RAPIDS Operational Blending of Nowcasting and NWP QPF Wai-kin Wong and Edwin ST Lai Hong Kong Observatory The Second International Symposium on Quantitative Precipitation Forecasting and Hydrology 5-8 June 2006 1
Lin et al (2004) 2
extrapolation effective in advective cases more effective in nonlinear moving; rapidly changing cases Nowcast High resolution NWP high resolution, rapidly updated seamless very-short-range QPF 3
RAPIDS Rainstorm Analysis and Prediction Integrated Data-processing System Nowcasting component SWIRLS 1-6 hr QPF by extending the linear extrapolation of radar echoes NWPcomponent Non-hydrostatic Model (NHM) 1 6 hr QPF by non-hydrostatic numerical model Hourly update 2 km resolution T+1 T + 6 hour forecast 4
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Extending SWIRLS F/C to 6 hr modified semi-lagrangian advection scheme (SLAS) Robert scheme (3 iterations) Bi-cubic Lagrangian interpolation Flux limiter (local max, min constraint) One-way nesting resolution 1.1 km -> 0.5 km Less dispersive Circulation preserved dz dt = Z t Z + u x = 0 TREC wind Forecast reflectivity TREC wind Up to 6 hr (6-min interval) Forecast reflectivity pure rotation Up to 6 hr (6-min interval) 7
Performance Verification data sets : 8 May 20 Dec 2005 Overall, similar performance For Amber, SLA slightly better than LE 1.0 0.9 POD (SLA) POD (LE) 0.8 FAR (SLA) FAR (LE) Performance 0.7 0.6 0.5 0.4 CSI (SLA) PIL (SLA) CSI (LE) PIL (LE) 0.3 0.2 0.1 0.0 Amber Rain Red Rain Flood Landslip Warning Guidance Issued By SWIRLS 8
Non-hydrostatic Model (NHM) 5-km horizontal resolution 121x121 grid-points, 45 vertical levels (lowest at 10m ) Trial operation started in April 04 (two runs per day) and upgraded to hourly update in April 05 Initial : RSM + LAPS moisture Boundary : RSM KF + 3 ice bulk cloud microphysics 9
Remote sensing data assimilated in HKO-LAPS Radar reflectivity and Doppler velocity Geostationary satellite imagery GPS PWV Radar derived echo movement (TREC wind) QuikSCAT retrieved wind 10
LAPS + NHM Initialized by ORSM 15 UTC 7 May 2004 T + 8 hr forecast Initialized by LAPS (no radar data) 11
Initialized by LAPS with radar and GPS data 12
Blending SWIRLS and NHM QPF QPF ( t) = (1 w( t)) QPF + w( t) SLAS QPF NHM 1. NHM rain pattern adjustment translation, rotation, deformation 2. Dynamical blending hyperbolic function with varying end points adjustment β α β α w( T ) = α + T 2 { 1+ tanh[ γ (3 9)] } α, β determined dynamically by past performance 13
Location adjustment Rigid and projective transforms J ( M ) = = = 1 2 1 2 1 2 e 2 x, y [ I ( x', y') I( x, y) ] f [ I ( x', y') I( x, y) ] f 2 2 dxdy nonlinear coordinates transformation where x' y' = x M y I f ( x, y) I ( x, y) Input image reference image transformed image I f ( x', y') I f ( x, y) Szeliski (1996) 14
α and β derived from real-time verification of QPFs from NHM and SWIRLS β α γ 1 β α w( T ) = α + T 2 { 1 + tanh[ γ ( 3)] } 15
ν SWIRLS w( t) = ( t = 0; t = ν + ν SWIRLS NHM 6) ν = max( h( R1, R2 ), h( R2, R1 )) 2μR μ 2 1 R σ 2 R σ 1 R2 2 2 2 2 μ + μ σ + σ R 1 R 2 R 1 R 2 Measure of spatial error Intensity difference mean value of R 1 NHM QPF Radar rainfall analysis standard deviation of R 1 ν = 0 (perfect match) ν -> (totally mismatch) Venugopal et.al. (2005) 16
Re-visit of blending weight Frequency distribution of α and β Lost of pattern matching skill in SWIRLS SLA T+6 hr forecast 17
Re-visit of relocation vector NHM Forecast Rainfall Analysis min [ R NHM ( x, y) R an ( x u, y v)] 2 da 18
T + 1 hr T + 3 hr x - component y - component 19
T + 6 hr T + 9 hr x - component y - component 20
SWIRLS SLAS F/C NHM DMO F/C NHM F/C (rigid transformed) + Radar observation (verification) RAPIDS F/C SWIRLS good intensity F/C NHM good storm development F/C RAPIDS the best F/C 21
Red rainstorm 2 June 2006 22
Red rainstorm on 2 June 2006 23
T+5 and T+6 hr f/c starting at 06HKT SWIRLS SLA NHM DMO ACTUAL 24
NHM with phase correction RAPIDS ACTUAL 25
T+3 hr and T+4hr f/c starting from 08HKT SWIRLS SLA NHM DMO ACTUAL 26
NHM with phase correction RAPIDS ACTUAL 27
22 HKT 29 July 2005 (outer rain-bands due to TS Washi) Relocation of rainband based on projective transform Actual rainfall analysis at 22 HKT Relocation of rainband based on rigid transform 28
6-hr forecast from NHM 6-hr forecast from NHM Rigid transform 3-hr forecast from SWIRLS SLAS Projective transform 29
RAPIDS : Performance in 2005 More skillful rainfall forecast using blending Similar performance for two pattern adjustment schemes Grid-based (2km resolution) rain/no-rain verification Rainstorm cases in 2005 ~ 170 # of forecast 30
Concluding remarks RAPIDS combines QPF from SWIRLS: frequently update radar obs + improved advection forecast NHM: information on development of precipitation Optimal blending to add further skills in QPF using nowcast and NWP Future development Intensity change in SWIRLS QPF Improve the data assimilation system for NHM Regional phase correction guidance on potential precipitation development from other model forecast elements Probabilistic QPF 31
The End Thank you 32