Rugged Topography Research Articles

Weighted Goal-oriented Adaptive Finite-element for 3D Transient EM Modeling

The unstructured finite-element method has been widely used in 3D time-domain electromagnetic (EM) modeling due to its flexibility for modeling rugged topography and complex underground structures. However, how to generate high-quality grids becomes the key to high-accuracy EM responses. We have developed a weighted goal-oriented adaptive finite-element method based on hybrid posterior error estimation in combination with unstructured vector finite-element method and Backward Euler scheme to create an effective mesh. By introducing a weighting factor and adjusting the relative weights of the hybrid posterior errors, the numerical accuracy and convergence rate are greatly improved. To handle the huge difference of EM responses at different time channels, we introduce another weighting factor defined by the exponential power of time to achieve a synchronous refinement of shallow and deep meshes. The numerical experiments on a homogenous half-space model show that our algorithm performs better than the traditional adaptive method both from the accuracy and convergence. Further, we also test the effectiveness of our algorithm for modeling different abnormal bodies under a topographic earth.

Reverse Time Migration in Euclidean and Riemannian coordinates

Reverse time migration in zones with rugged topography is a method that presents some challenging issues. We present an analysis of reverse time migration in transformed domains, in particular for a technique that goes from an Euclidian to a Riemannian scenario, as suggested by some authors in previous literature. Computational results show that there is not significant improvement in the final image when the Riemannian approach is used as compared with images obtained with an Euclidean metric.

The Geomorphic Impact of Outburst Floods: Integrating Observations and Numerical Simulations of the 2000 Yigong Flood, Eastern Himalaya

AbstractOutburst floods in mountainous landscapes traverse complex topography and interact with the channel and valley walls, producing intense flow hydraulics that drive geomorphic change and impact people and infrastructure. Evidence of modern and ancient outburst floods is scattered around the eastern Himalaya, but hydraulics related to these geomorphic features are uncharacterized, limiting our understanding of the role of large floods in long‐term evolution of the region. Here we combine remote and field observations of the 2000 Yigong River landslide‐dam outburst flood with 2‐D numerical flood simulations using the software GeoClaw. Modeling results agree with field evidence to the extent that we judge the simulated hydraulics to be relevant to flood hazard and geomorphic investigations. Results show that the hydraulics of outburst floods through rugged topography differ from those expected for nonflood flows, in magnitude and in the spatial patterns of flow speed, direction, and shear stress. The flood produced sustained high bed shear stresses capable of plucking meter‐scale blocks immediately downstream of breach, in the steep Tsangpo Gorge, and in isolated locations associated with valley constrictions. Simulated shear stresses suggest that outburst floods deposited numerous kilometer‐scale boulder bars observed along the flood pathway, armoring the bed, increasing channel roughness, and inhibiting incision in locations that would not be predicted for nonflood flows. Our findings highlight the potential for different magnitude flows to promote not only different amounts, but also different patterns of bedrock erosion, with implications for the role of prehistoric megafloods in the topographic evolution of the eastern Himalaya.

Controlling soil erosion in smallholder potato farming systems using legume intercrops

