the impact of gravity wave/undular bore dissipation on the june 22, 2003 deshler and aurora nebraska...
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![Page 1: The Impact of Gravity Wave/Undular Bore Dissipation on the June 22, 2003 Deshler and Aurora Nebraska Tornadic Supercells AARON W. JOHNSON NOAA/NWS Weather](https://reader035.vdocuments.mx/reader035/viewer/2022062515/56649d0b5503460f949de632/html5/thumbnails/1.jpg)
The Impact of Gravity Wave/Undular Bore Dissipation on the The Impact of Gravity Wave/Undular Bore Dissipation on the June 22, 2003 Deshler and Aurora Nebraska Tornadic June 22, 2003 Deshler and Aurora Nebraska Tornadic
Supercells Supercells
AARON W. JOHNSONAARON W. JOHNSON
NOAA/NWS Weather Forecast Office, Hastings, NebraskaNOAA/NWS Weather Forecast Office, Hastings, Nebraska
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Brief Review of June 22, 2003Brief Review of June 22, 2003
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06/23 00Z 250 MB Chart06/23 00Z 250 MB Chart
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06/22 21Z HPC Surface Analysis06/22 21Z HPC Surface Analysis
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RUC40 21Z Analysis Sounding between RUC40 21Z Analysis Sounding between Deshler and AuroraDeshler and Aurora
• CAPE = 5170 J/kg• LCL Hgt = 3549 ft AGL• LFC Hgt = 4393 ft AGL
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Fairbury Profiler Hodograph at 23ZFairbury Profiler Hodograph at 23Z
• 0-1 km SRH ~ 120 m2/s2• 0-6 km Bulk Shear = 36
KTS• 0-6 km Mean Wind ~ 220
at 27 KTS
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RUC40 21Z Analysis of ID Method for Left/Right-Moving RUC40 21Z Analysis of ID Method for Left/Right-Moving SupercellsSupercells
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HOWEVER…both Supercells became nearly stationary HOWEVER…both Supercells became nearly stationary within 5-10 minutes after rapid gravity wave/undular bore within 5-10 minutes after rapid gravity wave/undular bore
dissipation was observed.dissipation was observed.
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Severe Storm ReportsSevere Storm Reports
• Large Hail: 27 reports of ¾” or larger (including the Aurora Volleyball sized hail)
• Tornado: 10 reports of Tornadoes (1 Killer Tornado at Deshler)
• Strong Winds: 5 reports of 60+ mph winds
• Flooding: 5 reports of Flooding
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Research from EventResearch from Event
• Wakimoto (2004) – via the BAMEX project, mainly looked at Eldora Observations of the Superior Supercell.
• Guyer and Ewald (2004) – mainly looked at WSR-88D characteristics of Aurora Supercell/hailstone.
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Hindsight is always 20/20 however…Hindsight is always 20/20 however…• The environmental setup was more complex
than previous literature has discussed.• Only brief mention of Storm Motion• Several inaccuracies exist in the literature
including: – Incorrect labeling of the Deshler and Superior
Supercells as being the same storm.– Insufficient surface boundary analysis/detection.– Assumption of Dropsonde data well south and much
later than the Aurora and Deshler storms being representative of the mesoscale environment for the entire event.
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2145Z Visible Satellite Imagery2145Z Visible Satellite Imagery
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KUEX Base Reflectivity at 2145 ZKUEX Base Reflectivity at 2145 Z
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KUEX Base Velocity at 2243 ZKUEX Base Velocity at 2243 Z
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Quick review on Gravity Quick review on Gravity Waves/Undular BoresWaves/Undular Bores
• Much has been written about the environmental setup needed for undular bores to exist including: Christie et al. 1978, 1979; Simpson (1987); Maxworthy (1980); Crook (1988); Smith (1988); Rottman and Simpson (1989); Haase and Smith (1989b); and Doviak and Ge (1984).
• The main feature coming out of this literature is the need to trap energy in the low levels via one or multiple atmospheric characteristics
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Quick review on Gravity Quick review on Gravity Waves/Undular BoresWaves/Undular Bores
• Crook (1988) defined these trapping methods into 3 main features:– a wind profile above 4 KM that opposes the
motion of the waves– a low level jet that opposes the motion of the
waves – temperature inversion at or below 4 KM
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Relative wind speed normal to movement of Relative wind speed normal to movement of gravity wave/undular bore.gravity wave/undular bore.
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Inversion below 4 kmInversion below 4 km
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LLJ and winds above 4 km LLJ and winds above 4 km opposing motionopposing motion
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KUEX Base Reflectivity at 2258 ZKUEX Base Reflectivity at 2258 Z
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KUEX Base Reflectivity at 2345 ZKUEX Base Reflectivity at 2345 Z
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KUEX Base Velocity at 2345 ZKUEX Base Velocity at 2345 Z
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KUEX Base Reflectivity at 0028 ZKUEX Base Reflectivity at 0028 Z
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KUEX Base Reflectivity at 0046 ZKUEX Base Reflectivity at 0046 Z
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Backed boundary layer winds eliminate one form Backed boundary layer winds eliminate one form of low level energy trapping.of low level energy trapping.
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Impact of backing winds on hodograph Impact of backing winds on hodograph curvature.curvature.
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Large updrafts and circular Large updrafts and circular hodograph???hodograph???
• Past studies have shown that the storm motion is located at the center of curvature of a perfectly circular hodograph.
• However…Davies-Jones (2002) suggests that propagation off the hodograph occurs in the presence of a large updraft.
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Impact of backed surface windsImpact of backed surface winds
• Appears to have caused both the rapid decay of the gravity wave/undular bore field and change in storm propagation.
• Observational network was slow to show these changes in wind direction due to scarcity of automated sites and slow reporting frequency.
• What may have caused local backing of surface winds???
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Regional Surface plot 22Z.Regional Surface plot 22Z.
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Regional Surface plot 00Z.Regional Surface plot 00Z.
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Regional Surface plot 01Z.Regional Surface plot 01Z.
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Few clues exist in Synoptic dataFew clues exist in Synoptic data
- Mass field adjusting to Meso or smaller scale changes
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Meso-low development along converging boundaries?Meso-low development along converging boundaries?
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Meso-low development along converging boundaries?Meso-low development along converging boundaries?
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ConclusionsConclusions
• Rapid backing of low-level winds appears to be connected to meso-low development.
• Changes in wind direction/speed impacted dissipation of gravity wave/bore field and storm motion.
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ConclusionsConclusions• Given inherit weaknesses in the observational
network to report rapid changes, it appears a dissipating portion of a gravity wave/bore field may be an indication of changes in the low-level wind field that could be observed closer to real-time.
• This type of observed change may indicate rapid changes in: – Low and deep layer shear profiles– Storm motion– Storm type and duration (LL or SL supercells)
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Questions???Questions???