An interdisciplinary project for investigating secondary particle production by large hydrometeors inside atmospheric clouds: a study on activation of cloud aerosols (Activation of Aerosols: ActivAero).
Geophysics
Fluid Mechanics
Final Report Abstract
Weather forecasting models suffer from our limited knowledge of the interconnected physical and chemical processes over the wide scales of clouds, which remain a source of uncertainty in climate science and atmospheric circulation. Secondary particle production is one such process that actively controls the life cycle of clouds, their radiative properties, and the broadening of particle size by collisions, but is still not well understood. This Walter Benjamin project examined several research questions relevant to understanding secondary particle production. This project involved multidisciplinary training in numerical, experimental, and theoretical physics, and several interdisciplinary collaborations. The question of the production of secondary particles within clouds by the activation of aerosols in the supersaturated wake of large precipitation hydrometeors required the development of new numerical software. The detailed investigation revealed that numerical methods for simulating temperature or water vapor diffusion from the surface of such hydrometeors need to be significantly improved. The precipitation or settling behavior of nonspherical hydrometeors or atmospheric particles, such as, snow particles, volcanic ash, microplastics or pollens greatly depend on their shape, which also affects their tendency to collide or aggregate. There is a large knowledge gap even in understanding the settling dynamics of individual such particles. A series of high-precision particle tracking experiments is performed for non-spherical particles of spheroidal and ellipsoidal shape with size less than one millimeter. Experimental data show that such particles oscillate around their stable settling orientation at different frequencies, depending on the particle shape, and fall with their largest surface area facing gravity. A theoretical study of the dynamic forces and torques to which the particles are subjected shows that the inertia of the particles predominates and delays the transition of the particles to their stable settling orientation. Such behavior usually disappears when a similar particle falls through water and instead stabilizes in its stable settling orientation without any oscillations. Such dynamics would lead to strong differences between particles of different shapes, e.g. between snowflakes and ice needles, and would increase the probability of collisions.
Publications
-
Inertial angular dynamics of non-spherical atmospheric particles
T. Bhowmick et al.
-
Shape matters: long-range transport of microplastic fibers in the atmosphere
D. Tatsii; S. Bucci & T. Bhowmick et al.
