Assessment of landslide susceptibility using DBSCAN-AHD and LD-EV methods

Landslide susceptibility assessment plays a vital role in understanding landslide information in advance and taking preventive as well as control measures.The n...     

Radiative forcing from surface NO x emissions: spatial and seasonal variations

The global three-dimensional Lagrangian chemistry-transport model STOCHEM has been used to follow changes in the tropospheric distributions of methane CH₄ and ozone O₃ following the emission of pulses of the oxides of nitrogen NO _x . Month-long emission pulses of NO _x produce deficits in CH₄ mixing ratios that bring about negative radiative forcing (climate cooling) and decay away with e-folding times of 10–15 years. They also produce short-term excesses in O₃ mixing ratios that bring about positive radiative forcing (climate warming) that decay over several months to produce deficits, with their attendant negative radiative forcing (climate cooling) that decays away in step with the CH₄ deficits. Total time-integrated net radiative forcing is markedly influenced by cancellation between the negative CH₄ and long-term O₃ contributions and the positive short-term O₃ contribution to leave a small negative residual. Consequently, total net radiative forcing from NO _x emission pulses and the global warming potentials derived from them, show a strong dependence on the magnitudes, locations and seasons of the emissions. These dependences are illustrated using the Asian continent as an example and demonstrate that there is no simple robust relationship between continental-scale NO _x emissions and globally-integrated radiative forcing. We find that the magnitude of the time-integrated radiative forcing from NO _x -driven CH₄ depletion tends to approach and outweigh that from ozone enhancement, leaving net time-integrated radiative forcings and global warming potentials negative (climate cooling) in contrast to the situation for aircraft NO _x (climate warming). Control of man-made surface NO _x emissions alone may lead to positive radiative forcing (climate warming).     

Local meteoric water lines describe extratropical precipitation

Stable water isotopes δ¹⁸O and δ²H are used to investigate precipitation trends and storm dynamics to advance knowledge of precipitation patterns in a warming world. Herein, δ¹⁸O and δ²H were used to determine the relationship between extratropical cyclonic precipitation and local meteoric water lines (LMWLs) in the eastern Ohio Valley and the eastern United States. Precipitation volume weighted and unweighted central Ohio LMWLs, created with samples collected during 2012–2018, showed that temperature had the greatest effect on precipitation isotopic composition. HYSPLIT back trajectory modelling showed that precipitation was primarily derived from a mid-continental moisture source. Remnants of major hurricanes were collected as extratropical precipitation during the 2012–2018 sampling period in central Ohio. Extratropical precipitation samples were not significantly different from the samples that created the central Ohio LMWL. Six additional LMWLs were derived from United States Geological Survey (USGS) Atmospheric Integrated Research Monitoring Network (AIRMoN) samples collected in Pennsylvania, Delaware, Tennessee, Vermont, New Hampshire, and Oxford, Ohio. Meteoric water lines describing published samples from Superstorm Sandy, plotted with these AIRMoN LMWLs, showed isotopic composition of Superstorm Sandy precipitation was commonly more depleted than the average isotopic composition at the mid-latitude locations. Meteoric water lines describing the Superstorm Sandy precipitation were not significantly different in slope from LMWLs generated within 300 km of the USGS AIRMoN site. This finding, which was observed across the eastern Ohio Valley and eastern United States, demonstrated a consistent precipitation δ²H–δ¹⁸O relationship for extratropical cyclonic and non-cyclonic events. This work also facilitates the analysis of storm development based on the relationship between extratropical event signature and the LMWL. Analysis of extratropical precipitation in relation to LMWLs along storm tracks allows for stronger development of precipitation models and understanding of which climatic and atmospheric factors determine the isotopic composition of precipitation.     

Developing a model of climate change behavior among adolescents

Research on adolescent climate change perceptions has uncovered key insights about how knowledge, concern, and hope might relate to behavior and the potential for educational interventions to influence these factors. However, few of these studies have employed treatment/control designs that might address causality and none have addressed how these factors might interact to influence behavior. We developed a model of behavior change where a climate education treatment impacted knowledge, knowledge impacted hope and concern, and hope and concern together impacted behavior. We empirically tested the utility of this model and the causal relationships within it using a pre/post, treatment/control evaluation of climate education among adolescents in North Carolina, USA (n?=?1041). We found support for a causal relationship between the treatment and gains in knowledge, but not between treatment and behavior. However, we did find support for a path model in which climate change knowledge positively relates to increased climate change concern and hope, and increases in concern and hope predict changes in pro-environmental behavior. Low SES was related to smaller gains in knowledge, concern, and behavior. Our results contribute to a theoretical understanding of climate change behaviors among adolescents and suggest that climate education aiming to change behavior should focus on building hope and concern.     

