1

Canary Islands eddies

Pablo SangràUniversidad de Las Palmas de G.C.

Outline1. Kinematics

1.1 Initial size and shape1.2 Vertical structure1.3 Evolution

2. Dynamics2.1 Generation mechanisms 2.2 Evolution: a simple advective-diffusive model2.3 Inertial/centrifugal stability

3. Ongoing studies3.1 The Canary Eddies Corridor3.2 ROMS-UCLA modeling 3.3 Physical-biogeochemical coupling

Warm Wake

Eddies

Arístegui et al., 1994

1.1 Initial size and shapeInitial radius: Rd =25 km, island radius

1. Kinematics

• Eddies are initially Rakine like vortex with a core rotating in solid body rotation and a cylindrical shape

Sangrà et al., 2005

0

100

200

300

400

500

Dept

h (m

)

Pot-Temp-Anomaly

0 50 100 150

Distance (Km)

64 65 66 67 68 69 70 71 7272 73 7474 75 76 7777 78 79 80 81 82 83

-16 -15

27

28

6465

6667

6869

7071

7273

7475

7677

7879

8081

8283

center

middle

periphery

Unpublished

Buoys rotating rate

Arïstegu et al., 1994

1.2 Vertical Structure Depth: 300-700 m, NACWTemperature anomalies, 1-2.5°CIsotherms perturbation: 40 -70 mShalow wake, 25 m

6

1.3 Evolution Coherent structures. Can last many monthsInitial rotating rate : 2.5 d (anticyclone), 4.5 d (cyclone)Radius and period increase with time Propagating SW (Canary Current) and West ( β effect)Due to the inertial stability anticyclones rotates faster

Anticyclonic (Sangrà et al., 2005)Cyclonic (Sangrà et al., 2007)

YS (0-35 days)

MS (50-120 days)

DS (150-200 days)

buoy 60buoy 59

buoy 61

days 35-50. A1 C1, A1 + A2

days 85-90. A1 + C1

days 120-150. A1 + AT

• Eddies evolution stages

Young stage: solid body rotation

Mature stage: periphery slowing rotating

Decay stage : small values of rotation rateall over the eddy

Eddy evolves pulsating. May be related withwind/eddy interactions (under study)

Wind

A, W>O

After Martin & Richards, 2001

Anticyclonic (Sangrà et al., 2005)

8

2.1 Generation mechanisms. Topographic and Atmospheric forcing (Jiménez, Sangrà & Mason 2008)

• Topographic forcing

( )( ) HH E

RoA

LUviscosityO

inertyO 2Re ===

Streak lines/isovortity lines for the barotropic QG model Re=250 (Sangrà, 1995)

6040Re −>Shedding when

2. Dynamics

9

• Atmospheric Forcing: Vorticity injection at the island wake

Dynamics: Relative importance of topographic and atmospheric frocing(Jiménez, Sangrà and Mason, 2008),

Dynamics: atmospheric forcing mechanism (Jiménez, Sangrà and Mason, 2008)

Observations: Gran Canaria (Basterretxeaet al., 2002)

10

Generation frequencyObservational evidences topographic/wind forcing

Mooring

Wind shearTides gauges

Winter- Sping 2006

Only topographic forcing can generate eddiesOnly wind is not able to generate eddiesMain mechanism the topographic forcing

• Field experiment on generation mechanisms (Piedeleu et al., in prep.)

0 20 40 60 80 100(k )

0

1

2

3

|ω| (s

-1.1

0-5 )

t=15 d t=50 d t=100 d t=180 d

0 20 40 60 80 100(k )

0

1

2

3

ω (s

-1.1

0-5 )

t=10 dt=30 dt=70 dt=90 d

0 20 40 60 80 100r (km)

0

0.4

0.8

1.2

1.6

2

ω(s

-1.1

0-5 )

t=70 d

t=0 dt=10 dt=30 d

t=100 d

• Stages: diffusion of angular velocity

r=25 kmk=25 ms-2

Anticyclonic Cyclonic

r=30 km k=20 ms-2 r=25 km k=25 ms-2

( )2

21

r

Kr

rru

t r ∂

∂=

∂

∂+

∂

∂ ωωω

2.2 Evolution: a simple advective-diffusive model (Sangràet al., 2007)

Model Model and observations

2.3 Inertial stability of Rankine-like vortex (Sangrà et al., 2007)

( ) 022 ≥ΩΩ=+⎟⎠⎞

⎜⎝⎛

∂∂

++ sbfrrf ωωω

Gent and McWilliams (1986)

Pelegrí et al. (2004)

0 20 40 60 80 100r (km)

-5

0

5

10

15

20

Ω.Ω

sb (

s-2 .1

0-9 )

t=2.5 dt=30 dt=70 dt= 100 d

0 20 40 60 80 100r (km)

0

2

4

6

8

10

Ω.Ω

sb (

s-2 .1

0-9 )

t=1 dt=30 dt=70 dt= 100 d

Tm=2.2 d

Anticyclone Cyclone

Stables anticyclones ⎪w⎪

14

3. 1 The Canary Eddies Corridor. (Sangrà et al., in prep)

SWESTY propagation (R. Pingree, 1996)Anticyclonic Shallow Subtropical Subducting Westward Propagating Eddies

