Scientific Basis and Specifications for an Arctic High Resolution RMR Lidar

The occurrence of Horizontally Oriented Ice Crystals (HOIC) can perturb the radiative properties of a cloud, such as albedo, and the physical cloud properties such as particle residence time. It is crucial, therefore, to quantify the occurrence frequency of HOIC and the conditions under which they form to better understand their significance in affecting the global radiation budget. Previous work has related some natural dependencies, such as temperature, to the occurrence of HOICs. A ground based lidar technique measuring relevant elements of the scattering Mueller matrix has been shown to be sensitive to HOIC. The Clouds Aerosols Polarization and Backscatter Lidar (CAPABL) system, located at Summit, Greenland (72° 36'N, 38° 25'W, 3250m), was designed to make the necessary polarization measurements. In an attempt to measure the predicted critical dependencies, a Raman lidar system is under construction, which will measure water vapor and temperature profiles coincident with the ongoing polarization measurements at Summit. This presentation will discuss CAPABL's unique measurement ability to quantify occurrence frequency then demonstrate the scientific need for a second polarization sensitive Raman lidar system to help answer questions related to HOIC occurrence conditions. Finally, this presentation will develop critical measurement specifications needed to make accurate and precise observations of temperature and water vapor year round at Summit.