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Problems with the term “overrunning”

August 15, 2011 Filed under Blog, Featured, Uncategorized, Writing 

Several authors have criticized the use of the term overrunning to represent warm-frontal lifting here and here.

I don’t need to add anything to those Web pages, but I do want to point out that the definition provided in the American Meteorological Society’s Glossary of Meteorology is wrong and ambiguous.

overrunning—A condition existing when an air mass aloft is in motion relative to another air mass of greater density at the surface.
This term is usually applied in the case of warm air ascending the surface of a warm front or quasi-stationary front.

An air mass aloft will always be less dense than air at the surface. Therefore, every instance of sheared flow could classify as overrunning by that definition. As Stoelinga et al. (2002, BAMS) point out about ascent over fronts, it’s not the density or temperature that is important, but the static stability. The warm air flows over a warm-frontal zone because the warm air is less stable than the frontal zone (highly stable). With this ambiguity and the problems already stated, I recommend that everyone avoid the use of overrunning.

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