HF radar role in an integrated ocean observing system

The Australian Coastal Ocean radar Network (ACORN) is a monitoring network of HF radars which are being installed around Australia under a National Collaborative Research Infrastructure Strategy (NCRIS). It is a five-year project, at the end of which there will be five pairs of radar stations and one triplet installed and operating, enabled by the central pool of funding for the Integrated Marine Observing System (IMOS) which is a part of NCRIS, and augmented by funding from other sources. At each chosen site there is a pair (or triplet) of radar stations, mounted on the shore, which receive radar echoes from the rough sea. The two stations provide a triangulation which enables the data analysis software to extract surface currents, wave heights and directional wave spectra over the coastal ocean. The NCRIS strategy is to support research into coastal dynamics and exchange between the open ocean and the continental shelf. Research is being undertaken into the use of maps of surface currents, well resolved in time and space, in mixing of different bodies of water, physical connectivity between reefs and islands, and nowcasting and short-term forecasting of surface currents. There is potential for application of the data to management of coastal marine resources, and in marine safety areas. Real-time maps of surface currents and the prospect of short-term forecasting have the potential to reduce search areas in coastal waters and to make pollution/spill mitigation more effective. With the establishment of HF radar monitoring stations like those in ACORN, there is growing opportunity for researchers around the world to access data from well curated archives to carry out basic research on physical oceanography, or applications research without having direct access to the measuring facility. One of the features of IMOS is to establish such an archive which is easy to access and free to research users. This feature brings the ACORN HF radars into GEOSS for coastal process- es and dynamics

HF radar for port management: case study in the Port of Rotterdam

The phased array HF ocean radar installed at the Port of Rotterdam gives good quality near real-time information on surface currents for port management. This paper examines the potential to infer current profiles from HF radar and wind station data using prior knowledge of the site. It is shown that tidal currents follow a logarithmic boundary layer profile, and the wind-driven currents have an approximately exponential profile. These two models are combined to estimate the current profiles

Evolution and dynamics of tropical river plumes in the Great Barrier Reef: an integrated remote sensing and in situ study

The short-lived but intense discharge of freshwater from tropical rivers into the Great Barrier Reef (GBR) Lagoon and the associated salinity reductions are a critical consideration in marine research and management of the ecologically sensitive GBR World Heritage Area. Salinity provides a unique tracer that gives clues to the origin of river-borne contaminants and allows the influences of storm-induced resuspension and river discharge on turbidity to be clearly distinguished. We describe a field investigation of the evolution and dynamics of the Herbert River plume in the central GBR. Its primary goals were to use an airborne salinity mapper and in situ instruments to study the three-dimensional structure and evolution of the plume and to lay a foundation for numerical modeling studies of its dynamics. The aircraft surveys provided a rapid assessment of the plumes spatial extent, while the in situ data revealed details of its subsurface structure. The Herbert River plume was produced by heavy rainfall associated with tropical storms during the La Nina-dominated 1999/2000 monsoon season. In the near field, the surface expression of the plume boundaries was indicated by sharp color and salinity fronts that were clearly visible from the air and sea surface. In the far field and middle Lagoon, the plume was more dispersed and ultimately merged with the larger-scale salinity gradients and with the remnant plume of the more distant, and larger, Burdekin River. The plume location and structure evolved in response to changing river flows, tidal and subtidal circulation, and wind. Using Garvine’s Kelvin number-based scheme, the plume was classified as intermediate in dynamical character and thus is subject to a variety of forcings. The plume evolved in response to changes in the relative intensity of tidal currents and low-frequency circulation due to wind and western boundary current forcing. It also displayed a characteristic ‘‘hook-shaped’’ structure, which has been identified previously in numerical plume model studies. This structure appeared in the presence of accelerating along-shelf current flow and horizontal shear and it indicates that the plume circulation had a strongly three-dimensional character. The approach demonstrates the efficacy of combining airborne and in situ methods to observe rapidly evolving coastal salinity structure and dynamics and sets the stage for future satellite-borne studies of larger-scale features showing contrasting salinity distributions

Evolution and Dynamics of Tropical River Plumes in the Great Barrier Reef: An Integrated Remote Sensing and In Situ Study

[1] The short-lived but intense discharge of freshwater from tropical rivers into the Great Barrier Reef (GBR) Lagoon and the associated salinity reductions are a critical consideration in marine research and management of the ecologically sensitive GBR World Heritage Area. Salinity provides a unique tracer that gives clues to the origin of river-borne contaminants and allows the influences of storm-induced resuspension and river discharge on turbidity to be clearly distinguished. We describe a field investigation of the evolution and dynamics of the Herbert River plume in the central GBR. Its primary goals were to use an airborne salinity mapper and in situ instruments to study the three-dimensional structure and evolution of the plume and to lay a foundation for numerical modeling studies of its dynamics. The aircraft surveys provided a rapid assessment of the plumes spatial extent, while the in situ data revealed details of its subsurface structure. The Herbert River plume was produced by heavy rainfall associated with tropical storms during the La Nina-dominated 1999/2000 monsoon season. In the near field, the surface expression of the plume boundaries was indicated by sharp color and salinity fronts that were clearly visible from the air and sea surface. In the far field and middle Lagoon, the plume was more dispersed and ultimately merged with the larger-scale salinity gradients and with the remnant plume of the more distant, and larger, Burdekin River. The plume location and structure evolved in response to changing river flows, tidal and subtidal circulation, and wind. Using Garvine\u27s Kelvin number-based scheme, the plume was classified as intermediate in dynamical character and thus is subject to a variety of forcings. The plume evolved in response to changes in the relative intensity of tidal currents and low-frequency circulation due to wind and western boundary current forcing. It also displayed a characteristic hook-shaped\u27\u27 structure, which has been identified previously in numerical plume model studies. This structure appeared in the presence of accelerating along-shelf current flow and horizontal shear and it indicates that the plume circulation had a strongly three-dimensional character. The approach demonstrates the efficacy of combining airborne and in situ methods to observe rapidly evolving coastal salinity structure and dynamics and sets the stage for future satellite-borne studies of larger-scale features showing contrasting salinity distributions

