Quality Assessment of a 1985-2007 Mediterranean Sea Reanalysis

M. Adani, G. Coppini, C.Fratianni, P.Oddo, M.Tonani, GNOO, INGV Sez Bologna

N. Pinardi, M. Zavatarelli, Univ. of Bologna

V. Lyubartsev, S. Dobricic, CMCC, Bologna

Ocean General Circulation Model:OPA code (Tonani et al., 2008)1/16 x 1/16 and 71 unevenly spaced levels

Daily Mean output: Temperature Salinity Velocities Wind Stress Sea Surface Height Heat Flux Water Flux Shortwave Radiation

Observations: T/S in situ profiles (MedAtlas, MFS) SLA along track (T/P,ERS1,ERS2, ENVISAT,J1)

Observations: OI-SST

Assimilation schemes:• OceanVar (Dobricic, S., and N., Pinardi, 2007)

• SOFA (De Mey, P., and M. Benkiran, 2002)Assimilation schemes:RELAXATION

Experimental set-up

Atmospheric and hydrological forcing: ➔ ECMWF operational analysis + ERA15 ➔ Monthly mean climatological NCEP precipitation ➔ Monthly mean climatological river runoff (GRDC)

Experimental set-up cont.

Data Distribution

Examples of spatial distribution of in situ and satellite observations in one day.

Experiment Name Description

SIM Forced simulation: 85-07

OV-RE Re-analysis using OceanVar (3dvar): 85-07

SO-RERe-analysis using SOFA (ROOI): 85-90;

93-96;00-07 restart from OceanVar

Experimental set-up cont.

•Multivariate part of the error background covariance matrix (B) is common to both assimilation scheme and the observational error matrix (R) is identical.

•Major difference between the two implementations is that OceanVar uses a barotropic model to estimates the corrections on SLA and SOFA uses formula of level of no-motion. In the latter case the SLA data can be assimilated only in area deeper then 1000 meters resulting in 12% less satellite observations assimilated for SO-RE.

yxyxxxxxx Tb

Tb HRHBJ 11

2

1

Results

)()()()(

u

4321

TttVCp

yxTTTQ

yxQ

zyxV

TKT

V

zyxT0

M

sTT

o

M

4H

M

s

1. Mediterranean Volume Temperature2. Gibraltar advective/diffusive part3. Solar radiation4. Relaxation term

relaxationdata assimilation

Results cont.

RMSE

BIAS

TEMPERATURE SALINITY

Results cont.

SLA RMSE

Large scale low frequency ocean variability

Mean circulation at 15 m

The interpretation

Mea

n c

ircu

lati

on

in t

he

200

-300

m

Ionian reversal

Strengthening of the Levantine circulation

1987-1996

1997-2006Dec

adal

var

iab

ility

The mean vs Eddy Kinetic Energy (EKE)

u

ru

ru

ru

1

ru dt

0

EKE 1

2u 2 v 2

TKE 1

2u2 v2

0-bot:0,03 m s-1

0-150 m:0,07 m s-1

EKE is 70-90%of TKE

udtT

1u

uuu '

Water mass formation rates: results

Four major events:1)1987 for WMDW

2) 1992-1993 for LIW,

CDW and EMDW

3) 1999-2000 for WMDW and EMDW

4) 2005-2006 WMDW, EMDW and LIW

WMDW EMDW

CDWLIW

Sv

Eastern Med Transient

Conclusions• Two re-analysis and a simulation has been carried out for the Mediterranean Sea from 1985 to 2007 .

• All available in situ and satellite information for the past 23 years have been used with two assimilation schemes, a Reduced Order Optimal Interpolation scheme, so-called SOFA, and a three-dimensional variational scheme, so-called OceanVar.

•OV-RE gives better results for abundant data such as SLA, improving by about 10% the RMSE with respect to SO-RE, but giving the same RMSE of SO-RE for sparse data sets, such as temperature and salinity profiles.

•Reanalysis is a useful dataset to study the low frequency variability of the ocean

References:M. Adani, S. Dobricic, N. Pinardi, 2011: Quality Assessment of a 1985–2007 Mediterranean Sea Reanalysis. J. Atmos. Oceanic Technol., 28, 569–589. doi: 10.1175/2010JTECHO798.1

N. Pinardi, M. Adani, G. Coppini, C. Fratianni, P. Oddo, M. Tonani, V. Lyubartsev, S. Dobricic, M. Zavatarelli.. The Mediterranean Sea large scale low frequency ocean variability from 1987 to 2007: a retrospective analysis., in preparation.