Investigation of the spatial variability of the convective boundary layer heights over an isolated mountain: Cases from the MATERHORN-2012 experiment

Spatiotemporal variability in the convective boundary layer height z_i over complex terrain is governed by numerous factors such as land surface processes, topography, and synoptic conditions. Observational datasets to evaluate weather forecast models that simulate this variability are sparse. This study aims to investigate the z_i spatial variability (along a total leg length of 1800 km) around and over a steep isolated mountain (Granite Mountain) of horizontal and vertical dimensions of 8 and 0.9 km, respectively. An airborne Doppler lidar was deployed on seven flights during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) campaign conducted at Dugway Proving Ground (Utah) from 25 September to 24 October 2012. During the afternoon, an east-west z_i gradient over the region with z_i that was approximately 200 m higher on the eastern side than on the western side of Granite Mountain was observed. This gradient illustrates the impact of two different land surface properties on z_i spatial variability, with a sparsely vegetated desert steppe region on the east and a dry, bare lake-bed desert with high subsurface soil moisture to the west of Granite Mountain. Additionally, the z_i spatial variability was partly attributed to the impact of Granite Mountain on the downwind zi. Differences in z_i were also observed by the radiosonde measurements in the afternoon but not in the morning as the z_i variability in morning were modulated by the topography. The high-resolution lidar-derived z_i measurements were used to estimate the entrainment zone thickness in the afternoon, with estimates ranging from 100 to 250 m.