Can fractal analysis of a lava flow’s margin enable classification of the lava’s morphologic type (e.g., pāhoehoe)? Such classifications would provide insights into the rheology and dynamics of the flow when it was emplaced. The potential to classify lava flows from remotely-sensed data would particularly benefit the analysis of flows that are inaccessible, including flows on other planetary bodies. The technique’s current interpretive framework depends on three assumptions: (1) measured margin fractality is scale-invariant; (2) morphologic types can be uniquely distinguished based on measured margin fractality; and (3) modification of margin fractality by topography, including substrate slope and confinement, would be minimal or independently recognizable. We critically evaluate these assumptions at meter scales (1–10 m) using 15 field-collected flow margin intervals from a wide variety of morphologic types in Hawaiʻi, Iceland, and Idaho. Among the 12 margin intervals that satisfy the current framework’s suitability criteria (e.g., geomorphic freshness, shallowly-sloped substrates), we show that 5 exhibit notably scale-dependent fractality and all 5 from lava types other than ‘a‘ā or pāhoehoe would be classified as one or both of those types at some scales. Additionally, an ‘a‘ā flow on a 15° slope (Mauna Ulu, Hawaiʻi) and a spiny pāhoehoe flow confined by a stream bank (Holuhraun, Iceland) exhibit significantly depressed fractalities but lack diagnostic signatures for these modifications. We therefore conclude that all three assumptions of the current framework are invalid at meter scales and propose a new framework to leverage the potential of the underlying fractal technique while acknowledging these complexities.

The metropolitan Los Angeles region represents a zone of high-seismic risk due to its proximity to several fault systems, including the San Andreas fault. Adding to this problem is the fact that Los Angeles and its surrounding cities are built on top of soft sediments that tend to trap and amplify seismic waves generated by earthquakes. In this study, we use three dense petroleum industry surveys deployed in a 16x16-km area at Long Beach, California, to produce a high-resolution model of the top kilometer of the crust and investigate the influence of its structural variations on the amplification of seismic waves. Our velocity estimates reveal substantial lateral contrasts and correlate remarkably well with the geological background of the area, illuminating features such as the Newport-Inglewood fault, the Silverado aquifer, and the San Gabriel river. We then use computational modeling to show that the presence of these small-scale structures have a clear impact on the intensity of the expected shaking, and can cause ground-motion motion acceleration to change by several factors over a sub-kilometer horizontal scale. These results shed light onto the scale of variations that can be expected in this type of tectonic settings and highlight the importance of resolution in modern-day seismic hazard estimates.

The global ocean overturning circulation carries warm, salty water to high latitudes, both in the Arctic and Antarctic. Interaction with the atmosphere transforms this inflow into three distinct products: sea ice, surface Polar Water, and deep Overflow Water. The Polar Water and Overflow Water form estuarine and thermal overturning cells, stratified by salinity and temperature, respectively. A conceptual model specifies the characteristics of these water masses and cells given the inflow and air/sea/land fluxes of heat and freshwater. The model includes budgets of mass, salt, and heat, and parametrizations of Polar Water and Overflow Water formation, which include exchange with continental shelves. Model solutions are mainly controlled by a linear combination of air/sea/ice heat and freshwater fluxes and inflow heat flux that approximates the meteoric freshwater flux plus the sea ice export flux. The model shows that for the Arctic, the thermal overturning is likely robust, but the estuarine cell appears vulnerable to collapse via a so-called heat crisis that violates the budget equations. The system is pushed towards this crisis by increasing Atlantic Water inflow heat flux, increasing meteoric freshwater flux, and/or decreasing heat loss to the atmosphere. The Antarctic appears close to a so-called Overflow Water emergency with weak constraints on the strengths of the estuarine and thermal cells, uncertain sensitivity to parameters, and possibility of collapse of the thermal cell.

