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

Abstract

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 ∇φ that demonstrates that vorticity rotates ∇θ and ∇φ 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 ∇θ relative to ∇φ that can contribute to the initiation of along-flow geostrophic temperature advection.

Climatological and case analyses of lower‐stratospheric fronts over North America

“…Schultz and Doswell (1999) determined that upper‐tropospheric fronts primarily develop in southwesterly flow based upon their climatology of upper‐tropospheric fronts associated with landfalling cyclones on the west coast of North America. However, when Lang and Martin (2013a) repeated a similar climatology of upper‐tropospheric fronts in a domain over North America, their results supported the conceptual model of upper‐tropospheric frontogenesis in northwesterly flow proposed by Shapiro (1983). The differences in the climatology results are attributed to differences in the climatology domain of interest.…”

“…The domain of the climatology is shown in Figure and is represented by a box centred on North America bounded zonally between 131°W and 64°W and meridionally between 25°N and 61°N. This study utilized the North America domain and employed similar methods to the Lang and Martin (2013a) climatology of upper‐tropospheric fronts so that the results of this lower‐stratospheric front climatology can be easily compared to their upper‐tropospheric front climatology.…”

“…Similarly to the geographically dependent results of upper‐tropospheric front climatologies by Schultz and Doswell (1999) and Lang and Martin (2013a), the composite and case‐study analyses of southwesterly flow lower‐stratospheric fronts over the Intermountain West and eastern North America revealed different lower‐stratospheric frontal structures and evolutions based on their geographic location. The Intermountain West composite and case‐study lower‐stratospheric fronts had isotropic structures (Figures (a) and (a) and (c)), whereas the eastern North America composite and case‐study lower‐stratospheric fronts had anisotropic structures (Figures (c) and (a) and (c)).…”

“…The upper‐tropospheric front portion of tropopause jet–front systems have been studied in the context of their role in surface cyclogenesis (e.g. Bosart, 1970; Uccellini et al , 1985; Sanders, 1988; Whitaker et al , 1988; Barnes and Colman, 1993; Lackmann et al , 1997; Schultz and Doswell, 1999; Lang and Martin, 2013a), the dynamics of mesoscale weather systems (e.g. Clark et al , 2010; Rose et al , 2010; Kocin et al , 2016), the generation of gravity waves (e.g., Koch et al , 2005; Lin and Zhang, 2008), stratosphere‐to‐troposphere exchange (e.g.…”

Quasi‐geostrophic diagnosis of the influence of vorticity advection on the development of upper level jet‐front systems

“…An intense upper level jet-front system developed in northwesterly flow just off the west coast of North America on 8 April 2013. This event is fairly representative of northwesterly flow cases that affect western and central North America during the cold season (Lang and Martin, 2013a). At 0000 UTC 8 April, the baroclinic zone involved in the frontogenesis was clearly evident at 500 hPa and had a geostrophic vorticity maximum along its entire length (Figure 8(a)).…”