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Combination of Wind Profiler Networks and Weather Watch Radar Networks in Determining Rainfall Parameters in Near
Real Time
Bronwyn Dolman1,2 and Iain Reid1,2
1ATRAD Pty Ltd20 Phillips St Thebarton
South Australiawww.atrad.com.au
2University of Adelaide, Australia
Profiler Network
Precipitation Retrievals
Clear-air peak centred near 0 m/s (Bragg scatter)
Deviations from zero are the result of the mean vertical motion of the atmosphere
Width of the peak affected by beam broadening and turbulent motions within the sampled volume
Precipitation Retrievals
Precipitation peak centred near -10 m/s (Rayleigh scatter)
Echo needs to be corrected for clear-air effects, as it is both broadened by turbulence and shifted due to the mean vertical air motion
Precipitation Retrievals
Separate peaks, as close to minimum of merger as possible
Fit Gaussian to clear-air peak
Add tail to precipitation peak
Deconvolve using a Fourier transform
Convert to a DSD using a known fall speed to drop diameter relationship
Precipitation Retrievals
Drop Size Distribution is the number of drops of a given size in a sampled volume of the atmosphere
Often generalised to the median drop diameter, D0
Large concentration of small drops, with a smaller number of large drops
Precipitation Retrievals
Retrieval Frequency
• UHF profilers (typically ~920 or 1270 MHz) are more sensitive to Rayleigh scatter from precipitation, but can only detect Bragg scatter from turbulence at low rainfall rates or at low altitude
– Due to higher Rayleigh sensitivity, UHF profilers are able to resolve drops with a diameter smaller than 1 mm
Retrieval Frequency
• Previous research has combined the relative advantages of both frequencies, taking the clear-air information from the VHF system, and applying it to the UHF system
– Obvious fiscal drawback of requiring two co-located profilers
– Retrieve smaller drops
– Errors introduced with increasing spectral width are less prominent
– More robust across a variety of conditions
Retrieval Frequency
• Operating at 449 MHz puts us approximately in the middle of the precipitation/clear-air sensitivity spectrum
– Single frequency retrievals at limited heights (limited by clear-air information)
– Dual frequency retrievals are possible when combined with the Boundary Layer Profiler at Buckland Park
Precipitation Retrievals
• 27 February 2013 (summer conditions), the UHF and 55 MHZ BLP were co-located at BP during widespread stratiform rainfall
• Examine DSD retrievalsfrom the BL (VHF), UHFas a single frequency, and combined with the VHF as dual frequency
Precipitation Retrievals
449 MHz UHF dish antenna 55 MHz BL
Precipitation peak Clear-air peak
Precipitation Retrievals
449 MHz UHF dish antenna 55 MHz BL
Precipitation peak Clear-air peak
Precipitation Retrievals
UHF single frequency retrieval
UHF/VHF BL dual frequency retrieval
Plots show reflectivity due to precipitation, which is proportional to the number of drops per unit volume, and the sixth power of the drop diameter. The excellent agreement between the single and dual frequency reflectivities demonstrates that the technique works.
Median Drop Diameter
UHF single frequency retrieval
UHF/VHF BL dual frequency retrieval
Plots show the median drop diameter, which is used to describe the drop size distribution. Larger median diameters indicate a higher proportion of large drops, and typically heavier rainfall.
Microphysics
Microphysics
Z LWC D0
Evaporation
Collision Coalescence
Break-up
Climatology
Evaporation Collision-coalescence Break-up Other
Stratiform 4 1 - 2
Convective 6 - - 2
Evaporation Collision-coalescence Break-up Other
Build-up 2 - - -
Monsoon 4 1 - 1
Break 4 - - 3
Real Time Retrievals
Separate peaks, as close to minimum of merger as possible
Can cause problems when the merger point is not clear
Real Time Retrievals
Fit Gaussian to clear-air peak
Real Time Retrievals
Fit Gaussian to clear-air peak
Can cause problems when there is a spike within the peak
Real Time Retrievals
Fit Gaussian to clear-air peak
Can cause problems when there is a spike within the peak
Or when the peak is not Gaussian shaped
Real Time Retrievals
Add tail to precipitation peak
Real Time Retrievals
Add tail to precipitation peak
Precip peak can be poorly represented when the merger is incorrectly identified
Real Time Retrievals
• Problems can also arise due to interference, incorrectly identified peaks in extreme up/down-draughts, etc…..
• Not typically a problem in post processing, but presents a challenge for real-time operation
– How do you identify the cause of bad retrievals?
Real Time Retrievals
• Developed pre-retrieval quality control algorithms to identify relevant portions of the spectrum
Identify all peaks in spectrum
• Clear – air• Precipitation• Interference
Real Time Retrievals
• Developed pre-retrieval quality control algorithms to identify relevant portions of the spectrum
Identify all peaks in spectrum
• Clear – air• Precipitation• Interference
If CA & precipidentified
Find merger between peaks
Real Time Retrievals
• Developed pre-retrieval quality control algorithms to identify relevant portions of the spectrum
Identify all peaks in spectrum
• Clear – air• Precipitation• Interference
If CA & precipidentified
Find merger between peaks
Perform deconvolution
Real Time Retrievals
• Retrieve vertical profiles of the rain rate as the storm system passes over the profiler
– Can be used in conjunction with weather radars
Microphysics example
Reflectivity Median Drop Diameter
Rain Rate Liquid Water Content
Buckland Park S-band weather watch radar
Microphysics exampleRadar bright band, characteristic of stratiformrainfall
Reflectivity Median Drop Diameter
Rain Rate Liquid Water Content
Buckland Park S-band weather watch radar
Microphysics exampleRadar bright band, characteristic of stratiformrainfall
Rain rate intensifies
Reflectivity Median Drop Diameter
Rain Rate Liquid Water Content
Buckland Park S-band weather watch radar
Microphysics exampleRadar bright band, characteristic of stratiformrainfall
Rain rate intensifies
Rain rate decreases
Reflectivity Median Drop Diameter
Rain Rate Liquid Water Content
Buckland Park S-band weather watch radar
Profiler Network
Profiler Network
Profiler Network
• Examine evolution of weather patterns as systems move across profiler sites
Halls Creek Carnarvon
Profiler Network
• Examine evolution of weather patterns as systems move across profiler sites
Halls Creek Tennant Creek
Satellite Comparison
CPOL - Darwin TRMM
Adelaide Airport
• ATRAD in collaboration with the University of Adelaide are developing an instrument cluster at Adelaide Airport
– 55 MHz WPR
– prototype 449 MHz UHF WPR
– precipitation radar
– backscatter ceilometer
– Disdrometer
– all sky infrared camera
Adelaide Airport
BoM office
ARM instrumentation
BL Profiler
BL Profiler 54.1 MHz7.5 kW27 3-element Yagi antennas, arranged in 3 groups of 9SA FCA technique to measure winds300 – 4000 m in two modes2 min resolution
Adelaide Airport
• AAP is within the scanning footprint of the BP radar, and is therefore an ideal site for rainfall studies, and evaluating real time data products
Conclusion
• Pre-processing spectra results in relatively clean near real-time retrieval of rainfall information
– Can be used in conjunction with other instruments, and also as a network, to contribute to rainfall information gains across Australia
• Currently near is ~ 1 minute
– A project in conjunction with the University of Adelaide is looking at processing techniques and dwell times, which may result in the generation of spectra in < 1 minute
• Adelaide Airport cluster will provide an ideal test environment
Thank You
ATRAD Pty Ltd20 Phillips St Thebarton
South Australiawww.atrad.com.au