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Large-Scale vs Mesoscale Contribution to Severe Convection: A Case Study

This case study examines the distinction between large-scale and mesoscale processes in severe thunderstorm development, focusing on a tornadic event in Topeka, Kansas on May 6th, 1983. It explores the interaction between synoptic-scale patterns, mesoscale features, and their impact on convective initiation.

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Large-Scale vs Mesoscale Contribution to Severe Convection: A Case Study

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  1. The Distinction Between Large-Scale and Mesoscale Contribution to Severe Convection : A Case Study Example

  2. What Case Do We Study? • May 6th, 1983 • Event: Tornadic Severe Thunderstorm at Topeka, Kansas

  3. What So Special about it? • F3 Tornado • Hypothesis stated: Mesoscale and Large-scale processes can interact with each other as Large-scale process can’t “work alone” in this case.

  4. Synoptic-scale approach

  5. Synoptic Approach • Dryline/Cold Front on surface chart (Figure 3) • 700-500mb lapse rate over 8.5C/km

  6. Obstacles to convective development • Strong capping inversion in the morning sounding • low-level dew-point temperature is low

  7. Hit or Miss • Subsynoptic features: Strong covection over much of the Nebraska and Western Kansas by 2130Z. • Modest Increase of Low-Level Moisture • Cold Front Intensifies and approaches the dryline and both ultimately intersects • Squall Line & Tornadic Storm develop on the edge of the intersection and

  8. So…Why does the obstacle become an non-issue? • Doswell believes the intensified front has something to do with it. • Can’t explain in large-scale process • Large-scale process / mesoscale process

  9. Large-Scale Process • Three elements to help forecast deep, moist convection: moisture, condition instability and source of lift • Restricted to those are adiabatic, hydrostatic, mass continuity is satisfied • Or…quasi-geostrophic in a textbook sense

  10. Mesoscale Process • Simply the process that cannot be understood without considering large scale and microscale processes. • Hard to neglect any terms in the governing equation (eg. Eqt of motion) and retain any generality.

  11. Difference between both • “Large-scale flows create the favorable thermodynamic environment while mesoscale processes serve to provide the lift needed for convective initiation.”

  12. Conclusion • Most of the processes can be explained by large-scale process • Some residual which is unexplained from the large-scale viewpoint can be called by “subsynoptic scale” • Primary role of mesoscale processes is to provide the lifting to initiate deep, moist convection

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