sea level variability in the kuroshio extension ...os45g-08 sea level variability in the kuroshio...
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OS45G-08SEA LEVEL VARIABILITY IN THE KUROSHIO EXTENSION: STERIC AND NONSEA LEVEL VARIABILITY IN THE KUROSHIO EXTENSION: STERIC AND NONSEA LEVEL VARIABILITY IN THE KUROSHIO EXTENSION: STERIC AND NON---STERIC COMPONENTSSTERIC COMPONENTSSTERIC COMPONENTS
D. Randolph Watts*, Karen L. Tracey, and Kathleen A. Donohue Graduate School of Oceanography, University of Rhode Island, 215 South Ferry Road, Narragansett, RI 02882
KESS Observing Array
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175
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Yokohama
CPIES
Profiler/ADCP/CM
Ferry XBT/ADCP
Profiling Float Deployments
KEO
Feature Survey
136°E 138°E 140°E 142°E 144°E 146°E 148°E 150°E 152°E29°N
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May to September 2004 a series of rapid, eastward propagating (25-30 km/d) meanders were observed by the CPIES.
PROBLEM 1: MESOSCALE FEATURES ALIAS SATELLITE SSH
Non-steric (deep barotropic) eddies contribute independently to local SSH with different (x,y,t) dependence than the steric (baroclinic) component.
Cases (a) and (b) show the joint baroclinic and barotropic features are more developed than just the baroclinic meanders.
Because satellite SSH is only a single measurement the barotropic and baroclinic contributions cannot be separated to identify their independent dynamical roles.
If SSH were interpreted solely as steric height or heat content, examples (a) and (b) would overestimate the baroclinic signal by ~25%.
DATA COLLECTION VIAACOUSTIC TELEMETRY
One year of daily measurements of travel time, pressure, and current were telemetered from the CPIES to the ship.
The CPIES remain on the sea floor for recovery later in 2006.
Geopotential height is determined from travel time vialook-up tables.
SSH COMPRISES STERIC AND NON-STERIC PARTS
Sea Surface Height (η)η = Φ⁄g + P⁄ρgwhereΦ = Geopotential Height
(0 re 5000 dbar)
g = GravityP = Bottom Pressureρ = Density
Φ⁄g(m)
Ρ⁄ρg(m)
η(m)
ση (std dev)
(m)Kuroshio Jet 1.3 0.5 1.7 0.2
Quiet Intervals 0.3 0.2 0.4 0.1
Meanders & Rings 1.0 0.3 1.2 0.15
These short wavelength (160 km) meanders were not resolved by satellite SSH.
SATELLITES MONITOR THE LARGE SCALE, SLOWLY CHANGING SSH FIELD
Largest differences between in situ and satellite SSH maps occurred along jet axis during this period.
Steric and non-steric parts have similar amplitudes but different processes and different spectra
GOAL of KESS: Identify the dynamic and thermodynamic processes governing the variability of the Kuroshio Extension and the recirculation gyre and their interactions. MEASURE: Time-varying density and velocity fields. DETERMINE: Dynamical balances and exchanges of heat, salt, momentum and potential vorticity.
KUROSHIO EXTENSION SYSTEM STUDYKESS Observing Array
200
175
150
Yokohama
CPIES
Profiler/ADCP/CM
Ferry XBT/ADCP
Profiling Float Deployments
KEO
Feature Survey
136°E 138°E 140°E 142°E 144°E 146°E 148°E 150°E 152°E29°N
30°N
31°N
32°N
33°N
34°N
35°N
36°N
37°N
38°N
39°N
Bottom pressures at 42 sites exhibit common fluctuations Pcom~0.035 dbar, likely driven by the atmosphere. Note this is NOT an isostatic response.
With periods of 2-20 days, these fluctuations alias the satellite SSH maps created from measurements with Nyquist period 20-34 days. The different elevations along neighboring or crossing groundtrackscause mapping errors.
Spectrum shows that more than half the (Pcom/ρg) variance,~ 1.7 cm, is aliased for ERS 17d sampling interval.
This should NOT be interpreted as steric signal.
PROBLEM 2: COMMON MODE OSCILLATIONS ALIAS SATELLITE SSH MAPS, CREATE ‘TRACKINESS’
Good agreement is often observed between the in situ(color; red = high SSH, blue = low SSH) and AVISO merged satellite SSH (contours).
But problems (next panel) arise when satellite SSH is interpreted solely as steric signal…
SATELLITES MONITOR THE LARGE SCALE, SLOWLY CHANGING SSH FIELD
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29 MAY 2005
BT (cm)
143oE 144oE 145oE 146oE 147oE 148oE 149oE
30oN
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BCBC+BT
−20 0 20
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8 DEC 2004
BT (cm)
143oE 144oE 145oE 146oE 147oE 148oE 149oE
30oN
32oN
34oN
36oN
38oN
BCBC+BT
−20 0 20
PROBLEM 3: IMPORTANT FRACTION OF TOTAL SSH CONTRIBUTED BY NON-STERIC COMPONENT
(b)(a)