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
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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