Current-eddy interaction in the Agulhas Return Current region from the seismic oceanography perspective

Interleaving in the Agulhas Return Current (ARC) frontal region is commonly manifested in the form of thermohaline intrusions, as sub-tropical and sub-polar water masses of similar density meet. In Jan/Feb 2012, the Naval Research Laboratory and collaborators carried out a field experiment in which seismic and traditional hydrographic observations were acquired to examine frontal zone mixing processes. The high lateral resolution (10 m) of the seismic observations allowed fine-scale lateral tracking of thermal intrusions, which were corroborated with simultaneous XBT casts. Between seismic deployments both salinity and temperature data were acquired via CTD, Underway-CTD and microstructure profiles. This study focuses on analyzing seismic reflection data in a particular E-W transect where the northward flowing ARC interacted with the southward flowing portion of a large anticyclonic eddy. Strong reflectors were most prominent at the edge of a hyperbolic zone formed between the eddy and ARC, where sub-polar waters interacted with waters of sub-tropical origin on either side. Reflectors were shallow within the hyperbolic zone and extended to 1200 m below the ARC. The nature of the observed reflectors will be determined from comparison of seismic reflection and derived ∂T/∂z fields, and XBT and TS profiles from the available hydrographic data

Plimne oscilacije u sjevernom Jadranu: opažanja, modeliranje varijacijskom asimilacijom podataka i linearna plimna dinamika

Fifteen open-sea time-series observations of tidal velocities and tidal bottom pressures for more than six months duration provide a new database for North Adriatic tides. The observations show nearly reversing tidal currents at most locations and increasing tidal-current strength near Istria. Tidal elevation amplitudes and phases respectively increase northwestward and counterclockwise, strongly for semidiurnal tides and weakly for diurnal tides. The data are used for optimal determination of boundary conditions for a linear strong-constraint variational data assimilation model and the resulting average rms difference errors for tidal elevations and currents are below 1 cm and 0.5 cm/s, respectively. The Q factors from the model are 14.0 for M2 and 22.4 for K1, but comparisons between frictional dissipation estimated from the model and from the data suggest that model dissipation values could be too high by a factor of two and Q factors too small. Model potential energy is 1.5 times kinetic energy for M2 and 6.1 times kinetic energy for K1. Observational and modeling results suggest that energy fluxes from Kvarner Bay are significant in the North Adriatic tidal energy balance. M2 energy fluxes support the concept of an incident and reflected Kelvin wave in the North Adriatic with some modification. K1 energy fluxes show a northeastward cross-basin flux near the 50 m isobath where the bathymetric slope is particularly steep, with Kelvin-wave-like structures north of the ridge and departures from Kelvin--wave structure south of the ridge.Petnaest vremenskih nizova mjerenja plimnih struja i pridnenih tlakova na otvorenom moru, u razdoblju duljem od šest mjeseci, predstavlja novu bazu podataka za plimne oscilacije sjevernog Jadrana. Opažanja pokazuju gotovo obrat plimnih struja na većini lokacija i povećanje njihove snage u blizini Istre. Amplitude plimnih denivelacija povećavaju se prema sjeverozapadu, a faze rastu u smjeru suprotno od kazaljke na satu, jako za poludnevnu komponentu, slabo za dnevnu. Podaci su upotrijebljeni za optimalno određivanje rubnih uvjeta u linearnom modelu koji je korišten kao strogi uvjet u varijacijskoj asimilaciji. Dobiveno srednje kvadratno odstupanje za plimne denivelacije je manje od 1 cm, a za plimne struje manje je od 0.5 cm/s. Izračunati Q-faktori za model su 14.0 za M2 komponentu i 22.4 za K1 komponentu, ali usporedbe između disipacije trenjem procijenjene iz modela i iz mjerenja sugerira da su vrijednosti disipacije u modelu prevelike za faktor 2, te da su vrijednosti Q faktora premale. Modelirana potencijalna energija je 1.5 puta veća od kinetičke energije za M2 komponentu i 6.1 puta veća od kinetičke energije za K1 komponentu. Rezultati mjerenja i modela sugeriraju da protoci energije iz Kvarnerskog zaljeva daju značajan doprinos ravnoteži plimne energije u sjevernom Jadranu. Protoci energije M2 komponente podržavaju koncept upadnog i reflektiranog Kelvinovog vala u sjevernom Jadranu uz neke modifikacije. Protoci energije K1 komponente pokazuju poprečni tok u smjeru sjeveroistoka u blizini 50 m izobate gdje je nagib dna osobito strm, sa strukturama sličnima Kelvinovom valu sjeverno od grebena i odstupanja od Kelvinovog vala južno od grebena