Soil and nutrient losses due to soil erosion are pronounced in potato growing areas of East Africa due largely to the rugged topography and high soil disturbance associated with potato cultivation. This study intercropped potato (Solanum tuberosum L.) with three grain legumes: lablab bean (Lablab purperous L.), garden pea (Pisum sativa L.) and climber bean (Phaseolus vulgaris L.) in runoff plots and assessed their impact on soil and nutrient losses in central Kenya highlands. Bare plots and sole potato stands were included as controls. Vegetal cover was measured at different potato growth stages while runoff and soil loss were quantified at every runoff generating event and used for nutrient analyses. Yields were expressed as potato equivalents (PEY) at the end of each season. Mean cumulative sediment yield decreased from 169 t/ ha in sole potato plots to 50–83 t/ ha in potato-legume intercropping, representing a reduction of 51–70%. The eroded sediment exported in large quantity the SOC (16.6–39.5 kg C ha−1 yr−1), N (5.5–29.8 kg N ha−1 yr−1), P (3.9–16.4 kg P ha−1 yr−1) and K (5.2–14.6 kg K ha−1 yr−1) and were consistently higher in sole potato plots relative to potato-legume intercropping. These losses occurred mainly at potato emergence following fertilizer application. Stronger associations of sediment nutrient enrichments was found with the micro-aggregates (250–50 μm) than with the macro-aggregates (>250 μm) pointing to the different degree of nutrient mobilization and distribution in eroded sediment. The PEY were significantly greater in potato-lablab bean system than in sole potato, while intercropping with garden pea and climber bean showed similar PEY to that of sole potato, suggesting that potato-lablab system may be preferred by the smallholder farmers. These results justify the need to intercrop potato with indeterminate legume intercrops, a strategy that must be done in a way guaranteeing high yield stability to the smallholder farmers.

A simple topographical model to predict Golden Eagle Aquila chrysaetos space use during dispersal

Many large raptors exploit or rely on anabatic and orographic winds which provide vertical lift, to supplement or provide the energy fuelling flight. Airspace is therefore a critical habitat for such large raptors and its use is subject to the underlying terrestrial topography, because particular topographical features are more likely to provide wind‐energetic lift. Accordingly, ridges and/or ‘rugged topography’ are common preferred features in habitat use by large raptors. Our study aimed to provide a simple model of space use for a large raptor, the Golden Eagle Aquila chrysaetos, based on thousands of GPS telemetry records during juvenile dispersal of 92 birds tagged as nestlings between 2007 and 2016 across upland Scotland. Model development was based on the hypothesis that four topographical variables would be influential: slope, aspect, altitude and distance from ridge. The telemetry dataset was divided into training and two testing components. The first testing set was derived by a temporal split resulting in approximately equal sample size on records and some temporal overlap in individuals’ records with training data. The second testing set involved no individuals from the training set. Aspect was removed early in training model development because it was not influential. The model found that young Golden Eagles preferred, or used according to availability, space above slopes greater than 10°, at an altitude of ≥ 300 m, and within 300 m of a ridge. The test data were highly correlated with those from the training data in the model variables, and performance as regard to expected preferences from the model was improved in both test datasets, indicating the model was robust. Given the apparent universal nature of large raptor dependence on topography, that topography is relatively immutable according to time and use, and that topographical data are readily available, we commend our approach to other habitat preference studies of Golden Eagles and other large raptors elsewhere.

Modelling of Soil Erosion and Accumulation in an Agricultural Landscape—A Comparison of Selected Approaches Applied at the Small Stream Basin Level in the Czech Republic

This article deals with the modelling of erosion and accumulation processes in the contemporary cultural landscape of Central Europe. The area of interest is the headwater part of the small stream catchment—the Kopaninský Stream in central Czech Republic. It is an agricultural and forest–agricultural landscape with a relatively rugged topography and riverbed slope, which makes the terrain very vulnerable to water erosion. The main aim of this article is to compare the results of four selected soil erosion and sediment delivery models, which are currently widely used to quantitate the soil erosion and sediment accumulation rates, respectively. The models WaTEM/SEDEM, USPED, InVEST and TerrSet work on several different algorithms. The model outputs are compared in terms of the total volume of eroded and accumulated sediment within the catchment per time unit, and further according to the spatial distribution of sites susceptible to soil loss or sediment accumulation. Although each model is based partly on a specific calculation algorithm and has different data pre-processing requirements, we have achieved relatively comparable results in calculating the average annual soil loss and accumulation. However, each model is distinct in identifying the spatial distribution of specific locations prone to soil loss or accumulation processes.