Dawn storms are among the brightest events in the Jovian aurorae. Up to now, they had only been observed from Earth-based observatories, only showing the Sun-facing side of the planet. Here we show for the first time global views of the phenomenon, from its initiation to its end and from the nightside of the aurora onto the dayside. Based on Juno's first 20 orbits, some patterns now emerge. Small short-lived spots are often seen for a couple of hours before the main emission starts to brighten and evolve from a straight arc to a more irregular one in the midnight sector. As the whole feature rotates dawn-ward, the arc then separates into two arcs with a central initially void region that is progressively filled with emissions. A gap in longitude then often forms before the whole feature dims. Finally, it transforms into an equatorward-moving patch of auroral emissions associated with plasma injection signatures. Some dawn storms remain weak and never fully develop. We also found cases of successive dawn storms within a few hours. Dawn storm thus share many fundamental features with the auroral signatures of the substorms at Earth. These findings demonstrate that, whatever their sources, mass and energy do not always circulate smoothly in planetary magnetospheres. Instead they often accumulate until the magnetospheres reconfigure and generate substorm-like responses in the planetary aurorae, although the temporal and spatial scales are different for different planets.

Low-frequency earthquakes (LFEs) are detected within tremor, as small, repetitive, impulsive low-frequency (1-8 Hz) signals. While the mechanism causing this depletion of the high frequency content of their signal is still debated, this feature may indicate that the source processes at the origin of LFEs are different from those for regular earthquakes. Key constraints on the LFE-generating physical mechanisms can be obtained by establishing scaling laws between their seismic moment and source durations. Here we apply a simple spectral analysis method to the S-waveforms of LFEs from Guerrero, Mexico to measure their seismic moments and corner frequencies, a proxy to source duration. We find characteristic values of seismic moment around 3e12 N.m (Mw 2.3) and of corner frequencies around 3 Hz with the corner frequency very weakly dependent on the seismic moment. This moment-duration scaling observed for Mexican LFE is similar to one previously reported in Cascadia and is very different from the established one for regular earthquakes. This suggests that they could be generated by sources of nearly constant size with strongly varying intensities. LFEs do not exhibit the self-similarity characteristic of regular earthquakes, suggesting that the physical mechanisms at their origin could be intrinsically different.

It has been standard practice for about two decades to compute GPS-based station velocity uncertainties using the apparent noise statistics of the non-linear position residuals rather than assume white noise (WN) behavior. The latter choice would yield unrealistic velocity uncertainties. The most common noise types used are power-law, usually close to flicker noise (FN), over most frequencies mixed with WN at the shortest periods. The complicating impact of offsets in the position time series, mostly caused by equipment changes or tectonic events, has not been fully appreciated. These are far less benign than recently suggested. In addition to contributing a pseudo-random walk noise (RW) component to the velocity errors, estimating offset parameters changes the apparent noise color towards whiter. Spectral power is effectively drained by offsets at periods longer than roughly the mean span between them. This consequently promotes a Gauss-Markov process as the apparently preferred noise model and, importantly, obscures the presence of RW and long-period Earth deformation in the series. Both effects can lead to potentially under-estimated velocity uncertainties. The full value of decadal-long GPS time series for geodynamical applications is thereby greatly eroded by recurring offsets, especially when they occur quasi-regularly. In addition, contrary to common assumption, the noise color is generally not fixed with time, but clearly becomes whiter in more recent data. The origin of the colored noise and its whitening over time remain elusive.

Despite increasing evidence of intensification of extreme precipitation events associated with a warming climate, the magnitude of extreme river flows is decreasing in many parts of the world. To better understand the range of relationships between precipitation extremes and floods, we analyzed annual precipitation extremes and flood events over the Contiguous United States from 1980 to 2014. A low spatial correlation (less than 0.2) between changes in precipitation extremes and changes in floods was found, attributable to a weak causal relationship. The co-variation between precipitation extremes and floods is also substantially low, with a majority of catchments having a coefficient of determination of less than 0.5, even among the catchments with a relatively strong causal relationship. The findings indicate a need for more investigations into causal mechanisms driving a non-linear response of floods to intensified precipitation extremes in a warming climate.

