We conduct a global assessment of the spatial heterogeneity of cloud
phase within the temperature range where liquid and ice can coexist.
Single-shot CALIOP lidar retrievals are used to examine cloud phase at
the 333-m scale, and heterogeneity is quantified according to the
frequency of switches between liquid and ice along the satellite's path.
In the global mean, heterogeneity is greatest from -15 to -2C with a
peak at -4C, when small patches of ice are prevalent within
liquid-dominated clouds. Above -20C, heterogeneity is greatest in the
northern midlatitudes and lower over the Southern Ocean, where
supercooled liquid clouds dominate. Zonal mean heterogeneity undergoes
an annual cycle with a peak that follows seasonal shifts in the
extratropical storm track. These results can be used to improve the
representation of subgrid-scale heterogeneity in general circulation
models, which has the potential to reduce model biases in phase
partitioning and radiation balance.