On the propagation of the Lg phase

1960 ◽  
Vol 50 (2) ◽  
pp. 197-210
Author(s):  
Eugene Herrin ◽  
Jean Richmond
Keyword(s):  
Gulf Of Mexico ◽  
Continental Crust ◽  
East Coast ◽  
Shear Waves ◽  
Surface Velocity ◽  
Upper Crust ◽  
Ray Theory ◽  
The Mean ◽  
Bodies Of Water ◽  
Sedimentary Layer

ABSTRACT Empirical determinations of the mean surface velocity of Lg indicate a range from 3.47 to 3.54 km/sec., with one set of velocities off the east coast of Mexico as low as 3.20 km/sec. Computations based on ray theory show that Lg with these velocities may be shear waves guided in the upper crust by an alternation of refractions and surface reflections. The slower velocities would result from shear waves traveling almost entirely in the sedimentary layer. Polarization of Lg is related to the angle at which the guided shear waves are incident at the surface. Calculations show that Lg would travel in a continental crust covered by a considerable thickness of water, thus supporting the hypothesis that the absence of Lg indicates that an oceanic crust underlies such bodies of water as the Gulf of Mexico. All computations were run on the Univac 1103 at Southern Methodist University.

Travel times for shear waves in a granitic layer*

1938 ◽  
Vol 28 (1) ◽  
pp. 49-56 ◽  
Author(s):  
Francis Birch
Keyword(s):  
New England ◽  
Shear Waves ◽  
Surface Velocity ◽  
Laboratory Work ◽  
Travel Times ◽  
Approximate Evaluation ◽  
The Mean ◽  
Granitic Layer ◽  
Recent Laboratory

Abstract Travel times for shear waves in a layer of granite have been computed on the basis of recent laboratory work which permits an approximate evaluation of the variation of velocity with depth. The results are found to agree very closely with those of Leet, found by the method of timed blasts, for New England. The mean surface velocity of shear waves in granite having their focus at the surface is computed to be 3.52 km/sec. at 568 km., decreasing to 3.26 at 25 km.; the curvature is shown to be too small to be easily recognized from records of near earthquakes. A depth of 15 km. for the granitic layer is shown to be consistent with Leet's observations of pulses through a second layer.

scholarly journals On the non-geostrophic appearance of some mean surface velocity observations in the Gulf of Mexico

2021 ◽  
Author(s):  
WILTON STURGES
Keyword(s):  
Gulf Of Mexico ◽  
Surface Flow ◽  
Sea Surface ◽  
Surface Velocity ◽  
Geostrophic Balance ◽  
Sea Surface Heights ◽  
The Mean ◽  
Surface Drifters ◽  
Good Agreement

AbstractA previous study of currents in the Gulf of Mexico by the author used long-term means from three independent data sources. Ship-drift results are in good agreement with surface drifters, but these two do not agree with satellite sea-surface heights (SSH). The agreement between the first two suggested the possibility that there could be errors in the SSH or that the mean surface flow is not in geostrophic balance. The present results, using the addition of a fourth long-term mean from hydrographic data, which agrees with the SSH, resolves the issue. The lack of agreement between different long-term means is from inadequate coverage in space and time in data from ship drifts and drifters.

scholarly journals The Flow through the Gulf of Mexico

2019 ◽  
Vol 49 (6) ◽  
pp. 1381-1401 ◽  
Author(s):  
J. Candela ◽  
J. Ochoa ◽  
J. Sheinbaum ◽  
M. López ◽  
P. Pérez-Brunius ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Straits Of Florida ◽  
The North ◽  
Astronomical Tide ◽  
Flow Through ◽  
Sverdrup Transport ◽  
The Mean ◽  
Yucatan Channel ◽  
Range Variation

