Cloud Physics - Current Research and Other Activities
A "random sampling" of some of our recent activities:
Our research has been sponsored by the US National Science Foundation, through the Physical and Dynamic Meteorology Program, and by the US Department of Energy through the Atmospheric System Research program, and by NASA, through the Earth Science Enterprise.
Our group recently participated in the IDEAS 4 (Instrument Development and Education in Airborne Science 4) field project, held at the Research Aviation Facility of the National Center for Atmospheric Research in October and November 2011. HOLODEC, shown below on the wing pod of the NCAR C130 (top instrument), made extensive measurements of liquid and mixed phase clouds. A reconstructed image of an ice crystal sampled by HOLODEC is also shown (approximately 100 micrometers in width).
Our group has developed a "turbulent cloud in a box" to study the interactions between particles and turbulent flows (shown below). The chamber is a cube with "woofers" on each corner, and with this setup we can control the rate at which kinetic energy is dissipated by turbulence. We also simultaneously control the particle size distribution. Particle spatial distributions are measured via digital in-line holography.
In collaboration with colleagues at the Institute for Tropospheric Research in Leipzig, Germany, and the Max Planck Institute for Dynamics and Self Organization in Göttingen, Germany, we have made measurements of clouds at the Environment Research Station Schneefernerhaus on mount Zugspitze in the German Alps. Two phase Doppler interferometers are shown below (with a rainbow in the background).
In collaboration with colleagues at the Institute for Tropospheric Research (IfT) in Leipzig, Germany, we have flow a new instrument for measuring droplet size and spatial distributions. The instrument was installed on IfT's helicopter-borne ACTOS (Airborne Cloud Turbulence Observation System). This project provides a unique opportunity to obtain extremely high-resolution, simultaneous turbulence and cloud particle measurements. Our instrument is the Phase-Doppler Interferometer for Clouds and Turbulence (PICT), developed jointly with Artium Technologies and UC Santa Cruz.
In the laboratory we study the statistical nature of ice nucleation by cooling a water droplet until it freezes, capturing the process with a high speed camera. The work has provided insight into surface crystallization, which is of fundamental interest in nucleation theory. The movie below shows two types of freezing: on the left is a crystal forming at the edge of the water droplet (three phase contact line) and on the right is a hexagonal ice crystal forming on the substrate. (The movies show a few milliseconds of growth.)
We study the physics and chemistry of clouds by holding single aerosol particles in a quadrupole trap, where its environment can be controlled and its properties determined through light-scattering studies. The photo below shows a typical quadrupole trap setup (droplet injector is above).
Work with colleagues at Universidad Nacional Autónoma de México and with Alex Kostinski from Michigan Tech, on the topic of "superterminal" raindrops, was featured in many newspapers and blogs. They included Science Magazine, Scientific American, New Scientist, Discovery, Daily Telegraph, Chicago Tribune, and LA Times.
Our group's research on ice nucleation at water surfaces was highlighted in a News and Views article "Water: Ins and outs of ice nucleation" in the December 8, 2005 issue of Nature.