Following the emergence of a novel coronavirus in Wuhan, the People’s Republic of China instituted a number of strict lockdown and more general socio-economic shutdown measures throughout the country starting in late January and continuing into February 2020 in order to arrest the spread of the disease. This resulted in a sharp economic contraction unparalleled in recent Chinese history. Satellite remote sensing shows that nitrogen oxide pollution declined by an unprecedented amount (~50% regionally) from its expected unperturbed value, but regional-scale column aerosol loadings and cloud microphysical properties were not detectably affected. The disparate impact may be tied to differential economic impacts of the shutdown, in which the transportation sector, a disproportionate source of nitrogen oxide emissions, underwent drastic declines (~90% reductions in passenger traffic), whereas industry and power generation, responsible for >90% of particulate emissions, were relatively less affected (~10% reductions in electricity and thermal power generation).

This paper describes a technique for identifying hydrometeor particle types using airborne HIAPER Cloud Radar (HCR) and High Spectral Resolution Lidar (HSRL) observations. HCR operates at a frequency of 94 GHz (3 mm wavelength), while HSRL is an eye-safe lidar system operating at a wavelength of 532 nm. Both instruments are deployed on the NSF-NCAR HIAPER aircraft. HCR is designed to fly in an underwing pod and HSRL is situated in the cabin. The HCR and HSRL data used in this study were collected during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES). Comprehensive observations of the vertical distributions of liquid and mixed-phase clouds were obtained using in-situ probes on the aircraft and remote sensing instruments. Hydrometeor particle types were retrieved from HCR, HSRL, and temperature fields with a newly-developed fuzzy logic particle identification (PID) algorithm. The PID results were validated with in-situ measurements collected onboard the HIAPER aircraft by a 2D-Stereo (2D-S) cloud probe. Particle phases derived from the PID results compare well with those obtained from the 2D-S observations and agree in over 70 % of cases. Size distributions are also consistent between the two methods of observation. Knowledge of the particle type distribution gained from the PID results can be used to constrain microphysical parameterization and improve the representation of cloud radiation effects in weather and climate models.

We present a novel methodology for exploring 4D seismic data in the context of monitoring subsurface resources. Data-space exploration is a key activity in scientific research, but it has long been overlooked in favour of model-space investigations. Our methodology performs a data-space exploration that aims to define structures in the covariance matrix of the observational errors. It is based on Bayesian inferences, where the posterior probability distribution is reconstructed through trans-dimensional (trans-D) Markov chain Monte Carlo sampling. The trans-D approach applied to data-structures (termed ”partitions’) of the covariance matrix allows the number of partitions to freely vary in a fixed range during the McMC sampling. Due to the trans-D approach, our methodology retrieves data-structures that are fully data-driven and not imposed by the user. We applied our methodology to 4D seismic data, generally used to extract information about the variations in the subsurface. In our study, we make use of real data that we collected in the laboratory, which allows us to simulate different acquisition geometries and different reservoir conditions. Our approach is able to define and discriminate different sources of noise in 4D seismic data, enabling a data-driven evaluation of the quality (so-called ”repeatability’) of the 4D seismic survey. We find that: (1) trans-D sampling can be effective in defining data-driven data-space structures; (2) our methodology can be used to discriminate between different families of data-structures created from different noise sources. Coupling our methodology to standard model-space investigations, we can validate physical hypothesis on the monitored geo-resources.

We synthesized N2O emissions over North America using 17 bottom-up (BU) estimates from 1980-2016 and five top-down (TD) estimates from 1998-2016. The BU-based total emission shows a slight increase owing to U.S. agriculture, while no consistent trend is shown in TD estimates. During 2007-2016, North American N2O emissions are estimated at 1.7 (1.0-3.0) Tg N yr-1 (BU) and 1.3 (0.9-1.5) Tg N yr-1 (TD). Anthropogenic emissions were twice larger than natural fluxes from soil and water. Direct agricultural and industrial activities accounted for 68% of total anthropogenic emissions, 71% of which was contributed by the U.S. Our estimates of U.S. agricultural emissions are comparable to the EPA greenhouse gas (GHG) inventory, which includes estimates from IPCC tier 1 (emission factor) and tier 3 (process-based modeling) approaches. Conversely, our estimated agricultural emissions for Canada and Mexico are twice as large as the respective national GHG inventories based on tier 1 approaches.

