Convection initiation in complex terrain – can it be linked to meso-scale convergence?

In the summer of 2021, the Swabian MOSES (Modular Observation Solutions for Earth Systems) field campaign was carried out in southwestern Germany. The campaign focused on the initiation and development of deep convective systems between the Black Forest and the Swabian Jura. During the campaign, the first measurements with a new airborne Doppler lidar system were conducted and a ground-based Doppler lidar network consisting of eight stations was deployed.

This contribution presents combined airborne and ground-based lidar observations which provide new insight into meso-scale flow processes in the vicinity of deep convective systems initiating in complex terrain. The unique spatial sampling characteristics of the airborne Doppler lidar are exploited to evaluate whether a quantitative retrieval of meso-scale convergence during convection initiation in complex terrain is possible and meaningful. The combination with radar observations provides context for the convective activity associated with the observed flow field. The convergence estimation approach is then also applied to the ground-based Doppler lidar network, providing also insight into the temporal evolution of the flow field.

The observations and convergence estimates are compared to the operational convective-scale analysis produced by the Icosahedral Nonhydrostatic modelling framework (ICON) of the German Weather Service. This facilitates the evaluation of the validity of assumptions inherent to the network-based convergence retrieval. Subsequently, the network-based convergence estimates can be used to gain insight into the analysis accuracy.

Overall, the influence of meso-scale convective systems on flow characteristics is detectable both in airborne and ground-based measurements. A quantitative estimation of convergence appears possible and can be used to enhance process understanding and improve model evaluation. The combination of airborne Doppler lidar measurements with a ground-based Doppler lidar network proves useful. While the former provides both extended spatial coverage and high resolution during intensive observation periods, the latter allows for temporally resolved observations over extended periods. Thus, together these measurement systems prove to be a suitable and promising technique to gain new insights into flow phenomena in the vicinity of convective systems in complex terrain.