A small gradient in the densities (Δρ) of two rivers was recently shown to develop coherent streamwise orientated vortices (SOVs) in the mixing interface of their confluence. We further investigate this phenomenon at the Coaticook and Massawippi confluence (Quebec, Canada) using eddy-resolved numerical modelling to examine how the magnitude and direction of Δρ; affect this secondary flow feature. Results show that a front from the denser channel always slides underneath the lighter channel independent of the direction of Δρ. When the fast tributary (Coaticook) is denser, coherent clockwise rotating density SOVs tend to form on the slow (Massawippi) side. However, when the slow Massawippi is denser by the same magnitude, anticlockwise secondary flow caused principally by shear induced interfacial instabilities develop on the fast Coaticook side. This shows the inertia of the tributary opposing the lateral propagation of the dense front shapes the secondary flow characteristics of the mixing interface. Moreover, in the absence of a density difference, anticlockwise SOVs are predicted by the model which correspond well to new aerial observations of anticlockwise SOVs at the site. A densimetric Froude number (Fd) convention accounting for the direction of Δρ is proposed to accurately convey the local inertial forces that oppose the lateral propagation of the dense front. Finally, a conceptual model of the mixing interface’s secondary flow structure over a spectrum of plausible Fd values is proposed. The Fd convention provides a flexible and consistent metric for use in future studies examining the effects of Δρ on river confluence hydrodynamics.

We study how the vertical distribution of relative humidity (RH) affects climate sensitivity, even if it remains unchanged with warming. Using a radiative-convective equilibrium model, we show that the climate sensitivity depends on the shape of a fixed vertical distribution of humidity, tending to be higher for atmospheres with higher humidity. We interpret these effects in terms of the effective emission height of water vapor. Differences in the vertical distribution of RH are shown to explain a large part of the 0 to 30% differences in clear-sky sensitivity seen in climate and storm-resolving models. The results imply that convective aggregation reduces climate sensitivity, even when the degree of aggregation does not change with warming. Combining our findings with relative humidity trends in reanalysis data shows a tendency toward Earth becoming more sensitive to forcing over time. These trends and their height variation merit further study.

Vertical motions of Earth’s surface are used to inform almost all branches of the Earth Sciences, and central role in understanding geological, biological and climatic processes. An important challenge is generating enough information to reliably constrain histories of vertical motion. Significant effort has been expended in generating information about denudation (e.g. from thermochronometry), uplift (e.g. from stable isotopes or drainage analyses) and subsidence patterns. However, a canonical inventory of measurements that determine continental uplift on timescales pertinent to growth and decay of continental topography does not exist. We address this issue using the distribution of unequivocally marine rock recorded in new, detailed, paleobiological inventories. We show that these new compilations of paleobiological and paleoenvironmental data, that were generated to address paleobiological problems, also provide an unprecedented number of self-consistent, high-resolution measurements of continental and ocean island uplift. We focus on the Cretaceous to Recent history, which captures the large-scale marine incursions of the continents. Our results highlight that significant improvements can be made in understanding the histories of the continents in using these measurements of uplift. We present examples from North and South America, southern Africa and Australia to show how this new database can be explored to better understand the processes that generate high topography. They emphasize the importance of large inventories of paleobiological data for understanding long-wavelength uplift and the role tectonic and mantle convective processes play in generating continental topography.

We discover a remarkable correlation between the inter-tremor time interval and the slenderness ratio of the overriding plate in subduction zones all over the world. In order to understand this phenomenon better, we perform numerical simulations of 3D deformation. The numerical bending studies show that critical bending load and slenderness ratio indeed have an inverse nonlinear relation between them – identical to the classical Euler’s critical load relation, and closely resembling the relationship observed between the inter-tremor time interval and the slenderness ratio of the overriding plate. From the above analysis, we conclude that the observed relation is the result of bending of the overriding continental plate. In addition, we analyze the surficial 3D spatio-temporal displacements of the overriding plates in Cascadia and Alaska using 3-component GPS data. We find that these deformations are consistent with the bending of the overriding continental crust. Based on these novel observations and guided by numerous existing scientific observations and findings, we propose an Episodic Bending and Collapse model of subduction zones, wherein periodic geodetic changes and tectonic-tremor activity, result from the episodic bending of the overriding continental crust and its rapid collapse on the subducting oceanic slab. According to this model, geodetic measurements, previously inferred as slow slip, are the surficial expressions of slowly-evolving bending and rapid collapse of the overriding plate, while tremor swarms result from the striking of the collapsing overriding plate on the subducting slab (as opposed to slipping or shearing).

