ResearchPad - Geophysics https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[The Propagation Effects of Lightning Electromagnetic Fields Over Mountainous Terrain in the Earth‐Ionosphere Waveguide]]> https://www.researchpad.co/product?articleinfo=N1dfcb8d9-37b3-4eb7-8743-ae3fafeb31fd

Abstract

In this paper, a full‐wave two‐dimensional Finite‐Difference‐Time‐Domain model is developed to evaluate the propagation effects of lightning electromagnetic fields over mountainous terrain in the Earth‐ionosphere waveguide. In the model, we investigate the effect of the Earth‐ionosphere waveguide structure and medium parameters, including the effect of the ionospheric cold plasma characteristics, the effect of the Earth curvature, and the propagation effects over mountainous terrain. For the first time, the obtained results are validated against simultaneous experimental data consisting of lightning currents measured at the Säntis Tower and electric fields measured in Neudorf, Austria, located at 380‐km distance from the tower. It is shown that both the time delays and amplitudes of the lightning electromagnetic fields at 380‐km distance can be strongly affected by the ionospheric electron density profile, the mountainous terrain, and the Earth curvature. After taking into account the effect of the irregular terrain between the Säntis Tower and the field measurement station, the vertical electric fields calculated by using our model are found to be in good agreement with the corresponding measured cases occurred in both daytime and nighttime. The ideal approximation used in either the classical solutions or the simplified models might lead to inaccuracies in the estimated reflection height. Furthermore, we discuss the sensitivity of our results by considering different return stroke models, as well as different typical values of the return stroke speed and of the ground conductivity.

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<![CDATA[Analysis of the Spatial Nonuniformity of the Electric Field in Spectroscopic Diagnostic Methods of Atmospheric Electricity Phenomena]]> https://www.researchpad.co/product?articleinfo=N4ee2dca9-9c17-4481-b682-58634ff16627

Abstract

The spatial nonuniformity of the electric field in air discharges, such as streamers, can influence the accuracy of spectroscopic diagnostic methods and hence the estimation of the peak electric field. In this work, we use a self‐consistent streamer discharge model to investigate the spatial nonuniformity in streamer heads and streamer glows. We focus our analysis on air discharges at atmospheric pressure and at the low pressure of the mesosphere. This approach is useful to investigate the spatial nonuniformity of laboratory discharges as well as sprite streamers and blue jet streamers, two types of transient luminous events taking place above thunderclouds. This characterization of the spatial nonuniformity of the electric field in air discharges allows us to develop two different spectroscopic diagnostic methods to estimate the peak electric field in cold plasmas. The commonly employed method to derive the peak electric field in streamer heads underestimates the electric field by about 40–50% as a consequence of the high spatial nonuniformity of the electric field. Our diagnostic methods reduce this underestimation to about 10–20%. However, our methods are less accurate than previous methods for streamer glows, where the electric field is uniformly distributed in space. Finally, we apply our diagnostic methods to the measured optical signals in the second positive system of N2 and the first negative system of N2+ of sprites recorded by Armstrong et al. (1998, https://doi.org/10.1016/S1364-6826(98)00026-1) during the SPRITE's 1995 and 1996 campaigns.

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<![CDATA[Slow slip source characterized by lithological and geometric heterogeneity]]> https://www.researchpad.co/product?articleinfo=Na5d4410d-524c-4ab3-8c5c-f6f22e149a1b

Slow slip events on subduction megathrusts are linked to subduction of rough crust and heterogeneous fault rock properties.

