Convection-permitting forecasts initialized with continuously- cycling limited-area 3DVAR, EnKF and “hybrid” data assimilation systems Craig Schwartz and Zhiquan Liu NCAR/NESL/MMM [email protected]NCAR is sponsored by the National Science Foundation
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Convection-permitting forecasts initialized with continuously-cycling limited-area 3DVAR, EnKF and “hybrid” data assimilation systems Craig Schwartz and.
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Convection-permitting forecasts initialized with continuously-cycling
limited-area 3DVAR, EnKF and “hybrid”data assimilation systems
NCAR is sponsored by the National Science Foundation
Introduction• Convection-permitting forecasts have
commonly been initialized from operational analyses (e.g., GFS, NAM)– Example: Interpolate GFS analysis onto WRF
domain
• Continuously cycling mesoscale data assimilation systems can produce initial conditions for convection-permitting forecasts– Dynamically consistent analysis/forecast
system
A few data assimilation approaches• Three-dimensional variational (3DVAR)
– Background error covariances (BECs) typically fixed/time-invariant
– May yield poor results when actual flow differs from that encapsulated within the fixed “climatology”
• All of the previous material was summarized in this publication:
Schwartz, C. S., and Z. Liu, 2014: Convection-permitting forecasts initialized with continuously-cycling limited-area 3DVAR, ensemble Kalman filter, and “hybrid” variational-ensemble data assimilation systems. Mon. Wea. Rev., 142, 716–738, doi: 10.1175/MWR-D-13-00100.1.
Preview of new work• Recently, the exact same experiments
were performed but over a new period:– May 4 – June 30, 2013– 55 4-km forecasts
• Near identical configuration as before, except used Thompson microphysics
• Also performed dual-resolution hybrid analyses with a 4-km deterministic background and 20-km ensemble
Cycling data assimilation: Hybrid/EnKF flowchart
4-km
20-km
FSS: The first 12-hrs2013 experiments: FSS aggregated over
55 forecasts
0.25 mm/hr 1.0 mm/hr
5.0 mm/hr 10.0 mm/hr
FSS: The first 12-hrs2013 experiments: FSS aggregated over
55 forecasts
0.25 mm/hr 1.0 mm/hr
5.0 mm/hr 10.0 mm/hr
Dual-resolution hybrid: 4-km analyses and subsequent forecasts
FSS: Forecast hours 18-362013 experiments: FSS aggregated over
55 forecasts
0.25 mm/hr 1.0 mm/hr
5.0 mm/hr 10.0 mm/hr
Summary• Precipitation bias characteristics similar
in the cycling experiments• Differences in precipitation placement
evident– Hybrid and EnSRF performed best– Shows the benefit of flow-dependent
background errors
• Further improvement possible with high-resolution analyses