Because energy is conserved along an isentrope in dry-adiabatic motions
[i.e., d(h + gz)/dt = 0, where \(h=C_{p}\theta\) is the enthalpy],
the acceleration of the wind, and consequently formation of the first
OLLJ core (C1), is attained by transformation of potential energy into
kinetic energy as the air on top of the Guanipa Mesa loses height
downstream (see the bending isentropes at C1 locations in Fig. 6). A
simple energy-transformation calculation for near midnight, using
reduced gravity to account for the buoyancy effects opposing the
gravitational force, yields just a –3 m s–1difference with the wind speed given by the model, even though the
nonhydrostatic effects of pressure were not considered.
The diurnal cycle of different surface variables at a selected point
over the Guanipa Mesa (8.9ºN– 64.5ºW), shows evidence of the
gravity-current nature of the sea breeze (Fig. 7). Starting at 1500 LST,
a drop in potential temperature occurs, while there is an increase in
surface pressure and mixing ratios. These are characteristics typical of
the passage of a cool maritime density current (Simpson, 1987, 1994).