Combination of Wind Profiler Networks and Weather …...Combination of Wind Profiler Networks and Weather Watch Radar Networks in Determining Rainfall Parameters in Near Real Time

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

http://www.atrad.com.au/

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 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


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


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


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


• 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


449 MHz UHF dish antenna 55 MHz BL

Precipitation peak Clear-air peak


449 MHz UHF dish antenna 55 MHz BL

Precipitation peak Clear-air peak


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





Can cause problems when there is a spike within the peak



Can cause problems when there is a spike within the peak

Or when the peak is not Gaussian shaped





Precip peak can be poorly represented when the merger is incorrectly identified


• 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?


• 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





If CA & precipidentified

Find merger between peaks

Perform deconvolution


• 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





Rain rate intensifies





Rain rate intensifies

Rain rate decreases




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

http://www.atrad.com.au/

Documents

Combination of Wind Profiler Networks and Weather …...Combination of Wind Profiler Networks and Weather Watch Radar Networks in Determining Rainfall Parameters in Near Real Time