Bower Amy S.

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Amy S.

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Now showing 1 - 9 of 9
  • Article
    Equilibration and circulation of Red Sea Outflow water in the western Gulf of Aden
    (American Meteorological Society, 2005-11) Bower, Amy S. ; Johns, William E. ; Fratantoni, David M. ; Peters, Hartmut
    Hydrographic, direct velocity, and subsurface float observations from the 2001 Red Sea Outflow Experiment (REDSOX) are analyzed to investigate the gravitational and dynamical adjustment of the Red Sea Outflow Water (RSOW) where it is injected into the open ocean in the western Gulf of Aden. During the winter REDSOX cruise, when outflow transport was large, several intermediate-depth salinity maxima (product waters) were formed from various bathymetrically confined branches of the outflow plume, ranging in depth from 400 to 800 m and in potential density from 27.0 to 27.5 σθ, a result of different mixing intensity along each branch. The outflow product waters were not dense enough to sink to the seafloor during either the summer or winter REDSOX cruises, but analysis of previous hydrographic and mooring data and results from a one-dimensional plume model suggest that they may be so during wintertime surges of strong outflow currents, or about 20% of the time during winter. Once vertically equilibrated in the Gulf of Aden, the shallowest RSOW was strongly influenced by mesoscale eddies that swept it farther into the gulf. The deeper RSOW was initially more confined by the walls of the Tadjura Rift, but eventually it escaped from the rift and was advected mainly southward along the continental slope. There was no evidence of a continuous boundary undercurrent of RSOW similar to the Mediterranean Undercurrent in the Gulf of Cadiz. This is explained by considering 1) the variability in outflow transport and 2) several different criteria for separation of a jet at a sharp corner, which indicate that the outflow currents should separate from the boundary where they are injected into the gulf.
  • Technical Report
    Warm water pathways in the northeastern North Atlantic ACCE RAFOS float data report November 1996 - November 1999
    (Woods Hole Oceanographic Institution, 2001-11) Furey, Heather H. ; Bower, Amy S. ; Richardson, Philip L.
    This is the final data report of all acoustically tracked RAFOS float data collected by the Woods Hole Oceanographic Institution in 1996-1999 during the Atlantic Climate Change Experiment (ACCE). The RAFOS float component of ACCE, entitled "Warm Water Pathways and Intergyre Exchange in the Northeastern North Atlantic," was designed to measure the warm water currents entering the northeastern North Atlantic which become the source of intermediate and deep waters in the subpolar region. The experiment was comprised of three RAFOS float deployments on the R/V Knorr: the first in fall 1996 along the continental slope seaward of Porcupine Bank, the second in spring 1997 along the mid-Atlantic Ridge, and the final deployment in fall 1997 along both the Ridge and the Bank. Seventy floats were deployed, 13 RAFOS and 2 ALFOS in fall 1996, 14 RAFOS in spring 1997, and 41 RAFOS in fall 1997. The isobaric ALFOS floats were ballasted for 800 decibars and were launched to monitor the regions' sound sources during the experiment. The RAFOS floats were isopycnal and ballasted for the 27.5 sigma-t surface to target the intermediate-depth North Atlantic and Poleward Eastern Boundary Currents. The objectives of the Lagrangian float study were (1) to provide a quantitative description of the bifurcation of the North Atlantic Current east of the Mid-Atlantic Ridge, (2) to assess the importance of meridional eddy fluxes, compared to large-scale advection, in the northward flux of heat and salt in the northeastern North Atlantic, and (3) to establish the degree of continuity of the Poleward Eastern Boundary Current as it flows to the entrance of the Norwegian Sea and the fate of the Mediterranean Outflow Water carried by this current.
  • Article
    Mixing and entrainment in the Red Sea outflow plume. Part I : plume structure
    (American Meteorological Society, 2005-05) Peters, Hartmut ; Johns, William E. ; Bower, Amy S. ; Fratantoni, David M.
