characteristics of sub-diurnal extreme precipitation-producing systems
DESCRIPTION
Characteristics of Sub-diurnal Extreme Precipitation-Producing Systems. Nathan M. Hitchens Robert J. Trapp Michael E. Baldwin. Motivation. Significant impact on life, property, and agriculture Little focus on precipitation at time scales less than daily - PowerPoint PPT PresentationTRANSCRIPT
Characteristics of Sub-diurnal Extreme Precipitation-Producing
Systems
Nathan M. Hitchens
Robert J. Trapp
Michael E. Baldwin
Motivation
• Significant impact on life, property, and agriculture
• Little focus on precipitation at time scales less than daily
• Little quantitative data available to assess the predictability of the systems that produce extreme precipitation
Extreme Precipitation Example
Radar reflectivity from 0500 to 0600 UTC
1-hr Accumulated Precipitation
Maximum precipitation: 62 mm
Methods
• Feature-specific approach– Baldwin Object-Oriented Identification Algorithm
(BOOIA)
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• Size: 15,856 km2• Maximum: 62 mm
Precipitation BOOIA Output
#21
BOOIA OutputPrecipitation BOOIA Output
28 August 1998 @ 0600 UTC
Methods
• Data– Stage 2 precipitation data:
May 1996 – Dec 2008 (hourly)
• Multi-sensor product
• Analysis– BOOIA applied to each hour– Attributes include:
• Object size• Maximum precipitation
Midwestern United States Region
Precipitation Objects
275 210 164 101 61 36 240
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Maximum Precipitation (mm)
Fre
qu
ency
99th Percentile
Precipitation Analysis
• Threshold of 55 mm for ‘extreme’
• BOOIA identified 2,733 occurrences of extreme precipitation identified in Midwest
• Mean extreme precipitation object has size of 8,000 km2 and maximum precipitation of 68 mm
Precipitation Analysis
• Mean object size: 7,808 km2
• Standard deviation: 9,972 km2
• Minimum: 176 km2
• Maximum: 126,080 km2
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Object Size (km2)
Fre
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ency
Precipitation Analysis
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Month
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Precipitation Analysis
• Characteristics of precipitation not sufficient to characterize systems that produce it– Analysis of reflectivity better suited for this
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Time (UTC)
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Methods (Cont.)
• Data– NOWrad reflectivity available 1996 – 2008
(quarter hourly)
• Analysis– Apply BOOIA to reflectivity mosaic from
halfway through the hour of accumulation for each extreme precipitation occurrence
– Match precipitation object with nearest reflectivity ‘entity'
• Size: 15,856 km2• Maximum: 62 mm
Precipitation BOOIA Output
#21
BOOIA OutputPrecipitation BOOIA Output
28 August 1998 @ 0600 UTC
28 August 1998 @ 0530 UTC
• Maximum: 56 dBZ • Size: 162,320 km2
Reflectivity BOOIA Output
#11
Reflectivity Analysis
• Mean entity size: 32,180 km2
• Standard deviation: 47,365 km2
• Minimum: 80 km2
• Maximum: 393,664 km2
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Entity Size (km2)
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Reflectivity Analysis
• In the mean, the smallest extreme precipitation-producing systems occur in the summer months
Season
Ent
ity S
ize
(km
2 )
Reflectivity Analysis
Ent
ity S
ize
(km
2 )
Time of Day
• Smallest extreme precipitation-producing systems occurring in late afternoon (individual cells or small cluster of cells), opposed to larger during overnight hours (larger MCSs)
Take-home Point
• Sizes of extreme precipitation-producing convective systems range from single, relatively isolated cells to large convective systems
– Smaller systems are more common producers of extreme precipitation than typically considered
Ongoing Work• Simulating specific events using Weather Research and
Forecasting (WRF) model to assess predictability of extreme hourly precipitation-producing systems
WRF (NARR: 32 km) WRF (R1: 210 km)Stage 2
NSF ATM 0541491
Data provided by NCAR/EOL under sponsorship of the National Science Foundation. http://data.eol.ucar.edu/
This is part of a larger collaborative effort, advancing Purdue’s Climate and Extreme Weather (CLEW)
initiative
Acknowledgements
Reflectivity Analysis
• Threshold of 35 dBZ maximum for matched entities, but entities defined by threshold of 20 dBZ
• Identified 1,249 entities that matched with an occurrence of extreme precipitation
• Mean matched entity has size of 32,000 km2 and maximum reflectivity of 47 dBZ