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Water & Energy Cycles

Total water measurements help provide a direct means of identifying cirrus that have formed in situ in the tropopause region and when combined with water vapor measurements, a measure of cloud ice water content. Identification and characterization of these tropopause cirrus is important for understanding their role in dehydrating the air ascending through the tropical tropopause layer. The measurement of cirrus cloud ice water content is critically important for relating the microphysical properties of ice particles to their radiative properties. The Harvard total water instrument (HTW) integrates an aerodynamically shaped inlet and an in-stream heater with photofragment resonance fluorescence detection to quantitatively measure the total water content of ambient air. The instrument is mounted in a pallet in the fuselage of the WB57. The air is isokinetically drawn into the instrument through the inlet positioned about a meter from the skin of the aircraft fuselage. Calibration and validation procedures for it and the accompanying water vapor instrument are identical, and provide an accuracy of 5% for water vapor measurements. Derived IWC has a 1 sigma uncertainty of 18% using the HTW and Harvard water vapor (HWV) measurements. Data taken during a mission over Costa Rica in August 2001, the CRYSTAL FACE mission from Key West, FL during July 2002, and the MidCiX mission from Houston TX in the spring of 2004 highlight instrument performance and illustrate the scientific utility of simultaneous measurements of water vapor and total water. The data show a rapid response to orders of magnitude changes in total water at cloud edges. We present observations of high thin cirrus in the tropics, and examples of high water vapor events well into the lower tropical stratosphere.

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/

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Started: Sep 27, 2010

Last Activity: Mar 16, 2011

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