Reply to comments on 'The influence of rotational frontogenesis and its associated shearwise vertical motions on the development of an upper-level front'

Schultz (2012) proposes that our previous arguments regarding the initiation of along-flow geostrophic cold air advection during the upper frontogenesis process are incomplete. The core of his criticism, and the motivation for his call to include additional diagnostic calculations, hinges upon the assertion that the vertical vorticity can rotate isentropes relative to isohypses. In this response we derive an expression for the rate of change of del phi that demonstrates that vorticity rotates del theta and del phi equally, in accord with our original statement to that effect. The derived expression also provides motivation to propose a revision of our previous conceptual model, highlighting the role of deformation instead of vorticity in the differential rotation of del theta relative to del phi that can contribute to the initiation of along-flow geostrophic temperature advection. Finally, we present a four-year synoptic-climatology suggesting that upper frontogenesis over central North America is, in fact, biased toward environments characterized by northwesterly flow. Copyright (c) 2012 Royal Meteorological Society