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SCUD. Diagnostic Surface Currents SCUD and application to marine debris. Jan Hafner and Nikolai Maximenko, IPRC/SOEST University of Hawaii. Hydrodynamics of Marine Debris workshop 5IMDC – 20 March 2011 Honolulu, Hawaii. Outline . Motivation

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Diagnostic Surface Currents SCUD

and application to marine debris

Jan Hafner and Nikolai Maximenko,

IPRC/SOEST University of Hawaii

Hydrodynamics of Marine Debris


5IMDC – 20 March 2011 Honolulu, Hawaii



  • Motivation

  • Methodology

  • Data

  • Model formulation

  • Application to Marine Debris

  • Future



  • Ocean Surface Currents – important factor in marine debris problem

  • Direct measurements difficult – few in situ observations

  • Utilize satellite data to arrive with surface ocean currents

  • supported by the following agencies:

  • NASA Physical Oceanography Program (Ocean Surface Topography Science Team)

  • US National Fish and Wildlife Foundation


  • NOAA sponsoring IPRC

  • Our direct motivation is from applications on marine debris



  • Task: to develop a simple diagnostic model of surface ocean currents to fit drifters' trajectories

  • Input parameters: AVISO sea level anomaly (geostrophic current component)‏

  • Ocean surface wind data: daily QSCAT – wind driven current component ( Ekman)‏



  • Drifter data: AOML - Atlantic Oceanographic and Meteorological Laboratory

  • 8058 drifters, drogued at 15m

  • from 1979 till 2008, interpolated on 6 hourly intervals



  • AVISO mean sea level anomaly maps: 1/3 degree maps, merged product (up 4 satellites), weekly time frequency, starting Oct. 1992 (‏

  • MDOT - Mean Dynamic Ocean Topography, developed by Maximenko et al. (2009), ½ degree map produced using combined drifters, sea altimetry, GRACE and surface wind data, 1992-2002.

  • QSCAT 3-day moving averages of surface winds (10 m), ¼ degree daily maps July 1999 – November 2009, (


Formulation of the diagnostic model

USCUD(x,y,t) =

U0 + uhx⋅∇xh(x,y,t) + uhy⋅ ∇yh(x,y,t) + uwx⋅wx(x,y,t) + uwy⋅wy(x,y,t)‏

And similarly

VSCUD(x,y,t) =

V0 + vhx⋅∇xh(x,y,t) + vhy⋅ ∇yh(x,y,t) + vwx⋅wx(x,y,t) + vwy⋅wy(x,y,t)‏

Where: USCUD , VSCUD- modeled ocean current components

U0 , V0 - constant coefficient (mean)‏

h - sea level anomaly

wx, wy U and V component of surface wind (QSCAT)

uhx, uhy , uwx , uwy - U component coefficients corresponding to sea level gradient and surface wind (function of x and y only)‏

vhx, vhy , vwx , vwy- similarly corresponding V component coefficients


Formulation of the diagnostic model

The coefficients are solved by minimizing the cost function:

Fcost=Σ[(Udrifter ‐ USCUD)2 + (Vdrifter ‐ VSCUD)2]

where the summation is over all drifters' data in a given lat/lon box (total 5,700,000 6-hourly data points).



Local Scale


SCUD application on marine debris

transport and convergence

Where the marine debris goes?

How it gets there ?

Numerical Experiment: SCUD currents

applied on ocean tracers released daily

from coast and weighted by coastal population



SCUD model application on marine debris

What model can do:

zones of convergence

structure of the patches

trajectories = pathways

What model cannot do:


vertical structure of marine debris

coastal processes – emission and deposition of marine debris


Future – what is needed

1. operational SCUD product requires QSCAT to be replaced

with ASCAT winds

2. global inventory of marine debris sources and sinks

in the ocean and onshore is needed

3. effect of vertical mixing on floating debris needs to be

included in the model

4. coastal dynamical processes, esp. high frequency and debris

deposition processes, need to be considered in the model

5. validation of SCUD model results by in situ data needed

Thank you


Data preprocessing

  • AVISO, MDOT and QSCAT wind data were interpolated on times and locations of 6-hourly drifters' data

  • Filtering out high frequency signal by Hanning cosine filter with halfwidth = inertial frequency, minimum frq. ~ 3 days (9°37' lat.)‏


Fit to the data

Absolute misfit to drifters' data

R.M.S. of cost function (m/s)‏

Global average misfit : 0.162 m/s

(0.118 m/s for USCUD

and 0.107 m/s for VSCUD)‏

Relative misfit to the drifters' data

Ratio of cost function and drifters'


Global average : 0.566

(0.541 and 0.653, for U and V components respectively)‏


Data and Access

  • ¼ degree surface currents maps: daily from 01Aug1999 till 19Nov2009 (span of QSCAT data)‏

  • SCUD dataset is open for free unrestricted use and distribution

  • Disseminated by APDRC servers :


  • LAS, LAS7, OpeNDAP, DChart

  • SCUD manual :

  • SCUD users listserver:


From S.Pacific ST gyre

To S.Pacific ST gyre

From N.Pacific ST gyre

To N.Pacific ST gyre

From Hawaii

To Hawaii

Trajectories of real drifter starting from (left column) and ending in (right column) the South Pacific (top row), North Pacific (middle row), and Hawaii (bottom row).



R.M.S. of modeled velocities related to

sea level (m/s)

R.M.S. of modeled velocities related to surface winds (m/s)