Influence of along-valley terrain heterogeneity on exchange processes over idealized valleys
Atmospheric Chemistry and Physics Discussions
Idealized numerical simulations of thermally driven flows over various valley-plain topographies are performed under daytime conditions. Valley floor inclination and narrowing valley cross sections are systematically varied to study the influence of along-valley terrain heterogeneity on the developing boundary layer structure, as well as horizontal and vertical transport processes. Valley topographies with inclined valley floors of 0.86° increase upvalley winds by about 100% due to smaller
... y volumes (volume effect) and by about 62% due to additional upslope buoyancy forces. Narrowing the valley cross section by 20 km per 100 km along-valley distance increases upvalley winds by about 75%. Vertical mass fluxes out of the valley are strongly increased by about 57 to 84% by narrowing the valley cross sections and by 22 to 32% by reducing the valley volume (e.g., by inclining the valley floor). Trajectory analysis shows intensified horizontal transport of parcels from the foreland into the valley within the boundary layer in cases with inclined floors and narrowing cross sections due to increased upvalley winds.