Lagrangian Based Methods for Coherent Structure Detection

There has been a proliferation in the development of Lagrangian analytical methods for detecting coherent structures in fluid flow transport, yielding a variety of qualitatively different approaches. We present a review of four approaches and demonstrate the utility of these methods via their application to the same sample analytic model, the canonical double-gyre flow, highlighting the pros and cons of each approach. Two of the methods, the geometric and probabilistic approaches, are well established and require velocity field data over the time interval of interest to identify particularly important material lines and surfaces, and influential regions, respectively. The other two approaches, implementing tools from cluster and braid theory, seek coherent structures based on limited trajectory data, attempting to partition the flow transport into distinct regions. All four of these approaches share the common trait that they are objective methods, meaning that their results do not depend on the frame of reference used. For each method, we also present a number of example applications ranging from blood flow and chemical reactions to ocean and atmospheric flows. (C) 2015 AIP Publishing LLC.ONR N000141210665Center for Nonlinear Dynamic

Eulerian and Lagrangian correspondence of high-frequency radar and surface drifter data : effects of radar resolution and flow components

Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 31 (2014): 945–966, doi:10.1175/JTECH-D-13-00146.1.This study investigated the correspondence between the near-surface drifters from a mass drifter deployment near Martha’s Vineyard, Massachusetts, and the surface current observations from a network of three high-resolution, high-frequency radars to understand the effects of the radar temporal and spatial resolution on the resulting Eulerian current velocities and Lagrangian trajectories and their predictability. The radar-based surface currents were found to be unbiased in direction but biased in magnitude with respect to drifter velocities. The radar systematically underestimated velocities by approximately 2 cm s−1 due to the smoothing effects of spatial and temporal averaging. The radar accuracy, quantified by the domain-averaged rms difference between instantaneous radar and drifter velocities, was found to be about 3.8 cm s−1. A Lagrangian comparison between the real and simulated drifters resulted in the separation distances of roughly 1 km over the course of 10 h, or an equivalent separation speed of approximately 2.8 cm s−1. The effects of the temporal and spatial radar resolution were examined by degrading the radar fields to coarser resolutions, revealing the existence of critical scales (1.5–2 km and 3 h) beyond which the ability of the radar to reproduce drifter trajectories decreased more rapidly. Finally, the importance of the different flow components present during the experiment—mean, tidal, locally wind-driven currents, and the residual velocities—was analyzed, finding that, during the study period, a combination of tidal, locally wind-driven, and mean currents were insufficient to reliably reproduce, with minimal degradation, the trajectories of real drifters. Instead, a minimum combination of the tidal and residual currents was required.I.R. was supported by the WHOI Coastal Ocean Institute Project 27040148 and by the WHOI Access to the Sea Program 27500036. I.R. and A.K. acknowledge support fromthe NSF project 83264600. A.K. acknowledges support from the Massachusetts Clean Energy Center (MassCEC) via the New England Marine Renewable Energy Center (MREC).2014-10-0

Death of three Loop Current rings

The life cycle of large anticyclonic rings in the Gulf of Mexico (GOM) is widely described by pinch off from the Loop Current, migration across the Gulf and eventual spin down along the western slope. Extensive observational and modeling efforts provide a relatively consistent picture of rings pinching off from the Loop Current and of complex interaction between anticyclones and cyclones driven by bathymetry along the western and northwestern shelf. The observational record for Loop Current rings (LCRs) during the intermediate period of westward translation is less clear. A number of studies recognize distinct anomalies in LCR characteristics in deep water as the rings enter the western Gulf near 92-94W. These include abrupt changes in the geometry of observed drifter trajectories and derived eddy parameter fits as well as changes in both ring translation speeds and the estimated rate of ring decay. Such observations are consistent with intense interaction and mass exchange between the rings and other coherent mesoscale features known to be present in the western Gulf. We test the hypothesis that interactions with the ambient mesoscale field can lead to rapid loss of coherence of some LCRs well before they reach the \u27eddy graveyard\u27 in the western Gulf. We use the data-assimilating, eddy-resolving numerical GOM model described by Kantha et al. (2005) to assess the fates of readily identified LCRs Fourchon, Juggernaut, and Millenium during the period July 1998 to August 2001. Lagrangian metrics, including relative dispersion of small drifter clusters seeded in the ring cores, analysis of evolving blobs seeded in the ring cores, and finite-scale Lyapunov exponents, are used to track model ring evolution. These metrics clearly show that interactions with existing mesoscale cyclones and anticyclones caused Fourchon and Juggernaut to break up near 92W on advective time scales. In addition, Millenium also experienced an intense deformation, stirring, and mixing episode near 92W. Blob studies showed that the core fluid of Millenium was ultimately dispersed over much of the western basin. Our results show that some LCRs may break up through interactions with existing western Gulf cyclones and anticyclones prior to reaching the western slope

