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NAE 4D-Var – Testing and Issues EWGLAM/SRNWP meeting Zurich 9 th -12 th October 2006. Mark Naylor Data Assimilation, NWP. NAE 4DVar. The Met Office’s 4DVar NAE went operational on the 14 th March 2006 after much testing and tuning. We will present results from:- - PowerPoint PPT Presentation
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NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 1
Mark NaylorData Assimilation, NWP
NAE 4D-Var – Testing and IssuesEWGLAM/SRNWP meeting Zurich 9th-12th October 2006
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 2
NAE 4DVar
The Met Office’s 4DVar NAE went operational on the 14th March 2006 after much testing and tuning. We will present results from:-
Two season’s trials (Spring and Summer 2005)Pre-operational real-time trials – 5 weeks in Dec 2005
Problems, particularly with screen temperature (T2m) scores.
Future development plans
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 3
Spring 2005 Trial
6th – 20th March
Mixed conditions:
anticyclonic with widespread frost
lows bringing gale force winds
very mild south-westerlies
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 4
Spring 2005 Trial
6th – 20th March
The NWP UK index is used to asses skill in the NAE and consists of verification against screen temperature, visibility, wind, cloud
amount and precipitation amount.
NWP UK Index (NAE area): +1.5%
NWP UK Index (UK Mes area): +2.6%
NWP UK Index (UK stations): +1.9%
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 5
Spring 2005 Trial - Pressure
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 6
Spring 2005 Trial – Screen Temperature
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Spring 2005 Trial
Summary
• good positive impacts
• wind and pressure particularly good
• hint of improved balance at T+0
• detriment in screen temperature fit up to T+12
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 8
Summer 2005 Trial
18th June – 2nd July
Week 1 anticyclonic with thunderstorms
Week 2 anticyclonic and more mobile weather with rain over UK
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 9
Summer 2005 Trial
18th June – 2nd July
NWP UK Index (NAE area): +2.0%
NWP UK Index (UK Mes area): +3.7%
NWP UK Index (UK stations): +5.4%
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 10
Summer 2005 Trial - Pressure
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Summer 2005 Trial – Screen Temperature
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Summer 2005 Trial summer rainfall
t+9 3DVAR
t+9 4DVAR radar
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Summer Trial 2005
Summary
• again good scores, especially ppn
• screen level temperature ok after T+0
• better balance in analysis
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 14
Real-time trial setup
4DVAR real-time trial (Dec 2005) final settings
12km UM /36km PF Visibility Assimilation on ‘operational’ 3-hourly 3D-Var control 6 weeks real-time from Dec 2005 4 forecasts per day
4DVar gave consistently positive results, similar to the seasonal trials
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 15
Equitable Threat Score precipitation ETS
3D-Var
4D-Var
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 16
Screen Temperature Scores
3D-Var
4D-Var
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 17
Screen Temperature investigation
An investigation into the poor initial screen temperature scores, involving experimental reruns in March 2006, was undertaken.
The 1st week of March 2006 included some especially poor screen temperature forecasts.
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 18
Single reruns
18Z on 2nd March was particularly bad so was rerun and compared with experiments including:-
PF Persistence
No Screen Temperature obs
3DVar
No T2m obs after T+0 (i.e. obs only from T-3 to T+0)
Halving period of all obs (i.e. obs only from T-90m to T+90m)
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 19
Screen Temperature VER results
The UM ran to T+6 and RMS’s produced:-
Operational NAE (3DVar 3-hourly) is still better than 4DVar Control at T+0 RMS fit.
PF Persistence has a lower RMS fit than Control 4DVar at T+0 !
Using T obs only upto T+0 increased RMS.
3DVar (with 6 hours obs) is similar to 3DVar
Using 3-hours of all obs halves the gap
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 20
Issues with Screen Temperature experiments
PF persistence has a lower RMS error to obs at T+0 than 4DVAR.
Removing the 2nd half of the time-window for screen temperature obs increases the RMS error.
Halving the number of all the obs (to between T-90m to T+90m) decreases the T2m RMS but has a major detriment on scores for other variables (especially pressure).
Is the PF model dealing correctly with Surface Temperature?
Stats reflect only one case, but 1-week reruns indicate similar results.
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 21
Linearisation tests
In PF-linearisation tests low-level theta in persistence also beats control for the first 2 hours (8 timesteps):-
4DVar Persistence
After the first 2 hours the PF model has a higher correlation. Why isn’t this feeding into the analysis?
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 22
Damping Coefficient
Theta damping coefficient from analysis increment.
The Theta Damping coefficient is the ratio the average PF model increment size to the average UM increment size
In the lower levels, the Theta PF increment is up to 20% larger than the UM increment
Can we improve the physics to remedy this feature?
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 23
Future Improvements
New PF physics package is expected later this year. Includes better boundary layer mixing and PF
convection.
We wait to see how this will influence the screen temperature near T+0.
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 24
Recent Improvement
The Screen temperature skill in Summer was improved through soil moisture modifications
We now get soil moisture (outside the UK) from the Global Model nudging scheme replacing climatology
NAE 4DVAR Oct 2006 © Crown copyright 2006 Page 25
Questions?
Any questions?........