Lagrangian dispersion in the Atmospheric Boundary Layer: Results from the IMPACT campaign

With length scales ranging from millimeters to kilometers, the ABL presents a complex and dynamic environment that demands further exploration. Whereas field experiments typically focus on large-scale stratospheric phenomena, we have focused on the small-scale mechanisms (1e2 - 1e4)m within the spectral gap of the ABL, emphasising the influence of turbulence on particle dispersion (itself a proxy for turbulent mixing). Understanding these dynamics is of practical importance for risk assessment for wildfires, chemical disasters or industrial accidents, as well as providing detailed insight into cloud physics and aiding climate modeling efforts.

With this motivation, in the IMPACT (In-situ Measurement of Particles, Atmosphere, Cloud, and Turbulence) field campaign, conducted in May and June 2024 in northern Finland, we launched 53 small, lightweight, and biodegradable balloons into the atmosphere and tracked them for periods ranging from 10 minutes to 2 hours, and we measured their mean relative separation rate by releasing them both near the ABL limit (see photo) and from the ground.

In this talk, we will present our preliminary findings, which show that relative dispersion is enhanced under certain conditions, providing new insights into mesoscale transport in the ABL and its impact on mixing.