Shallow Slope Research Articles

Eikonal Equation Reproduces Natural Landscapes With Threshold Hillslopes

AbstractMany natural landscapes maintain steep planar hillslopes bounded at a typical angle, beyond which shallow landslides or slope failures remove the excess sediment volume by mass wasting. Here we show that the celebrated eikonal equation, derived from a landscape evolution model in conditions of negligible soil diffusion and fluvial erosion, accurately portrays the organization of these topographies. Referred to as “eikonal landscapes,” such solutions feature constant‐slope hillslopes originating from downstream boundary conditions and culminating in sharp upstream ridges. We demonstrate that the eikonal landscapes reproduce well a variety of natural landforms, including small islands, a volcano, and an extended mountain ridge. The boundary condition for the eikonal representation is specified through the natural landscape's slope‐area relation. Going beyond merely representing landscape statistical features, the present results provide a first‐of‐kind direct match of mathematical and natural landscapes.

The Impact of Vegetation Roots on Shallow Stability of Expansive Soil Slope under Rainfall Conditions

The impact of reinforcing vegetation roots on the stability of expansive soil slopes with moisture absorption and expansion was investigated. Then, poinsettia is selected as the slope protection plant, and ABAQUS software (version 2022) with secondary development is used to simulate the moisture absorption and expansion of the expansive soil slope. After that, the strength reduction method is employed to study the effects on the displacement and plastic zone, and on the shallow layer of the expansive soil slope at different rainfall conditions. The following points are revealed: (1) The roots of the poinsettia can reduce the displacement of the slope. But, when the rainfall intensity exceeds the soil permeability coefficient, the soil reinforcement effect decreases. (2) The poinsettia root system can alleviate the concentration of plastic strain, disperse the plastic zone, and increase slope stability along the distribution of the roots. (3) The poinsettia roots can improve the shallow stability of the slope. But when the rainfall intensity exceeds the surface permeability coefficient, the magnitude of the reinforcement decreases. The results demonstrate that the poinsettia roots can enhance shallow slope stability. However, with increasing rainfall intensity, the ability of the poinsettia roots to enhance shallow slope stability gradually weakens.

The use of a video and a small-scale model for rain-induced landslides in geotechnical engineering education

Small-scale physical models of geotechnical problems are thought-provoking didactic tools that motivate students by arousing their curiosity and facilitating the understanding of physical phenomena and theoretical concepts. This work presents the development of an educational video about slope stability failures and its contributing factors. It shows several small-scale models built in a glass wall tank measuring 150 x 50 x 10 cm. Layers of fine gravel were placed on a sloping surface of polystyrene to represent a slope with a layer of residual soil on rock. Toy houses and cars were used to represent anthropogenic agents, and water with dye represents the groundwater flow. Each model depicts a different scenario of shallow slope failure. The objective of the video is to show that most slope failures in urban areas result from natural and anthropogenic factors. Several influence factors are shown: porewater level rise, excavation, surcharge application, and solid urban waste deposition. The 6-minute video has had more than 130,000 views on YouTube. Thanks to its simple and concise language, the video is shown in basic education and science museum, as well as in graduate and undergraduate courses. A questionnaire survey was carried out with undergraduate students to assess how helpful the video was for the learning process. This article explains the construction of the model, the video script, and the strategies for its use, as well as its reception. It was found that the video promoted motivational and learning benefits of providing context, establishing relevance, and teaching inductively.

Artificial neural network-aided decoupled prediction of earthquake-induced shallow and deep sliding displacements of slopes

The Newmark-type predictive models are extensively used to estimate earthquake-induced sliding displacements (D) of slopes. Most existing models are designed for shallow slope failure using polynomial regression. Based on a large amount of decoupled sliding-block analyses, this paper proposes an artificial neural network (ANN)-aided model to predict D for both shallow and deep slope failures using peak ground acceleration and spectral acceleration at the 2 s period (SA(2 s)). Three sub-models are included for estimating shallow sliding displacement, representing dynamic response of sliding mass, and modifying the displacement for deep failure, respectively. The key features achieved are as follows: (1) the inputted SA is more easily accessible than the mean period (Tm) required by the existing models; (2) impedance ratio (IR) is utilized to account for stiffness conditions of geo-materials underlying slip surfaces; (3) powerful ANN is introduced for the first time as a surrogate of the decoupled analysis. The SA-based model generally yields lower biases and uncertainty than the existing models. Since larger D is produced for smaller IR, the existing models with a single IR value would be unconservative for relatively stiff underlying soils and/or soft overlying soils. Coefficients of the proposed model are provided for practical applications.