The impact of assimilating along-track SLA data on simulated Eddy characteristics in the Agulhas system

The Agulhas Current System is a vital element of the global ocean-climate system by virtue of its role in the transfer of energy, nutrients and organic material. In the context of working towards better climate change projections, it is necessary to develop a robust understanding of the complex dynamical mechanisms which facilitate this transfer. Mesoscale cyclonic and anticyclonic eddies transport heat, salt, organic matter and nutrients from the Indian Ocean into the South Atlantic Ocean. In so doing, they are key drivers of the Atlantic Meridional Overturning Circulation (AMOC). As such, it is important that they are adequately simulated by numerical models in order to advance the accuracy of climate prediction. In the absence of spatially and temporally coherent observing systems, numerical models provide the capacity to describe the oceanographic conditions of the region. Given the complexity of the regional dynamics, and the challenges it presents to free-running numerical models, data assimilation is a valuable tool in improving simulation quality. An important step in this continuing process is the objective, quantitative evaluation of model configurations, such that they can be continuously refined. In this study, the impact of assimilating along-track sea level anomaly (SLA) data is investigated with regard to the simulation of mesoscale eddies in the Agulhas System. Two configurations of a Hybrid Coordinate Ocean Model (HYCOM) configuration are analysed; one free run (hereafter 'Free') and one with along-track SLA data from satellite altimetry assimilated (hereafter 'Assim.') via an Ensemble Optimal Interpolation (EnOI) data assimilation scheme. The results of these two configurations are compared with each other, and against a set of corresponding observational data from satellite altimetry (hereafter 'Aviso'). To this end, an automatic eddy detection and tracking algorithm is implemented, in order to quantify eddy characteristics in a coherent and consistent manner

Water mass exchange, pathways and the mesoscale eddy field in the Lofoten Basin of the Norwegian Sea

