Model studies of the coast effect on geomagnetic variations

1968 ◽  
Vol 5 (3) ◽  
pp. 515-522 ◽  
Author(s):  
John F. Hermance
Keyword(s):  
Thin Sheet ◽  
Current Source ◽  
Field Measurements ◽  
Finite Conductivity ◽  
Analog Model ◽  
Geomagnetic Variations ◽  
Model Studies ◽  
Coast Effect ◽  
Model Study ◽  
Complete Neglect

The effect of a highly conducting ocean on geomagnetic variations has been studied by means of an analog model. Analog model results for a straight coastline show good agreement with analytical results derived for the case of a concentrated current source over the edge of an infinitely conducting ocean. The analog model was extended to the case of a poorly conducting island of irregular shape in a highly conducting ocean by cutting a hole the desired shape (in this case Iceland) from a large thin sheet of lead. Although anomalous contributions in the H, D, and Z components are observed, the distortion of the horizontal field components is restricted to the seaward side of the coast. Over the interior of the island only the vertical field is affected. The model study was undertaken to provide corrections to measurements made in Iceland for deep conductivity studies. Some field observations were in fact made near the coastline, which show general agreement with the model results, but suggest that the model overemphasized the coast effect through complete neglect of the finite conductivity of the island. The field measurements indicate that at distances of 50 km or more from the coast, for periods longer than a few minutes, the coast effect can be neglected.

scholarly journals Multi-model study of mercury dispersion in the atmosphere: Vertical distribution of mercury species

2016 ◽  
Author(s):  
Johannes Bieser ◽  
Franz Slemr ◽  
Jesse Ambrose ◽  
Carl Brenninkmeijer ◽  
Steve Brooks ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Atmospheric Chemistry ◽  
Lower Troposphere ◽  
Elemental Mercury ◽  
Mercury Species ◽  
Substantial Impact ◽  
Model Studies ◽  
Model Study ◽  
The Impact ◽  
The Vertical Distribution

Abstract. Atmospheric chemistry and transport of mercury play a key role in the global mercury cycle. However, there are still considerable knowledge gaps concerning the fate of mercury in the atmosphere. This is the second part of a model inter-comparison study investigating the impact of atmospheric chemistry and emissions on mercury in the atmosphere. While the first study focused on ground based observations of mercury concentration and deposition, here we investigate the vertical distribution and speciation of mercury from the planetary boundary layer to the lower stratosphere. So far, there have been few model studies investigating the vertical distribution of mercury, mostly focusing on single aircraft campaigns. Here, we present a first comprehensive analysis based on various aircraft observations in Europe, North America, and on inter-continental flights. The investigated models proved to be able to reproduce the distribution of total and elemental mercury concentrations in the troposphere including inter-hemispheric trends. One key aspect of the study is the investigation of mercury oxidation in the troposphere. We found that different chemistry schemes were better at reproducing observed oxidized mercury (RM) patterns depending on altitude. High RM concentrations in the upper troposphere could be reproduced with oxidation by bromine while elevated concentrations in the lower troposphere were better reproduced by OH and ozone chemistry. However, the results were not always conclusive as the physical and chemical parametrizations in the chemistry transport models also proved to have a substantial impact on model results.

scholarly journals The chemistry influencing ODEs in the Polar Boundary Layer in spring: a model study

2008 ◽  
Vol 8 (2) ◽  
pp. 7391-7453 ◽  
Author(s):  
M. Piot ◽  
R. von Glasow
Keyword(s):  
Boundary Layer ◽  
Ozone Depletion ◽  
Chemical Species ◽  
Field Measurements ◽  
The Arctic ◽  
Direct Reaction ◽  
Mixing Ratios ◽  
Model Study ◽  
Sensitivity Studies ◽  
Chemical Conditions

