Transcript Canadian Dual Pole - Mark Alliksaar, Environment Canada

Dual Polarization Radar and Rainfall
Nowcasting
• by Mark Alliksaar
National Lab for Remote Sensing and Nowcasting
Dual Polarization can potentially improve
rainfall nowcasting in three ways:
1. Radar attenuation can be corrected using the
polarimetric parameter Φdp. This improves rain rate
estimates and QPE derived from reflectivity factor Z.
2. Rain rate and QPE can also be derived directly from Kdp
instead of Z.
3. Hail identification. In conventional QPE estimates, hail
contamination is always a possibility in convective
situations.
National Lab for Remote Sensing and Nowcasting
Rain rate estimation from Kdp
RK dp   cK
b
dp
• R is rain rate in mm/hr
• b,c are empirical constants
• R derived from Kdp is more accurate because Kdp not
subject to attenuation
National Lab for Remote Sensing and Nowcasting
Attenuation correction using Φdp
Z r    dp r 
• ΔZ is attenuation correction
• r is range along radial
• α is an empirical constant
National Lab for Remote Sensing and Nowcasting
August 2, 2005
(day of Air France accident at
YYZ)
Cloud Physics & Severe Weather Research Division
King City
Corrected Radar Reflectivity
0.4° PPI
Cloud Physics & Severe Weather Research Division
King City
Enhanced View near YYZ
Radar Reflectivity
Corrected Radar Reflectivity
Cloud Physics & Severe Weather Research Division
King City
Attenuation Calculation
(Radial 200.5°)
Cloud Boundary
Zcorr
Z
φdp
Cloud Physics & Severe Weather Research Division
King City
Validation with Buffalo NEXRAD
Frequency Histograms of Reflectivity
near YYZ
Cloud Physics & Severe Weather Research Division
King City
August 19, 2005
(flash flood event in North Toronto)
Cloud Physics & Severe Weather Research Division
King City
Radar Reflectivity
Corrected
Reflectivity
Reflectivity
Z ZCORR
Cloud Physics & Severe Weather Research Division
King City
One Hour Precipitation Accumulation (Z)
Enhanced View in North Toronto
Rain Accumulation (Z)
Cloud Physics & Severe Weather Research Division
King City
One Hour Precipitation Accumulation (Zc)
Enhanced View in North Toronto
Rain Accumulation (ZCORR)
Cloud Physics & Severe Weather Research Division
King City
Improved QPE Using Zcorr
(Location near MSC HQ in Downsview)
Cloud Physics & Severe Weather Research Division
King City
Summer Applications:
Hail Detection
Cloud Physics & Severe Weather Research Division
King City
iParCA (interactive Particle Classification
Algorithm)
• developed by Environment Canada, King City research
•
•
group
input: 6 polarimetric radar products (Zh, Zdr, ρHV, Kdp as
well as standard deviations of Zh and Zdr)
output: hydrometeor type at each range gate
determined by fuzzy logic routines
National Lab for Remote Sensing and Nowcasting
an example of a fuzzy logic membership
function for moderate rain
National Lab for Remote Sensing and Nowcasting
iParCA GUI interface
National Lab for Remote Sensing and Nowcasting
Comparison of URP and iParCA Hail
Algorithms
URP Hail Algorithm:
• Related to storm structure
• Based on vertical integration of
cell’s reflectivity profile
• Disadvantages:
– Difficult to quantify
– Exact hail location not
specified
iParCA Hail Algorithm:
• Measurements directly related
to hail properties
• iParCA Fuzzy Logic
Thresholds:
•
•
•
•
Z : 50 – 75 dBZ
ZDR : 0 – 1 dB
ρHV : 0.80 – 0.90
φDP : abrupt changes
Cloud Physics & Severe Weather Research Division
King City
Grimsby Hailstorm
July 23rd 2008 – 0140 Z
Radar Reflectivity
Enhanced View
Cloud Physics & Severe Weather Research Division
King City
Grimsby Hailstorm
July 23rd 2008 – 0140 Z
ρHV
φdp
VIL
Cloud Physics & Severe Weather Research Division
King City
Grimsby Hailstorm
July 23rd 2008 – 0140 Z
1
1
2
2
Location
201/94
202/97.5
Zcorr
46.18
(39.35)
50.42
(49.21)
ZDRcorr
1.05
0.14
ρHV
0.93
0.82
Hail Pixel Map
: iParCA
: URP
Cloud Physics & Severe Weather Research Division
King City
Grimsby Hailstorm
July 23rd 2008 – 0230 Z
Hail Pixel Map
: iParCA
: URP
Cloud Physics & Severe Weather Research Division
King City
Detection Statistics of URP vs iParCA
Hail Algorithms
• 74 cells examined for 21 days
during the summers of 20052008.
• Cases were selected by
meteorologist M. Leduc
targeting those cells which may
contain high impact weather
based on reflectivity patterns.
iParCA
URP
Hit
63
51
Miss
4
16
False Alarm
5
3
Correct Negative
2
4
Total
Skill Scores
74
74
CSI
88
73
Bias
1.5
-19.4
POD
94
76
FAR
7
6
Cloud Physics & Severe Weather Research Division
King City
Summary Statistics of URP vs iParCA
Hail Algorithms
• 30 cells on 10 of the study days were examined in depth
•
•
to assess the physical reasoning for the differences in
the algorithm performance.
In 21/30 cells iParCA was subjectively determined to be
better in terms of the quality of the information
Reasons for iParCA superiority:
–
–
–
–
Geometry/Timing
Attenuation Correction
Dual Polarization Discrimination
Location
4 cases
5 cases
11 cases
5 cases
• iParCA Hail Product superior for 70% of cells studied
Cloud Physics & Severe Weather Research Division
King City
Questions?
National Lab for Remote Sensing and Nowcasting