Modeling Two‐Phase Debris Flows With Grain‐Fluid Separation Over Rugged Topography: Application to the 2009 Hsiaolin Event, Taiwan

Landslides or debris flows usually arise in mountainous areas and slide over a rough topography. As the flow body is typically a mixture of particles and interstitial fluid, this paper aims at developing a binary mixture model and its numerical implementation for shallow debris flows on rugged topography. The mathematical formulation of this saturated solid‐fluid mixture is developed with respect to a terrain‐fitted coordinate system. Employing the thin layer assumption, a system of depth‐integrated equations is derived, where the interstitial fluid is supposed to be a viscous Newtonian fluid and the granular material is treated as a frictional Coulomb‐like continuum. At the basal surface, the Coulomb sliding condition for the granular constituent and Navier slip for the fluid phase are applied. The interaction between granular material and interstitial fluid is depicted by the buoyancy and a drag force induced by the velocity difference of both the phases. Numerical investigations are performed for studying the features of the proposed model, where a shock‐capturing nonoscillatory scheme is employed. A thorough parameter study of flows over three idealized terrain geometries illustrates the distinct impacts of the applied material parameters on the flow dynamics and deposit shapes. The phase separation such as the solid‐phase‐dominated flow front and how this changes with parameter values are presented. The simulation of the Hsiaolin landslide successfully retraces the approximate flow path recognized in satellite images as well as the measured deposition given in Kuo et al. (2011, https://doi.org/10.1029/2010JF001921).

Analysis of heterogeneity of aridity index periodicity over Lebanon

Lebanon, with its geographic location facing the Mediterranean Sea and dominant rugged topography, is characterized by a strong climatic variability even between zones located few kilometres apart. The investigation of the climatic indices is necessary to delineate such diverse climatic situation over Lebanon. In this context, this paper investigates the periodic behaviour in annual Emberger aridity index (AIE) of 14 weather stations in representative sites of Lebanon. The AIE indicates that the dominant climate of Lebanon, which is mainly varying from humid to semi-arid, follows cyclonic meteorological patterns. The periodicities of AIE identified by using a robust technique seem almost altitude related and range between 2 and 21 years. The geographic distribution of periodicities implies two major zones in the northern and southern parts of Lebanon, being featured by longer and shorter periodicities, respectively. The formation of these two periodicity zones can be related to regional climatic zoning. The remarkable diversity in periodicity indicates predominant microclimates with specified cyclonic climate that characterizes Lebanon’s climate rather than a merely existence of climate change.

Evaluation of multiple satellite rainfall products over the rugged topography of the Tekeze-Atbara basin in Ethiopia

ABSTRACTSatellite rainfall products are an important source of rainfall data in un-gauged catchments. However, these products need to be validated as their accuracy can be affected by geographical position, topography, climate and embedded algorithms. Eight satellite rainfall products such as African Rainfall Climatology (ARC2), Climate Hazards Group InfraRed Precipitation with Stations (CHIRPs), Global Precipitation Climatology Project GPCP), CPC Morphic technique (CMorph), Atmospheric Administration Climate Prediction Center (NOAA-CPC) merged analysis (CMap), Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN), African Rainfall Estimation Algorithm version 2 (RFEv2) and Tropical Rainfall Measurement Mission (TRMM) were evaluated against ground observations over the complex topography of the upper Tekeze-Atbara basin in Ethiopia. The accuracy of the datasets was evaluated at different temporal and larger spatial scales over the period 2002–2015. The results show that the rainfall data of CHIRPS outperformed all other products at all temporal and spatial scales. Next to CHIRPS, estimates from RFEv2, 3B42v7, and PERSIANN products are closest to the measurements at rain gauges for all spatiotemporal scales: daily, monthly and seasonal, and both at point and spatial scales. The percentage bias (PBias) and correlation coefficient (r) of these products were within ±25% and >0.5 for all scales. The remaining products performed poorly with PBias up to 200% and lower r (<0.5) at all scales. However, the performance of all products improved as the temporal scale increased to month and season at all spatial scales. Compared to low altitudes <2000 m above sea level (m.a.s.l.), the PBias at high altitude (>3000 m.a.s.l.) increased by 35% whilst r dropped by 28%. CHIRPS and 3B42v7 products showed best agreement in mountainous terrains. However, all datasets show no consistency of the error sign. CMorph and 3B42v7 consistently overestimate rainfall relative to all rain gauges during the pixel-to-point rainfall comparison approach and at lowland areas during the areal averaged rainfall comparison. The other six products showed a clear underestimation at all spatial scales. In summary, the results show that rainfall estimates by CHIRPS, RFEv2 and 3B42v7 have a consistently better agreement with ground rainfall at all spatiotemporal scales. Considering the complex topography and limited gauges, the performance of CHIRPS, RFEv2 and 3B42v7 indicates that these products can be used for hydrological and overall water management applications in the region.

