Observations of vortices and vortex Rossby waves in the lee of an island

A 9-month deployment of high-frequency radio (HFR) current meters and moored ADCPs in the lee of Oahu, Hawaii, gives some dynamical insights in the generation and evolution of vortices in the lee of islands. For mountainous islands lying in relatively strong and steady winds, such as the Hawaiian archipelago in the trade winds, vortices can be generated by Ekman pumping associated with orographic wind stress curls. An anticyclone generated in the lee of Oahu in October 2002 reaches a negative absolute vorticity for 4 days, before quickly decaying and broadening, possibly as a result of inertial instability. A large cyclone, generated in December 2002 in the lee of Hawaii, drifted northwestward and stalled southwest of Oahu in March-April 2003. Vortex Rossby waves developing on its periphery were observed by the HFRs with a northeastward phase propagation, 110 km wavelength and 16 days period

Pyrene Mineralization by Mycobacterium sp. Strain KMS in a Barley Rhizosphere

To determine whether the soil Mycobacterium isolate KMS would mineralize pyrene under rhizosphere conditions, a microcosm system was established to collect radioactive carbon dioxide released from the labeled polycyclic aromatic hydrocarbon. Microcosms were designed as sealed, flow-through systems that allowed the growth of plants. Experiments were conducted to evaluate mineralization of 14C-labeled pyrene in a sand amended with the polycyclic aromatic hydrocarbons degrading Mycobacterium isolate KMS, barley plants, or barley plants with roots colonized by isolate KMS. Mineralization was quantified by collecting the 14CO2 produced from 14C-labeled pyrene at intervals during the 10-d incubation period. Roots and foliar tissues were examined for 14C incorporation. Mass balances for microcosms were determined through combustion of sand samples and collection and quantification of 14CO2 evolved from radiolabeled pyrene. No pyrene mineralization was observed in the sterile control systems. Greater release of 14CO2 was observed in the system with barley colonized by KMS than in microcosms containing just the bacterium inoculum or sterile barley plants. These findings suggest that phytostimulation of polycyclic aromatic hydrocarbons mineralization could be applied in remediation schemes

Wind Direction Inversion from Narrow-Beam HF Radar Backscatter Signals in Low and High Wind Conditions at Different Radar Frequencies

Land-based, high-frequency (HF) surface wave radar has the unique capability of monitoring coastal surface parameters, such as current, waves, and wind, up to 200 km off the coast. The Doppler spectrum of the backscattered radar signal is characterized by two strong peaks that are caused by the Bragg-resonant scattering from the ocean surface. The wavelength of Bragg resonant waves is exactly half the radio wavelength (grazing incidence), and these waves are located at the higher frequency part of the wave spectral distribution. When HF radar operates at higher frequencies, the resonant waves are relatively shorter waves, which are more sensitive to a change in wind direction, and they rapidly respond to local wind excitation and a change in wind direction. When the radar operates at lower frequencies, the corresponding resonant waves are relatively longer and take longer time to respond to a change in wind direction due to the progress of wave growth from short waves to long waves. For the wind inversion from HF radar backscatter signals, the accuracy of wind measurement is also relevant to radar frequency. In this paper, a pattern-fitting method for extracting wind direction by estimating the wave spreading parameter is presented, and a comparison of the pattern-fitting method and a conventional method is given as well, which concludes that the pattern-fitting method presents better results than the conventional method. In order to analyze the wind direction inversion from radar backscatter signals under different wind conditions and at different radar frequencies, two radar experiments accomplished in Norway and Italy are introduced, and the results of wind direction inversion are presented. In the two experiments, the radar worked at 27.68 MHz and 12 MHz, respectively, and the wind conditions at the sea surface were quite different. In the experiment in Norway, 67.4% of the wind records were higher than 5 m/s, while, in the experiment in Italy, only 18.9% of the wind records were higher than 5 m/s. All these factors affect the accuracy of wind direction inversion. The paper analyzes the radar data and draws a conclusion on the influencing factor of wind direction inversion

Evaluation of an HF-radar ship detection and tracking algorithm by comparison to AIS and SAR data

Since several years, High Frequency (HF) Over-The-Horizon (OTH) radar is used to measure océanographie parameters, such as currents, waves, and wind direction over large areas up to 200 km off the coast. Cost effective low power systems transmitting less than 50 Watts have been developed, e.g. the WERA (WEUen RAdar), and are now commercially available. Besides their applications in oceanography within coastal monitoring systems, these systems can also be used to detect and track ships, if they are modified for this functionality. A ship detection and tracking algorithm for HF-radar has been developed at the University of Hamburg (UHH) in cooperation with the Technical University of Hamburg-Harburg (TUHH). A first evaluation of this algorithm has been done using a data set acquired at Figueira, Portugal, using an 8 MHz WERA system. In May 2009, the NATO Undersea Research Centre (NURC) initiated a measurement campaign in the Ligurian Sea off La Spezia, Italy, which involved two WERA HF-radar systems operated at 12.5 MHz, one directional waverider and a meteorological buoy. In addition AIS data were recorded and satellite borne synthetic aperture radar (SAR) images were acquired. This paper presents preliminary results which show the effectiveness of the HF-radar as a long range (∼130 km) continuous-time coverage surveillance system, despite of its low spatial resolution of 1.5 km. The performance of the HF-radar ship detection and tracking algorithms are evaluated by comparison to AIS and SAR. The detection error found for this data set is less than 1 km for ∼68% of the comparisons between HF-radar and (AIS) reported locations, which is comparable to previous results from the Figueira data set

Ensemble perturbation smoother for optimizing tidal boundary conditions by assimilation of High-Frequency radar surface currents - application to the German Bight

