Anafront and Katafronts


Browning (1985) introduced the conveyor belt paradigm, according to which clouds and precipitation patterns in mid-latitude cyclones are understood in terms of the storm-relative motion fields on isentropic surfaces. The conveyor belt model assumes that the system (cyclone or front, depending upon the application) translates without change of shape or amplitude. The key feature in this model is the band of clouds associated with the "warm conveyor belt "within the general region of baroclinic ascent ahead of the upper-level trough. Air within the warm conveyor belt flows along the length of the cold front, with part of it originating from the southerly low-level jet ahead of the surface front. Nevertheless, the relatively small (mainly ageostrophic) component perpendicular to the front has an important bearing on the frontal structure, as shown in the figure below:


Schematic depictions of katafronts and anafronts and the associated rainband types according to the conveyor belt paradigm of Browning (1985). The gold arrows show the warm conveyor belt in a relative isentropic framework for each case. The flow relative to the front is forward in the katafront cases and rearward in the anafront case. Rainbands are depicted by bands of hatching.

When the air within the warm conveyor belt has a component of motion forwards relative to the movement of the cold front, the main region of ascent and precipitation occur ahead of the cold front, either in the warm sector as "surge bands" (or "prefrontal squall lines") or ahead of the warm front. Such cold fronts are termed "katafronts". By contrast, a "rearward sloping ascent" configuration describes anafronts, as the air within the warm conveyor belt has a component of motion rearwards relative to the movement of the cold front.

Thus, anafronts and katafronts are differentiated on the basis of the front-relative flow patterns, meaning that in the vertical plane oriented along the direction in which the front propagates, the motion of the front is subtracted from the winds in this plane. The schematic diagram presented below is that of a katafront. The front-relative flow for a katafront is one in which the ascent core slopes forward, resulting in all the precipitation being prefrontal.


The schematic diagram presented below is that of an anafront. The front-relative flow for an anafront is one in which the ascent core slopes rearwards over the top of the cold frontal surface, resulting in all the precipitation being postfrontal.


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