Canary Islands eddies. Pablo Sangrà Universidad de Las Palmas de G.C.

Transcription

1 Canary Islands eddies Pablo Sangrà Universidad de Las Palmas de G.C. 1

2 1. Kinematics 1.1 Initial size and shape 1.2 Vertical structure 1.3 Evolution 2. Dynamics Outline 2.1 Generation mechanisms 2.2 Evolution: a simple advective-diffusive model 2.3 Inertial/centrifugal stability 3. Ongoing studies 3.1 The Canary Eddies Corridor 3.2 ROMS-UCLA modeling 3.3 Physical-biogeochemical coupling

3 1. Kinematics 1.1 Initial size and shape Initial radius: R d =25 km, island radius Eddies Warm Wake Arístegui et al., 1994

4 Eddies are initially Rakine like vortex with a core rotating in solid body rotation and a cylindrical shape 28 Buoys rotating rate center middle Pot-Temp-Anomaly periphery Depth (m) Sangrà et al., Distance (Km) Unpublished

5 1.2 Vertical Structure Depth: m, NACW Temperature anomalies, C Isotherms perturbation: m Shalow wake, 25 m Arïstegu et al., 1994

6 1.3 Evolution Coherent structures. Can last many months Initial 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) 6

7 Eddies evolution stages Young stage: solid body rotation YS (0-35 days) Mature stage: periphery slowing rotating days A1 C1, A1 + A2 Decay stage : small values of rotation rate all over the eddy MS ( days) days A1 + C1 Eddy evolves pulsating. May be related with wind/eddy interactions (under study) Wind DS ( days) days A1 + AT A, W>O After Martin & Richards, 2001 buoy 61 buoy 60 buoy 59 Anticyclonic (Sangrà et al., 2005)

8 2.1 Generation mechanisms. Topographic and Atmospheric forcing (Jiménez, Sangrà & Mason 2008) Topographic forcing ( inerty) U L = ( ) AH EH O 2 Ro Re = = O viscosity Shedding when 2. Dynamics Re > Streak lines/isovortity lines for the barotropic QG model Re=250 (Sangrà, 1995) 8

9 Atmospheric Forcing: Vorticity injection at the island wake Dynamics: atmospheric forcing mechanism (Jiménez, Sangrà and Mason, 2008) Dynamics: Relative importance of topographic and atmospheric frocing (Jiménez, Sangrà and Mason, 2008), Observations: Gran Canaria (Basterretxea et al., 2002) 9

10 Field experiment on generation mechanisms (Piedeleu et al., in prep.) Generation frequency Observational evidences topographic/wind forcing Tides gauges Wind shear Winter- Sping 2006 Mooring Only topographic forcing can generate eddies Only wind is not able to generate eddies Main mechanism the topographic forcing 10

11 2.2 Evolution: a simple advective-diffusive model (Sangrà et al., 2007) Stages: diffusion of angular velocity 2 ω ω 1 Kr ω + u = r 2 t r r r ( ) t=0 d t=10 d t=30 d t=70 d t=100 d 3 t=15 d t=50 d t=100 d t=180 d 3 r=30 km k=20 ms -2 r=25 km k=25 ms -2 t=10 d t=30 d t=70 d t=90 d ω(s ) r=25 km k=25 ms -2 ω (s ) 2 Anticyclonic ω (s ) 2 Cyclonic r (km) Model (k ) Model and observations (k )

12 2.3 Inertial stability of Rankine-like vortex (Sangrà et al., 2007) f Gent and McWilliams (1986) ω 2 ω + r r ( f + 2 ω ) = Ω Ω 0 + sb Pelegrí et al. (2004) Anticyclone Cyclone Tm=2.2 d Ω.Ω sb (s ) t=1 d t=30 d t=70 d t= 100 d Ω.Ω sb (s ) t=2.5 d t=30 d t=70 d t= 100 d r (km) r (km)

