Investigating turbulent properties within the atmospheric boundary layer during the afternoon-evening transition with high resolution scanning Doppler lidar
Abstract
The daytime turbulent atmospheric boundary layer is usually dominated by convective mixing. The positive sensible heat flux at the surface provides the source of convective mixing that is responsible for boundary layer growth during the day. One challenging aspect is the evolution of the boundary layer during the afternoon-evening transition when the sign of the sensible heat flux at the surface changes and the source term for surface-driven convection is switched off; turbulent mixing does not cease immediately as there are still large turbulent eddies present which take time to decay through energy cascade to smaller eddies. Understanding the development of the afternoon-evening transition is crucial for predicting the evolution of the nocturnal boundary layer and the thermodynamic stability profile, which in turn is essential for forecasting night-time minimum temperatures, air quality, and fog formation. This is also important for predicting the diurnal cycle for the next day.
Preliminary results show that turbulent mixing continues for longer at altitudes closer to the height of the fully-developed daytime convective boundary layer than towards the surface, which is presumably due to larger eddies being generated away from the surface. Here, we investigate the timescales and length scales of the decaying turbulent mixing during the afternoon-evening transition with special focus on the vertical profile. We use high resolution scanning Doppler lidar data to obtain vertical profiles of the turbulent properties in the boundary layer, together with the vertical profile of horizontal wind. Recent developments in Doppler lidar observations allow for long-term and continuous measurements of these properties in various climate regimes.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A11M2795M
- Keywords:
-
- 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSES;
- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 3379 Turbulence;
- ATMOSPHERIC PROCESSES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES