Impact of air parcel history on Arctic cloud glaciation: a large-scale back trajectory analysis

The Arctic is warming at unprecedented rates, yet climate models struggle to accurately represent key processes such as aerosol–cloud interactions in polar regions. The coexistence and interactions of liquid droplets and ice crystals within clouds, and the influence of aerosols acting as ice-nucleating particles or condensation nuclei, remain poorly understood because of the complexity of the microphysical processes involved. Previous studies have primarily focused on the relationship between cloud phase and instantaneous aerosol properties, often neglecting the physico-chemical evolution of air parcels during long-range transport.

To address this gap, we introduce the ARctic Clouds History and ThermodYnamic PhasE dataset (ARCHTYPE), which leverages DARDAR-MASKv2 retrieval products. These products combine data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and the CloudSat Cloud Profiling Radar (CPR), both part of the A-Train constellation. In DARDAR-MASKv2, each atmospheric pixel (60 m vertical resolution, 1.7 km along-track) is classified into specific categories, for example, warm rain, clear sky, or ice cloud. Using a cloud detection algorithm, we extract cloud positions and parameters, including ice fraction and the spatial distribution of ice and liquid pockets within mixed-phase clouds.

For each identified cloud, we compute 96-hour back trajectories initialised at the top layer of the cloud using NOAA’s Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) with the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5) reanalysis as input meteorological data. We then co-locate along the back trajectories several environmental parameters: sea ice concentration from the Advanced Microwave Scanning Radiometer satellite observations (AMSR2), meteorological parameters from ERA5 and aerosol mixing ratios from the Modern-Era Retrospective analysis for Research and Applications, v2 (MERRA-2). The final ARCHTYPE product comprises millions of co-located back trajectories, offering a statistically robust dataset to investigate how air parcel history influences the thermodynamic phase of Arctic clouds.

In this presentation, we showcase the first results derived from this dataset, covering the period from 2006 to 2011. Preliminary analysis focusing on sea salt and dust aerosols indicates that cloud homogeneity increases with dust and decreases with sea salt. It also shows that, at low cloud top temperatures, ice fraction increases with dust content.

Beyond examining the general impact of air parcel history on cloud thermodynamic phases, we explore specific research questions: Are there regions that consistently receive aerosols from distant sources, and how do these transport patterns vary across the Arctic? What is the effect of sea ice variations on biogenic compound concentrations and sea spray aerosol production, and how does this influence low-level cloud formation? Finally, which aerosol ageing processes dominate during the long-range transport of air masses contributing to Arctic cloud formation?