AbstractFour years (September 2012 to August 2016) of simultaneous current observations across the Yucatan Channel (~21.5°N) and the Straits of Florida (~81°W) have permitted us to investigate the characteristics of the flow through the Gulf of Mexico. The average transport in both channels is 27.6 Sv (1 Sv = 106 m3 s−1), in accordance with previous estimates. At the Straits of Florida section, the transport related to the astronomical tide explains 55% of the observed variance with a mixed semidiurnal/diurnal character, while in the Yucatan Channel tides contribute 82% of the total variance and present a dominant diurnal character. At periods longer than a week the transports in the Yucatan and Florida sections have a correlation of 0.83 without any appreciable lag. The yearly running means of the transport time series in both channels are well correlated (0.98) and present a 3-Sv range variation in the 4 years analyzed. This long-term variability is well related to the convergence of the Sverdrup transport in the North Atlantic between 14.25° and 18.75°N. Using 2 years (July 2014–July 2016) of simultaneous currents observations in the Florida section, the Florida Cable section (~26.7°N), and a section across the Old Bahama Channel (~78.4°W), a mean northward transport of 28.4, 31.1, and 1.6 Sv, respectively, is obtained, implying that only 1.1 Sv is contributed by the Northwest Providence Channel to the mean transport observed at the Cable section during this 2-yr period.

VARIATION IN ANAL FIN RAY COUNT OF THE REDSIDE SHINER RICHARDSONIUS BALTEATUS (RICHARDSON)

1953 ◽  
Vol 31 (3) ◽  
pp. 211-225 ◽  
Author(s):  
C. C. Lindsey
Keyword(s):  
Morphological Characteristics ◽  
Introduced Populations ◽  
Fin Ray ◽  
Parent Stock ◽  
Different Populations ◽  
The Mean ◽  
Redside Shiner ◽  
Richardsonius Balteatus ◽  
Bodies Of Water ◽  
Different Parts

Anal fin rays were counted on 4766 specimens of Richardsonius balteatus from 61 localities in British Columbia. Individual counts varied from 10 to 21, and mean counts of different populations varied from 12.06 to 17.51. Significant differences in counts occurred between different bodies of water, between recently introduced populations and their parent stock, between different parts of the same lake, and between different year classes. Ray counts tended to be higher amongst females in populations with high over-all means, and higher amongst males in populations with low over-all means. A positive correlation was demonstrated between water temperatures recorded in the vicinity of developing fry and the mean numbers of anal rays produced. Within each latitudinal zone a similar correlation occurred between mean ray count and average air temperature during the spawning season, but data on 109 means of populations in U.S.A. and Canada indicated a tendency, probably genetic, towards production, at equivalent temperature, of higher ray count towards the northern end of the range. Loose correlations between anal ray count and certain other morphological characteristics suggest that these may be dependent on more or less common environmental factors but are not linked by direct causality.

scholarly journals Glacier Sliding Down an Inclined Wavy Bed

1976 ◽  
Vol 17 (77) ◽  
pp. 447-462 ◽  
Author(s):  
L. W. Morland
Keyword(s):  
Order Term ◽  
High Viscosity ◽  
Second Order ◽  
Temperature Fields ◽  
Surface Velocity ◽  
Flow Equations ◽  
Basal Sliding ◽  
Pressure Melting ◽  
The Mean ◽  
Bed Slope

The treatments by Nye and Kamb of glacier sliding over a wavy bed with small slope, which assume the ice to be approximated by a Newtonian fluid of high viscosity, are complemented by the inclusion of the glacier depth and the inclination of the bed to the horizontal. The driving force of the motion, gravity, is therefore present in the flow equations and defines immediately the mean drag on the bed. A geothermal heal flux is also included in order to estimate its possible effect on the flow. A complex variable method is used to determine the velocity and temperature fields to second order in the bed slope. These fields satisfy the zero shear traction and pressure-melting-regelation conditions to the same order on the actual bed profile. It is the balance of the second-order term which determines explicitly the (zero order) basal-sliding velocity and surface velocity in terms of the geometry and physical properties of both ice and bed. An explicit solution is illustrated for a sinusoidal bed. and a simple criterion for the onset of cavitation is obtained.