Plimne oscilacije u sjevernom Jadranu: opažanja, modeliranje varijacijskom asimilacijom podataka i linearna plimna dinamika

Fifteen open-sea time-series observations of tidal velocities and tidal bottom pressures for more than six months duration provide a new database for North Adriatic tides. The observations show nearly reversing tidal currents at most locations and increasing tidal-current strength near Istria. Tidal elevation amplitudes and phases respectively increase northwestward and counterclockwise, strongly for semidiurnal tides and weakly for diurnal tides. The data are used for optimal determination of boundary conditions for a linear strong-constraint variational data assimilation model and the resulting average rms difference errors for tidal elevations and currents are below 1 cm and 0.5 cm/s, respectively. The Q factors from the model are 14.0 for M2 and 22.4 for K1, but comparisons between frictional dissipation estimated from the model and from the data suggest that model dissipation values could be too high by a factor of two and Q factors too small. Model potential energy is 1.5 times kinetic energy for M2 and 6.1 times kinetic energy for K1. Observational and modeling results suggest that energy fluxes from Kvarner Bay are significant in the North Adriatic tidal energy balance. M2 energy fluxes support the concept of an incident and reflected Kelvin wave in the North Adriatic with some modification. K1 energy fluxes show a northeastward cross-basin flux near the 50 m isobath where the bathymetric slope is particularly steep, with Kelvin-wave-like structures north of the ridge and departures from Kelvin--wave structure south of the ridge.Petnaest vremenskih nizova mjerenja plimnih struja i pridnenih tlakova na otvorenom moru, u razdoblju duljem od šest mjeseci, predstavlja novu bazu podataka za plimne oscilacije sjevernog Jadrana. Opažanja pokazuju gotovo obrat plimnih struja na većini lokacija i povećanje njihove snage u blizini Istre. Amplitude plimnih denivelacija povećavaju se prema sjeverozapadu, a faze rastu u smjeru suprotno od kazaljke na satu, jako za poludnevnu komponentu, slabo za dnevnu. Podaci su upotrijebljeni za optimalno određivanje rubnih uvjeta u linearnom modelu koji je korišten kao strogi uvjet u varijacijskoj asimilaciji. Dobiveno srednje kvadratno odstupanje za plimne denivelacije je manje od 1 cm, a za plimne struje manje je od 0.5 cm/s. Izračunati Q-faktori za model su 14.0 za M2 komponentu i 22.4 za K1 komponentu, ali usporedbe između disipacije trenjem procijenjene iz modela i iz mjerenja sugerira da su vrijednosti disipacije u modelu prevelike za faktor 2, te da su vrijednosti Q faktora premale. Modelirana potencijalna energija je 1.5 puta veća od kinetičke energije za M2 komponentu i 6.1 puta veća od kinetičke energije za K1 komponentu. Rezultati mjerenja i modela sugeriraju da protoci energije iz Kvarnerskog zaljeva daju značajan doprinos ravnoteži plimne energije u sjevernom Jadranu. Protoci energije M2 komponente podržavaju koncept upadnog i reflektiranog Kelvinovog vala u sjevernom Jadranu uz neke modifikacije. Protoci energije K1 komponente pokazuju poprečni tok u smjeru sjeveroistoka u blizini 50 m izobate gdje je nagib dna osobito strm, sa strukturama sličnima Kelvinovom valu sjeverno od grebena i odstupanja od Kelvinovog vala južno od grebena

Ispravak u radu: „Plimne oscilacije u sjevernom Jadranu: opažanja, modeliranje varijacijskom asimilacijom podataka i linearna plimna dinamika“