The effects of dock shading on the seagrass Halodule wrightii in Perdido Bay, Alabama

Aboveground and belowground biomass, density, blade length, and chlorophyll content of seagrass growing directly under docks were compared with adjacent unshaded sites. The amount of light reduction due to dock shading was measured using quantum spherical irradiance meters. Seagrasses were present under docks; they were shaded such that light levels were 19% and 16% of surface irradiance, at shallow and deep sites, respectively. Shoot density was 40–47% lower in shaded plots than in unshaded plots; total biomass was 30–33% lower in shaded plots than in unshaded plots. In contrast, blade length and chlorophyll content were increased at shaded plots relative to unshaded plots. Seagrasses were not found under docks at light levels less than 14% of surface irradiance. These results are in agreement with published in situ compensation irradiance estimates of 15–18% for Halodule wrightii in Texas coastal waters. Shading effects were most apparent between the hours of 1000 and 1500; therefore, the light received during the early morning and late afternoon hours may be critical for plants growing under docks. The north-south orientation of the docks in this study is likely an important factor contributing to the continued survival and growth of the seagrasses.     

A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval

We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar?Cheliospheric?Cplanetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March??C?16 April 2008) extending from below the solar photosphere, through interplanetary space, and down to Earth??s mesosphere. Nearly 200 people participated in aspects of WHI studies, analyzing and interpreting data from nearly 100 instruments and models in order to elucidate the physics of fundamental heliophysical processes. The solar and inner heliospheric data showed structure consistent with the declining phase of the solar cycle. A closely spaced cluster of low-latitude active regions was responsible for an increased level of magnetic activity, while a highly warped current sheet dominated heliospheric structure. The geospace data revealed an unusually high level of activity, driven primarily by the periodic impingement of high-speed streams. The WHI studies traced the solar activity and structure into the heliosphere and geospace, and provided new insight into the nature of the interconnected heliophysical system near solar minimum.     

Lava penetrating water: the different behaviours of pāhoehoe and ‘a‘ā at the Nesjahraun, Tingvellir, Iceland

The Nesjahraun is a basaltic lava flow erupted from a subaerial fissure, extending NE along the Tingvellir graben from the Hengill central volcano that produced pāhoehoe lava followed by ‘a‘ā. The Nesjahraun entered Iceland’s largest lake, Tingvallavatn, along its southern shore during both phases of the eruption and exemplifies lava flowing into water in a lacustrine environment in the absence of powerful wave action. This study combines airborne light detection and ranging, sidescan sonar and Chirp seismic data with field observations to investigate the behaviour of the lava as it entered the water. Pāhoehoe sheet lava was formed during the early stages of the eruption. Along the shoreline, stacks of thin (5–20 cm thick), vesicular, flows rest upon and surround low (<5 m) piles of coarse, unconsolidated, variably oxidised spatter. Clefts within the lava run inland from the lake. These are 2–5 m wide, >2 m deep, ∼50 m long, spaced ∼50 m apart and have sub-horizontal striations on the walls. They likely represent channels or collapsed tubes along which lava was delivered into the water. A circular rootless cone, Eldborg, formed when water infiltrated a lava tube. Offshore from the pāhoehoe lavas, the gradient of the flow surface steepens, suggesting a change in flow regime and the development of a talus ramp. Later, the flow was focused into a channel of ‘a‘ā lava, ∼200–350 m wide. This split into individual flow lobes 20–50 m wide along the shore. ‘A‘ā clinker is exposed on the water’s edge, as well as glassy sand and gravel, which has been locally intruded by small (<1 m), irregularly shaped, lava bodies. The cores of the flow lobes contain coherent, but hackly fractured lava. Mounds consisting predominantly of scoria lapilli and the large paired half-cone of Grámelur were formed in phreatomagmatic explosions. The ‘a‘ā flow can be identified underwater over 1 km offshore, and the sidescan data suggest that the flow lobes remained coherent flowing down a gradient of <10°. The Nesjahraun demonstrates that, even in the absence of ocean waves, phreatomagmatic explosions are ubiquitous and that pāhoehoe flows are much more likely to break up on entering the water than ‘a‘ā flows, which, with a higher flux and shallow underlying surface gradient, can penetrate water and remain coherent over distances of at least 1 km.     