Runoff events play an important role for nitrate export from catchments, but the variability of nutrient export patterns between events and catchments is high and the dominant drivers remain difficult to disentangle. Here, we rigorously asses if detailed knowledge on runoff event characteristics can help to explain this variability. To this end, we conducted a long-term (1955 - 2018) event classification using hydro-meteorological data, including soil moisture, snowmelt and the temporal organization of rainfall, in six neighboring mesoscale catchments with contrasting land use types. We related these event characteristics to nitrate export patterns from high-frequency nitrate concentration monitoring (2013 - 2017) using concentration-discharge relationships. Our results show that small rainfall-induced events with dry antecedent conditions exported lowest nitrate concentrations and loads but exhibited highly variable concentration-discharge relationships. We explain this by a low fraction of active flow paths, revealing the spatial heterogeneity of nitrate sources within the catchments and by an increased impact of biogeochemical retention processes. In contrast, large rainfall or snowmelt-induced events exported highest nitrate concentrations and loads and converged to similar chemostatic export patterns across all catchments, without exhibiting source limitation. We explain these homogenous export patterns by high catchment wetness that activated a high number of flow paths. Long-term hydro-meteorological data indicated an increase of events with dry antecedent conditions in summer and decreased snow-influenced events. These trends will likely continue and lead to an increased nitrate concentration variability during low-flow seasons and to changes in the timing of largest nitrate export peaks during high-flow seasons.

The transient climate response (TCR) is 20% higher in the Alfred Wegener Institute Climate Model (AWI-CM) compared to the Max Planck Institute Earth System Model (MPI-ESM) whereas the equilibrium climate sensitivity (ECS) is only by less than 10% higher in AWI-CM. These results are largely independent of the two considered model resolutions for each model. The two coupled CMIP6 models share the same atmosphere-land component ECHAM6.3 developed at the Max Planck Institute for Meteorology (MPI-M). However, ECHAM6.3 is coupled to two different ocean models, namely the MPIOM sea ice-ocean model developed at MPI-M and the FESOM sea ice-ocean model developed at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). A reason for the different TCR is related to ocean heat uptake in response to greenhouse gas forcing. Specifically, AWI-CM simulations show stronger surface heating than MPI-ESM simulations while the latter accumulate more heat in the deeper ocean. The vertically integrated ocean heat content is increasing slower in AWI-CM model configurations compared to MPI-ESM model configurations in the high latitudes. Weaker vertical mixing in AWI-CM model configurations compared to MPI-ESM model configurations seems to be key for these differences. The strongest difference in vertical ocean mixing occurs inside the Weddell Gyre and the northern North Atlantic. Over the North Atlantic, these differences materialize in a lack of a warming hole in AWI-CM model configurations and the presence of a warming hole in MPI-ESM model configurations. All these differences occur largely independent of the considered model resolutions.

Detection of chemical signatures from the core-mantle boundary (CMB) could provide an unprecedented glimpse into our planet’s deep interior and ancient past. Several isotopic and elemental anomalies in ocean island basalts (OIBs) have been proposed as core tracers. However, the process(es) by which particular chemical signatures from the core are conveyed into the mantle remain uncertain. Here we propose a hybrid mechanism that results from a collaborative feedback between dynamic topography, porous infiltration of liquid metal into submerged rock, gravitational collapse of weakened metal-silicate mush, and draw-down of additional rocks from above in the induced small-scale mantle circulation. Using a mantle convection model coupled to gravitational spreading of a thin layer, we show that this mechanism achieves parity with metal-mush interaction alone when the layer is $\sim$10$^5$ times less viscous than overlying mantle.

