Andreas Plach

Paleoclimate reconstructions of wildfire using ice cores often rely on high‐resolution aerosol records of refractory black carbon (rBC) or ammonium (NH ₄ ⁺ ). The interpretation of such records, however, can be hindered by uncertainties related to long‐range atmospheric transport, spatial distribution and strength of emissions, as well as glaciochemical noise introduced to the record during and after deposition. Here, we use arrays of parallel ice cores collected from two sites in Greenland, each with differing characteristics including accumulation rate, elevation, and meteorology, to assess the spatial variability and site representativeness of their rBC and NH ₄ ⁺ records. The higher accumulation site, Summit, was found to preserve a more coherent signal of both aerosols across multiple ice core records and was more representative of the total site signal than the lower accumulation site, Tunu. Representativeness analyses indicate that a single core at Summit is as representative of the theoretical total site signal as a combined three core composite record from Tunu for rBC and NH ₄ ⁺ at annual resolution. This work suggests that high temporal resolution records of these aerosols using a single core from either site have considerable uncertainties, highlighting the need for careful consideration of the effects of site conditions on aerosol representativeness for wildfire reconstruction.

Sulfur hexafluoride (SF₆) is an extremely potent (GWP100 = 24,300) and long-lived greenhouse gas whose atmospheric concentrations continue to rise due to anthropogenic emissions. Europe represents a particularly relevant test case for investigating SF₆ emissions, as successive EU F-gas regulations over the past two decades have aimed to substantially reduce emissions. A key question is whether these regulatory measures are reflected in observed emission trends and whether reported national inventories are consistent with observation-based estimates. In this study, we quantify European SF₆ emissions for the period 2005–2021 using a large ensemble of atmospheric inversions with a strong focus on uncertainty characterization. Uncertainties are assessed using an extensive set of sensitivity tests in which key inversion parameters are systematically varied, while final uncertainties are quantified via a Monte Carlo ensemble that randomly samples combinations of these parameters. This allows us to identify the main sources of uncertainty and to evaluate the robustness of inferred emission trends.Our analysis focuses on countries with relatively dense observational coverage - the United Kingdom, Germany, France, and Italy - while also examining aggregated emissions for the EU-27. The inversion results reveal declining SF₆ emissions in all studied regions except Italy, broadly consistent with the timing of EU F-gas regulations (842/2006, 517/2014). In several countries, inferred emissions exceed reported national inventories, although the agreement generally improves in more recent years. At the EU-27 scale, emissions exhibit a pronounced decline between 2017 and 2018, coinciding with a marked reduction in emissions from southwestern Germany, suggesting regional actions were taken as the 2014 regulation took effect.Our sensitivity tests highlight the crucial role of dense and sustained atmospheric monitoring networks for robust inversion-based emission estimates. In particular, expansions of the UK observing system in 2012 and 2014 lead to significant reductions in emission uncertainties, demonstrating the importance of comprehensive observational networks in refining emission estimates.

Arctic Amplification is not well understood. It is the result of a complicated interplay between remote and local forcing and feedback processes. Therefore, it is crucial to enhance our understanding of the transport of energy and moisture from lower latitudes. The amount of aerosol in the Arctic is also an important quantity as their role in Arctic Amplification, via direct radiative forcing and aerosol-cloud interactions, remain poorly quantified.In this work, we aim to better quantify how aerosols, energy, and moisture are transported to and distributed within the Arctic. We investigate observations at Arctic stations, including, Villum and Zeppelin, and perform backward-in-time simulations with the Lagrangian atmospheric transport model FLEXPART (Pisso et al., 2019; Bakels et al., 2024) to derive so-called emission sensitivities and use these sensitivities to better quantify source regions of aerosols, energy, and moisture.In general, we aim to better describe the spatial and temporal atmospheric transport characteristics into the Arctic and how these characteristics have changed in recent years. We focus on the transport during warm-air intrusions, since almost 30% of the total poleward transport of moisture (during winter) occurs during such events (Woods et al., 2013). Warm-air intrusions are often associated with large-scale atmospheric blocking patterns forcing a change in transport direction from east to more poleward, bringing warm, moist, and cloudy air into the Arctic. Warm-air intrusions can also be favourable for an enhanced transport of aerosols (e.g., Dada et al., 2022).Since climate models show large biases in moisture flux during these events (Woods et al., 2017), there is clearly a need to better quantify the transport of moisture, energy, and aerosols during these events. This will also help to provide better forcing for climate simulations.Bakels et al. (2024): 10.5194/gmd-17-7595-2024; Dada et al. (2022): 10.1038/s41467-022-32872-2; Lapere et al. (2024): 10.1029/2023JD039606; Pisso et al. (2019): 10.5194/gmd-12-4955-2019; Woods et al. (2013): 10.1002/grl.50912; Woods et al. (2017): 10.1175/JCLI-D-16-0710.

