8B.3 Processes Governing Elevated Convective Systems, as Inferred from Models and Observations

Wednesday, 25 January 2017: 9:00 AM
Conference Center: Tahoma 3 (Washington State Convention Center )
Russ S. Schumacher, Colorado State Univ., Fort Collins, CO

As outlined by Corfidi et al. (2008), there exists a continuum describing the source regions for air ascending in deep convection.  On one end is "surface-based'' (or more precisely, "PBL-based") convection, which arises from the daytime heating of the land surface, the development of a well-mixed boundary layer, and the ascent of air parcels from throughout that boundary layer.  On the other end is "elevated'' convection, in which near-surface air is too stably stratified to become buoyant, but air originating from above that layer is sufficiently buoyant to ascend in deep convection.  In between, there is a murky area consisting of situations where the most unstable air is aloft and the near-surface air is stable but has the potential to become buoyant given sufficient lift.  This part of the continuum is characteristic of the transition from evening to overnight, which brings the stabilization of the near-surface layer owing to radiational cooling, and often the destabilization of the layer above it owing to the advection of warm, moist air by a low-level jet.

This presentation will review the current state of knowledge of both truly elevated convective systems and those that might be considered "mostly elevated".  Much of the existing understanding comes from numerical model simulations, in large part because they enable the calculation of parcel trajectories or tracers that can definitively attribute whence the air originated.  But how well do these calculations represent the real-world processes?  Observations from the 2015 Plains Elevated Convection at Night (PECAN) field campaign, as well as innovative methods for analyzing those observations, will yield some answers to these questions.  The stability profiles observed during PECAN, and the convective systems associated with them, span the continuum from surface-based to elevated.  Finally, "so what?"  Recent modeling and observational studies highlight that convective structure and the production of heavy rainfall and severe weather can be quite sensitive to the details of the near-surface stability profiles, suggesting that the distinctions between surface-based and elevated convection is more than simply an academic argument, and may have important implications for forecasts.

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