Numerical circulation modeling and observational studies have been conducted to understand the Loop Current (LC) system behaviors in the Gulf of Mexico (GoM). One of the factors that may influence the LC are upstream eddies from within the Caribbean Sea. By combining satellite altimetry, sea surface salinity and ocean color data, we demonstrate that mesoscale eddies from the western tropical Atlantic Ocean can eventually make their way to the Gulf of Mexico and affect the LC. In addition, our study shows that freshwater of Amazon and Orinoco River origin trapped within mesoscale eddies can also enter the GoM affecting the GoM stratification. This study provides insights into understanding variations of the LC system and showcases the roles of mesoscale eddies in connecting the open ocean and regional seas.

Fracture characterization is essential to hydrocarbon and geothermal exploration and production as well as carbon geo-sequestration. Active and passive measurements have been extensively applied to map fractures across various scales. Active and passive measurements have inherent advantages and limitations that complement each other. In this study, to improve the mapping of embedded fractures and the surrounding geomechanically altered regions, we integrate active shear-wave transmission measurement with passive acoustic-emission measurement collected during a lab-scale hydraulic-fracturing experiment. The proposed approach leverages the advantages of the two modalities of measurements, while minimizing the limitations. Polarized shear-wave transmission (active) measurement was collected before and after the hydraulic fracturing, and the acoustic emission (passive) measurement was collected during hydraulic fracturing. Two sets of two-dimensional maps of fracture and fracture-induced damage in axial, median and frontal planes were obtained by separately processing the physics-informed transformations of active and passive measurements. These 2D maps are then fed to wavelet-based image-fusion technique to integrate the two sources of information for the reliable mapping/imaging of the embedded fractures and the surrounding geomechanically altered regions. Plain word summary Fractures and geomechanical alterations embedded in a solid material can be characterized using active or passive measurements. Signal type, timing, duration and location of the source is controlled during an active measurement to allow optimal interactions of the propagating wave and the fractured material, whereas the signals due to waves generated by the processes of fracturing and geomechanical alterations are captured during a passive measurement. Active and passive measurements have advantages and limitations that complement each other. In this study, physics-informed transformations and wavelet-based image fusion are used to integrate the active and passive measurements to get the best of the two measurement modalities for purposes of reliable imaging of fractures and the surrounding geomechanically altered regions. Key points  Integration of active and passive measurements will leverage their strengths and minimize the limitations of individual measurement techniques.  To the best of authors’ knowledge, no reference exists where the two modalities are combined to characterize the fractures either in the field or laboratory scale.  We integrate active ultrasonic measurements with passive acoustic-emission measurements using physics-informed transformations and data fusion techniques.  The proposed method improves the imaging of embedded fractures and the surrounding geomechanically altered regions.  Two-dimensional maps of fracture and fracturing-induced damage is generated in axial, median and frontal planes.

The spectral-element method (SEM) for simulating wave propagation is widely used with adjoint methods for full-waveform inversion. Typically, SEM is used to compute forward and adjoint wavefields, which is then applied to evaluate the Fréchet derivatives for updating the seismic structural model. The Hessian is rarely computed as the high computational and storage costs, although it can improve the accuracy of the model update and model convergence. Instead the approximate Hessian is determined, which is obtained with less computational effort. We present a method for simultaneously constructing Fréchet and Hessian kernels on the fly, which we call Multi-solver spectral-element and adjoint methods (Multi-SEM). Rather than storing all the wavefields, Multi-SEM is computed on the fly and requires only about a 2-fold computational cost when compared to the computation of Fréchet kernels. Numerical examples demonstrate the functionality of the method and the computer codes are provided with this contribution.

River channels store large volumes of water globally, critically impacting ecological and biogeochemical processes. Despite the importance of river channel storage, there is not yet an observational constraint on this quantity. We introduce a 26-year record of entirely remotely sensed volumetric channel water storage anomaly (VCWS) on 26 major world rivers. We find mainstem VCWS climatology amplitude (VCWSCA) represents an appreciable amount of basin-wide terrestrial water storage variability (median 2.2%, range 0.05-13.8% across world rivers), despite the fact that mainstem rivers themselves represent an average of just 0.2% of basin area. We find that two global river routing schemes coupled with land surface models reasonably approximate VCWSCA (within {plus minus}50%) in only 19.2 % and 23.1 % of rivers considered (by model). These findings demonstrate VCWS is a useful measurement for assessing global hydrological model performance, and for advancing understanding of spatial patterns in global hydrology.

