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A Case Study: The Omaha Derecho June 27, 2008

A Case Study: The Omaha Derecho June 27, 2008. By Steve Gronstal. Outline. What caught my attention? What is a Gravity Wave? Gravity wave Lifespan. CISK. Synoptic Enhancements. Evidence of the Gravity Wave. Synopsis. References. Little Warning. A small scale storm.

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A Case Study: The Omaha Derecho June 27, 2008

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  1. A Case Study: The Omaha DerechoJune 27, 2008 By Steve Gronstal

  2. Outline • What caught my attention? • What is a Gravity Wave? • Gravity wave Lifespan. • CISK. • Synoptic Enhancements. • Evidence of the Gravity Wave. • Synopsis. • References.

  3. Little Warning

  4. A small scale storm.

  5. Brutal Winds and Extreme Rainfall

  6. The Aftermath:

  7. The Push

  8.                                                                                                                        <>

  9. What is a Gravity Wave? (A.K.A a Buoyancy Wave) • A wave where Buoyancy acts to oscillate an air parcel

  10. Wave Covariance & Quadrature

  11. Why Wave Covariance? • Without it, the Pressure Gradient Force would actually work against the wind vector, thereby dissipating the wave’s energy.

  12. Why Wave Quadrature? • Omega = 0 at the lowest temperature. • Thereafter, Omega < 0 == upwards motion. • This adiabatically warms the parcel.

  13. Life Span of a Gravity Wave • Typically they die out unless: • A sufficiently thick duct traps energy from dissipating into the upper atmosphere. • A continual supply of energy acts against dissipation.

  14. An Atmospheric Duct • Must have a statically stable layer • Real Valued Brunt-Vasala Frequency (N)

  15. CISK • Convective Instability of the Second Kind. • A propagating line of convection that cyclically enhances more convection.

  16. How CISK Propagates a Gravity Wave • Gravity Wave creates a localized low with upward motion • Condensation & Convection creates surface divergence. • Surface Divergence enhances a new localized low.

  17. Synoptic Enhancement

  18. Synoptic Enhancement

  19. Synoptic Enhancement

  20. Evidence of a Gravity Wave • Pressure Perturbation • Wave Covariance • Wave Quadrature • Wave Ducting

  21. The Pressure Change • A dip followed by an increase in Pressure • 0.2 in Hg = 5 mb!

  22. Wave Covariance • Wind changes and pressure changes happen simultaneously.

  23. Wave Quadrature • Temperature changes exhibit a 90º phase shift from Pressure changes.

  24. The Duct The duct aught to be about ¼ the vertical wavelength

  25. Why Call it a Derecho? • A gravity wave with extreme downdrafts • Winds oscillate always pointing towards the local low pressure area.

  26. Synopsis of Events • South Dakota Thunderstorm induced a gravity wave. • This gravity wave triggered more convection (CISK), which helped propagate it. • The Synoptic Adjustments helped release even more energy into the wave. • These events provided the energy needed to cause $10,000,000 dollars in damage!

  27. Overall Effect • 70-90 mph winds with gusts up to 115 mph. • 0.50–0.86 inches of rain within 15-25 min. • Hail ranged from peas to marbles to golf balls.

  28. References & Thank You’s • Thank you to my advisor Arlen Huggins for his support and direction throughout my time at UNR. • Thank you to my instructor Mike Kaplan for his efforts and lessons imparting the fundamentals of Synoptic Meteorology. • References: • Hendee, David, “Thunderstorm lands heavy blow; many still without power”, Omaha.com, published June 28, 2008. • Geller, Marvin A.; Liu, Hanli; Richter, Jadwiga H. “Gravity Waves in Weather, Climate, and Atmospheric Chemistry: Issues and Challenges for the Community”, White paper from the June 2006 Gravity Wave Retreat, The Institute for Integrative and Multidisciplinary Earth Studies (TIIMES). • McNoldy, Brian. “Gravity Waves: What's the Attraction?”, for Multi-community Environmental Storm Observatory, www.mcwar.org/articles/cafe/gw/gravwaves.html. • Bauck, B.H., 1992: An Unusually Strong Gravity Wave over Western Washington. Wea. Forecasting, 7, 389–397. • Vaughan, Online paper, “Mathematical treatment of gravity waves.” • Bosart, L.F., and A. Seimon, 1988: A Case Study of an Unusually Intense Atmospheric Gravity Wave. Mon. Wea. Rev., 116, 1857–1886. • Fiorino, S.T., and J. Correia Jr, 2002: Analysis of a Mesoscale Gravity Wave Event Using Empirical Orthogonal Functions. Earth Interactions, 6, 1–19. • Einaudi, F., W. Clark, J. Green, T. VanZandt, and D. Fua, 1987: Gravity Waves and Convection in Colorado during July 1983. J. Atmos. Sci., 44, 1534–1553. • Raymond, D.J., 1976: Wave-CISK and Convective Mesosystems. J. Atmos. Sci., 33, 2392–2398. • Kaplan, Mike, 2005, “Mesoscale Gravity Waves”, MEA 444. http://www.dri.edu/People/Mike.Kaplan/mea444/lectures/lect03.ppt • Images • 4-quad Jet http://www4.ncsu.edu/~nwsfo/storage/training/jets/straightjet.html • CISK http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/grow/cisk.rxml

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