Wake studies. Research challenges & opportunities.

Transcription

1 Wake studies Research challenges & opportunities 1

2 Acknowledgements CIIMAR / CIIMAR-Madeira CCM - UMa Obrigado organização (João Tasso) pela hospitalidade! 2

3 Outline Portuguese ZEE and the islands Perturbing planetary flows Scales in geophysical processes Atmospheric wakes Oceanic wake studies Challenges & Opportunities 3

4 Portuguese ZEE 3rd largest ZEE in EU; 11th in the world Portugal (continental) 327,667 (19%) Açores 953,633 (55%) Madeira 446,108 (26%) Total 1,727,408 km² PT(continental) ~1.5% GDP R&D Azores ~0.3% GDP R&D Madeira ~0.1% GDP R&D EU27 ~2.03% GDP R&D 4

5 Azores Perturbing the incoming flow... 5

6 Atmospheric & Oceanic wakes leeward of Madeira MODIS-terra, 1-jan SST/MODIS 12 Sept MODIS-terra, 28-Apr CHL/MODIS 12 Sept 2006 (log10 scale) Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC ( 6

7 Island wakes => Turbulent flows!. UCLA Turbulence notes Energy Density Decreasing Scale Forcing Dissipation 7

8 Chelton et al., Scales in geophysical flows 8

9 Measuring turbulent flows 9

10 EUFAR: i-wake Sounding IWAKE N European Facility for Airborne Research 33.0 N N N 6 Sounding IWAKE W 33.0 N 17.5 W 17.0 W 16.5 W 16.0 W A) 32.5 N 32.0 N 10 m/s 18.0 W 17.5 W 17.0 W 16.5 W 10

11 Nondimensional Mountain Height N 32.5 N Wake formation with vortices Wake formation with reversed flow 0.5 Subcritical flow no wake 0 0 Wake formation no reversed flow Upstream Froude Number N 1K 10 m/s 18.0 W 17.5 W 17.0 W 16.5 W 11

