IGARSS-July-2011-final radarsat application in ocean wind measurements.ppt
r1178
1. Reprint 1178
Probabilistic Quantitative Precipitation Forecast
for Tropical Cyclone Rainfall
W.C. Woo, K.M. Lok* & W.K. Wong
The Third International Workshop on Tropical Cyclone
Landfall Processes (IWTCLP-III), Jeju, 8-10 Nov 2014
* Cambridge University, UK
2. Probabilistic Quantitative
Precipitation Forecasts
for Tropical Cyclone Rainfall
WOO WANG CHUN
HONG KONG OBSERVATORY
IWTCLP-III, JEJU 10, DEC 2014
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
3. Scales of Atmospheric Systems
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
6. Steps in Nowcasting
1. Quantitative Precipitation Estimation
2. Storm Motion Field Estimation by “ROVER”
3. Extrapolation by “Semi-Lagrangian
Advection”
4. Products for Rainfall up to 6 hours
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
8. SWIRLS - Domain
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
• Based on single radar
• Domain Size:
• Input: 512 x 512 km
• Output: 256 x 256 km
• Grid
• 480 x 480
(about 500 m)
9. Location-specific Rainfall
Nowcast
Rainfall Forecast in
half hour interval in
the next two hours
Displayed as icons
and as maps
Notifications!
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
11. QPE in SWIRLS
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
least square matching (Zawadzki 1987)
based on latest radar reflectivity and raingauge
data
linear regression to find a & b:
updated every 5 min
rainfall accumulations estimated by integrating the
rainfall rates at different times
cx
i
my
i aRbdBZ log10log10
20
25
30
35
40
45
50
55
60
5 7 9 11 13 15 17 19 21
dBG
dBZ
12. Quantitative Precipitation
Forecast (QPF) in SWIRLS
“ROVER“ - Real-time Optical-flow by Variational method for Echoes of
Radar –
◦ Radar images pre-processed:
◦ Based on the “VarFlow” algorithm developed by Bruhn et al. (2003 & 2005)
13. More on “ROVER” the radar
echo tracking algorithm…
There are 6 tunable parameters in ROVER:
1. Gaussian convolution for field smoothing s (SIGME)
2. Gaussian convolution for “local” vector field smoothing (thru
the field gradients) r (RHO)
3. regularization parameter, i.e. the weight of smoothness
constraint on motion field a (ALPHA)
4. “min_scale” for setting the finest spatial scale
Lf(MIN_SCALE)
5. “max_scale” for setting the coarsest spatial scale
Lc(MAX_SCALE)
6. the time interval for tracking radar echoes Tr
(INTERVAL_FOR_VARFLOW)
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
14. TC Module in SWIRLS
Original Advection Scheme:
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
15. TC Module in SWIRLS
Enhancement Method:
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
Separate the motion of TC before radar echo tracking
16. TC Module in SWIRLS
Improvements:
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
18. Why?
1. Better support for Rainfall Warning
System
2. Facilitate cost-benefit analyses
3. More tailored to the needs of
organizations under various operational
constraints
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
19. Experimental SWIRLS
Ensemble Rainfall Nowcast
By tuning the 6 parameters, 36 sets of
parameters have been experimented, i.e.
ensemble of 36 members.
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
23. PQPF Product 2
Probability Contour Map
For Specific Intensity Threshold
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
27. Verification and Analyses
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
Verified against Radar QPE data:
• resolution 480X480 pixels
• Generated every 6 minutes
One datum for each grid
480
480
•Data from March, April and May
•Data size ~ 5 × 109
(Five Billion)
31. Relative Operating
Characteristics (ROC)
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
Contingency Table
Observed
Total
Yes No
Forecast
Yes hits false
alarms
forecast
yes
No misses correct
negatives
forecast
no
Total observed
yes
observed
No
Total
• Together with the “observed” QPE data and the contingency table, count the
number of “hits”, “false alarms”, “misses” or “correct negatives”
• Plot probability of detection (POD) vs probability of false detection (POFD)
𝑃𝑂𝐷 =
ℎ𝑖𝑡𝑠
ℎ𝑖𝑡𝑠 + 𝑚𝑖𝑠𝑠𝑒𝑠
𝑃𝑂𝐹𝐷 =
𝑓𝑎𝑙𝑠𝑒 𝑎𝑙𝑎𝑟𝑚𝑠
𝑐𝑜𝑟𝑟𝑒𝑐𝑡 𝑛𝑒𝑔𝑎𝑡𝑖𝑣𝑒𝑠 + 𝑓𝑎𝑙𝑠𝑒 𝑎𝑙𝑎𝑟𝑚𝑠
[1]
[1]
33. Conclusions
1. This study introduces a method to
generate probabilistic rainfall nowcast, by
perturbing motion vectors of radar
echoes.
2. Arrives at fairly reliable PQPF for light and
moderate rainfall, though somewhat
overestimated heavy rain
3. ROC curves indicate an capability to
distinguish between rain and no-rain
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
34. Future Work
Verification for Other Seasons
Verification for Land-falling TCs
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECASTS
FOR TROPICAL CYCLONE RAINFALL
