Evaluating Turbulent Kinetic Energy Dissipation Parametrizations Using Doppler Lidars in the Convective Boundary Layer

In mesoscale models, turbulent kinetic energy (TKE) dissipation is commonly parameterized as a function of bulk TKE, implicitly assuming isotropic turbulence in the convective boundary layer (CBL). In this study, we use long-term Doppler lidar observations at the Land-Atmosphere Feedback Observatory (LAFO), University of Hohenheim, Stuttgart, Germany to evaluate this assumption. Two continuously operated Doppler lidars, one in vertical staring mode and one in six-beam scanning mode, provide high-resolution wind measurements within the CBL (Späth et al., 2023). We have analyzed the statistical relationships between vertical velocity variance <w’²>, TKE dissipation (Wulfmeyer et al., 2024), and TKE (Bonin et al., 2017) under daytime convective conditions (06:00–18:00 UTC). The results reveal a nonlinear relationship between <w’²> and TKE, with dissipation scaling to (<w’²>)^3/2. The TKE-based dissipation parametrization from Mellor-Yamada-Nakanishi-Niino (MYNN) shows only lower agreement (R² = 0.50) with lidar observation, whereas the <w’²>-based dissipation shows a significantly stronger agreement (R² = 0.80). Despite this difference, the turbulent length scales derived from TKE and <w’²> exhibits similar characteristics. These findings highlight limitations of bulk-TKE-based parameterizations and demonstrate the value of Doppler-lidar-based diagnostics for improving the turbulence representation in mesoscale models.

References:

Bonin et al., 2017, https://doi.org/10.5194/amt-10-3021-2017

Späth et al, 2023, https://doi.org/10.5194/gi-12-25-2023

Wulfmeyer et al, 2024, https://doi.org/10.5194/amt-17-1175-2024