A Lagrangian Perspective of Microphysical Impact on Ice Cloud Evolution and Radiative Heating

We generate trajectories in storm-resolving simulations in order to quantify the effect of ice microphysics on tropical upper-tropospheric cloud-radiative heating. The pressure and flow field tracked along the trajectories are used to run different ice microphysical schemes, both one- and two-moment formulations within the Icosahedral Non-hydrostatic Model model and a separate offline box microphysics model (CLaMS-Ice). This computational approach allows us to isolate purely microphysical differences in a variant of “microphysical piggybacking;” feedbacks of microphysics onto pressure and the flow field, for example, via latent heating, are suppressed. Despite these constraints, we find about a 5-fold difference in median cloud ice mass mixing ratios (q$_i$) and ice crystal number (N$_i$) between the microphysical schemes and very distinct q$_i$ distributions versus temperature and relative humidity with respect to ice along the trajectories. After investigating microphysical formulations for nucleation, depositional growth, and sedimentation, we propose three cirrus lifecycles: a weak source-strong sink lifecycle whose longwave and shortwave heating are smallest due to short lifetime and low optical depth, a strong source-weak sink lifecycle whose longwave and shortwave heating are largest due to long lifetime and high optical depth, and a strong source-strong sink lifecycle with intermediate radiative properties.