Marine cold-air outbreaks (MCAOs) in the Arctic lead to the formation of mixed-phase clouds that downwind from the sea ice edge transition from stratocumulus clouds organized as convective rolls to open convective cells. Results from modelling studies of MCAOs suggest that increases in ice nucleating particles (INP), ice crystal number concentrations (Ni) and frozen hydrometeors in general, cause a decrease in cloud water, which can accelerate the cloud transition. In this study, we make use of observations conducted during MCAOs characterized by both high INP concentrations, potentially linked to long-range transport, and low INP concentrations, most likely associated with local sources. We perform quasi-Lagrangian large-eddy simulations of two MCAOs in the Arctic with distinctly different meteorological conditions and investigate the impact of differences in the aerosol and INP concentrations and origin. We examine how perturbations in aerosols, INPs and the predicted cloud ice in the model affect the evolution of the mixed-phased clouds, aerosol processing, and the cloud radiative feedback during these cold air outbreaks.

The up-area is warming faster than the rest of the large rock we are living on. This is not well understood. It is caused by many things happening near and far from the up-area. We need to better understand how things in the air move from further down into the up-area, and how these things are moved around inside the up-area. With “things” we mean the warmth of the air, the water in the air, and tiny rocks and water drops in the air. It is very important to know how many tiny rocks and water drops are in the air in the up-area, because they can throw back sun light or make the air white if the air can not hold the water anymore. This is important to understand why the up-area is warming faster.In this work, we try to better figure out how much warmth and water in the air, and how many tiny rocks and water drops in the air move to the up-area and how they are moved around. We can see these things in the air at a few points in the up-area and use a move-with-parts computer picture to follow them back in time to see where they came from.We focus on short time windows in which a lot of warm and wet air is moved to the up-area, because we know that almost 30% of all air water that is moved to the up-area in a year, is moved there during these short time windows (in the cold time of the year). Many of these warm and wet time windows happen during large air blocking which makes the mean air move direction change from right to up, bringing more warm, wet, and white air into the up-area. These warm and wet time windows also show more tiny rocks and water drops being move to the up-area.

The Arctic has seen dramatic changes in recent decades. Here we use a simple metric, the Arctic residence time of air, that is, the time air spends uninterruptedly north of 70N, to evaluate how these changes have affected the high‐latitude atmospheric circulation in the last 40 years. We find that, on average, near‐surface air resides between 7 (winter) and 12 (summer) days in the Arctic. This residence time has decreased almost year‐round since the 1980s, especially pronounced in the seasonal transition periods (fall: 0.9 days; spring: 1.4 days). The more pronounced reduction in spring also affects higher atmospheric layers. Our analysis indicates that this reduction is likely linked to the observed sea ice loss, decrease in snow cover, and increase in temperature. Furthermore, it indicates a speed‐up of the circulation, effectively making the Arctic less isolated and more prone to influences from mid‐latitudes.

