Analysis of mixed-phase clouds via surface Raman lidar and spaceborne lidar feature extinction profiles

Abstract:

The formation of ice in mixed-phase clouds remains poorly understood – further observations are vital for obtaining insight into this process. Fortunately, we have new measurements that can provide this much-needed insight into their behavior. To this end, Raman lidar products from the Department of Energy’s Atmospheric Radiation Measurement (ARM) Eastern North Atlantic (ENA) atmospheric observatory on Graciosa Island in the Azores archipelago have been analyzed. By measuring Raman scattering and utilizing an automated algorithm for Feature detection and EXtinction (FEX), this instrument can distinguish different cloud phase with high confidence up to twenty kilometers into the atmosphere. With the help of interpolated radiosonde temperature data, the fraction of clouds that are liquid and ice dominated (the liquid phase fraction) as a function of temperature can be determined.

Furthermore, data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on the NASA satellite CALIPSO has been utilized for further analysis of cloud phase and temperature. Because the Raman lidar is ground-based, and thereby primarily observes phase close to cloud base, CALIOP provides a different cloud top perspective that may differ in liquid phase fraction for given temperature bins. By using ground based and spaceborne lidars, we can attain a more holistic view of the cloud phase in this area. Climate models have long struggled to represent the partitioning of cloud phase, and better observational constraints are needed – this research aims to contribute to model accuracy improvement by providing constraints on phase partitioning from both a cloud top and a cloud base perspective.