Warm–Moist Intrusions as a Key Regulator of Arctic Aerosols, Clouds, and Precipitation

Recent studies show that warm and moist air intrusions are major sources of aerosol particles in the Arctic, affecting local radiative impacts by supplying Cloud Condensation Nuclei (CCN). However, their influence on aerosol size modes, CCN, and cloud droplet number concentrations remains poorly constrained. Here, we use long-term aerosol observations from five Arctic observatories to quantify intrusion impacts. We find that intrusions strongly perturb Arctic CCN, especially in summer, when accumulation-mode and CCN concentrations increase markedly at all sites. In winter and spring, two regimes emerge: intrusions reduce number concentrations at sites near 0° longitude (Zeppelin, Villum, Alert) but enhance them near 180° (Tiksi, Utqiaġvik/Barrow), consistent with competing effects of pollution sources and wet scavenging along trajectories. Intrusions also systematically modify cloud droplet number concentration (Nd): Nd increases at all sites in summer, while in winter it increases at Tiksi and Utqiaġvik/Barrow but decreases at Zeppelin, Villum, and Alert. Overall, intrusions are a key regulator of Arctic aerosol and cloud properties and an important component of the evolving Arctic climate system.Beyond aerosol–cloud number effects, it is unclear how intrusion events modulate cloud optical depth, liquid water content, and precipitation across Arctic sites and seasons. To address this, we will combine cloud and precipitation observations from the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition with reanalysis data to quantify systematic intrusion-driven changes in liquid water content and precipitation occurrence. Finally, we will use the non-hydrostatic mesoscale Weather Research and Forecasting (WRF) model to examine the sensitivity of mixed-phase cloud lifetime and associated precipitation to intrusion occurrence, providing process-level constraints on how intrusions shape Arctic mixed-phase cloud persistence and hydrometeor production.