A Report of Data and Preliminary Analysis from Discovery 247 A Process Study of the Faroe Bank Channel Overflow by James F. Price, WHOI and the scientific.

Slides:



Advertisements
Similar presentations
An analysis of transport and water masses in the Straits of Florida and the Bahamas Moulin Aurélie Moulin Department of Marine and Environmental Systems.
Advertisements

Convection.
Consider a spherical earth of radius R=6.37*10 6 meters, rotating at a rate of  =7.29*10 -5 s -1. Starting from rest at point 1 on the surface of the.
Wind-Driven Circulation in a Stratified Ocean Consider the ocean in several isopycnal layers that can be separated into two groups: Layers that outcrop.
m/s Water mass subduction & eddy effects on phytoplankton distributions in the Santa Barbara Channel, California Libe Washburn 1, Mark Brzezinski.
..perhaps the hardest place to use Bernoulli’s equation (so don’t)
Suspended particle property variation in Gaoping Submarine Canyon Ray T. Hsu and James T. Liu Institute of Marine Geology and Chemistry, National Sun Yat-sen.
D A C B z = 20m z=4m Homework Problem A cylindrical vessel of height H = 20 m is filled with water of density to a height of 4m. What is the pressure at:
Baroclinic Instability in the Denmark Strait Overflow and how it applies the material learned in this GFD course Emily Harrison James Mueller December.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Ekman Spiral and Transport The motion of the water at the surface is driven by the wind. Each.
Define Current decreases exponentially with depth. At the same time, its direction changes clockwise with depth (The Ekman spiral). we have,. and At the.
Hydraulic Routing in Rivers
Temperature and Salinity Variabitlity on the Scotian Shelf and in the Gulf of Maine BRIAN PETRIE AND KENNETH DRINKWATER.
1. 2 ocean circulation thermohaline conceptual model.
Define Current decreases exponentially with depth and. At the same time, its direction changes clockwise with depth (The Ekman spiral). we have,. and At.
Two research cruises were successfully conducted in 2013 and Shipboard and moored observations show that: at first glance no significant decadal.
Mode (Eighteen Degree) Water V.Y. Chow EPS Dec 2005.
Alternative derivation of Sverdrup Relation Construct vorticity equation from geostrophic balance (1) (2)  Integrating over the whole ocean depth, we.
U.S. Department of the Interior U.S. Geological Survey Modeling sand transport and sandbar evolution along the Colorado River below Glen Canyon Dam.
General Ocean Circulation. Wind driven circulation About 10% of the water is moved by surface currents Surface currents are primarily driven by the wind.
Steffen M. Olsen, DMI, Copenhagen DK Center for Ocean and Ice Interpretation of simulated exchange across the Iceland Faroe Ridge in a global.
Rossby Wave Two-layer model with rigid lid η=0, p s ≠0 The pressures for the upper and lower layers are The perturbations are 
OCEAN CURRENTS.
ISPOL Ocean Turbulence Project Miles McPhee McPhee Research Co. Naches WA USA.
Modelling the evolution of the Siple Coast ice streams. Tony Payne 1*, Andreas Vieli 1 and Garry Clarke 2 1 Centre for Polar Observation and Modelling,
Distributed Flow Routing Surface Water Hydrology, Spring 2005 Reading: 9.1, 9.2, 10.1, 10.2 Venkatesh Merwade, Center for Research in Water Resources.
Channel Flow Routing Reading: Applied Hydrology Sections 8.4, , 9.7.
WOCE hydrographic Atlas, 1 As a result of the World Ocean Circulation Experiment (WOCE), a hydrographic survey of the world oceans occurred from
THOR CT3 Meeting – Torshavn 2009 – Fischer/Visbeck/Zantopp/Nunes In the Labrador Sea, overflow water from the Denmark Strait and from the Iceland-Scotland.
An example of vertical profiles of temperature, salinity and density.
Measuring the South Atlantic MOC – in the OCCAM ocean model Povl AbrahamsenJoel Hirschi Emily ShuckburghElaine McDonagh Mike MeredithBob Marsh British.
Thermohaline Circulation Lecture Outline 1)What is thermohaline circulation 2)History of understanding 3)Key water masses 4)Formation of deep water 5)Theory.
Ekman pumping Integrating the continuity equation through the layer:. Assume and let, we have is transport into or out of the bottom of the Ekman layer.
Water Mass Distribution OEAS 604 Lecture Outline 1)Thermohaline Circulation 2)Spreading pathways in ocean basins 3)T-S diagrams 4)Mixing on T-S diagrams.
OC3230-Paduan images Copyright © McGraw Hill Chap 7-8: Distributions SPECIAL DATES: MPA meeting…6 Jul R/V Pt Sur Cruise…14 Jul R/V Pt Sur Cruise…25 Jul.
Land-Ocean Interactions: Estuarine Circulation. Estuary: a semi-enclosed coastal body of water which has a free connection with the open sea and within.
Jets Dynamics Weather Systems – Fall 2015 Outline: a.Why, when and where? b.What is a jet streak? c.Ageostrophic flow associated with jet streaks.
A Synthetic Drifter Analysis of Upper-Limb Meridional Overturning Circulation Interior Ocean Pathways in the Tropical/Subtropical Atlantic George Halliwell,
12.808, Problem 1, problem set #2 This is a 3 part question dealing with the wind-driven circulation. At 26 o N in the N. Atlantic, the average wind stress.
Geopotential and isobaric surfaces
Introductory Physical Oceanography (MAR 555) - Fall 2009
Cross-Gyre Thermohaline Transport in the Tropical Atlantic: The role of NBC Rings Bill Johns Zulema Garraffo Division of Meteorology and Physical Oceanography.
Mixing and Entrainment in the Orkney Passage Judy Twedt University of Washington Dept. of Physics NOAA, Geophysical Fluid Dynamics Lab Dr. Sonya Legg Dr.
Lab 5 Physical and Chemical Properties of Sea Water
Basic Hydrology & Hydraulics: DES 601 Module 16 Open Channel Flow - II.
Discovery 247; A field study of the Faroe Bank Channel Overflow By Jim Price, WHOI, and the science party of Discovery 247, Tom Sanford, James Girton and.
Sediment Transport Modelling Lab. The Law of the Wall The law of the wall states that the average velocity of a turbulent flow at a certain point is proportional.
Bogi Hansen, Hjálmar Hátún, Regin Kristiansen, Steffen M. Olsen and Svein Østerhus Iceland Scot- land Nordic Seas Faroes 0.8 Sv 3.8 Sv Greenland Østerhus.
Norwegian Meteorological InstituteM/S Nordkapp Fall 2003 Pathways of Atlantic Water Cecilie Mauritzen – Norwegian Meteorological Institute NOClim 2 Workshop,
Identifying amplifying African waves from analysis of their temperature anomalies: how can the NAMMA aircraft, radiosonde and satellite data be merged.
Basic Hydraulics: Open Channel Flow – II
Horizontal density structure and restratification
What is the Bradshaw model?
Open Channel Hydraulic
Shelf and slope circulation inshore of the Charleston Bump H. Seim, W. Stark, UNC Chapel Hill C. Edwards, Skidaway Institute Of Oceanography.
Mixing of the Faroe Bank Channel Overflow
Define and we have • At the sea surface (z=0), the surface current flows at 45o to the right of the wind direction Depends on constant Az => • Current.
Define and we have • At the sea surface (z=0), the surface current flows at 45o to the right of the wind direction Depends on constant Az => • Current.
Define and we have • At the sea surface (z=0), the surface current flows at 45o to the right of the wind direction Depends on constant Az => • Current.
Preliminary Results from the Global Ocean Simulations with the Baringer-Price-Yang Marginal Sea Boundary Condition Model Wanli Wu, William Large and Gokhan.
Lesson 7: Ocean Layers II Physical Oceanography
Josh Kohut1, Elias Hunter1, and Bruce Huber2
Spatial Modes of Salinity and Temperature Comparison with PDO index
Erin McCabe Alison Gray, Keith Rodgers, Ping Zhai
with contributions from Jan Aure, Roald Sætre and Didrik Danielssen
The coupling between Atlantic inflow and overflow in the Iceland-Scotland region Bogi Hansen, Karin M. H. Larsen, Hjálmar Hátún, Svein Østerhus, Steffen.
Linear and non-linear properties
Lesson 7: Ocean Layers II Physical Oceanography
Lecture Fluids.
Estimating ocean-shelf flux and exchange with drifters
Presentation transcript:

