Seasonal variations of the near-surface odd nitrogen (NOX=NO+NO2) and ozone (O3) mixing ratios at Zotino Tall Tower (ZOTTO), a remote site in central Siberia, are described for years 2007–2014. Conditional probability function analysis and back trajectories are used to determine the origins of clean (continental background, CB) and regional emissions-influenced air. High NOX levels at the site are observed for air from industrial regions of western Siberia and Ural Mountains, whereas CB air originates from remote areas of North Eurasia within 55°–70°N. The estimated annual means of daytime O3 and NOX mixing ratios for CB air are 27.0 ppbv and 0.44 ppbv, correspondingly, vs. the similar quantities of 27.9 and 0.79 ppbv for all data. Monthly ozone for CB air shows a distinct maximum in April, as is the case for Northern Hemisphere midlatitude background (NHMLB) air at the European inflow boundary according to the surface ozone data for Mace Head and Norwegian monitoring sites, and a minimum in late summer – early autumn reflecting a weak continental-scale ozone production from biogenic sources of ozone precursors and wildfire emissions throughout a warm season. During spring and early summer under hot weather conditions, regional anthropogenic and wildfire emissions are an important source for ozone in the continental boundary layer over southern and central Siberia, resulting in surface ozone levels compared to or larger than those observed in NHMLB air. Throughout the remaining part of a year, the central North Eurasia represents a sink for tropospheric ozone on a hemispheric scale.

Understanding the initiation and arrest of earthquakes is one of the long-standing challenges of seismology. Here we report on direct observations of borehole displacement by a meter-sized shear rupture induced by pressurization of metamorphic rock at 1.5 km depth. We observed the acceleration of sliding, followed by fast co-seismic slip and transient afterslip. Total displacements were about 7, 5.5 and 9.5 micrometers, respectively for the observed pre-slip, co-seismic slip and afterslip. The observed pre-slip lasted about 0.4 seconds. Co-seismic slip was recorded by the 1 kHz displacement recording and a 12-component array of 3-C accelerometers sampled at 100 kHz. The observed afterslip is consistent with analytical models of arrest in a velocity-strengthening region and subsequent stress relaxation. The observed slip vector agrees with the activation of a bedding plane within the phyllite, which is corroborated by relocated seismic events that were observed during the later stages of the injection experiment.

The successful application of simple statistical methods in economic modelling suggest that similar methods could provide insight into global climate. We apply an autoregressive method to observed time series to determine the dependence of atmospheric CO2 concentration on carbon emissions and, in turn, the dependence of globally averaged temperature on atmospheric CO2 concentration. We ascribe physical meaning to the regression parameters in terms of first order differential equations describing the diffusion of CO2 and temperature between reservoirs, viz.: the diffusion of CO2 between the atmosphere and the deep ocean and the transport of heat from the mixed layer. A strong feature of regression models is their built-in mechanism for deciding when a model provides an adequate description of the given data. Two implications of this statistically robust approach are that CO2 diffuses from the atmosphere within a time scale of decades and that global average temperatures are unlikely to exceed 2 deg C above pre-industrial values.

On the bow shock in front of Earth flows current due to the curl of interplanetary magnetic field across the shock. It is uncertain whether the bow shock current closes on the magnetopause, into the ionosphere along magnetic field lines, or both. We present simultaneous observations from MMS, AMPERE, and DMSP during a period of strong $B_y$, weakly negative $B_z$, and small $B_x$. This IMF orientation should lead to current flowing mostly south-north on the shock. AMPERE shows current poleward of the Region 1 currents flowing into the northern polar cap and out of the south, consistent with bow shock current closing along open field lines; a DMSP flyover confirms that this current is poleward of the convection reversal boundary. Additionally, we investigate bow shock current closure for these conditions using an MHD simulation. We conclude that the evidence points to partial closure of bow shock current through the ionosphere.

