1. 8th EnKF Workshop
Discussion

2. Limits to EnKF:
Great progress over the last 10 years thanks to ensemble based data assimilation.
limits: model error (boundary layer + stratosphere microphysics).
How to deal with slowly evolving model error?

3. Hybrids
Ensemble size: we would like to use very large ensembles with members or more. How to obtain such a big ensemble efficiently? Mix-resolution ensembles? ETLM?
An alternative is the use of hybrids. Does this work at high resolution?

4. Radar
The direct assimilation of radar observations with forward operators based on our best microphysics has a only modest impact beyond 6h. The Frankenstate directly links the radar image with a best member. Is this a good way to avoid the complexity of microphysics in data- assimilation and have longer lasting impacts?

5. Particle filters
Are non-Gaussian issues best solved using particle filters? How many particles should we have? 1000?
Should we use iterative smoother algorithms or particle filters to link radar measurements with large-scale precursors of precipitation?

6. B-localization B-localization seems to give best result.
In EnKF formulations this is expensive (factor of 10).
Is it worth it?
Study by Mitchell showed the main problem for AMSU-A data assimilation is the structure of B, not the localization. What would create deep modes in B? Should we sample uncertainty in bias correction? Something else?
Should we do a Principal Component Analysis of radiance observations and does this affect the above?

7. System (aka model) error
Many different ways to account for system error are in use: RTPP, RTPS, Additive covariance inflation, adaptive multiplicative inflation.
Schemes are often combined and used in an engineering fashion (tuned for optimal results).
A few schemes are/seem “physically informed”: SKEB, randomized transport. No schemes feed back to system/model improvement.
How to connect system error simulation with system development?

8. Forecast sensitivity to observations
Should system error parameterizations (additive inflation, RTPP, etc. ) be undone?

9. Next workshop Any suggestions for a 9th EnKF workshop?
Issue of having too many similar meetings. The EnKF workshop is every two years. ISDA every year.
Also note the yearly Bergen workshop for a slightly different crowd (oceanography + oil reservoir modeling).

10. Closure