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<![CDATA[Modeling the Relationship of Groundwater Salinity to Neonatal and Infant Mortality From the Bangladesh Demographic Health Survey 2000 to 2014]]> https://www.researchpad.co/product?articleinfo=N282f9af1-03b6-46af-ab8d-637967f089d1

Abstract

We evaluated the relationship of drinking water salinity to neonatal and infant mortality using Bangladesh Demographic Health Surveys of 2000, 2004, 2007, 2011, and 2014. Point data of groundwater electrical conductivity (EC)— a measure of salinity—were collated from the Bangladesh Water Development Board and digitizing salinity contour map. Data for groundwater dissolved elements (sodium, calcium, magnesium, and potassium) data came from a national hydrochemistry survey in Bangladesh. Point EC and dissolved minerals data were then interpolated over entire Bangladesh and extracted to each cluster location, the primary sampling unit of Bangladesh Demographic Health Surveys. We used restricted cubic splines and survey design‐specific logistic regression models to determine the relationship of water salinity to neonatal and infant mortality. A U‐shaped association between drinking water salinity and neonatal and infant mortality was found, suggesting higher mortality when salinity was very low and high. Compared to mildly saline (EC ≥0.7 and < 2 mS/cm) water drinkers, freshwater (EC < 0.7 mS/cm) drinkers had 1.37 (95% CI: 1.01, 1.84) times higher neonatal mortality and 1.43 (95% CI: 1.08, 1.89) times higher infant mortality. Compared to mildly saline water drinkers, severe‐saline (EC ≥10 mS/cm) water drinkers had 1.77 (95% CI: 1.17, 2.68) times higher neonatal mortality and 1.93 (95% CI: 1.35, 2.76) times higher infant mortality. We found that mild‐salinity water had a high concentration of calcium and magnesium, whereas severe‐salinity water had a high concentration of sodium. Freshwater had the least concentrations of salubrious calcium and magnesium.

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<![CDATA[Spatial Accessibility and Social Inclusion: The Impact of Portugal's Last Health Reform]]> https://www.researchpad.co/product?articleinfo=Nfdc1fbe5-ff6a-4d7a-b20c-9f51d93f1a6a

Abstract

Health policies seek to promote access to health care and should provide appropriate geographical accessibility to each demographical functional group. The dispersal demand of health‐care services and the provision for such services at fixed locations contribute to the growth of inequality in their access. Therefore, the optimal distribution of health facilities over the space/area can lead to accessibility improvements and to the mitigation of the social exclusion of the groups considered most vulnerable. Requiring for such, the use of planning practices joined with accessibility measures. However, the capacities of Geographic Information Systems in determining and evaluating spatial accessibility in health system planning have not yet been fully exploited. This paper focuses on health‐care services planning based on accessibility measures grounded on the network analysis. The case study hinges on mainland Portugal. Different scenarios were developed to measure and compare impact on the population's accessibility. It distinguishes itself from other studies of accessibility measures by integrating network data in a spatial accessibility measure: the enhanced two‐step floating catchment area. The convenient location for health‐care facilities can increase the accessibility standards of the population and consequently reduce the economic and social costs incurred. Recently, the Portuguese government implemented a reform that aimed to improve, namely, the access and equity in meeting with the most urgent patients. It envisaged, in terms of equity, the allocation of 89 emergency network points that ensured more than 90% of the population be within 30 min from any one point in the network. Consequently, several emergency services were closed, namely, in rural areas. This reform highlighted the need to improve the quality of the emergency care, accessibility to each care facility, and equity in their access. Hence, accessibility measures become an efficient decision‐making tool, despite its absence in effective practice planning. According to an application of this type of measure, it was possible to verify which levels of accessibility were decreased, including the most disadvantaged people, with a larger time of dislocation of 12 min between 2001 and 2011.

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<![CDATA[Population of the temperate mosquito, Culex pipiens, decreases in response to habitat climatological changes in future]]> https://www.researchpad.co/product?articleinfo=Nc80f32d5-17e1-4238-9793-c85a5a3de49a