Crater morphology and surface age of asteroid (162173) Ryugu are characterized using the high-resolution images obtained by the Hayabusa2 spacecraft. Our observations reveal that the abundant boulders on and under the surface of the rubble-pile asteroid affect crater morphology. Most of the craters on Ryugu exhibit well-defined circular depressions, unlike those observed on asteroid Itokawa. The craters are typically outlined by boulders remaining on the rim. Large craters (diameter >100 m) host abundant and sometimes unproportionally large boulders on their floors. Small craters (<20 m) are characterized by smooth circular floors distinguishable from the boulder-rich exterior. Such small craters tend to have dark centers of unclear origin. The correlation between crater size and boulder number density suggests that some processes sort the size of boulders in the shallow (<30 m) subsurface. Furthermore, the crater size-frequency distributions (CSFDs) of different regions on Ryugu record multiple geologic events, revealing the diverse geologic history on this 1-km asteroid. Our crater counting analyses indicate that the equatorial ridge is the oldest structure of Ryugu and was formed 23-29 Myr ago. Then, Ryugu was partially resurfaced, possibly by the impact that formed the Urashima crater 5-12 Myr ago. Subsequently, a large-scale resurfacing event formed the western bulge and the fossae 2-9 Myr ago. Following this process, the spin of Ryugu slowed down plausibly due to the YORP effect. The transition of isochrons in a CSFD suggests that Ryugu was decoupled from the main belt and transferred to a near-Earth orbit 0.2-7 Myr ago.

In 2015, the Olympic Mountains contain 255 glaciers and perennial snowfields totaling 25.34 ± 0.27 km2, half of the area in 1900, and about 0.75 ± 0.19 km3 of ice. Since 1980, glaciers shrank at a rate of -0.59 km2 yr-1 during which 35 glaciers and 16 perennial snowfields disappeared. Area changes of Blue Glacier, the largest glacier in the study region, was a good proxy for glacier change of the entire region. A simple mass balance model of the glacier, based on monthly air temperature and precipitation, correlates with glacier area change. The mass balance is highly sensitive to changes in air temperature rather than precipitation, typical of maritime glaciers. In addition to increasing summer melt, warmer winter temperatures changed the phase of precipitation from snow to rain, reducing snow accumulation. Changes in glacier mass balance are highly correlated with the Pacific North American index, a proxy for atmospheric circulation patterns and controls air temperatures along the Pacific Coast of North America. Regime shifts of sea surface temperatures in the North Pacific, reflected in the Pacific Decadal Oscillation (PDO), trigger shifts in the trend of glacier mass balance. Negative (‘cool’) phases of the PDO are associated with glacier stability or slight mass gain whereas positive (‘warm’) phases are associated with mass loss and glacier retreat. Over the past century the overall retreat is due to warming air temperatures, almost +1oC in winter and +0.3oC in summer. The glaciers in the Olympic Mountains are expected to largely disappear by 2070.

The rivers in the Peruvian Amazon basin are the veins that feed the largest rainforest on the planet. They connect habitats and ecosystems and are considered a source of high biodiversity. Since before the conquest, many indigenous peoples have settled along riverbanks to be supplied with water, food, and many other ecosystem services. Furthermore, the Amazonian rivers have been the basis for the sociability of those population groups. For many years, the indigenous riverine people, such as the Kukama and the Shipibo-Conibo, have developed an empirical knowledge about the rivers from their coexistence and lifestyle. Therefore, indigenous communities have learned how to be adapted under the physical dynamics by shaping their culture. It evidenced the great understanding of rivers that communities developed over the years, endowed with affective and spiritual links, which has allowed them to be preserved for many years. As part of a scientific study of the hydrogeomorphological characteristics of the main Peruvian Amazonian rivers, it was considered important to involve indigenous perceptions and knowledge. Recognizing these views is necessary for a holistic understanding of rivers; however, these have been absent from the plans and projects developed by government institutions. “River Stories” (https://www.historiasdelrio.com) is a digital storytelling platform that supports the dissemination of indigenous cosmovision in terms of experiences, in which the knowledge, memory and spirituality are displayed. It hosts more than 100 stories from indigenous people (including children and teenagers), students, local authorities, and scientists that reveal the importance of rivers in their daily life. In this way, different perspectives of the rivers from science, civil society, and the indigenous worldview are exchanged. Integrating this knowledge is essential to highlight the vital role that rivers play at the social, cultural and environmental areas. This, especially in the current context, where multiple threats, such as infrastructure and energy projects, put Amazonian rivers at risk.

