resolving surface currents and heat advection with the global drifter array

Rick LumpkinAtlantic Oceanographic and Meteorological Laboratory,

National Oceanic and Atmospheric AdministrationAtlantic Oceanographic and Meteorological Laboratory,

National Oceanic and Atmospheric Administration

NOAA Climate Observation Program3rd Annual System Review

April 25-27, 2005

Resolving Surface Currents and Heat Advection with the Global Drifter Array

Resolving Surface Currents and Heat Advection with the Global Drifter Array

1. What we can resolve1. What we can resolve

Time-mean currents75% of 1°1°bins!

Seasonal variations of SSTSeasonal variations of SST

Differences with satellite SST productsDifferences with satellite SST products

Differences with satellite SST productsDifferences with satellite SST products

Mean heat advectionMean heat advectionSST gradient (°C per degree)

Mean heat advection, upper 30m (W/m2)

Advection of SST anomaliesAdvection of SST anomalies

W/m

2

Anomalous heat advection, upper 30m (W/m2)

Surface current anomaliesSurface current anomalies

378 drogued

2. What we aren’t resolving2. What we aren’t resolving

(Drifters alone: any process happening in data gaps)

Eddy fluxes and anomalous advection of mean SSTEddy fluxes and anomalous advection of mean SST

Evaluating the drifter arrayEvaluating the drifter array

SURFACE CURRENTSAccuracy: 2 cm/sResolution: 600 kmNumber of measurements per month: 1

From Needler et al. 1999: Action plan for GOOS/GCOS and Sustained Observations for CLIVAR.

SST: GOOS evaluated by NOAA/NCDCSST: GOOS evaluated by NOAA/NCDC

Evaluating the drifter array

Before and after

3. How can we improve?3. How can we improve?

Predicting the arrayPredicting the array

Predicting the arrayPredicting the array

Include information from other measurements (altimetry, winds)Include information from other

measurements (altimetry, winds)

OSCARPilot project for a NOAA/NESDIS Operational Surface Current Processing and Data Center(F. Bonjean, J. Gunn, G. Lagerloef, E. Johnson)

Pilot project for a NOAA/NESDIS Operational Surface Current Processing and Data Center(F. Bonjean, J. Gunn, G. Lagerloef, E. Johnson)

170ºE-130ºW, 10ºS-10ºN

AvisoAVISO Altimetry productCollecte Localisation Satellites (CLS)Topex/Poseidon, Jason-1, ERS-1 and ERS-2

AVISO Altimetry productCollecte Localisation Satellites (CLS)Topex/Poseidon, Jason-1, ERS-1 and ERS-2

U(t)=U + A u’(t)

(methodology of Niiler et al., 2003)(methodology of Niiler et al., 2003)

Absolu

te speed (m

/s)

Drifters+wind, altimetryDrifters+wind, altimetry

altimeteraltimeter

large Rossby number flowlarge Rossby number flow

hgfvr

vr

2

(centrifugal) (Coriolis) (Pressure gradient)

L pg Corioliscentrifugal

H Cor pgcentrifugal

If we ignore centrifugal(assume geostrophy), we:

Underestimate Coriolis(underestimate v)

Overestimate Coriolis(overestimate v)

H

L

Drifters: calibrating satellite SSVDrifters: calibrating satellite SSV1

0.5

0

Drifters: in-situ calibration to reduce global bias in satellite SSV

Drifters: in-situ calibration to reduce global bias in satellite SSV

R. Lumpkin and G. Goni, NOAA/AOML

Summary: Global Drifter ArraySummary: Global Drifter Array• What we can resolve:

<U>, <SST>, <U>·<SST>, U(x,t) where coverage is sufficient mean eddy statistics

Drifter SST(x, t): cal/val of satellite products <U>· SST’

• What we can’t resolve:Anything in the “data holes”U(x,t) at sufficient resolution for time series

of eddy fluxes

•What we can do about this:Plan ahead: anticipate gapsSynthesize drifters, winds and altimetry for

operational surface currentsDrifter U(x,t) cal/val of satellite products

Rick.Lumpkin@noaa.gov

fin

Terms in NINO3 region