ocean/sea-ice

Transcription

ocean/sea-ice
Recent Advances in the Mercator-Ocean
reanalysis system : Assimilation of sea-ice
concentration in the Arctic sea
C.-E. Testut,
G. Garric, L. Parent, C.Bricaud (Mercator-Ocean, Toulouse, France)
G. Smith (CMC, Environnement Canada), Y. Lu (BIO, DFO Canada)
WWOSC, August 16-21, 2014, Montreal
Outline
Assimilation of Sea Ice Concentration in Glorys2v3
Main features of the Glorys2v3 simulation
Overview of the results in the Arctic sea
Recent developments in the Sea Ice Analysis
-
Restart strategies for the sea ice model update
Use of multivariate analysis
Use of Gaussian Anamorphosis Approach
Conclusions and Future developments
2
WWOSC, August 16-21, 2014, Montreal
Assimilation of Sea Ice Concentration :
Main features of the GLORYS2v3 simulation
GLORYS: GLobal Ocean ReanalYses and Simulations
- French Reanalysis project, supported by GMMC (Mercator, Coriolis). PI: B. Barnier
- main partners: Drakkar consortium, CORIOLIS, MERCATOR
- project started at national level in 2008 + cooperation with EU funded FP7 MyOcean project
MOTIVATION :
The need for a realistic description of the ocean state and variability over the recent decades,
at the global scale, and at the scale of the ocean basins and regional seas.
OBJECTIVES :
- Produce an eddy permitting global ocean/sea-ice reanalysis spanning the “altimetric +
ARGO" era 1992-today
- To iterate / produce different reanalysis along the 1992-today time period
- Start to design the ERA-Interim reanalysis scenario : 1979-today
- Promote the use of reanalysis products in the climate community
3
WWOSC, August 16-21, 2014, Montreal
Assimilation of Sea Ice Concentration :
Main features of the GLORYS2v3 simulation
Model
-
Nemo 3.1, LIM2-EVP
Global ¼, 75 levels
1992-2012
Assimilation
- Analysis based on a 2D local multivariate SEEK filter
- Weakly-coupled DA system using 2 separate analyses :
- Ocean Analysis (SLA, InSitu Data from CORA3.2, SST) ,
IAU on (h,T,S,U,V)
Sea Ice Concentration
from CERSAT (IFREMER)
- Ice Analysis (SIC), IAU on (SIC)
- SIC Error: 1% open ocean, linear from 25% to 5% for SIC values between 0.01 and 1
- Forecast error covariances are built from a prior ensemble of Sea Ice Concentration
anomalies => Fixed basis background error
- Temperature and salinity bias correction using Argo (3DVar method)
4
WWOSC, August 16-21, 2014, Montreal
SAM2 Data Assimilation System :
Pf: Fixed Basis Background error covariances
Representation by a prior ensemble of anomalies
 We generate a pseudo-ensemble from a forced simulation
Model trajectory
anomaly
Temporal window
Running mean of the model trajectory
 We use these anomalies to compute Pf in the analysis
2005
2003
2001
2002
2006
2004
Analysis date 1
Analysis date 2
Model trajectory
5
WWOSC, August 16-21, 2014, Montreal
SAM2 Data Assimilation System :
Background Error specification : Correlation fields
(80N,0W)
Cersat
ORCA025/LIM2noEVP
(80N,150W)
Concentration (SIC) correlation fields from 1 single concentration observation
(~280 modes, February)
6
WWOSC, August 16-21, 2014, Montreal
Assimilation of Sea Ice Concentration :
Impact in Arctic region with GLORYS2V3 System
Sea Ice Concentration on 15th September 1992 (assimilation start in December 1991)
CERSAT
Sea Ice Concentration RMS misfits
GLORYS2V3-ASSIM/ICE
GLORYS2V3-NOASSIM/ICE
Global ¼°, 75 levels
Global ¼°, 75 levels
G2V3-NOASSIM/ICE
Jan 1992
Sep 1992
May 1993
G2V3-ASSIM/ICE
Jan 1992
Sep 1992
May 1993
Sea Ice Concentration Misfits to Observation (CERSAT)
on 15th September 1992
7
WWOSC, August 16-21, 2014, Montreal
Assimilation of Sea Ice Concentration :
Impact in Arctic region with GLORYS2V3 System
September 2001
March 2001
G2V3 - CERSAT
Arctic
G2V1 - CERSAT
8
WWOSC, August 16-21, 2014, Montreal
Assimilation of Sea Ice Concentration :
Impact in Arctic region with GLORYS2V3 System
GLORYS2V3
CERSAT data
Extreme Events
Sept 1996
Good behaviour of GLORYS2V3
during extreme events
Sept 2007
9
WWOSC, August 16-21, 2014, Montreal
Assimilation of Sea Ice Concentration :
Impact in Arctic region with GLORYS2V3 System
Sea Ice extent anomaly
SIC >85%
2001
Correlation: 0.8
2001
Correlation:
0.4  0.9
10
WWOSC, August 16-21, 2014, Montreal
Assimilation of Sea Ice Concentration :
Impact in Arctic region with GLORYS2V3 System
Anomalies of Monthly Volume
Monthly Volume
11
WWOSC, August 16-21, 2014, Montreal
Recent developments
in the Sea Ice Analysis
12
WWOSC, August 16-21, 2014, Montreal
Restart Strategies for the sea ice model update
Different Restart Strategies: IAU on SIC + …
- … nothing using an implicit concept of thickness conservation
DSICi, Dhi = 0, hi = cte <=>
DVi = hi . DSICi
+
hi
SICi
Work in Progress
=
DSICi
Analysis of Sea Ice Concentration (y2006m10d15, 3 days cycle)
Innovation
CERSAT- ORCA025/LIM2noEVP
Model update
using IAU method
Residual
13
WWOSC, August 16-21, 2014, Montreal
Restart Strategies for the sea ice model update
Different Restart Strategies: IAU on SIC + …
- … nothing using an implicit concept of thickness conservation
DSICi, Dhi = 0, hi = cte <=>
DVi = hi . DSICi
+
hi
SICi
=
DSICi
- correction on thickness using a reference thickness h*=1m
DSICi , DVi = h* . DSICi <=>
Dhi = ( h* - hi )
+
hi
SICi
G2V3
Work in Progress
h*
.
(Tietsche et al.)
DSICi / ( SICi +
DSICi )
=
DSICi
TEST(G2V3 with Dh)
TEST – G2V3
14
Thickness in March
1994
WWOSC, August 16-21, 2014, Montreal
Development of a multivariate Sea Ice Analysis
Monovariate state vector for G2V3 sea ice analysis
Work in Progress
[SIC] with (SIC) observations
SIC RMS Misfit
Multivariate state vector for G2V4 sea ice analysis
[SST,SIC,Thickness] with (SST,SIC) observations
SST restricted to open ocean close to the marginal zone
FREE
G2V4
Test_G2V4 Sea Ice Model update (y2011m11d11)
SIC Model update
Thickness Model update
15
WWOSC, August 16-21, 2014, Montreal
Development of a multivariate Sea Ice Analysis
Monovariate state vector for G2V3 sea ice analysis
Work in Progress
[SIC] with (SIC) observations
SIC RMS Misfit
Multivariate state vector for G2V4 sea ice analysis
[SST,SIC,Thickness] with (SST,SIC) observations
SST restricted to open ocean close to the marginal zone
G2V3
TEST_G2V4
FREE
G2V4
TEST_G2V4 – G2V3
Thickness (y2011m11d11)
16
WWOSC, August 16-21, 2014, Montreal
SAM2 Parameterization in progress :
The Gaussian Anamorphosis approach
The Gaussian anamorphosis method consists to define an appropriate
transformation T of the space leading to gaussian distribution of the variables.
Analysis step
in the physical space
in the anamorphosed space
innovation
Error sub-space
Forecast error
Kalman gain
Observational update

