Impact of Cloud Microphysical Properties and Meteorological Parameters on Cloud Freezing Temperature

Cloud phase has an important impact on precipitation, cloud radiative properties and the Earth radiation budget. Unfortunately, factors that impact the temperature of the phase transition from liquid to ice remain poorly understood with observations and numerical models differing by orders of magnitude.

Using POLDER-3 and MODIS space-based instruments, both part of the A-Train, we analyzed cloud microphysical and radiative properties, spatially and temporally colocated with meteorological parameters from ERA-Interim reanalyses. From cloud top temperature distributions of liquid and ice clouds, we estimated the temperature at which clouds freeze for different latitudes, regimes of liquid-droplet effective radius, and regimes of large-scale vertical velocity. Our results show that the freezing temperature increases by 20°C between a regime where the effective radius ranges from five to nine micrometers to a regime where the effective radius ranges from 21 to 25 μm. Updraft velocity and latitude have a smaller impact on the freezing temperature.

We also colocated concentrations of a passive tracer of aerosols in a tracer transport model with cloud properties and meteorological parameters to observe that, locally, pollution concentrations lower the cloud freezing temperature by approximately 4°C, while the impact on freezing temperatures through changes in effective radius is relatively small.