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Atmospheric Composition

We propose to fly the Harvard water vapor instrument in support of the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX), an airborne field campaign to investigate the properties of mid-latitude cirrus clouds, and the processes affecting these properties and their impact on radiation. Because of the controversy surrounding the accuracy of water vapor measurements in the lower stratosphere, we specifically propose to combine the Harvard photofragment fluorescence water vapor and the Harvard Herriott Hygrometer (HHH) for integration into the spearpod of the NASA WB-57 aircraft. Through a combination of laboratory investigation and airborne intercomparison, Harvard water vapor has proved its reliability and accuracy during the CRYSTAL-FACE, Pre-AVE, MidCiX, CRAVE, and TC4 missions. HHH, a new, high accuracy, IR laser absorption instrument developed under the NASA IIP program will provide a completely independent measure of the absolute water vapor concentration with a minimal addition of mass and power to the integrated water vapor instrument package. Preliminary laboratory tests and intercomparisons have shown that HHH has a precision of < 0.05 ppmv for 1-second data. This will pin our water vapor calibrations to an absolute concentration scale using three independent methods: (1) The UV absorption cross section at Lyman alpha (121.6 nm); (2) The water vapor partial pressure determined by the temperature at the water vapor bubbler; and (3) The strength of the IR rotationvibration lines used in absorption. This will also constrain the magnitude of any nonwhite noise sources that can often lead to systematic errors when fitting direct absorption data at very low water vapor mixing ratios.

Project PI: James Anderson/Harvard University

Harvard University 12 Oxford Street, Link Bldg. Cambridge, MA 02138

Phone: (617) 495-5922

Fax: (617) 495-4902

Email: anderson@huarp.harvard.edu

http://www.arp.harvard.edu/

http://www.seas.harvard.edu/directory/janders

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Started: Sep 27, 2010

Last Activity: Mar 16, 2011

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