Abstract

Predictions of the temporal distribution of vector mosquitoes are an important issue for human health because the response of mosquito populations to climate change could have implications for the risk of vector‐borne diseases. To elucidate the effects of climate change on mosquito populations inhabiting temperate regions, we developed a Physiology‐based Climate‐driven Mosquito Population model for temperate regions. For accurately reproducing the temporal patterns observed in mosquito populations, the key factors were identified by implementing the combinations of factors into the model. We focused on three factors: the effect of diapause, the positive effect of rainfall on larval carrying capacity, and the negative effect of rainfall as the washout mortality on aquatic stages. For each model, parameters were calibrated using weekly observation data of a Culex pipiens adult population collected in Tokyo, Japan. Based on its likelihood value, the model incorporating diapause, constant carrying capacity, and washout mortality was the best to replicate the observed data. By using the selected model and applying global climate model data, our results indicated that the mosquito population would decrease and adults’ active season would be shortened under future climate conditions. We found that incorporating the washout effect in the model settings or not caused a difference in the temporal patterns in the projected mosquito populations. This suggested that water resources in mosquito habitats in temperate regions should be considered for predicting the risk of vector‐borne diseases in such regions.

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<![CDATA[Sea level fingerprinting of the Bering Strait flooding history detects the source of the Younger Dryas climate event]]> https://www.researchpad.co/product?articleinfo=N03398dfe-4375-4a06-a7dd-a3641982ccf1

Two-phased flooding of Bering Strait is reconciled by melting North American ice saddle during Younger Dryas.

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<![CDATA[Magma Degassing as a Source of Long‐Term Seismicity at Volcanoes: The Ischia Island (Italy) Case]]> https://www.researchpad.co/product?articleinfo=N978e9b20-749d-4a9f-ac68-8956762af4c2

Abstract

Transient seismicity at active volcanoes poses a significant risk in addition to eruptive activity. This risk is powered by the common belief that volcanic seismicity cannot be forecast, even on a long term. Here we investigate the nature of volcanic seismicity to try to improve our forecasting capacity. To this aim, we consider Ischia volcano (Italy), which suffered similar earthquakes along its uplifted resurgent block. We show that this seismicity marks an acceleration of decades‐long subsidence of the resurgent block, driven by degassing of magma that previously produced the uplift, a process not observed at other volcanoes. Degassing will continue for hundreds to thousands of years, causing protracted seismicity and will likely be accompanied by moderate and damaging earthquakes. The possibility to constrain the future duration of seismicity at Ischia indicates that our capacity to forecast earthquakes might be enhanced when seismic activity results from long‐term magmatic processes, such as degassing

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<![CDATA[Bund removal to re-establish tidal flow, remove aquatic weeds and restore coastal wetland services—North Queensland, Australia]]> https://www.researchpad.co/product?articleinfo=Neac5db12-b809-4a22-afa7-0c243544d6ab

The shallow tidal and freshwater coastal wetlands adjacent to the Great Barrier Reef lagoon provide a vital nursery and feeding complex that supports the life cycles of marine and freshwater fish, important native vegetation and vital bird habitat. Urban and agricultural development threaten these wetlands, with many of the coastal wetlands becoming lost or changed due to the construction of artificial barriers (e.g. bunds, roads, culverts and floodgates). Infestation by weeds has become a major issue within many of the wetlands modified (bunded) for ponded pasture growth last century. A range of expensive chemical and mechanical control methods have been used in an attempt to restore some of these coastal wetlands, with limited success. This study describes an alternative approach to those methods, investigating the impact of tidal reinstatement after bund removal on weed infestation, associated changes in water quality, and fish biodiversity, in the Boolgooroo lagoon region of the Mungalla wetlands, East of Ingham in North Queensland. High resolution remote sensing, electrofishing and in-water logging was used to track changes over time– 1 year before and 4 years after removal of an earth bund. With tides only penetrating the wetland a few times yearly, gross changes towards a more natural system occurred within a relatively short timeframe, leading to a major reduction in infestation of olive hymenachne, water hyacinth and salvina, reappearance of native vegetation, improvements in water quality, and a tripling of fish diversity. Weed abundance and water quality does appear to oscillate however, dependent on summer rainfall, as changes in hydraulic pressure stops or allows tidal ingress (fresh/saline cycling). With an estimated 30% of coastal wetlands bunded in the Great Barrier Reef region, a passive remediation method such as reintroduction of tidal flow by removal of an earth bund or levee could provide a more cost effective and sustainable means of controlling freshwater weeds and improving coastal water quality into the future.