The Arctic has seen dramatic changes in recent decades. Here we use a simple metric, the Arctic residence time of air, that is, the time air spends uninterruptedly north of 70 ^◦ N, to evaluate how these changes have affected the high-latitude atmospheric circulation in the last 40 years. We find that, on average, near-surface air resides between 7 (winter) and 12 (summer) days in the Arctic. This residence time has decreased almost year-round since the 1980s, especially pronounced in the seasonal transition periods (fall: − 0.9 day; spring: − 1.4 days). The more pronounced reduction in spring also affects higher atmospheric layers. Our analysis indicates that this reduction is likely linked to the observed sea ice loss, decrease in snow cover, and increase in temperature. Furthermore, it indicates a speed-up of the circulation, effectively making the Arctic less isolated and more prone to influences from mid-latitudes.

Sulfur hexafluoride (SF₆) is a highly potent and long-lived greenhouse gas whose atmospheric concentrations are increasing due to human emissions. In this study, we determine European SF₆ emissions from 2005 to 2021 using a large ensemble of atmospheric inversions. To assess uncertainty, we systematically vary key inversion parameters across 986 sensitivity tests and apply a Monte Carlo approach to randomly combine these parameters in 1003 additional inversions. Our analysis focuses on high-emitting countries with robust observational coverage – UK, Germany, France, and Italy – while also examining aggregated EU-27 emissions. SF₆ emissions declined across all studied regions except Italy, largely attributed to EU F-gas regulations (2006, 2014), however, national reports underestimated emissions: (i) UK emissions dropped from 68 (47–77) t yr⁻¹ in 2008 to 19 (15–26) t yr⁻¹ in 2018, aligning with the reports from 2018 onward; (ii) French emissions fell from 78 (51–117) t yr⁻¹ (2005) to 35 (19–54) t yr⁻¹ (2021), exceeding reports by 88 %; (iii) Italian emissions fluctuated (25–48 t yr⁻¹), surpassing reports by 107 %; (iv) German emissions declined from 182 (155–251) t yr⁻¹ (2005) to 97 (88–104) t yr⁻¹ (2021), aligning reasonably well with reports; (v) EU-27 emissions decreased from 403 (335–501) t yr⁻¹ (2005) to 225 (191–260) t yr⁻¹ (2021), exceeding reports by 20 %. A substantial drop from 2017 to 2018 mirrored the trend in southern Germany, suggesting regional actions were taken as the 2014 EU regulation took effect. Our sensitivity tests highlight the crucial role of dense monitoring networks in improving inversion reliability. The UK system expansions (2012, 2014) significantly enhanced result robustness, demonstrating the importance of comprehensive observational networks in refining emission estimates.

We determine European emissions of sulfur hexafluoride (SF₆) from 2005 to 2021 using a large ensemble of atmospheric inversions. To assess uncertainty, we systematically vary key inversion parameters across 986 sensitivity tests and apply a Monte Carlo approach to randomly combine these parameters in 1,003 additional inversions. Our analysis focuses on high-emitting countries with robust observational coverage — UK, Germany, France, and Italy — while also examining aggregated EU-27 emissions. SF₆ emissions declined across all studied regions except Italy, largely attributed to EU F-gas regulations (2006, 2014), however, national reports underestimated emissions: (i) UK emissions dropped from 65 (±13) t yr⁻¹ in 2008 to 20 (±6) t yr⁻¹ in 2018, aligning with the reports from 2018 onward; (ii) French emissions fell from 88 (±37) t yr⁻¹ (2005) to 51 (±28) t yr⁻¹ (2021), exceeding reports by 73 %; (iii) Italian emissions fluctuated (31–67 t yr⁻¹), surpassing reports by 88 %; (iv) German emissions declined from 166 (±41) t yr⁻¹ (2005) to 95 (±11) t yr⁻¹ (2021), aligning reasonably well with reports; (v) EU-27 emissions decreased from 484 (±213) t yr⁻¹ (2005) to 255 (±58) t yr⁻¹ (2021), exceeding reports by 40 %. A substantial drop from 2017 to 2018 mirrored the trend in southern Germany, suggesting regional actions were taken as the 2014 EU regulation took effect. Our sensitivity tests highlight the crucial role of dense monitoring networks in improving inversion reliability. The UK system expansions (2012, 2014) significantly enhanced result robustness, demonstrating the importance of comprehensive observational networks in refining emission estimates.