Intercomparison of tropospheric and stratospheric mesoscale kinetic energy resolved by the high‐resolution global reanalysis datasets

AbstractWith the development of advanced data assimilation and computing techniques, many modern global reanalysis datasets aim to resolve the atmospheric mesoscale spectrum. However, large uncertainties remain with respect to the representation of mesoscale motions in these reanalysis datasets, for which a clear understanding is lacking. The aforementioned challenges have served as a strong motivation to reveal and quantify their mesoscale differences. This study presents the first comprehensive global intercomparison of the tropospheric and stratospheric mesoscale kinetic energy and its spectra over two selected periods of summer and winter events among six leading high‐resolution atmospheric reanalysis products: European Centre for Medium‐Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5), China Meteorological Administration Reanalysis, Modern‐Era Retrospective Analysis for Research and Applications version 2, National Centers for Environmental Prediction's Climate Forecast System version 2 (CFSv2), Japanese 55‐year Reanalysis, and ECMWF Reanalysis‐Interim. A state‐of‐the‐art global operational model is adopted as a supplementary reference. Although all reanalysis datasets can reproduce broad distribution characteristics that are grossly consistent with the 9 km model, there are substantial discrepancies among them in magnitudes. The ability to capture mesoscale signals is closely linked to their resolutions, but it is also impacted by other factors, including, but not limited to, the selected types of energy, seasons, altitudes, latitudes, model diffusions, parametrization schemes, moist condition, assimilation methods, and observation inputs. Moreover, all datasets illustrate conclusive behaviors for the prevalence of the rotational component in the troposphere, whereas only very few products fail to exhibit the dominance of the divergent component in the stratosphere. Overall, stratospheric ERA5 and CFSv2 outperform the other reanalysis datasets, and only these two can reproduce the feature of the canonical kinetic energy spectrum with a distinct shift from a steeper slope (approximately −3) at lower wave numbers to a shallower slope (approximately −5/3) at higher wave numbers. In addition, the relative disparities among datasets increase dramatically with height, and they are more pronounced in the divergent component. It is also found that the correlations among these datasets are much weaker in the Tropics.

Effects of Speaking Rate on Variability of Second Formant Frequency Transitions in Dysarthria

Introduction: This study examined the utility of multiple second formant (F2) slope metrics to capture differences in speech production for individuals with dysarthria and healthy controls as a function of speaking rate. In addition, the utility of F2 slope metrics for predicting severity of intelligibility impairment in dysarthria was examined. Methods: Twenty three speakers with Parkinson’s disease and mild to moderate hypokinetic dysarthria (HD), 9 speakers with various neurological diseases and mild to severe ataxic or ataxic-spastic dysarthria (AD), and 26 age-matched healthy control speakers (CON) participated in a sentence repetition task. Sentences were produced at habitual, fast, and slow speaking rate. A variety of metrics were derived from the rising F2 transition portion of the diphthong /ai/. To obtain measures of intelligibility for the two clinical speaker groups, 15 undergraduate SLP students participated in a transcription experiment. Results: Significantly shallower slopes were found for the speakers with HD compared to control speakers. Steeper F2 slopes were associated with increased speaking rate for all groups. Higher variability in F2 slope metrics was found for the speakers with AD compared to the two other speaker groups. For both clinical speaker groups, there was a negative association between intelligibility and F2 slope variability metrics, indicating lower variability in speech production was associated with higher intelligibility. Discussion: F2 slope metrics were sensitive to dysarthria presence, dysarthria type, and speaking rate. The current study provided evidence that the use of F2 slope variability measures has additional value to F2 slope averaged measures for predicting severity of intelligibility impairment in dysarthria.