The Lofoten Basin situated in the Norwegian Sea, plays a central role in redistributing and modifying the warm Atlantic Water carried poleward with the Norwegian Atlantic Current. Increased residence time of the warm Atlantic Water in this region, leads to a large cooling and the largest surface heat losses in the Nordic Seas. This thesis studies the exchange of Atlantic Water with the Lofoten Basin using observations and numerical models, and Lagrangian and Eulerian approaches. A key focus is the study of the mass and heat exchange with the basin outlined by the 3000-m isobath. Surface drifters are analyzed to study the surface circulation in the Nordic Seas and to estimate the water mass exchange with the Lofoten Basin. Fields from Eulerian models and trajectories from Lagrangian simulations at multiple levels are further used to study the processes leading to the exchange, by delineating the mean and eddy component of the flows. Analyses aimed to quantify the mesoscale eddy properties, their interaction with the ambient, heat and vorticity budgets, and to assess the importance of eddies relative to the ambient flow and other submesoscale processes in the mass and heat exchange with the Lofoten Basin. The geographical origins of the water masses having largest interaction with the basin are identified, and these sites are studied in detail to investigate the processes behind the exchange. The thesis also investigates the fate of water masses in the basin to study how their properties evolve with time, and compare this with other regions. The first main finding, obtained from surface drifter observations, indicates an increased exchange of Atlantic Water across the southern sector of the Lofoten Basin. The drifters show a meandering motion between the eastern and western branches of the Norwegian Atlantic Current towards the basin, and Eulerian simulations suggest that the inflow is primarily related to a mean component of the flow. The warm waters experience long residence times and large temperature losses in the basin. In contrast with earlier literature, there is less evidence of near-surface exchange with the waters carried by the slope current along the continental slope off Norway. However, the net heat transport into the basin is dominated by eddy fluxes. Furthermore, the divergence of eddy heat fluxes obtained from Eulerian calculations on the continental slope is large, and particularly enhanced at depths of about 400 m. It is therefore suggested that the flow from the south dominates the near-surface exchange of Atlantic Water with the basin, but eddy fluxes from the slope region are important at deeper levels. Lagrangian simulations of particles deployed at several depths reveal variations in the vertical structure of the inflows to the Lofoten Basin. Of the water parcels that are cooled most (more than 1^oC) while in the basin, those at the surface mainly enter from the south, and those at deeper levels (about 500 m) come from the slope. The inflows also have a seasonal variability. In winter, cooling and vertical mixing result in weak stratification and distribute the particles vertically, while strong stratification in summer limits their vertical excursions from their deployment depths. During winter, water masses close to the surface therefore tend to sink and give weaker inflows (less particles) close to the surface and stronger inflows (more particles) at deeper levels (100-300 m). The eddy activity in the basin and on the continental slope is quantified. Eddy signals extracted from Lagrangian trajectories, using multivariate wavelet ridge analysis, show that water masses in coherent vortices experience larger changes in their water properties (such as temperature and density) than water masses in the ambient flow, with enhanced warming in cyclones and enhanced cooling in anticyclones. There is also evidence of upwelling in the cyclones and downwelling in the anticyclones. The change of water properties and net vertical displacement is most pronounced in the Lofoten Basin. The anticyclones have a longer lifetime, more circular shape and larger radius than the cyclones. However, the eddies only cover a small portion of the Nordic Seas (about 6%) and the ambient flow and filaments around eddies therefore play an important role in balancing the Lofoten Basin heat and vorticity budgets. Ridge analysis confirms the role of eddy activity at deeper levels on the slope, and further reveals that the anticyclonic eddies generated on the slope bring warm water into the basin. Energetics and energy-conversion rates calculated from mooring observations from the upper slope, supported by volume-averaged calculations from an Eulerian model, are consistent with the Lagrangian and Eulerian analyses. Estimated baroclinic conversion rates imply that potential energy is extracted from the mean flow to eddies. The role of filaments in the upper layers, the link between the generation of eddies on the slope and their exchange with the LB at deeper layers, and contribution of these eddies and filaments to the Lofoten Basin heat and vorticity budgets merit further studies

Transformations and pathways of Southern Ocean waters into the South Atlantic Ocean