A Nd- and O-isotope study of the REE-rich peralkaline Strange Lake granite: implications for Mesoproterozoic A-type magmatism in the Core Zone (NE-Canada)

It is well established that A-type granites enriched in high field strength elements, such as Zr, Nb and the REE, form in anorogenic tectonic settings. The sources of these elements and the processes controlling their unusual enrichment, however, are still debated. They are addressed here using neodymium and oxygen isotope analyses of samples from the 1.24 Ga Strange Lake pluton in the Paleoproterozoic Core Zone of Québec-Labrador, an A-type granitic body characterized by hyper-enrichment in the REE, Zr, and Nb. Age-corrected εNd values for bulk rock samples and sodic amphiboles (mainly arfvedsonite) from the pluton range from ?0.6 to ?5.7, and ?0.3 to ?5.3, respectively. The εNd values for the Napeu Kainiut quartz monzonite, which hosts the pluton, range from ?4.8 to ?8.1. The ¹⁴⁷Sm/¹⁴⁴Nd ratios of the suite and the host quartz monzonite range from 0.0967 to 0.1659, large variations that can be explained by in situ fractionation of early LREE-minerals (Strange Lake), and late hydrothermal HREE remobilization. Oxygen isotope analyses of quartz of both Strange Lake and the host yielded δ¹⁸O values between +8.2 and +9.1, which are considerably higher than the mantle value of 5.7 ± 0.2‰. Bulk rock oxygen isotope analyses of biotite-gneisses in the vicinity of the Strange Lake pluton yielded δ¹⁸O values of 6.3, 8.6 and 9.6‰. The negative εNd values and positive δ¹⁸O values of the Strange Lake and Napeu Kainiut samples indicate that both magmas experienced considerable crustal contamination. The extent of this contamination was estimated, assuming that the contaminants were sedimentary-derived rocks from the underlying Archean Mistinibi (para-) gneiss complex, which is characterized by low εNd and high δ¹⁸O values. Mixing of 5–15% of a gneiss, having an εNd value of ?15 and a δ¹⁸O value of +11, with a moderately enriched mantle source (εNd = +0.9, δ¹⁸O = +6.3) would produce values similar to those obtained for the Strange Lake granites. Based on analogies between the Nain Plutonic Suite and the Gardar alkaline igneous province (SW-Greenland), we conclude that the Strange Lake pluton and associated REE-mineralized anorogenic bodies formed from a combination of subduction-induced fertilization of the sublithospheric mantle, crustal extension and in situ magma evolution.     

Aftershock Sequences Modeled with 3-D Stress Heterogeneity and Rate-State Seismicity Equations: Implications for Crustal Stress Estimation

In this paper, we present a model for studying aftershock sequences that integrates Coulomb static stress change analysis, seismicity equations based on rate-state friction nucleation of earthquakes, slip of geometrically complex faults, and fractal-like, spatially heterogeneous models of crustal stress. In addition to modeling instantaneous aftershock seismicity rate patterns with initial clustering on the Coulomb stress increase areas and an approximately 1/t diffusion back to the pre-mainshock background seismicity, the simulations capture previously unmodeled effects. These include production of a significant number of aftershocks in the traditional Coulomb stress shadow zones and temporal changes in aftershock focal mechanism statistics. The occurrence of aftershock stress shadow zones arises from two sources. The first source is spatially heterogeneous initial crustal stress, and the second is slip on geometrically rough faults, which produces localized positive Coulomb stress changes within the traditional stress shadow zones. Temporal changes in simulated aftershock focal mechanisms result in inferred stress rotations that greatly exceed the true stress rotations due to the main shock, even for a moderately strong crust (mean stress 50 MPa) when stress is spatially heterogeneous. This arises from biased sampling of the crustal stress by the synthetic aftershocks due to the non-linear dependence of seismicity rates on stress changes. The model indicates that one cannot use focal mechanism inversion rotations to conclusively demonstrate low crustal strength (≤10 MPa); therefore, studies of crustal strength following a stress perturbation may significantly underestimate the mean crustal stress state for regions with spatially heterogeneous stress.     

Modeling Spatial Accessibility of Immigrants to Culturally Diverse Family Physicians

This article uses accessibility as an analytical tool to examine health care access among immigrants in a multicultural urban setting. It applies and improves on two widely used accessibility models—the gravity model and the two-step floating catchment area model—in measuring spatial accessibility by Mainland Chinese immigrants in the Toronto Census Metropolitan Area. Empirical data on physician-seeking behaviors are collected through two rounds of questionnaire surveys. Attention is focused on journey to physician location and utilization of linguistically matched family physicians. Based on the survey data, a two-zone accessibility model is developed by relaxing the travel threshold and distance impedance parameters that are traditionally treated as a constant in the accessibility models. General linear models are used to identify relationships among spatial accessibility, geography, and socioeconomic characteristics of Mainland Chinese immigrants. The results suggest a spatial mismatch in the supply of and demand for culturally sensitive care, and residential location is the primary factor that determines spatial accessibility to family physicians. The article yields important policy implications.