| Cirrus clouds exert an influence on the Earth's radiation budget that is disproportionate to their mass, due both to their location in the cold upper troposphere and to their unique optical and microphysical properties. Accurate knowledge of cirrus microphysical properties is essential to improving numerical weather predictions and general circulation climate models [Sun and Rikus, 1999]. Furthermore, detailed microphysical information may lead to better small-scale models, assisting in the understanding of cloud formation (i.e., nucleation and freezing) processes. In situ measurements of cirrus cloud microphysical properties are also needed to validate new satellite-based sensors and remote sensing techniques. Possibly most importantly, this information will be useful for gaining a better understanding of water vapor in the tropics and localized troposphere/stratosphere exchange.; A new technique for the in situ measurement of total water (water vapor and particulate water) in tropopause cirrus has been developed by modifying the open-path, near-infrared tunable diode laser spectrometer commonly used for water vapor measurements [May, 1998] into a closed-path system with a shorter optical cell. The new instrument, the closed-path tunable diode laser hygrometer (CLH) is attached to a subisokinetic inlet for increased sensitivity to very thin cirrus layers. The CLH has flown on two major campaigns, SOLVE and CRYSTAL-FACE.; This thesis will discuss the deployment of the CLH in the field, along with post-mission calibrations performed in collaboration with other research groups using similar techniques. These calibrations improved the accuracy of the CLH and characterized different regimes in which the instrument performance is especially suited. Furthermore, both the field experience and calibrations have led to plans for improving the instrument's design and post-mission data analysis for future campaigns.; When flown in combination with an accurate water vapor measurement, as was the case during both campaigns, ice water content (IWC) can be calculated from the bulk total water measurement. During the SOLVE mission, the CLH IWC data was compared to simultaneous measurements made by an FSSP-300 particle probe instrument. During the CRYSTAL-FACE mission, the CLH IWC was used in combination with other instruments (both remote and in situ) to characterize cirrus clouds near the tropical tropopause. |
