain’. These scenarios are also key elements for the integration of PROVIDE findings in the outward-looking stakeholder Dashboard of the project. Here we describe the set of scenarios that has been developed and will be used within PROVIDE. In total, PROVIDE explores three complementary approaches: 1) 10 distinct tier 1 scenarios extending until 2100, mostly based on the existing literature, used for short-term assessments of impacts 2) 15 distinct tier 1 scenarios extending until 2300, based on different extensions of the 10 literature scenarios, used for assessing longer-run impacts and the geophysical impact of significant temperature overshoot 3) ~1350 distinct tier 2 scenarios, exploring several dimensions of emissions space systematically, such as CO2 net zero date and relative methane intensity. This is used to explore which scenarios are compatible with given climate outcomes. These scenarios can be used to reverse the traditional impact chain, going from acceptable climate risks to descriptions of acceptable emissions.

Extraction of internal tidal (IT) signals is central to the interpretation of Sea Surface Height (SSH) data. The increased spatial resolution of future wide-swath satellite missions poses a challenge for traditional harmonic analysis, due to prominent and unsteady wave-mean interactions at finer scales. However, the wide swaths will also produce spatially two-dimensional SSH snapshots, which allows us to treat IT extraction as an image translation problem for the first time. We design and train TITE, a conditional Generative Adversarial Network, which, given a snapshot of raw SSH from an idealized numerical eddying simulation, generates a snapshot of the embedded IT component. We test it on data whose dynamical regimes are different from the data provided during training. Despite the diversity and complexity of data, it accurately extracts ITs in most individual snapshots considered and reproduces physically meaningful statistical properties. Predictably, TITE’s performance decreases with the intensity of the turbulent flow.

In the Arctic, the spatial distribution of boreal forest cover and soil profile transition characterizing the taiga-tundra ecological transition zone (TTE) is experiencing an alarming transformation. The SIBBORK-TTE model provides a unique opportunity to predict the spatiotemporal distribution patterns of vegetation heterogeneity, forest structure change, arctic-boreal forest interactions, and ecosystem transitions with high resolution scaling across broad domains. Within the TTE, evolving climatological and biogeochemical dynamics facilitate moisture signaling and nutrient cycle disruption, i.e. permafrost thaw and nutrient decomposition, thereby catalyzing land cover change and ecosystem instability. To demonstrate these trends, in situ ground measurements for active layer depth were collected to cross-validate below-ground-enhanced modeled simulations from 1996-2017. Shifting trends in permafrost variability (i.e. active layer depth) and seasonality were derived from model results and compared statistically to the in situ data. The SIBBORK-TTE model was then run to project future below-ground conditions utilizing CMIP6 scenarios. Upon visualization and curve-integrated analysis of the simulated freeze-thaw dynamics, the calculated performance metric associated with annual maximum active layer depth rate of change yielded 76.19%. Future climatic conditions indicate an increase in active layer depth and shifting seasonality across the TTE. With this novel approach, spatiotemporal variation of active layer depth provides an opportunity for identifying climate and topographic drivers and forecasting permafrost variability and earth system feedback mechanisms.

The China-France Oceanography Satellite (CFOSAT) was successfully launched on October 29, 2018, which carried two innovative payloads, i.e., the surface waves investigation and monitoring (SWIM) instrument and the rotating fan beam scatterometer (RFSCAT). CFOSAT scatterometer (CSCAT) is dedicated to the monitoring of sea surface wind vectors and variety of climate studies, but also provides useful data for the applications over land and polar regions. CSCAT employs a “rotationg fan-beam” design rather than “pen-beam” approach previously used with SeaWinds on NASA QuikSCAT and “fixed fan-beam” approach with ASCAT on METOP-A. The CSCAT produces large overlaps on the observation regions within the total swath by successive sweeps and provides a large number of backscatter acquisitions with diverse azimuth and elevation combinations for a single surface resolution cell. In order to obation higher resolution and precise backscatter of rotating fan-beam scatterometer, however, some special considerations have been made in the design of CSCAT signal and data processing. In this paper, the data processing approach of CSCAT are proposed completely for the first time. The geolocation reference mapping model is employed in CSCAT slice geolocation. In noise processing, CSCAT adopts the method of weighted least square polynomial surface fitting to conduct the adaptive noise correction factor estimation. The attitude cubic algorithm used for X integral factor computation is developed to obtain the precise backscatter coefficients based on the radar equation. Because of the high relevance between the CSCAT data processing and the hardware configuration and onboard signal processing of the instrument, the instrument module configuration and signal processing design are also analyzed and presented comprehensively. Especially, the influence and compensation of Doppler frequency on signal processing and range filtering processing are introduced. The instrument performance and data processing algorithm are verified by the accuracy analysis on the CSCAT backscattering coefficient data. The backscatter coefficient accuracy is estimation on the Amazon forest, and the results shows that the backscattering coefficient accuracy of CSCAT on 25km × 25km grid is less than 0.5dB except that the near end and far end of the beam are slightly higher. The statistical results of wind field obtained from the backscattering coefficient inversion of CSCAT are also provided, and the better wind field inversion results are obtained based on the CSCAT backscattering coefficient measurement.