[eng] The returning limb of Atlantic Meridional Overturning Circulation (AMOC) is partly supplied by the cold-fresh waters that enter through the Drake Passage. Up to the isoneutral 28.0 kg m−3, the mean water inflow through the Drake Passage to the Scotia Sea is 140.8 ± 7.4 Sv and the outflow through the Northern Passages is 115.9 ± 8.3 Sv. Below this isoneutral reference and down to 2000 m, an additional 23.4 Sv enters through the Drake Passage. The mean barotropic contribution always represents over half the total transports, with substantial seasonal and moderate interannual variability in the water transports. The water mean-residence time is about 6 - 8 months. Combining the Argo floats data with other observational measurements, we apply a climatological high-resolution inverse model over the Scotia Sea boundaries up to the 28.0 kg m-3 isoneutral. The ACC enters 136.7 ± 1.0 Sv through the Drake Passage and exits 137.9 ± 1.0 Sv through the northern boundary, with the difference responding to the South Scotia Ridge and Philip Passages contributions. Along its northward path, the ACC waters lose heat but gain equatorward freshwater transport. Within the Scotia Sea, the surface-modal and modal-intermediate waters experience production in all biogeochemical variables. Finally, regarding anthropogenic DIC, the Scotia Sea stores 0.123 Pg C yr-1. Then, the ROD method compares actual drifters' displacements with numerical trajectory predictions; the observed-predicted differences in final positions respond to diffusive motions not captured by the numerical models. The ROD method is applied in the western South Atlantic Ocean leading to maximum diffusivities of 4630 - 4980 m2 s-1 in the upper 200 m of the water column, presenting an inverse relationship with depth. The diffusivities near the surface are fairly constant in latitude but the diffusion coefficients at 1000 m decrease considerably south of the Southern Boundary. With the horizontal diffusion coefficients obtained previously, we use the Lagrangian technique to determine the fraction of the upper-ocean transport that remains in the ACC flow as it crosses the South Atlantic Ocean and the fraction that contributes to the South Atlantic subtropical gyre. The mean results reveal that 94.8 Sv remains in the ACC, whereas a total of 15.1 Sv contributes directly to the AMOC. This AMOC transport takes a median of 14.3 years to arrive to the Brazilian Current from the Drake Passage. Furthermore, 78.1% of the particles that recirculate in the subtropical gyre perform one recirculation. The results confirm that the water masses entering the subtropical gyre through its eastern edge warm up substantially and lose density, partly transformed to surface waters. Furthermore, the contributions at the eastern edge of the South Atlantic subtropical gyre from the warm-water and the cold-water routes are compared. We perform numerical simulations of Lagrangian trajectories to identify the multiple direct and indirect pathways of intermediate waters. The total cold-route contribution represents between 17.9 and 18.9%, substantially higher than the 7.1 to 12.3% warm- route contribution. Several individual pathways form both routes, but the direct path is the preferential pathway followed by 83.6 to 87.2% of the water parcels. The direct cold route is the one that undergoes a greater transformation of its water masses, and it is confirmed that also feeds the Agulhas Current, contributing similarly to that coming from the Indonesian Throughflow.[spa] La rama de retorno de la circulación meridional del Atlántico (AMOC) es parcialmente sustentada por las aguas frías y frescas que proceden del océano Pacífico a través del pasaje de Drake. Hasta la isoneutra de 28.0 kg m-3, la entrada de agua media a través del paso de Drake hacia el mar de Scotia es de 140.8 ± 7.4 Sv mientras que la salida a través de los pasos del Norte corresponde a 115.9 ± 8.3 Sv. Su componente barotrópica media siempre representa más de la mitad de los transportes totales, con una variación interanual moderada y estacional considerable en los transportes de agua. El tiempo medio estimado de residencia en el mar de Scotia es de unos 6 - 8 meses. Combinando los datos de boyas Argo con otras medidas observacionales y aplicando un modelo inverso climatológico en los límites del mar de Scotia con el fin de definir el flujo de entrada y salida de la ACC hasta la isoneutra de 28.0 kg m-3 se estima que 136.7 ± 1.0 Sv del ACC entran por el paso de Drake y salen 137.9 ± 1.0 Sv por el límite norte. A lo largo de su trayectoria hacia el norte, las aguas del ACC pierden calor pero ganan transporte de agua dulce. Dentro del mar de Scotia, las aguas superficiales- modales y las superficiales-intermedias experimentan producción en todas las variables biogeoquímicas. Finalmente, en cuanto al DIC antropogénico, el mar de Scotia almacena 0.123 Pg C año-1. El método ROD compara los desplazamientos reales de los derivadores con las trayectorias de las partículas simuladas en modelos numéricos; las diferencias observadas-predichas en las posiciones finales responden a movimientos difusivos no capturados por los modelos numéricos. Dicho método es aplicado en el Atlántico Sur occidental obteniendo difusiones máximas de 4630 - 4980 m² s-1 en los primeros 200 m de la columna de agua, presentando una relación inversa con la profundidad. Cerca de la superficie, los coeficientes de difusión son bastante constantes en latitud, sin embargo, a 1000 m los coeficientes disminuyen considerablemente en el sur del frente Límite Sur. Con los coeficientes de difusión horizontal anteriores, se realizan simulaciones Lagrangianas para determinar qué fracción de transporte permanece en la ACC y qué cantidad de transporte se desvía en el norte para alimentar el giro subtropical del Atlántico Sur. Los resultados medianos revelan que 94.8 Sv permanecen en la ACC, mientras que un total de 15.1 Sv contribuyen directamente a la AMOC. Este transporte que se incorpora a la AMOC tarda una mediana de 14.3 años al llegar al corriente del Brasil. Los resultados confirman que las masas de agua que entran al giro subtropical por el borde oriental se calientan sustancialmente y la mayoría pierden densidad, parcialmente transformadas en aguas superficiales, mientras que las masas de agua que permanecen a la ACC se transfieren en gran medida a las capas superficiales y profundas. En cuanto a las contribuciones de la ruta cálida y la ruta fría en el margen oriental del giro subtropical del Atlántico Sur, se realizan simulaciones numéricas para identificar las múltiples vías directas e indirectas de las aguas intermedias. La contribución total de las aguas de la ruta fría representa entre un 17.9 y 18.9%, siendo sustancialmente mayor que el 7.1 y 12.3% de la contribución por parte de la ruta cálida. Ambas rutas están formadas por múltiples vías individuales pero la vía directa es la vía preferente seguida por el 83.6 – 87.2% de las parcelas de agua, siendo la ruta fría directa la que sufre una mayor transformación de sus aguas.[cat] La branca de retorn de la circulació meridional de l'Atlàntic (AMOC) és parcialment sustentada per les aigües fredes i fresques que procedeixen a través del passatge de Drake. Fins a la isoneutra de 28.0 kg m-3, l'entrada d'aigua mitja al mar de Scotia és de 140.8 ± 7.4 Sv mentre que la sortida a través dels passos del Nord correspon a 115.9 ± 8.3 Sv. La seva component barotròpica mitjana sempre representa més de la meitat dels transports d’aigua totals, amb una variació interanual moderada i estacional considerable. El seu temps mig de residència és d'uns 6 - 8 mesos. Mitjançant les dades de boies Argo amb altres mesures observacionals, apliquem un model invers en el mar de Scotia. Exactament, 136.7 ± 1.0 Sv del ACC entren pel pas de Drake i surten 137.9 ± 1.0 Sv pel límit nord. Al llarg de la seva trajectòria, les aigües perden calor però guanyen transport d'aigua dolça; a més les aigües superficials-modals i les superficials- intermèdies experimenten producció en totes les variables biogeoquímiques. El mar de Scotia emmagatzema 0.123 Pg C any-1 de DIC antropogènic. El mètode ROD revela que a l'Atlàntic Sud la difusió horitzontal té una relació inversa amb la profunditat. Les difusions són màximes de 4630 - 4980 m² s-1 en els primers 200 m i bastant constants en latitud, no obstant això a 1000 m els coeficients disminueixen considerablement al sud del front Límit Sud. Les simulacions Lagrangianes revelen que 94.8 Sv romanen en el ACC, mentre que un total de 15.1 Sv contribueixen directament a la AMOC. Aquest transport triga una mediana de 14.3 anys en arribar al corrent del Brasil. Les masses d'aigua que entren al gir subtropical s'escalfen substancialment i la majoria perden densitat, parcialment transformades en aigües superficials. Finalment, comparem les contribucions de la ruta càlida i la ruta freda en el marge oriental del gir subtropical de l'Atlàntic Sud obtenint que la ruta freda representa entre un 17.9 i 18.9%, sent substancialment major que la ruta càlida. Totes dues rutes estan formades per múltiples vies individuals però la via directa sempre és la via preferent