Land use/cover change in the Three Gorges Reservoir area, China: Reconciling the land use conflicts between development and protection

Development and protection are both vital human demands in ecologically vulnerable areas. An estimation of the land use/cover changes and their ecological responses could help to understand the regional ecosystem dynamics under various human demands and provide the scientific basis for managing and regulating ecosystems. In this paper, we analysed the spatial-temporal variations in land use/cover types and systematically quantified the relationships between these changes and environmental variables in the Three Gorges Reservoir area. Our results revealed that forestland coverage increased linearly to 53.48%, and that of construction land increased exponentially from 0.25% to 2.75% during 1990–2015. The land use/cover changes exhibited two distinct transformation phases: before and after impoundment. The mutual transformations among vegetation types were significant before 2000, while the forest, water and construction land coverages increased continuously by occupying cropland after 2000. The land use/cover changes were significantly correlated with environmental variables and were sensitive to three topographic variables namely, elevation, surface-height-fluctuation and slope. The vegetation dynamics were easily affected by the complex and rugged topography. Moreover, the responses of land use/cover changes varied among topographic variables. The two parameters estimated in the multiple linear regression, elevation and slope, were −0.164 and −0.268 for forestland change, −0.391 and 0.378 for water area change, and −0.068 and −0.061 for construction land change. Forest cover was so larger in the regions of higher elevation and steeper slope that afforestation occurred in the regions of moderate elevation and slope. Urbanization and impoundment mainly occurred in the regions of lower elevation, and the regions of steeper slope were more easily submerged, while urbanization mainly occurred in the regions of gentler slope. Therefore, the land use/cover changes due to ecological protection and economic development responded to the interactions among environmental variables and was targeted to different regions to reconcile the land use conflicts, providing a reference for ecosystem management in ecologically vulnerable areas.

Persistent geophysical effects of mining threaten ridgetop biota of Appalachian forests

Surface coal mining can permanently alter the rugged topography of Appalachia, which plays an important role in creating and maintaining the structure, composition, and diversity of this North American region's ecological communities. We used remote‐sensing datasets to characterize the past and future topographic impacts of surface coal mining on the mixed‐mesophytic forests of eastern Kentucky. To provide context, we examined the consequences of widespread topographic rearrangement for an imperiled ridgetop‐associated predator, the timber rattlesnake (Crotalus horridus). We found that surface mining disproportionately impacts ridgetop habitats, causing large reductions in suitable habitat for C horridus, and most likely other ridgetop‐dependent biota as well. Land permitted for surface mining is also concentrated in high topographic positions, and patterns of habitat loss are therefore likely to remain concentrated within these ecosystems. These permanent topographic shifts complicate restoration of pre‐existing microhabitats, create homogenized landscapes, threaten long‐term ecosystem health, and reduce the diversity of ecological communities.