Shark Nursery Grounds of the Gulf of Mexico and the East Coast Waters of the United States

2007 ◽  
Keyword(s):  
United States ◽  
Gulf Of Mexico ◽  
East Coast ◽  
Gulf Coast ◽  
Atlantic Coast ◽  
The United States ◽  
Shark Species ◽  
Carcharhinus Plumbeus ◽  
Nursery Areas ◽  
Pesticide Metabolites

<em>Abstract.</em>—Because of their tendency to accumulate in estuaries and coastal regions, organochlorine (OC) contaminants such as pesticides and polychlorinated biphenyls (PCBs) represent potential threats to the quality of essential fish habitat for many shark species. These compounds pose special risks to immature sharks in particular because of their ability to impair growth and sexual maturation in juvenile fish at environmentally relevant levels of exposure. In order to assess the extent of these risks in shark populations on the East Coast of the United States, the present study examined concentrations of 30 OC pesticides/pesticide metabolites and total PCBs in juvenile sandbar <em>Carcharhinus plumbeus </em>and blacktip <em>C. limbatus </em>sharks from seven major nursery areas in the western Atlantic Ocean and eastern Gulf of Mexico. Quantifiable levels of PCBs and 13 OC pesticides/ pesticide metabolites were detected via gas chromatography and mass spectrometry in liver of 25 young-of-the-year blacktip sharks from the southeastern U.S. Atlantic coast and three regions on Florida’s gulf coast: Cedar Key, Tampa Bay, and Charlotte Harbor. Similarly, quantifiable levels of PCBs and 14 OC pesticides/metabolites were detected in 23 juvenile <em>C. plumbeus </em>from three sites on the northeastern U.S. coast: middle Delaware Bay, lower Chesapeake Bay, and Virginia’s eastern shore. Liver OC concentrations in Atlantic sandbar and blacktip sharks were higher than expected and, in some cases, comparable with elevated levels observed in deep-sea and pelagic sharks. Although significantly lower than those observed in Atlantic sharks, pesticide and PCB levels in Florida blacktip sharks were similar to, if not greater than, OC concentrations reported in adults of other coastal shark species. Based on these data, OC contamination appears to pose significant threats to habitat quality in sandbar and blacktip shark nursery areas on the U.S. Atlantic coast.

scholarly journals Loop Current Variability as Trigger of Coherent Gulf Stream Transport Anomalies

2019 ◽  
Vol 49 (8) ◽  
pp. 2115-2132 ◽  
Author(s):  
Joël J.-M. Hirschi ◽  
Eleanor Frajka-Williams ◽  
Adam T. Blaker ◽  
Bablu Sinha ◽  
Andrew Coward ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Gulf Stream ◽  
Time Lag ◽  
Ocean Model ◽  
Surface Velocity ◽  
Loop Current ◽  
Intrinsic Variability ◽  
Cape Hatteras ◽  
Florida Straits ◽  
Stream Transport

AbstractSatellite observations and output from a high-resolution ocean model are used to investigate how the Loop Current in the Gulf of Mexico affects the Gulf Stream transport through the Florida Straits. We find that the expansion (contraction) of the Loop Current leads to lower (higher) transports through the Straits of Florida. The associated surface velocity anomalies are coherent from the southwestern tip of Florida to Cape Hatteras. A simple continuity-based argument can be used to explain the link between the Loop Current and the downstream Gulf Stream transport: as the Loop Current lengthens (shortens) its path in the Gulf of Mexico, the flow out of the Gulf decreases (increases). Anomalies in the surface velocity field are first seen to the southwest of Florida and within 4 weeks propagate through the Florida Straits up to Cape Hatteras and into the Gulf Stream Extension. In both the observations and the model this propagation can be seen as pulses in the surface velocities. We estimate that the Loop Current variability can be linked to a variability of several Sverdrups (1Sv = 106 m3 s−1) through the Florida Straits. The exact timing of the Loop Current variability is largely unpredictable beyond a few weeks and its variability is therefore likely a major contributor to the chaotic/intrinsic variability of the Gulf Stream. However, the time lag between the Loop Current and the flow downstream of the Gulf of Mexico means that if a lengthening/shortening of the Loop Current is observed this introduces some predictability in the downstream flow for a few weeks.

