Leibniz Institute for Tropospheric Research

Low-level clouds play a crucial role in the Arctic climate system, for example by contributing to surface warming. Although many efforts have been made to investigate low-level clouds, there is still a significant in-situ data gap within the atmospheric boundary layer (ABL) and the lower troposphere. While long-term ground-based observatories provide valuable continuous measurements, they cannot resolve the vertical structure of aerosols and clouds.To address this data gap, five uncrewed aerial systems (UAS) were deployed during two intensive measurement campaigns at the Pallas Atmosphere-Ecosystem Supersite in northern Finland in spring (4–12 April 2025) and autumn (16–30 September 2025). Fixed-wing, vertical take-off and landing (VTOL), and multirotor platforms were operated jointly by the Finnish Meteorological Institute (FMI) and the Technische Universität Braunschweig. In total, 246 measurement flights were conducted, reaching altitudes of up to 2 km above ground level and conducting over 80 hours of in-situ sampling.The UAS were equipped with different sensors to measure aerosols, including two condensation particle counters with different cut-offs to measure the aerosol particle number concentration, a Partector 2 Pro to measure the size distribution between 10 and 300 nm and a POPS to measure the size distribution between 115 and 3370 nm. In addition meteorological parameters, and cloud droplet properties were also measured. This enables a detailed characterization of the vertical distribution of aerosols and their interaction with the ABL and low-level clouds. These measurements were compared to long-term observations from the nearby ground-based observatory Sammaltunturi. This study demonstrates the value of combining ground-based measurements with UAS profiling when investigating aerosol-cloud interactions.Preliminary results indicate pronounced seasonal differences. Spring conditions were dominated by new particle formation events associated with long-range air mass transport from the central Arctic. In contrast, autumn measurements were strongly influenced by low-level cloud formation and local aerosol sources. Overall, this campaign demonstrates the added value of UAS observations in improving the understanding of aerosol-cloud interactions in the sub-Arctic and enhancing the interpretability of existing ground-based datasets.

The region of the Southern Ocean (SO) is a current hot-spot of research related to aerosol-cloud interactions. On the one hand, detailed observations of aerosols and clouds and their interactions are required to explain the shortwave radiation bias in model simulations. On the other hand, the clean environment of the SO atmosphere allows the study of the impact of even slight variabilities in the aerosol load on cloud and precipitation processes and on the radiation budget of the atmosphere.The goSouth-2 project led by Leibniz Institute for Tropospheric Research (TROPOS) contributes with a unique long-term dataset of remote-sensing and in-situ measurements of cloud-relevant aerosol properties and associated cloud properties for the northern edge of the SO. The core facility of goSouth-2 is the ACTRIS station LACROS (Leipzig Aerosol and Cloud Remote Observations System) which has been deployed on the premises of the New Zealand MetService in Invercargill (46.4173 °S, 168.3307 °E, 3 m a.s.l., https://cloudnet.fmi.fi/site/invercargill) at the southern tip of the New Zealand’s South Island. The characterization of aerosol optical properties is observed by a newly-built PollyXT lidar. This system yields backscatter coefficient and depolarization ratios at 355, 532, and 1064 nm. Extinction coefficients are derived from Raman scattering at 387 and 607 nm. Raman scattering by water vapour at 407 nm yields observations of the water vapour mixing ratio. In addition, it is the first PollyXT lidar which includes a 460-nm fluorescence channel enabling a more refined discrimination between smoke, biological aerosols, and other types of pollution. Cloud properties are covered by 94- and 35-GHz cloud radar observations, of which the latter provides RHI and PPI scans for characterization of hydrometeor shapes and the horizontal wind field. Surface in-situ observations of the aerosol size distribution, cloud condensation nuclei concentrations, and off-line characterization of ice nucleating particle (INP) concentrations are performed. goSouth-2 is involved in the project ACADIA jointly run by Leipzig University and TROPOS, the HALO-South aircraft campaign, ongoing EarthCARE Cal/Val activities, and is conducted in close collaboration with partners from University of Canterbury, Earth Sciences New Zealand, and MetService, NZ. The latter contributes 2 radiosonde launches per day and weather radar observations.First conclusions drawn from the dataset to date are that aerosol in the cloud-free troposphere is rare. If present, it can mostly be assigned to wildfires or dust from Africa or Australia. In SO air masses ice formation in clouds warmer than -4°C is frequently absent, confirming the lack of efficient INPs. The majority of stratiform precipitation systems is found to be embedded in Australian air masses. A remarkable feature is that enhanced loads of Australian aerosols (dust, smoke) are frequently associated with enhanced turbulence in the affected cloud systems, similar to the dusty-cirrus phenomenon. Observations of the lowest 3 km of marine atmosphere, show a complex aerosol structure containing multiple embedded sub-layers of differing aerosol properties, whose effects on cloud formation remain to be identified. We use co-located observations from goSouth-2, the HALO-South aircraft campaign, and EarthCARE to characterize the observed scenarios.

