AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Response of Clouds to Aerosol Concentration: Results from Mixing Clouds in a Multiphase, Turbulent Reaction Chamber
WILL CANTRELL, Kamal Kant Chandrakar, Kelken Chang, David Ciochetto, Dennis Niedermeier, Raymond Shaw, Michigan Technological University
Abstract Number: 698 Working Group: Aerosols, Clouds, and Climate
Abstract The microphysical properties of liquid water clouds are influenced by aerosol properties such as the number concentration, chemical composition, and size. In turn, a cloud's microphysical properties play a dominant role in its optical properties and in the likelihood that it will produce precipitation. For example, an increase in the number of aerosol particles can lead to an increase in the number that will serve as cloud condensation nuclei, which can increase cloud droplet number and decrease the effective droplet radius, which results in an increase in the cloud's albedo for a constant liquid water path. This logical chain is difficult to quantify in natural clouds because changes in microphysical properties caused by aerosol are almost always entangled with those caused by dynamics.
We have developed a multiphase, turbulent reaction chamber which is uniquely suited to address this problem. It is capable of pressures ranging from sea level to ~ 100 mbar, and can sustain temperatures of +40 to -55 C. More importantly, we can independently control the temperatures on the surfaces of three heat transfer zones, which allows us to establish a temperature gradient between the floor and ceiling inducing Rayleigh-Benard convection and a turbulent environment. The mixing cloud which forms when the boundaries are wet has a constant forcing – i.e. the dynamics are fixed. We can thus explore both the transient and steady state response of cloud microphyiscs to changes in aerosol concentration, composition, and size.
Our initial results show that the cloud droplet effective radius and concentration respond quickly to changes in the aerosol number concentration. Furthermore, if the aerosol in the chamber are not replenished as droplets are removed from sedimentation and collisions with the walls, the fraction of large droplets (> 40 micron diameter) increases, leading to a rapid collapse of the cloud.