Download - Assimilation opérationnelle et analyse de données glider 2) gliders et etudes de processus 1) donnees in-situ gliders ???

assimilation opérationnelle

et analyse de données “glider”

2) gliders et etudes de processus

1) donnees in-situ gliders

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Assimilation de données « glider »1) Premiers essais et assimilation des donnees gliders « routiniere » dans le cadre

de projet d'oceanographie operationnelle:

Projets europeens MFSTEP (2004-2005) et MERSEA (2006-2008) IFM-GEOMAR, LPO et IMEDEA

2) Experience specifique d'assimilation de donnees glider dans le cadre de MFSTEPINGV, IFM-GEOMAR, SIODobricic et al. (2010)

3) Specificites des donnes gliders (action LEFE-Assim) LOCEAN

- simulateur de glider dans un OGCM, L'Heveder et al (2009 & in prep)- assimilation « lagrangienne » Taillandier et al (2009)

Coriolis ftp server

Data Access

http://www.ifm.uni-kiel.de/fb/fb1/po2/research/mersea/gliders/spray004_position.html

http://www.coriolis.eu.org/cdc/dataSelection/cdcDataSelections.asp

Mersea In-Situ Portaldata visualization

Coriolis data selection websitedata visualization and download

Quality Control and Metadata

QC procedures at Coriolis like for profiling floats. Profiles are considered as vertical.

- T and S outsiders based on historical data- Density inversions

are rejected

+ visual inspection

Metadata:Vehicle name, project, PIWaypoint (heading)Angle of ascent/descentTarget depthClimb depthTarget altitudeTime between surfacingCurrent correction

Dive #260 – “dirt“ in the conductivity cell (1/400)

Assimilation of glider data

Temperature differences between MERCATOR North Atlantic 1/15° and the

in-situ observations

Before data assimilation

After data assimilation

glider

The model trajectory is modified by the data assimilation process,

to better fit the observations.

development required to better assimilate in-situ data

at the moment: correlation criteria for profiling floats

1 profile per 1°x1° per week>> in progress

Assimilation de données glider en mer Ionienne (MFSTEP)

Assimilation des donnees TS et courants moyens (derive residuelle)


Daily averaged vertical profiles along the path of theglider for the period October-December 2004.

- Upper panel: glider observations, averaged daily;

- Middle panel: control daily analyses.

- Lower panel: glider assimilation analyses.

temperature salinity


Temperature de surface avec et sans assimilation de donnees glider

Meilleure representation de l'ecoulement a meso-echelle


« Impact a grande echelle des donnees glider »

Daily averaged sea level differences between glider and controlexperiments (cm).

The differences are shown at the end of each of six monthsfollowing the introduction of glider observations.


Simulateur de gliders dans MERCATOR

Modele de « vol » quasi-statique


Specificites des donnees glider pour l'assimilationhaute resolution et caractere lagrangien

Tous les 2 jours données (TS, dr) gliders. ces perturbations sont propagées dans le champ de courant géostrophique associé.

Après trois mois d’analyse: champ de masse 4D, Des structures de moyenne échelle apparaissent le long de la côte continentale, bordant un dôme d’eau dense qui couvre la partie centrale du bassin. Ces structures documentent les fluctuations du jet géostrophique porté en bordure de ce réservoir d’eau dense.

Structures de grande échelle et de moyenne échelle caractéristiques de la circulation hivernale sur cette façade nord Méditerranéenne mieux representées grace au réseau de surveillance gliders mis en place lors de la campagne EGO2008.

analyse séquentielle d’états géostrophiques successifs à partir des gradients de densité,

et indirectement déduits à partir de la dérive résiduelle dans la direction normale du transect.

L ≈ 20kmto – 2d

to + 2d

to + 4d

to

VGlider ≈ 25km/d moyenne et la variance à 150m de la salinité.

RECONSTRUCTION A PARTIR DES DONNEES IN-SITU EGO2008RECONSTRUCTION A PARTIR DES DONNEES IN-SITU EGO2008

To be continued...