A Report of Data and Preliminary Analysis from Discovery 247 A Process Study of the Faroe Bank Channel Overflow by James F. Price, WHOI and the scientific part of D247 sponsored by the National Science Foundation May, 2006 additional, associated files stored in WHOAS include 1) the complete set of CTD section plots from this cruise (only a small fraction of the total can be shown here) 2) the archive of the station data, XCP, LADCP, CTD and nutrients

Discovery 247; Snapshots of the Faroe Bank Channel Overflow By Jim Price, WHOI, and the science party of Discovery 247, Tom Sanford, James Girton and John Dunlap, APL/UofW, Cecilie Mauritzen, Dan Torres, George Tupper, Deb West-Mack and Dicky Allison, WHOI, and Mark Prater, URI. Our thanks to Cpt Robin Plumley and the crew of RRS Discovery, to Jeff Benson and the UKOR technical staff and the CTD crew, Liz Hawker, Peter Huybers, Patricia Kassis, Heather Deese, Avon Russell and Laura Cornick. Supported by the US National Science Foundation and the US Office of Naval Research.

Faroe-Shetland Trough Wyville-Thomson Ridge Faroe-Bank Channel

Longitude Latitude A,2 B,2 C D,4 E F,3 G,2 H,2 I section name, repeats 220 CTD/LADCP 105 XCP 17 sections RRS Discovery 247

sill

The following two slides show a sample of the data collected at most stations: 1) CTD cast, including oxygen concentration 2) LADCP velocity at every CTD station (less one) 3) XCP velocity at about half of the CTD stations, mostly those west of the FBC sill.

