Spatial Differences in Turbulent Mixing Within the Planetary Boundary Layer in the Houston, Texas Metropolitan Area

Many factors, including surface characteristics, moisture content, wind speed, and the amount of daytime surface heating can affect turbulent mixing within the planetary boundary layer (PBL). For example, compared to surrounding rural areas, nocturnal cooling in urban areas is often weaker resulting in less stable or even unstable stratification and stronger turbulent mixing in the urban boundary layer overnight. These types of changes in PBL structure and dynamics can have significant implications for predicting convection, pollutant dispersion, and air quality. Understanding the effects of heterogeneity within the PBL is an important aspect for human health, weather forecasts, and other applications. How heterogeneous surfaces influence the temporal and spatial variability of turbulent mixing across a region is still not fully understood. In this study, we investigate the spatial differences in turbulent mixing across a heterogeneous region utilizing Doppler wind lidar vertical velocity measurements gathered during the Coastal Urban Boundary layer Interactions with Convection (CUBIC) field campaign in the summer of 2022 in the Houston, Texas region as part of the parent TRacking Aerosol Convection interactions ExpeRiment (TRACER) campaign. CUBIC deployed three PBL profiling systems: one to sample urban boundary-layer characteristics north of the Houston city center in Aldine; another on the southern outskirts of Houston’s urban sprawl to sample a suburban environment; and a third to sample less urban-influenced conditions at a coastal location southeast of downtown Houston. Previous analysis of PBL height based on data collected at these sites showed comparatively deeper PBL heights at Aldine through different periods of the diurnal cycle. This work explores a hypothesized relationship between observed differences in PBL evolution at the CUBIC sites and urban influences. Vertical profiles of vertical velocity variance are compared between sites to highlight the differences in magnitude, shape, and height of peak variance. Additionally, correlations between vertical velocity variance and other atmospheric properties (temperature, humidity, and wind speed) are investigated to determine which factors may contribute to observed differences between sites given knowledge of dominant advection patterns and wind direction.