SCUDDiagnostic Surface Currents SCUD

and application to marine debris

Hydrodynamics of Marine Debris workshop

5IMDC – 20 March 2011 Honolulu, Hawaii

Jan Hafner and Nikolai Maximenko

jhafner@hawaii.edu, maximenk@hawaii.edu

IPRC/SOEST University of Hawaii

Outline Motivation Methodology Data Model formulation Application to Marine Debris Future

Motivation 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

JAMSTEC

NOAA sponsoring IPRC

Our direct motivation is from applications on marine debris

Methodology

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)

DATA Drifter data: AOML - Atlantic Oceanographic and

Meteorological Laboratory www.aoml.noaa.gov 8058 drifters, drogued at 15m from 1979 till 2008, interpolated on 6 hourly

intervals

DATAAVISO mean sea level anomaly maps: 1/3 degree maps, merged product (up 4 satellites), weekly time frequency, starting Oct. 1992 (www.aviso.oceanobs.com)

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, (www.ssmi.com)

Formulation of the diagnostic model

USCUD

(x,y,t) = U

0 + u

hx⋅∇

xh(x,y,t) + u

hy ⋅ ∇

yh(x,y,t) + u

wxwx(x,y,t) + ⋅ u

wywy(x,y,t)⋅

And similarly

VSCUD

(x,y,t) = V

0 + v

hx⋅∇

xh(x,y,t) + v

hy ⋅ ∇

yh(x,y,t) + v

wxwx(x,y,t) +⋅ v

wywy(x,y,t)⋅

Where: USCUD

, VSCUD

- modeled ocean current components U

0 , V

0 - constant coefficient (mean)

h - sea level anomaly

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

u

hx, u

hy , u

wx , u

wy - U component coefficients corresponding to

sea level gradient and surface wind (function of x and y only) v

hx, v

hy , v

wx , v

wy - 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).

RESULTS

RESULTSLocal Scale

Numerical Experiment: SCUD currents applied on ocean tracers released daily from coast and weighted by coastal populationcount

Where the marine debris goes?How it gets there ?

SCUD application on marine debris transport and convergence

Animation of tracer transport by SCUD currents

Structure of SCUD tracers “patches”

SCUD model application on marine debris

What model cannot do: prediction vertical structure of marine debris coastal processes – emission and

deposition of marine debris

What model can do: zones of convergencestructure of the patchestrajectories = pathways

Future – what is needed

Thank you

1. operational SCUD product requires QSCAT to be replaced with ASCAT winds2. global inventory of marine debris sources and sinks

in the ocean and onshore is needed3. effect of vertical mixing on floating debris needs to be included in the model4. coastal dynamical processes, esp. high frequency and debris deposition processes, need to be considered in the model5. validation of SCUD model results by in situ data needed

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 U

SCUD

and 0.107 m/s for VSCUD

)

Relative misfit to the drifters' dataRatio of cost function and drifters' R.M.Ss. 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 :

http://apdrc.soest.hawaii.edu/projects/SCUD/

LAS, LAS7, OpeNDAP, DChart SCUD manual :

http://apdrc.soest.hawaii.edu/projects/SCUD/SCUD_manual_02_17.pdf

SCUD users listserver: http://apdrc.soest.hawaii.edu/projects/SCUD/registration.html

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).

Statistics

R.M.S. of modeled velocities related to sea level (m/s)

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