Uturuncu volcano is situated in the Bolivian Andes, directly above the world’s largest crustal body of silicic partial melt, the Altiplano-Puna Magma Body (APMB). Uturuncu last erupted 250,000 years ago, yet is seismically active and lies at the centre of a 70 km diameter uplifted region. Here, we analyse seismicity from 2009 to 2012. Our earthquake locations, using a newly developed velocity model, delineate the top and bottom of the APMB, reveal individual faults, and reconcile differences in depth distribution between previous studies. Spatial clustering analysis of these earthquakes reveals the orientations of the faults, which match stress orientations from seismic anisotropy. Earthquake b-values derived from moment magnitudes (1.4) differ significantly from those using local magnitude measurements (0.8). We suggest that, if possible, moment magnitudes should always be used for accurate b-value analysis. We interpret b-values > 1 in terms of fluid-enhanced seismicity. Shallow seismicity local to Uturuncu yields b-values > 1.1 with some temporal variation, suggesting fluid migration along pre-existing faults in a shallow hydrothermal system, likely driven by advection from the APMB. Intriguingly, events deeper than the APMB also yield large b-values (1.4), mapping the ascent into the lower crust of fluids originating from a subducting slab. Cumulatively, these results provide a picture of an active magmatic system, where fluids are exchanged across the more ductile APMB, feeding a shallow, fault-controlled hydrothermal system. Such pathways of fluid ascent may influence our understanding of arc volcanism, control future volcanic eruptions and promote the accumulation of shallow hydrothermal ore deposits.

GRACE-FO (GFO) and Swarm are two LEO missions that, among others, provide non-gravitational acceleration measurements required for geopotential model development and modelling of non-gravitational forces acting upon them. Unfortunately, the performance of the accelerometers on board for both missions is not the expected. Measurements from both missions present dominant bias jumps that occur on all accelerometer axes and they have been linked to the satellites’ entrance to and exit from the Earth’s shadow. These jumps are estimated and corrected at Level 1A of GFO C and at Level 2 of Swarm C in an optimal way using Least Squares methodology. The corresponding variances of the jumps are also calculated. Furthermore, the measurements contain spurious signals and dominant spikes mostly connected with thruster activation, mainly in the equatorial region or high temperature sensitivity. These disturbances have a significant impact on the data analysis. We propose an alternative weighting filter methodology to generate Level 1B data from Level 1A for GFO C that includes the attenuated spikes and their corresponding variances and does not involve the removal of the spikes nor does it include any interpolation to fill data gaps. This methodology is used for Swarm C accelerometer Level 2 dataset as well. Using spectral domain methods, we show that the newly generated GFO Level 1B and Swarm Level 2 data are not contaminated by the presence of spikes and data jumps. In the polar regions, mostly at the South pole, spikes in the measurements are connected to magnetic disturbances when the satellites enter these regions. Our proposed methodology contains an optimal and unbiased dataset of non-gravitational acceleration measurements that can be used for the estimation of geopotential models and also for the investigation of the accelerometer’s response to electromagnetic disturbances and the modelling of other non-gravitational accelerations to derive thermospheric neutral densities.

The plumes of Enceladus produce a cloud of neutral H2O molecules and, via dissociation, OH and O. These neutrals are ionized by charge exchange, solar UV, and electron impacts, producing the thermal water group ions W+ (O+, OH+, H2O+, and H3O+) which become energized in Saturn’s magnetosphere. We first separate the components of energetic (~96 keV) W+ using Cassini Charge-Energy-Mass Spectrometer (CHEMS) data from 78 near equatorial main ring current passes (dipole L = 7-16, ±10° in latitude) in 2004-2010. We find ~53% O+, ~22% OH+, ~22% H2O+, and ~3% H3O+ when averaged over L = 7-16, resulting in a mean water group mass of 16.7 amu. At 7 < L < 21, we find abundance ratios for O+/W+, OH+/W+, and H2O+/W+ that vary little with L. However, while H3O+/W+ is nearly constant at L > 13, H3O+/W+ tends to increase persistently at L < ~10. The large O+ abundance qualitatively agrees with the broad atomic O cloud observed by Cassini and predicted by some models. Our observation of H2O+/W+ > ~20% out to L ~ 21 suggests that neutral H2O spreads throughout the magnetosphere rather than being confined to a narrow H2O torus centered on Enceladus’ orbit.