Dynamics of polar outlet glaciers vary with ocean tides, providing a natural laboratory to understand basal processes and ice rheology. We apply Terrestrial Radar Interferometry to close the spatiotemporal gap between GNSS and satellite observations. Three-hour flowfields collected over an eight day period at Priestley Glacier, Antarctica, validate and provide the spatial context for concurrent GNSS measurements. Ice flow is fastest during falling tides and slowest during rising tides. Principal components of the timeseries prove upstream propagation of tidal signatures $>$ 10 km away from the grounding line. Hourly, cm-scale horizontal and vertical flexure patterns occur $>$6 km upstream of the grounding line. Vertical uplift upstream of the grounding line is consistent with ephemeral re-grounding during low-tide impacting grounding-zone stability. Taken together, these observations identify tidal imprints on ice-stream dynamics on new temporal and spatial scales providing constraints for models designed to isolate dominating processes in ice-stream mechanics.

The long-wavelength geoid is sensitive to Earth’s mantle density structure as well as radial variations in mantle viscosity. We present a suite of inversions for the radial viscosity profile using whole-mantle models that jointly constrain the variations in density, shear- and compressional-wavespeeds using full-spectrum tomography. We use a Bayesian approach to identify a collection of viscosity profiles compatible with the geoid, while enabling uncertainties to be quantified. Depending on tomographic model parameterization and data weighting, it is possible to obtain models with either positive- or negative-buoyancy in the large low shear velocity provinces (LLSVPs). We demonstrate that whole-mantle density models in which density and $V_S$ variations are correlated imply an increase in viscosity below the transition zone, often near ~1000~km. Many solutions also contain a low-viscosity channel below 650~km. Alternatively, models in which density is less-correlated with $V_S$ – which better fit normal mode data – require a reduced viscosity region in the lower mantle. This feature appears in solutions because it reduces the sensitivity of the geoid to buoyancy variations in the lowermost mantle. The variability among the viscosity profiles obtained using different density models is indicative of the strong non-linearities in modeling the geoid and the limited resolving power of the geoid kernels. We demonstrate that linearized analyses of model resolution do not adequately capture the posterior uncertainty on viscosity. Joint and iterative inversions of viscosity, wavespeeds, and density using seismic and geodynamic observations are required to reduce bias from prior assumptions on viscosity variation and scalings between material properties.

Physics-based numerical modeling of earthquake source processes strives to predict quantities of interest for seismic hazard, such as the probability of an earthquake rupture jumping between fault segments. How to assess the predictive power of numerical models remains a topic of ongoing debate. Here, we investigate how sensitive are the outcomes of numerical simulations of sequences of earthquakes and aseismic slip to choices in numerical discretization and treatment of inertial effects, using a simplified 2-D crustal fault model with two co-planar segments separated by a creeping barrier. Our simulations demonstrate that simplifying inertial effects and using oversized cells significantly affects the resulting earthquake sequences, including the rate of two-segment ruptures. We find that a number of fault models with different properties and modeling assumptions can produce comparable frequency-magnitude statistics and static stress drops but have rates of two-segment ruptures ranging from 0 (single-segment ruptures only) to 1 (two-segment ruptures only). For sufficiently long faults, we find that long-term sequences of events can substantially differ even among simulations that are well-resolved by standard considerations. In such simulations, some outcomes, such as static stress drops, are stable among adequately-resolved simulations, whereas others, such as the rate of two-segment ruptures, can be highly sensitive to numerical procedures and physical assumptions, and hence cannot be reliably inferred. Our results emphasize the need to examine the potential dependence of simulation outcomes on the modeling procedures and resolution, particularly when assessing their predictive value for seismic hazard assessment.

Mesospheric winds from two longitudinal sectors at 53$^\circ$N latitude are combined to investigate quasi-two-days (Q2DWs) and their nonlinear interactions with tides. In a summer 2019 case study, we diagnose the zonal wavenumber $m$ of spectral peaks at expected frequencies through two dual-station approaches, a phase differencing technique (PDT) on individual spectral peaks and a least-squares procedure on family-batched peaks. Consistent results from the approaches verify the occurrences of Rossby-gravity modes ($m$=3 and 4 at periods $T$= 2.1d and 1.7d), and their secondary waves (SWs) generated from interactions with diurnal, semi-diurnal, ter-diurnal and quatra-diurnal migrating tides. We further extend the PDT to 2012$\textendash$2019, illustrating that Q2DWs exhibit significant interannual variability. Composite analysis reveals seasonal and altitude variations of the Rossby-gravity modes and their SWs. The Rossby-gravity modes maximize in local summer, whereas their 16- and 9.6-hr SWs appear more in winter, potentially originating from Q2DW-tide interactions in the opposite hemisphere.