At kilometer-scale resolution, convective systems start to be explicitly resolved in atmospheric models, albeit coarsely. This allows a more process-based analysis of certain aspects of aerosol–cloud interactions in tropical regions. Convective clouds are a ubiquitous feature above the Amazon rainforest and develop under strongly contrasting aerosol conditions, with particle number concentrations during the dry season often exceeding those in the wet season by an order of magnitude.In this context, we explore aerosol and convective cloud processes over the Amazon rainforest by analyzing case studies that combine observations and km-scale cloud-resolving simulations with interactive aerosols in a limited-area configuration. Regional simulations are performed at approximately 1.6 km horizontal resolution using the Icosahedral Nonhydrostatic (ICON) model coupled to the one-moment aerosol scheme HAM-lite. The realism of the simulations is evaluated through comparison with a combination of ground-based, satellite, and aircraft observations.For the wet season, we analyze a case study based on flight RF15, conducted with the German research aircraft HALO during the CAFE-Brazil (Chemistry of the Atmosphere: Field Experiment in Brazil; CAFE-BR) campaign in 2022–2023. Three simulations are presented for this case: a best-estimate factual simulation and two counterfactual sensitivity experiments representing background “green ocean” conditions and heavy aerosol loading associated with biomass burning during dry season periods. For the dry season, we also revisit two research flights from the ACRIDICON-CHUVA 2014 campaign, representing one clean and one polluted case, to further assess the representation of aerosol–cloud processes under different convective regimes. Combining these cases, we discuss the impact of changing aerosol environments on convective systems and draw conclusions relevant to a transition toward a post-fossil aerosol regime.

At the end of May 2025, extremely strong wildfires in Canada produced several pyrocumulonimbus clouds which lifted wildfire smoke particles up to the lower stratosphere (> 10 km height). A dense stratospheric smoke plume developed which reached stratospheric aerosol optical depths up to 3.2 which is comparable with a moderate volcanic eruption. EarthCARE’s lidar ATLID captured this event and enabled us to study stratospheric smoke shortly after emission and to track a single smoke plume on its transport way towards Europe.The spaceborne lidar allowed to precisely study the maximum plume height and revealed a lofting of the smoke plume top height from 13.6 km above Canada to 17.4 km above Europe and a further slight ascent during the transport towards Asia. The self-lofting of dense smoke plumes can be explained by the absorption of solar radiation which heats the ambient air and creates buoyancy. The self-lofting is strongest for optically thick smoke plumes close to the source region and gets weaker when the plume is horizontally more spread and thus optically thinner.ATLID detected an enhanced depolarization ratio of 0.26±0.02 which indicates non-spherical smoke particles in the stratosphere. This finding is in line with previous observations of stratospheric smoke layers, but clearly demonstrates a difference to tropospheric observations of Canadian smoke in Europe, which are characterized by a low depolarization ratio and hence a spherical shape (Haarig et al., 2018).The novel high-spectral-resolution lidar (HSRL) capability of ATLID allowed us for the first time to study the evolution of the lidar ratio of a stratospheric smoke layer during long-range transport. Higher values around 70 sr were observed shortly after emission, which decreased during the first days of transport to values of 49±7 sr.As another highlight, EarthCARE observed a significant downmixing of stratospheric smoke at a strong tropopause fold over the Mediterranean and North Africa (Haarig et al., 2025). These observations directly show a pathway of removal of the stratospheric smoke and closes the life cycle from injection to removal. Additionally, the synergistic EarthCARE observations will be used to estimate the radiative impact of this strong stratospheric smoke event.ReferencesHaarig, M., et al. (2018), Depolarization and lidar ratios at 355, 532, and 1064 nm and microphysical properties of aged tropospheric and stratospheric Canadian wildfire smoke. Atmospheric Chemistry and Physics, 18 (16), 11847–11861.Haarig, M. et al. The life cycle of a stratospheric smoke plume as seen from EarthCARE - tracking a plume from Canada to Europe. ESS Open Archive. October 22, 2025.