A carbonate palustrine system with marshes and shallow ephemeral lakes (Campanian, northeastern Iberian Basin)

The sedimentary and stratigraphic features of the low-gradient slope carbonate palustrine system of the Fortanete Formation (northeast Spain) during the early Campanian have been studied. The succession of the Fortanete Fm provides depositional record of a progressive transition to continental settings in an area that was predominantly marine for most of the Late Cretaceous. Palustrine systems can be developed in a wide variety of environments, however, modern analogues are scarce. The Fortanete Fm thus presents a great opportunity to study the stratigraphy, the sedimentary features and isotopic composition of a palustrine–marine influenced system. A total of 10 stratigraphic sections distributed along a 40 km wide and 80 km long area have been carried out in order to decipher the facies distribution in the system. This study led to the differentiation of three palaeoenvironments based on predominant lithofacies and sedimentary structures: (1) marshes and shallow low-gradient slope lakes; (2) ephemeral lakes, lake margins and prairies with variable water level and marine influence; and (3) mudflats with evaporites and fine siliciclastic input. The Fortanete Fm serves as an excellent case study for palustrine environments with the presence of typical palustrine features such as pseudomicrokarst, brecciation, black pebbles, desiccation cracks, nodules, Microcodium, and fenestral fabric. Most palustrine systems are associated with continental freshwater settings, whereas the Fortanete Fm displays evidence of intermittent marine influence in the distal studied sections. Carbon and oxygen isotope composition is within the range of typical freshwater lake carbonates and also corresponds to isotope composition of palustrine carbonates with marine influence. The Fortanete Fm shares a number of characteristics with freshwater continental and freshwater modern analogues. Comparison with these systems provides new insights on how modern analogues can be used to decipher the complexity of the processes developing these systems in the past.

On the issue of improving forecasting and prospecting complexes for identifying new sources of acutely scarce mineral raw materials (using the example of placer boulder chromium ores)

Te purpose of the work is to improve forecasting and search complexes to identify new sources of extremely scarce mineral raw materials for the Russian industry. Research methodology. Analysis of the available information on the features of the geological structure and conditions for the placement of shallow slope placers of boulder chromium ores, reconstruction of the buried relief of the bedrock, study of the structural features of the bedrock and modern (daytime) surface of the placers using analytical methods (trend analysis, etc.), study of the spatial variability of the estimated parameters of placer objects, identifcation of factors controlling the distribution of placer productivity. Results. Te reconstruction of the bedrock surface of the most fully studied type placer of cobblestone chrome ores of the Saranovskaya group (placer no. 2) was performed, the spatial variability of the estimated parameters of the placer was studied in the plan, and the factors controlling the distribution of the productivity of loose deposits were determined. Te longitudinal profle of the bedrock surface of the placer is an alternation of slightly inclined and subhorizontal areas, the formation of which is probably due to the repeated manifestation of erosion cycles in the history of the development of the region. Te distribution of productive deposits thickness in the direction of placer elongation is periodic. Te increased thickness of the productive layer runs to areas where slightly inclined sections of the bedrock are replaced by more gentle (sub-horizontal) ones, to the bases of “terraced” steps in the relief. Overall, there is a general trend towards an increase in the thickness of the productive layer down the slope. Te distribution of placer productivity indicators is uneven; in the direction of the elongation of the placer, zones of increase, maximum and decrease in productivity are distinguished, which are typical features of the “elementary placer” according to N. A. Shilo. Tere is a clear confnement of the most productive areas to the subhorizontal morphostructural elements of the buried bedrock in the middle part of the placer. Te microforms of the buried relief, which are associated with the most productive areas of the slope deposits, manifest themselves as negative “remains” of the linear trend of the bedrock surface marks. Te morphostructural elements of the buried bedrock of the shallow placer are inherited in the modern relief. Conclusions. Te analysis of the presented materials emphasizes the importance of morphostructural studies in predicting and searching for placers of pebble chromium ores of close ablation. During prospecting, the task of ultra-precise surveying of the day surface relief with additional mathematical transformations of the obtained data seems to be an urgent task.

