Upload
ariel-dawson
View
220
Download
0
Embed Size (px)
Citation preview
© Crown copyright 2004 Page 1
SRNWP Lead Centre Report on Data Assimilation 2005
for EWGLAM/SRNWP Annual Meeting 2005
3-5 October 2005, Ljubljana, SloveniaMike Bush
NWP
© Crown copyright 2004 Page 2
1. SRNWP/Met Office/HIRLAM workshop in Exeter
2. Global model 4D-VAR
3. NAE model 4D-VAR
4. U.K 4km model 3D-VAR
© Crown copyright 2004 Page 3
SRNWP/Met Office/HIRLAM Workshop
Joint SRNWP/Met Office/HIRLAM Workshop on High resolution data assimilation: towards 1-4km resolution
Held at the Met Office, Exeter 15 -17 November 2004
What is different for the convective scale?
High resolution observations – their assimilation & utility
Assimilating cloud and precipitation observations
Analysis techniques, 3D-Var and error covariances
4D-Var issues
© Crown copyright 2004 Page 4
1. SRNWP/Met Office/HIRLAM workshop in Exeter
2. Global model 4D-VAR
3. NAE model 4D-VAR
4. U.K 4km model 3D-VAR
© Crown copyright 2004 Page 5
4D-VAR: The Perturbation Forecast (PF) model
PF model is an approximation to the tangent linear model
Dynamical core:
Start from continuous equations
ECMWF start from the discrete equations for the dynamical core
scale analysis
Choose appropriate terms at an asymptotic limit
then discretize
Physics:
Simplified physics
© Crown copyright 2004 Page 6
4D-VAR : PF model physics
Simplified physics:
Boundary layer: friction and vertical diffusion of heat and momentum (following Buizza).
Latent heating scheme (simplified microphysics).
No convection.
No radiation.
No gravity wave drag
© Crown copyright 2004 Page 7
Global 4D-VAR
G33 5th October 2004Introduction of 4D-VAR.Single outer loopHalf model resolution (N108)Positive benefit – greatest impact in the SHSatellite data is asynoptic and so particularly suited to 4D-VAR
© Crown copyright 2004 Page 8
PMSL NH T+24 RMS Error against analysis
8
4DVAR4DVAR
© Crown copyright 2004 Page 9
500hPa Height SH T+24 RMS Error against analysis
9
4DVAR
© Crown copyright 2004 Page 10
250hPa Wind SH T+72 RMS Vector Error vs analysis
10
4DVAR4DVAR
© Crown copyright 2004 Page 11
1. SRNWP/Met Office/HIRLAM workshop in Exeter
2. Global model 4D-VAR
3. NAE model 4D-VAR
4. U.K 4km model 3D-VAR
© Crown copyright 2004 Page 12
NAE 4D-VAR: how to treat the boundaries
Increments zero at the lateral boundaries
Weights of 0, 0, 0, 0, 0, 0.25, 0.5, 0.75 applied going away from the rim
Simple but cheap way of treating the boundaries
HIRLAM have a more sophisticated system using periodic boundaries
Only obs within ½ gridlength of the boundary are excluded
© Crown copyright 2004 Page 13
NAE 4D-VAR testing
2-week run at half-resolution was completed
Encouraging benefit to PMSL verification.
Other fields are more neutral/slight detriments.
Global 4DVAR does not assimilate screen level data, nor does it assimilate hourly sequences of the surface obs that it does use.
These new aspects of regional 4DVAR might need further tuning.
No problems with using persistence as the PF forecast for aerosol in the 2-week run
This means that experiments with visibility assimilation can go ahead
© Crown copyright 2004 Page 14
NAE 3D-VAR vs 4D-VAR PMSL Bias and RMSE
14
© Crown copyright 2004 Page 15
3D-VAR vs 4D-VAR Temperature Bias and RMSE
15
© Crown copyright 2004 Page 16
1. SRNWP/Met Office/HIRLAM workshop in Exeter
2. Global model 4D-VAR
3. NAE model 4D-VAR
4. U.K 4km model 3D-VAR
© Crown copyright 2004 Page 17
U.K 4km model: 3D-VAR
Initial solution is to introduce 3D-VAR assimilation system (plus Analysis Correction scheme for cloud and precipitation)
So far 12 case studies run from June – September 2005
Parallel Suite running scheduled for October 2005
Implementation scheduled for November 2005
Later upgrade will address consistency with larger scale increments from the driving model
© Crown copyright 2004 Page 18
U.K 4km model 3D-VAR impact: PMSL
© Crown copyright 2004 Page 19
U.K 4km model 3D-VAR impact: 1.5m Temperature
© Crown copyright 2004 Page 20
U.K 4km model 3D-VAR impact: 10m wind
© Crown copyright 2004 Page 21
U.K 4km model 3D-VAR impact: cloud
© Crown copyright 2004 Page 22
Questions?