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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Unpublished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
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