A study of the magnetoresistance of the charge-transfer salt (BEDT-TTF)(3)Cl-2 center dot 2H(2)O at hydrostatic pressures of up to 20 kbar: Evidence for a charge-density-wave ground state and the observation of pressure-induced superconductivity

The magnetoresistance of single crystals of the quasi-two-dimensional (Q2D) organic conductor (BEDT-TTF)3Cl2 2H2O has been studied at temperatures between 700 mK and 300 K in magnetic fields of up to 15 T and hydrostatic pressures of up to 20 kbar . Measurements of the resistivity using a direct-current van der Pauw technique at ambient pressure show that the material undergoes a metal-to-insulator transition at ̃150 K; below this temperature the resistivity increases by more than five orders of magnitude as the samples are cooled to 4.2 K. If the current exceeds a critical value, the sample resistivity undergoes irreversible changes, and exhibits non-ohmic behaviour over a wide temperature range. Below 30 K, either an abrupt increase of the resistivity by two orders of magnitude or bistable behaviour is observed, depending on the size and/or direction of the measurement current and the sample history. These experimental data strongly suggest that the metal-insulator transition and complex resistivity behaviour are due to the formation of a charge-density wave (CDW) with a welldeveloped domain structure. The magnetotransport data recorded under hydrostatic pressure indicate that pressure has the effect of gradually reducing the CDW ordering temperature. At higher pressures, there is a pressure-induced transition from the CDW state to a metallic, superconducting state which occurs in two distinct stages. Firstly, a relatively small number of Q2D carriers are induced, evidence for which is seen in the form of the magnetoresistance and the presence of Shubnikov-de Haas oscillations; in spite of the low carrier density, the material then superconducts below a temperature of ̃2-3 K. Subsequently, at higher pressures, the CDW state collapses, resulting in QID behaviour of the magnetoresistance, and eventual suppression of the superconductivity

Estimating present day extreme water level exceedance probabilities around the coastline of Australia: tropical cyclone-induced storm surges

The incidence of major storm surges in the last decade have dramatically emphasized the immense destructive capabilities of extreme water level events, particularly when driven by severe tropical cyclones. Given this risk, it is vitally important that the exceedance probabilities of extreme water levels are accurately evaluated to inform risk-based flood and erosion management, engineering and for future land-use planning and to ensure the risk of catastrophic structural failures due to under-design or expensive wastes due to over-design are minimised. Australia has a long history of coastal flooding from tropical cyclones. Using a novel integration of two modeling techniques, this paper provides the first estimates of present day extreme water level exceedance probabilities around the whole coastline of Australia, and the first estimates that combine the influence of astronomical tides, storm surges generated by both extra-tropical and tropical cyclones, and seasonal and inter-annual variations in mean sea level. Initially, an analysis of tide gauge records has been used to assess the characteristics of tropical cyclone-induced surges around Australia. However, given the dearth (temporal and spatial) of information around much of the coastline, and therefore the inability of these gauge records to adequately describe the regional climatology, an observationally based stochastic tropical cyclone model has been developed to synthetically extend the tropical cyclone record to 10,000 years. Wind and pressure fields derived for these synthetically generated events have then been used to drive a hydrodynamic model of the Australian continental shelf region with annual maximum water levels extracted to estimate exceedance probabilities around the coastline. To validate this methodology, selected historic storm surge events have been simulated and resultant storm surges compared with gauge records. Tropical cyclone induced exceedance probabilities have been combined with estimates derived from a 61-year water level hindcast described in a companion paper to give a single estimate of present day extreme water level probabilities around the whole coastline of Australia. Results of this work are freely available to coastal engineers, managers and researchers via a web-based tool (www.sealevelrise.info). The described methodology could be applied to o

Sea breezes drive currents on the inner continental shelf off southwest Western Australia

