Temperature transport and motional induction in the Florida Current

Differences of electrical potential across the Florida Current between Jupiter, Florida, and Settlement Point, GBI, are interpreted in terms of mean and seasonal temperature transports. The potential differences arise from the lateral transport of electrical conductivity through the vertical component of the earth\u27s magnetic field. Using the temperature and conductivity relation in the Current, the conductivity transport can be converted to temperature transport...

Accurately monitoring the Florida Current with motionally induced voltages

A new experimental technique for appraising how accurately submarine-cable (subcable) voltages monitor oceanic volume transport is presented and then used to study voltages induced by the northern Florida Current. Until recently, subcable voltages have been largely dismissed as an oceanographic tool because their interpretation can be ambiguous. They depend upon the transport field, the electrical conductance of the environment, and the mutual spatial distribution of these two quantities. To examine how these three factors affect subcable voltages at a particular site, we combine data from two different velocity profilers: XCP and PEGASUS. These instruments provide vertical profiles of velocity, temperature, and motion ally induced voltage at several sites across a transect. From this information, we determine if and why subcable voltages track volume transport. We conclude that subcable voltages measured in the northern Florida Straits accurately monitor the Florida Current transport because they are insensitive to the spatial distribution of the flow—a result that stems from a large and rather uniform seabed conductance. Subcable voltages should be reconsidered for oceanic monitoring elsewhere because the validity of their interpretation can now be assessed

On the relationship between transport and motional electric potentials in broad, shallow currents

Knowledge of the volume transport is of great practical importance in many studies of the flow through or within shallow channels and estuaries. However, transport measurements are often difficult to obtain because of the temporal or spatial variability of the flow. The bulk motion of a stream has been inferred from measurements which integrate the electric field induced by the motion of seawater through the earth\u27s magnetic field...

Ocean response to a hurricane, part II : data tabulations and numerical modeling

Field observations of the ocean's forced stage response to three hurricanes, Norbert (1984), Josephine (1984) and Gloria (1985), are analyzed and presented in a storm-centered coordinate system. All three hurricanes had a non-dimensional speed of O(1) and produced a strongly rightward biased response of the ocean surface mixed layer (SML) transport and current. The maximum layer-averaged SML currents varried from 0.8 m S-1 in response to Josephine, which was a fairly weak hurricane, to 1.7 m S.l in response to Gloria, which was much stronger. In these two cases the current amplitude is set primarly by the strength of the wind stress and its efficiency of coupling with the SML current, and the depth of vertical mixing of the SML. The Norbert case (SML Burger number ≈ 1/2) was also affected by significant pressure-coupling with the thermocline that caused appreciable upwellng by inertial pumping and strong thermocline-depth currents, up to 0.3 m S-l, under the trailing edge of Norbert. The observed SML current has a vertical shear in the direction of the local wind of up to 0.01 S-l. This vertical shear causes the surface current to be larger than the layer-averaged SML current described above by typically 0.2 m S.l.Funding was provided by the Office of Naval Research under grant No. N00014-89-J-I053

Upper-ocean response to Hurricane Frances (2004) observed by Profiling EM-APEX floats

Author Posting. © American Meteorological Society, 2011. 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 Physical Oceanography 41 (2011): 1041–1056, doi:10.1175/2010JPO4313.1.Three autonomous profiling Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats were air deployed one day in advance of the passage of Hurricane Frances (2004) as part of the Coupled Boundary Layer Air–Sea Transfer (CBLAST)-High field experiment. The floats were deliberately deployed at locations on the hurricane track, 55 km to the right of the track, and 110 km to the right of the track. These floats provided profile measurements between 30 and 200 m of in situ temperature, salinity, and horizontal velocity every half hour during the hurricane passage and for several weeks afterward. Some aspects of the observed response were similar at the three locations—the dominance of near-inertial horizontal currents and the phase of these currents—whereas other aspects were different. The largest-amplitude inertial currents were observed at the 55-km site, where SST cooled the most, by about 2.2°C, as the surface mixed layer deepened by about 80 m. Based on the time–depth evolution of the Richardson number and comparisons with a numerical ocean model, it is concluded that SST cooled primarily because of shear-induced vertical mixing that served to bring deeper, cooler water into the surface layer. Surface gravity waves, estimated from the observed high-frequency velocity, reached an estimated 12-m significant wave height at the 55-km site. Along the track, there was lesser amplitude inertial motion and SST cooling, only about 1.2°C, though there was greater upwelling, about 25-m amplitude, and inertial pumping, also about 25-m amplitude. Previously reported numerical simulations of the upper-ocean response are in reasonable agreement with these EM-APEX observations provided that a high wind speed–saturated drag coefficient is used to estimate the wind stress. A direct inference of the drag coefficient CD is drawn from the momentum budget. For wind speeds of 32–47 m s−1, CD ~ 1.4 × 10−3.The Office of Naval Research supported the development of the EM-APEX float system through SBIR Contract N00014-03-C-0242 to Webb Research Corporation and with a subcontract to APL-UW. Sanford and J. Girton were supported by the Office of Naval Research through GrantsN00014-04-1-0691 and N00014- 07-1-024, and J. Price was supported through Grant N00014-04-1-0109