A precision/round-off error has been discovered in the tidal analysis routines used in the paper “North Adriatic tides: observations, variational data assimilation modeling, and linear tide dynamics” by J. W. Book, H. Perkins, and M. Wimbush (2009, Geofizika, 26, 115–143). Tidal elevation phases for 12 of the 15 stations are, on average, too low by 3.9° for the diurnal constituents and 7.9° for the semidiurnal constituents in Tabs. 4 and 5. These tables have been corrected and are republished here. The error also had an effect on the input data used for the linear variational data assimilation model, and combined with a nearest neighbor interpolation scheme produced an approximate 15 minute forward shift in time for 6 of the 43 synthesized tidal records. The error produced final model solutions that had tidal elevation phases 3.5° too high for M2, 1.6° too high for K1, and similar matching phase shifts for other semidiurnal and diurnal constituents. The errors in the input data have been corrected, the interpolation scheme has been changed to a piecewise cubic spline method, and the model runs have all been redone. The new model results suggest a minor change in optimal friction parameter, which in turn alters model Q factors and dissipation. However, the original finding that these values are not well determined by this methodology remains true. Model and observational results originally shown in Figs. 5–7 and Figs. 13–14 have slightly changed and are republished here. The main conclusions from the original work regarding Kelvin waves and TRW dynamics for the North Adriatic basin remain unaltered by these corrections.Otkrivena je pogreška zaokruživanja u rutinama za plimnu analizu u radu J. W. Book, H. Perkins i M. Wimbush: „Plimne oscilacije u sjevernom Jadranu: opažanja, modeliranje varijacijskom asimilacijom podataka i linearna plimna dinamika“ (Geofizika, 26, 2009, 115–143). Faze plimnih denivelacija, dane u tablicama 4. i 5., za 12 od 15 postaja podcijenjene su u prosjeku 3,9° za dnevne komponente te 7,9° za poludnevne komponente. Ovdje dajemo tablice s ispravljenim vrijednostima. Greška je utjecala na ulazne podatke koji su korišteni u linearnom modelu za varijacijsku asimilaciju podataka te je, u kombinaciji s interpolacijskom shemom najbližeg susjeda, uzrokovala vremenski pomak unaprijed od približno 15 minuta za 6 od ukupno 43 sintetizirana plimna zapisa. Greška je proizvela konačna modelska rješenja koja su precijenila faze plimnih denivelacija za 3,5° za M2 komponentu, 1,6° za K1 komponentu, te fazne pomake sličnih iznosa kod drugih poludnevnih i dnevnih komponenti. Greške u ulaznim podacima su ispravljene, interpolacijska shema je promijenjena tako da koristi po dijelovima kubne spline-ove te su ponovno provedeni modelski računi. Novi rezultati modela sugeriraju malu promjenu u optimalnom parametru trenja, koji dalje mijenja Q faktore modela i disipaciju. Međutim izvorni nalaz, da te vrijednosti nisu dobro određene ovom metodologijom, ostaje nepromijenjen. Rezultati modela i opažanja, izvorno prikazani na slikama 5.–7. i 13.–14., malo su se promijenili i ovdje su nanovo prikazani. Glavni zaključci iz izvornoga rada u vezi s Kelvinovim valovima i TRW dinamikom u sjevernom Jadranu nakon ovih ispravki ostaju isti

Ispravak u radu: „Plimne oscilacije u sjevernom Jadranu: opažanja, modeliranje varijacijskom asimilacijom podataka i linearna plimna dinamika“

A precision/round-off error has been discovered in the tidal analysis routines used in the paper “North Adriatic tides: observations, variational data assimilation modeling, and linear tide dynamics” by J. W. Book, H. Perkins, and M. Wimbush (2009, Geofizika, 26, 115–143). Tidal elevation phases for 12 of the 15 stations are, on average, too low by 3.9° for the diurnal constituents and 7.9° for the semidiurnal constituents in Tabs. 4 and 5. These tables have been corrected and are republished here. The error also had an effect on the input data used for the linear variational data assimilation model, and combined with a nearest neighbor interpolation scheme produced an approximate 15 minute forward shift in time for 6 of the 43 synthesized tidal records. The error produced final model solutions that had tidal elevation phases 3.5° too high for M2, 1.6° too high for K1, and similar matching phase shifts for other semidiurnal and diurnal constituents. The errors in the input data have been corrected, the interpolation scheme has been changed to a piecewise cubic spline method, and the model runs have all been redone. The new model results suggest a minor change in optimal friction parameter, which in turn alters model Q factors and dissipation. However, the original finding that these values are not well determined by this methodology remains true. Model and observational results originally shown in Figs. 5–7 and Figs. 13–14 have slightly changed and are republished here. The main conclusions from the original work regarding Kelvin waves and TRW dynamics for the North Adriatic basin remain unaltered by these corrections.Otkrivena je pogreška zaokruživanja u rutinama za plimnu analizu u radu J. W. Book, H. Perkins i M. Wimbush: „Plimne oscilacije u sjevernom Jadranu: opažanja, modeliranje varijacijskom asimilacijom podataka i linearna plimna dinamika“ (Geofizika, 26, 2009, 115–143). Faze plimnih denivelacija, dane u tablicama 4. i 5., za 12 od 15 postaja podcijenjene su u prosjeku 3,9° za dnevne komponente te 7,9° za poludnevne komponente. Ovdje dajemo tablice s ispravljenim vrijednostima. Greška je utjecala na ulazne podatke koji su korišteni u linearnom modelu za varijacijsku asimilaciju podataka te je, u kombinaciji s interpolacijskom shemom najbližeg susjeda, uzrokovala vremenski pomak unaprijed od približno 15 minuta za 6 od ukupno 43 sintetizirana plimna zapisa. Greška je proizvela konačna modelska rješenja koja su precijenila faze plimnih denivelacija za 3,5° za M2 komponentu, 1,6° za K1 komponentu, te fazne pomake sličnih iznosa kod drugih poludnevnih i dnevnih komponenti. Greške u ulaznim podacima su ispravljene, interpolacijska shema je promijenjena tako da koristi po dijelovima kubne spline-ove te su ponovno provedeni modelski računi. Novi rezultati modela sugeriraju malu promjenu u optimalnom parametru trenja, koji dalje mijenja Q faktore modela i disipaciju. Međutim izvorni nalaz, da te vrijednosti nisu dobro određene ovom metodologijom, ostaje nepromijenjen. Rezultati modela i opažanja, izvorno prikazani na slikama 5.–7. i 13.–14., malo su se promijenili i ovdje su nanovo prikazani. Glavni zaključci iz izvornoga rada u vezi s Kelvinovim valovima i TRW dinamikom u sjevernom Jadranu nakon ovih ispravki ostaju isti