High-Frequency (HF) radars measure the ocean surface currents at various spatial and temporal scales. These include tidal currents, wind-driven circulation, density-driven circulation and Stokes drift. Sequential assimilation methods updating the model state have been proven successful to correct the density-driven currents by assimilation of observations such as sea surface height, sea surface temperature and in-situ profiles. However, the situation is different for tides in coastal models since these are not generated within the domain, but are rather propagated inside the domain through the boundary conditions. For improving the modeled tidal variability it is therefore not sufficient to update the model state via data assimilation without updating the boundary conditions. The optimization of boundary conditions to match observations inside the domain is traditionally achieved through variational assimilation methods. In this work we present an ensemble smoother to improve the tidal boundary values so that the model represents more closely the observed currents. To create an ensemble of dynamically realistic boundary conditions, a cost function is formulated which is directly related to the probability of each boundary condition perturbation. This cost function ensures that the boundary condition perturbations are spatially smooth and that the structure of the perturbations satisfies approximately the harmonic linearized shallow water equations. Based on those perturbations an ensemble simulation is carried out using the full three-dimensional General Estuarine Ocean Model (GETM). Optimized boundary values are obtained by assimilating all observations using the covariances of the ensemble simulation.ECOO

Performance assessment of HF-radar ship detection

Recently, significant efforts have gone into developing more reliable Integrated Maritime Surveillance (IMS) systems. The main purpose of these systems is to detect and track, and identify and classify cooperative and non-cooperative targets crossing maritime national boundaries. In such a context, each kind of sensor (i.e. shipborne or airborne, on-shore or off-shore) has its own tasks. Great attention has been paid to High-Frequency (HF) Surface-Wave (SW) radars as a long-range early-warning tool for applications in open waters. This paper presents the results from the NURC BP09 HF-radar experiment which took place in the Ligurian Sea (Mediterranean Sea), between May and December 2009. The effectiveness of the 3D constant false alarm rate (CFAR) detection algorithm, developed at the Institute of Technology of the University of Hamburg (TUHH), is investigated by means of ground-truth data sent from ships carrying Automatic Identification System (AIS) transponders. Under conservative assumptions, some preliminary results about the probabilities of detection and false alarm are presented and discussed. In the last part of the paper, foundations about future investigations are provided as well

Ensemble smoother for optimizing tidal boundary conditions and wind forcing by assimilation of High-Frequency Radar surface currents measurements of the German Bight

An ensemble smoother scheme is presented to assimilate HF radar surface currents to improve tidal boundary conditions and wind forcings of a circulation model of the German Bight. To create an ensemble of dynamically realistic tidal boundary conditions, a cost function is formulated which is directly related to the probability of each perturbation. This cost function ensures that the perturbations are spatially smooth and that the structure of the perturbations satisfies approximately the harmonic linearized shallow water equations. Based on those perturbations an ensemble simulation is carried out using the full three-dimensional General Estuarine Ocean Model (GETM). Optimized boundary values are obtained using all observations within the assimilation period using the covariances of the ensemble simulation. The approach acts like a smoother scheme since all observations are taken into account. Since the scheme aims to derive the optimal perturbation, it might be called Ensemble Perturbation Smoother. The final analysis is obtained by rerunning the model using the optimal perturbation to the boundary conditions. The analyzed model solution satisfies thus the model equations exactly and does not suffer from spurious adjustments often observed with sequential assimilation schemes. Model results are also compared to independent tide gage data. The assimilation did also reduce the model error compared to those sea level observations. The same scheme has also been used to correct surface winds. Surface winds are crucial for accurately modeling the marine circulation in coastal waters. The method is validated directly by comparing the analyzed wind speed to in situ measurements and indirectly by assessing the impact of the corrected winds on sea surface temperature (SST) relative to satellite SST

Estimation of tidal boundary conditions and surface winds by assimilation of high-frequency radar surface currents in the German Bight

Numerical ocean models are affected by errors of various origins: errors in the initial conditions, boundary conditions and atmospheric forcings, uncertainties in the turbulence parametrization and discretization errors. In data assimilation, observations are used to reduce the uncertainty in the model solution. Ensemble-based assimilation schemes are often implemented such that the expected error of the model solution is minimized. It is shown that the observations can also be used to obtain improved estimates of the, in general, poorly known boundary conditions and atmospheric forcings. An ensemble smoother scheme is presented to assimilate high-frequency (HF) radar surface currents to improve tidal boundary conditions and wind forcings of a circulation model of the German Bight. To create an ensemble of dynamically realistic tidal boundary conditions, a cost function is formulated which is directly related to the probability of each perturbation. This cost function ensures that the perturbations are spatially smooth and that the structure of the perturbations satisfies approximately the harmonic linearized shallow water equations. Based on those perturbations an ensemble simulation is carried out using the full three-dimensional General Estuarine Ocean Model (GETM). Optimized boundary values are obtained using all observations within the assimilation period using the covariances of the ensemble simulation. The approach acts like a smoother scheme since past and future observations are taken into account. The final analysis is obtained by rerunning the model using the optimal perturbation of the boundary conditions. The analyzed model solution satisfies thus the model equations exactly and does not suffer from spurious adjustments often observed with sequential assimilation schemes. Model results are also compared to independent tide gauge data. The assimilation also reduces the model error compared to those sea level observations. The same scheme is also used to correct surface winds. Surface winds are crucial for accurately modeling the marine circulation in coastal waters. The method is validated directly by comparing the analyzed wind speed to in situ measurements and indirectly by assessing the impact of the corrected winds on sea surface temperature (SST) relative to satellite SST