In Arctic warm-air intrusions, air masses undergo a series of radiative, turbulent, cloud, and precipitation processes, the sum of which constitutes the air mass transformation. During the Arctic air mass transformation, heat and moisture are transferred from the air mass to the Arctic environment, melting the sea ice and potentially reinforcing feedback mechanisms responsible for the amplified Arctic warming. We tackle this complex, poorly understood phenomenon from a Lagrangian perspective using the warm-air intrusion event on 12–14 March captured by the 2022 HALO-(𝒜𝒞)³ campaign. Our trajectory analysis of the event suggests that the intruding air mass can be treated as a cohesive air column, therefore justifying the use of a single-column model. In this study, we test this hypothesis using the Atmosphere–Ocean Single-Column Model (AOSCM). The rates of heat and moisture depletion vary along the advection path due to the changing surface properties and large-scale vertical motion. Cloud radiative cooling and turbulent mixing in the stably stratified boundary layer are constant sinks of heat throughout the air mass transformation. Boundary layer cooling intensifies over the marginal ice zone and forces the development of a low-level cloud underneath the advected one. As the air mass flows past the marginal ice zone, large-scale updrafts dominate the temperature and moisture changes through adiabatic cooling and condensation. The ability of the Lagrangian AOSCM framework to simulate elements of the air mass transformation seen in aircraft observations, reanalysis, and operational forecast data makes it an attractive tool for future model analysis and diagnostics development. Our findings can benefit the understanding of the timescales and driving mechanisms of Arctic air mass transformation and help determine the contribution of warm-air intrusions in Arctic amplification.

Warm and moist air masses intruding into the Arctic are transformed by the combined effects of multiple, still poorly decribed, physical processes while exchanging energy with the local environment. We use the Lagrangian configuration of the Atmosphere-Ocean Single-Column Model (AOSCM) to simulate a suite of ten major warm-air intrusions from the recent observational record, distributed across the seasonal cycle. In our simulations, the changes in the heat and moisture content of these air masses, as well as their vertical structure, are in reasonable agreement with both observations and ERA5 reanalysis. Most air masses undergo their largest transformations under large-scale ascent that consistently occurs as the air is  advected over sea ice. The ascent, through vertical moisture advection and adiabatic cooling, brings the air masses close to saturation over a deep layer. The continued adiabatic cooling activates microphysical processes at different levels within the emerging deep clouds that accelerate glaciation, precipitation and the overall air mass transformation, thereby impacting the Arctic thermodynamic structure and surface energy budget.

Boundary layer cloud transformations at high latitudes play a key role for the Arctic climate and are partially controlled by large-scale dynamics such as subsidence. While measuring large-scale and mesoscale divergence on spatial scales on the order of 100 km has proven notoriously difficult, recent airborne campaigns in the subtropics have successfully applied measurement techniques using multiple dropsonde releases in circular flight patterns. In this paper, it is shown that this method can also be effectively applied at high latitudes, in spite of the considerable differences in atmospheric dynamics compared to the subtropics. To show the applicability, data collected during the airborne High Altitude and Long Range Research Aircraft–Transregional Collaborative Research Center TRR 172-Arctic Amplification: Climate Relevant Atmospheric and Surface Processes and Feedback Mechanisms [HALO–(AC)3] field campaign near Svalbard in spring 2022 were analyzed, where several flight patterns involving multiple dropsonde launches were realized by two aircraft. This study presents a first overview of the results. We find that the method indeed yields reliable estimates of mesoscale gradients in the Arctic, producing robust vertical profiles of horizontal divergence and, consequently, subsidence. Sensitivity to aspects of the method is investigated, including dependence on sampling area and the divergence calculation.

Model representation of Arctic air mass transformation and its impact on the local surface energy budget is subject to significant uncertainty due to simplified parameterizations of complex turbulent, cloud, and radiative processes. This study investigates the sensitivity of Arctic air mass transformation using the Atmosphere–Ocean Single-Column Model. Lagrangian simulations are performed for ten warm-air intrusion cases in different seasons. The sensitivity analysis targets turbulent mixing, cloud microphysics, and precipitation through a wide range of parameter perturbations. The evolution of the air masses' bulk thermodynamic properties remained largely robust to microphysical perturbations, with only minor variations in cooling, primarily linked to changes in high-cloud properties and their radiative effects. In contrast, changes in cloud properties produced a notable response in the energy budget at the sea ice surface and the top of the atmosphere, with a clear seasonal dependence. Enhanced longwave effects dominated in winter, while variations in cloud phase and optical properties significantly modulated solar energy input in summer. Perturbations on parameters controlling turbulent mixing induced significant changes in the surface energy budget that were consistent for simulations in all seasons. Despite stable stratification over sea ice, strong wind forcing promoted deep boundary layers. We found a convergence of turbulent heat fluxes in the lower half of the boundary layer that leads to near-surface warming and appears to be stronger in layers deeper than 1 km. This behavior was sensitive to parameters controlling the intensity and structure of turbulent mixing and diminished in the absence of vertical advection.