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Assessment of Tropical Rainfall Potential (TRaP) forecasts during the 2003-04 Australian tropical cyclone season. Beth Ebert BMRC, Melbourne, Australia with thanks to Sheldon Kusselson, Mike Turk, Ralph Ferraro and Bob Kuligowski. 2 nd IPWG Meeting, Monterey, 25-28 October 2004. - PowerPoint PPT Presentation
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Assessment of Tropical Rainfall Potential (TRaP) forecasts
during the 2003-04 Australian tropical cyclone season
Beth Ebert
BMRC, Melbourne, Australia
with thanks to Sheldon Kusselson, Mike Turk, Ralph Ferraro and Bob Kuligowski
2nd IPWG Meeting, Monterey, 25-28 October 2004
TRaP - Tropical Rainfall PotentialNESDIS nowcasts of rain in tropical cyclones
Generation of TRaP:
1. Compute areal rain rates from passive microwave sensor (SSM/I, AMSU, or TRMM)
2. Using operational forecast cyclone track, advect rainfall for 24 h, assuming steady state storm structure
3. Analyst vets TRaP prior to public release
TC Craig, 10 March 2003
DARWIN
DARWIN
SSM/I"snapshot"
TRaP
Validation of TRaP over U.S. for 2002 Atlantic hurricane season(Ferraro et al., 2004, Wea. Forecasting, submitted)
SSM/IAMSUTRMM
42 TRaPs verified against Stage IV radar/gauge analyses at 4 km resolution.
TRaP under-estimated rain rate, volume, max.
TRaPs from TRMM performed best, closely followed by AMSU.
TRaP outperformed Eta NWP model forecasts at 50 km resolution.
Sensor (cases)
Rain rate (TRaP /
Stage IV)
Rain volume (TRaP /
Stage IV)
TRaP maximum rain
(mm d-1)
Stage IV maximum rain
(mm d-1)
AMSU (11) 0.59 0.55 90.1 351.8
SSM/I (16) 0.71 0.65 106.1 345.0
TRMM (15) 0.84 0.77 140.5 355.9
Atlantic vs. South Pacific hurricane rainfall
Mean rain rate from TRMM TMI as a function of radial distance from storm center, 1998-2000
Lonfat et al., 2004, Mon. Wea. Rev.
Atlantic
South Pacific
2003-2004 Australian tropical cyclones
Validation strategies: maximum 24 h rain at landfall vs. rain gauge observations ±3h (±12 h) spatial rainfall distribution in 10° box vs. operational 0.25° gauge analysis ±3h contiguous rain area (CRA) bounded by 20 mm d-1 threshold vs.
operational 0.25° gauge analysis ±3h
(25)
(9)
(19)
(29)(3)
Tropical Cyclone Fay (17-28 March 2004)
TRaP too great on most days, especially near landfall Some extreme values for SSM/I and TRMM
* Areal TRaP vs gauge observations not ideal but no radar data available
landfall
Tropical Cyclone Fay (28 March 2004)
Maximum 24 h rain (mm)
Observed159.4
0100 UTC 28 March 2004
AMSU111.6
0233 UTC 28 March 2004
SSM/I478.1
1304 UTC 27 March 2004
TRMM251.0
0156 UTC 28 March 2004
AMSU
SSM/I TRMM
OBS
Maximum rain at landfall
TRaP estimated maximum rain well for some TCs, overestimated for others
AMSU less likely to overestimate
Mea
n
* statistics for land grid boxes only
Spatial validation - TC Fay (28 March 2004)
Aggregated results – all vs. vetted (checked by analyst) TRaPs
Rain area and volume too small by ~50% POD for heavy rain is ~0.2-0.6, FAR is ~0.2-0.6 Vetted TRaPs perform better than all (unvetted + vetted) TRaPs
Aggregated results – sensor intercomparison
SSM/I TRaPs had some large errors, AMSU had smallest errors AMSU TRaPs gave largest rain area AMSU TRaPs showed best performance, then TRMM, then SSM/I
CRA verification method (Ebert and McBride, 2000)
Define entities using threshold (Contiguous Rain Areas)
Location error determined by pattern matching (minimum total squared error, maximum correlation, or
maximum overlap)
external specification using best track data
Verify properties of CRA (size, mean and maximum intensity, etc.)
Error decomposition
MSEtotal = MSEdisplacement + MSEvolume + MSEpattern
Version for pattern matching using correlation:
(r=correlation, s=std.dev.)
ObservedX
ForecastF
2)XF(MSEvolume
)rr(ssMSE optXFntdisplaceme 2
2 12 )ss()r(ssMSE XFoptXFpattern
...track errors
...rain retrieval, no growth/decay
...steady state rain structure
Related to:
CRA validationTC Fay (0303 UTC 25 March 2004)
CRA validationTC Monty (2216 UTC 1 March 2004)
CRA validation results for vetted TRaPs
Pattern error most important, followed by volume error, then displacement error
150
100
50
0
(km) (%) (%) (%)
Comparison to operational NWP
Mesoscale model (mesoLAPS, 12 km resolution) TC-centered mesoscale model (TC-LAPS, 15 km resolution)
24 h rain forecasts for TC Monty, ~00 UTC 2 March 2004
Verification on 0.25° grid consistent with TRaP verification
Comparison to operational NWP
NWP models overestimated rain area and volume Correlations comparable between TRaP and models Threat score best for TC-LAPS
Fairer comparison might use vetted TRaPs but not enough days in common
TRaP
Comparison of Australian and US results (median values for vetted TRaPs)
Australia United States
Maximum rainfall too large by ~1/3 ~ 1/3 of observed
Heavy rain area ~ half of observed ~ 2/3 of observed
Heavy rain volume ~ half of observed ~ 2/3 of observed
Error magnitude RMS error R RMS error R
POD (heavy rain) ~0.45 ~0.50
FAR (heavy rain) ~0.30 ~0.25
Sensor intercomparison
AMSU outperformed SSM/I, not enough
TRMM to judge
TRMM best, then AMSU, then SSM/I
Comparison to NWP Worse in many respectsBetter in almost all
respects
Reasons for differences
Australia United States
Reference data Rain gauge analysis,Stage IV radar-gauge
analysis
Spatial scale ~25 km 4 km
Temporal matching ± 3 h ± 30 min
NWP model High resolution (12-15 km) Low resolution (50 km)
Typical TC size Bigger than average Smaller than average
Atmospheric moisture Drier Moister
CRA validation suggests...
LocationError18%
Volumeerror34%
Patternerror48%
track forecasts
satelliterainretrieval
no growthor decay
steady state rain structure
sources of error related to assumptions in the TRaP formulation...
Improve satellite rain algorithms
Adjust for atmospheric moisture, shear
Orographic enhancement
Include storm rotation
Statistical filter
Improve tracks (multi-model NWP)
that might be improved using a variety of strategies.
Living with uncertainty – Ensemble TRaP
Perturb or vary: Cyclone track Parameters of microwave rain rate retrieval Satellite sensors included in the ensemble, including VIS/IR Sources of TC rain forecasts: R-CLIPER, NWP, ...
TC Monty, 00 UTC 2 March 2004Ensemble of 27 TRaP forecasts (15 AMSU, 8 SSM/I, 4 TRMM) valid within ± 12 hMean includes histogram transformation
Thank you!