Seismic oceanography imaging of thermal intrusions in strong frontal regions

The Naval Research Laboratory and collaborating partners carried out two dedicated seismic oceanography field experiments in two very different strong frontal regions. ADRIASEISMIC took seismic oceanography measurements at the confluence of North Adriatic Dense Water advected along the Western Adriatic Current and Modified Levantine Intermediate Water advected around the topographic rim of the Southern Adriatic basin. ARC12 took seismic oceanography measurements in and around the Agulhas Return Current as it curved northwards past the Agulhas Plateau and interacted with a large anticyclone that had collided with the current. Despite one study focused on coastal boundary currents and the other focused on a major Western Boundary Current extension, the complex horizontal structures seen through seismic imaging are tied to the processes of thermal intrusions and interleaving in both systems. Seismic Oceanography provides a unique capability of tracking the fine-scale horizontal extent of these intrusions

Sediment dynamics in the Adriatic Sea investigated with coupled models

Several large research programs focused on the Adriatic Sea in winter 2002-2003, making it an exciting place for sediment dynamics modelers (Figure 1). Investigations of atmospheric forcing and oceanic response (including wave generation and propagation, water-mass formation, stratification, and circulation), suspended material, bottom boundary layer dynamics, bottom sediment, and small-scale stratigraphy were performed by European and North American researchers participating in several projects. The goal of EuroSTRATAFORM researchers is to improve our ability to understand and simulate the physical processes that deliver sediment to the marine environment and generate stratigraphic signatures. Scientists involved in the Po and Apennine Sediment Transport and Accumulation (PASTA) experiment benefited from other major research programs including ACE (Adriatic Circulation Experiment), DOLCE VITA (Dynamics of Localized Currents and Eddy Variability in the Adriatic), EACE (the Croatian East Adriatic Circulation Experiment project), WISE (West Istria Experiment), and ADRICOSM (Italian nowcasting and forecasting) studies

Mean structure and variability of the Kuroshio from northeastern Taiwan to southwestern Japan

Author Posting. © The Oceanography Society, 2015. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 28, no. 4 (2015): 84-95, doi:10.5670/oceanog.2015.84.In the subtropical western North Pacific Ocean, the Kuroshio delivers heat, salt, and momentum poleward, much like its North Atlantic analog, the Gulf Stream. Though the Kuroshio generally flows along the western boundary from Taiwan to southeastern Japan as an “attached” current, the Kuroshio’s strength, vertical structure, and horizontal position undergo significant temporal and spatial variability along this entire route. Ubiquitous mesoscale eddies and complicated topography associated with a string of marginal seas combine to make the western North Pacific a region with complex circulation. Here, we synthesize results from the recent US Origins of the Kuroshio and Mindanao Currents and Taiwan Observations of Kuroshio Transport Variability observational programs with previous findings to build a comprehensive picture of the Kuroshio on its route from northeastern Taiwan to southeastern Japan, where the current finally transitions from a western boundary current into the Kuroshio Extension, a vigorously meandering free jet.ONR sponsored many of the field programs that are reported on in this study, including grant N00014-12- 1-0445 to MA and grant N00014-10-1-0468 to TBS. Additionally, MA received support from The Andrew W. Mellon Foundation Endowed Fund for Innovative Research. LC and the drifter work were supported by ONR grant N0001-10-1-0273 and NOAA grant NA10OAR4320156, “The Global Drifter Program.” SJ was sponsored by the Ministry of Science and Technology, ROC (Taiwan) grant NSC-101-2611-M- 002-018-MY3

Spring 2009 water mass distribution, mixing and transport in the southern Adriatic after a low production of winter dense waters

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