CAIBEX workshop Mesoscale experiments and modelling Cape Ghir

Transcription

1 CAIBEX workshop Mesoscale experiments and modelling Cape Ghir C. Troupin 1, P. Sangrà 2, J. Arístegui 2 1 GHER-MARE, AGO Department, University of Liège, Belgium 2 Facultad de Ciencias del Mar, Universidad de Las Palmas de Gran Canaria, Spain 29 November 1 December 21

2 CAIBEX workshop Mesoscale experiments and modelling Cape Ghir C. Troupin 1, P. Sangrà 2, J. Arístegui 2 1 GHER-MARE, AGO Department, University of Liège, Belgium 2 Facultad de Ciencias del Mar, Universidad de Las Palmas de Gran Canaria, Spain 29 November 1 December 21

3 Data locations year = 4, month = 9, day = 12 T ( C) o W 11 o W 1 o W 9 o W 32 o N o N o N CTD HPS Bongo Incubation Monitoring Transect o W 11 o W 1 o W Sampling strategy model results 9 SeaSoar tracks, 56 CTDs, 6 drifters High spatial resolution

4 T S diagram North Atlantic Central Water: 1 C T 16 C Antarctic Intermediate Water: salinity minimum (7 1 m) Mediterranean Water: T > 9 C and S > 35.5 North Atlantic Deep Water: T 3 C, S 35

5 Horizontal mapping 32 o N 25 m T ( C) 4 21 overall picture of the filament o N 19 Variables: T, S, [O 2], Fluorescence Depths: from 5 to 3 m 12 o W 32 o N o N o W 1 o W 9 o W 3 m T ( C) Near-surface: upwelling and filament T min 16.5 C T max 21.5 C 2-3 m: warm core close to coast T max C subsurface anticyclonic eddy? 12 o W 11 o W 1 o W 9 o W

6 Drifters Locations SeaSoar measurements Date: September 3, o N filament core 5 1 m-drogue drifters 29 o N = Start anticyclonic eddy 1 3 m-drogue drifter median velocity: O(.35 m/s) 3 m-drogue drifter: T 5 6 d, R 3 4 km 28 o N 14 o W 13 o W 12 o W 11 o W 1 o W

7 SeaSoar tracks August 17-2 (tracks no. 1 6): synoptic picture of the filament 31 o N 4 8 August (track no. 7): variation of the filament position September 2-3 (tracks no. 8 and 9): drifter locations + final picture of the filament 12 o W 11 o W 1 o W Issues: 1. Fluorescence calibration (tracks 1 7) 2. Rough sea conditions no measurements near surface (tracks 7 9)

8 SeaSoar measurements Left: fluorescence before and after calibration Right: temperature

9 SeaSoar interpolated temperature Track 6 T ( C) Latitude ( N) Track 7 T ( C) Tracks 1 3: descent of isotherms possible surface anticyclonic eddy Tracks 4 7: filament more visible descent of isotherms at 2 4 m Tracks 8 9: descent of the isotherms few near-surface data Latitude ( N) 12

10 SeaSoar interpolated salinity and fluorescence Track 8 S Fluorescence: lack of surface data maximal concentration: 5 m Salinity: filament signal less evident subsurface anticyclonic eddy Latitude ( N) Track 8 Fluorescence <=.5 Fluorescence <=.5 Track 9 S Latitude ( N) Latitude ( N) Latitude ( N)

11 CTD meridional transect T ( C) S Fluorescence T13 T12 T11 T1 T9 T8 T7 T6 T5 T4 T3 T2 T1 2 T13 T12 T11 T1 T9 T8 T7 T6 T5 T4 T3 T2 T T13 T12 T11 T1 T9 T8 T7 T6 T5 T4 T3 T2 T Latitude ( N) Latitude ( N) Latitude ( N) Light Trans. (%) 9 Longitude: 1 36 W; Date: August Filament between T9 and T1 Chlorophyll maximum: 25 m, below filament Very low light transmission T13 T12 T11 T1 T9 T8 T7 T6 T5 T4 T3 T2 T Latitude ( N)

12 Summary checklist Data pre-processing Prelimary analysis: property diagrams, mean profiles Horizontal property maps Vertical interpolation + interpretation Drifter analysis Current-meter processing Thermosalinograph data?