We examine long-term energetic heavy ion measurements including three planets’ magnetospheres, focusing on Fe ions (specifically, but not exclusively, Fe+) in and near Earth’s magnetosphere. We compare Fe data to that of other energetic ion species with masses greater than C (carbon) and consider the relationship(s) of energetic Fe ion measurements at the three planets to internal (ionospheres, exospheres, moons, rings, and trapped radiation) and external (solar wind and interplanetary dust) source candidates. Fe+ has been observed at Earth and Saturn, but not yet at Jupiter, as our observations there were brief. The measurements are from two functionally identical charge-energy-mass ion spectrometers: one on Geotail (~87-212 keV/e), orbiting Earth at ~9-30 Re; and the other on Cassini (~83-167 keV/e), in interplanetary space, during Jupiter flyby, and at ~4-20 Rs on its constantly varying orbits around Saturn. These ion spectrometers efficiently separate energetic light and heavy ions by mass, as well as lower charge state ions from higher charge state ions by mass-per-charge. Energetic low charge state ions often derive from magnetospheric sources, while energetic high charge state ions most often derive from the solar wind. We also enlist heavy ion measurements closer to the Earth from AMPTE/CCE which are used for C and Fe radiation-belt- modeling content, consideration, and estimation.

Increasing extent and duration of seasonally ice-free area in the western Arctic Ocean suggests increased air-sea coupling, specifically fluxes of momentum and heat between the lower atmosphere and the upper ocean. The dependence of these fluxes on ice concentration and its dynamical characteristics is still uncertain. As part of the Stratified Ocean Dynamics of the Arctic (SODA) project, year-long time series of upper-ocean velocity profiles were obtained across a range of ice conditions and are used to infer momentum fluxes. We consider the structure of observed current profiles as a function of sea state and ice cover. During the summer and in open water with minimal stratification, the wind forcing is in local equilibrium with surface gravity waves, and there is a direct transfer of momentum from the atmosphere to the upper ocean. The presence of ice modifies the momentum budget through both the inclusion of ice-atmosphere and ice-ocean stresses, and by damping short surface gravity waves and thus changing the surface roughness that the atmosphere acts upon. Ice presence is also associated with increased near-surface stratification, which can act to decouple the sub-surface ocean from atmospheric forcing. Our observations show frequent decoupling of a thin surface layer (<10 m depth), including case studies in which the relatively fresh surface waters formed by “ice puddles” have entirely different motion from the relatively salty water a few meters below. Ice formation in the fall affects both the ocean stratification and the ice characteristics, leading to competing effects affecting momentum transfer. Initial results across the annual cycle are presented.

The Gondwana Late Paleozoic Ice Age is probably best represented by the Dwyka Group in South Africa. Striated and grooved surfaces or pavements are commonly considered to be subglacially formed, as are diamictites which have been interpreted as in situ or reworked tillites. These interpretations were tested by investigation of outcrops in formerly well studied areas, throughout South Africa. Detailed analyses focused on striated surfaces/pavements and surface microtextures on quartz sand grains in diamictites. The sedimentological context of four pavements, interpreted to be glaciogenic, display features commonly associated with sediment gravity flows, rather than glaciation. A total of 4271 quartz sand grains were subsampled from outcrops that are mainly considered to be tillites formed by continental glaciation. These grains, analyzed by SEM, do not demonstrate the characteristic surface microtextures combinations of fracturing and irregular abrasion associated with Quaternary glacial deposits, but mainly a mix of surface microtextures associated with multicyclical grains. The Dwyka Group diamictites warrant reinterpretation as non-glacial sediment gravity flow deposits.

Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5-10 min periods can induce geomagnetically-induced currents (GICs) that can harm technological systems. In this study we compare the occurrence and amplitude of nighttime MPEs with |dB/dt| ≥ 6 nT/s observed during 2015 and 2017 at five stations in Arctic Canada ranging from 75.2° to 64.7° in corrected geomagnetic latitude (MLAT) as functions of magnetic local time (MLT), the SME and SYM/H magnetic indices, and time delay after substorm onsets. Although most MPEs occurred within 30 minutes after a substorm onset, ~10% of those observed at the four lower latitude stations occurred over two hours after the most recent onset. A broad distribution in local time appeared at all 5 stations between 1700 and 0100 MLT, and a narrower distribution appeared at the lower latitude stations between 0200 and 0700 MLT. There was little or no correlation between MPE amplitude and the SYM/H index; most MPEs at all stations occurred for SYM/H values between -40 and 0 nT. SME index values for MPEs observed more than 1 hour after the most recent substorm onset fell in the lower half of the range of SME values for events during substorms, and dipolarizations in synchronous orbit at GOES 13 during these events were weaker or more often nonexistent. These observations suggest that substorms are neither necessary nor sufficient to cause MPEs, and hence predictions of GICs cannot focus solely on substorms.