This paper analyses the sensitivity of flood inundation due to levee breach against breach model parameters. A parametric levee breach model integrated into the 2D hydrodynamic numerical model Telemac-2D is used to simulate a levee breach flood event at Wonji, Ethiopia. Levee breach process parameters are systemically varied to find out their effect on the modelled flood inundation.The analysis of the model results show that the modelled flood inundation is sensitive to the final breach dimensions and breach location. However, the parameters describing the levee breach development have negligible influence on the modelled flood inundation. This implies that final breach dimension and breach location in an event of levee breach are the most important and decisive factors affecting the resulting inundation of the flood plain and as such should be given due consideration when creating flood inundation maps due to levee breach modelled by employing parametric breach model.

Wetlands are extremely dynamical systems and their behavior depends on the characteristics of the surroundings (topography, geology and vegetation, among others) as well as on meteorological and hydrological processes. Wetlands receive groundwater through diffuse upwelling and through springs. Studying upwelling is of great importance to e.g. evaluate the overall ecology or capacity to remove nitrate of the wetland system. One problem is that diffuse upwelling is difficult locate and measure. We analyze the temporal dynamics of a groundwater-fed wetland in central Jutland (Denmark) by the use of a range of thermal methods across a lowland stream valley. A monitoring system consisting of Distributed Temperature Sensing (DTS), wells with temperature depth profiles and thermal infrared (TIR) imaging on an unmanned aerial vehicle, in conjunction with hydrological and atmospheric data, provide a quasi 3D time-lapse characterization of the thermal behavior of the system, both on the ground and in the subsurface, over a period of two years. We infer potential locations of groundwater upwelling to the land surface by studying the temperature in both the wetland surface and the groundwater. Each thermal method provides different, partially overlapping estimates of the upwelling location and magnitude, highlighting the need to incorporate classic hydrological metrics to constrain the results obtained using heat as a tracer. The integration of these data indicates that temperature measurements can be used to study groundwater upwelling in stream valleys.

Most of the large terrestrial bodies in the solar system display evidence of past and/or current magnetic activity, which is thought to be driven by thermo-chemical convection in an electrically conducting fluid layer. The discovery of a large number of extrasolar planets motivates the search of magnetic fields beyond the solar system. While current observations are limited to their radius and minimum mass, studying the evolution of exoplanetary magnetic fields and their interaction with the atmosphere can open new avenues for constraining interior properties from future atmospheric observations. Here, we investigate the evolution of massive planets ($0.8-2$~$M_{\rm Earth}$) with different bulk and mantle iron contents. Starting from their temperature profiles at the end of accretion, we determine the structure of the core and model its subsequent thermal and magnetic evolution over $5$~Gyr. We find that the planetary iron content strongly affects core structure and evolution, as well as the lifetime of a magnetic field. Iron-rich planets feature large solid inner cores which can grow up to the liquid outer core radius, shutting down any pre-existing magnetic activity. As a consequence, the longest magnetic field lifetimes ($\sim 4.15$~Gyr) are obtained for planets with intermediate iron inventories ($50-60$~wt.\%). The presence of a small fraction of light impurities keeps the core liquid for longer and extends the magnetic field lifetime to more than $5$~Gyr. Even though the generated magnetic fields are too weak to be detected by ground facilities, indirect observations can help shedding light on exoplanetary magnetic activity.

The positive trend of the Southern Annular Mode (SAM) will impact the Southern Ocean’s role in Earth’s climate, however the details of the Southern Ocean’s response remain uncertain. We introduce a methodology to examine the influence of SAM on the Southern Ocean, and apply this method to a global ocean–sea-ice model run at three resolutions (1$^{\circ}$, 1/4$^{\circ}$ and 1/10$^{\circ}$). Our methodology drives perturbation simulations with realistic atmospheric forcing of extreme SAM conditions. The thermal response agrees with previous studies; positive SAM perturbations warm the upper ocean north of the windspeed maximum and cool it to the south, with the opposite response for negative SAM. The overturning circulation exhibits a rapid response that increases/decreases for positive/negative SAM perturbations and is insensitive to model resolution. The longer term adjustment of the overturning circulation, however, depends on the representation of eddies, and is faster at higher resolutions.

