engleski

Boundary-layer variations due to orographic-wave breaking in the presence of rotation

A mesoscale numerical model is used to study the atmospheric boundary-layer (ABL) response to nonlinear orographic forcing with Coriolis effect, f, over a mountain with length (the cross-wind component) comparable to the Rossby radius of deformation, L-R. The orographic-wave breaking occurring for Froude number Fr < 1, affected by f > 0, intensifies on the northern flank for westerly flows, as also found in other recent studies. A cumulative effect occurs as the Coriolis force lifts the northern ABL top and generates a stronger low-level jet (LLJ) than on the southern side. A differential layering also appears, since the specific humidity is higher in the lower southern ABL than in the related northern ABL, and vice versa. By contrast, there are higher values of the turbulent kinetic energy and humidity in the upper northern ABL. The breaking of flow symmetry around the orography due to f changes both the vertical vorticity and horizontal divergence field, (zeta, D), it modulates eddies and turbulence leading to the differential layering of the ABL. The stronger northern LLJ and its weaker southern counterpart, both meandering, together with the asymmetric wave breaking, induce strong lee-side fluctuations of the (zeta, D) field in the presence of f. The enhanced (zeta, D) production due to wave breaking over the distance approximate toL(R), the primary atmosphere-orography resonance occurs mainly in the vertical, while the 'f-enhancement' occurs in the horizontal plane. In this way, the initial mesoscale forcing may extend its effects over the synoptic scale.

jet; numerical modelling; resonance; turbulence

Rad je pripremljen u Stockholmu, gdje je 1. autor radio kao 'assoc. prof.', a zavrsen je u Zagrebu na projektu prof.dr.sc. Mirka Orlića. Ideje rada su iskoristene u projektu 0119339.