The Autonomous Ocean Profiler: a current-driven oceanographicsensor platform

The development and initial field test results of the Autonomous Ocean Profiler (AOP) are described. The profiler uses a hydrodynamic lift device to fly the instrument package up and down the water column along a taut vertical cable. Because the local currents drive the platform's vertical motion, power requirements are low, and therefore long, unattached deployments are possible. By using ARGOS or GOES satellite retrieval networks, the system can supply near-real-time data. The system provides profile data at very high vertical resolution in contrast to conventional buoys, which gather data only at fixed sensor depths. Because only a single set of sensors is required to cover the vertical range desired, the system is low cost and, for many applications, expendable. The initial deployment configuration is as an Arctic drifting buoy     

Simultaneous multi-frequency imaging observations of solar microwave bursts

We review the results of simultaneous two-frequency imaging observations of solar microwave bursts with the Very Large Array. Simultaneous 2 and 6 cm observations have been made of bursts which are optically thin at both frequencies, or optically thick at the lower frequency. In the latter case the source structure may differ at the two frequencies, but the two sources usually seem to be related. However, this is not always true of simultaneous 6 and 20 cm observations. The results have implications for the analysis of non-imaging radio data of solar and stellar flares.     

Finite element analysis of a centrifuge model of a retaining wall embedded in a heavily overconsolidated clay

The current study is aimed at the behaviour right upto collapse of a retaining wall embedded in overconsolidated clay. It is found that the excess pore pressures generated due to the excavation are fairly well simulated. The rupture lines on the passive side in the centrifuge model test were closely matched by two lines along which the stress state was reaching the critical state in the analysis. The displacements on the active side were not well matched especially the vertical settlements near to the wall. The bending moments were significantly overpredicted. The prop force due to excavation was also overpredicted. This is to be expected because the prop was modelled as rigid in the analysis.     

Rapid evaluation of the critical slip surface in slope stability problems

Existing approaches for locating the critical slip surfaces are briefly reviewed. A number of techniques and strategies are proposed whereby the efficiency and robustness of some of the existing approaches can be enhanced. A new solution scheme is also developed for rapid calculation of the factor of safety. The new solution scheme requires only one level of iterations in contrast to the conventional solution scheme which invoives two levels of iterations. It is also applicable to a variety of stability models. A new compound iterative procedure is developed whereby the factor of safety can be calculated to a high accuracy within a few iterations. This reduces greatly the total computer time required for locating the critical slip surfaces.     

Sediments, nutrients and pesticide residues in event flow conditions in streams of the Mackay Whitsunday Region, Australia

The Mackay Whitsunday region covers 9000 km(2) in northeastern Australia. A study of diffuse pollutants during high flow events was conducted in coastal streams in this region. Sampling was conducted in the Pioneer River catchment during a high flow event in February 2002 and in Gooseponds Creek, Sandy Creek and Carmila Creek in March 2003. Concentrations of five herbicides; atrazine (1.3 microg l(-1)), diuron (8.5 microg l(-1)), 2,4-D (0.4 microg l(-1)), hexazinone (0.3 microg l(-1)) and ametryn (0.3 microg l(-1)) and high concentrations of nutrients (total nitrogen 1.14 mg l(-1), total phosphorus 0.20 mg l(-1)) and suspended sediments (620 mg l(-1)) were measured at Dumbleton Weir on the lower reaches of the Pioneer River. Drinking water guidelines for atrazine and 2,4-D were exceeded at Dumbleton Weir, low reliability trigger values for ecosystem protection for diuron were exceeded at three sites and primary industry guidelines for irrigation levels of diuron were also exceeded at Dumbleton Weir. Similar concentrations were found in the three smaller streams measured in 2003. Herbicides and fertilisers used in sugarcane cultivation were identified as the most likely major source of the herbicide residues and nutrients found.     

Will coastal wetlands continue to sequester carbon in response to an increase in global sea level?: a case study of the rapidly subsiding Mississippi river deltaic plain

The highly visible coastal phenomenon of wetland loss in coastal Louisiana (LA) was examined through the prism of carbon accumulation and loss. Carbon storage or sequestration in rapidly subsiding LA coastal marsh soils was based on vertical marsh accretion and aerial change data. Marshes sequester significant amount of carbon through vertical accretion however, large amounts of carbon previously sequestration in the soil profile is lost through annual deterioration of these coastal marshes. Hurricanes, such as Katrina and Rita, have triggered instantaneous large carbon losses of sequestered soil carbon through the destruction of large areas of marsh. This analysis shows proposed coastal restoration efforts will not be sufficient to restore carbon losses by storms and marsh deterioration. Further, we have estimated the economic benefit of carbon sequestration for coastal wetland restoration efforts. Results show that LA coastal marshes may not serve as a net sink of carbon. These results may serve as a predictor of the impact of future predictions of increasing global sea level rise on carbon sequestration for other coastal regions.     

Modeled seasonality of glacial abrupt climate events

Greenland ice cores, as well as many other paleo-archives from the northern hemisphere, recorded a series of 25 warm interstadial events, the so-called Dansgaard-Oeschger (D-O) events, during the last glacial period. We use the three-dimensional coupled global ocean–atmosphere–sea ice model ECBILT-CLIO and force it with freshwater input into the North Atlantic to simulate abrupt glacial climate events, which we use as analogues for D-O events. We focus our analysis on the Northern Hemisphere. The simulated events show large differences in the regional and seasonal distribution of the temperature and precipitation changes. While the temperature changes in high northern latitudes and in the North Atlantic region are dominated by winter changes, the largest temperature increases in most other land regions are seen in spring. Smallest changes over land are found during the summer months. Our model simulations also demonstrate that the temperature and precipitation change patterns for different intensifications of the Atlantic meridional overturning circulation are not linear. The extent of the transitions varies, and local non-linearities influence the amplitude of the annual mean response as well as the response in different seasons. Implications for the interpretation of paleo-records are discussed.     

Testing cosmological structure formation using redshift-space distortions

Observations of redshift-space distortions in spectroscopic galaxy surveys offer an attractive method for observing the build-up of cosmological structure. In this paper, we develop and test a new statistic based on anisotropies in the measured galaxy power spectrum, which is independent of galaxy bias and matches the matter power spectrum shape on large scales. The amplitude provides a constraint on the derivative of the linear growth rate through   f σ₈(mass)  . This demonstrates that spectroscopic galaxy surveys offer many of the same advantages as weak lensing surveys, in that they both use galaxies as test particles to probe all matter in the Universe. They are complementary as redshift-space distortions probe non-relativistic velocities and therefore the temporal metric perturbations, while weak lensing tests the sum of the temporal and spatial metric perturbations. The degree to which our estimator can be pushed into the non-linear regime is considered and we show that a simple Gaussian damping model, similar to that previously used to model the behaviour of the power spectrum on very small scales, can also model the quasi-linear behaviour of our estimator. This enhances the information that can be extracted from surveys for Λ cold dark matter (ΛCDM) models.