Quaternary Glaciotectonics of the Ural-Siberian North

Abstract This is a review of previous works on glaciotectonics and recent epeirogenesis of the northern West Siberian sedimentary basin and adjacent parts of the Urals and the Siberian Craton. It is supported by the addition of detailed structural profiles of the disharmonic dislocations around Malyi Atlym settlement on the Lower Ob’ never published before. The collected data highlight sources and results of neotectonic phenomena in the north of West Siberia and their impact on distribution of hydrocarbon deposits. The rugged topography of the northern Urals and Mid-Siberian Plateau, discordant with the regional tectonic structure, is generated by compensation uplifts along the margins of thick ice sheets in the West Siberian North. Ice load vacillations were an important factor of geographical separation of hydrocarbons liquid and gaseous phases. This is evident from the west–east zonation of petroleum deposits, discordant with the south–north strike of ancient structures but concordant with thickness zonation of ice sheets. The structure of the alpine-type dislocations penetrating up to 400 m into the sedimentary basin on the Lower Ob’ reveals that the variations of their tectonic style do not fit the mechanical properties of thawed Paleogene rocks. However, they are more understandable assuming their origin from deviatoric stress in pressurized perennially frozen Paleogene rocks. Such conditions are feasible at the base of a growing thick ice sheet. Ice sheets did significant work of glaciotectonic erosion of soft Paleogene rocks of the perennially frozen substrate soldered with glacial ice. This type of erosion is evident in the Ob’ catchment area where whole blocks of intact sand and clay were transported by glaciers over hundreds of kilometers. Glaciotectonic erosion of glacier substrate is sufficient for explaining the well-known stratigraphic hiatus between Quaternary and Upper Cretaceous formations of the Siberian Arctic instead of the popular but illogical tectonic inversion of the sedimentary basin.

Factors Controlling the Development of Wine-Glass Forms in the Mountains of the Kurdistan Region, Iraq

The northern and northeastern parts of Iraq are mountainous areas and rugged topography with different erosional and morphological forms; among them are the wine-glass (erosional cirques) forms. They are developed in different shapes, sizes, and depths. In the outlets of the wine-glass forms; usually, alluvial fans are formed. The studied area is characterized by the presence of long and narrow anticlines with NW–SE trend that changes westward to E–W trend. The Cretaceous carbonate rocks form the main carapace of the majority of the mountains; however, locally Paleogene and/or Jurassic rocks form the carapace. In the core, rocks down to Devonian are exposed. In those anticlines where only Cretaceous rocks are exposed, no or very rarely wine-glass forms are developed. This is attributed to the Cretaceous carbonate rocks, which exist in huge thicknesses in many formations, with thickly bedded to massive nature and very hard erosion resisting rocks. Tens of the existing wineglass forms are studied to indicate the factors that control their development, which are the type of exposed rocks, their thicknesses, and hardness. To perform the aim of this study, different satellite imagery with different resolutions was used; besides using GIS technique and field check to improve the acquired date.

The plants of Waya Island, Fiji

"An annotated species-list is given for Waya Island (Yasawa Is. Group, Fiji). It contains 38 ferns and lycophytes, 1 cycad, 55 monocotyledons, and 224 dicotyledons. Nearly all these 318 species are indigenous to Fiji or are likely to be ancient (pre-European) introductions. Except for six species, post-European introductions (weeds and cultivated species) have not been included. Two species are endemic to Waya: Embelia deivanuae (Myrsinaceae) and Psychotria volii (Rubiaceae). Five are rare in Fiji: Guettarda wayaensis (Rubiaceae), Mollugo pentaphylla (Molluginaceae), Ormocarpum orientale (Leguminosae), Polystichum pilosum (Dryopteridaceae), and Prosaptia vomaensis (Polypodiaceae). Another two Fijian rarities, Euphorbia plumerioides (Euphorbiaceae) and Sarcolobus stenophyllus (Asclepiadaceae), were found on Waya in 1937 but have not been seen since. Waya’s taller native vegetation is situated mostly on rugged rocky topography and is dominated by members of Leguminosae (Cynometra, Kingiodendron, Maniltoa), Sapindaceae and Sapotaceae. In Fiji at large such “dry zone” cover has been greatly reduced by continual fires, so Waya’s remnants, though small and discontinous, have substantial biodiversity value. "

