Gildas Cambon IRD, LEGOS, France

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Downscaling of atmospheric forcing for ROMS for the period

1958-2008 :Application to the Peru-Chile

system

Gildas Cambon IRD, LEGOS, France

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ROMS_AGRIF development team:

Gildas Cambon (a) , Boris Dewitte (a,c,d), Katerina Goubanova (a,d), Vincent Echevin (a), Christophe Hourdin (b), Ali Belmadani (b), Timothée Brochier (b), Colas Francois (e)

(a): IRD/LEGOS, France ; (b): IRD/LOCEAN, France ; (c): IGP, Peru ; (d) : IMARPE, Peru ; (e) : IGPP, UCLA, USA

Application Humbolt : PEPS project (ANR)

Cambon, G. (a), Marchesiello, P. (a) ; Debreu L. (b) ; Penven P. (c)

(a): IRD/LEGOS, France ; (b): INRIA/LJK, France ; (c) : IRD/LPO, France

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ROMS_AGRIF is a branch of ROMS developed in France by IRD and INRIA and based at LEGOS, Toulouse.

Its main particularity is the AGRIF online nesting capability (Debreu et al, 2005, 2010) : http://roms.mpl.ird.fr

This French branch of ROMS is developed to respond to the objectives of IRD in terms of support to developing countries.

In this community experiment, the model code is developed in parallel with a powerful pre- and post- processing set of tools: the ROMSTOOLS matlab toolbox (Penven et al, 2008).

ROMS_AGRIF general context

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ROMS_AGRIF general context

A world-wide community of users :

Today, the ROMS_AGRIF community well spread developed around the world, with more than 1100 registered users.

A more restricted community of about 40 beta testers exist also and is referenced on our SVN development website at INRIA: http://gforge.inria.fr/projects/romsagrif.

Here we present an application of ROMS_AGRIF for the Peru-Chile current system conducted in collaboration with Peruvian partners.

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Outlines

1. Introduction & Issues

2. The statistical atmospheric model

3. The interannual ROMS simulation

4. Impact of the stat. downscaling

5. Perspectives

6. Summary & Conclusions

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Scientific context & main objectives

Humboldt Current system (HSC) is the most productive eastern boundary current system with permanent upwelling.

Its fisheries represent about 20% of world wide marine fish catch.

There is a need for evaluating the impact of regional climate variability on the Peru-Chile upwelling system

Introduction & Issues

In this context:

Use of global model simulations of the recent past (1958-present)

ROMS is use for oceanic downscaling

Downscaling methods for atmospheric forcing are needed.

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AOGCM model needed for these long periods : NCEP, ERA …but large errors are found in coastal areas.

Dynamical downscaling using WRF : experienced in our group in New Caledonia (Lefevre et al., 2010, Jourdain et al., 2001) and over the Central Chile region (Renault et al 2009, see poster)

Statistical downscaling approach, (Goubanova et al , 2010, Clim. Dyn., revised)

Introduction & Issues

Strategy

• Interannual regional configuration of ROMS_AGRIF at 1/6° from 1958 to 2008 period.

• For the moment, hind casts over a test period 1992-2005 to evaluate the realism of the solution and 98 El Nino event.

• Set up of atmospheric downscaling methods

Atmopheric downscaling strategy :

In this study, statistical approach have been choose in reason of his low computational cost but others are also evaluating (not presented)

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Outlines





5. Perspectives


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1. Find a statistical relationship F between large-scale predictors X and regional variables Y for the observed period

F – Multiple linear regression Y – 10 m wind/stress from QSCAT, 0.5x0.5° X – 10 m wind + SLP from NCEP, 2.5°x2.5°

2. In order to derive regional variables Y for a period of interest apply the relationship F to corresponding large-scale predictors X

)( 2008200020082000NCEPQSCAT XFY

1999199119991991 )( YXF NCEP

10m wind speedfrom QuikSCAT

10m wind speedfrom NCEP

Goubanova et al 2010

Description

Statistical downscaling of NCEP reanalysis

QuikSCAT is a good product to reproduce upwelling processes (Capet et al, 2004) but we only have it for recent years (2000 – 2008)

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Improvements on spatial structure

In coastal area with NCEP_DS :

•Wind curl is more realistic, which leads to better estimates of along shore currents. (PCC closer to the coast)

•Wind stronger near the coast : upwelling intensity intensified and more realistic

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Differences in wind amplitude between the warm phase and the cold phase of the 1997/1998 El Niño-La Niña.

Data were 6-month low-pass filtered and the warm (cold) phase corresponds to September 1997 (December 1998).

satellite data products outputs

Improvements on interannual variability


Stat downscaling induces a better representation of wind interannual variability near the coast.

