Variability of the Western Iberian Buoyant Plume to wind events

Pablo Otero1, Manuel Ruiz-Villarreal1, Álvaro Peliz2 and Jesús Dubert2

1 Instituto Español de OceanografíaMuelle de las Ánimas s/n, 15002, A Coruña (Spain)

2 Departamento de Física, Universidade de Aveiro, 3810-194, Aveiro, (Portugal)

pablo.otero@co.ieo.es

2006 ROMS/TOMS European WorkshopAlcalá de Henares (Spain), November 6-8

How to?

Hydrography of the area

Analysis of freshwater discharge

Design of the simulation

Real forcing

Isohaline coordinates

Spatial variability

Front detection

Classification of the WIBP

PREVIOUS KNOWLEDGE

NUMERICAL MODEL

ANALYSIS OF MODEL OUTPUTS

The downwelling season

IPCCoastal Front

River plume

WIBP

IPC

Wind

Freshwater discharge

Climatologic value and scale correction for Nov-Dec 2002.Inter-annual variability (and daily: reservoirs!) is a strong problem

ROMS (Regional Ocean Modelling System, Haidvogel et al., 2002) with nesting capability (Penven et al., 2004).

Three grids with 15Km, 5Km, and 1.8Km

30 vertical s-layers.

OSU tidal inverse model (Egbert and Erofeeva, 2002)

Forcing (MM5: 30Km, 1h).

3 grids… …3 stages

State-of-the-art

Circulation after the Prestige accident (Sea surface salinity from November 19th to 29th)

-0.3

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0

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Date

Pa

November-December 2002Silleiro Buoy

MM5

Case 1:Confinement (downwelling)

Case 2:Expansion (relaxation)

Case 3:Expansion (upwelling)

REALISTIC SIMULATION

DO

WN

WEL

LIN

GU

PWEL

LIN

G

Case 1: Confinement (downwelling)

SECTION

Jet

Smoothing

River Douro

River Miño

Upwards Cape Fisterra

20Nov 21Nov 22Nov

Enhanced slope current

Case 2: Expansion (relaxation)

SECTION

Jet

22Nov 23Nov 24Nov

Weakness

Case 3: Expansion (upwelling)

SECTIONMeandering

Northern limit

Detachment

Upwellingof slope current:

Reported on the bottom of Rías Baixas

Wind mixing

Stratification

AVHRR25Nov 3h

ROMS25Nov 3h

Flooding event Climatologic discharge

SW wind overestimated in earlier hours by MM5

Stronger surface signal of IPC

Comparison to observations

SeaWiFS5-7 Dec 2002composite

ROMS6 Dec 2002

AUTOMATIC DETECTION OF RIVER PLUME FRONTS

Potential density

Vertical gradient

Maximum local value

Map of Mixed layer depth

Sobel Edge Filter

Thresholding

Downwelling event

Relaxation of a downwelling event

ISOHALINE COORDINATES

Mixed layer depth

River plume front

Wind mixing Shear mixing

EstuaryOcean

Isohaline coordinatesA coordinate method based in salinity

Consider calculations between salinity classes (isohalines)Why?River plume as a systemTemporal variability can be analysed neglecting spatial variabilityProblems?To delimit the plume, it is necessary toestablish the ocean (‘ambient’) isohaline, and this is not obvious in a realistic study.

Salinity classes

S=0 0.1 0.2 0.3 0.4 35.5 35.6River Ocean

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SV

log f10

Near field Far field

Salinity classes

Time

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5.4

5.6

5.8

6

6.2

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7

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8

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Dat

e

Pa

Downwelling Upwelling

Wind stress

Total freshwater volume increases in time

Downwelling winds -> accumulation of freshwater at lower salinity classes

Confinement

Upwelling winds -> displacement of freshwater at higher salinity classes

Expansion and mixing

Freshwater volume between isohalines dV

S

SSSV

upperilower SSSif

0

0

Downwelling Upwelling

hz10 z

SKlog

Near field Far field

Salinity classes

Time

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-9 .8-9.6-9.4-9.2-9-8.8-8.6-8.4-8.2-8-7.8-7.6-7.4-7.2-7-6.8-6.6-6.4-6.2-6-5.8-5.6-5.4