Analysis of Slope Stability with Different Vegetation Types under the Influence of Rainfall

Rainfall-prone shallow landslides account for one-fifth of the global land area, and rainfall is critical to the mechanics and hydrology of shallow slopes. In typical geological disaster-prone areas, the hydrodynamic responses of slopes with different vegetation types under rainfall conditions require further study. The purpose of this study was to analyze the hydraulic stability of soils with different vegetation types under rainfall conditions and their effects on slope stability. Thus, the soil–water characteristic curves and water-stable aggregate characteristics of soils with three vegetation types were analyzed. A two-dimensional finite element model was used to simulate the slope stability of extreme rainfall environments with different rainfall durations. The results showed that the matric suction of soil with trees was less affected by rainfall with a better stability of water-stable aggregates than that of soil with shrubs and grass. The plastic strain cloud map showed that the maximum plastic strain occurred at the toe of the slope. In addition, the potential slip depth of slopes with trees was smaller than that of slopes with shrubs and grass. Under the two rainfall durations, the factor of safety (FoS) of slopes with trees changed by 0.06, whereas that of slopes with shrubs and grass changed by 0.1. The findings of this study provide valuable insights into changes in the stability of slopes with different vegetation types under varying rainfall conditions. It is of great significance to provide a scientific basis for the application of ecological measures in the prevention and control of mountain disasters and guide the implementation of appropriate land management measures.

Vegetation growth promotion and overall strength improvement using biopolymers in vegetated soils

Planting vegetation is a sustainable and eco-friendly method for shallow slope stabilization. However, in water-limited regions, this method is facing challenges such as retarded vegetation growth, which leads to unprotected soils. Biopolymers, with potentials in both vegetation growth promotion and soil strength enhancement, are therefore tested in this study with regard to their possibility in assisting soil reinforcement with vegetation through vegetation cultivation and direct shear tests. Both sugar-based and protein-based biopolymers improved water availability to growing plants and nutrient uptake. The most suitable polysaccharide xanthan gum was adopted to further explore the effects of treatment conditions (i.e., blending content) and external environment (i.e., precipitation) on the vegetated soil performance. Under a variety of water supplies, xanthan gum with a medium blending content of 0.5% (i.e., with respect to dry soil mass) led to the most substantial improvement in the ability to resist shear loading. This indicates that the appropriate dosage of biopolymers used at the initial stage of plant growth should provide moderate bond strength between soil particles, while not impeding root penetration. Supported by the obtained results, biopolymers are suggested to be used in combination with plants for soil reinforcement for the best efficiency.

The Mass–Metallicity Relation of Dwarf Galaxies at Cosmic Noon from JWST Observations

We present a study of the mass–metallicity relation (MZR) of 51 dwarf galaxies (M ⋆ ≈ 106.5–109.5 M ⊙) at z = 2–3 from the A2744 and SMACS J0723-3732 galaxy cluster fields. These dwarf galaxies are identified and confirmed by deep JWST/NIRISS imaging and slitless grism spectroscopic observations. By taking advantage of the superior performance of JWST and the gravitational lensing effect, we extend the previous MZR relation at z = 2–3 to a much lower-mass regime down by ≈2.5 orders of magnitude as compared with previous studies. We find that the MZR has a shallower slope at the low-mass end (M ⋆ < 109 M ⊙), with a slope turnover point of ≈109 M ⊙. This implies that the dominating feedback processes in dwarf galaxies may be different from that in massive galaxies. From z = 3, to z = 2, the metallicity of the dwarf galaxies is enhanced by ≈0.09 dex for a given stellar mass, consistent with the mild evolution found in galaxies with higher mass. Furthermore, we confirm the existence of a fundamental metallicity relation (FMR) between the gas-phase metallicity, stellar mass, and star formation rate in dwarf galaxies at z = 2–3. Our derived FMR, which has no significant redshift evolution, can be used as a benchmark to understand the origin of the anticorrelation between the star formation rate and metallicity of dwarf galaxies in the high-z Universe.

Assessing Variations in the Predictive Skill of Ensemble Snowband Forecasts with Object-Oriented Verification and Self-Organizing Maps