    When the salty and heavy water of the Red Sea exits from the Strait of Bab el Mandeb, it continues downslope into the Gulf of Aden mainly along two channels. The 130-km-long “Northern Channel” (NC) is topographically confined and is typically only 5 km wide. In it, the Red Sea plume shows unanticipated patterns of vertical structure, turbulent mixing, and entrainment. Above the seafloor a 25–120-m-thick weakly stratified layer shows little dilution along the channel. Hence this bottom layer undergoes only weak entrainment. In contrast, a 35–285-m-thick interfacial layer shows stronger entrainment and is shown in a companion paper to undergo vigorous turbulent mixing. It is thus the interface that exhibits the bulk of entrainment of the Red Sea plume in the NC. The interfacial layer also carries most of the overall plume transport, increasingly so with downstream distance. The “Southern Channel” (SC) is wider than the NC and is accessed from the latter by a sill about 33 m above the floor of the NC. Entrainment into the bottom layer of the SC is diagnosed to be strong near the entry into the SC such that the near-bottom density and salinity are smaller in the SC than in the NC at the same distance from Bab el Mandeb. In comparison with winter conditions, the authors encountered weaker outflow with shallower equilibration depths during the summer cruise. Bulk Froude numbers computed for the whole plume varied within the range 0.2–1. Local maxima occurred in relatively steep channel sections and coincided with locations of significant entrainment.
  • Technical Report
    Red Sea Outflow Experiment (REDSOX) : DLD2 RAFOS float data report February 2001 - March 2003
    (Woods Hole Oceanographic Institution, 2005-01) Furey, Heather H. ; Bower, Amy S. ; Fratantoni, David M.
    This is the final data report of all acoustically tracked second-generation Deep Lagrangian Drifter (DLD2) RAFOS float data collected by the Woods Hole Oceanographic Institution in 2001-2003 during the Red Sea Outflow Experiment (REDSOX). The float component of REDSOX was comprised of two deployments on the R/V Knorr and R/V Ewing: the first in February-March 2001, with 26 floats, and the second in August-September 2001, with 27 floats. The isobaric floats were ballasted for 650 decibars to target the intermediate-depth, high-salinity outflow waters from the Red Sea. The objectives of the Lagrangian float study were (1) to identify the spreading pathways of the equilibrated Red Sea outflow, and to quantify the velocities and eddy variability typical of this outflow and of the background oceanic environment in the Gulf of Aden, and (2) to identify and describe the mesoscale processes which contribute to the seaward transport of Red Sea Overflow Water properties through the Gulf of Aden and into the western Indian Ocean. In addition to floats activated and launched during the two cruises, four time-series sites were chosen for dual-release float moorings. The dual-release floats were released every two months between cruises and every two months after the second cruise, with the final release in March 2002. A pirate attack on the R/V Ewing forced some modification of the float deployment plan during the second cruise.
  • Preprint
    Discrete eddies in the northern North Atlantic as observed by looping RAFOS floats
    ( 2004-10-29) Shoosmith, Deborah R. ; Richardson, Philip L. ; Bower, Amy S. ; Rossby, H. Thomas
    RAFOS float trajectories near the 27.5 density level were analyzed to investigate discrete eddies in the northern North Atlantic with the objective of determining their geographical distribution and characteristics. Floats that made two or more consecutive loops in the same direction (loopers) were considered to have been in an eddy. Overall 15% (24 float years) of the float data were in loopers. One hundred and eight loopers were identified in 96 different eddies. Roughly half of the eddies were cyclonic (49%) and half were anticyclonic (51%), although the percentages varied in different regions. A few eddies were quasi-stationary for long times, one for over a year in the Iceland Basin, and many others clearly translated, often in the direction of the general circulation as observed by non-looping floats. Several floats were trapped in eddies in the vicinity of the North Atlantic Current just upstream (west) of the Charlie Gibbs (52ºN) and Faraday (50ºN) Fracture Zones, which seem to be preferred routes for flow crossing the mid-Atlantic ridge. Five floats looped in four anticyclones which translated southwestward away from the eastern boundary near the Goban Spur (47ºN-50ºN). These could have been weak meddies forming from remnants of warm salty Mediterranean Water advected northward along the eastern boundary.