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<![CDATA[Insignificant QBO‐MJO Prediction Skill Relationship in the SubX and S2S Subseasonal Reforecasts]]> https://www.researchpad.co/product?articleinfo=N80d62339-fdd5-4539-8af8-fbb9aaf795dd

Abstract

The impact of the stratospheric quasi‐biennial oscillation (QBO) on the prediction of the tropospheric Madden‐Julian oscillation (MJO) is evaluated in reforecasts from nine models participating in subseasonal prediction projects, including the Subseasonal Experiment (SubX) and Subseasonal to Seasonal (S2S) projects. When MJO prediction skill is analyzed for December to February, MJO prediction skill is higher in the easterly phase of the QBO than the westerly phase, consistent with previous studies. However, the relationship between QBO phase and MJO prediction skill is not statistically significant for most models. This insignificant QBO‐MJO skill relationship is further confirmed by comparing two subseasonal reforecast experiments with the Community Earth System Model v1 using both a high‐top (46‐level) and low‐top (30‐level) version of the Community Atmosphere Model v5. While there are clear differences in the forecasted QBO between the two model top configurations, a negligible change is shown in the MJO prediction, indicating that the QBO in this model may not directly control the MJO prediction and supporting the insignificant QBO‐MJO skill relationship found in SubX and S2S models.

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<![CDATA[Quantifying the Timescale and Strength of Southern Hemisphere Intraseasonal Stratosphere‐troposphere Coupling]]> https://www.researchpad.co/product?articleinfo=Ne2d0b07a-2452-4f6d-ba26-c3d3b5569795

Abstract

The Southern Hemisphere zonal circulation manifests a downward influence of the stratosphere on the troposphere from late spring to early summer. However, the strength and timescale of the connection, given the stratospheric state, have not been explicitly quantified. Here, SH zonal wind reanalysis time series are analyzed with a methodology designed to detect the minimal set of statistical predictors of multiple interacting variables via conditional independence tests. Our results confirm from data that the variability of the stratospheric polar vortex is a predictor of the tropospheric eddy‐driven jet between September and January. The vortex variability explains about 40% of monthly mean jet variability at a lead time of 1 month and can entirely account for the observed jet persistence. Our statistical model can quantitatively connect the multidecadal trends observed in the vortex and jet during the satellite era. This shows how short‐term variability can help understand statistical links in long‐term changes.

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<![CDATA[The Role of Crustal Buoyancy in the Generation and Emplacement of Magmatism During Continental Collision]]> https://www.researchpad.co/product?articleinfo=Ndcd87f00-8e1e-43c1-80a9-861fe954de26

Abstract

During continental collision, considerable amounts of buoyant continental crust subduct to depth and subsequently exhume. Whether various exhumation paths contribute to contrasting styles of magmatism across modern collision zones is unclear. Here we present 2D thermomechanical models of continental collision combined with petrological databases to investigate the effect of the main contrasting buoyancy forces, in the form of continental crustal buoyancy versus oceanic slab age (i.e., its thickness). We specifically focus on the consequences for crustal exhumation mechanisms and magmatism. Results indicate that it is mainly crustal density that determines the degree of steepening of the subducting continent and separates the models' parameter space into two regimes. In the first regime, high buoyancy values (∆ρ > 500 kg/m3) steepen the slab most rapidly (to 45–58°), leading to opening of a gap in the subduction channel through which the subducted crust exhumes (“subduction channel crustal exhumation”). A shift to a second regime (“underplating”) occurs when the density contrast is reduced by 50 kg/m3. In this scenario, the slab steepens less (to 37–50°), forcing subducted crust to be placed below the overriding plate. Importantly, the magmatism changes in the two cases: Crustal exhumation through the subduction channel is mainly accompanied by a narrow band of mantle melts, while underplating leads to widespread melting of mixed sources. Finally, we suggest that the amount (or density) of subducted continental crust, and the resulting buoyancy forces, could contribute to contrasting collision styles and magmatism in the Alps and Himalayas/Tibet.

