Observing Microphysical Properties of Atmospheric Water Using Polarization and Raman Lidar

• Main Author: Stillwell, Robert Andrew
• Format: Text
• Language: unknown
• Published: CU Scholar 2017
• Subjects: arctic; clouds; Greenland; Lidar; water; Meteorology; Remote Sensing; Arctic; Climate change; Ice Sheet
• Online Access: https://scholar.colorado.edu/asen_gradetds/170; https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1171&context=asen_gradetds

Signatures of climate change have been shown by observation and climate model studies to be most evident in the polar regions, so called polar amplification. However, the polar regions are among the least studied regions on Earth, limited largely due to harsh measurement environments and the logistical challenges of maintaining presence in such environments. A lack of high vertical and temporal resolution measurements of cloud properties and atmospheric state directly relates to uncertainty in climate model predictions inhibiting scientific understanding of the specific response of the polar regions within the context of global climate change. This thesis focuses on measurements of water in the polar regions in its 3 thermodynamic phases, i.e. water vapor, liquid and ice. Uncertainty in water's 3-dimensional distribution and properties contributes to the uncertainty in specific response of the Arctic system to large-scale perturbations. By directly and indirectly modulating the surface energy and mass budgets of the region, water contributes to much of the fundamental uncertainty of model projections in the polar regions. It is hypothesized that ground-based, active optical remote sensing measurements can contribute to the knowledge of atmospheric state and cloud properties by providing unmatched data resolution and quality to help identify and elucidate key cloud microphysical and cloud state properties. To address this hypothesis, 3 main questions are posed: 1) How to accurately identify and distinguish liquid and ice water in Arctic clouds using polarimetric lidar? 2) What unique signatures about Arctic cloud microphysical properties can be revealed using polarimetric and Raman lidar? 3) How do we meet the needs of the next generation cloud and atmospheric state observations in the Arctic using lidar? This thesis addresses these questions using two lidar systems, the Clouds Aerosols Polarization and Backscatter Lidar (CAPABL) currently deployed to the top of the Greenland Ice Sheet at Summit, Greenland, and by developing a next-generation Arctic lidar, the Summit Polarized Raman Lidar (SuPR). Unique polarization processing of CAPABL data allows for separation of cloud thermodynamic phase and ice crystal orientation. Specific microphysical properties of these subclasses of cloud particle as well as uncertainties in lidar data are identified and linked directly to their impact on the surface radiation budget, using CAPABL data and ancillary sensors at Summit. First of their kind observations of radiative effects of the preferential orientation of ice crystals are demonstrated. These results from CAPABL inform the development of the design requirements of SuPR which is a first of its kind 3-phase water observing system designed specifically for the Arctic. The design and first measurements of the SuPR system are demonstrated.