Research Interests:

My atmospheric physics research interests are in the fundamental processes associated with the formation of ice and clouds. The issues central to my research are:

• the role of biogenic material and bacteria in ice and cloud formation
• the dependence of water vapor pressure on the chemistry of aqueous cloud droplets
• the dominant ice nucleation mode in the upper tropospheric clouds
• the growth rate of ice particles and its dependence on ice nucleation mode
• the determining factors for tropospheric ice particle shape
• the light scattering properties of ice particles
• the microphysics of thunderstorm electrification
• the physical and chemical properties near the surfaces of ice and aqueous solutions.

My experimental approach is to develop new table-top scale instruments and high-precision methods to study these processes. I am particularly concerned with effectively removing potential contamination and surface effects that have been systematic problems in previous measurements. The broader impact of this work is to improve the precision of cloud and climate models in describing the influence of clouds on the radiative properties of the Earth. Global climate change may greatly impact society, making it crucial that policy makers have the most accurate possible assessments from climate models.

Current Research Projects:

1. Ice Nucleation:
   
   In our laboratory we study ice nucleation by observing the freezing of supercooled droplets using various methods. Some experiments are done using free-fall inside a freezing tube which makes possible the observation of the freezing process with high repitition rates and away from contamination, particle-particle interactions, and the possible influence of substrates. Experiments range from studying the activity of sea ice bacteria, comparing the ice nucleating properties of sea-ice bacteria and other mesophylic bacteria, to measuring the frozen fraction curves of homogeneous droplets containing common tropospheric aqueous solutions.
   
   
• Swanson 2009
• Junge and Swanson 2008
• Larson and Swanson 2006
• Junge et al. 2006
• Laucks et al. 2005
• Kay et al. 2003
• Wood et al. 2002
• Bacon et al. 1998
  
  
2. Growth and Sublimation rates and Ice particle habit Evolution
   
   We study the growth, sublimation and light scattering properties of tropospheric ice particles. One of the instruments we use is a low temperature electrodynamic balance which allows us to observe single ice particles away from the influence of surfaces. Our work focuses measuring growth rates, particle shape evolution and the influence of ice nucleation mode on ice particles grown in the laboratory under conditions similar to those observed in cold clouds. We have a plan to develop, in collaboration with Jon Nelson, a new twin capillary instrument to study ice crystal growth. The new instrument will provide much more precise temperature, supersaturation and nucleation mode control than has been available in previously used methods.
   
   
   • Bacon et al. 2003
   • Qu et al. 2001
   • Swanson et al. 1999
     
     
3. Light Scattering Properties of Ice Particles
   
   Uncertainty in the light scattering properties of clouds is one of the major sources of error in cloud and climate models. We are interested to measure the differential light-scattering cross section and phase functions of single ice particles with the various shapes found in ice clouds. To date we have determined the phase function for hexagonal-hexagonal prismatic ice particles for a range of aspect ratios and particle orientations. Future experiments will explore the non-prismatic ice particle shapes which commonly are common in upper tropospheric clouds.


• Bacon et. al. 2000
• Bacon et al. 1998
  
  
4. Ions and pH near the solution-air and ice-air interface
   
   Brant Wilson and I have been interested in the microphysics of ions and molecules that reside near an air-water or air-ice interface. We have built a cryostat and integral confocal microscope to measure the ion and pH profile near these interfaces. This instrument is also useful fluorescence microscopy and resonant Raman spectroscopy studies of molecules at interfaces. Our goal is a better understanding of the microphysics of charge transfer between colliding particles which is thought to be responsible for the electrification in thunderstorms.
   
   
   • Wilson 2007
   • Volny et al. 2007
     
     
5. Sap Crystal morphology and growth mechanism
   
   Kathleen Jensen and I have been looking at ice crystal formation on alder and maple tree surfaces. This is an ongoing study to determine how sap crystal morphology depends on plant type. It appears that frost damage on many plants is caused by the growth of sap crystals. Comparisons between the crystals found on North American plants and those observed on Dock family plants observed in Ladakh, India show the influence of plant anatomy on crystal shape. Our goal is to better understand the growth rates and formation mechanism of these crystals. We also attempt to determine the extent to which these processes are responsible for frost damage in some species of plants.
   
   
   • See cover of Glaciology V. 39 (1993) for our picture of sap crystals on Dock family plant.

Publications:

A summary of publications for Brian Swanson is found here.