Vertical directionality of ambient noise at 32°N as a functionof longitude and wind speed

Measurements of the ambient-noise field between 50 and 300 Hz with vertical arrays at 32°N (124°W, 136°W, and 150°W) have been made. Substantial differences in the vertical distribution of noise have been measured (especially at the higher frequencies), which can be interpreted in the context of attenuation by seawater sound absorption of coastal shipping noise. Under low wind-speed conditions, the vertical distribution of ambient noise is clearly concentrated within approximately ±15° of the horizontal. High wind speed has the effect of filling in the higher vertical angles, while leaving the level within the low-angular region unchanged     

Influence of the seagrass,Zostera marina L., on current flow

A salt-water flume was used to describe the mechanics of current flow around an articial Zostera marina meadow. Shear velocity and roughness height were positively correlated with seagrass surface area, and were positively/negatively correlated with current velocity. Current velocity intrusion into the meadow before diminution and maximum reduction (both at the 2 cm height line) proceed by factors of 1·25 and 2·07 cm into the meadow per cm s^?1 of current velocity, respectively.Froude number was correlated with mean bending angle of the canopy as a whole. Maximum bending had occurred with Froude = 1, but most bending had taken place by Froude = 0·4, a velocity of 40–50 cm s^?1 in this experiment.The meadow edge is the most dynamic zone of a seagrass meadow in regard to current flow. Bending of the shoot canopy is a mechanism for re-direction of current flow and in-canopy reduction of current velocity. Meadow dimensions may be regulated by scouring processes in different hydraulic regimes. Shoot bending and subsequent in-meadow current velocity reduction are mechanisms that affect self-shading and photosynthetic capabilities as well as providing habitat stability.     

Mainstreaming local perceptions of hurricane risk into policymaking: A case study of community GIS in Mexico

This article suggests a framework for incorporating and communicating local perceptions of hurricane risk into policymaking through a case study conducted at El Zapotito commune in the State of Veracruz, Mexico. The authors constructed a geographical information system (GIS)-based model to quantify and spatially assess specific household-level vulnerabilities from information generated through interviews. This research developed a household vulnerability index applied to a participatory GIS to map vulnerability to hurricane hazard. The results indicate that infrastructural weaknesses are the most important factor contributing to vulnerability, explaining on their own 72.2% of the variation in the vulnerability patterns. These findings are corroborated by a vulnerability and capacity assessment (VCA), which shows that the community lacks strategies to cope with unsafe housing. It is suggested that linking community participation with modern techniques to analyse risk can empower communities and mobilise their capacities to address very specific vulnerabilities.     

An East-West Comparison of the Transition Zone Coastal Pelagic Nekton of the North Pacific Ocean

During the 1980s and 1990s, scientific research cruises were conducted in both the eastern and western boundary regions of the North Pacific Ocean. The main purpose of these cruises was to examine the abundance and distribution patterns of juvenile salmon in coastal waters. These studies created one of the most extensive databases ever collected on the species composition of coastal Transition Zone epipelagic nekton in the North Pacific Ocean. Catch data from two purse seine and two surface trawl surveys (one each from off northern Japan and eastern Russia and off the West Coast of the U.S.) were examined using multivariate techniques to analyze the community structure of nektonic cephalopods, elasmobranchs, and teleosts in the coastal zone during the summer and autumn months. Juvenile salmonids are generally among the most common species caught, but in terms of overall abundance, other potential competitors with juvenile salmon, such as small squids and clupeoid fishes predominated the catches. Species diversity and dominance varied among areas and gear types. Distinct assemblages were found in each area, but the two regions had closely related species occupying similar ecological positions in each habitat. This revised version was published online in August 2006 with corrections to the Cover Date.     

Gravity-flow deposits from the St. Croix Ridge: Depositional history

Gravity-flow sediments from the South Virgin Islands Trough Escarpment (west of the island of St. Croix) contain Late Cretaceous through Late Miocene nannofossils that are well mixed even within individual samples. These sediments, reworked and redeposited in latest Miocene or Early Pliocene, apparently occur within a sequence of Late Miocene-to-recent fan deposits. Marine source beds representing all pre-Pliocene epochs of the Cenozoic and latest Cretaceous must have been exposed along the NW-facing West St. Croix Escarpment. Southward tilting of the St. Croix Ridge has subsequently altered the depositional pattern.     

Vibracore splitting jig

A lightweight, inexpensive jig for splitting 7.6 cm diameter vibracores is described. The advantage of the jig is its simplicity, low cost and portability to the coring site whether on land, ice or a boat. Core splitting at the coring site can guide additional coring activity, similar to other coring devices that extrude sediment as part of the coring process. The simple jig ensures straight and even cuts through the aluminum tube wall, leading to precise core splitting in the field or lab.     