3. Ongoing studies

W20o 19o 18o 17o 16o 15o 14o

buoy 61

N

29o

28o

27o

26o

4.5 km/d

2.7 km/d

4.1 km/d

3.4 km/d

5.6 km/d

0

20

4060

80

100120

140

160

180

199

Altimetry (A. Pascual, 2008, unpublished) and buoys trajectories showing that the eddies corridor is generated by Canary Island flow perturbation

Sangrà et al. (2005)

• Swesties-island generated eddies connection

16

• Altimetry data are quite robust

ADCP and buoy trajectory versus sea surface height and velocities as obtained from altimetry

17

• A Zonal Subtropical Eddies Corridor

19

• Corridor Importance Its a permanent structure not previously describedIt could be one of the major long lived eddies source on the SubtropicalAtlantic

Eddies Age Pyramid for the Canary Corridor

months

Eddies Age Pyramid for the Canary Corridor>3 months

monthsR=A/C

0.91

1.71

2.50

infcyclonesanticycl.

Trajectories Life-span > 6 months

It can be an important structure for the zonal balance and exportingphysical (heat) and biological (Particulate Organic Matter) properties

J98

A1

C1

A2

C2

Chlorophyll (mg m-3)-Alimeter velocity/height

3.2 ROMS-UCLA modeling: Collaboration betweenULPGC and UCLA. Developed mainly by E. Mason

• Objectives

Develop robust multi-year high-resolutionclimatological Canary Basin model solution

Tool to study:• Regional circulation & variability• Canary Island wake and its interaction with theupwelling

• Cape Ghir filament

Grid hierarchy – offline nesting using roms2roms

• Model Domains

• Large Domain Validation

Snapshot of model SST(month 9, year 6)

AVHRR SST(10 August, 2003)

C CF F

• Small Domain validation

• Vertical section: Alongshore velocity/temperature

• Canary Eddies Corridor

3.3 Physical-biogeochemical coupling

• RODA project: Interdisciplinary study of the biological pump inside de eddies:Biogeochemical cycles outside an inside of the eddiesSampling from atmospheric nutrient sources to virus

• Coupling mechanisms

Isotherm/isopicnals/DCM perturbation

Diapicnal mixing

Secondary circulation

Remote advection

0 50 100 150Distance (km )

Depth (m)

14

16

18

20

22T

empe

ratu

re

65 67 69 7172 74 76 78 80 820

50

100

150

200

250

300

Dep

th (m

)

Pot-Temperature

0 50 100 150

Distance (Km)

64 66 68 70 72 74 76 78 80 82

0 50 100 150

Distance (km )

Depth anomaly (m )

14

16

18

20

22

Tem

pera

ture

65 67 69 7172 74 76 78 80 82

-16 -15

27

28

6465

6667

6869

7071

727374

7576

7778

7980

8182

83

• Isotherm/isopicnals/DCM perturbationIsopicnal/isotherms coordinates → Depth anomalies

• Diapicnal mixing

Properties distribution in isopcinalcoordinates. Semicuantitave

Cuantification: Ri→K→F

⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

= 22

ρPKF Z

-16 -15

27

28

6465

6667

6869

7071

727374

7576

7778

7980

8182

83

P150

0

50

100

150

200

250

300

Dep

th (m

)

Pot-Density

0 50 100 150

Distance (Km)

64 66 68 70 72 74 76 78 80 82 66 68 70 72 74 76 78 80 8225

25.5

26

26.5

27

Den

sity

Isopicnal F luorescence

0 50 100 150D istance (km)

Pot-Density/Fluorescence66 68 70 72 74 76 78 80 8266 68 70 72 74 76 78 80 82

0 50 100 150

Distance (Km)

0

50

100

150

Dep

th (m

)

Rakine-like eddies→strongdiapicnal mixing at the boundaries

• Secondary circulationCalculation from buoys trajectories

0 20 40 60 80 100 120 140 160 180days

0

10

20

30

40

50

r (km

)

buoy 61

(a)

Convergences/divergences ADCP transects

Wind/eddy interaction

W=-3.5 m/day (Sangrà et al 2005)

From Mcgillicudy et al. (2007)

• Remote advection: Chlorophyll Images

• Synthesis Table: physical forcing

EDDY C1 R1C R2A R3A R4C R5A

Origin Gran Canaria La Palma El hieero Gran Canaria Gran Canaria Gran Canaria

Eddy Type Cyclonic Cyclonic Anticyclonic Anticyclonic Cyclonic Anticyclonic

Data type CTD-XBT XBT-CTD(L) XBT XBT CTD CTD-ADCP-buoy

Submesocale yes no no no yes Yes

St Biogeochimic no yes yes yes yes Yes

T. anomaly -4.5 °C

H anomaly 90 m

Depth 300 m

Inte

nsity

/T-∂

per

tu.

T rotation Vgeos. Vgeos. Vgeos. Vgeos. Vgeos. Vgeos., B, A

isopicnal yes no no no yes Yes

Ri, K, F Geo./high Geo./low Geo./low Geo./low Geo./high Ageo/high

Dia

picn

al m

ixin

g

F

Secondary .Circulat (w) Eddy//Wind Eddy//Wind Eddy//Wind Eddy//Wind Eddy//Wind Eddy//Wind, B,A

Advection (Seawif)

Phase. Island distance

Thanks for your attention