3d-var data assimilation experiments for the double-nested limited area model aladin/hungary

EWGLAM meetingEWGLAM meeting

3D-VAR data assimilation experiments for the double-nested limited area model3D-VAR data assimilation experiments for the double-nested limited area modelALADIN/HungaryALADIN/Hungary

117-10 October, 20027-10 October, 2002

3D-VAR data assimilation experiments 3D-VAR data assimilation experiments for the double-nested limited area model for the double-nested limited area model

ALADIN/HungaryALADIN/Hungary

Steluta Alexandru

Supervisor: Andras Horanyi



227-10 October, 20027-10 October, 2002

Introduction

• The aim: to get an idea about the best strategy of the 3D-VAR data assimilation scheme for a double nested-limited area model.

• Variational assimilation consists in minimizing a cost function J(x).

• The adjoint operator is used to compute the gradient of the cost function J(x).



337-10 October, 20027-10 October, 2002

What does it mean a double-nested model?What does it mean a double-nested model?

ARPEGE

ALADIN/LACE

ALADIN/Hungary

boundary

conditions



447-10 October, 20027-10 October, 2002

What does it mean a double-nested model?What does it mean a double-nested model?

12 km resolution

8 km resolution



557-10 October, 20027-10 October, 2002

The experiments performed (I)The experiments performed (I)

Different lateral boundary techniques:

Time-consistency

Space-consistency



667-10 October, 20027-10 October, 2002

ResultsResults

• Statistical measures• RMSE

• BIAS

• Diagnostic measures• Time evolution of the fields

• Spectral energy on ellipses

• Subjective evaluation• Maps with increments

• Maps with meteorological fields



777-10 October, 20027-10 October, 2002

Verification of the analysisVerification of the analysis

RMSE RMSE ssppaceace

RMSE RMSE timetime

RMSE operRMSE oper

Period

25.02 - 02.03.2002

00 UTC

The fields are closer to the observations using 3D-VAR scheme.

The fields are closer to the observations using 3D-VAR scheme.



887-10 October, 20027-10 October, 2002

Verification of 6h forecastVerification of 6h forecast

RMSE RMSE ssppaceace

RMSE RMSE timetime

RMSE operRMSE oper

• The fields with 3D-VAR are keeping the initial improvement, but not for all levels.

• The time-consistency is a better technique for the double-nested limited area model.


• The time-consistency is a better technique for the double-nested limited area model.



997-10 October, 20027-10 October, 2002

The experiments performed (II)The experiments performed (II)

Different initialization methods:

Digital FiIter Initialization

Incremental Digital FiIter Initialization

no initialization



10107-10 October, 20027-10 October, 2002

Time evolution of the pressure in cyclingTime evolution of the pressure in cycling

time IDFItime IDFI

time no DFItime no DFI

time DFItime DFI

In 3D-VAR cycling, digital filter initialization has to be applied.

In 3D-VAR cycling, digital filter initialization has to be applied.

02.03.2002

00 UTC



11117-10 October, 20027-10 October, 2002

Time evolution of the pressure in productionTime evolution of the pressure in production

time DFI cycling;time DFI cycling;

DFI productionDFI production

time no DFI cycling;time no DFI cycling;

no DFI productionno DFI production

time IDFI cycling;time IDFI cycling;

DFI productionDFI production

In production, digital filter initialization is need.

In production, digital filter initialization is need.

operoper

02.03.2002

00 UTC



12127-10 October, 20027-10 October, 2002

The experiments performed (III)The experiments performed (III)

Different lateral boundary conditions files:

ALADIN/LACE

ARPEGE



13137-10 October, 20027-10 October, 2002

Verification of the analysisVerification of the analysis

RMSE RMSE LACELACE

RMSE RMSE ARPEGEARPEGE

RMSE operRMSE oper

Period

25.02 - 25.03.2002

00 UTC

• The fields are closer to the observations using 3D-VAR scheme.

• There is no signifficant difference for the analyses with 3D-VAR, when different LBC files were used.

• The fields are closer to the observations using 3D-VAR scheme.

• There is no signifficant difference for the analyses with 3D-VAR, when different LBC files were used.



14147-10 October, 20027-10 October, 2002

Verification of 6h forecastVerification of 6h forecast

RMSE RMSE LACELACE

RMSE RMSE ARPEGEARPEGE

RMSE operRMSE oper


• The choice of the LBC files is not so important.


• The choice of the LBC files is not so important.



15157-10 October, 20027-10 October, 2002

ConclusionsConclusions

• The forecast with 3D-VAR keeps the improvement of the analysis.

• Using time-consistency, a better forecast is obtained.

• In 3D-VAR cycling and in production, digital filter initialization method is need.

• The choice of the lateral boundary conditions files is not so important.



16167-10 October, 20027-10 October, 2002

Future plansFuture plans

• Case studies

• More data to be used.

• Tests with lagged statistics.

• Use of the spectral blending procedure.



17177-10 October, 20027-10 October, 2002

THANK YOU FOR YOUR ATTENTION!

3d-var data assimilation experiments for the double-nested limited area model aladin/hungary

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