Metamorphic core complexes (MCC) provide a rare glimpse into thermomechanical processes in the lithosphere and play a substantial role in the evolution of the crust. The North American Cordillera contains a northwest trending line of MCCs, which have been extensively studied using bedrock thermochronology and modelling approaches to better understand extensional processes related to Cordilleran collapse. While these studies have proposed a wide variety of models to explain the timing and mechanism behind MCC formation, few have considered the syn-deformational basin record, which preserves a unique archive of sediment sources in adjacent MCC highlands. This study focuses on the Deer Lodge Valley, located in the hanging-wall of the Anaconda MCC. We utilize detrital zircon (U-Pb)-(U-Th)/He double dating in the context of stratigraphic and sedimentologic analyses, and HeFTy time-temperature modelling to reconstruct basin evolution. Stratigraphic analysis shows that the basin was dominated by deposition of coalescing alluvial fans, with sediment sourced directly from the footwall of the detachment fault. U-Pb maximum depositional ages indicate late Paleocene to early Eocene proximal basin sedimentation. (U-Th)/He analyses from U-Pb dated zircons range from 194-32 Ma; >70% of dates are Eocene. Preliminary HeFTy modelling shows a period of rapid cooling between 65-55 Ma, which is supported by short (<10 Myr) sediment lag times and inferred rapid exhumation in the MCC. Our findings support a link between MCC exhumation and basin formation. They further depict a potentially earlier period of MCC exhumation than previous work has proposed, indicating an earlier onset of extension in western Montana.

The Noerdlinger Ries is regarded as one of the best studied terrestrial impact craters. Because of its accessibility and its excellent preservation this area continues to be a research target for numerous international students, geoscientists and impact researchers. Here astronauts from the Apollo 14 and 17 missions studied the identification and sampling of impact rocks to prepare for their trip to the Moon. Today it is a regular training area for ESA astronauts and project planners. As an ‘In-crater museum’, the Ries Crater Museum offers insights into the spectacular event 15 million years ago. It illuminates the significance and the larger context of the Ries event to a wider audience: our Solar System, comets, asteroids, meteorites, and the special role of impacts in the evolution of our Solar System and Earth. Permanent didactic challenges in this context are: Most of the relevant processes cannot be observed directly. The time scale considered is very large and very different from that of a human being. Large impact-events took place long ago (Millions and billions of years ago) and were/are very rare events by human standards. Also, only remains of large and relatively new impacts are preserved and visible to some extent. All this often leads to the conclusion that impact processes are part of the past without actual relevance except at the cinema. In reality objects from space hit Earth every day, every hour, every minute, every second. But since they are usually very small, their fall is rarely spectacular and usually not noticed. We are currently working on the renewal of the meteorite area in our museum. In this context we plan to draw visitors’ attention to recent fall events and to show their special importance for science and society. To demonstrate the ongoing bombardment of the earth we present online or ‘near online’ observations to make visible the usually invisible to the ‘normal’ eye. We try to overcome the restrictions of timescale and take a sharp look into the present by reducing time slots and using a ‘magnifying glass’. We present concepts and approaches. Suggestions and comments are welcome!

Numerous recent studies found significant correlations between weakening of the Gulf Stream (GS) and rising coastal sea level (CSL) along the U.S. East Coast. Based on monthly altimeter data and Florida Current transport, Chi et al. (2023; here, CH23) argued that geostrophic adjustment of the GS is unlikely to drive variations in CSL in the Mid-Atlantic Bight (MAB). It is argued here that this conclusion cannot be universally applicable to all cases, since the monthly data disregard correlations previously found for short time scales based on hourly and daily data; the impact of GS variability on time scales of decades and longer as well as potential time lags between the GS and CSL variability were also not considered by CH23. Examples are given here to demonstrate the important role of the GS in post hurricane coastal flooding.

