Long-term evaluation of turbulence parameterisations using Doppler lidar

Turbulence in the atmospheric boundary layer governs the exchange of heat, moisture, and other atmospheric constituents between the surface and the free troposphere. This exchange plays a pivotal role in initiating moist convection which influences the timing and location of convective rainfall. As operational weather forecasts increasingly move towards km and sub-km grid spacing, resolving larger boundary layer turbulent structures becomes possible, necessitating adjustments to turbulence parameterisation schemes. The UMBRELLA (UM Boundary-layer REpresentation with Land-Atmosphere Interactions) project aims to evaluate the performance of the UM (Met Office Unified Model) boundary layer turbulent parameterisation schemes for different grid spacings, ranging from 100m to 10km. 

Here, analysis of long-term Doppler lidar and sonic anemometer observations at Chilbolton, Hampshire is presented, with particular focus on long-term statistics on boundary layer vertical velocity, vertical velocity variance and skewness, along with sensible heat flux. These quantities are combined with the presence of cloud and aerosol height to classify the boundary-layer into different regimes and used to evaluate the UM turbulence parameterisations. The Doppler lidar statistics are compared to an 18-member ensemble UM run at 300m grid spacing for the 3-month WesCon field campaign which took place in the UK during summer 2023. While the primary focus of this project is on the UK and the UM, the developed methodology could be applied to other locations worldwide.