A New Approach for Improving Measurements of Cloud Water Contents from Aircraft

Rainwater, Bryan

Graduate Thesis Or Dissertation

A New Approach for Improving Measurements of Cloud Water Contents from Aircraft Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/kp78gh82s

Abstract

This work addresses the need for improved measurements of condensed water in clouds from research aircraft. First, new spectral line fitting codes are shown to improve retrievals of H₂¹⁶O in evaporated clouds by traditional near-infrared tunable diode laser spectroscopy. These codes are then applied to measurements of cloud water contents (CWC) with the University of Colorado Closed-Path Laser Hygrometer (CLH-2) during a series of flights in 2018 into clouds of varying types over the Southern Ocean. By comparing with observations of CWCs from cloud probes ranging from hot wires to droplet imagers, it is found that measurements of CWC using bulk water are generally accurate, but they can also be adversely affected by inlet artifacts such as icing, especially in the presence of mixed phases of water. Because the same can be true of other methods, there is currently no one instrument that accurately measures CWC under all conditions.Second, using knowledge gained from improvements in optics and electronics for CWC measurements, alongside improved retrievals of H₂¹⁶O abundances using sophisticated line-fitting methods developed for those CWC measurements, it is demonstrated through a series of laboratory studies that traditional hygrometer measurements of multiple isotopologues of water may be possible on research aircraft with distributed feedback lasers operating in the near-infrared (1.4 𝜇𝑚 and 2.6 𝜇𝑚). It is proposed to conduct these measurements as the ratio of absorbances of pairs of adjacent absorption lines of two isotopologues (e.g., H₂¹⁶O and H₂¹⁶O to characterize fractionation that can be used to elucidate important issues related to properties of clouds, such as liquid and ice-water contents and precipitation, and the microphysics of cloud particle formation. Through such measurements it should be possible to reduce outstanding uncertainties in cloud processes and the hydrological cycle, such as precipitation efficiency related to the aerosol indirect effect, mixed-phase cloud microphysics, and atmospheric transport and mixing in the vicinity of clouds. In addition, augmenting existing TDLAS instruments with the capability to detect isotopologue pairs will allow for characterization of inlet artifacts, such as condensation on sample lines and icing on inlet surfaces.

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