i-Box: Studying boundary layers in very complex terrain

Boundary layers in very complex terrain, though a subject of growing research, nonetheless remain elusive to a large degree. This is mostly due to limited data availability – and the few available data sets are typically from short campaigns. Despite this, there is a basic desire for understanding physical processes that will ultimately results in improved parameterizations In order to provide comprehensive answers about BL structure, vertical extent, turbulence characteristics, exchange efficiency, interaction with terrain induced meso-scale flows etc. a test bed for studying boundary layers in truly complex topography is therefore needed. Such a platform has been set up by the University of Innsbruck within the so called ‘i-Box' (short for Innsbruck Box). i-Box uses an integrated approach to study exchange processes and turbulence characteristics in complex terrain, combining three-dimensional long-term (several years) turbulence observations and high-resolution numerical modeling. Located in the Inn Valley, the six i-Box measurement sites cover representative topographic features of different slope (0 - 30°), elevation (600m - 2000m), exposition (N and S) and surface characteristics, ranging from valley bottom to mountain top. Apart from the in situ measurements, continuous remote sensing allows for truly three-dimensional boundary layer study. The numerical modeling efforts focus on idealized and real case LES simulations.

In this contribution we will present the i-Box concept, with focus on first results obtained from more than a year of measurements at several sites. The key difficulties plaguing in-situ and remote sensing measurements in complex terrain and their effects on the results will be discussed. Special emphasis will be given to the problem of disentangling turbulence, meso- and sub-meso motions in complex terrain, and its effects on surface exchange processes