Abstract. Near-total depletions of ozone have been observed in the Arctic spring since the mid 1980s. The autocatalytic cycles involving reactive halogens are now recognized to be of main importance for Ozone Depletion Events (ODEs) in the Polar Boundary Layer (PBL). We present sensitivity studies using the model MISTRA in the box-model mode on the influence of chemical species on these ozone depletion processes. In order to test the sensitivity of the chemistry under polar conditions, we compared base runs undergoing fluxes of either Br2, BrCl, or Cl2 to induce ozone depletions, with similar runs including a modification of the chemical conditions. The role of HCHO, H2O2, DMS, Cl2, C2H4, C2H6, HONO, NO2, and RONO2 was investigated. Cases with elevated mixing ratios of HCHO, H2O2, DMS, Cl2, and HONO induced a shift in bromine speciation from Br/BrO to HOBr/HBr, while high mixing ratios of C2H6 induced a shift from HOBr/HBr to Br/BrO. Cases with elevated mixing ratios of HONO, NO2, and RONO2 induced a shift to BrNO2/BrONO2. The shifts from Br/BrO to HOBr/HBr accelerated the aerosol debromination, but also increased the total amount of deposited bromine at the surface (mainly via increased deposition of HOBr). These shifts to HOBr/HBr also hindered the BrO self-reaction. In these cases, the ozone depletion was slowed down, where increases in H2O2 and HONO had the greatest effect. The tests with increased mixing ratios of C2H4 highlighted the decrease in HOx which reduced the production of HOBr from bromine radicals. In addition, the direct reaction of C2H4 with bromine atoms led to less available reactive bromine. The aerosol debromination was therefore strongly reduced. Ozone levels were highly affected by the chemistry of C2H4. Cl2-induced ozone depletions were found unrealistic compared to field measurements due to the rapid production of CH3O2, HOx, and ROOH which rapidly convert reactive chlorine to HCl in a "chlorine counter-cycle". This counter-cycle efficiently reduces the concentration of reactive halogens in the boundary layer. Depending on the relative bromine and chlorine mixing ratios, the production of CH3O2, HOx, and ROOH from the counter-cycle can significantly affect the bromine chemistry. Therefore, the presence of both bromine and chlorine in the air may unexpectedly lead to a slow down in ozone destruction. For all NOy species studied (HONO, NO2, RONO2) the chemistry is characterized by an increased bromine deposition on snow reducing the amount of reactive bromine in the air. Ozone is less depleted under conditions of high mixing ratios of NOx. The production of HNO3 led to the acid displacement of HCl, and the release of chlorine out of salt aerosols (Cl2 or BrCl) increased.

Neuromuscular transmission in the jellyfish Aglantha digitale

1985 ◽  
Vol 116 (1) ◽  
pp. 1-25 ◽  
Author(s):  
P. A. Kerfoot ◽  
G. O. Mackie ◽  
R. W. Meech ◽  
A. Roberts ◽  
C. L. Singla
Keyword(s):  
Dimensional Space ◽  
Thin Sheet ◽  
Current Source ◽  
Giant Axon ◽  
The Body ◽  
Two Dimensional ◽  
Bathing Medium ◽  
Giant Axons ◽  
Motor Neurones ◽  
Stimulation Of

In the jellyfish Aglantha digitale escape swimming is mediated by the nearly synchronous activity of eight giant motor axons which make direct synaptic contact with contractile myoepithelial cells on the under-surface of the body wall. The delay in transmission at these synapses was 0.7 +/− 0.1 ms (+/− S.D.;N = 6) at 12 degrees C as measured from intracellular records. Transmission depended on the presence of Ca2+ in the bathing medium. It was not blocked by increasing the level of Mg2+ to 127 mmol l-1. The myoepithelium is a thin sheet of electrically coupled cells and injection of current at one point was found to depolarize the surrounding cells. The potential change declined with distance from the current source as expected for two-dimensional current spread. The two-dimensional space constant (lambda) was 770 micron for current flow in the circular direction and 177 micron for radial flow. The internal resistance of the epithelium (178–201 omega cm) and the membrane time constant (5–10 ms) were direction independent. No propagated epithelial action potentials were observed. Spontaneous miniature synaptic potentials of similar amplitude and rise-time were recorded intracellularly at distances of up to 1 mm from the motor giant axon. Ultrastructural evidence confirms that neuro-myoepithelial synapses also occur away from the giant axons. It is likely that synaptic sites are widespread in the myoepithelium, probably associated with the lateral motor neurones as well as the giant axons. Local stimulation of lateral motor neurones generally produced contraction in distinct fields. We suppose that stimulation of a single motor giant axon excites a whole population of lateral motor neurones and hence a broad area of the myoepithelium.

Coastal Engineering Analysis, Field Measurements, Numerical Modeling and Design for the Optimized Extension of the Beach in Ras Al-Ardh Area, Salmiya, Kuwait

2019 ◽  
Author(s):  
S. Neelamani ◽  
Bassam N. Shuhaibar ◽  
Khaled Al-Salem ◽  
Yousef Al-Osairi ◽  
Qusaie E. Karam ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Sandy Beach ◽  
Field Measurements ◽  
Beach Nourishment ◽  
Beach Sand ◽  
Design Parameters ◽  
Model Study ◽  
Sea Bed ◽  
Waves And Currents ◽  
Tourism Enterprises