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The statistical downscaling was applied to both the NCEP (top) and ERA40 (bottom)

• ERA40 and NCEP reanalysis have a very different pattern near the coast.

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Improvements on interannual variability


The downscaling allows correcting the interannual biases between reanalyses products.

For these reasons, use of these downscaled NCEP wind stress in an interannual Peru-Chile regional ROMS simulation

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Outlines





5. Perspectives


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Ocean model : ROMS_AGRIF http://roms.mpl.ird.fr

Resolution : 1/6°

Test Period : 1992 - 2005

Bathymetry : Etopo 2

Atmospheric forcing:

NCEP heat fluxes (2.5° x 2.5°)

NCEP_Downscalled wind stress (0.5°x0.5°)

Bulk formulation (Fairall et al.) for latent and sensible heat fluxes

Lateral forcing : SODA model (Carton & Giese), 0.5°x0.5°, 5-days T, S, u, v, U2d, V2d, imposed at the open boundaries

OBC : active open boundaries conditions (Marchesiello et al, 2001)

The interannual ROMS experiment : Set-up

Numerical Set-Up

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Annual mean SST and Surface currents ROMS

Annual mean SST from Pathfinder satellite observation

Mean SST well reproduced

NECC

POC

SEC PCC

PCC

The interannual ROMS experiment : Validations

Oceanic circulation scheme for the eastern Tropical Pacific (figure from Montes et al., 2010, JGR) Surface currents in agreement

with the obs. and literature : PCC, SEC and POC

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The interannual ROMS experiment : Validations

Currents vertical structures across Eq. and across 12.S

• Surface equatorial currents SEC and NECC ok

• Equatorwards subsurface currents EUC, p-SSCC, s-SSCC: good amplitude and position.

U V

EUC

SEC

NECC

pSSCC

sSSCC

PCC

PCUC

• Along coast poleward current PCUC : main source for coastal upwelling (Peru–North Chile)

• Quite well reproduced, consistent with previous studies description.

12°S Meridional velocity in m/s86° W Zonal velocity in m/s

This simulation compared well to the obs. It reproduce well the mean state circulation and thermohaline structure

Coastal jet

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4. Impact of the atmospheric downscaling

5. Perspectives

6. Conclusions

Outlines

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The interannual ROMS experiment : Stat. downscaling impact

On EKE from SSH and SSH variability

ROMS with NCEP_DS wind stress compared very well to the observations

• Mesoscale variability well represented in NCEP_DS run.

• Mean current baroclinic instability much better represented in NCEP_DS run

• Significative improves compared to the run using original NCEP wind stress

Annual mean EKE from SSH in cm2/s2

TOPEX/ERS ROMS NCEP_DS ROMS – NCEP

NCEP_DS NCEP

Irrealistic offshore shift of EKE max

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On the upwelling intensity

The interannual ROMS experiment: Stat. downscaling impact

With NCEP_DS stress :

Near coast wind are more realistic and stronger upwelling better represented.

SST Pathfinder

The statistical downscaling methodology employed to downscale the NCEP wind stresses in the region clearly improves the ROMS simulation near the coast : upwelling and eddy activity !

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Outlines





5. Perspectives


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Perspectives

During El Nino event :

Collapse of the upwelling

Strong modifications of the subsurface poleward PCUC, intensified, uplifted to the surface and moved offshore extensions

Intensifications of currents and quasi-reverse of currents ay coast

With our statistical downscaling approach, we improve the realism of the simulation: investigation of the vertical along shore currents structure and its reverse during El Nino events (as complementary works of Colas et al, 2008)

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• Dynamical atmospheric downscaling using WRF :

Experienced successfully in our group with ROMS_AGRIF and WRF in Nouméa by Marchesiello’s group (Lefevre et al, Jourdain et al).

Perspectives

Recover in a dynamically consistent way the energy spectra of atmospheric circulation at the mesoscale range (absent in the NCEP data)

Figure from Marchesiello et al

Applied for shorter periods by Renault et al over the Central Chile region :to reproduce the specific wind burst event called ‘Coastal Jet’ and his associated oceanic response. (98-2000)

Renault et al., 2010, in preparation and see poster

Atmospheric model: WRF

two nested grids : 30km and 10km

Oceanic model: ROMS : spatial resolution : 10km

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Perspectives

• Ocean downscaling using online AGRIF 2 -way procedure capability of ROMS_AGRIF (Debreu et al 2010, submitted) to improve the ocean downscaling performance : there is an update on 2D and 3D time stepping for the parent grid.