Prehospital neuromuscular blockade post OHCA: UK's first paramedic-delivered protocol

2020 ◽  
Vol 12 (5) ◽  
pp. 202-207
Author(s):  
Mark Durham ◽  
Pete Westhead ◽  
David Griffiths ◽  
Richard Lyon ◽  
Margaret Lau-Walker
Keyword(s):  
Cardiac Arrest ◽  
Neuromuscular Blockade ◽  
Patient Outcomes ◽  
East Coast ◽  
Service Evaluation ◽  
Spontaneous Circulation ◽  
Airway Control ◽  
Adverse Incident ◽  
The Mean ◽  
A Minor

Background: Since 2016, critical care paramedics from the South East Coast Ambulance Service have offered neuromuscular blockade to patients for ventilatory/airway control after cardiac arrest. Aims: To examine the first cases of paramedic-delivered neuromuscular blockade, and evaluate the prevalence of its use and safety. Methods: Retrospective service evaluation of patients receiving post-arrest paralysis during the study period from 1 April 2016 until 31 July 2017. Findings: The study included 127 patients. The mean age of administration was 63 years, mean weight was 80 kg (SD: 19 kg), dose was 1 mg/kg and median time from rocuronium administration to hospital was 32 minutes (IQR 20–43 minutes). Three patients (2.3%) experienced a minor adverse incident. There were no major airway complications, nor other significant adverse incidents. Thirty-seven patients (31%) survived to discharge. Conclusion: From this patient group, paramedic-administered rocuronium in intubated patients who have experienced a cardiac arrest and a return of spontaneous circulation appears to be safe, but further interventional research is required to determine whether this improves patient outcomes.

scholarly journals Changes in glacier dynamics in the northern Antarctic Peninsula since 1985

2018 ◽  
Vol 12 (2) ◽  
pp. 577-594 ◽  
Author(s):  
Thorsten Seehaus ◽  
Alison J. Cook ◽  
Aline B. Silva ◽  
Matthias Braun
Keyword(s):  
Antarctic Peninsula ◽  
West Coast ◽  
East Coast ◽  
Hierarchical Cluster ◽  
Flow Speed ◽  
Climatic Conditions ◽  
Surface Velocity ◽  
Ice Shelf ◽  
The West ◽  
Ice Dynamics

Abstract. The climatic conditions along the northern Antarctic Peninsula have shown significant changes within the last 50 years. Here we present a comprehensive analysis of temporally and spatially detailed observations of the changes in ice dynamics along both the east and west coastlines of the northern Antarctic Peninsula. Temporal evolutions of glacier area (1985–2015) and ice surface velocity (1992–2014) are derived from a broad multi-mission remote sensing database for 74 glacier basins on the northern Antarctic Peninsula ( <  65° S along the west coast and north of the Seal Nunataks on the east coast). A recession of the glaciers by 238.81 km2 is found for the period 1985–2015, of which the glaciers affected by ice shelf disintegration showed the largest retreat by 208.59 km2. Glaciers on the east coast north of the former Prince Gustav Ice Shelf extent in 1986 receded by only 21.07 km2 (1985–2015) and decelerated by about 58 % on average (1992–2014). A dramatic acceleration after ice shelf disintegration with a subsequent deceleration is observed at most former ice shelf tributaries on the east coast, combined with a significant frontal retreat. In 2014, the flow speed of the former ice shelf tributaries was 26 % higher than before 1996. Along the west coast the average flow speeds of the glaciers increased by 41 %. However, the glaciers on the western Antarctic Peninsula revealed a strong spatial variability of the changes in ice dynamics. By applying a hierarchical cluster analysis, we show that this is associated with the geometric parameters of the individual glacier basins (hypsometric indexes, maximum surface elevation of the basin, flux gate to catchment size ratio). The heterogeneous spatial pattern of ice dynamic evolutions at the northern Antarctic Peninsula shows that temporally and spatially detailed observations as well as further monitoring are necessary to fully understand glacier change in regions with such strong topographic and climatic variances.

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