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<![CDATA[Seismic evidence for megathrust fault-valve behavior during episodic tremor and slip]]> https://www.researchpad.co/product?articleinfo=Na2469064-99f2-4427-af80-6edb7aebfd7e

Recurring slow slip and tremor events at subduction zones are accompanied by fluctuations in pore-fluid pressure.

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<![CDATA[Pinpointing nitrogen oxide emissions from space]]> https://www.researchpad.co/product?articleinfo=N5f85182e-ac1b-4a38-91cf-3e27d6e07134

Power plant exhausts can be identified and quantified from satellite observations.

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<![CDATA[Blue light-dependent human magnetoreception in geomagnetic food orientation]]> https://www.researchpad.co/product?articleinfo=5c6f149bd5eed0c48467a3d1

The Earth’s geomagnetic field (GMF) is known to influence magnetoreceptive creatures, from bacteria to mammals as a sensory cue or a physiological modulator, despite it is largely thought that humans cannot sense the GMF. Here, we show that humans sense the GMF to orient their direction toward food in a self-rotatory chair experiment. Starved men, but not women, significantly oriented toward the ambient/modulated magnetic north or east, directions which had been previously food-associated, without any other helpful cues, including sight and sound. The orientation was reproduced under blue light but was abolished under a blindfold or a longer wavelength light (> 500 nm), indicating that blue light is necessary for magnetic orientation. Importantly, inversion of the vertical component of the GMF resulted in orientation toward the magnetic south and blood glucose levels resulting from food appeared to act as a motivator for sensing a magnetic field direction. The results demonstrate that male humans sense GMF in a blue light-dependent manner and suggest that the geomagnetic orientations are mediated by an inclination compass.

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<![CDATA[Slow slip events in the roots of the San Andreas fault]]> https://www.researchpad.co/product?articleinfo=5c8014d0d5eed0c484a9e442

By analyzing GPS time series, we have detected an averaged Mw 4.9 slow slip event in the roots of the San Andreas fault.

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<![CDATA[Historical observations of algal blooms in Mazatlan Bay, Sinaloa, Mexico (1979-2014)]]> https://www.researchpad.co/product?articleinfo=5c5b529ad5eed0c4842bcc8c

A 35-year record of algal blooms in Mazatlan Bay is reviewed in order to register bloom-forming species and their seasonal presence, duration, degree of toxicity and environmental impact. A total of 202 algal blooms have been recorded and 25 dominant species identified: 6 toxic, 5 harmful and 14 harmless species. A harmless species, Myrionecta rubra, tended to decrease in frequency, while toxic species Gymnodinium catenatum and Margalefidinium polykrikoides showed a clear trend towards an increase in frequency. The number of discoloration days attributable to blooms was highly variable in each year, but a decadal analysis revealed a tendency to increase. The monthly distribution of algal blooms for decades showed two peaks of high frequency, the larger from February to May and the smaller from September to November. The duration of blooms varied from a few days to more than three months; the ephemeral blooms were the most frequent, but in the last decade, the frequency of the longer-lasting blooms has increased. An absence of blooms in 1983–4 and 1992–3 coincided with strong El Niño events, but this pattern was not consistent in subsequent El Niño years. Years with more or fewer discolorations days appear to be associated with cold or warm phases of the Pacific Decadal Oscillation.