12 ICOVBIO (CNRS+CIIMAR) 12

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14 Slocum G2 W/ ADCP 14

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17 Ocean Dynamics (2012) 62: DOI /s Complex geophysical wake flows Madeira Archipelago case study Rui Miguel A. Caldeira Pablo Sangrà Received: 24 June 2011 / Accepted: 3 February 2012 / Published online: 11 March 2012 Springer-Verlag2012 Abstract Idealized studies of island wakes often use a cylinder-like island to generate the wake, whereas most realistic studies use a close representation of the oceanic bathymetry immersed in a complex representation of the ambient geophysical flows. Here, a system of multiple islands was placed into numerical and experimental channels, in order to focus on the complexity of the archipelago wake, including (a) the influence of small neighboring islands and (b) the role of the island-shelf. The numerical geostrophic and stratified channel was built using a three-dimensional primitive equation model, considering a realistic representation of the Madeira archipelago bathymetry, with prescribed initial and boundary conditions. Results from the simulations show that the neighboring islands Responsible Editor: Emil Vassilev Stanev Electronic supplementary material The online version of this article (doi: /s ) containssupplementary material, which is available to authorized users. R. M. A. Caldeira (B) CIIMAR Interdisciplinary Centre of Marine and Environmental Research, Rua dos Bragas, 289, Porto, Portugal rcaldeira@ciimar.up.pt R. M. A. Caldeira CCM Center for Mathematical Sciences, Universidade da Madeira, Campus Universitário da Penteada, Funchal, Madeira, Portugal URL: P. Sangrà Departamento de Fisica, Edificio de Ciencias Basicas, Universidad de Las Palmas de Gran Canaria, Campus Universitario de Tafira, 35002, Las Palmas, Gran Canaria, Spain alter the near-field wake. Small eddies generated by the neighboring islands lead to destabilization of the shear layers of the larger island. Laboratory experiments carried out in the Coriolis rotating tank corroborated this near-field disruptive mechanism. The neighboring island perturbation effect was present whatever the direction of the incoming flow, but under different regimes. North south wakes produced geostrophic eddies ( Rd), whereas west east wakes produced (exclusively) ageostrophic submesoscale eddies (<<Rd) which traveled offshore with wave-like motion. The archipelago shelf contributed to the asymmetric vertical migration of oceanic vorticity. Cyclonic vorticity dominated the surface dynamics, whereas anticyclonic circulation prevailed at the bottom part of the linearly stratified upper layer. This study identifies several likely wake scenarios induced by the Madeira archipelago, and may serve as guide for future multiscale numerical studies and in situ campaigns. Keywords Island wake Submesoscale eddies Boundary layer disruption Hydrodynamic drafting Topographic trapped waves Vertical shear Subinertial instabilities 1 Introduction Several classical studies have discussed on the deepocean island wake problem (e.g., Tomczak 1988; Heywood et al. 1996; Dietrich et al. 1996). For the deepsea island case, most of the frictional forces inducing wake formation originate from the (near-field) island coastal boundary, whereas for a shallow water wake, the surface and bottom boundary Ekman layers are Boundary-Layer Meteorol DOI /s y ARTICLE Wake Response to an Ocean-Feedback Mechanism: Madeira Island Case Study Rui M. A. Caldeira Ricardo Tomé Received: 17 February 2012 / Accepted: 18 March 2013 Springer Science+Business Media Dordrecht 2013 Abstract We focus on an island wake episode that occurred in the Madeira Archipelago region of the north-east Atlantic at 32.5 N, 17 W. The Weather Research and Forecasting numerical model was used in a (one-way) downscaling mode, considering initial and boundary conditions from the European Centre for Medium-range Weather Forecasts system. The current literature emphasizes adiabatic effects on the dynamical aspects of atmospheric wakes. Changes in mountain height and consequently its relation to the atmospheric inversion layer should explain the shift in wake regimes, from a strong-wake to weak-wake scenario. Nevertheless, changes in sea-surface temperature variability in the lee of an island can induce similar regime shifts because of exposure to stronger solar radiation. Increase in evaporation contributes to the enhancement of convection and thus to the uplift of the stratified atmospheric layer above the critical height, with subsequent internal gravity wave activity. Keywords Air-sea interaction Convective boundary layer Inertial gravity waves Marine atmospheric boundary layer Resonance waves Electronic supplementary material The online version of this article (doi: /s y) contains supplementary material, which is available to authorized users. R. M. A. Caldeira (B) CIIMAR Interdisciplinary Centre of Marine and Environmental Research, Rua dos Bragas, 289, Porto, Portugal rcaldeira@ciimar.up.pt R. M. A. Caldeira CCM Center for Mathematical Sciences, University of Madeira, Campus da Penteada, Funchal, Madeira, Portugal R. Tomé CCMMG Centro do Clima, Meteorologia e Mudanças Globais, University of Azores, Polo Universitário de Angra do Heroísmo, Angra do Heroísmo, Portugal R. Tomé Instituto Dom Luiz (IDL), Faculdade de Ciências da Universidade de Lisboa Campo Grande, Edifício C8, Piso 3, Lisbon, Portugal 123 Dynamics of Atmospheres and Oceans 58 (2012) Contents lists available at SciVerse ScienceDirect Dynamics of Atmospheres and Oceans journal homepage: Wind mediated vorticity-generation and eddy-confinement, leeward of the Madeira Island: 2008 numerical case study X. Couvelard a,, R.M.A. Caldeira b,a, I.B. Araújo b, R. Tomé c,d a CCM - Center for Mathematical Sciences, Universidade da Madeira, Portugal b CIIMAR/UP - Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Portugal c CCMMG, University of Azores, Portugal d IDL, Lisbon University, Portugal a r t i c l e i n f o Article history: Received 28 February 2012 Received in revised form 12 September 2012 Accepted 24 September 2012 Available online xxx Keywords: Wind-wake Oceanic wake Eddy containment Madeira Island a b s t r a c t Corresponding author. Tel.: address: xaviercouvelard@gmail.com (X. Couvelard) /$ see front matter 2012 Elsevier B.V. All rights reserved. This study assesses the influence of the atmospheric wind-wake of the Madeira Island on oceanic-eddy generation. Ocean surface wind fields derived from the QuikSCAT scatterometer were compared to the Weather Research and Forecast (WRF) modeled winds at 6 km resolution. The main difference between the two wind products is found southwest of Madeira where QuikSCAT s spatial resolution [0.5 ] does not resolve the near-field atmospheric wake dynamics. Nevertheless, high resolution wind extracted from ENVISAT Advanced Synthetic Aperture Radar (ASAR) confirms that WRF is able to realistically reproduce the island-induced windwake. The Regional Oceanic Modeling System (ROMS) was used to simulate the oceanic effects of the wind-wake. A no-windwake case was simulated with ROMS using the QuikSCAT wind, whereas the WRF wind was used for an island-induced wind-wake simulation. Oceanic surface kinetic energy and vorticity are found to increase during the summer months concurrently with strong wind-wake episodes resolved by WRF. The downstream propagation of this oceanic vorticity, as a result of the shedding of the leeward eddies, was captured with an eddy tracking algorithm. In the initial stage, the oceanic leeward eddy corridor was delimited by the zonal wind-shear. This study suggests that the wind-wake is the main contributor to the generation and containment of the oceanic eddies in the lee of the Madeira Island Elsevier B.V. All rights reserved. 17

18 Challenges & Opportunities Limited public investment in R&D (Semi-)isolated locations (extra) logistics Need sophisticated (expensive means) to measure open ocean processes Narrow shelf High-resolution sampling and models required to resolve near-field dynamics Turbulent flows abundant in ocean and atmosphere Multi-scale processes captured around islands i.e. open-ocean observatories Best studied using a multi-platform approach Physical processes associated with nutrient enrichment and increase productivity Fast access to pelagic environment 18

19 Thanks! 19