Abstract
Squall lines are known to be the consequence of the interaction of
low-level shear with cold pools associated with convective downdrafts.
Also, as the magnitude of the shear increases beyond a critical shear,
squall lines tend to orient themselves at an angle to the shear. The
existing literature suggests that this angle conserves the projection of
the shear on the direction perpendicular to the squall line. However,
this hypothesis has never been clearly demonstrated. Here, we confront
this theory with tropical squall lines obtained by imposing a vertical
wind shear in cloud resolving simulations in radiative convective
equilibrium. In the sub-critical regime, squall lines are indeed
perpendicular to the shear. In the super-critical regime, their
orientation optimizes the projection of the background shear, which
supports existing theories.
We also find that as shear
increases, cold pools become more intense. However, this intensification
has little impact on the squall line orientation.