Nitrous oxide (N2O), a potent greenhouse gas that contributes significantly to climate change, is emitted mostly from soils by a suite of microbial metabolic pathways that are nontrivial to identify, and subsequently, to manage. Using either natural abundance or enriched stable isotope methods has aided in identifying microbial sources of N2O, but each approach has limitations. Here, we conducted a novel pairing of natural abundance and enriched assays on two dissimilar soils, hypothesizing this pairing would better constrain microbial sources of N2O. We incubated paired natural abundance and enriched soils from a corn agroecosystem and a subalpine forest in the laboratory at 10-95% soil saturation for 28 hr. The natural abundance method measured intramolecular site preference (SP) from emitted N2O, whereas the enriched method measured emitted 15N2O from soils amended with 15N-labelled substrate. The isotopic composition of emitted N2O was measured using a laser-based N2O isotopic analyzer, yielding three key findings. First, isotopic signatures from natural abundance and enriched N2O generally agreed in interpretation. Second, our novel pairing of isotopic methodologies refined understanding of microbial N-transformations in drier agricultural soil. In the 50% saturation agricultural soil, nitrification might have been deemed an important process based on SP alone, but enrichment helped reveal that its contribution to N2O emissions was minor. Finally, we quantified, to our knowledge for the first time, persistent (>50%) β-position-specific enrichment in emitted 15N2O, which is far in excess of SP-level fractionation expectations. This counter-intuitive enrichment pattern raises the possibility of previously unrecognized N-transformations in these soils.

Volcanic radiative forcing reconstruction is an important part of paleoclimate simulation and attribution efforts, and the conversion factor used to transfer ice core-based sulfate observation into stratospheric volcanic aerosol loading (LTD factor) is critical for such reconstruction. A Pinatubo-based LTD was proposed and adapted in the CMIP5 and CMIP6 volcanic forcing, under the assumption that all tropical eruptions follow the same atmospheric transport and deposition pattern. This study revisits the LTD factor using a large collection of polar ice core records of Tambora deposition and a Monte Carlo sampling model. A new set of LTDs with associated uncertainties are obtained, which is in approximate with our previous Pinatubo-based LTD estimation in Greenland, while corrects the bias of over-representing the west Antarctic. The uncertainties revealed from the Monte Carlo simulation suggest that, difference in the ice core abundance only introduce limited uncertainty in LTD for individual eruption, once reach a certain threshold (about 15 in Greenland and 20 in Antarctic). The comparison of Southern Hemispheric LTD among Tambora, Agung, and Pinatubo suggests that, the conversion factor may vary for individual eruption. Results obtained from this study may ease our conventional proneness to use as much ice core observations as available to estimate icecap volcanic deposition, while emphasize the importance to build a distribution of the LTD ideally for eruptions with different size and locations. Meanwhile, the estimated sets of Tambora-based LTDs could serve as a compromising choice in future volcanic forcing reconstruction work, especially when Tambora is utilized as a reference

Nano-darcy level permeability measurements of porous media, such as nano-porous mudrocks, are frequently conducted with gas invasion methods into granular-sized samples with short diffusion lengths and thereby reduced experimental duration; however, these methods lack rigorous solutions and standardized experimental procedures. For the first time, we resolve this by providing an integrated technique (termed as gas permeability technique) with coupled theoretical development, experimental procedures, and data interpretation workflow. Three exact mathematical solutions for transient and slightly compressible spherical flow, along with their asymptotic solutions, are developed for early- and late-time responses. Critically, one late-time solution is for an ultra-small gas-invadable volume, important for a wide range of practical usages. Developed as applicable to different sample characteristics (permeability, porosity, and mass) in relation to the storage capacity of experimental systems, these three solutions are evaluated from essential considerations of error difference between exact and approximate solutions, optimal experimental conditions, and experimental demonstration of mudrocks and molecular-sieve samples. Moreover, a practical workflow of solution selection and data reduction to determine permeability is presented by considering samples with different permeability and porosity under various granular sizes. Overall, this work establishes a rigorous, theory-based, rapid, and versatile gas permeability measurement technique for tight media at sub-nano darcy levels.