Abstract We used object-oriented verification and self-organizing maps (SOMs) to identify patterns in environmental parameters correlating with mesoscale snowband predictive skill by the High-Resolution Ensemble Forecast (HREF) system between 2017 and 2022. First, HREF snowband forecasts for 305 banding events were verified based on similarities between forecast and observed feature properties. HREF members performed comparably, demonstrating large positional errors, but the non-time-lagged High-Resolution Rapid Refresh member demonstrated the greatest overall skill. Observed banding events were clustered by 500-hPa geopotential height anomalies, mean sea level pressure, vertical velocity, frontogenesis, and saturation equivalent potential vorticity from the European Centre for Medium-Range Weather Forecasts Reanalysis version 5 using SOMs. Clusters reaffirmed the presence of midlevel frontogenesis, ascent, and reduced stability in most banding cases, and the predominant synoptic environments conducive to band development. Clusters were compared to determine whether patterns in the variables were correlated with predictive skill. Strength of upward motion was correlated with skill, with the strongest upward motion cases verifying 10% better than the weakest upward motion cases due to smaller positional error. Additionally, events with a single region of strong upward motion verified better than events with disorganized, but comparably intense, upward motion. The magnitude of frontogenesis was uncorrelated with skill, but events with more upright frontogenesis collocated with the band centroid were better predicted than events with shallower slopes and low-level frontogenesis displaced toward warmer air. The skill variance associated with different vertical motion magnitudes could assist forecasters in modulating forecast confidence, while the most common types of errors documented here may be beneficial to model developers in refining HREF member snowfall forecasts. Significance Statement High-resolution numerical weather prediction (NWP) models generally have limited predictive skill for mesoscale snowband forecasts. Even so, some snowbands are forecast by NWP models with much greater skill than others. In this work, we apply artificial intelligence to group snowband events based on atmospheric conditions and then determine whether different groups are easier or harder for models to predict. Identification of these groups could help forecasters know when to trust or be skeptical of NWP output and help developers improve snowband formation processes in NWP models.

The contribution of faint Lyman-αemitters to extended Lyman-αhalos constrained by MUSE clustering measurements

Recent detections of extended Lyman-αhalos around Lyαemitters (LAEs) have been reported on a regular basis, but their origin is still under investigation. Simulation studies predict that the outer regions of the extended halos contain a major contribution from the Lyαemission of faint, individually undetected LAEs. To address this matter from an observational angle, we used halo occupation distribution (HOD) modeling to reproduce the clustering of a spectroscopic sample of 1265 LAEs at 3 &lt; z &lt; 5 from the MUSE-Wide survey. We integrated the Lyαluminosity function to estimate the background surface brightness due to discrete faint LAEs. We then extended the HOD statistics inwards towards small separations and computed the factor by which the measured Lyαsurface brightness is enhanced by undetected close physical neighbors. We considered various clustering scenarios for the undetected sources and compared the corresponding radial profiles. This enhancement factor from LAE clustering depends strongly on the spectral bandwidth Δvover which the Lyαemission is integrated and this value can amount to ≈20 − 40 for small values of Δv(around 200 − 400 km s−1) as achieved by recent studies utilizing integral-field spectrographic data. The resulting inferred Lyαsurface brightness of faint LAEs ranges between (0.4 − 2)×1020 erg s−1 cm−2 arcsec−2, with a very slow radial decline outwards. Our results suggest that the outer regions of observed Lyαhalos (R ≳ 50 pkpc) could indeed contain a strong component from external (but physically associated) LAEs, and may even be dominated by them. It is only for a relatively shallow faint-end slope of the Lyαluminosity function that this contribution from clustered LAEs would be rendered insignificant. We also confirm that the observed emission from the inner regions (R ≤ 20 − 30 pkpc) is too bright to be substantially affected by clustering. We compare our findings with predicted profiles from simulations and find good overall agreement. We outline possible future measurements to further constrain the impact of discrete undetected LAEs on observed extended Lyαhalos.

Evaluating the likelihood of slope failure in ageing earthworks using Bayesian updating

Earthwork assets, including cut slopes and embankments, are essential components of the infrastructure supporting road and rail transportation networks. Asset owners must assess the stability of these slopes as they deteriorate, to prevent unwanted slope failures. Assessing the stability of individual earthworks within a portfolio using slope stability analyses can be expensive and time consuming. Hence, a Bayesian logistic regression model was developed to evaluate the probability of slope failure, using training data from published case histories of slope failures. The Bayesian model was then used to assess the probability of failure for the more specific case of clay cut slopes within a railway earthwork asset portfolio owned by Network Rail (NR) in the UK. The portfolio includes earthworks at various stages of degraded strength and with different drainage conditions. The results from models with material properties that were equivalent to those for the deteriorated strength of clays compared most closely with clay cut slope failures within the NR data set. Steeper slopes (&gt;35°) had the highest probability of failure, regardless of slope height, and drainage condition. However, for shallower slopes, poorly drained slopes had a ≈20% higher probability of failure than well-drained slopes.

