globcurrent: advancing the estimation of surface current...

GlobCurrent: Advancing the estimation of surface current

from space

A ESA funded project under DUE up to December 2016

UCM, PML, Plymouth, UK, 12-13 November 2014


The Team Nansen Center J.A. Johannessen, R. Danielson, A. Korosov, R. Raj, M. Hansen Ifremer B. Chapron, J.-F. Piollé PML G. Quartly, M. Warren, P. Miller CLS M.-H. Rio, G. Larnicol, S. Labroue isardSAT C. Martin-Puig, M. Roca, R. Escola ODL F. Collard Univ. of Exeter J. Shutler

• To advance the quantitative estimation of ocean surface currents from satellite sensor synergy that combines altimetry (both conventional and SAR mode), gravimetry, SAR, scatterometry, optical (VIS and TIR) and passive microwaves.

• In so doing the project will demonstrate impact in user-led scientific, operational and commercial applications that, in turn, is expected to increase the uptake of satellite measurements.


The main goal

An initial depiction of the Gulf Stream (circulated by Benjamin Franklin, circa 1770)


Map of global surface current features and eddies obtained from a high-resolution 1/10th degree ocean model (courtesy R. Ferrari).

CAN THIS BE ADEQUATELY VALIDATED??


Partly similar structure in the monthly mean SST gradients and SSH gradients (anomalies)


IR OC Sun Glint Alt SAR Scatt PMW Gravity

RANGE OF TWO DIMENSIONAL SURFACE EXPRESSIONS WHICH OFTEN HAVE ONE THING IN COMMON – NOTABLY RELATED TO UPPER

OCEAN DYNAMICS

SST Chl. Anomaly Sea level Sea state Windvector Windspeed Geoid distri. reflected surface current curl stress SST Mean dyn. light geostrophic SSS topography current

Satellite Sensor Synergy

Optical, Microwaves (passive, radars), Accelerometers

Meandering fronts and eddies, filaments, spirals, convergence (downwelling) – divergence (upwelling),

Langmuir circulation, deformation, shear, rotation



The Work Breakdown Task 1: Federate the international user producer community for ocean surface

Task 2: Undertake research and development activities to define, evolve, and maintain Algorithm Theoretical Baseline Descriptions and validate the performance of each algorithm.

Task 3: Define and document a Technical Specification for each GlobCurrent system elements and products that shall be implemented in Task 4.

Task 4: Implement, qualify and accept each successive version of the GlobCurrent system and operate each system to produce the required outputs.

Task 5: Define, plan and implement user-led application case studies (e.g. assimilation by ocean modelling systems, sub-mesoscale and mesoscale OSC dynamics, ship- routing, renewable energy sector etc).

Task 6: Deliver the GlobCurrent final report and close out the contract.

Task 7: Management of the GlobCurrent Project.


U S E R

G R O U P


S C I E N C E

T E A M

THE SURFACE CURRENT PRODUCTS

• the Geostrophic Current induced by the balance between the surface pressure and the Coriolis force resulting from the rotation of the Earth (Altimetry + GOCE MDT); SPATIAL Scale: Rossby Def. Rad (30-100 KM); TEMPORAL SCALE: 10-100 days


• The motion is Eulerian


Surface geostrophic current is directed parallel to the isobars, with the high (low) pressure to the right of the flow in the Northern Hemisphere (Southern Hemisphere) .


Surface geostrophic current in an eddy.


Surface Geostrophic Current 1 September 2012 at 0000


• the Ekman Current that is set-up by the wind field (SAR and SCATT);

SPATIAL Scales: Dominated by the near pressure field (e.g.500-1000 km); TEMPORAL Scales: 1- 3 days; Special conditions near coast wrt sea breeze




Current profile in the upper layer induced by the Ekman spiral.


Surface

15m

EKMAN CURRENT 1 September 2012 at 0000


• the Stokes drift which is predominantly wind and wave driven (SAR and SCATT);

SPATIAL Scales: Dominated by the near pressure field (e.g.500-1000 km) but strongly modified by fetch; TEMPORAL Scales: 1-3 days


• The motion is Lagrangian


Modification of the classical Ekman induced current spiral by Stokes drift.

Usf: filtered Stokes drift UE: Eulerian current (upper 2 m) UR: HF-radar detected current


Stokes drift 1 September 2012 at 0000


• the Tidal Current that results from the gravitational forces exerted on the ocean by the moon and the sun (temporal resolution very demanding for space remote sensing – HF-radars will do);




Tidal current 1 September 2012 at 0000


http://web.nersc.no/globcurrent/

ONLINE UCM/USER FEEDBACK

http://web.nersc.no/globcurrent/�


• the Ageostrophic Current connected with the deformation of the flow field such as surface divergence and/or convergence along fronts, eddies and associated with formation of Langmuir circulation (SAR and IR, PMR);

SPATIAL Scales: from hundred of meters to 10 km; TEMPORAL Scales: 1-3 days




Surface Signatures of Coupled Eddies (Kudryavtsev et al., 2012)

SST DIV

MSS SAR


Courtesy Isern-Fontanet


Annual range Doppler mean over Agulhas and Gulf stream using ASAR Wide swath ascending tracks


SUMMARY The GlobCurrent project has emerged to the first release of data products. They are global and interpolated to a 10-km grid at 3-hour intervals and cover 3 years from 2010 to 2012. They include: - Surface geostrophic current - Surface and 15-m Ekman current - Stokes drift - Tidal current (from Flather model) They can be downloaded from www.globcurrent.org/products-data. Currently only 1 month of data, but will shortly be extended to the full 3–year data set, except the tidal current

http://www.globcurrent.org/products-data�


Characteristic features and processes that influence the upper ocean current.

turbulent mixing in the vertical

Stokes drift and wave breaking


Characterization of the spatial and temporal scales of ocean dynamics (after Chelton, 2001).


(top) Surface currents derived from altimeter SSHs and microwave SSTs (right) Associated temperature gradient norms within the Agulhas return current on January 1, 2004.


An example GlobCurrent SMOS SSS (color) together with surface geostrophic currents from altimetry integrated over the period 1 to 15 July 2012. Spatial resolution is about 25 km.

SYNTOOL animation starts with SST/altimeter streamline then SSS/altimeter streamline

Summary • Satellite sensor synergy clearly strengthen the opportunity to study 2D

surface expressions of dynamic features in the upper ocean

• SQG provides a way to estimate 3-D velocity fields from surface temperature (and salinity) fields (proxy for density) at > 30-100 km

• Interaction of Ekman and QG yield estimates of surface divergence fields at ~ 10 km

• Relationship between SAR based sea surface roughness field (and sunglint mss), radiometer based SST and SSS fields and high resolution altimetry based SSH field should be more consistently investigated at ~ 1 – 10 km.

• The possibility to go from 2D surface expressions to upper layer 3D dynamics would become highly valuable for complementary high resolution (order 1- 10 km) model validation and assimilation.

• Importance of air-sea interactions must be included in this approach And not to forget – High quality In-situ data NEEDED! EGU General Assembly, Vienna, Austria, 27 April – 2 May 2014

globcurrent: advancing the estimation of surface current...

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