Extensive cloud cover over the Southern Ocean is a key contributor to global cloud radiative forcing. The region hosts some of the most pristine clouds on Earth, as its air masses originate largely over the open ocean and Antarctica with minimal influence from continental emissions. This provides an opportunity to investigate aerosol–cloud interactions under near-preindustrial aerosol conditions. However, the scarcity of in-situ measurements in this region leads to a misrepresentation of the Southern Ocean cloud properties in climate models, resulting in biases of simulated shortwave radiation and near-surface temperatures. To address these points, the HALO-South airborne campaign was conducted in September and October 2025, based out of Christchurch, New Zealand. Using DLR’s High Altitude and Long Range Research Aircraft (HALO), 20 research flights were carried out over the Southern Ocean in the vicinity of New Zealand, extending into the Antarctic marginal sea ice zone. The campaign targeted a broad suite of cloud regimes, from boundary-layer clouds to multilayer mixed-phase systems and high-level cirrus clouds. In addition, the flights sampled clouds embedded in a variety of synoptic weather systems, including cold-air outbreaks and convective systems. Flights were planned in synergy with satellite overpasses and with support from weather prediction models to ensure coverage of representative conditions. Here, we present a statistical overview of over 20 hours of cloud dataset collected by underwing probes during the HALO-South campaign, including cloud microphysical properties such as particle number concentration, liquid and ice water content, and particle size distributions. This dataset enables a deeper understanding of aerosol–cloud interactions, mixed-phase processes, and cloud radiative effects in the Southern Ocean. It provides critical observational constraints for evaluating satellite retrievals, assessing weather and climate model performance, and informing model development aimed at reducing long-standing regional radiation biases. Comparisons with Northern Hemisphere field campaigns further highlight hemispheric contrasts in cloud–aerosol coupling, offering new opportunities to investigate how differing aerosol environments shape cloud properties and climate feedbacks.

We present a novel staggered discontinuous Galerkin method on general polytopal meshes for solving the shallow water equation on the sphere. Every polygon is decomposed into so called kite quads by joining the vertices with the midpoints of the adjacent edges and the midpoint of the polygon. The shallow water equation is solved in vector-invariant form whereby vorticity is determined diagnostically. Height and momentum are discretized on the primal respectively dual cells whereby the composed finite elements are continuous over internal edges and discontinuous over boundary edges. This results in block-diagonal mass matrices. Mass lumping can reduce the fill in of these matrices further. The method is implemented in Julia in the package CGDycore.jl which unifies different numerical dycores under one umbrella. Numerical results are presented for standard test cases on different spherical grids.

