Transcript Etherton
Survey and summary of ensemble systems
Brian J. Etherton
Developmental Testbed Center
21 November 2011
HFIP Regional Ensemble Team
As alluded to in talk by Carolyn Reynolds, HFIP Regional
Ensemble, formed by consensus, to be put into real-time
(stream 1.5) for 2012.
To develop consensus, bi-weekly conference calls have been
held during the past 2 months, with eight presentations on
ensemble systems.
Most presentations from these calls also featured this morning
Collection of presentations to form foundation of plan for
ensemble system design
Functions/Requirements for
DA/Ensemble Hybrid System
DA
Ensemble
• Accurate estimate of the state
of a system
• Dynamically conditioned forecast
error covariance
• Estimate of error variance
- GSI does not provide this
• Initial error variance reflecting
analysis error variance
Regional DA & Ensemble systems fully consistent with global DA / Ensemble
Initial Perturbations
Most ensemble systems presented earlier account for
uncertainty in initial conditions, with differing approaches
EnKF
Cycling of Perturbations
Vortex Uncertainty
Consideration of growth rate of initial perturbations?
Some ensemble systems have moving nests, and thus, each
ensemble member may have the nest in a different location,
and these differences can impact covariance information
Default to coarser nest
Make inner nest fixed, larger area
Model Perturbations
Some, but not all, ensemble systems presented earlier
include a method for incorporating model error into the
ensemble
Convective parameterization
Cloud Microphysics (parameter and scheme)
Aerosols/radiation
Boundary layer
Since not all ensembles include model error, is it not as
important as initial condition error?
Number of ensemble members (different for DA than for
forecast? can HWRF/EMC do this?)
Ensemble metrics
Want to improved predictability of…
Rapid Intensification?
Size?
Intensity?
Track?
Will we investigate the error statistics from the ensemble...
Innovations as a means of assessment?
Summary of the Summary
For the HWRF regional ensemble – must work towards:
Domain (moving inner nests used for DA? Just outer?)
Ens Initial perturbations (the flow, the vortex)
Ens Model perturbations (physics schemes, physics parameters)
As applied to the GSI-Hybrid, additional issues:
Observations (the more the better: radar, TCvitals, but how?)
GSI itself (localization, balances)
Maintain operational needs while allowing for research
testing and evaluation – modularity and flexibility
Robustness for operations
Flexibility for research
Next Steps
Conclude introductory talks (Mon Dec 12):
Zhan Zhang, EMC
Altug Askoy, AOML
Resources for testing and evaluation (FTEs and CPUs)
Reach consensus on ensemble system
For DA, DTC will start with ESRL version of GSI-Hybrid for
HWRF
For the ensemble, a few more questions to be answered