The intertropical convergence zone (ITCZ) exports energy and imports moisture in a way that has been well-understood for decades. By analyzing a set of uniform, non-rotating aquaplanet simulations we show that energy export and moisture convergence are general characteristics of warm humid regions, and not just of the ITCZ. Using an analysis method based on the column relative humidity, we find that the absorption of longwave radiation by clouds provides the necessary energy source to balance the horizontal energy export out of humid regions. The longwave absorption also induces a thermally direct circulation which lifts water vapor and leads to low-level moisture convergence into regions that are already quite humid. This feedback is similar to other cloud-longwave feedbacks which have been previously studied.

A water-steam two-phase fractured geothermal reservoir model is presented in this paper. Coupled flow and thermal processes are solved in the reservoir and fractures using the pressure-enthalpy formulation and water-steam phase behavior correlations. Both an implicit pressure, explicit enthalpy and a fully implicit solution algorithm have been developed. After model validation, this simulator is used to model the heat extraction rate from enhanced geothermal systems (EGS). The temperature and energy flux from the production well are plotted and analyzed. The effects of several key parameters on enhanced geothermal systems are investigated. It is found that injection rate, fracture spacing, well spacing, and effective fracture surface area have the biggest impact on the heat extraction rate. It is also found that heat conduction is the main contributor to the heat flux while convective fluid flow does not contribute much when the reservoir permeability i.e., the rate of gravity driven convection is low. The heat flux from the earth does not affect short-term EGS production but can be an important factor for long-term EGS development. The geothermal reservoir simulator presented in this paper can be used to optimize and design EGS in geothermal fields (fracture spacing, well spacing, injection rate, etc.).

We propose to make the damping time scale, which governs the decay of pseudo-elastic waves in the Elastic Viscous Plastic (EVP) sea ice solvers, independent of the external time step and large enough to warrant numerical stability for a moderate number of internal time steps. In this case, EVP becomes very close to the recently proposed modified EVP (mEVP) method in terms of stability. With the proposed damping time scale, the numerical stability of EVP is independent of mesh resolution in setups where the sea ice model component is called every time step of the ocean model. In a simple test case dealing with sea ice breaking under the action of a moving cyclone, EVP with specified damping time scales can produce linear kinematic features very similar to those from the mEVP method. There is more difference in simulated Arctic sea ice thickness and linear kinematic features in realistic configurations, but the difference is minor considering model uncertainties associated with parameter choices in sea ice models.

Radiocarbon (14C) is commonly used as a tracer of the carbon cycle to determine how fast carbon moves between different reservoirs such as plants, soils, rivers or oceans. However such studies mostly emphasize the mean value (as Δ14C) of an unknown probability distribution. We introduce a novel algorithm to compute Δ14C distributions from knowledge of the age distribution of carbon in compartmental systems at equilibrium. Our results demonstrate that the shape of the distributions might differ according to the speed of cycling of ecosystem compartments and their connectivity within the system, and are mostly non-normal. The distributions are also sensitive to the variations of Δ14C in the atmosphere over time, as influenced by the counteracting anthropogenic effects of fossil-fuel emissions (14C-free) and nuclear weapons testing (bomb 14C). Lastly, we discuss insights that such distributions can offer for sampling and design of experiments aiming to capture the precise variability of Δ14C values in ecosystems.

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!

Drought conditions significantly impact human and natural systems in the Tropics. Here, multiple observational and reanalysis products and ensembles of simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are analyzed with respect to drought areal extent over tropical land regions and its past and future relationships to the El Niño/Southern Oscillation (ENSO). CMIP5 models forced with prescribed sea surface temperatures compare well to observations in capturing the present day time evolution of the fraction of tropical land area experiencing drought conditions and the scaling of drought area and ENSO, i.e., increasing tropical drought area with increasing ENSO warm phase (El Niño) strength. The ensemble of RCP8.5 simulations suggests lower end-of-the-century El Niño strength-tropical drought area sensitivity. At least some of this lower sensitivity is attributable to atmosphere-ocean coupling, as historic coupled model simulations also exhibit lower sensitivity compared to the observations.