Example of 4 grid nested simulation with the 2-way AGRIF procedure (coarser grid not shown): Menkes C. & Marchesiello P., Debreu L., 2010

Left : vertical velocity, right : vorticity

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Interannual ROMS_AGRIF simulation of the Peru-Chile region using the

SODA OGCM interannual boundary conditions and outputs and

adapted NCEP atmospheric forcing.

Statistical downscaling based on the QuikSCAT (2000 -2008) periods

applied on the NCEP wind-stress (soon the heat fluxes) to improve near

shore winds over long periods.

Important improvements for the interannual simulation near

the coast, on the PCC equatorwards current drive by the wind

stress curl.

Large improve on the upwelling structure and intensity due to

stronger and more realistic wind intensity .

Flexible method and an efficient alternative to the costly

dynamical downscaling that improves the results.

Conclusions (1)

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Observational programs related

+ PAITA

+ CHICAMA

+ CHIMBOTE

+ HUACHO

+ CALLAO

+ PISCO

+ SAN JUAN

+ ILO+ ATICO

Tracks Filamentos and VOCALS Peru cruisesLong-term cross-shelf sections

Coastal stations (SST, SSS, Winds)

Filamentos and VOCALS-Rex coastal cruises (2008)

Filamentos, VOCALS-Rex.

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Thank you

Picture: Paracas, South of Pisco, Peru

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Conclusions (2)

Perspectives :

WRF atmospheric modeling for

long periods.

2-way AGRIF nesting to have a

high quality ocean embedding.

Investigate of the alongshore

vertical structure of PCUC and

especially its reverses during

El Nino events with this

simulation.

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Some validations to WOA Annual Mean 92-2004

WOAROMS • Maximum biases of 2°C in surface:

Roms colder near the equator : equatorial. upwelling

Warmer southern in upper layer

Colder near the coast coastal upwelling.

The interannual ROMS experiment: Validations

Eq.

20.S

12.S

Eq.12° S

20°S

This simulation compared quite well to the obs.

It reproduce well the mean state circulation and thermohaline structure

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The interannual ROMS experiment : Stat. downscaling impact

On EKE from SSH and SSH variability

SSH variability in cm

ROMS with NCEP_DS wind stress compared well observation:

• Mesoscale variability well represented in NCEP_DS run.

• Significative improves compared to the run the original NCEP wind stress

Annual mean EKE from SSH in cm2/s2

AVISO ROMS ROMS

NCEP_DS NCEP

AVISO ROMS

NCEP_DS

NCEP

ROMS with NCEP_DS wind stress compared well observation:

• Mean state pattern well represented.

•As well, significative impact of the statistical downscaling of NCEP stresses, especially near the equator

ROMS

NCEP

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Scientific perspectives

Scientific perspectives:

Evaluation of the pathways from the EUC towards the Peru-Chile undercurrent (PCUC) at interannual time scale: as complementary works of Montes et al., JGR, 2010

Impact of equatorial Kelvin waves on the PCUC during the 1997 El Niño as complementary works of Colas et al, 2008, PIO.

Equatorial Kelvin wave along the equator in SODA (baroclinic modes 1 and 2) (in cm)

Out El Nino

Starting El Nino, EK m=1

Mature El Nino,

EK m=1,2

June 97

Dec 97

Mars 97

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On the SST

El Nino 97-98 The upwelled water ~[15-18°C] near shore( upwelling of PCUC waters mainly)

Offshore ~[21-25°C]

During El Nino, shift of + 5°C near shore and 2-3°C offshore

@12S

The interannual ROMS experiment : El Nino signature

Different phases in El Nino (Colas et al, 2008) : P1, Relax, P2

Can be linked to the different modes of Kelvin waves arrivals

P1

Relax

P2

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Scientific perspectives

Evaluation of the pathways from the EUC towards the Peru-Chile undercurrent (PCUC) at interannual time scale: as complementary works of Montes et al., JGR, 2010

Contribution of the different vertical mode of equatorial Kelvin waves on the PCUC during the 1997 El Niño as complementary works of Colas et al, 2008, PIO.

~60% of EUC alimented by subsurface equatorial flows (EUC, p-SSCC & s-SSCC): Lagrangian studies did for climatological runs.

Interest to take in account the interannual variability of large scale currents, in particular the ENSO modulation.

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Outlines



Description

Improvements


Numerical set up

Validations

Impact of the stat. downscaling

El Nino signature

4. Scientific perspectives

5. Modeling perspectives

6. Conclusions

Documents

Gildas Cambon IRD, LEGOS, France