P. Cunningham et D. Keyser, Frontogenesis and frontal motion due to confluent deformation with a translating dilatation axis, Q J R METEO, 125(559), 1999, pp. 2563-2573
Citations number
25
Categorie Soggetti
Earth Sciences
Journal title
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY
A two-dimensional model of primitive-equation frontogenesis is formulated i
n which the forcing is due to a basic-state field of confluent deformation
with a dilatation axis that translates in the cross-front direction. Althou
gh the translation speed and direction of motion of the basic-state dilatat
ion axis have no effect on frontal structure when the total deformation is
spatially uniform, they can influence considerably the motion of the front.
At the surface, this motion may be separated into two components: (i) inte
rnal motion, directed towards the warm air, which is associated with the se
condary ageostrophic circulation of the front itself; and (ii) external mot
ion, either towards cold or warm air, which is associated with the initial
location and translation speed of the basic-state dilatation axis. The latt
er component ultimately dominates, and thus the motion of a mature front ma
y be thought of as being controlled by the large-scale flow. However, the f
ormer may dominate early on in the frontal evolution, resulting in signific
antly different frontal trajectories depending on the initial location of t
he basic-state dilatation axis and on whether this axis is moving towards t
he cold or the warm air. The relative locations of various conventional fro
ntal measures are examined in the special case of a uniformly translating d
ilatation axis. Of these measures the axes of maximum baroclinicity and vor
ticity become collocated at the surface as the front intensifies. However,
the basic-state dilatation axis and the confluence axis, the latter being d
efined as the location of zero total wind in the cross-front direction, may
be displaced considerably from this merger point, with this displacement d
epending on the initial location and subsequent motion of the basic-state d
ilatation axis. Potential extensions of the model are discussed with regard
to improved understanding of the difference in structure and motion betwee
n cold and warm fronts.