Analyse de donnees « glider »

Exemple de l'experience glider Vocals-Peru:

« Caracterisation de circulations de submesoechelle dans le systeme d'upwelling du Perou »

Pietri et al. (in prep)

Peruvian Upwelling

VOCALS: Ocean-Cloud-Atmoshpere-Land-Study on the Southeast Pacific Climate System

VOCALS-Rex-Peru:

International multidisciplinary

field experiment (CTD and

ADCP - 15 days )

Meso-scale sampling

2 months glider's deployment

for the fisrt time in this region.

Vertical Sections

9 sections

100km

200m

~ 5 days

DENSITY

SALINITY

OXYGEN

FLUORESCENCE

TURBIDITY

TEMPERATURE

(a)

(a)

(b)

(b)

Salinity Stripes

t /rho

Ekman transport, advect surface water offshore:

~ 0.2 Sv

Salinity Stripes

vek

~ 0.1 m/s

t /rho


~ 0.1 m/s~ 0.2 Sv

δek

~ 20m

To compensate, a subsurface coastward current appears:

Vreturn

= Vek

~ 0.01m/s ~ 1km/day

Salinity Stripes

vek

~ 0.1 m/s

t /rho


~ 0.1 m/s~ 0.2 Sv

δreturn

~ 200mv

return ~ 0.01 m/s

δek

~ 20m

δek

δreturn

Salinity Stripes

Salinity Stripes

~ 5km in 4 days

Salinity Stripes

Propagation towards the shore ~ 1.5 cm/s

evidence of vertical motion:

Quasi vertical stripes of high and

low salinity.

High fluorescence and turbidity

up to 70m deep.

Vertical motion

Mixing phenomenum creating

cross isopycnal stripes Scale of the phenomenum: 25-

30km

Other mechanism (Thomas and Lee, 2005):

Advection of surface dense coastal water

Destabilization of the water column -> wind driven buoyancy flux

Mixing by convection -> ageostrophic secondary circulations

Thomas and Lee (2005)

Vertical motion

Density filter:

Weighted moving average (15km*2m)

Elimination of ageostrophic process

«Absolute» geostrophic velocities

Estimates of absolute géostrophic currents:

Smoothed density gradient

Thermal wind relation:

Glider mean current (integrated on the water column) used as a reference


Perpendicular projection of the "glider"

mean current.

Filter: moving average on a 45h period

Glider

section 2 (form October 08th to 12th)

(cm/s)


(m/s)Humboldt Current: Nothward (Equator)

Maximum speed: 30 cm/s

Peru Chili Undercurrent: Situated above the continental slope Southward (Pole) Maximum speed on the section: 15 cm/s

ADCP onboard R/V Jose Olaya

on the same section (October 12th)

Ageostrophic secondary circulation

Two-dimensional Potential Vorticity:

Negative PV at the front:

Strong vertical shear

Horizontal density gradient

Cross-front width :

~ 30 km

-> coherent with the scale of the

salinity stripes

vertical circulation:

subduction on the dense side of the

front

upwelling along the frontal interface

Meridional feature

du 14 au 16 Novembre 200km long filament

meridional phenomenum

crossed by the glider

Observational evidence of circulation features

- Observation of the upwelling front at very high resolution (200m horiz, 5 days, 100km sections)

with physical and biogeochemical parameters.

- Estimates of absolutes geostrophic currentsSurface current: umax ~20 cm/s, L~40km, z~100m

Under current: umax~15 cm/s,L>50km, z>150m

- Evidence of a return flow

- Evidence of vertical motion at submesoscale wind driven ageostrophic secondary circulations.

Conclusions

Oceanographie operationelle &

gliders

– Chaine deja operationnelle &

benefice certain (repetitivite

des mesures)

– Couverture deja globale

(Testor et al., OceanObs09)

– sous-exploite pour les modeles

'globaux'

– Ideal pour les modeles

regionaux/cotiers a haute

resolution

Etudes de processus

– outil de mesure a haute resolution spatiale et

temporelle.

– Vision verticale de la colonne d'eau

– Flotille → 3D

observer & comprendre