Changes in the lower-trophic marine ecosystem and biogeochemical cycles were considered with respect to the warming Arctic Ocean. The time series monitoring of the hydrography and marine settling particles supplies a large amount of information regarding the marine lower-trophic ecosystem in with respect to the changing Arctic Ocean. To investigate the interannual relationship between the settling particles and hydrographic conditions of the western Arctic Ocean, bottom-tethered sediment trap moorings were deployed at the Northwind Abyssal Plain (NAP) and at the Chukchi Abyssal Plain from October 2010 to September 2014 to the east and west of the Chukchi Borderland. The settling particles at both stations contained a significant amount of lithogenic matter, with biogenic particles being a lateral advection of shelf materials from shelf to basin. The many peaks of settling particle fluxes at Station NAP in 2013–2014 corresponded to the hydrographic events of passing oceanic eddies over the station, in addition to seasonal biological production. Additionally, abundant gelatinous matter was found in some summer samples. The settling flux data of particulate organic matter and the mole ratio and stable isotope ratios of particulate organic carbon and nitrogen in the settling particles reflected the changes in the composition of trapped plankton assemblages under various hydrographic conditions over the course of the four years of the study.

It is important to perform the quantitative interpretation of the continental margin lithosphere for a more accurate and comprehensive understanding of its tectonic behavior. In this study, we derived the seismic and elastic properties from the 2D seismic data recorded by the Korea Meteorological Administration (KMA) in 2014. In general, most of the previous researches have been based on travel time tomography or Full Waveform Inversion (FWI) methods. However, these methods are not robust to directly apply to the seismic ambient noise data due to its low signal-to-noise ratio (SNR). Therefore, we conducted L2-norm model-based impedance inversion to not only delineate the local geological structures but also suppress the meaningless footprints in the observed data. Moreover, we used FWEA18 models (Tao et al., 2018) as initial velocity and density models to create the inversion result more stable and accurate. Then, we interpreted the lithosphere and asthenosphere from the inverted P-impedance model, which is more obvious than the interpretation of the pre-existing data. The average depths of Moho and Lithosphere-Asthenosphere-Boundary (LAB) are 30 km and 80km, respectively. Furthermore, we estimated the change of bulk density as well as P- and S-wave velocities of the crust, lithospheric mantle, and asthenospheric mantle. Also, we predicted four elastic properties of each layer from the inverted seismic properties, such as bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio. These model results can help to understand the physical state and elastic behavior variations of the lithospheric and asthenospheric mantle as well as local lithospheric structures beneath the peninsula.

Many regions worldwide have replaced quotas, as a means to controlling irrigation-water usage, with a hybrid policy that integrates private quotas and uniform prices. This paper characterizes the political equilibrium in a game in which farmers lobby for lower prices and larger quotas. We show that combining the two instruments reinforces the robustness of each against political distortion; consequently, a hybrid policy that follows a quotas-only regime reduces water usage. However, the social welfare rank of the hybrid policy versus the quotas-only and price-only counterparts is an empirical question. We use the equilibrium conditions to derive a structural discrete/continuous choice model that enables estimating the agricultural sector’s lobbying power and the level of political organization used to reduce prices. We employ the model to data from Israel during the 1980s; during that period, quotas were set at a village-specific level and prices were set at a region-specific level, thereby generating the variability required to estimate the model’s parameters. We obtain empirical support for the reinforcement hypothesis and evidence of strong political influence, but also evidence of considerable free-riding regarding price reduction. Simulations of political equilibria under the quotas-only, price-only and hybrid regimes indicate a domination of the latter in terms of social welfare.