Relating bed character and subglacial morphology using seismic data from Thwaites Glacier, West Antarctica

Seismic measurements on Thwaites Glacier show a spatially variable bed character, with implications for ice-sheet stability. The West Antarctic Ice Sheet is losing mass rapidly through outlet glaciers and ice streams in the Amundsen Sea Embayment, including Thwaites Glacier, where limited observations and modeling suggest that ice-flow rates depend on bed properties. Here we characterize bed properties of Thwaites Glacier based on amplitude analysis of reflection-seismic data from a ∼40-km-long profile collected in the approximate flow direction and two ∼10-km-long profiles transverse to flow. The upstream portion of the seismic profile reveals a ∼12-km long sedimentary basin with ice-flow-aligned bedforms capped by a continuous till layer that is likely soft and deforming (porosity ∼0.4–0.45), with several locations where water has pooled at the bed. Downstream of the sedimentary basin, the bed rises by ∼400 m over ∼25 km into subglacial highlands. Our seismic survey of these subglacial highlands reveals strong spatial variations in bed character across rugged topography (∼200 m amplitude at ∼2- to 5-km wavelength) resembling crag-and-tails. Till on the stoss sides (facing upglacier) of topographic highs is more consolidated (porosity ∼0.3–0.35 or lower), whereas the lee sides (facing downglacier) and flat regions exhibit porosity similar to the till of the upstream sedimentary basin. Modeling studies could use the observed correlation between bed character and bed aspect and slope to extend our observations to other parts of Thwaites Glacier, resulting in more-realistic models of future grounding-line retreat. Our findings highlight the need for more geophysical constraints on bed properties for important outlets in Antarctica and Greenland.

Full Waveform Inversion in generalized coordinates for zones of curved topography

Full waveform inversion (FWI) has been recently used to estimate subsurface parameters, such as velocity models. This method, however, has a number of drawbacks when applied to zones with rugged topography due to the forced application of a Cartesian mesh on a curved surface. In this work, we present a simple coordinate transformation that enables the construction of a curved mesh. The proposed transformation is more suitable for rugged surfaces and it allows mapping a physical curved domain into a uniform rectangular grid, where acoustic FWI can be applied in the traditional way by introducing a modified Laplacian. We prove that the proposed approximation can have a wide range of applications, producing precise near-surface velocity models without increasing the computing time of the FWI.

Nesting habitat selection and distribution of an avian top predator in the Canadian Arctic

Detecting and planning for ecosystem changes from climate and land-use alteration is limited by uncertainty about the current distribution of many species. This is exacerbated in remote areas like the Arctic, where the impacts of climate change are the strongest and where industrial exploration and development are expanding. Using remotely-sensed environmental information and known nest sites, we estimated the breeding distribution and habitat selection of the peregrine falcon (Falco peregrinus) throughout most of Nunavut, a massive northern Canadian territory (&gt;1.8 M km2) encompassing ∼15% of the world’s tundra biome. Our results show that peregrine falcons selected features of prior known importance such as rugged topography, but also sites with higher than average summer temperatures, more productive land classes, lower mean elevations, and lower mean summer precipitation. Our model identifies several areas of high relative probability of peregrine occurrence, some of which were unrecognized to date. Some of these areas may be targets for future industrial developments and are located in an area where some of the fastest climate changes are expected. Our model will allow managers to identify the areas that could be the most critical for monitoring in the context of future development and climate change.