Field observations on hydro-thermal regimes of loess cut slopes in cold and arid regions: A comparative study of sunny and shady slopes

In cold and arid regions, the maintenance of roadways and railways faces significant challenges due to serious spalling and sheet erosion, rill erosion, and shallow sliding of loess slopes. Moreover, the frequency and severity of these shallow failures, as well as the vegetation cover, differ greatly between sunny and shady slopes, further complicating slope maintenance. This study focuses on field observations conducted over two consecutive years along a highway at the western end of Chinese Loess Plateau, specifically examining soil temperatures and moisture content within two cut slopes. By analyzing the differences in hydro-thermal regimes within a depth of 100 cm between the sunny and shady slopes, and considering the meteorological data collected at the study site, the research aims to provide insights into these failures of loess slopes. The results indicate that the shady slope undergoes significant seasonal freeze-thaw cycles from the surface down to a depth of 100 cm. The freezing duration ranges from 96 to 120 days, with a freezing index ranging from −250 °C·d to −850 °C·d. Additionally, the shallow layer on the shady slope experiences significant daily freeze-thaw cycles in late autumn and early winter. In contrast, the sunny slope experiences minimal seasonal freeze-thaw processes. Although the shallow surface layer of the sunny slope undergoes some daily freeze-thaw cycles in late winter and early spring, the amplitudes of soil temperature fluctuations are significantly smaller compared to those on the shady slope. Given that the precipitation is concentrated in summer and autumn, the moisture content of the soil on the shady and sunny slopes exhibits noticeable seasonal changes. The soil layers on the shady slope tend to be relatively dry, while those on the sunny slope remain relatively moist. The moisture content within the observed depth on the sunny slope remains relatively consistent, while on the shady slope, a clear gradient is evident. The moisture content of the shallow slope layers within a depth25 cm primarily responses to heavy rainfall events, with a greater response observed on the shady slope compared to the sunny slope. The field-observed hydro-thermal data collected in this study serve a valuable basis for implementing revegetation strategies and enhancing the stability of loess slopes in cold and arid regions.

Shallow stability of soil slope with frame protection considering rainwater seepage: A calculation method

This paper introduces an integrated calculation method for analyzing the impact of frame protection engineering on the safety factor of shallow stability for soil slopes. The calculation method is based on the infinite long slope model, but it produces superior results by comprehensively taking into account the anti-sliding effect of the shallow slope sliding body. It combines the tension zone at the upper edge, the main sliding zone in the middle section, and the compression zone at the lower edge, while considering the anti-sliding force system of the frame protection structure and its contact surface with the soil. By converting the three-dimensional force system into a two-dimensional plane problem, an approximate calculation method for the shallow stability analysis of soil slopes with frame protection under rainfall seepage was established and numerically verified using the finite element method. The analysis indicates that the safety factor of the slope decreases significantly when seepage force is considered. As the length of the main sliding zone increases, the safety factor gradually decreases and approaches the result of the infinite long slope model. When the length decreases to zero, the safety factor gradually increases and approaches the result of the circular slip model. The use of frame protection significantly improves slope stability under rainfall seepage, and the safety factor increases with the number and embedded depth of the frame structure.

Environmental Temperature Effect on Hydraulic Behavior and Stability of Shallow Slopes

This study established a study framework to quantify the safety factors of unsaturated shallow slopes at different temperatures. This study is based on a non-isothermal soil water characteristic curve model quantifying the temperature-dependent hydraulic properties of soils. The hydraulic coupling analysis models HYDRUS 2D and The Slope Cube Module were used for finite element modeling. A slope stability analysis was performed based on the local factor of safety (LFS) theory. An increased temperature decreased the soil matric suction, suction stress, effective stress, and LFS, weakening the soil strength. Slope modeling analysis showed that soils were dominated by different water retention mechanisms before and after rainfall infiltration, and the trends caused by temperature changes also changed accordingly. This study provides insights into the relationship between soil mechanical properties and temperature, which is valuable for maintaining soil stability and preventing geological hazards.

