Session 7.3 Composite bow echo observed during BAMEX

Tuesday, 7 November 2006: 5:00 PM
St. Louis AB (Adam's Mark Hotel)
David A. Ahijevych, NCAR, Boulder, CO; and G. H. Bryan, M. Weisman, S. Trier, C. Davis, and D. Dowell

Presentation PDF (1.3 MB)

During the Bow Echo and MCV Experiment of 2003, several warm season bow echoes were sampled over the central United States. A Lear jet released several dozen dropsondes while mobile surface units released rawinsondes ahead of, within and behind the convective line. By combining these observations in a system-relative composite, we obtain a three-dimensional analysis of a mature bow echo and its environment with unprecedented resolution, particularly for the thermodynamic fields. Both non-severe and severe bow echoes are used in the composite. Sounding positions are remapped in terms of distance from the convective line and distance right or left of the bow echo apex path. The system motion vector is subtracted from the wind observations, and wind direction is relative to the system motion vector. The average thermodynamic profile ahead of each bow echo is subtracted from the observations, so the composite fields are deviations from the environmental mean.

These observations are consistent with conclusions drawn from past numerical simulations, such as the importance of low-level environmental wind shear perpendicular to the convective line and the existence of an elevated rear inflow jet due to a horizontal buoyancy gradient at the back edge of the system. But other aspects of the composite bow echo have not been well documented in previous work. The observed cold pool is quite deep (4 km) and has a double minimum in temperature perturbation in the vertical. Additionally, the environment ahead of the convective line exhibits a shallow stable layer at the surface (probably due to nocturnal events) and a hint of a baroclinic zone. The ubiquity of these features will be evaluated in more detail and presented on a case-to-case basis.

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