The mechanism by which the Gulf Stream sea surface temperature (SST)
front anchors a band of precipitation on its warm edge is still a matter of debate
and little is known about how synoptic activity contributes to the mean
state. In the present study, the influence of the SST front on precipitation
is investigated during the course of a single extratropical cyclone using a regional
configuration of the Met Office Unified Model. The comparison of a
control run with a simulation in which SST gradients were smoothed brought
the following conclusions: a band of precipitation is reproduced for a single
extratropical cyclone and the response to the SST gradient is dominated by
a change of convective precipitation in the cold sector of the storm. Several
climatological features described by previous studies, such as surface wind
convergence on the warm edge or a meridional circulation cell across the SST
front, are also reproduced at synoptic time scales in the cold sector. Based on
these results, a simple boundary layer model is proposed to explain the convective
and dynamical response to the SST gradient in the cold sector. In this
model, cold and dry air parcels acquire more buoyancy over a sharp SST gradient
and become more convectively unstable. The convection sets a pressure
anomaly over the entire depth of the boundary layer which drives wind convergence.
This case study offers a new pathway by which the SST gradient
can anchor a climatological band of precipitation.