IGF


Research group

Cloud dynamics and atmospheric turbulence

Atmospheric Physics Department

We study the dynamics of clouds in the full range of scales from the movement of individual droplets to flows in scale of clouds and cloud systems. We focus on the phenomenon of turbulence and (direct and indirect) influence of small- and moderate- scale turbulence in clouds and surrounding atmosphere on larger scale flows like weather patterns and even general circulation.

One of our experimental achievements is the Ultra Fast Thermometer, an airborne sensor to measure temperature in clouds. The instrument is in constant development since the early nineties. With recent versions we are able to measure temperature in clouds with 5 mm resolution.

 

Ultra Fast Thermometer UFT-M mounted on CIRPAS Twin Otter in the course of POST research campaign
Monterey, California, July 2008.

 

Example of numerical simulation:

None This animation (click on the thumbnail) shows the amount of liquid water (cloud condensate) in a simulation of the stratocumulus-topped boundary layer. The simulation is based on measurements from the DYCOMS-II field campaign, and the animation is showing vertical cross-sections through the computational domain.   By Jesper Pedersen

 

Animations of droplets motion in the idealized vortical flow


The motion of cloud droplets in a very strong vortex, a model of the smallest structure in small turbulent flow was numerically simulated. The aim was theoretical reproduction and understanding of the phenomenon called „cloud voids” („Swiss cheese” clouds), observed at the mountain meteorological and environmental laboratory at the Zugspitze summit in Germany.

At the cylindrical edge of a stationary (not changing in time) Burgers vortex stretching, cloudloud droplets are randomly added. Their initial velocity corresponds to the radial component of the vortex velocity field, their motion is then governed by gravity and interaction with the flow. Thus, the equation of motion of a single drop, the Stokes viscosity force, and the force of gravity are taken into account. Virtual droplets in the virtual flow do not collide, they also no influence the fluid flow. The droplet size distribution is similar to the observed one, whilst the color and the size in the animation reflect the intensity of the Mie scattering of the green laser light used in the experiment. The vortex axis is inclined relative to the direction of gravity. Trajectories of droplets in this system show existence of various attractors in the plane perpendicular to the vortex axis: limit cycles and different equilibrium points, stable and unstable. The three presented animations illustrate selected examples of vortex parameters for which the droplets show quite different behavior.

Animation 1 Animation 1 Animation 1: no voids are present in the droplet field.
     
Animation 2 Animation 2 Animation 2: the void is present but in a "fuzzy" condition.
     
Animation 3 Animation 3 Animation 3: the void is clearly visible

 

These simulations allow us to conclude about intensive clustering and possible large impact on the probability of droplet collisions in strong vortex tubes in real clouds.

Research project

Research & Organizational Project

Field Experiment

dr Dariusz Baranowski
dr Jesper G. Pedersen
dr Yongfeng Ma
mgr Emmanuel Akinlabi
mgr Anna Górska
mgr Marta Kopeć
mgr Jacek Kopeć