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GMAO Hybrid Ensemble 3D-Var
Amal El Akkraoui and Ricardo TodlingGlobal Modeling and Assimilation Office
Many thanks to: D. Kleist, D. Parish, J. Whitaker, and R. Treadon.
Sep 27, 2012 1 / 17
Outline
1 Background and motivation
2 Experiment Settings
3 Results
4 Summary and ongoing work
Sep 27, 2012 2 / 17
Background and motivation
Background and motivation
Use flow-dependent background error information derived fromensemble techniques but still within the variational framework.The 3D-Var cost function:
J(δx) =12δxTB−1δx +
12(Hδx − y′)TR−1(Hδx − y′)
The hybrid 3D-Var cost function:
J(x′) =12x′T (βB + (1− β)Pe ◦ S)−1x′ +
12(Hx′ − y′)TR−1(Hx′ − y′)
x′ = δx +K∑
k=1
ak ◦ xek , and Pe =K∑
k=1
xek(xek)
T
Sep 27, 2012 3 / 17
Experiment Settings
Experiment setting
Control run (Ctl):
Conventional 3D-Var;analysis at 0.5o ;forecasts at 0.5o ;close run to ops.
Ensemble:32 members at 1o ; S-EnKF;Additive inflation; Verticallyvarying localization scales;Re-centering around ctl ana.
Hyrid run (Hyb):
Dual resolution (central at 0.5o , ensemble at 1o); β = 0.5;members re-centered around the central analysis.Time frame: mid-November through end of december 2011.2-week spin up period, and hybrid starts on Dec 1st.
Sep 27, 2012 4 / 17
Results
Results: OMF —— Hyb —— Ctl
Uwind
Temp
Sep 27, 2012 5 / 17
Results
Results: Monthly means (Temperature)
Ctl vs. NCEP Hyb vs. NCEP
Sep 27, 2012 6 / 17
Results
Results: Monthly means (Temperature)
Ctl vs. ECMWF Hyb vs. ECMWF
Sep 27, 2012 7 / 17
Results
Results: Monthly means (U-winds)
Ctl vs. NCEP Hyb vs. NCEP
Sep 27, 2012 8 / 17
Results
Results: Monthly means (U-winds)
Ctl vs. ECMWF Hyb vs. ECMWF
Sep 27, 2012 9 / 17
Results
Results: Monthly means (U-winds at 200 mb)
vs. NCEP vs. ECMWF
Ctl
Hyb
Sep 27, 2012 10 / 17
Results
Forecast skills: Anomaly correlations ( 500 mb height)
—— Ctl —— hyb
Sep 27, 2012 11 / 17
Results
Forecast skills: Anomaly correlations (500 mb Uwind)
—— Ctl —— hyb
Sep 27, 2012 12 / 17
Results
Forecast skills: Anomaly correlations (200/850 Uwind)
—— Ctl —— hyb
Sep 27, 2012 13 / 17
Results
Forecast skills: RMS ( Temperature tropics )
—— Ctl —— hyb
Sep 27, 2012 14 / 17
Results
Forecast skills: RMS ( Uwind tropics )
—— Ctl —— hyb
Sep 27, 2012 15 / 17
Summary and ongoing work
Summary
Overall, the results are significantly positive : largely positive for thetropical winds around 500-200mb, and slightly positive to neutralelsewhere;Ensemble likely to be pointing to a weakness in the static B in thetropics;Still need to examine why the hybrid impact is marginal fortemperature for instance.
Sep 27, 2012 16 / 17
Summary and ongoing work
What next?
Better understand the added value of the ensemble in a hybrid modeby exploring other hybrid configurations:− Experiment with a different values of the weighting parameter β;− Experiment with a higher resolution ensemble; 32 members at 1/2
degree. (Ongoing) ;− Experiment with a larger ensemble size (64 members at 1 degree);− Evaluate which is more beneficial, reducing the sampling error
(large ens. size) or the representiveness error (higher resolutionensemble).Examine the stratospheric levels.
Sep 27, 2012 17 / 17
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