The difference in time of occurrence of the diurnal maxima mean wind
speeds at the center of each core location (Fig. 3), shows that there is
an acceleration of the wind in the streamwise direction, with the
maximum mean wind speed occurring at C1 around 2300 LST and C2 around
0400 LST. In contrast, at C3 and C4, the maxima mean wind speeds start
approximately at 0700 LST and 0900 LST. The mean wind speeds are a
minimum everywhere in the afternoon (~8 m
s-1, 1300–1600 LST). Table 1 summarizes the main
characteristics of the OLLJ cores.
Based on the traditional mechanisms for LLJ formation (i.e., the
Blackadar and Holton mechanisms), the acceleration of the wind should
occur almost simultaneously at all locations once the
upper-boundary-layer wind decouples from the surface layer; statically
stabilized via radiative cooling, this layer impedes the upward
propagation of frictionally retarded air. However, in the hourly
950–800-hPa-layer streamwise-acceleration field
[\(\partial V_{s}/\partial t\) in Eq. (1)] (Fig. 4) it can be seen
that acceleration is not uniform across the domain; rather, there are
distinct areas of acceleration coming from the Atlantic Ocean, the
Caribbean Sea, and the Coastal Cordillera. Additionally, even though
these mesoscale pockets of acceleration propagate in the streamwise
direction, the C1–C4 wind-speed cores do not exhibit any propagation,
just diurnal intensification (as shown in Fig. 3); they occur at precise
locations (Fig. 2, Table 1).