Abstract
The project DECIPHER (Disentangling mechanisms controlling atmospheric transport and mixing processes over mountain areas at different space- and timescales) will investigate processes controlling exchange of momentum, energy and substances between the Earth surface and the atmosphere, and transport processes, across a variety of scales, including turbulent mixing and removal by precipitation scavenging. The overall goal of DECIPHER is to disentangle the effects of the various physical and chemical factors on atmospheric processes in mountain sites at different time and space scales. This will be obtained through field measurements and remote sensing approaches in two supersites, chosen with specific topographic and ambient features. a) Assessment of particle transport at high altitude. The main patterns of transport will be linked to thermally driven circulations developing in mountainous areas and reconstructed through the identification of sources and particles' paths to the receptors. Moreover, the role of different sources of air pollution in high altitude areas will be assessed. b) Understanding connections between orographic convection, precipitation and aerosol. Progress in our understanding of aerosol as a possible factor for enhancing nucleation for cloud formation and precipitation, following orographic convection, and the role of orographic precipitation in the removal of atmospheric aerosol. c) Scaling relationships and similarity functions. The combined analysis of data from measurements and from high-resolution numerical simulations will enable us to investigate connections among the physical variables involved in the processes. In particular, suitable scaling schemes and similarity functions will be explored and tested. d) Datasets The project will produce a rich benchmark of datasets, both from intensive field campaigns and from laboratory measurements, as well as from high-resolution model runs under various configurations. These will provide a basis for both the implementation of suitable parametrizations and for model verification. After a preliminary embargo, datasets will be published and shared to a broader scientific community.
Results achieved
: The main DIFA Research Unit role in DECIPHER was to provide detailed precipitation information during the Project’s campaigns. We took part in two experimental campaigns: Passo Valles (July-October 2024) and Monte Baldo (July-November 2025). The OTT-Parsivel2 disdrometer was installed at the two experimental locations and operated automatically, with a remote control. All the research reported here was carried on in close cooperation with other members of the Consortium. Disdrometric data were collected for more than 40 days with precipitation solid or liquid in both sites, and parameters of the Drop Size Distribution (DSD) were computed to characterize the precipitation microphysical structure. We focused mainly on liquid precipitation. Thanks to the presence of other instruments deployed in the sites, two main objectives were pursued: 1) to study the impact of various precipitation structures on the lidar back scattering measurements, and 2) to study the role of precipitation in removing aerosol from the atmosphere after comparison with lidar data and Optical Particle Counter (OPC). The comparison between different instruments was performed at one minute time scale. Preliminary results show that for cases of light-moderate precipitation with prevalence of water droplets below two mm of diameter, the lidar backscattering coefficient is correlated with most of the DSD moments or integral parameters. Especially low-order moments (number of drops and the distribution of droplets’ surfaces) are positively related to the amount of lidar backscattering close to the ground. For a number of different events, the relationship was not so clear, with different behaviors. A possible reason is that, since both experimental sites are at high altitudes, the occurrence of clouds reaching the ground was high, for at least a part of the event. In this case the signal of small cloud droplets could affect both lidar and disdrometer measurements and mask the effect of precipitation. A further and deeper analysis of lidar data would solve this ambiguity, using also independent instruments, such as a ceilometer. As for the scavenging properties of precipitation, the vertically averaged lidar backscattering coefficient in the lower layer (between 70 and 200 m a.g.l.) were compared for the minutes before, within and after a precipitation episode. The tendency of reducing the aerosol load by rainfall episodes is clearly present in most of the cases, with different impact, that seems to be mainly related to the number of raindrops. Also in this cases, there are events with more uncertain interpretation, for which the scavenging process seems to be less effective, and almost unrelated to the precipitation microphysical structure. A better classification of the aerosol populations, available by means of a co-located OPC, would improve the understanding of the process. All the data collected during the campaigns were uploaded to the Zenodo repository of the project and can be used by project’s partners. Finally, the DIFA research unit provided the meteorological analysis of the Monte Baldo preliminary campaign (July-November 2024), to contextualize at larger scale the data collected by local instrumentation and to select the more interesting periods for the data analysis. This campaign was mainly devoted to the study of local winds and dry processes, so the disdrometer was not deployed. The synoptic analysis was based mainly on the reanalysis from NCEP CFSR (geopotential height at 500 and 850 hPa, surface pressure and temperature) and the RBG-airmass product obtained from satellite (Meteosat-SEVIRI) data made available by EUMETSAT. Deutsche Wetterdienst forecasts, with front analysis, were also used. Results shown that, overall, the more favourable periods for the development of local winds were: 12 to 15 October, with transient high-pressure conditions and potential instabilities; 1 to 4 November, sustained and stable high-pressure conditions. This second period can be extended to 30 October to 10 November with a loss in stationarity of the high pressure and the presence of potential instabilities not necessarily associated with clouds or precipitation.Project details
Unibo Team Leader: Federico Porcù
Unibo involved Department/s:
Dipartimento di Fisica e Astronomia "Augusto Righi"
Coordinator:
Università degli Studi di Trento(Italy)
Total Unibo Contribution: Euro (EUR) 56.329,00
Project Duration in months: 24
Start Date:
28/09/2023
End Date:
28/02/2026
