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Raymond ShawProfessor, Physics Director - Michigan Tech
The degree to which an atmospheric cloud entrains and mixes with clear air from the surrounding environment largely determines the maximum liquid water content achieved by the cloud, the droplet size distribution within the cloud, and therefore influences the rate of rain formation and radiative properties of the cloud. We wish to understand how the turbulent mixing progresses and how the cloud particles respond to the fluctuating thermodynamic environment that results from mixing. Simply put, if a cloud is diluted, do all droplets evaporate uniformly or does a subset of droplets evaporate completely, leaving the remaining drops unaffected? We use an airborne digital holographic instrument (Holodec) to show that cloud edges are inhomogeneous down to centimeter scales and that the droplet size distribution fluctuates strongly in number density but with a nearly unchanging mean droplet diameter. This unique three dimensional view of the cloud structure provides evidence in support of relatively simple approaches for representing mixing in coarse models.
Holodec and the resulting science are a result of a ten-year collaboration between Michigan Technological University (M. Beals, J. Lu, and the speaker), Mainz University (J. Fugal), and NCAR/EOL (S. Spuler, J. Stith, and many others). The collaboration has seen the instrument go from a concept first flown in the Instrument Development and Education in the Airborne Sciences (IDEAS) project in 2003, through development of hologram reconstruction and analysis software, design and construction of a new instrument, and deployment in several subsequent IDEAS projects on three different airborne platforms.
Tuesday, 8 April 2014, 3:30 PM
Refreshments 3:15 PM
3450 Mitchell Lane
Bldg 2 Small Seminar Room (Rm1001)