Lagrangian studies, circulation and mixing in the Southern Ocean

Oceans play a vital role as one of the major components of Earth's climate system. The study of oceanic processes and the complexity inherent in dynamic ows is essential for understanding their regulatory character on the climate's variability. A key region for the study of such intrinsic oceanic variability is the Southern Ocean. In the form of a wind-driven, zonally unbounded, strong eastward ow, the Antarctic Circumpolar Current (ACC) circumnavigates the Antarctic continent connecting each of the ocean basins. The dynamics of the ACC, which is characterised by the absence of land barriers, apart from when crossing Drake Passage, have long been a topic of debate [Rintoul et al., 2001]. The main interests of this study focus on inferring and mapping the dynamic variability the ACC exhibits by means of transient disturbances [Hughes, 2005] (such as mesoscale eddies) and subsequent mixing from Lagrangian trajectories. The distribution of eddy transport and intensity, the mixing of conservative quantities and ow dynamics through to the interaction of eddy kinetic energy, mean ow and topography are examined. The sparseness of observations in the Southern Ocean and the necessity to understand the role of the oceanic circulation in the climate by a holistic approach highlights computational ocean circulation models as indispensable. In the context of this study, output from the run401 of the Ocean Circulation and Climate Advance Model (OCCAM) 1/12� ocean model, developed at the U.K. National Oceanography Centre, is utilised. In order to deduce the temporal and spatial variability of the ow dynamics, as well as its vertical distribution, simulation of monthly releases of passive particles using di�erent schemes (i.e. cluster or linear alignment) on isobaric and isoneutral surfaces was conducted. An analysis of the Lagrangian trajectories reveals the characteristics of the dynamics that control the ow and depict regions of enhanced eddy activity and mixing. The model's ability to simulate real oceanic ows is established through comparison with a purposeful release of the tracer CF3SF5, which is conducted as part of the DIMES experiment (http://dimes.ucsd.edu/). We �nd that topography plays a fundamental role in the context of Southern Ocean mixing through the association of high EKE regions, where the interaction of vortical elements and multi �lamented jets in non-parallel ows supports an e�ective mechanism for eddy stirring, resulting in the enhanced dispersion of particles. Suppression of mixingin regions where the ow is delineated by intensi�ed and coherent, both in space and time, jets (strong PV gradients) signifying the separation of the ow in di�erentiated kinematic environments, is illustrated. The importance of a local approximation to mixing instead of the construction of zonal averages is presented. We present the caveats of classical di�usion theory in the presence of persistent structures and �nd that values of 1000-2000 m2