Department of Water Resources (DWR), in partnership with the Merced Irrigation District (MID), is conducting a reconnaissance level study to assess the potential of implementing Flood-MAR in the Merced River watershed within the San Joaquin Valley. One aspect of the Flood-MAR study focuses on reservoir operations using synthetic hydrology generated based on the Paleoclimate (Tree-Ring) Study methodology. The MID HEC-ResSim model was calibrated to simulate water supply and flood control operations over the water year. The model was modified to estimate water available for Flood-MAR based on flow at a downstream location, conveyance capacity and groundwater recharge capacity. Results include changes in storage at Lake McClure, flow in Merced River, water supply deliveries, and Flood-MAR deliveries due to Flood-MAR implementation. The study also assesses the vulnerability of reservoir operations due to changing hydrology by evaluating the effects of climate change on flood management, water supply reliability, and drought resiliency. The flood management aspect of the vulnerability analysis assesses change in peak flow, flow volume, and duration of flooding events. The water supply reliability assesses change in carryover storage and deliveries for irrigation demands. The drought resiliency assessment includes change in magnitude and duration of the historical and synthetic drought events. The results of the reservoir operations vulnerability analysis will be used to determine the multiple benefits of Flood-MAR implementation.

Improved monitoring of inundation area variations in lakes and reservoirs is crucial for assessing surface water resources in a growing population and a changing climate. Although long-record optical satellites, such as Landsat missions, provide sub-monthly observations at fairly fine spatial resolution, cloud contamination often poses a major challenge for producing temporally continuous time series. We here proposed a novel method to improve the temporal frequency of usable Landsat observations for mapping lakes and reservoirs, by effectively recovering inundation areas from contaminated images. This method automated three primary steps on the cloud-based platform Google Earth Engine. It first leveraged multiple spectral indices to optimize water mapping from archival Landsat images acquired since 1992. Errors induced by minor contaminations were next corrected by the topology of isobaths extracted from nearly cloud-free images. The isobaths were then used to recover water areas under major contaminations through an efficient vector-based interpolation. We validated this method on 428 lakes/reservoirs worldwide that range from ~2 km2 to ~82,000 km2 with time-variable levels measured by satellite altimeters. The recovered water areas show a relative root-mean-squared error of 2.2%, and the errors for over 95% of the lakes/reservoirs below 6.0%. The produced area time series, combining those from cloud-free images and recovered from contaminated images, exhibit strong correlations with altimetry levels (Spearman’s rho mostly ~0.8 or larger) and extended the hypsometric (area-level) ranges revealed by cloud-free images alone. The combined time series also improved the monthly coverage by an average of 43%, resulting in a bi-monthly water area record during the satellite altimetry era thus far (1992–2018). Given such performance and a generic nature of this method, we foresee its potential applications to assisting water area recovery for other optical and SAR sensors (e.g., Sentinel-2 and SWOT), and to estimating lake/reservoir storage variations in conjunction with altimetry sensors.

Remote sensing observations are our primary method of studying planetary surfaces, and in the inner solar system, in situ exploration quickly provided ground truth to these remote sensing observations. Our view of the surface appearance of worlds like the Moon, Mars, and even Venus has grown in tandem with our understanding of the large-scale structure from remote sensing. However, our knowledge of the icy worlds of the outer solar system is based solely on decades of remote sensing observations without any in situ surface data to help understand how geological processes are manifest on these worlds. The surfaces of icy worlds like Europa are likely to be truly alien in appearance, dominated by processes such as impact gardening, sputtering, sintering, and other types of physical and chemical weathering that act together in ways we have never yet observed in situ. Remote sensing has revealed that Europa’s surface consists of an icy layer, exposed to the vacuum of space at cryogenic temperatures. The airless rocky Moon may be the best landed analog for Europa’s surface, but the Moon is an old, battered world covered with impact craters, which have gardened the surface to a highly-mixed regolith depth of 5-15 meters overlying kilometers of broken-up megaregolith. Europa’s young surface, approximately tens of millions of years old, likely has a gardening depth on the scale of centimeters up to a meter (Costello et al., AGU Fall Meeting, 2019). The rocky Moon is also compositionally different from icy Europa, and the thermal and radiolytic processes that shape the texture of the uppermost surface of an icy body have no rocky analog. As study of icy worlds has continued on the basis of remote sensing data only, multiple competing models exist for the formation of various surface features. Follow-up flyby and orbital missions may not be able to resolve these situations even with higher-resolution remote sensing data and digital elevation models. Images taken by an in situ surface lander on an icy world such as Europa, coupled with ground truth compositional and other measurements, will be essential to our understanding of how geologic processes work on these worlds. A mission such as a Europa Lander is the necessary next step, and will revolutionize our ability to interpret remote sensing data from myriad other bodies in the outer solar system.

