Impact of gravity waves on ice-cloud microphysics in a global NWP model using online coupling

Gravity waves (GWs) are well known for their role in shaping large-scale dynamics of the atmosphere, but they also induce strong local variability in the vertical velocity, temperature, and other fields.  Such variability is often omitted when it comes to global effects due to averaging and resolution limitations. However, small-scale dynamics, such as gravity waves, have a crucial role in cirrus microphysics and life cycle. Ice clouds, on the other hand, can have a pronounced effect on the Earth’s radiation budget and global moisture distribution, making their accurate representation in climate and numerical weather prediction (NWP) models particularly important.

This work investigates the effects of gravity waves on cirrus cloud microphysics using the global ICON (Icosahedral Nonhydrostatic) model. A novel, self-consistent parameterization of GW-induced homogeneous ice nucleation developed by Dolaptchiev et al. (2023) is employed, and additional GW effects on depositional ice growth are considered. The local GW field is represented using the Multi-Scale Gravity Wave Model (MS-GWaM), which supports multiple GW source types and three-dimensional wave propagation, thereby enhancing the physical realism of the parameterized GW dynamics. The full coupling of GW forcing, along with feedback from the supplemented ice scheme into the overall microphysics and radiation schemes, has been implemented and assessed within the ICON model.

The results of the global test runs reveal significant GW impacts on ice formation mechanisms, leading to enhanced homogeneous nucleation in the upper troposphere–lower stratosphere (UTLS) compared to the baseline ICON configuration. Furthermore, GW-induced temperature fluctuations obtained from MS-GWaM and coupled online to depositional growth substantially increase ice growth efficiency. It results in larger ice mixing ratios in the mid-latitudes and subtropical regions. Further analyses are planned to assess the sensitivity of the coupled version to different MS-GWaM configurations, the role of lateral GW propagation, and the relative contributions of different gravity wave sources.