 

d  T [y]  H T [x f0 ]
d  y H x f0
An i  xi  xi
An i  T[x] i  T[x] i
1
AA T  A n A Tn
n
1
T
T
1
K  A n I H A n  R H A n  H A n  R 1
Pf 


x a  x f  T 1[T [x f ]  Kd]  T 1[T [x f ]]
x a  x f  Kd
The Gaussian anamorphosis transformation T could be estimated from the ensemble forecast {xf}i
17
WWOSC, August 16-21, 2014, Montreal
The Gaussian Anamorphosis approach
SIC percentiles
SIC
Anamorphosed SIC
Local transformation of
the sea ice concentration
(SIC) pdf
Physical space
Anamorphosed space
Innovation
Physical space
Increment
18
WWOSC, August 16-21, 2014, Montreal
Conclusions and future developments
Assimilation of Sea Ice Concentration only in G2V3
-
Good representation of the sea ice extent and the sea ice concentration
Lack in the time evolution of the sea ice thickness
Work in progress on the Sea Ice analysis
- Identify of a more efficient restart strategy for the sea ice thickness
- Use of multivariate analysis where the state vector is extent to [SST,SIC,thickness]
- Use of Gaussian Anamorphosis Approach to improve the sea ice thickness update
=> obtain a more robust Sea Ice analysis for the next reanalysis and for the real time
Next steps of the development
-
Coupling between SAM2 and NEMO3.6/LIM3
Use of Arctic-Northern Atlantic Configurations (CREG4 and
CREG12 with NEMO3.6) which are in development in
partnership with Canada (Env. Can. and Fisheries and Oceans)
- CREG4 : research application, dev. of the sea ice
analysis and/or an Ensemble approach
- CREG12 : benchmark reanalysis over the last 10 years
in order to prepare the Mercator global 1/12°reanalysis
Source: G. Smith, Env. Canada, Montréal
19
WWOSC, August 16-21, 2014, Montreal
Thank You!!
20
WWOSC, August 16-21, 2014, Montreal

Similar documents