Planetary evolution with atmospheric photoevaporation

Context. Observations by the Kepler satellite have revealed a gap between larger sub-Neptunes and smaller super-Earths that atmospheric escape models had predicted as an evaporation valley prior to discovery. Aims. We seek to contrast results from a simple X-ray and extreme-ultraviolet (XUV)-driven energy-limited escape model against those from a direct hydrodynamic model. The latter calculates the thermospheric temperature structure self-consistently, including cooling effects such as thermal conduction. Besides XUV-driven escape, it also includes the boil-off escape regime where the escape is driven by the atmospheric thermal energy and low planetary gravity, catalysed by stellar continuum irradiation. We coupled these two escape models to an internal structure model and followed the planets’ temporal evolution. Methods. To examine the population-wide imprint of the two escape models and to compare it to observations, we first employed a rectangular grid, tracking the evolution of planets as a function of core mass and orbital period over gigayear timescales. We then studied the slope of the valley also for initial conditions derived from the observed Kepler planet population. Results. For the rectangular grid, we find that the power-law slope of the valley with respect to orbital period is −0.18 and −0.11 in the energy-limited and hydrodynamic model, respectively. For the initial conditions derived from the Kepler planets, the results are similar (−0.16 and −0.10). While the slope found with the energy-limited model is steeper than observed, the one of the hydrodynamic model is in excellent agreement with observations. The reason for the shallower slope is caused by the two regimes in which the energy-limited approximation fails. The first one are low-mass planets at low-to-intermediate stellar irradiation. For them, boil-off dominates mass loss. However, boil-off is absent in the energy-limited model, and thus it underestimates escape relative to the hydrodynamic model. The second one are massive compact planets at high XUV irradiation. For them, the energy-limited approximation overestimates escape relative to the hydrodynamic model because of cooling by thermal conduction, which is neglected in the energy-limited model. Conclusions. The two effects act together in concert to yield, in the hydrodynamic model, a shallower slope of the valley that agrees very well with observations. We conclude that a hydrodynamic escape model that includes boil-off and a more realistic treatment of cooling mechanisms can reproduce one of the most important constraints for escape models, the valley slope.

Physical properties of the Didymos system before and after the DART impact

Context. On September 26, 2022, the Double Asteroid Redirection Test (DART) successfully changed the trajectory of the asteroid Dimorphos (i.e. 65803 Didymos I), a satellite circling (65803) Didymos. Aims. We aim to characterize the consequence of this collision and derive the physical properties of the ejecta features based on ground-based observations in East Asia. Methods. Filtered photometric observations were made between September 21 2022 (~5 days before DART impact) and January 5 2023 using the Lulin 1-m telescope to identify the taxonomy, size, and rotational period of Didymos. The Finson-Probstein dust dynamical models were used to determine the grain sizes (mm–cm) released after the DART impact and the date of the activity. Results. We report a rapid increase in the brightness by about one order of magnitude after the impact, to be followed by a gradual 0.07 mag decrease over the first two weeks producing a relatively shallow brightness slope at the end of October. The size and rotation period at post-impact were 0.7−0.10+0.12 km and 2.27 h, respectively. The Principal Component Index (PCI), relative reflectance, and colors were all classified as S-complex. The Dydimos system became bluer after the collision before returning to its original color. The formation of a comet-like trail containing debris in the anti-sunward direction can be explained by expansion driven by the pressure of solar radiation. A Finson-Probstein modeling approach led to an estimate of the grain size in the mm-cm range. The splitting of the tail into two components is shown in the image acquired on October 12, which may possibly be interpreted as being due to the secondary impact of fallback ejecta about a week after DART.

Uplift, deflation and marine onlap of a Jurassic rift dome, illustrated by a backstepping Middle–Upper Jurassic shelf‐to‐slope succession, Geographical Society Ø, East Greenland

Abstract“Doming–rifting–spreading” constitute the main phases of classical plate tectonics. The Middle–Upper Jurassic succession of East Greenland is interpreted as reflecting formation, deflation and onlap of a rift dome, similar to contemporaneous rift domes in the North Sea, Denmark and southern Sweden. The succession forms a northwards backstepping and onlapping early rift succession in the N–S oriented basin. Deposition ranged from coastal over shallow marine and slope sands, through offshore siltstones to deep basinal mudstones. An outlier on the island Geographical Society Ø fills an important gap in the documentation of the doming, deflation and progressive onlap. Bajocian deposition took place in a shallow marine shelf. This was followed in the late Oxfordian by slope and base‐of‐slope deposition. The backstepping succession onlaps progressively older rocks towards the north, illustrating the gradual deflation, erosion and onlap of the dome, constituting the early part of the doming–rifting–spreading phases of classical plate tectonics.