  • Article
    Interannual variability in the pathways of the North Atlantic Current over the Mid-Atlantic Ridge and the impact of topography
    (American Meteorological Society, 2008-01) Bower, Amy S. ; von Appen, Wilken-Jon
    Recent studies have indicated that the North Atlantic Ocean subpolar gyre circulation undergoes significant interannual-to-decadal changes in response to variability in atmospheric forcing. There are also observations, however, suggesting that the southern limb of the subpolar gyre, namely, the eastward-flowing North Atlantic Current (NAC), may be quasi-locked to particular latitudes in the central North Atlantic by fracture zones (gaps) in the Mid-Atlantic Ridge. This could constrain the current’s ability to respond to variability in forcing. In the present study, subsurface float trajectories at 100–1000 m collected during 1997–99 and satellite-derived surface geostrophic velocities from 1992 to 2006 are used to provide an improved description of the detailed pathways of the NAC over the ridge and their relationship to bathymetry. Both the float and satellite observations indicate that in 1997–99, the northern branch of the NAC was split into two branches as it crossed the ridge, one quasi-locked to the Charlie–Gibbs Fracture Zone (CGFZ; 52°–53°N) and the other to the Faraday Fracture Zone (50°–51°N). The longer satellite time series shows, however, that this pattern did not persist outside the float sampling period and that other branching modes persisted for one or more years, including an approximately 12-month time period in 2002–03 when the strongest eastward flow over the ridge was at 49°N. Schott et al. showed how northward excursions of the NAC can temporarily block the westward flow of the Iceland–Scotland Overflow Water through the CGFZ. From the 13-yr time series of surface geostrophic velocity, it is estimated that such blocking may occur on average 6% of the time, although estimates for any given 12-month period range from 0% to 35%.
  • Technical Report
    R/V Oceanus Voyage 449-6 Red Sea Atlantis II Deep Complex Area 19 October–1 November 2008
    (Woods Hole Oceanographic Institution, 2009-07) Bower, Amy S.
    The purpose of this report is to summarize the research activities conducted during R/V Oceanus Voyage 449-6 (also referred to as KAUST Leg 2) in the Red Sea. The cruise began on 19 October 2008 at 1700 Local Time (LT), when the R/V Oceanus departed Jeddah Commercial Port. On the cruise were 15 scientists from five countries, including Saudi Arabia, United States, Egypt, Hong Kong and Sudan. The cruise ended on 1 November 2008 when the Oceanus returned to the Jeddah Commercial Port.
  • Article
    Somali Current rings in the eastern Gulf of Aden
    (American Geophysical Union, 2006-09-30) Fratantoni, David M. ; Bower, Amy S. ; Johns, William E. ; Peters, Hartmut
    New satellite-based observations reveal that westward translating anticyclonic rings are generated as a portion of the Somali Current accelerates northward through the Socotra Passage near the mouth of the Gulf of Aden. Rings thus formed exhibit azimuthal geostrophic velocities exceeding 50 cm/s, are comparable in overall diameter to the width of the Gulf of Aden (250 km), and translate westward into the gulf at 5–8 cm/s. Ring generation is most notable in satellite ocean color imagery in November immediately following the transition between southwest (boreal summer) and northeast (winter) monsoon regimes. The observed rings contain anomalous fluid within their core which reflects their origin in the equator-crossing Somali Current system. Estimates of Socotra Passage flow variability derived from satellite altimetry provide evidence for a similar ring generation process in May following the winter-to-summer monsoon transition. Cyclonic recirculation eddies are observed to spin up on the eastern flank of newly formed rings with the resulting vortex pair translating westward together. Recent shipboard and Lagrangian observations indicate that vortices of both sign have substantial vertical extent and may dominate the lateral circulation at all depths in the eastern Gulf of Aden.
  • Article
    Science under sail : ocean science education program combines traditional vessels with state-of-the-art technology
    (Oceanography Society, 2004-09) Bower, Amy S. ; Zettler, Erik R. ; Gawarkiewicz, Glen G.
    Sea Education Association (SEA), located in Woods Hole, Massachusetts, offers introductory oceanographic instruction in the classroom and hands-on research training at sea to create a unique educational experience for undergraduate students and other groups. Founded by Corwith Cramer in 1971, SEA has been taking students to sea for over 30 years, first on the 125-foot research vessel R/V Westward, and now on two custom-built Sailing School Vessels, the 134-foot steel brigantines SSV Corwith Cramer and SSV Robert C. Seamans. SEA vessels have sailed over 800,000 miles in the Atlantic and Pacific Oceans, and educated over 7,000 students in oceanography, nautical science, and in maritime history, literature, and policy. This article describes recent developments and opportunities in oceanographic education and research at SEA.