Diffractive Deep-Inelastic Scattering

Diffractive deep inelastic events with a large rapidity gap are analyzed by using a Regge model for the pomeron flux and a gluonic content for the pomeron. Contrary to the expectations, the simplest assumption for the pomeron trajectory gives the best agreement with the data on the ratio of diffractive to the total number of events. In this case the main properties of the model are described by an analytic expression.Comment: 18 pages (postcript file

Swell wave direction off Tweed Heads monitored by HF ocean surface radar

We present results of an analysis of data collected in coastal waters off Tweed Heads during an ocean surface monitoring survey using the HF Ocean Surface Radar (COSRAD). The radar was deployed for a 30-day period during February and March of 2001 to routinely measure surface currents and wind wave parameters. The deployment also offered an opportunity to develop techniques for measuring swell wave parameters. This paper presents theory and a case study showing how second order swell peaks are observed in the Doppler spectrum. COSRAD produces an entire sweep every 30 min with spatial resolution of the order of 3 km. We average 8 adjacent pixels over a 2 h period to produce swell parameters. Swell parameters are produced from second-order (sideband) energy near the strong first-order Bragg peaks in the spectrum. Space and time averaging is done to reduce spectral noise. Our analysis indicates that the COSRAD HF radar is suitable for monitoring swell in the near-shore zone

Unraveling many-body effects in ZnO: Combined study using momentum-resolved electron energy-loss spectroscopy and first-principles calculations

We present a detailed study of the dielectric response of ZnO using a combination of low-loss momentum-resolved electron energy-loss spectroscopy (EELS) and first-principles calculations at several levels of theory, from the independent particle and the random phase approximation with different variants of density functional theory (DFT), including hybrid and DFT$+U$ schemes; to the Bethe-Salpeter equation (BSE). We use a method based on the $f$-sum rule to obtain the momentum-resolved experimental loss function and absorption spectra from EELS measurements. We characterize the main features in the direct and inverse dielectric functions of ZnO and their dispersion, associating them to single-particle features in the electronic band structure, while highlighting the important role of many-body effects such as plasmons and excitons. We discuss different signatures of the high anisotropy in the response function of ZnO, including the symmetry of the excitonic wave-functions.Comment: 25 pages, 18 figure

Tsunami observations by coastal ocean radar

When tsunami waves propagate across the open ocean, they are steered by the Coriolis effect and refraction due to gentle gradients in the bathymetry on scales longer than the wavelength. When the wave encounters steep gradients at the edges of continental shelves and at the coast, the wave becomes nonlinear and conservation of momentum produces squirts of surface current at the head of submerged canyons and in coastal bays. High frequency (HF) coastal ocean radar is well conditioned to observe the surface current bursts at the edge of the continental shelf and give a warning of 40 minutes to 2 hours when the shelf is 50 to 200km wide. The period of tsunami waves is invariant over changes in bathymetry and is in the range 2 to 30 minutes. Wavelengths for tsunamis (in 500 to 3000m depth) are in the range 8.5 to over 200 km, and on a shelf where the depth is about 50m (as in the Great Barrier Reef (GBR)) the wavelengths are in the range 2.5 to 30 km. In the use of HF radar technology, there is a trade-off between the precision of surface current speed measurements and time resolution. It is shown that the phased array HF ocean surface radar being deployed in the GBR and operating in a routine way for mapping surface currents, can resolve surface current squirts from tsunamis in the wave period range 20 to 30 minutes and in the wavelength range greater than about 6 km. An advantage in signal-to-noise ratio can be obtained from the prior knowledge of the spatial pattern of the squirts at the edge of the continental shelf, and it is estimated that, with this analysis, the time resolution of the GBR radar may be reduced to about 2.5 minutes, which corresponds to a capability to detect tsunamis at the shelf edge in the period range 5 to 30 minutes. It is estimated that the lower limit of squirt velocity detection at the shelf edge would correspond to a tsunami with water elevation of about 2.5 cm in the open ocean. This means that the GBR HF radar is well conditioned for use as a monitor of small, as well as larger, tsunamis and has the potential to contribute to the understanding of tsunami genesis research

Heavy-quark contributions to the ratio F_L/F_2 at low x

We study the heavy-quark contribution to the proton structure functions F_2^i(x,Q^2) and F_L^i(x,Q^2), with i=c,b, for small values of Bjorken's x variable at next-to-lading order and provide compact formulas for their ratios R_i=F_L^i/F_2^i that are useful to extract F_2^i(x,Q^2) from measurements of the doubly differential cross section of inclusive deep-inelastic scattering at DESY HERA. Our approach naturally explains why R_i is approximately independent of x and the details of the parton distributions in the small-x regime.Comment: 11 pages, 1 figur