Using Acoustic Travel Time to Determine Dynamic Height Variations in the North Atlantic Ocean

There is often an approximately linear relationship between various water-column integrals, in particular between surface dynamic height anomaly ΔD and acoustic round-trip travel time τ. Consequently, the record from an inverted echo sounder, which measures τ, can be interpreted in terms of ΔD. Nevertheless, the slope m of this linear relation is not everywhere well defined, and varies from place to place. This study seeks to establish where, in the extratropical North Atlantic, one can reasonably assume a linear relation between ΔD and τ, and for these regions compute m. Using climatological atlas data and historic hydrographic data, it is shown that a well-defined, linear relation exists between ΔD and τ in a region centered on the Gulf Stream and extending from the northern Sargasso Sea almost to Ireland. Where m is well defined, it is negative, and its value is usually similar to that associated with first-baroclinic-mode excitation. Its magnitude generally decreases with increasing latitude. The value of m typically ranges from −40 dyn m s−1 in the northern Sargasso Sea to −20 dyn m s−1 in the North Atlantic Current. In the Gulf Stream it is typically between −30 and −35 dyn m s−1

Simultaneous pressure, velocity and temperature measurements in the Florida Straits

We present a descriptive picture of the variability in the Florida Current as measured by a large number of current meters, temperature sensors, and bottom mounted pressure sensors in the period March-August, 1974. Because of the very high velocities, only measurements made in the near-bottom region were possible. The tidal regime is found to be somewhat more complex than postulated from earlier measurements...

Bottom Temperatures Related to Gulf Stream Displacement off the Southeast United States Shelf

Bottom temperature time series recorded beneath the Gulf Stream at 265 and 589 m depth off the Georgia coast are compared with simultaneous time series of main thermocline depth determined from inverted echo sounder and bottom pressure gauge records at the same sites. Bottom temperature is found to be coherent with vertical displacement of the thermocline, suggesting that bottom temperature under the Gulf Stream front is a potentially useful indicator of Gulf Stream displacement. Additional evidence is provided by the similarity of bottom temperature and thermocline depth coherences with longshore current at the shelf break. Bottom temperature at the deeper station appears to be the better indicator of Gulf Stream meandering for periods longer than five days

Model results of flow instabilities in the tropical Pacific Ocean

A two‐and‐a‐half‐layer model of the tropical Pacific Ocean is used to investigate the energy source for the intraseasonal dynamic‐height variability observed near 6°N. A simulation of equatorial circulation is produced by forcing the model with mean‐monthly wind‐stress climatology. Two westward‐propagating waves appear in the upper layer in the central and eastern portion of the model basin. These two waves are distinguished by period and meridional structure. An off‐equatorial wave with period of 30 days and wavelength of 1100 km has a meridional sea‐level maximum near 6°N similar to that of the 30–50 day intraseasonal wave observed in the ocean. The meridional velocity signal also is asymmetric with respect to the equator, with maximum near 4°N. The second wave with period of 15 days has a strong meridional velocity signal centered on the equator. The sea‐level and zonal velocity signals associated with this equatorial wave have maxima near 1.5°N and 1.5°S. The eddy‐energy budget reveals strong conversions from the mean‐flow to eddy field through baroclinic and upper‐layer barotropic conversion terms. Conversion terms north of the equator exhibit a bimodal structure: one maximum between the equator and 3°N is dominated by upper‐layer barotropic conversion spatially coincident with the cyclonic shear along the equatorward edge of the South Equatorial Current (SEC), and a second smaller maximum between 3°N and 5°N is a combination of upper‐layer barotropic conversion along the poleward edge of the SEC (anticyclonic shear) and baroclinic conversion near the core of the SEC. The two peaks in the conversion terms, combined with similar structure in the flux‐divergence terms in the model eddy‐energy budget, provide evidence that two wave processes are generated at the different source regions: one near the equator and a second between 2°N and 5°N

Using modern time series analysis techniques to predict ENSO events from the SOI time series

We analyze the monthly 1866–2000 Southern Oscillation Index (SOI) data to determine: whether the SOI data are sufficiently noise-free that useful predictions can be made from them, and in particular, whether future ENSO events can be predicted from the SOI data. The “Hilbert-EMD” technique is used to aid the analysis. This new frequency-time algorithm, based on the Hilbert transform, may be applied to time series for which the conventional assumptions of linearity and stationarity may not apply. With the aid of the EMD procedure, a cleaner representation of ENSO dynamics is obtained from the SOI data. A polynomial function is then used to predict SOI values. Using only the data from January 1866 through December 1996, this prediction correctly indicated a warm event in 1997–1998 and a cold event in 1999. Using all the data (through December 2000), this prediction shows no strong ENSO events (positive or negative) during the time period January 2001 through December 2004

Near bottom speed and temperature observations on the Blake-Bahama outer ridge

Speed and temperature measurement made in the bottom boundary layer (BBL) in the region of the Western Boundary Undercurrent at 28°22′N, 74° 13′W over an ∼11 day period are presented. The observations suggest that the BBL structure is consistent with that of a turbulent Ekman layer formed in an initially stably stratified fluid over a uniform surface even though they were obtained in and above an abyssal furrow. The inferred friction velocities u*(ū* = 0.66 cm/s) generally are larger than those inferred by Weatherly (1972) under the Florida Current and at times sufficiently large to result in erosion of some of the finer cohesive sediments if the criterion for their erosion summarized in McCave (1978) is assumed to apply at the site of the observations

Wind–Current Coupling on the Southern Flank of Georges Bank: Variation with Season and Frequency

Comparison of several years of current observations on the southern flank of Georges Bank with nearby wind data shows that the wind–current coupling is primarily between longshelf wind stress and longshelf current. The strongest wind–current coupling occurs in winter, when the water column is homogeneous. The weakest coupling is in late summer and early fall, when the water column is highly stratified. The coherence and transfer coefficient between longshelf wind and longshelf current is highest for periods between 4 and 12 days, decreasing both for longer periods (out to 56 days) and shorter periods (down to 2 days). Models of the wind–current coupling indicate that a highly damped resonance may exist on Georges Bank and that a smaller current response is expected when the water column is stratified. The observations also indicate that the wind-driven currents on Georges Bank are strongly controlled by friction. The near-surface current moves to the right of wind stress and there is a spring–neap modulation of the wind–current transfer coefficient caused by the modulation of the bottom stress associated with the spring–neap tidal cycle. The longshelf current is linearly related to wind stress and responds almost symmetrically to wind forcing

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

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