Wildfires and the role of their drivers are changing over time in a large rural area of west-central Spain

During the last decades, wildfires have been changing in many areas across the world, due to changes in climate, landscapes and socioeconomic drivers. However, how the role of these drivers changed over time has been little explored. Here, we assessed, in a spatially and temporally explicit way, the changing role of biophysical and human-related factors on wildfires in a rural area in west-central Spain from 1979 to 2008. Longitudinal Negative Binomial (NB) and Zero-Inflated Negative Binomial (ZINB) mixed models, with time as interacting factor (continuous and categorical), were used to model the number of fires of increasing size (≥1–10 ha, >10–100 ha, >100 ha) per 10 × 10 km cell per year, based on fire statistics. We found that the landscape was rather dynamic, and generally became more hazardous over time. Small fires increased and spread over the landscape with time, with medium and large fires being stable or decreasing. NB models were best for modelling small fires, while ZINB for medium and large; models including time as a categorical factor performed the best. Best models were associated to topography, land-use/land cover (LULC) types and the changes they underwent, as well as agrarian characteristics. Climate variables, forest interfaces, and other socioeconomic variables played a minor role. Wildfires were initially more frequent in rugged topography, conifer forests, shrublands and cells undergoing changes in LULC types of hazardous nature, for all fire sizes. As time went by, wildfires lost the links with the initial fire-prone areas, and as they spread, became more associated to lower elevation areas, with higher solar radiation, herbaceous crops, and large size farms. Thus, the role of the fire drivers changed over time; some decreased their explaining power, while others increased. These changes with time in the total number of fires, in their spatial pattern and in the controlling drivers limit the ability to predict future fires.

Preconditioning and Formation of Maud Rise Polynyas in a High-Resolution Earth System Model

AbstractOpen-ocean polynyas (OOPs) in the Southern Ocean are ice-free areas within the winter ice pack that are associated with deep convection, potentially contributing to the formation of Antarctic Bottom Water. To enhance the credibility of Earth system models (ESMs), their ability to simulate OOPs realistically is thus crucial. Here we investigate OOPs that emerge intermittently in a high-resolution (HR) preindustrial simulation with the Energy Exascale Earth System Model, version 0.1 (E3SMv0), an offspring of the Community Earth System Model (CESM). While low-resolution (LR) simulations with E3SMv0 show no signs of OOP formation, the preindustrial E3SMv0-HR simulation produces both large Weddell Sea polynyas (WSPs) as well as small Maud Rise polynyas (MRPs). The latter are associated with a prominent seamount in the eastern Weddell Sea, and their preconditioning and formation is the focus of this study. The steep flanks of the rugged topography in this region are in E3SMv0-HR sufficiently well resolved for the impinging flow to produce pronounced Taylor caps that precondition the region for convection. Aided by an accumulation of heat in the Weddell Deep Water layer, the ultimate trigger of convection that leads to MRPs is the advection of anomalously high upper-ocean-layer salinity. The crucial difference to WSP-producing LR ESM simulations is that in E3SMv0-HR, WSPs are realistically preceded by MRPs, which in turn are a result of the flow around bathymetry being represented with unprecedented detail.

Square-wave processing of MEGATEM data

The recording of raw or streamed EM survey data, as done by CGG during MEGATEM surveys, allows for the reprocessing of the acquired EM data, including square-wave processing. During the latter, the recorded EM response to the actual half-sine waveform is replaced by the EM response to a square-wave, derived via deconvolution/convolution in the frequency domain. This makes the on- and early-time information more accessible for data modelling, including 1D inversions and conductivity-depth transformations. Square-wave EM data can also be corrected for survey height, transmitter-receiver offset and transmitter attitude. That correction allows for the interpretation of early-time EM response grids, which generally offer better spatial resolution than derived conductivity-depth slices. The advantages of square-wave processing are demonstrated on a MEGATEM data set acquired in 2013 in South America. With survey terrain clearance ranging from 100 – 1600 m, due to the rugged topography, early-time grids of elevation-corrected square-wave data outlined the shallow conductivity structure, whereas early-time grids of the original half-sine data mostly reflected the variable system elevation. Further, derived conductivity-depth sections of the square-wave data show more lateral continuity than the sections derived from the original half-sine data. These results show that the early-time information of square-wave is more accessible than in the original data, facilitating interpretation of shallow conductivity structures.