In southwest Western Australia, strong and persistent sea breezes are common between September and February. We hypothesized that on the inner continental shelf, in the absence of tidal forcing, the depth, magnitude, and lag times of the current speed and direction responses to sea breezes would vary though the water column as a function of the sea breeze intensity. To test this hypothesis, field data were used from four sites were that were in water depths of up to 13 m. Sites were located on the inner continental shelf and were on the open coast and in a semi-enclosed coastal embayment. The dominant spectral peak in currents at all sites indicated that the majority of the spectral energy contained in the currents was due to forcing by sea breezes. Currents were aligned with the local orientation of the shoreline. On a daily basis, the sea breezes resulted in increased current speeds and also changed the current directions through the water column. The correlation between wind–current speeds and directions with depth, and the lag time between the onset of the sea breeze and the response of currents, were dependent on the intensity of the sea breezes. A higher correlation between wind and current speeds occurred during strong sea breezes and was associated with shorter lag times for the response of the bottom currents. The lag times were validated with estimates of the vertical eddy viscosity. Solar heating caused the water column to stratify in summer and the sea breezes overcame this stratification. Sea breezes caused the mixed layer to deepen and the intensity of the stratification was correlated to the strength of the sea breezes. Weak sea breezes of <5 m?s?1 were associated with the strongest thermal stratification of the water column, up to 1°C between the surface and bottom layers (6 and 10 m below the surface). In comparison, strong sea breezes of >14 m?s?1 caused only slight thermal stratification up to 0.5°C. Apart from these effects on the vertical structure of water column, the sea breezes also influenced transport and mixing in the horizontal dimension. The sea breezes in southwest Western Australia rotated in an anticlockwise direction each day and this rotation was translated into the currents. This current rotation was more prominent in surface currents and in the coastal embayment compared to the open coast

Tracking Hurricanes using GPS atmospheric precipitable water vapor field

Tropical cyclones are one of the most powerful severe weather events that produce devastating socioeconomic and environmental impacts in the areas they strike. Therefore, monitoring and tracking of the arrival times and path of the tropical cyclones are extremely valuable in providing early warning to the public and governments. Hurricane Florence struck the East cost of USA in 2018 and offers an outstanding case study. We employed Global Positioning System (GPS) derived precipitable water vapor (PWV) data to track and investigate the characteristics of storm occurrences in their spatial and temporal distribution using a dense ground network of permanent GPS stations. Our findings indicate that a rise in GPS-derived PWV occurred several hours before Florence’s manifestation. Also, we compared the temporal distribution of the GPS-derived PWV content with the precipitation value for days when the storm appeared in the area under influence. The study will contribute to quantitative assessment of the complementary GPS tropospheric products in hurricane monitoring and tracking using GPS-derived water vapor evolution from a dense network of permanent GPS station

Annelids, arthropods or molluscs are suitable as surrogate taxa for selecting conservation reserves in estuaries

The urgent need to conserve aquatic biodiversity and the lack of spatial data on biodiversity has motivated conservation planners and researchers to search for more readily obtainable information that could be used as proxies or surrogates. The surrogate taxon approach shows promise in some aquatic environments (e.g. intertidal) but not others (e.g. coral reefs, temperate rocky reefs). Estuaries are transitional environments at the land–sea junction with a unique biodiversity, but are the most threatened of aquatic environments because of high levels of human use. The comparatively small numbers of conservation reserves means that estuarine biodiversity is poorly protected. Selecting additional conservation reserves within estuaries would be facilitated by the identification of a suitable surrogate that could be used in conservation planning. In one estuary in Southeast Australia, we evaluated separately the effectiveness of annelids, arthropods, and molluscs as surrogates for predicting the species richness, abundance, assemblage variation, and summed irreplaceability of other species and for coincidentally representing other species in networks of conservation reserves selected for each surrogate. Spatial patterns in the species richness and assemblage variation (but not summed irreplaceability) of each surrogate were significantly correlated with the spatial patterns of other species. The total abundance of annelids and the total abundance of arthropods were each significantly correlated with the total abundances of other species. Networks of conservation reserves selected to represent each surrogate performed significantly better than random selection in representing other species. The greatest number of non-surrogate species was coincidentally included in reserves selected for the group of mollusc species. We conclude that annelids and arthropods are effective surrogate taxa for identifying spatial variation in several measures of conservation value (species richness, abundance, assemblage variation) in estuaries. We also conclude that spatial data on annelids, arthropods or molluscs can be used to select networks of conservation reserves in estuaries. The demonstrated effectiveness of these surrogates should facilitate future conservation planning within estuaries