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

Abstract

Abstract 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 (qi) and ice crystal number (Ni) between the microphysical schemes and very distinct qi 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.

Keywords

• ice microphysics
• cirrus lifecycle
• cloud‐radiative heating
• trajectories
• storm‐resolving simulations
• Asian monsoon