Novel airborne and ground-based Doppler lidar observations of mountain wind systems: Validation of volume flux estimates during TEAMx

Quantifying the exchange of mass, momentum and energy between the earth’s surface and the atmosphere is essential for understanding - and therefore modeling - weather and climate processes. Compared to flat terrain, exchange processes in complex terrain are especially efficient due to valley and slope wind circulations. The international TEAMx observational campaign (TOC) in summer 2025 focused on the observation of exchange processes on different scales in the mountain boundary layer. 

The LIVAVERT(EX)² project - linking valley flow and vertical exchange in complex terrain - is embedded in TEAMx and focuses on observing valley winds in combination with exchange processes in the Sarntal Alps region, a local hotspot of convective initiation within the Alps. As part of the project, a novel airborne Doppler lidar (ADL) was used for its first extended measurement campaign in complex terrain. The new ADL system, called AIRflows, measures profiles of 3D wind at 100 m along-track and vertical resolution, and thereby provides spatially resolved insight into valley wind systems and vertical exchange.

During TEAMx, AIRflows was used on 33 research flights onboard the TU Braunschweig Cessna F406 research aircraft. Additionally, an extensive ground-based Doppler lidar (GDL) network was established as part of a KITcube deployment in the Sarntal Alps region. The obtained GDL observations, as well as synchronized airborne in-situ measurements by a second aircraft (DLR Cessna), allow for the first real-world validation of high-resolution ADL observations in complex terrain. This contribution provides estimates of the ADL and GDL wind profiling accuracy and their spatial representativeness. In a second step, the spatially resolved ADL wind profiles are used to validate existing GDL-based volume flux estimation methods. The goal of the validation is to obtain accurate volume flux budgets in the valleys surrounding the Sarntal Alps. Combining volume flux budget and direct vertical exchange observations then allows for a more quantitative insight into valley flow and its relation to convective initiation over the surrounding mountains than ever before.

Key words: TEAMx, KITcube, airborne research, Doppler lidar, validation, valley flow, volume flux budget, complex terrain, convective initiation, boundary layer meteorology