Highly resolved observations and simulations of the ocean response to a hurricane

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 34 (2007): L13604, doi:10.1029/2007GL029679.An autonomous, profiling float called EM-APEX was developed to provide a quantitative and comprehensive description of the ocean side of hurricane-ocean interaction. EM-APEX measures temperature, salinity and pressure to CTD quality and relative horizontal velocity with an electric field sensor. Three prototype floats were air-deployed into the upper ocean ahead of Hurricane Frances (2004). All worked properly and returned a highly resolved description of the upper ocean response to a category 4 hurricane. At a float launched 55 km to the right of the track, the hurricane generated large amplitude, inertially rotating velocity in the upper 120 m of the water column. Coincident with the hurricane passage there was intense vertical mixing that cooled the near surface layer by about 2.2°C. We find consistent model simulations of this event provided the wind stress is computed from the observed winds using a high wind-speed saturated drag coefficient.The development of the EM-APEX float system was supported by the Office of Naval Research through SBIR contract N00014-03-C-0242 to Webb Research Corporation and with a subcontract to APL-UW

Internal tides on the East China Sea Continental Slope

Strong semidiurnal internal tides are observed on the continental slope of the East China Sea (ECS) using an array of subsurface moorings and EM-APEX floats. A Princeton Ocean Model (POM) is used to simulate the effects of stratification profiles on the generation and propagation of M2 internal tides; model simulations are compared with observations. On the ECS continental slope northeast of Taiwan, the semidiurnal barotropic tidal current flows nearly perpendicular to the shelf break and continental slope, favoring the generation of internal tides. Both the critical slope analysis and numerical model results suggest multiple generation sites on the continental slope, shelf break and around North MienHua Canyon. Unique high-wavenumber semidiurnal internal tides with a dominant vertical scale of ∼100 m are found on the continental slope. The high-wavenumber semidiurnal internal tides appear in a form of spatially coherent shear layers across the ECS slope. They propagate vertically both upward and downward. Patches of strong energy and shear at a typical vertical scale of O(50 m) are present at the intersections of the upward and downward propagating high-wavenumber internal tides. The strong shear of high-wavenumber semidiurnal tides could play an important role in triggering shear instability on the ECS slope. The semidiurnal internal tidal energy flux, primarily in low wavenumbers, on the ECS slope, exhibits strong temporal and spatial variations. The observed depth integrated energy flux is 3.0–10.7 kW m–1, mostly seaward from the continental shelf/slope. The POM model predicts similar seaward energy fluxes at a slightly weaker magnitude, 1.0–7.2 kW m–1. The difference may be due to the absence of mesoscale processes in the model, e.g., the Kuroshio Current and eddies, the assumed horizontally uniform stratification profiles, insufficient model resolution for the abrupt canyon bathymetry, and the lack of the other major semidiurnal tidal constituent, S2, in the model. On the ECS slope, the total energy in the internal wave continuum, between 0.3 cph (beyond semidiurnal tidal harmonics) and the buoyancy frequency, is 6-13 times that of the Garrett–Munk model, presumably as a result of the energy cascade from strong inertial waves and internal tides in the region

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

Eddy-Kuroshio interaction processes revealed by mooring observations off Taiwan and Luzon

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 42 (2015): 8098–8105, doi:10.1002/2015GL065814.The influence and fate of westward propagating eddies that impinge on the Kuroshio were observed with pressure sensor-equipped inverted echo sounders (PIESs) deployed east of Taiwan and northeast of Luzon. Zero lag correlations between PIES-measured acoustic travel times and satellite-measured sea surface height anomalies (SSHa), which are normally negative, have lower magnitude toward the west, suggesting the eddy-influence is weakened across the Kuroshio. The observational data reveal that impinging eddies lead to seesaw-like SSHa and pycnocline depth changes across the Kuroshio east of Taiwan, whereas analogous responses are not found in the Kuroshio northeast of Luzon. Anticyclones intensify sea surface and pycnocline slopes across the Kuroshio, while cyclones weaken these slopes, particularly east of Taiwan. During the 6 month period of overlap between the two PIES arrays, only one anticyclone affected the pycnocline depth first at the array northeast of Luzon and 21 days later in the downstream Kuroshio east of Taiwan.Ministry of Science and Technology (MOST) of Taiwan Grant Number: NSC-101-2611-M-002-018-MY3; US Office of Naval Research (ONR) Grant Number: N00014-12-1-0445; MA Grant Number: N00014-15-1-2593; ONR Grant Numbers: N00014-10-1-0397, N00014-10-1-0308, N00014-10-1-04682016-03-0