Phase Determination in Tropical Mid-level Clouds

Liquid water scatters radiation more strongly than ice crystals, making correct knowledge of cloud phase necessary to accurately calculate the radiative properties of clouds. In mixed-phase temperature regions, it can be difficult to separate the amounts of cloud ice and water using remote sensing measurements, hindering development of accurate mixed-phase parameterizations. Mixed-phase clouds in the arctic have been the focus of many studies, because of the high frequency of mixed-phase clouds in that region. The phase of tropical mid-level clouds, however, has been less well studied, yet tropical mid-level clouds can be extensive and last for many hours. We apply phase retrieval methods developed in the arctic to multiple instrument datasets at Atmospheric Radiation Measurement (ARM) tropical western pacific sites, making adjustments for tropical cloud conditions. We use sensitivity studies and lidar and radar simulators to estimate uncertainties in our knowledge of the phase of mid-level clouds. We also create a climatology of tropical mid-level clouds and their macrophysical properties of height, thickness, and frequency of occurrence. Mid-level clouds are suspected to play an important dynamical role in the tropics in their complex interactions with convection and melting/freezing level stable layers. The cloud phase retrievals will be used in the future to characterize the relationship between phase and temperature, cloud lifetime, and connection to convection.