Abstract Maintaining and retaining a quality sandy beach is a primary requirement for attracting people and tourists in any coastal country. Tourism Enterprises Company (TEC) in Kuwait owns 230 m long sandy beach in Ras Al-Ardh Sea Club, Salmiya, Kuwait. The beach has been eroding because of strong hydrodynamics forces from waves and currents. TEC wants to develop a stable sandy beach of 30 m wide. Kuwait Institute for Scientific Research (KISR), Kuwait is assigned to carry out the required scientific studies. In order to make sure a stable quality beach will exist, KISR has carried out the needed studies, which involves the field measurements such as bbathymetry survey, current and tidal variations, physical characteristics of beach soil, beach and sea bed profile, establishing the design parameters such as waves, currents, tide and wind. Hydrodynamic model study using DELFT3D model for the present and for the proposed extended groin conditions with beach nourishment were carried out. Also numerical modeling using GENESIS model to understand the future shore line changes due to the proposed development was carried out. Design of Groins to estimate the weight of armor units and weight of inner layers were carried out. The particle size and quantity of sand needed for reclamation of 30 m wide beach was estimated. Based on the study, it is recommended that the sandy soil to be used for 30 m wide beach nourishment should have D50 greater than 0.42 mm (say 0.5 mm) and D10 greater than 0.25 mm. The borrow pit much be selected by keeping this soil characters in mind. It is recommended to use a submerged offshore breakwater in order to retain the beach sand in place and for reducing the maintenance nourishment. Otherwise, large quantity of the capital nourished beach sand will escape into the deeper water due to strong current coupled with waves and steep seabed slopes. Environmental Impact Study was carried out as per Kuwait Environment Public Authority requirements to bring out the impacts due to beach filling and the construction submerged offshore barrier and extension of east groin for a distance of 30 m. TEC will implement the recommendations for developing the beach in Ras Al-Ardh sea club and will be useful to attract more people to use this beach.

The Prediction of Combined Sewer Overflow Performance from Models – A Case Study

1994 ◽  
Vol 29 (1-2) ◽  
pp. 373-382 ◽  
Author(s):  
Peter D. Hedges
Keyword(s):  
Storm Events ◽  
Operating Characteristics ◽  
Combined Sewer Overflows ◽  
Model Studies ◽  
Original Proposal ◽  
Model Study ◽  
Storm Flow ◽  
Combined Sewer ◽  
The Uk ◽  
Main Programme

Hydrodynamic separators have been employed as combined sewer overflows (CSOs) in the UK since the early 1960s. Since little was known of their operating characteristics, Severn Trent Water Authority contracted Aston University to monitor the performance of a separator constructed during 1986-87 at James Bridge, Walsall, UK. Unfortunately only three overflow events were fully documented during the monitoring period, which was particularly dry. One separator was therefore artificially charged by pumping from the adjacent river to simulate storm flow conditions. A model study was not included in the original proposal, but one was established to complement the main programme since the characteristics of hydrodynamic separators were poorly understood. The arrangement of the field site is described, and the results from the monitored storm events, pump tests and model studies are summarised. Characteristics derived from the model study are combined with sewage settling velocity grading curves to predict the performance of the prototype hydrodynamic separator for one of the observed storm events. Given the limitations inherent in the sewage data used, a comparison of the predicted and observed separator efficiencies demonstrates the potential of this approach for the design and selection of CSOs for specific locations.

scholarly journals Multi-model study of mercury dispersion in the atmosphere: vertical and interhemispheric distribution of mercury species

2017 ◽  
Vol 17 (11) ◽  
pp. 6925-6955 ◽  
Author(s):  
Johannes Bieser ◽  
Franz Slemr ◽  
Jesse Ambrose ◽  
Carl Brenninkmeijer ◽  
Steve Brooks ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Lower Troposphere ◽  
Elemental Mercury ◽  
Mercury Species ◽  
Substantial Impact ◽  
Model Studies ◽  
Model Study ◽  
High Concentrations ◽  
Intercomparison Study ◽  
The Impact

Abstract. Atmospheric chemistry and transport of mercury play a key role in the global mercury cycle. However, there are still considerable knowledge gaps concerning the fate of mercury in the atmosphere. This is the second part of a model intercomparison study investigating the impact of atmospheric chemistry and emissions on mercury in the atmosphere. While the first study focused on ground-based observations of mercury concentration and deposition, here we investigate the vertical and interhemispheric distribution and speciation of mercury from the planetary boundary layer to the lower stratosphere. So far, there have been few model studies investigating the vertical distribution of mercury, mostly focusing on single aircraft campaigns. Here, we present a first comprehensive analysis based on various aircraft observations in Europe, North America, and on intercontinental flights. The investigated models proved to be able to reproduce the distribution of total and elemental mercury concentrations in the troposphere including interhemispheric trends. One key aspect of the study is the investigation of mercury oxidation in the troposphere. We found that different chemistry schemes were better at reproducing observed oxidized mercury patterns depending on altitude. High concentrations of oxidized mercury in the upper troposphere could be reproduced with oxidation by bromine while elevated concentrations in the lower troposphere were better reproduced by OH and ozone chemistry. However, the results were not always conclusive as the physical and chemical parameterizations in the chemistry transport models also proved to have a substantial impact on model results.

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