Jerome Fiechter, Andy Moore, Gregoire Broquet

Ocean Sciences Department

University of California, Santa Cruz

ROMS Workshop, Sydney, April 2009

Improving Ecosystem Model Predictions

through Data Assimilation

Outline

• Physical/biological properties of Coastal Gulf of Alaska (CGOA)

• Ocean circulation, ecosystem, and iron limitation models

• Simulation results for 1998-2002 without data assimilation

• Simulation results for 2001 with data assimilation

CGOA Physical and Biological Properties

Physical Variability• Downwelling-favorable wind regime (Stabeno et al., 2004)

• AS intrinsic mesoscale variability (Combes and Di Lorenzo, 2007)

• Anticyclonic (Yakutat) eddy passages (Okkonen et al., 2003)

Biological Variability• CGOA: high-productivity shelf, fisheries

• Subarctic Gyre: HNLC region (Lam et al., 2006)

• Iron limitation on primary production (Strom et al., 2006)

Interannual Variability• 1997-1998 El Niño; 1999 La Niña

• 1999 NEP “Cold” Regime Shift (Peterson and Schwing, 2003)

• 2002 NEP Subsurface Cold Event (Curchitser et al., 2005)

Coastal Gulf of Alaska Ocean Circulation Model

• ROMS: ~10 km horizontal resolution, 42 vertical levels

• One-way offline nesting with North East Pacific ROMS

• Monthly mean atmospheric and open boundary forcing

• Macro Nutrients from monthly WOA01 climatology

• Dissolved iron from VERTEX (Martin et al., 1989)

Lower Trophic Level Ecosystem Models

• NPZD+Fe (Powell et al., 2006; Fiechter et al., 2009)

• NEMURO+Fe (Kishi et al., 2007; Fiechter and Moore, 2009)

(from Kishi et al., 2007)

Strom et al., 2007

NPZD

PS: Nano P

PL: Diatoms

ZS: Ciliates

ZL: Copepods

ZP: KrillFe

RESULTS: PART I

INTERANNUAL VARIABILITY (1998-2002)

ROMS + NEMURO/NPZD + Fe-limitation

WITHOUT DATA ASSIMILATION

Surface Chlorophyll EOFs: Models vs. Observations

NEMURO+Fe NPZD+Fe SeaWiFS

NEMURO/NPZD Surface Chlorophyll, 1998-2002

Taylor diagrams with respect to SeaWiFS based on monthly means

(NEMURO+Fe, NPZD+Fe)

20012001

LACK OF VARIABILITY

Sea Surface Height: GAK Line, 1995-2004

ROMS AVISO

GAK Line GAK Line GAK Stations

ROMS vs. AVISO

RESULTS: PART II

SEASONAL VARIABILITY (2001)

ROMS + NPZD + Fe-limitation

WITH DATA ASSIMILATION

IS4DVAR Data Assimilation

CASE NAME7-DAY SSH

(AVISO)

5-DAY SST

(Pathfinder)

IN SITU T/S

(GLOBEC)

8-DAY CHL

(SeaWiFS)

FREE NO NO NO NO

SSHT YES YES YES NO

SSHTP (AD, PASS) YES YES YES YES

SSP (AD, PASS) NO NO NO YES

• Configuration: ROMS+NPZD+Fe, adjoint/passive biology

• Assimilation: 7-day cycle, 1 outer (NL) loop, 10 inner (TL/AD) loops

• Strong constraint (no model error), adjust IC only, model space search

• Univariate background error covariance:a) isotropic, homogeneous correlations (50km horiz., 30m vert.)b) std deviations based on 10-year non-assimilated solution

• Observation std deviations: SSH=2cm; T=0.25C; S=0.1; Chl=0.5mg/m3

Sea Surface Height, 2001

RMS errors and correlations with AVISO based on weekly means

FREE SSHT SSHTP-BIOAD SSP-BIOAD

Sea Surface Temperature, 2001

RMS errors and correlations with Pathfinder based on weekly means

FREE SSHT SSHTP-BIOAD SSP-BIOAD

Sea Surface Height, 2001

Taylor diagrams with respect to AVISO based on weekly means

NPZD Surface Chlorophyll, 2001

RMS errors and correlations with SeaWiFS based on monthly means

FREE SSHT SSHTP-BIOAD SSHTP-BIOPASS

NPZD Surface Chlorophyll, 2001

RMS errors and correlations with SeaWiFS based on monthly means

SSHT-BIOAD SSHT-BIOPASS SSP-BIOAD SSP-BIOPASS

NPZD Surface Chlorophyll, 2001

Taylor diagrams with respect to SeaWiFS based on monthly means

NO BIO ASSIM

NO BIO ASSIM

PASSIVE BIO ASSIM

PASSIVE BIO ASSIM

ADJOINT BIO ASSIMADJOINT

BIO ASSIM

NPZD Surface Chlorophyll: Seasonal Means, 2001

FREE SSHT SSHTP-BIOAD SeaWiFS

AP

R-J

UN

JUN

-AU

GA

UG

-OC

T

Surface Chlorophyll and Nutrients: GAK Stations, 2001

Comparisons between model, SeaWiFS, and in situ chlorophyll

RESULTS: PART III

SEASONAL VARIABILITY (2001)

ROMS + NEMURO + Fe-limitation

WITH DATA ASSIMILATION

NEMURO Surface Chlorophyll, 2001

RMS errors and correlations with SeaWiFS based on monthly means

FREE SSHT SSHTP-BIOPASS SSP-BIOPASS

NEMURO Surface Chlorophyll: Seasonal Means, 2001

FREE SSHT SSHTP-BIOPASS SeaWiFS

AP

R-J

UN

JUN

-AU

GA

UG

-OC

T

Summary

Interannual variability, no data assimilation, 1998-2002• Models reproduce spring bloom, underestimate fall bloom• Models good on “normal” years, not so good on “abnormal” years

Seasonal variability, data assimilation, 2001• Chlorophyll not improved by assimilation of physical data only• Chlorophyll improved by assimilation of biological data• Chlorophyll assimilation improved by using adjoint biology• Assimilation incompatibilities between physics and biology

Future work• Adjoint vs. passive NPZD solutions (sensitivity studies)• Assimilation with NEMURO (Chl to small/large phytoplankton)• Forecast skill assessment for physics and biology

Collaborators:

H. Arango (Rutgers), K. Bruland (UC Santa Cruz),

E. Curchitser (Rutgers), E. Di Lorenzo (Georgia Tech),

C. Edwards (UC Santa Cruz), K. Hedstrom (ARSRC),

A. Hermann (NOAA/PMEL), B. Powell (U. Hawaii),

T. Powell (UC Berkeley)

Funding:

National Science Foundation (U.S. GLOBEC)

Iron Limitation on Phytoplankton Growth

Nitrate-limited phytop. growth rate:

Dissolved (available) Iron:

Phytop.-associated Iron:

Iron uptake: Optimal Fe:C:

Realized Fe:C:

Iron-limited phytop. growth:

FeNmFepd IUp

P

GZRF

t

F

FeNpp Ip

P

GZUF

t

Fm

Fe

Fe t

NCP-RRI

:0adbFR 0

NCP

FR p

:

),min( *22

2

NFe

N UkR

RU

)(* Pz

NmN

PWekN

NVU

Chlorophyll Vertical Profiles: GAK Stations, 2001