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<![CDATA[The Low‐Resolution Version of HadGEM3 GC3.1: Development and Evaluation for Global Climate]]> https://www.researchpad.co/product?articleinfo=5c75654ed5eed0c484cbd987

Abstract

A new climate model, HadGEM3 N96ORCA1, is presented that is part of the GC3.1 configuration of HadGEM3. N96ORCA1 has a horizontal resolution of ~135 km in the atmosphere and 1° in the ocean and requires an order of magnitude less computing power than its medium‐resolution counterpart, N216ORCA025, while retaining a high degree of performance traceability. Scientific performance is compared to both observations and the N216ORCA025 model. N96ORCA1 reproduces observed climate mean and variability almost as well as N216ORCA025. Patterns of biases are similar across the two models. In the northwest Atlantic, N96ORCA1 shows a cold surface bias of up to 6 K, typical of ocean models of this resolution. The strength of the Atlantic meridional overturning circulation (16 to 17 Sv) matches observations. In the Southern Ocean, a warm surface bias (up to 2 K) is smaller than in N216ORCA025 and linked to improved ocean circulation. Model El Niño/Southern Oscillation and Atlantic Multidecadal Variability are close to observations. Both the cold bias in the Northern Hemisphere (N96ORCA1) and the warm bias in the Southern Hemisphere (N216ORCA025) develop in the first few decades of the simulations. As in many comparable climate models, simulated interhemispheric gradients of top‐of‐atmosphere radiation are larger than observations suggest, with contributions from both hemispheres. HadGEM3 GC3.1 N96ORCA1 constitutes the physical core of the UK Earth System Model (UKESM1) and will be used extensively in the Coupled Model Intercomparison Project 6 (CMIP6), both as part of the UK Earth System Model and as a stand‐alone coupled climate model.

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<![CDATA[Seismic site classification and amplification of shallow bedrock sites]]> https://www.researchpad.co/product?articleinfo=5c2d2ec3d5eed0c484d9b7b5

This study attempts to develop empirical correlations between average penetration resistance (NSPTR¯), averaged velocities over depth up to bedrock depth (VSR¯) and 30 m (VS30¯) for shallow depth sites (having bedrock at a depth less than 25 m). A total of 63 shallow sites were assessed for penetration resistance values up to the bedrock from Standard Penetration Tests (SPT) and dynamic soil property analysis, i.e., Shear Wave Velocity (VS) from Multichannel Analysis of Surface Waves. The study shows that 30 m averaged shear wave velocities are more than the average velocity up to bedrock depth in shallow bedrock sites because of inclusion of rock site velocity. Furthermore, averaged SPT-N(NSPTR¯) and average VS (VSR¯) up to bedrock depth were correlated with the 30 m average(VS30¯) values. This is the first attempt in developing empirical relationships of this kind for seismic site classification. These correlations can be made useful for seismic site classification of sites in regions with Standard Penetration Test (NSPT) values and limited VS values. Further surface and bedrock motion recordings of 12 selected KiK-net shallow depth sites were collected and amplifications were estimated with the respective peak ground acceleration, spectral acceleration and thereby related to the average shear wave velocity up to bedrock and 30 m. The results show that the amplification is better correlated to the VSR¯ than VS30¯ for shallow depth sites, and more data can be added to strengthen this correlation.

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<![CDATA[On the use of local weather types classification to improve climate understanding: An application on the urban climate of Toulouse]]> https://www.researchpad.co/product?articleinfo=5c1ab816d5eed0c4840269c8

This paper proposes a method based on a local weather type classification approach to facilitate analysis and communication of climate information in local climate studies. Presented herein is an application to urban climatology in Toulouse, France, but the method can be used in other applied fields of climatology as well. To describe the climatic context of this urbanized area, the local weather types that explain the plurality of weather situations Toulouse faces are presented in depth. In order to show the potential for use of this approach, this information is applied to the study of changes in local weather types in terms of frequency and intensity within a series of future climate projections, a classic urban canopy and a series of atmospheric boundary layer analyses, and as a support for communication aimed to initiate urban climate awareness in urban planning practices. The proposed classification method has been coded in an R script and is provided as a supporting information file. The paper concludes that a systematic pre-study using this kind of climatic analysis is a good practice for performing climatic contextualization in local scale applied studies, both for scientific analysis and communication.

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