93 Downdraft Convective Inhibition as a Means to Discriminate Elevated Convection

Monday, 23 January 2017
4E (Washington State Convention Center )
Patrick S. Market, Univ. of Missouri, Columbia, MO; and S. Rochette, J. Shewchuk, N. I. Fox, R. J. Difani, J. S. Kastman, and C. B. Henson

A method for evaluating the penetration into a stable layer by a convective downdraft is developed and tested.  The “overshooting” downdraft is evaluated in the same fashion as a convective updraft “overshoots” the equilibrium level (EL), with parcels rising some distance above the EL due to momentum.  Similarly, the downdraft convective inhibition (DCIN) is represented graphically by the area on a thermodynamic diagram where the moist adibat of the downdraft (which helps to define the downdraft convective available potential energy [DCAPE]) lies to the right of the ambient temperature curve, and is thus warmer than its surroundings.  By analogy, we are suggesting evaluation of the “overshooting downdraft.”  This DCIN area, when present, is nearly always found near the surface, in association with a low level thermal inversion.  By comparing the DCIN to the DCAPE, we determine that downdraft penetration potential is progressively enabled as the DCIN is progressively smaller than the DCAPE; inversely as the ratio DCIN/DCAPE increases, so does the likelihood of purely elevated convection.  Several cases are provided to support this finding.
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