SGER: New Approaches for the Measurement of Microphysics in Extratropical Hurricanes

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This is a Small Grant for Exploratory Research to support the participation of Dr. Garrett in the Extratropical Transition of Hurricanes Experiment (ETHEX) in the fall of 2003. The objective of ETHEX is to observe the characteristics of Atlantic hurricanes as they move north from the tropics and evolve to take on the characteristics of midlatitude cyclones. Such storms are often large and intense, and can cause heavy rain, flooding, property damage, and loss of life. As part of ETHEX, the Convair 580 research aircraft operated jointly by the National Research Council of Canada and the Canadian Meteorological Service will make storm-penetration flights to measure the microphysical properties of midlatitude storms that originated as hurricanes. The measurements include drop-size distributions, the amounts of cloud water and ice per unit volume, and ice crystal sizes and shapes. Dr. Garrett will install on the airplane a Cloud Integrating Nephelometer (CIN), an instrument built by Gerber Scientific for measuring certain volume-integrated optical properties of clouds, specifically the extinction coefficient and the asymmetry parameter, a measure of the importance of forward scattering compared with the total scattering. This parameter has a different value for ice clouds than for water clouds. The CIN contributes to the objectives of ETHEX by providing, through the asymmetry parameter, a direct measure of the proportion of ice present in mixed-phase clouds. This is important information, not otherwise obtainable, both for characterizing the microphysical structure of the clouds and for helping to interpret the measurements of other instruments, which are not always able to distinguish between water and ice. The independent measurement of extinction that the CIN provides also helps to validate the measurements of drop-size distribution by the other instruments. Broader impacts of the project include improving the ability to model and forecast extratropical hurricanes and encouraging the collaboration of American and Canadian cloud physicists.