Wind variations in Jupiter's equatorial atmosphere: A QQO counterpart?

Jupiter's equatorial atmosphere, much like the Earth's, is known to show quasi-periodic variations in temperature, particularly in the stratosphere, but variations in other jovian atmospheric tracers have not been studied for any correlations to these oscillations. Data taken at NASA's Infrared Telescope Facility (IRTF) from 1979 to 2000 were used to obtain temperatures at two levels in the atmosphere, corresponding to the upper troposphere (250 mbar) and to the stratosphere (20 mbar). We find that the data show periodic signals at latitudes corresponding to the troposphere zonal wind jets, with periods ranging from 4.4 (stratosphere, 95% confidence at 4° S planetographic latitude) to 7.7 years (troposphere, 97% confidence at 6° N). We also discuss evidence that at some latitudes the troposphere temperature variations are out of phase from the stratosphere variations, even where no periodicity is evident. Hubble Space Telescope images were used, in conjunction with Voyager and Cassini data, to track small changes in the troposphere zonal winds from 20° N to 20° S latitude over the 1994-2000 time period. Oscillations with a period of 4.5 years are found near 7°-8° S, with 80-85% significance. Further, the strongest evidence for a QQO-induced tropospheric wind change tied to stratospheric temperature change occurs near these latitudes, though tropospheric temperatures show little periodicity here. Comparison of thermal winds and measured zonal winds for three dates indicate that cloud features at other latitudes are likely tracked at pressures that can vary by up to a few hundred millibar, but the cloud altitude change required is too large to explain the wind changes measured at 7° S.     

Global Forces in Eruptive Solar Flares: The Lorentz Force Acting on the Solar Atmosphere and the Solar Interior

We compute the change in the Lorentz force integrated over the outer solar atmosphere implied by observed changes in vector magnetograms that occur during large, eruptive solar flares. This force perturbation should be balanced by an equal and opposite force perturbation acting on the solar photosphere and solar interior. The resulting expression for the estimated force change in the solar interior generalizes the earlier expression presented by Hudson, Fisher, and Welsch (Astron. Soc. Pac. CS-383, 221, 2008), providing horizontal as well as vertical force components, and provides a more accurate result for the vertical component of the perturbed force. We show that magnetic eruptions should result in the magnetic field at the photosphere becoming more horizontal, and hence should result in a downward (toward the solar interior) force change acting on the photosphere and solar interior, as recently argued from an analysis of magnetogram data by Wang and Liu (Astrophys. J. Lett. 716, L195, 2010). We suggest the existence of an observational relationship between the force change computed from changes in the vector magnetograms, the outward momentum carried by the ejecta from the flare, and the properties of the helioseismic disturbance driven by the downward force change. We use the impulse driven by the Lorentz-force change in the outer solar atmosphere to derive an upper limit to the mass of erupting plasma that can escape from the Sun. Finally, we compare the expected Lorentz-force change at the photosphere with simple estimates from flare-driven gasdynamic disturbances and from an estimate of the perturbed pressure from radiative backwarming of the photosphere in flaring conditions.     

Mapping bedrock lithologies through in situ regolith using retained element ratios: a case study from the Agnew-Lawlers area,Western Australia

Large, high-quality multi-element geochemical datasets are becoming widely available in the exploration industry, and afford excellent opportunities to investigate geochemical processes. A dataset of over 2500 analyses of unweathered and variably weathered mafic and ultramafic rocks for over 50 elements has been collected by Gold Fields Ltd. in the auriferous Agnew-Lawlers area of the eastern Yilgarn Craton of Western Australia. This dataset is used to investigate changes in element abundances and inter-element ratios through varying degrees and styles of weathering in an area of thick regolith characterised by deep in situ weathering. Systematic interrogation of the data, using lithostratigraphic controls derived from regional mapping and geophysics, reveals that a suite of elements, including Ti, Al, Zr, Th, La, Sc and Nb, and to a lesser extent Cr and Ni, behave as essentially immobile components during saprolite formation. In some cases diagnostic element ratios persist into siliceous duricrust. Ratios of these elements are used as reliable discriminants of bedrock type, and delineate features such as cryptic layering within fractionated sills and subtle geochemical variants in a sequence of tholeiitic and komatiitic basalts. Mapping on the basis of discriminant element ratios greatly extends previous trace-element ratio-based schemes for rock type discrimination. The potential to determine several of these elements with adequate precision and accuracy using portable XRF technology opens a potentially useful technique for rapid geochemical bedrock mapping in residual terrains.