Latent Heat Fluxes over Complex Terrain Measured by Airborne Water Vapour and Wind Lidars

Kurzfassung

The combination of a water vapour and a wind lidar on an aircraft is an interesting new tool that allows to measure latent heat flux profiles and to portray the small- to mesoscale variability beneath the aircraft trajectory with high accuracy and spatial resolution. During the Convective and Orographically-induced Precipitation Study (COPS) in July 2007 over the Black Forest low mountains range in south-western Germany, a differential absorption lidar (DIAL) and a heterodyne detection Doppler wind lidar were collo-cated onboard the DLR Falcon research aircraft. The DIAL “WALES” is a newly developed four-wavelength system (each 50 Hz, 40 mJ) operating on water va-pour absorption lines of different strengths. For the study of summertime convection initiation over com-plex terrain both airborne lidars were pointed nadir-viewing. From the remotely-sensed wind and water vapour fluctuations in the convective boundary layer, a representative latent heat flux profile can be obtained from a single over-flight of the area under investigation using the eddy-correlation technique. The lidars’ hori-zontal and vertical resolution is 200 m, sufficient to resolve the dominant contributions to the flux, as par-allel higher-resolved in-situ measurements by the DO 128 research aircraft show. Challenges arise due to the fact that the lidar profiles are occasionally inter-rupted by laser readjustment phases and small clouds. The presentation will highlight methodical advances, accuracy assessments, validations by collocated in-situ measurements over the mountains, as well as the study of a post-frontal situation in which the latent heat flux played a key role in humidifying the boundary layer.