Detailed coupled approach to ice particles nucleation induced by gravity waves in a global NWP model

One of the sources of uncertainties in climate models and numerical weather prediction (NWP) models is cirrus clouds. They are highly sensitive to subgrid-scale dynamics, such as gravity waves (GWs) and turbulence, making them challenging to model in detail within coarse-resolution settings.  Additionally, their net radiative effect remains poorly understood, highlighting the importance of accurately representing their microphysical properties as one of the main areas of focus for research and model refinement.

The current work focuses on a coupled approach to GW–ice microphysics interactions and its application in the global NWP model ICON. The ice scheme, developed by Dolaptchiev et al. (J. Atmos. Sci., 2023), describes GW-induced homogeneous nucleation of ice crystals and proposes a prototype parameterization used in this study. The representation of a local GW field is diagnosed using the Multi-Scale Gravity Wave Model (MS-GWaM) parameterization. MS-GWaM parameterization supports multiple GW source types, and allows for 3D GW propagation, enhancing its physical realism. The full coupling of GW forcing, along with feedback from the new scheme into the overall microphysics and radiation schemes, has been implemented in a test regime in ICON model.

To validate the approach and assess the impact of GWs, several global ICON simulations were conducted. The results show a significant influence of GWs on ice number density, indicating higher concentrations of ice crystals in tropical regions. These findings highlight the potential of the coupled approach to improve predictions of cloud microphysics and their radiative impacts. Further investigations will explore the role of different GW sources and account for the superposition of GWs, offering deeper insights into the broader effects of GW representation on global atmospheric processes.