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James-Paul Dice, Meteorologist WHNT-TV, Huntsville
Dr. Walt Petersen, Scientist, University of Alabama Huntsville
ARMOR: Advanced Radar for Meteorological and Operational Research.
• Location : Huntsville Intl. Airport• Transmit frequency: 5625 MHz• Peak Power: 350 kW• Antenna Diameter 3.7 m (12 ft CF
Parabolic)• Antenna Beam width: 1.0o
• Maximum rotation rate: 6 rpm• Transmit polarization: Simultaneous H and V,
or H• Receive polarization: SIGMET dual-channel;
H and V• Signal Process: SIGMET RVP/8• Variables: Z, V, W, ZDR, DP, KDP, hv, LDR
Partners: UAH, NASA, NSSTC, WHNT-TV
Deployed in Huntsville by the NWS in 1977 as a local warning radar (WSR-74C) then refurbished and upgraded to Doppler in 1991.
Radar donated to UAH in 2002 and upgraded to dual-polarimetry using the SIGMET Antenna Mounted Receiver 11/04. Renamed: ARMOR.
Digital dual-receiver
Simultaneous transmit and receive via 4-port switch and magic-T
Waveguide Assembly
Receiver
Polarimetric Variables1. Reflectivity factor Z at horizontal polarization
- Measure of size and concentration of scatters
(dominated by SIZE)
2. Differential reflectivity ZDR
- Measure of median drop diameter→ SIZE/SHAPE
- Useful for rain / hail / snow discrimination→ SIZE/SHAPE/PHASE
3. Differential phase ΦDP (Specific Differential Phase- KDP)
- Efficient for accurate rainfall estimation→ NUMBER/SHAPE
- Immune to radar miscalibration, attenuation, and partial beam blockage
4. Cross-correlation coefficient ρhv
- Indicator of mixed precipitation → SHAPE/PHASE
- Efficient for identifying nonmeteorological scatterers
Research:
NCAR, CSU, NASA, UND, DLR, BMRC, NOAA-ETL
ARMOR
Operational:
NEXRAD, TV
vs
Small ZDR Large ZDR
• More accurate rainfall estimation (10-20% max accumulation error as opposed to 200-300%).
• Why? Because we collect information on drop size/shape/concentration and are able to mitigate hail contamination.
• Identification of precipitation types and discrimination between
meteorological and non-meteorological scatterers
• Improvement in radar data quality: Self consistent way to calibrate using polarimetric variables
Advantages of a Dual-Polarization RadarReally just a self-consistent way of obtaining a more complete description of the particle types and shapes present in a given volume of space.
vs
Small ZDR Large ZDRSmall drops Large drops
vs
Hail Rain
vs
Insects Rain
Mitigates the multiple Z-R issues!
How Does Dual Polarimetric Radar Help Hydrology?RAINFALL: A CLASSIC EXAMPLE
The Fort Collins Flash Flood: A Robust Integrated Application of Dual-Polarization Radar
CSU-CHILL: 2145 L2108: RHI: dBZ, ZDR, KDP
Review Petersen et al., BAMS, 1999
• Spherical shape and tumbling of hail results in low ZDR’s (a ZDR “hole”).
• Large drop recirculation on edge of echo vault at x=25 km, z=2-3 km.
• Drop column clearly extends into sub-freezing portion of cloud- the hail process
ZDR in Range-Height mode …………..(ARMOR has this scanning capability and this mode provides an early look into the development of intense storms)
ZH
ZH
ZDR
ZDR
0 15 30 45 60
0 15 30 45 60
-1 0 1 2 3 4 5
-1 0 1 2 3 4 5
ZH
ZH
ZDR
ZDR
ZH
ZH
ZDR
ZDR
0 15 30 45 60
0 15 30 45 60
-1 0 1 2 3 4 5
-1 0 1 2 3 4 5
“ZDR Column” in developing convection
“ZDR Hole” in Hail
Winter: Rain-Snow lines- Application for ARMOR along AL-TN border
ZDRZe
CSU CHILL
• White line indicates a transition from snow to rain- e.g., melting. This process is amplified in the ZDR signal and not as apparent in the reflectivity (Z).
61+ dBZ in cells: Hail or Rain?ARMOR: 1541 UTC 12/09/04
ZDR
>3.5 dB ZDR: Big rain drops or melting hail
Note Lightning in LISDAD
ARMOR Dual-Polarimetric facility provides a unique opportunity for end-to-end transfer of research technology to public safety
• Flooding (Radar “state of the art” rainfall estimates and flexible scanning)
• Emergency Management
• Surveillance, threat detection, warning
• Mitigation
• Case study and climatological area- accurate rainfall boundary conditions (0.125 x 0.5 km) for modeled watershed response (improved flood plain planning)
• Severe Thunderstorms
• Additional local source for improving detection, monitoring of severe weather (tornadic, strong winds, hail, lightning)
• Winter Precipitation
• Rain-snow boundary (HSV Airport Authority very interested in this product); planning decision support
• Homeland Security
• Boundary layer winds for plume dispersion modeling- feasibility?
ARMOR Operates Like No Other TV Radar
• The radar alternates between a traditional Doppler mode and a multi-elevation polarimetric scan. This flexibility means more data into our office.
• Traditional radar measurements (reflectivity and Traditional radar measurements (reflectivity and velocity) are available at all times.velocity) are available at all times.
• Radar alternates its operation between a live .05Radar alternates its operation between a live .05oo surveillance scan and a 3 elevation volumetric scan at surveillance scan and a 3 elevation volumetric scan at .07.07oo,1.3,1.3oo, and 2.0, and 2.0oo
• Following each volume scan, a hydrometeor Following each volume scan, a hydrometeor identification algorithm produces a product.identification algorithm produces a product.
KHTX NEXRAD View of Storm
Note: Pink Baron Services Severe SCIT. Neither NEXRAD or Baron Hail algorithm detected presence of hail during this event.
-1.8 -0.9 0.1 1.0 1.9 2.9 3.6 -15 - 5 5 15 25 35 45
dBZ ZDR
ARMOR: 12/10/04 17:55:06 EL=1.3o
Rain
55+ dBZ
Hail
55+ dBZ
Rain
2 to 3.5 dB
Hail
-1 to 0.5 dB
Hail
-1.5 to 0.5 dB
Rain/Hail
-0.5 to 2 dB Rain/Hail
40-55 dBZ
Hail
50-55 dBZ
At 17:55 In-cloud (IC) flash rate ~ 3/minute in southern cell
No IC’s in northern cell at 17:55
No Cloud-to-Ground (CG) lightning in either cell for 20 minutes centered on 17:55
Only 3 CG’s detected for duration of stormsLMA S. Cell 17:52:30 – 17:57:30
LMA Total Lightning Data
(southern cell mass)