The high computational cost of large-scale, process-based hydrological simulations can be approached using variable resolution meshes, where only the region around significant topographic features is refined. However, generating quality variable resolution meshes from digital elevation data is non-trivial. In literature, usually a slope or curvature-based criterion is defined to detect regions of refinement. These techniques often involve a number of free parameters that control the finest and coarsest resolutions, and the transition between fine resolution to coarse resolution. The influence of these parameters on the resulting mesh is usually not well-understood. In order to overcome the large number of free parameters involved, we propose to carry out the Mallat decomposition of the digital elevation data using the Haar wavelet. This gives a nested multilevel representation of the elevation data, split into average coefficients and detail coefficients. Applying hard-thresholding to these detail coefficients assigns a required level of refinement to each data point. This reduces the number of free parameters to exactly one: the acceptable error threshold. In this presentation, we focus on identifying which geomorphometric parameter(s) should be used to steer mesh refinement. We compare zero-inertia model simulation runs on meshes generated by decomposing elevation and slope. We hypothesize that because of the form of the Haar wavelet, the first mesh refinement essentially is using the gradient information, while the latter is using the curvature as refinement criterion. Our results suggest that in high-elevation catchments the curvature of the topography is a far better indicator for refinement than the slope. Using the Mallat decomposition on the tensor of the first derivative of the bed elevation (i.e., bed slope) for mesh refinement yields better agreement in the hydrograph compared to the decomposition of the bed elevation. We present surface runoff results for the Lower Triangle catchment, CO, USA, to illustrate the performance of the wavelet-based local mesh refinement.

In this study, the authors explore simple concepts of persistence in streamflow forecasting based on the real-time streamflow observations. The authors use 15-minute streamflow observations from the year 2002 to 2018 at 140 U.S. Geological Survey (USGS) streamflow gauges monitoring the streams and rivers over the State of Iowa. The spatial scale of the basins ranges from about 7 km2 to 37,000 km2. Motivated by the need for evaluating the skill of real-time streamflow forecasting systems, the authors perform quantitative skill assessment of different persistence schemes across spatial scales and lead-times. They show that temporal persistence forecasts skill has strong dependence on basin size and weaker, but non-negligible, dependence on geometric properties of the river network of the basin. The authors show that anomaly persistence forecasting can serve as a good reference for the evaluation of real-time streamflow forecasts at scales of order 100 km2. Building on results from this temporal persistence, they extend the streamflow persistence to space through flow-connected river network. It simply assumes that streamflow at a station in space will persist to another station which is flow-connected, and refer to it as pure spatial persistence forecasts (PSPF). The authors show that skill of PSPF derived streamflow forecasts is strongly dependent on basin area-ratio and lead-times, and weakly related to the downstream flow distance between stations. They show that the skill depicted in terms of Kling-Gupta efficiency (KGE) > 0.5 can be achieved for basin area ratio > 0.5 and lead-time up to three days. Adding complexities of hydrologic routing and rainfall QPF to the PSPF further improves the skill. The authors discuss the implications of their findings for improvements of rainfall-runoff models as well as data assimilation schemes.