Characterising the convective environment with direct measurements of moisture flux from airborne wind and water vapour lidars

Kurzfassung

Tropospheric profiles of water vapour and wind were measured with differential absorption lidar (DIAL) and heterodyne detection wind lidar collocated onboard the DLR Falcon research aircraft during the COPS field phase in summer 2007. The DIAL is a new system and operated successfully on three wavelengths (two onlines, one offline at each 50 Hz, 40 mJ) around 935 nm, plus 532 and 1064 nm for aerosol characterisation. With either nadir-viewing or conical scans, the wind lidar observed the wind field below the aircraft. The high resolution lidar profiles resolve the dominant water vapour transport processes both over the complex terrain of the Black Forest and along extended flight legs in upstream regions over south-western Europe. Location and timing of convective initiation depend critically on the structure of the humidity field in the planetary boundary layer. Examples from the measurements will be shown to illustrate the variability and structures in the wind and water vapour fields in the pre-convective and convective environment. The availability of co-located wind and water vapour fields allows the direct calculation of vertical and horizontal moisture fluxes. Depending on the synoptic conditions horizontal and vertical fluxes play an important role for the setup of a convective environment. As minor errors in the model fields may have great impact on the forecast of convection, the observed fluxes will be compared with numerical model output, providing a valuable validation of a key component of the moisture budget.