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Random forests with spatial proxies for environmental modelling: opportunities and pitfalls
Carles Milà, Marvin Ludwig, Edzer Pebesma, Cathryn Tonne, and Hanna Meyer
Geosci. Model Dev., 17, 6007–6033, https://doi.org/10.5194/gmd-17-6007-2024, 2024
Spatial proxies, such as coordinates and distances, are often used as predictors in random forest models for predictive mapping. In a simulation and two case studies, we investigated the conditions under which their use is appropriate. We found that spatial proxies are not always beneficial and should not be used as a default approach without careful consideration. We also provide insights into the reasons behind their suitability, how to detect them, and potential alternatives.

Sound Velocities of Stishovite at Simultaneous High Pressure and High Temperature Suggest an Eclogite‐Rich Layer Beneath the Hawaii Hotspot

GRL - Wed, 08/14/2024 - 17:39

Abstract

Compressional and shear wave velocities of polycrystalline stishovite (SiO2) have been measured at simultaneous high pressures and temperatures up to 14.5 GPa and 800°C. By fitting velocities to the finite strain equations, the elastic moduli and density were determined to be K S0 = 306.6(46) GPa, K S′ = 4.92(10), ∂K S /∂T = −0.024(1) GPa/K, G 0 = 229.0(34) GPa, G′ = 1.07(10), ∂G/∂T = −0.017(1) GPa/K, ρ 0 = 4.287(2) g/cm3. Our modeling suggested that, in the eclogite, coesite-stishovite transition can increase P and S wave velocities by 2.4% and 3.5%, respectively. A comparison between geophysical observations and our model shows that the coesite-stishovite phase transition in the eclogite can potentially be responsible for the occurrence of the X discontinuity beneath Hawaii. In addition, our current results suggest an eclogite-rich layer between 340 and 450 km depth beneath Hawaii. The eclogite concentration at the top and bottom of the layer is 41–55 vol% and >77 vol%, respectively.

Caprock Remains Water Wet Under Geologic CO2 Storage Conditions

GRL - Wed, 08/14/2024 - 15:59

Abstract

Carbon storage technology is primarily targeted in saline formations, which is a porous rock matrix filled with brine, sealed with a low permeability caprock. There are significant variations of CO2 wetting properties, typically reported in the literature as contact angle of CO2 and brine interacting with a rock material, suggesting that CO2 could become wetting under geostorage conditions and negatively impact containment effectiveness. Here, we performed the first controlled laboratory measurements of CO2-brine contact angles on shale rocks from low permeability sealing formations with distinctive mineralogic properties—calcite-rich, quartz-rich, and dolomite-rich. We targeted temperatures at 40° and 100°C, pressures at 8.3, 34.5, and 62.1 MPa, and salinity at 35,000 and 260,000 ppm. Results show no significant change in contact angle with mineralogy, temperature, pressure, salinity, and CO2 bubble size. We conclude that caprocks will remain water-wet at geologic CO2 storage conditions and will not lose their capillary sealing capacity.

Assessing the Sources of the O+ in the Plasma Sheet

JGR:Space physics - Wed, 08/14/2024 - 15:39

Abstract

To study the average contributions of the cusp outflow through the lobes and of the nightside auroral outflow to the O+ in the plasma sheet (PS), we performed a statistical study of tailward streaming O+ in the lobes, plasma sheet boundary layer|the plasma sheet boundary layer (PSBL) and the PS, using MMS/Hot Plasma Composition Analyzer (HPCA) data from 2017 to 2020. Similar spatial patterns illustrate the entry of cusp-origin O+ from the lobes to the PS through the PSBL. There is an YGSM-dependent energy pattern for the lobe O+, with low-energy O+ streaming closer to the tail center and high energy (1–3 keV) O+ streaming near the flanks. Low energy (1–100 eV) O+ from the nightside auroral oval is identified in the near-Earth PSBL/PS with high-density (>0.02 cm−3), and energetic (>3 keV) streaming O+ with similar density (∼0.013 cm−3) is observed further out on the duskside of the PSBL/PS. The rest of the nightside auroral O+ in the PSBL is mixed with O+ coming in from the lobe, making it difficult to distinguish the source. We estimated the contributions of the different sources of H+ and O+ ions through the PS between 7 and 17 RE, using estimates from this work and data extracted from previous studies. We conclude that, during quiet times, the majority of the near-Earth PS H+ are from the cusps, the polar wind and Earthward convection from the distant tail. Similarly, while the O+ in the same region has a mixed source, cusp origin outflow provides the highest contribution.