13 Stables anticyclones w <f/2= s -1. Tm= 2.2 d, To= 2.5 d ω < 0 r Stables cyclones Tm= 4 d, To= 4.5 days Inertial stability can explain why observed anticyclones rotates faster than the cyclones Tm=2.5 d Tm=4.5 d 13

14 3. Ongoing studies 3. 1 The Canary Eddies Corridor. (Sangrà et al., in prep) SWESTY propagation (R. Pingree, 1996) Anticyclonic Shallow Subtropical Subducting Westward Propagating Eddies 14

15 Swesties-island generated eddies connection N 29 o 28 o 0 Sangrà et al. (2005) 27 o 3.4 km/d km/d 26 o km/d km/d km/d 40 buoy o W 19 o 18 o 17 o 16 o 15 o 14 o Altimetry (A. Pascual, 2008, unpublished) and buoys trajectories showing that the eddies corridor is generated by Canary Island flow perturbation

16 Altimetry data are quite robust ADCP and buoy trajectory versus sea surface height and velocities as obtained from altimetry 16

17 A Zonal Subtropical Eddies Corridor 17

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19 Corridor Importance Its a permanent structure not previously described It could be one of the major long lived eddies source on the Subtropical Atlantic months Eddies Age Pyramid for the Canary Corridor cyclones anticycl. Trajectories Life-span > 6 months months R=A/C inf Eddies Age Pyramid for the Canary Corridor>3 months 19

20 It can be an important structure for the zonal balance and exporting physical (heat) and biological (Particulate Organic Matter) properties Chlorophyll (mg m -3 )-Alimeter velocity/height C2 C1 A1 A2 J98

21 3.2 ROMS-UCLA modeling: Collaboration between ULPGC and UCLA. Developed mainly by E. Mason Objectives Develop robust multi-year high-resolution climatological Canary Basin model solution Tool to study: Regional circulation & variability Canary Island wake and its interaction with the upwelling Cape Ghir filament

22 Model Domains Grid hierarchy offline nesting using roms2roms

23 Large Domain Validation

24 Small Domain validation AVHRR SST (10 August, 2003) Snapshot of model SST (month 9, year 6) F C F C

25 Vertical section: Alongshore velocity/temperature

26 Canary Eddies Corridor

27 3.3 Physical-biogeochemical coupling RODA project: Interdisciplinary study of the biological pump inside de eddies: Biogeochemical cycles outside an inside of the eddies Sampling from atmospheric nutrient sources to virus Coupling mechanisms Isotherm/isopicnals/DCM perturbation Diapicnal mixing Secondary circulation Remote advection

28 Isotherm/isopicnals/DCM perturbation Isopicnal/isotherms coordinates Depth anomalies Pot-Temperature Depth (m) Depth anomaly (m) Depth (m) Temperature Temperature Distance (Km) Distance (km) Distance (km)

29 Diapicnal mixing 0 Pot-Density P Pot-Density/Fluorescence Isopicnal Fluorescence Properties distribution in isopcinal coordinates. Semicuantitave Rakine-like eddies strong diapicnal mixing at the boundaries Cuantification: Ri K F Depth (m) Depth (m) 50 Density F K 2 P ρ = Z Distance (Km) Distance (Km) Distance (km)

30 Secondary circulation Calculation from buoys trajectories (a) 50 r (km) W=-3.5 m/day (Sangrà et al 2005) 10 0 buoy days Wind/eddy interaction From Mcgillicudy et al. (2007) Convergences/divergences ADCP transects

31 Remote advection: Chlorophyll Images

32 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 Intensity/T- pertu. T. anomaly -4.5 C H anomaly 90 m Depth 300 m T rotation Vgeos. Vgeos. Vgeos. Vgeos. Vgeos. Vgeos., B, A Diapicnal mixing isopicnal yes no no no yes Yes Ri, K, F Geo./high Geo./low Geo./low Geo./low Geo./high Ageo/high F Secondary.Circulat (w) Eddy//Wind Eddy//Wind Eddy//Wind Eddy//Wind Eddy//Wind Eddy//Wind, B,A Advection (Seawif) Phase. Island distance

33 Thanks for your attention