Convective boundary layer turbulence profiling over an arid region using a 200m tall-tower and Doppler Lidar measurements

Date

2022-08

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Abstract

Parameterization of the convective boundary layer (CBL) in numerical models is an area of interest for many researchers due to the importance of transportation of heat, moisture, momentum, and tracers within the CBL and the exchange of those between CBL and free troposphere (FT). A better understanding of how the CBL turbulent characteristics evolve in time and at different heights within and above the CBL can improve the accuracy of CBL parameterizations and eventually develop new turbulence parameterization schemes for numerical weather prediction models. Also, understanding turbulence features and associated scaling laws in the daytime CBL remained a challenging topic in boundary layer meteorology for many decades. Within this work, we explored CBL turbulence features at a site located in an arid region of West Texas. Two of the key features that lie in the CBL over an arid region are strong heat fluxes and intense turbulent mixing. Additionally, turbulence characterization under diverse weather systems in an arid region remained underexplored. Vertical profiles of higher order moments (e.g., variance and skewness) of various parameters including moisture, vertical velocity, and potential temperature, can help identify turbulent characteristics within the CBL. We used sonic anemometer measurements of the u, v, w components of the wind, temperature, and moisture sensors deployed on the 200 m tower at Reese Technology Center, in Lubbock, Texas. To demonstrate the idea of obtaining multiparameter turbulence characteristics and their vertical variability in the lowermost part of the CBL over a site, we used measurements obtained for two cases (12 October 2019 and 18 July 2020) under the impact of a broad high-pressure system. We also characterized turbulence features using vertical velocity measurements within the CBL using a ground-based Doppler lidar at Reese on 28 April 2022 and 2 May 2022. Results from the lidar deployments revealed strong thermals caused large vertical velocity variance (σ_w^2 (z)) ( > 5 m2 s-2) and vertical velocity skewness Sw(z) (> 1.5). These results are compared with prior research to investigate the differences and similarities between the CBL over an Arid region with other climate types. Key findings from the tower and lidar measurements were an unexpected increase in kinematic heat flux (Kh) with height, an increase in potential temperature variance (σ_θ^2 (z)) at the end of the tower analysis (2330- 0000 UTC) for both 16 October 2019 and 18 July 2020, σ_w^2(z) not decaying to 0.1 m2 s-2 at the top of the ABL, and abnormally large thermals that reached up to 4 km in depth.

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Keywords

Turbulence, Convective Boundary Layer, Arid Region

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