This study investigated the synchronous responses of vegetation to extreme temperatures and/or precipitation in the middle to high latitudes of Asia using semi-monthly observations of the leaf area index (LAI) from 1982 to 2016. The extreme states of vegetation and climate were specified using standard anomalies of the annual cycle removed variables. The results show that the area with the maximum/minimum LAI increased or decreased in correspondence with global warming. The LAI reached its maximum mostly in spring and autumn, and its minimum in summer. Generally, extreme cold and/or wet conditions inhibited forest and crop growth in the area south of 60°N, particularly from October to November. In contrast, extremely hot and/or dry conditions promoted forest growth, particularly in the central and northern parts of Siberia from August to September. However, in the arid areas of Central Asia and the Mongolian Highlands which are covered mainly by sparse vegetation and grasses, low temperature extremes and/or strong precipitation promoted vegetation growth, while high temperature extremes and/or low precipitation had adverse effects on vegetation growth. The compound extreme climates of hot-and-dry and cold-and-wet were more frequent than the cold-and-dry and hot-and-wet climates. The overall positive response of vegetation was superior to that of the negative response. The results of this study suggest a continuous increase in vegetation density and coverage over the boreal region in the future if the warming trend persists. The consequent climate feedback at regional and global scales should be given more attention.

The field of MultiSector Dynamics (MSD) explores the dynamics and co-evolutionary pathways of human and Earth systems with a focus on critical goods, services, and amenities delivered to people through interdependent sectors. This commentary lays out core definitions and concepts, identifies MSD science questions in the context of the current state of knowledge, and describes ongoing activities to expand capacities for open science, leverage revolutions in data and computing, and grow and diversify the MSD workforce. Central to our vision is the ambition of advancing the next generation of complex adaptive human-Earth systems science to better address interconnected risks, increase resilience, and improve sustainability. This will require convergent research and the integration of ideas and methods from multiple disciplines. Understanding the tradeoffs, synergies, and complexities that exist in coupled human-Earth systems is particularly important in the context of energy transitions and increased future shocks.

With a unique biogeophysical signature relative to other freshwater sources, meltwater from glaciers plays a crucial role in the hydrological and ecological regime of high latitude coastal areas. Today, as glaciers worldwide exhibit persistent negative mass balance, glacier runoff is changing in both magnitude and timing, with potential downstream impacts on infrastructure, ecosystems, and ecosystem resources. However, runoff trends may be difficult to detect in coastal systems with large precipitation variability. Here, we use the coupled energy balance and water routing model SnowModel-HydroFlow to examine changes in timing and magnitude of runoff from the western Juneau Icefield in Southeast Alaska between 1980 to 2016. We find that under sustained glacier mass loss (-0.57 +/-0.12 m w.e. a-1), several hydrological variables related to runoff show increasing trends. This includes annual and spring glacier ice melt volumes (+10% and +16% decade-1) which, because of higher proportions of precipitation, translate to smaller increases in glacier runoff (+3% and +7% decade-1) and total watershed runoff (+1.4% and +3% decade-1). These results suggest that the western Juneau Icefield watersheds are still in an increasing glacier runoff period prior to reaching ‘peak water.’ In terms of timing, we find that maximum glacier ice melt is occurring earlier (2.5 days decade-1), indicating a change in the source and quality of freshwater being delivered downstream in the early summer. Our findings highlight that even in maritime climates with large precipitation variability, high latitude coastal watersheds are experiencing hydrological regime change driven by ongoing glacier mass loss.

Minibasins on continental margins trap turbidity currents transporting material downslope, but little is known about the inherently three-dimensional (3-D) mechanics of these confined flows. Utilizing new methodology, experimental results quantify flow dynamics in minibasins for the first time. It is shown that dynamics are dominated by 3-D circulation cell structures, across the fill-to-strip-to-spill transition that are controlled by flow discharge. Measurements of velocity throughout circulation cells indicate vorticity dominates strain rate with fluid rotating into the center of cells where it upwells: this influences minibasin sediment trapping potential and deposit heterogeneity. Flow properties link to depositional patterns on minibasin slopes. Specifically, higher input discharges are correlated with higher fluxes into the center of minibasins and reduced deposit tapering on minibasin slopes. This geometry is linked to the amount of sediment rich flow runup on the distal minibasin wall, where flow and sediment is delivered to circulation cells.