Constraints on the Fate of Delaminated Lithosphere in the Upper and Mid‐Mantle

GRL - Wed, 08/14/2024 - 15:33

Abstract

Delamination of lower continental lithosphere is known to have occurred under different tectonic settings. However, its fate in the mantle is poorly understood. By analyzing global seismic models, we find that most of likely lithosphere that delaminated during the Cenozoic and Mesozoic is preserved in the mantle transition zone, especially beneath North America and Africa. Numerical experiments indicates that delaminated lithosphere can remain stagnant in the mantle transition zone for tens of millions of years, followed by its potential sinking into the lower mantle or re-rising to shallower depths depending on its density, the Clapeyron slope of the spinel-to-post-spinel phase change and increase in mantle viscosity at ∼660–1,000 km depths. Re-ascent occurs when delaminated lithosphere is reheated so that its effective density becomes lower than its surrounding ambient mantle after ∼100 Myr. Delaminated fragments can also potentially be mobilized by underlying global mantle flow to move horizontally away from plume regions.

Plasma Mixing During Active Kelvin‐Helmholtz Instability Under Different IMF Orientations

JGR:Space physics - Wed, 08/14/2024 - 15:29

Abstract

When the velocity shear between the two plasmas separated by Earth's magnetopause is locally super-Alfvénic, the Kelvin-Helmholtz (KH) instability can develop. A crucial role is played by the interplanetary magnetic field (IMF) orientation, which can stabilize the velocity shear. Although, in a linear regime, the instability threshold is equally satisfied during both northward and southward IMF orientations, in situ measurements show that KH instability is preferentially excited during the northward IMF orientation. We investigate this different behavior by means of a mixing parameter which we apply to two KH events to identify both boundaries and the center of waves/vortices. During the northward orientation, the waves/vortex boundaries have stronger electrons than ions mixing, while the opposite is observed at their center. During the southward orientation, instead, particle mixing is observed predominantly at the boundaries. In addition, stronger local ion and electron non-thermal features are observed during the northward than the southward IMF orientation. Specifically, ion distribution functions are more distorted, due to field-aligned beams, and electrons have a larger temperature anisotropy during the northward than the southward IMF orientation. The observed kinetic features provide an insight into both local and remote processes that affect the evolution of KH structures.

The miscellaneous synoptic forcings in the four-day widespread extreme rainfall event over North China in July 2023

Natural Hazards and Earth System Sciences - Wed, 08/14/2024 - 15:13

The miscellaneous synoptic forcings in the four-day widespread extreme rainfall event over North China in July 2023
Jinfang Yin, Feng Li, Mingxin Li, Rudi Xia, Xinghua Bao, Jisong Sun, and Xudong Liang
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-145,2024
Preprint under review for NHESS (discussion: open, 1 comment)
A persistent severe rainfall event occurred over North China in July 2023, which was regarded as one of the precipitation extremes of 2023 globally. The extreme rainfall was significant underestimated by forecasters at that time. Flooding from this event affected 1.3 million people, causing severe human casualties and significant economic losses. In this study, we examined the convective initiation and subsequent persistent heavy rainfall over North China based on simulations with the WRF model.

