5.1 Understanding the spatial variability of convective boundary layer depth around an isolated mountain with a factor separation approach

Tuesday, 19 August 2014: 8:00 AM
Kon Tiki Ballroom (Catamaran Resort Hotel)
Stephan F. J. De Wekker, Univ. of Virginia, Charlottesville, VA; and S. Serafin

Granite Peak, located in the Dugway Proving Ground in western Utah, is an isolated mountain rising ~800 m above the surrounding terrain. It has an approximately ellipsoidal shape, with main north-south and east-west axes ~10 and ~6-km long, respectively. Granite peak separates a flat dry lake (playa) to the west from arid shrubland to the east. The plain east of Granite peak slopes gently towards the northwest. These topography and land-use features favor the evolution of different terrain-induced flows in the area. In particular, upslope winds along the sidewalls of Granite Peak and lake breezes between the playa and the adjacent plain develop on fair weather days with strong solar forcing. The presence of these terrain-induced flows may have a non-negligible impact on the structure of the convective boundary layer (CBL).

This study aims to understand how slope winds and lake breezes affect the atmospheric boundary layer around Granite Peak, with a particular focus on the CBL depth. It is known that upslope flows can cause a local reduction of CBL depth at the base of mountain slopes. However, the possibly nonlinear interaction between slope winds and the lake breeze system, and its impact on the CBL depth, is currently poorly understood.

A set of semi-idealized very-large eddy simulations is presented. A factor separation approach is employed to assess the pure contributions to the CBL depth of orographic effects and of the spatial heterogeneity of sensible heat fluxes. The interaction between these two factors is shown to locally reduce the CBL thickness compared to a case where neither is active. Different prototypical flows, with large-scale winds impinging on Granite Peak from southerly and northerly quadrants, are analyzed. Modeled scenarios are compared with estimates of the CBL depth obtained from airborne backscatter lidar scans, performed during a recent field campaign of the MATERHORN project.

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