Towards more accurate water vapour observations: Airborne lidar measurement examples and characteristics

Abstract

Airborne differential absorption lidar measurements of mid-latitude, subtropical and tropical water vapour were performed during several recent campaigns over North and South America, and Australia, as well as on the corresponding long-range transfer flights from and to Germany with the DLR “Falcon” research aircraft. These include tropospheric as well as lower stratospheric observations. Complex advection and rapid vertical transport associated with meso- and synoptic scale dynamical processes reflect in inhomogeneous water vapour distributions along the flight paths, as observed by the lidar. The tropical (Hadley) circulation, stratospheric intrusions and humidity transitions between different air masses are clearly detected. The measurements are compared to operational ECMWF analyses interpolated in space and time to the flight path. The relevant transport processes are adequately represented in the analyses as long as vertical and horizontal scales exceed roughly 0.5-1 km in the vertical and 50 km horizontally, while smaller structures and larger gradients are smoothed out. On the longer term, space-borne lidar instruments may provide unprecedented high-resolution (especially in the vertical) and high-precision, low-bias observations of water vapour throughout the troposphere with high added value to next generation observing systems for assimilation into NWP models.