CLOUD: Small drops interactions with the flow in shallow cumulus clouds (Progetti)

Type
Label
  • CLOUD: Small drops interactions with the flow in shallow cumulus clouds (Progetti) (literal)
Anno
  • 2012-01-01T00:00:00+01:00 (literal)
Alternative label
  • Alessandra Sabina Lanotte (2012)
    CLOUD: Small drops interactions with the flow in shallow cumulus clouds
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • Alessandra Sabina Lanotte (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
  • CNR ISAC (literal)
Titolo
  • CLOUD: Small drops interactions with the flow in shallow cumulus clouds (literal)
Descrizione sintetica
  • High Performance Computing ISCRA class B project of CINECA. PI Alessandra S. Lanotte (literal)
Abstract
  • In this project, computational and modelling efforts will mostly focus on two problems. The first is the parameterization of particle/turbulence interaction in terms of relations connecting particles statistics to flow properties. The second is the problem of strong spatial fluctuations of the particle number concentration and its interaction with scalar fields (temperature and water vapour), that can influence droplets size distribution at the early stage of cumulus cloud formation. We will perform computational investigations of the cumulus and stratocumulus cloud topped boundary layer by means of Large-eddy Simulations. The point-particles equation of motion is coupled to that for the microphysical evolution of CCN along Lagrangian trajectories, from heterogeneous nucleation until the end of the condensational growth. In numerical simulations, solid particles and droplets will be assumed to have spherical shape, and with diameter smaller 40-50 micron, beyond which growth by collision-coalescence might become important. To deal with the typical CCN number concentration, a new closure will be implemented to describe the microphysical evolution of an ensemble of droplets in terms of the microphysics of a single representative one. It is important to stress that recent results have questioned Koehler theory for cloud condensation nuclei activation, particularly in continental polluted environment, hence corrections will be explored and tested as a function of different vapour saturation conditions also. [Goals:] Main objective is to understand the small-scale features of aerosol/flow and aerosol/water vapour interactions. For this, we will: i) study small-scale features of particle/air flow interaction in the dry convection regime; ii) statistically detail the particle/flow dynamical interaction and particle/water vapour microphysical interaction in moist (warm air) convection; iii) assess the influences of these phenomena on the onset of cloud formation and its later evolution. [Tools:] These goals will be mostly achieved performing the following numerical experiments: -- High resolution Direct Numerical Simulations for three-dimensional convective turbulence, seeded with different initial distribution of aerosol number concentration; -- Large-eddy simulations (LES) for moist convective Planetary Boundary Layers (PBL), seeded with aerosol particles. Beside, theoretical study enters in the improvement of microphysical and sub-grid scale Lagrangian models. [Scientific rationale, state-of-the-art, outcomes:] Aerosol/precipitation interaction is a major challenge for atmospheric physics. In particular, it is crucial to describe quantitatively the spatial and temporal properties of those particles acting as CCN, and the modification of such properties by the interaction with water vapour. Large concentrations of aerosols induce an increase in the number of droplets for a given liquid water content, and induce the enhancement of multiple scattering within clouds, thereby increasing cloud-top albedo (Twomey effect). Also, large concentration of aerosols can cause the enhancement of cloud lifetime, which results in an increase in planetary shortwave albedo, and eventually in the atmospheric absorption of long-wave (thermal infrared) radiation, because of the increased content of liquid water and water vapour of the atmosphere . No computational model can give an exact and fully detailed description of these phenomena. Hence in general, simplified models involving parameterizations or statistical closures are applied. However, these are sometimes too coarse to lead to quantitative predictions for the cases of interest. The major innovation of this project is to describe cloud liquid phase not as a field, but in terms of Lagrangian drops dynamics and microphysics. (literal)
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