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The Sensitivity of a Real-Time Four-Dimensional Data Assimilation Procedure to Weather Research and Forecast Model
Simulations: A Case Study
Hsiao-ming Hsu and Yubao Liu
NCAR/RAP
MotivationsWRF real-case initialization schemes:
SI – interpolation from other models3DVAR – hopeful, but 3D, simplified balance 4DVAR – bright future
Hereby, we look into a method to initialize WRF with a four-dimensional dynamically and physically consistent analysis, which incorporates all available synoptic and asynoptic observations.
NCAR/ATEC MM5-based RT-FDDA system provides this kind of analysis to initialize WRF forecast.
NCAR/ATEC RTFDDA Built around MM5 (Jennifer et al. 2001, Liu et al. 2002)
Continuous observation nudging (Stauffer and Seaman 1994)
Multi-grids (1 km fine meshes) 3 hourly-cycling Operated at 5 ATEC ranges and support several special tasks (CO-fire,
Olympics…)
Coldstart t
Forecasts
FDDA
Day NDay 0
During Year-2002 Winter Olympics at SLC, RTFDDA was operational for 2 months. There was a snow storm event during March 13. A pair of contrast experiments of 12-hr WRF forecasts with different initial conditions were conducted, started at 00Z, March 13.
CASE
• EXP1- “Cold start” WRF WRF initial condition was generated by re-
analysis of ETA forecast with available observations at 00Z, March 13.
• EXP2 - “Warm start” WRF WRF initial condition was obtained from the
RTFDDA analysis which had been running continuously from a “cold start” 84 hours ago.
• EXP3 - “Warm start” MM5 Same as EXP2, but with MM5
(from op-RTFDDA).
Experiment Design
Domain configuration
82 x 70
dx = 36 km
36 layers
12 levels in 1 km AGL
Coarse mesh only
Hourly Precipitation of 1 – 12 Forecasts
Cold startWarm start
Subjective verification of 1 hour precipitation at 3-h forecast
A
A
A
B B
BB
C C
C
C
OBSIR
OBSRadar
Warmstart
Coldstart
WRF Forecast at 03ZRTFDDA forecast at 03Z
Summary
• Significant differences were observed between the “cold start” and the “warm start” WRF forecasts.
• The “warm-start” WRF run compares more favorable to observations.
• The “Warm start” WRF results are very similar to those from RTFDDA (MM5) during the first few fours of forecasts.
• It is evident that reasonable benefit of reduced dynamical and cloud/precipitation “spin-up” during first few hours can be obtained by interfacing MM5 RTFDDA process to WRF initialization.
Future Work
• Comparison study on higher resolutions and severe weather cases.
• Ingesting RTFDDA cloud/precipitation analyses into “warm start” WRF.
• Implement “warm start” WRF in the same operational environment of RTFDDA MM5
• Quantitative verification of “warm-start” WRF against various observations for a longer-term parallel tests with MM5.