FBC overflow N Atlantic inflow

The next three slides show a synthetic section along the axis of the overflow current.

The following sequence of seven slides shows potential temperature sections made from section A, well upstream of the sill, to section H, which is well west of the sill. Notice the thin black line that marks the approx upper limit of the dense water at section A, and kept at that level on subsequent slides. The same is done for the left side of the dense water by a small arrow. Notice how the dense water descends the topography downstream of the sill, especially.

The next slide shows total transport, the directly measured, outflowing transport of water colder than 6 C; source transport is the inferred transport of source water, inferred from the changing T/S relation (several slides hence). Notice that source transport shows no particular trend with distance downstream, but considerable variability. Total transport clearly increases downstream, but also varies significantly.

total transport, Q source transport, Qs sill outflowing

The next slide shows the downstream evolution of the transport-weighted potential temperature and salinity. Notice that temperature increases, consistent with entrainment of warmer Atlantic water by the overflow, while salinity increases, also due to entrainment of more saline Atlantic water.

sill

The next two slides show the transport weighted T and S, one point per section, on a T/S diagram. The presumed endpoints are in the source water and the Atlantic water above the overflow. The second slide shows the inferred fraction of entrained Atlantic water, phi; phi = 0 is none, phi = 1/2 indicates the overflow is 50% source water and 50% Atlantic water as a function of distance downstream and of source water transport.

Reykjanes Ridge climatology d L

Typical profiles from the core of the overflow current and just downstream of the sill. These data were used to estimate a bulk Froude number, Fr.

h T ocn T (x)

The next two slides develop a simple model of an entraining (and broadening) density current, and in the second slide compares this with the observed phi.

Bottom stress, estimated by fitting a log layer to the deepest 10 m of each XCP profile.

the local, boundary layer effect: Bottom stress causes a significant shear in a bottom (Ekman) layer of O(50 m) thickness at section G; Current speeds are otherwise nearly geostrophic.

this view is from the NW ctd D2 this view is from the SE

The next four slides show repeated sections run near the sill in Faroe Bank Channel. The thickness of the overflow layer and the transport of source water varies substantially, but the structure of the current, including the relative vorticity of the current, are not highly variable.

D1 D4 D3 D2

The next five slides show repeated hydrographic sections. Notice that there is substantial variation in the thickness of the overflow water layer.

The next seven slides show current and density measured on a single occupation of the sill section, D.

FBC Overflow; descent from the sill The topography opens up dramatically beyond the FBC narrows, and the overflow spreads out as width/distance ~ 0.6 as it descended the ISR slope and entrained overlying NAW. Bottom stress was significant, 1-2 Pa, and the Ekman number ~ 0.12 based upon stress or ~ 0.15 based upon descent rate. There was only modest veering in the bottom Ekman layer so that spreading appeared to be largely barotropic. The bottom and interfacial boundary layers began to merge, and mixing/entrainment and dissipation were important in the property and Bernoulli balances. Current speed was approximately geostrophic. -4. Froude numbers in the core of the current were , though smaller values can be found. The estimated entrainment rate and Fr are not inconsistent with a putative entrainment law, E(Fr). There is significant entrainment, E = We/U ~ 5x Froude numbers in the core of the current were , though smaller values can be found. The estimated entrainment rate and Fr are not inconsistent with a putative entrainment law, E(Fr). The net entrainment shows a significant sensitivity to source transport, being reduced when source transport was increased. Inference from a very simple model is that a primary process driving the overflow toward larger Fr is the spreading of the current. What’s missing? The entrainment law, E(Fr), is itself in need of an explanation. The FBC would be an excellent site for a detailed study of turbulent entrainment, but, what would constitute an answer? Is a layered formulation of mixing sufficient? The effect of bottom bed forms on bottom stress and mixing is potentially large but not known here, or generally.

FBC Overflow; exchange The mean transport of source water was 1.8 Sv, computed over 15 sections, and about as expected from previous studies. Bernoulli conservation suggests that the approach flow is on the left side Faroe-Shetland Trough. Relative vorticity was well-measured at the sill and was approx –f/5, suggesting not much squashing. There is some hint of partial blocking in the deepest part of the approach flow. (Note that PV and Bernoulli are likely not conserved strictly due to bottom drag.) The variability of transport was approx +- 50%, and somewhat larger than expected. The time scale of transport variability was roughly 10 days, but not well-observed here. The mode of transport variability is that the overflow thickness near the sill varied from a minimum of 250 m to a maximum of 500 m. Thickness variation persists well downstream of the sill. What’s missing? The connection to the upstream reservoir -- even the Faroe Shetland Trough -- is not clear in this data set. Averaged or typical values of upstream depth give excessive exchange, as found before. The mechanism or cause of the variability in the exchange is unknown. What is the effect of overflow across Wyville- Thomson Ridge ? Is there an influence of the highly variable, upper layer inflow?