13 Process study 48 o N 4 o N 32 o N 24 o N 16 o N D 28 Grid D3 D2 D D i D i+1: One-way, off-line nesting D : high-resolution climatology [Troupin et al. (21) JGR] D 1: solution from E. Mason Domain Res. (km) Size D D D o W 36 o W 27 o W 18 o W 9 o W o

14 Process-oriented experiments β-effect Wind intensity and wind curl Topographic effects Friction q (m 1 s 1 ) 42 o N o N o N 8 q (m 1 s 1 ) 1 33 o N o N o N o N (b) Summer 24 o W 2 o W 16 o W 12 o W 8 o W Mecanism: o N 5 1. Conversation of potential vorticity 18 o N (a) Summer 4 2. Injection of relative vorticity by the wind 3 o W 24 o W 18 o W 12 o W 6 o W

15 Realistic solution Validation against Medspiration satellite images (left) Correct scales and location of the filament (right) Agreement with in situ data year = 4, month = 9, day = 12 ( C) o N o W 11 o W 1 o W (a)

16 Sub-surface anticyclonic eddy year = 4, month = 9, day = 3 T ( C) 16 year = 4, month = 9, day = 3 ζ o N o N o W 11 o W 1 o W o W 11 o W 1 o W.25 Model agrees with CAIBEX observations Mechanism: interaction undercurrent + topography Similar in California Upwelling System

17 Sub-mesoscale study 29 Grid D 3 5 o N o N D2 1 D3 2 2 o N o N D o W 36 o W 27 o W 18 o W 9 o W o D i D i+1: One-way, off-line nesting [Mason et al. (21) Ocean Model.] D : high-resolution climatology [Troupin et al. (21) JGR] D 1: solution from E. Mason et al. (subm.) Domain Res. (km) Size D D D

18 Sub-mesoscale fields Temperature and normalized vorticity at 1 m 8-m horizontal resolution Broader filament; Frontal instabilities Animation:

19 Mapping Repeat sections (filament) Circulation modeling Publications and conferences EOF analysis Source: Medspiration project (ESA) Sensor: AATSR (1 km-resolution) Period: 29 ongoing Method: DINEOF [Alvera-Azcárate et al. (25, 29)] Objectives: 1. Extract dominant modes 2. Fill incomplete images be/dineof/dineof_allcan.html

20 EOF analysis: dominant mode Spatial modes: Temporal modes: EOF no. 1: seasonal cycle EOF no. 2: related to filament related to wind curl?

21 Summary checklist Realistic model results + validation Process-oriented experiments Generation mechanism Sub-mesoscale modeling effort EOF analysis Inter-annual forcing Publication

22 Publications 1. Generation of the Cape Ghir coastal upwelling filament: a numerical study [modelling] 2. High-resolution sampling of the Cape Ghir upwelling filament during the CAIBEX cruise [observations] 3. Observation and modeling of a subsurface anticyclonic eddy off Cape Ghir (NW Africa) [modelling + observation]

23 Conferences VLIZ Young Scientists day, Oostende (Belgium), November 27, 29: High-resolution measurements and modelling of the Cape Ghir upwelling filament during the CAIBEX cruise [oral presentation and poster] Ocean Science Meeting, Portland (USA), February 22-26, 21: Poleward front of upwelling filaments generates subsurface anticyclonic eddies (feddy): a CAIBEX project contribution [poster], P Sangrà, J. Arístegui, C. Troupin and E. D. Barton. The Cape Ghir (NW Africa) upwelling filament: Modeling and observation during the CAIBEX Campaign [poster], C Troupin, P Sangrà, J. Arístegui, J.-M. Beckers and E. D. Barton. 42 nd International Liège Colloquium on Ocean Dynamics: Liège (Belgium), April : High-resolution measurements of an upwelling filament during the CAIBEX campaign [oral presentation and poster], C. Troupin, J. Arístegui, J.-M. Beckers and P. Sangrà.