Structural Controls on Fault Slip Models of the 6 February 2023 Kahramanmaraş, Türkiye Earthquake Doublet With Finite Element Analyses

GRL - Wed, 08/14/2024 - 15:09

Abstract

Two major earthquakes of Mw7.8 and Mw7.5 ruptured the Southern East Anatolian Fault (SEAF) and the Savrun-Çardak-Sürgü fault (SCSF), devastating southeast Türkiye and northwest Syria on 6 February 2023. We adopt innovative nonlinear and linear approaches to analyze the coseismic ground displacements and estimate the complex slip geometry. Unlike conventional analytical solutions that simplify crust heterogeneity, finite-element fault models invert the displacement data and simulate the dual-fault geometry with non-uniformly distributed shallow crustal materials. Our results suggest the west-dipping SEAF and north-dipping SCSF accommodate earthquake slips of >10 m. Their respective slip distributions and proximal aftershocks correlate spatially with local seismic velocity anomalies (i.e., ΔVp and ΔVs), which implies differences in structural control along these two faults and provides insights into assessing the seismic hazard of mixed incipient-mature fault systems.

Leveraging RALI‐THINICE Observations to Assess How the ICOLMDZ Model Simulates Clouds Embedded in Arctic Cyclones

JGR–Atmospheres - Wed, 08/14/2024 - 10:39

Abstract

Despite their essential role in the high-latitude climate, the representation of mixed-phase clouds is still a challenge for Global Climate Models (GCMs)'s cloud schemes. In this study we propose a methodology for robustly assessing Arctic mixed-phase cloud properties in a climate model using airborne measurements. We leverage data collected during the RALI-THINICE airborne campaign that took place near Svalbard in August 2022 to evaluate the simulation of mid-level clouds associated with Arctic cyclones. Simulations are carried out with the new limited-area configuration of the ICOLMDZ model which combines the recent icosahedral dynamical core DYNAMICO and the physics of LMDZ, the atmospheric component of the IPSL-CM Earth System Model. Airborne radar and microphysical probes measurements are then used to evaluate the simulated clouds. A comparison method has been set-up to guarantee as much as possible the spatiotemporal co-location between observed and simulated cloud fields. We mostly focus on the representation of ice and liquid in-cloud contents and on their vertical distribution. Results show that the model overestimates the amount of cloud condensates and exhibits a poor cloud phase spatial distribution, with too much liquid water far from cloud top and too much ice close to it. The downward gradual increase in snowfall flux is also not captured by the model. This in-depth model evaluation thereby pinpoints priorities for further improvements in the ICOLMDZ cloud scheme.

Improving HONO Simulations and Evaluating Its Impacts on Secondary Pollution in the Yangtze River Delta Region, China

JGR–Atmospheres - Wed, 08/14/2024 - 10:23

Abstract

Secondary air pollution, especially ozone (O3) and secondary aerosols, are emerging air quality challenges confronting China. Nitrous acid (HONO), as the predominant source of hydroxyl radicals (OH), are acknowledged to be essential for secondary pollution. However, HONO concentrations are usually underestimated by current air quality models due to the inadequate representations of its sources. In the present study, we revised the Weather Research and Forecasting & Chemistry (WRF-Chem) model by incorporating additional HONO sources, including primary emissions, photo-/dark oxidation of NOx, heterogeneous uptake of NO2 on surfaces, and nitrate photolysis. By combining in-situ measurements in the Yangtze River Delta (YRD) region, we found the improved model show much better performance on HONO simulation and is capable of reproducing observed high concentrations. The source-oriented method is employed to quantitatively understand the relative importance of various processes, which showed that heterogeneous NO2 uptake on the ground surface was the major contributor to HONO formation in urban areas. Comparatively, photo-oxidation of NOx is a main contributor in rural areas. The introduction of multiple sources of HONO led to an apparent increase in OH and hydroperoxyl (HO2) radicals. The promoted HO2 levels further increased diurnal O3 concentration by 4.5–12.9 ppb, while secondary inorganic and organic concentrations were also increased by 14%–32% during a typical secondary pollution event. The improved description of HONO emission and formation in the model substantially narrowed the gaps between simulations and observations, highlighting the great importance in understanding and numerical representations of HONO in secondary pollution study.