Transcript Major transition in 4DWX modeling system

The Sensitivity of a Real-Time FourDimensional Data Assimilation Procedure
to Weather Research and Forecast Model
Simulations: A Case Study
Hsiao-ming Hsu and Yubao Liu
NCAR/RAP
Motivations
WRF real-case initialization schemes:
 SI – interpolation from other models
 3DVAR – 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
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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…)
Cold
start
FDDA
Day 0
Forecasts
t
Day N
CASE
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.
Experiment Design
• EXP1- “Cold start” WRF
WRF initial condition was generated by reanalysis 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).
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
Warm start
Cold start
Subjective verification of 1 hour precipitation at 3-h forecast
A
B
A
C
C
B
Warm
start
Cold
start
C
A
B
OBS
IR
C
B
OBS
Radar
WRF Forecast at 03Z
RTFDDA 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.