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Wind stress

Vertical salt flux responds immediately to wind changes -> key factor

Vertical salt flux is higher at higher salinity classes

PHYSICAL CLASSIFICATION

Physical parameters

0

5

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25

30

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50

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Plu

me

dep

th (

m)

0

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Fro

ud

e Nu

mb

er

Plume depthOffshore plume depth Fp

0

10

20

30

40

50

60

70

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Plu

me

wii

dth

(K

m)

0

0.02

0.04

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0.08

0.1

0.12

0.14

0.16

0.18

Slen

dern

ess

Lw

Lw max

Slenderness

FroudeKelvin

SlendernessPlume depth

Mean densityInertial radius

Scaled Ekman transportScaled basal friction

Residence time[…]

Outflow System

Fr K Li (Km)

U (m·s-1)

Discharge (m3·s-1)

h (m)

Lw (Km)

γ

Alaska 0.3 1 24000 0.16 Algerian 0.3 3 0.12 Amazon 0.6 0.6 200000 0.5 Chesapeake Bay 4.2 0.5 500 10 5-20 Columbia 0.6 0.1-0.4 3000-17000 <5 4 Connecticut 0.2 2000 3 1.5

Delaware ~0.1 ~4 0.06 2400

(peak of 5000)

0.2

Eel River* ~1.0 10 0.5-1 4000-12000 0.5-1.3

5-10

Fraser 0.4 10000 3 2 Gaspé 0.4 2.0 0.1 Great Whale 0.2 2 1 Hudson 2.0 500 4 10 Koombana Bay 0.0 2 1 La Grange 0.6 5 5 Lake Michigan ~2 ~0.1 1

Mississippi 1 0.0-0.2

19000 2 0.2 1

Niagara 1 1.0 1 Norwegian 0.1 4.0 0.1 Point Beach 2 0.1 1 Rhine 0.1 3.0 1700 0.2

SAB** 0.3 4.0 0.15-0.2

1000-4000 (peak of 7000)

10-20 0.2

Santa Clara 1.1-1.6

~1.0 10

(peak of 30)

0.2-0.5 100

(peak of 500) ~5 5-10

Scottish 0.1 10 0.2 St. Lawrence 5.0 13400 20 40 WIBP*** 0.2-

0.4 ~4 1-3 0.08 400-2500 4-15 10-

40 0.1-0.2

*results during floods **South Atlantic Bight

ConclusionsVariability of the Western Iberian Buoyant Plume (WIBP) is described with high spatial and temporal resolution (scale of hours) WIBP responds asymmetrically to upwelling and downwelling wind events, with an along-shore circulation during downwelling or steady state and with across-shore circulation during upwelling wind events (south-westwards off the mouth of main rivers).The Iberian Poleward Current (IPC) and the WIBP prove to be a coupled system.Good agreement with the spatial variability shown by satellite imagery. Good response to upwelling events.Isohaline coordinates are a good (although complex) tool to avoid the spatial variability of the plume, helping to understand the involved processes. The plume is characterised: A large-scale river plume, semi-geostrophically balanced (K>>1) and surface-advected (Yankovsky and Chapman, 1987). When compared with other buoyant plume systems, WIBP shares many physical characteristics with the SAB system.

Pablo Otero1, Manuel Ruiz-Villarreal1, Alvaro Peliz2 and Jesús Dubter2

1 Instituto Español de OceanografíaMuelle de las Ánimas s/n, 15002, A Coruña (Spain)

2 Departamento de Física, Universidade de Aveiro, 3810-194, Aveiro, (Portugal)

pablo.otero@co.ieo.es

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Dat

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Downwelling Upwelling

SA

Wind stress

Near field Far field

Salinity classes

Time

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Area increases in timeby increasing of river discharge

Northerly winds -> area increases at high salinity classes

Expansion

Cooling of the WIBP (1)

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Longitude

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Day

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Longitude

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Section 42N

Oil spill from Nov 19 06:00hCurrents + Wind stress (3%)

Coastal circulation before stranding of 2nd spill

River plumes

NorthWest Iberia is an important fishery and aquaculture area.

Strong variability in HABs and fish larvae are been reported. An answer beyond biological behaviour is required.

River plumes can play a role in enrichment, concentration and/or retention of biological material (factors pointed by Bakun, 1996)

Dispersion is enhanced in the frontal area.