Evaluating the Reliability of VIL Density for Determining Severe Hail in Iowa Penny Zabel.
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Transcript of Evaluating the Reliability of VIL Density for Determining Severe Hail in Iowa Penny Zabel.
![Page 1: Evaluating the Reliability of VIL Density for Determining Severe Hail in Iowa Penny Zabel.](https://reader035.fdocuments.in/reader035/viewer/2022062517/56649f145503460f94c28814/html5/thumbnails/1.jpg)
Evaluating the Reliability Evaluating the Reliability of VIL Density for of VIL Density for
Determining Severe Hail Determining Severe Hail in Iowain Iowa
Penny ZabelPenny Zabel
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OverviewOverview
• Data Analysis- Estimation by VIL Density- Baron Radar Algorithm
• Results• Future
• Introduction
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Vertically Integrated LiquidVertically Integrated Liquid
• VIL=∑ 3.44 x 10-6[(zi+zi+1)/2]4/7 dh
• zi and zi+1 are reflectivity values at top and bottom of layer with depth dh.
• VIL is the equivalent liquid water content value derived from radar reflectivity data.(American Meteorological Society, 2000)
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Cone of SilenceCone of Silence
(American Meteorological Society, 1993)
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VIL DensityVIL Density
• VIL Density = VIL / Echo Top
• Makes VIL independent of height.
• Reduces distance error in radar measurements
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Typical VIL and VIL DensityTypical VIL and VIL Density
VIL VIL Density
82 g/m^2 4.25 g/m^3
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Within Cone of SilenceWithin Cone of Silence
VIL VIL Density
23 g/m^2 5.25 g/m^3
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How Can VIL Density Estimate How Can VIL Density Estimate Hail Size?Hail Size?
• Reflectivity is proportional to the diameter of a target to the sixth power.
• Reflectivity increases exponentially as target size increases.
• VIL increases exponentially.
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Drop Size is Everything!Drop Size is Everything!
(American Meteorological Society, 1993)
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DataData• 110 Hail reports
• Recorded VIL, echo top, and calculated VIL Density for each report.
• 2 events each from spring, early summer, and late summer.
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Hail Size vs. VILHail Size vs. VIL
0
1
2
3
4
5
6
0 25 50 75 100VIL (g/m^2)
Hai
l Siz
e (i
n)
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Hail Size vs. VIL DensityHail Size vs. VIL Density
0
1
2
3
4
5
0 1 2 3 4 5 6 7VIL Density (g/m^3)
Ha
il S
ize
(in
)
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Average VIL DensityAverage VIL Density
• 0.75”-0.99” 4.39 g/m3
• 1.00”-1.99” 4.61 g/m3
• 2.00”or greater 5.30 g/m3
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Data SummaryData Summary
• This is a higher VIL density threshold than previous papers.
• A VIL density of 4.0 g/m3 correctly identified 93% of all hail reports.
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Data SummaryData Summary
• Amburn and Wolf 3.5g/m3 90%
• Baumgardt and King 3.5g/m3 90%
• Troutman and Rose 3.5g/m3 81%
• Roeseler and Wood 3.5g/m3 72%
(Amburn and Wolf, 1996)
(Baumgardt and King, 2002)
(Troutman and Rose, 1997)
(Roseler and Wood, 1997)
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Baron Estimated HailBaron Estimated Hail
0
1
2
3
4
5
0 1 2 3 4 5 6 7
VIL Density (g/m^3)
Ha
il S
ize
(in
)
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0
1
2
3
4
5
6
0 1 2 3 4 5 6
Hail Size
Est
imat
ed H
ail S
ize
Baron Estimated Hail cont.Baron Estimated Hail cont.
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Regional AdaptationRegional Adaptation
Hail SizeHail Size BaronBaron SuggestedSuggested
0.75”0.75” 4.00 g/m4.00 g/m33
1.00”1.00” 3.25 g/m3.25 g/m33 4.25 g/m4.25 g/m33
2.00”2.00” 4.75 g/m4.75 g/m33 4.50 g/m4.50 g/m33
3.00”3.00” 5.50 g/m5.50 g/m33 5.00 g/m5.00 g/m33
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Wet Bulb Zero HeightWet Bulb Zero Height
•Low wet bulb zero height means more of the energy that is back-scattered can be from frozen instead of liquid targets.
•A low wet bulb zero height also often signifies less instability, and smaller updrafts.
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Overestimate Hail SizeOverestimate Hail Size
•Low wet bulb zero height may lead to high VIL density, but small hail.
-April 8, 1999 WBZ 7,000 ft.
VIL density of 4.25 g/m3
Hail size 0.75”
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Underestimate Hail SizeUnderestimate Hail Size
•High wet bulb zero height may lead to large hail with small VIL density.
- July 2, 1999 WBZ 13,400 ft.
VIL density of 3.50 g/m3
Hail size 1.75”
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VIL is not the only thingVIL is not the only thing
• VIL Density is an indicator, but should be used in conjunction with other radar signatures of severe hail.
• Three Body Scatter Spike
• Bounded Weak Echo Region
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BWERBWERBREF 1BREF 1
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BREF 2BREF 2
BWERBWER
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BREF 3BREF 3
BWERBWER
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BWERBWER
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ResultsResults
•Wet bulb zero height is one factor in this.
• A greater VIL density is needed for large hail in Iowa than in the south where other studies have been done.
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Results (cont.)Results (cont.)
• Distance does not significantly affect calculations based on VIL density.
• When using Baron algorithm to estimate hail size, meteorologists should keep in mind differences in atmospheric conditions.
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FutureFuture
• Examine more data to determine any stronger correlations.
•Examine the possibilities of updating the radar algorithm to include a factor for wet bulb zero height.
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Thanks to:Thanks to:
KCCI-TVKCCI-TV*John McLaughlin*John McLaughlin
Greg WilsonGreg WilsonBaron Radar SystemsBaron Radar Systems
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Questions?Questions?