Disentangling atmospheric transport and mixing processes over mountains: overview of the preliminary field campaigns of the project DECIPHER

This paper presents the rationale, experimental design and preliminary outcomes of two field campaigns undertaken as part of the project DECIPHER at two mountain sites in the Italian Alps to investigate surface-layer processes and turbulent fluxes associated with slope-wind systems. The first campaign (23 July-29 October 2024) was concentrated at Col Margherita (2543 m above sea level (ASL) )and nearby Passo Valles. The second field campaign (2 October-10 November 2024) was carried out in the Monte Baldo mountain range on a steep east-facing slope. Deployed instruments included an optical particle counter (OPC) for aerosol measurements, a Doppler wind Lidar, a Raman Lidar, a disdrometer, a two-level eddy covariance tower, complemented by a four-way net radiometer, soil sensors and thermohygrometers distributed along the slope. Results showed that at Col Margherita, OPC measurements identified coarse-mode aerosol enhancement episodes on 30 July–1 August (Episode 1) and 15–17 August (Episode 2), both were linked to long-range dust transport, as supported by Copernicus Atmosphere Monitoring Service (CAMS) analyses and lidar observations. During non-episodic periods, variability in fine- and coarse-mode aerosols appeared to be strongly influenced by local moisture conditions, with specific humidity values greater than 10 g kg− 1 over the site. At the Monte Baldo site, the last 12 days of the field campaign (30 October–10 November) were characterized by meteorological conditions favorable for the development of slope winds. A representative case of a fully developed thermally driven slope-wind system on 7 November clearly highlighted the role of slope orientation and topographic geometry in controlling the timing, persistence, and intensity of transitions between upslope and downslope flow regimes. This occurred even during November, a period generally considered less favorable for thermally driven circulations than summer conditions. Further in-depth analyses will be the subject of forthcoming publications.