Arctic Warm and Moist Air Intrusions in ICON Simulations

Warm and moist air intrusions (WAI) contribute strongly to extreme warm events in the central Arctic and deliver a major part of the moisture transport into this region, with significant impacts on cloud formation and the surface energy balance. Within the PolarRES EU-project we use the ICON model to study such events both in case studies for the MOSAiC expedition and climate simulations.

MOSAiC provided comprehensive observations of two WAIs in mid-April 2020 when near-surface air temperatures reached the melting point for the first time in this spring. We evaluate different ICON-LAM set-ups, including a pan-Arctic domain with 11km horizontal resolution, as well as more confined domains at convection-permitting 2.5km resolution with varying cloud microphysics settings. A better agreement with local observations is found on the smaller model domains at higher resolution. Additionally, the representation of liquid water is improved by using a more complex two-moment cloud microphysics scheme, where a scenario with higher CCN (cloud condensation nuclei) concentration is found to be more suitable for the aerosol-rich intrusion around April 16.

In a climatological perspective we demonstrate the tracking of moisture intrusion events in decadal-scale climate simulations with ICON-LAM at 11km resolution in a pan-Arctic domain. We drive the regional model with ERA5 and selected CMIP6 GCMs to obtain vertically integrated water vapor transport at high spatial and temporal resolution. This is then used to identify, track and classify WAIs, to study their climatological characteristics, impacts and long-term trends under climate change.