Pyrogenic dissolved organic matter (pyDOM) is known to be an important biogeochemical constituent of aquatic ecosystems and the carbon cycle. While our knowledge of pyDOM’s production, composition, and photolability has been studied recently, we lack an understanding of potential microbial mineralization and transformation of pyDOM in the biogeosphere. Thus, leachates of oak charred at 400 and 650 °C, as well as their photodegraded counterparts, were incubated with a soil-extracted microbial consortium for up to 96 days. Over the incubation, significantly more carbon was biomineralized from the lower versus higher temperature char leachate (45% versus 37% lost, respectively). Further, the photodegraded leachates were biomineralized to significantly greater extents than their fresh non-photodegraded counterparts. Kinetic modeling identified the mineralizable pyDOC fractions to have half-lives of 9 to 13 days. Proton nuclear magnetic resonance spectroscopy indicated that the majority of this loss could be attributed to low molecular weight constituents of pyDOM (i.e., simple alcohols and acids). Further, quantification of benzenepolycarboxylic acid molecular markers indicated that condensed aromatic compounds in pyDOM were biomineralized to much less extents (4.4 and 10.1% decrease in yields of ΣBPCA-C over 66 days from Oak-400 and Oak-650 pyDOM, respectively), but most of this loss could be attributed to biomineralization of smaller condensed clusters (4 aromatic rings or less). These results highlight the contrasting bioavailability of different portions of pyDOM and the need to examine both to evaluate its role in aquatic heterotrophy and its environmental fate in the hydrogeosphere.

The ablation of phosphorus from interplanetary dust particles entering the Earth’s atmosphere is a potentially significant source of this key bio-element. In this study, the atmospheric chemistry of phosphorus is explored by developing a reaction network of possible routes from PO, the major ablation product in the upper mesosphere/lower thermosphere region, to the stable reservoirs H3PO3 and H3PO4 that become incorporated into meteoric smoke particles as metal phosphites and phosphates, respectively. The network is constructed with reactions whose kinetics have been measured experimentally, together with reactions where theoretical rate coefficients are estimated using a combination of electronic structure theory calculations and a Rice-Ramsperger-Kassel-Markus master equation treatment. The network is then incorporated into a global chemistry-climate model, together with a phosphorus meteoric input function. The estimated global mean P deposition flux, in the form of sub-micron sized meteoric smoke particles, is 1 × 10-8 g m-2 yr-1, with a maximum of ~5 × 10-8 g m-2 yr-1 over the northern Rockies, Himalayas and southern Andes. The estimated fraction of ablated phosphorus forming bio-available metal phosphites is 11%, which results from the very large concentrations of O and H compared to OH in the upper mesosphere. A layer of OPO is predicted to occur at 90 km with a peak of concentration of ~50 cm-3; this is the counterpart of the well-known layers of meteoric metals such as Na and Fe, and may be observable spectroscopically.

We provide high-resolution maps of quasi-static Poynting flux (PF) in each hemisphere based on nine-satellite years of Defense Meteorological Satellite Program (DMSP) data. Conjugate comparisons from ~850 km reveal more quasi-static PF arriving in the northern hemisphere (NH) than the southern hemisphere (SH). This tendency is clear in the dawn-dusk sectors and during intervals when Kp < 3, which accounts for ~80% of the study interval. Summer-to-summer comparisons indicate this asymmetry is partially associated with more NH solar illumination, which supports stronger NH field-aligned currents (FAC). Differing hemispheric FAC configurations may also play a role. Our findings support and broaden earlier reports of similar NH preference for the deposition of Alfvenic PF. Regionally the NH has stronger dusk-region PF, while the SH has stronger mid-morning PF. We find PF deposition in the near-cusp regions that rivals and often exceeds the PF intensity in the auroral zones.

We discuss results on plasma density profile modifications in the F-region ionosphere caused by HF heating with the frequency f0 in the range [(-150 kHz)-(+75 kHz)] around the 4th electron gyroharmonic 4fc. The experiments were conducted at the HAARP facility on June 2014. The multi-frequency Doppler Sounder (MDS) which measures the phase and amplitude of reflected sounding radio waves complemented by the observations of the Stimulated Electromagnetic Emission (SEE) were used for the diagnostics of the plasma perturbations. We detected noticeable plasma expulsion from the reflection region of the pumping wave, and from the upper hybrid region, the expulsion from the latter one had been strongly suppressed for f0≈4fc. The plasma expulsion from the upper hybrid region was accompanied with the sounding wave’s anomalous absorption slower developing for f0≈4fc. Also, slower developing and weaker expulsion was detected for the height region between the pump wave reflection and upper hybrid altitudes.