Although it has been well recognized that clouds tremendously affect the surface solar irradiance and its direct and diffuse partitions, accurately forecasting solar radiation in cloudy conditions remains a major challenge. This study focuses on two aspects of the challenge: impacts of cloud microphysics and model domain size. First, we will examine the sensitivity of surface solar radiation and its partitions to cloud microphysics by using the state of art Weather Research and Forecasting model specifically designed for simulating and forecasting solar radiation (WRF-Solar). A number of microphysical schemes will be tested, and comparison against the measurements of shallow cumulus clouds and stratiform clouds selected at the DOE ARM SGP Site. Efforts will be made to quantify the resultant uncertainty spread. Second, identifying the physical causes of the underlying model differences is even more challenging. To address this, we will introduce a new model evaluation framework based on different setups of WRF-Solar (single column, LES, and nested WRF). In particular, we will examine the effect of the number of LES grid columns and its lower limit producing reasonable results. Commonly used evaluation metrics will be used in our model evaluation, including the used RMSE, MAE, MAPE, and relative Euclidean distance. The results will provide physical insight into the understanding of cloud-radiation interactions and forecasting of solar radiation in cloudy conditions.

This manuscript presents the analysis of data from multiple ground- and space-based sensors in the North American region before, during, and after the 12 Oct. 2021 geomagnetic storm. The data show the formation and equatorward propagation of a density trough, which manifested within bottom-side and top-side electron density data as well as within maps of total electron content (TEC). During the recovery phase on the 13th, the equatorward edge of the trough settled at around 30° latitude and exhibited a steep density gradient. By the 14th, this sharp boundary had disappeared. Near this edge on the 13th, small-scale irregularities formed. The impact of these was observed within Global Positioning System (GPS) data as elevated rate of TEC index (ROTI) and presented as strong 35 MHz scintillations of cosmic radio sources as well as spread-F within ionograms from multiple digisonde systems. GPS and 35-MHz data demonstrated that the irregularity region was narrowly confined (≤5° wide) near the trough edge. The 35-MHz scintillation data also showed that the irregularities were moving relatively slowly at ~7 m s-1, likely toward the southeast. Density and velocity measurements demonstrate that the conditions near the trough boundary we highly favorable for the gradient drift instability (GDI) with the one-dimensional growth rate estimated to be ~0.01 s-1. Since these conditions persisted for many hours, this growth rate was more than sufficient for the GDI to be considered the primary driver of irregularity formation in this case.

Across diverse biomes and climate types, plants use water stored in bedrock to sustain transpiration. Bedrock water storage ($S_{bedrock}$, mm), in addition to soil moisture, thus plays an important role in water cycling and should be accounted for in the context of surface energy balances and streamflow generation. Yet, the extent to which bedrock water storage impacts hydrologic partitioning and influences latent heat fluxes has yet to be quantified at large scales. This is particularly important in Mediterranean climates, where the majority of precipitation is offset from energy delivery and plants must rely on water retained from the wet season to support summer growth. Here we present a simple water balance approach and random forest model to quantify the role of $S_{bedrock}$ on controlling hydrologic partitioning and land surface energy budgets. Specifically, we track evapotranspiration in excess of precipitation and mapped soil water storage capacity ($S_{soil}$, mm) across the western US in the context of Budyko’s water partitioning framework. Our findings indicate that $S_{bedrock}$ is necessary to sustain plant growth in forests in the Sierra Nevada — some of the most productive forests on Earth — as early as April every year, which is counter to the current conventional thought that bedrock is exclusively used late in the dry season under extremely dry conditions. We show that the average latent heat flux used in evapotranspiration of $S_{bedrock}$ can exceed 100 $W/m^{2}$ during the dry season and the proportion of water that returns to the atmosphere would decrease dramatically without access to $S_{bedrock}$.

A document by Bhagyashree Waghule. Click on the document to view its contents.