Coastal high-frequency radars in the Mediterranean ??? Part 1: Status of operations and a framework for future development

Due to the semi-enclosed nature of the Mediterranean Sea, natural disasters and anthropogenic activities impose stronger pressures on its coastal ecosystems than in any other sea of the world.With the aim of responding adequately to science priorities and societal challenges, littoral waters must be effectively monitored with high-frequency radar (HFR) systems. This land-based remote sensing technology can provide, in near-real time, fine-resolution maps of the surface circulation over broad coastal areas, along with reliable directional wave and wind information. The main goal of this work is to showcase the current status of the Mediterranean HFR network and the future roadmap for orchestrated actions. Ongoing collaborative efforts and recent progress of this regional alliance are not only described but also connected with other European initiatives and global frameworks, highlighting the advantages of this cost-effective instrument for the multi-parameter monitoring of the sea state. Coordinated endeavors between HFR operators from different multi-disciplinary institutions are mandatory to reach a mature stage at both national and regional levels, striving to do the following: (i) harmonize deployment and maintenance practices; (ii) standardize data, metadata, and quality control procedures; (iii) centralize data management, visualization, and access platforms; and (iv) develop practical applications of societal benefit that can be used for strategic planning and informed decision-making in the Mediterranean marine environment. Such fit-for-purpose applications can serve for search and rescue operations, safe vessel navigation, tracking of marine pollutants, the monitoring of extreme events, the investigation of transport processes, and the connectivity between offshore waters and coastal ecosystems. Finally, future prospects within the Mediterranean framework are discussed along with a wealth of socioeconomic, technical, and scientific challenges to be faced during the implementatio

Coastal high-frequency radars in the Mediterranean - Part 1: Status of operations and a framework for future development

Due to the semi-enclosed nature of the Mediterranean Sea, natural disasters and anthropogenic activities impose stronger pressures on its coastal ecosystems than in any other sea of the world. With the aim of responding adequately to science priorities and societal challenges, littoral waters must be effectively monitored with high-frequency radar (HFR) systems. This land-based remote sensing technology can provide, in near-real time, fine-resolution maps of the surface circulation over broad coastal areas, along with reliable directional wave and wind information. The main goal of this work is to showcase the current status of the Mediterranean HFR network and the future roadmap for orchestrated actions. Ongoing collaborative efforts and recent progress of this regional alliance are not only described but also connected with other European initiatives and global frameworks, highlighting the advantages of this cost-effective instrument for the multi-parameter monitoring of the sea state. Coordinated endeavors between HFR operators from different multi-disciplinary institutions are mandatory to reach a mature stage at both national and regional levels, striving to do the following: (i) harmonize deployment and maintenance practices; (ii) standardize data, metadata, and quality control procedures; (iii) centralize data management, visualization, and access platforms; and (iv) develop practical applications of societal benefit that can be used for strategic planning and informed decision-making in the Mediterranean marine environment. Such fit-for-purpose applications can serve for search and rescue operations, safe vessel navigation, tracking of marine pollutants, the monitoring of extreme events, the investigation of transport processes, and the connectivity between offshore waters and coastal ecosystems. Finally, future prospects within the Mediterranean framework are discussed along with a wealth of socioeconomic, technical, and scientific challenges to be faced during the implementation of this integrated HFR regional network