CROSSINN - a field experiment to study the three-dimensional flow structure in the Inn Valley, Austria

Abstract

The CROSSINN field experiment investigates the three-dimensional structure of thermally and dynamically driven flows and their impact on the boundary layer in a large Alpine valley using comprehensive state-of-the-art instrumentation.While the exchange of mass, momentum, moisture and energy over horizontally homogeneous, flat terrain is mostly driven by vertical turbulent mixing, thermally and dynamically driven mesoscale flows substantially contribute to the earth-atmosphere exchange in the atmospheric boundary layer over mountainous terrain (MoBL). The interaction of these processes acting on multiple scales leads to a large spatial variability in the MoBL, whose observational detection requires comprehensive instrumentation and a sophisticated measurement strategy. We designed a field campaign which targets the three-dimensional flow structure and its impact on the MoBL in a major Alpine valley. Taking advantage of an existing network of surface flux towers and remote sensing instrumentation in the Inn Valley, Austria, we added a set of ground-based remote sensing instruments, consisting of Doppler lidars, a ceilometer, a Raman lidar and a microwave radiometer, and performed radio soundings and aircraft measurements. The objective of the CROSSINN (Cross-valley flow in the Inn Valley investigated by dual-Doppler lidar measurements) experiment is to determine the mean and turbulent characteristics of the flow in the MoBL under different synoptic conditions and to provide an intensive data set for the future validation of mesoscale and large-eddy simulations. A particular challenge is capturing the two-dimensional kinematic flow in a vertical plane across the whole valley using coplanar synchronized Doppler lidar scans, which allows the detection of cross-valley circulation cells. This article outlines the scientific objectives, instrument setup, measurement strategy and available data, summarizes the synoptic conditions during the measurement period of two and a half months and presents first results.