  Particularly challenging classes of heterogeneous surfaces are ones where
strong secondary circulations are generated, potentially dominating the flow
dynamics. In this study, we focus on land-sea breeze circulations (LSBs)
resulting from surface thermal contrasts in the presence of increasing synoptic
pressure forcing. The relative importance and orientation of the thermal and
synoptic forcings are measured through two dimensionless parameters: a bulk
Richardson number (Mg is the geostrophic wind magnitude and Wstar a convective
buoyant velocity scale), and the angle alpha between the shore and geostrophic
wind. Large eddy simulations reveal the emergence of various regimes where the
dynamics are shown to be asymmetric with respect to alpha. Along-shore cases
result in deep LSBs similar to the quiescent scenario (zero synoptic
background), irrespective of the strength of Mg. Across-shore simulations
exhibit a circulation cell that decreases in height with increasing synoptic
forcing. However, at the highest synoptic winds simulated, the circulation cell
is advected away with sea-to-land winds, while a shallow circulation persists
for land-to-sea cases. Scaling analysis that relates the internal parameters
Qshore (net shore volumetric flux) and qshore (net shore advected heat flux) to
the external input parameters Mg and Wstar results in a succinct model of the
shore fluxes that also helps explain the physical implications of the
identified LSBs. Finally, the vertical profiles of the shore-normal velocity
and shore-advected heat flux are used, with the aid of k-means clustering, to
independently classify the LSBs in the (Ri, alpha) regime space diagram
(canonical LSB, sea-driven LSB, land-driven LSB, and advected LSB),
corroborating our visual categorization.
