Collecting and Assimilating Glider Transects in the Levantine Sea

D. Hayes1, P. Testor2 , S. Dobricic3, G. Zodiatis1

1Oceanography Center, University of Cyprus, Nicosia, Cyprus 2LOCEAN-IPSL/CNRS, Universite Pierre et Marie Curie, Paris, France3INGV/CMCC, Bologna, Italy

May-August ‘09 data show Cyprus Eddy

Goal: Accurate description of mean state----> Improve Forecast Accuracy• Method

• Collect high resolution temperature and salinity profiles over long periods in upper 1000 m (gliders)

• Implement glider data assimilation (3DVAR) in operational regional model (CYCOFOS)

• Results:

• Cyprus eddy + Atlantic Water always found (>3/2009 with gliders)

• Assimilation run shows difference from the control run

• Analysis:

• Cyprus Eddy dominates a complex circulation

• Work needed to quantify improvement in forecast

• Conclusions:

• RT glider observations gliders unique: improve ocean forecasts

• Battery-powered, buoyancy-driven

• 25-50 cm/s, 16-45o slope

• CTD, oxygen, fluorescence, optical backscatter, currents

• surface transmit/receive for data and instructions every 5h.

• 1000 m dive capability

Glider description

Photo: A. Hannides

Seaglider description• Low-drag fairing over hull of compressibility ~= seawater

• Lithium batteries, ~6 mo life (4600 km or 650 dives to 1km)

• Iridium satellite phone for data, instruction transfer

• Controlled with file exchange (commands, waypoints, configuration)

Photo: U of Washington

Missions Accomplished• Since March 2009, over 1930

dives (3860 profiles)

• Most to 1000 m

EYE of the LevantineTS properties

• Depth-ave velocity, Max 30 cm/s

• Anti-cyclonic• Radius

~40km• November

2009 to January 2010

• Near Eratosthenes Seamount

EYE of the Levantine (12/2009)• Sampling the warm core Cyprus Eddy• Labs: LOCEAN, LOV (fr), OGS (it), ULB (be), UCY-OC (cy)• Gliders: physical and biogeochemical context for shipborne

measurements

– 6 gliders deployed from Limassol

– 2 profiling floats– 4 surface drifters– shipborne

measurements by CYBO (Cyprus), TARA (French), Merian (German)

EYE of the Levantine (12/2009)• Sampling the warm core Cyprus Eddy• Labs: LOCEAN, LOV (fr), OGS (it), ULB (be), UCY-OC (cy)• Gliders: physical and biogeochemical context for shipborne

measurements

– 6 gliders deployed from Limassol

– 2 profiling floats– 4 surface drifters– shipborne

measurements by CYBO (Cyprus), TARA (French), Merian (German)

• 23 Nov-1 Dec 2009• Salinity (top)• Temperature (mid)• Dissolved Oxygen (bot)• Asymmetric: south

branch of core more focused

EYE of the LevantineGlider (Atalanta)

• 10 stations 4-5 Jan 2010• Dives 170-250 7-31 Jan 2010• Depth-average currents from glider

(1000m) and from ADCP (800m)

0

EYE of the LevantineGlider Comparisons with MS Merian

• 14-22 Jan 2010• Geostrophic Velocity (top) and

ADCP (bottom)

OceanVarDobricic and Pinardi, 2008

• Calculates T and S residuals (model “background” minus observations) at every time step data are present

• After POM, calculates “correction” T and S based on residuals in window (1.5d)

• Applies corrections at the beginning of the next run (20 time steps).

Glider (red) and model (blue) S,T profiles

Difference (black) and correction (green)

8 Dec 2009

Results• Numerical flow “hindcast” simulation: Nov. 2009-April 2010

• Daily update of surface forcing and open boundary conditions

• Quantify the value of 1 glider, vs 6 gliders, vs floats+ships+gliders

• EYE experiment (so far only 0 and 1 completed)

Corrections on S and T at 300 m

8 Dec 2009

Results• Numerical flow “hindcast” simulation: Nov. 2009-April 2010

• Correction to T at 280 m

• Glider positions

• DAILY

Results• EYE experiment assimilating only one glider’s T, S profiles

• Sea surface elevation map at end of simulation: 19 April 2012

Assimilating glider dataNo assimilating

The difference

Discussion• Quantify the value of 1 glider, vs 6 gliders, vs floats+ships+gliders

• EYE experiment (so far only 0 and 1 completed—see difference below)

• See problem at BC

Discussion• Quantify the value of 1 glider, vs 6 gliders, vs floats+ships+gliders

• EYE experiment (so far only 0 and 1 completed—see difference below)

• See problem at BC

Work in ProgressOperational Data Assimilation—TODAY:

Glider mission and simulations: 16 December 2011 to presentAssimilated in CYCOFOS, compared to control run

Work in ProgressOperational Data Assimilation—TODAY:

Salinity at 360 m for control run (L) and D/A run (R) for this WednesdayNeed to quantify the improvement by comparing to independent data

E.G.: SST, XBT, SLA+MDT, cruise CTD/ADCP

Future Work• New FP7 project, GROOM, has

started.

• Goal: to design a European Glider Infrastructure.

• Heavily based on existing, but integrated and improved.’

Photo: TARA Oceans

• Recommend payloads, protocols, operation centers, etc.

• Support policy AND research

• monitoring for parameter ‘X’

• availability for process study ‘Y

Conclusions

• Gliders improve forecasting skill

• Quantifying the improvement is not done yet

• Eastern Levantine highly variable and full of mesoscale: need real time data

Acknowledgements• Funding: FP7-ECOOP, FP7-GROOM,

Cyprus RPF and UCY, TARA/Oceans.

• Colleagues: MFS, U of Athens (ALERMO and Skiron providers)

• Launch/recovery support: Department of Fisheries and Marine Research Photo: A. Hannides