Primary marine organic aerosol (PMOA) constitutes an important fraction of the aerosol population over remote oceanic regions and plays a relevant role in aerosol–cloud–climate interactions. In the Arctic, ongoing sea-ice retreat and intensified summer ice loss are expected to enhance marine aerosol emissions. Here, we employ an extended version of the aerosol–climate model ECHAM6.3-HAM2.3 to examine the spatial distribution and long-term temporal evolution of PMOA emissions and transport in the Arctic for the period 1990–2019, accounting for changing climatic and sea-ice conditions. Marine biogeochemical fields are provided by the offline model FESOM2.1-REcoM3, from which three aerosol-relevant biomolecular species groups - polysaccharides (PCHO), amino acids (DCAA), and polar lipids (PL) - are represented. Their transfer from the ocean to the atmosphere is parameterized using OCEANFILMS, recently implemented in ECHAM6.3-HAM2.3 to enhance the marine emission scheme.The model results indicate that PMOA emission fluxes are primarily controlled by marine biological activity and sea-salt production, the latter mainly depending on near-surface winds. Biomolecular concentrations show limited variability in equatorial regions but pronounced seasonal cycles toward high latitudes. In seawater, PCHO dominates the simulated organic pool, followed by DCAA and PL. In contrast, PL contributes the largest fraction to aerosol-phase organic matter due to the comparatively strong air-seawater affinity of lipids. Arctic PMOA emissions and atmospheric transport peak between May and September, coinciding with the phytoplankton bloom and the seasonal sea-ice minimum. Substantial regional differences are evident in the timing of biomolecule production and aerosol emissions across the Arctic. Simulated PMOA seasonality agrees reasonably well with available ground-based observations, given the uncertainties in both measurements and model assumptions.Over the 30-year period, accumulated Arctic aerosol emissions and burdens increased by at least 7% and 4%, respectively, when comparing the first and second halves of the study period. Summer (June–August) trend analyses reveal a pronounced decline in sea ice that is associated with increasing concentrations of organic biomolecules in inner Arctic waters. Positive PMOA emission anomalies have become more frequent over the past 15 years, indicating a sustained upward trend. On average, PMOA production has increased by 0.8% per year since 1990, with changes varying among biomolecular groups and Arctic subregions.

Understanding particulate pollution in Eastern Mediterranean (EM) cities is challenging due to the combined influence of local urban emissions, marine aerosols, and long-range transported desert dust. Conventional surface-based measurements often fail to detect lofted dust layers, while satellite-derived Aerosol Optical Depth (AOD) provides only column-integrated information, limiting its ability to represent near-surface PM2.5 (fine particulate matter 2.5 micrometres or less in diameter) concentrations. Here, we combine five years of ground-based lidar observations with high resolution satellite AOD retrievals, PM2.5 measurements and meteorological data over the EM to investigate aerosol layering, source contributions, and column-to-surface relationships across three contrasting urban environments: regional background, urban traffic and semi-indoor sites located along highway/railroad. Lidar profiling identifies ten distinct aerosol layering types, from shallow anthropogenic layers to deep mixed structures composed of desert dust, marine aerosols, and urban pollution. We find that the AOD-PM2.5 relationship is strongly regime-dependent, and the degree of column-surface coupling varies sharply across the three urban environments. Machine-learning models that incorporate vertical lidar features significantly improve PM2.5 predictions across all sites, outperforming models without vertical information. Overall, our results demonstrate that reliable urban PM2.5 assessment requires explicit consideration of vertical aerosol structure. Integrating lidar-derived features enhances the interpretation of satellite AOD and improves urban exposure estimates in complex EM atmospheres.

Abstract This paper presents the dynamical core of the Climate Modeling Alliance (CliMA) atmosphere model, designed for efficient simulation of a wide range of atmospheric flows across scales. The core uses the nonhydrostatic equations of motion for a deep atmosphere, discretized with a hybrid approach that combines a spectral element method (SEM) in the horizontal and a staggered finite‐difference method in a height‐based, terrain‐following coordinate in the vertical. This approach leverages the high‐order accuracy and scalability of the SEM, while maintaining the computational efficiency and stability of finite differences on a staggered grid. The model's coordinate‐independent equation set allows for simulations in a variety of geometries and planetary configurations. The use of the specific total energy of moist air as a prognostic variable, along with a consistent thermodynamic formulation, ensures the conservation of energy, air mass, and water mass, even in moist atmospheres and in the presence of subgrid‐scale parameterizations, without ad hoc fixers. A horizontally explicit, vertically implicit (HEVI) timestepping strategy treats fast vertical processes implicitly and further enhances computational efficiency by allowing larger timesteps. The model demonstrates excellent strong and weak scaling on CPUs and GPUs, making it well‐suited for high‐resolution simulations on modern supercomputing architectures, including those on the cloud, which widens access to climate models.

<strong class="journal-contentHeaderColor">Abstract.</strong> This article, the ninth in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation. It covers an extension of the gas phase and photochemical reactions of halogenated alkanes, alkenes, and oxygenated organic compounds implemented on the IUPAC website since 2008. The article consists of a summary table of the recommended kinetic parameters for the evaluated reactions, and a supplement containing the data sheets providing information upon which the recommendations are made.