Articles | Volume 13, issue 11
https://doi.org/10.5194/gmd-13-5119-2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Special issue:
https://doi.org/10.5194/gmd-13-5119-2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Development and technical paper
| 
30 Oct 2020
Development and technical paper |
| 30 Oct 2020
| 30 Oct 2020
Collisional growth in a particle-based cloud microphysical model: insights from column model simulations using LCM1D (v1.0)
Simon Unterstrasser
CORRESPONDING AUTHOR
Deutsches Zentrum für Luft- und Raumfahrt (DLR) – Institut für Physik der Atmosphäre, Oberpfaffenhofen, 82234 Wessling, Germany
Fabian Hoffmann
Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, Boulder, CO, USA
NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, CO, USA
Marion Lerch
Deutsches Zentrum für Luft- und Raumfahrt (DLR) – Institut für Physik der Atmosphäre, Oberpfaffenhofen, 82234 Wessling, Germany
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Dennis Hillenbrand and Simon Unterstrasser
J. Env. Com. Air Transp. Sys. Discuss., https://doi.org/10.5194/jecats-2026-16, https://doi.org/10.5194/jecats-2026-16, 2026
Preprint under review for JECATS
Short summary
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We study contrail formation behind future fuel cell-based aircraft fueled by hydrogen. Simulations show that, under certain conditions, small droplets can form via a process not occurring in current plumes. This can increase ice crystal numbers in contrails, boosting their climate impact. The effect is strongest in cold air and for high plume mixing rates with air. We suggest to decrease the mixing rate and exhaust humidity by technical design to reduce the climate impact of such aircraft.
Simon Braun, Magdalena Pühl, Andreas Marsing, Daniel Sauer, Gregor Neumann, Elena de la Torre Castro, Valerian Hahn, Michael Lichtenstern, Paul Stock, Christopher Heckl, Dennis Hillenbrand, Anke Roiger, Christiane Voigt, Simon Unterstraßer, Arne Vasenden, Roberta Vasenden, Jean Cammas, Florian Thorey, Catherine Mackay, Charles Renard, and Tina Jurkat-Witschas
EGUsphere, https://doi.org/10.5194/egusphere-2026-2887, https://doi.org/10.5194/egusphere-2026-2887, 2026
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Short summary
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In this work, we share the results of first in-flight emission and contrail measurements behind a fuel cell exhaust emulator, with the goal of quantifying the contrail properties for this new aviation propulsion concept. An artificial dilution tracer system was used to assess plume dilution and derive emission indices. At ambient temperatures close to the homogeneous freezing threshold, a strong temperature-dependence of the number of contrail ice crystals, due to droplet freezing, was observed.
Hannes Bruder, Robin N. Thor, Malte Niklaß, Katrin Dahlmann, Roland Eichinger, Florian Linke, Volker Grewe, Sigrun Matthes, and Simon Unterstrasser
Geosci. Model Dev., 19, 3551–3567, https://doi.org/10.5194/gmd-19-3551-2026, https://doi.org/10.5194/gmd-19-3551-2026, 2026
Short summary
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We develop an easy-to-use tool to estimate the per-flight climate effect of CO2 and non-CO2 emissions, based only on aircraft size as well as origin and destination airports. The implemented model results from a comparison of Multiple and Symbolic Regression approaches and exhibits a mean relative error of 21 % with respect to climate response model results. The simplified method is designed for climate footprint assessment and covers jet-powered passenger aircraft with over 20 seats.
Josef Zink, Cornelius Weiß-Rehm, Simon Unterstrasser, and Ulrike Burkhardt
EGUsphere, https://doi.org/10.5194/egusphere-2026-1088, https://doi.org/10.5194/egusphere-2026-1088, 2026
Short summary
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The study introduces a novel parameterization for the number of contrail ice crystals formed on ambient aerosols entrained into the exhaust plume behind aircraft burning hydrogen. This parameterization can be integrated into large-scale models to assess the radiative impacts of contrails originating from a fleet of aircraft with hydrogen combustion.
Vanessa Santos Gabriel, Luca Bugliaro, Mara Montag, Sabrina Ries, Ziming Wang, Kai Widmaier, Matteo Arico, Simon Unterstrasser, Johanna Mayer, Deniz Menekay, Andreas Marsing, Elena de la Torre Castro, Liam Megill, Monika Scheibe, and Christiane Voigt
Earth Syst. Sci. Data, 18, 2397–2412, https://doi.org/10.5194/essd-18-2397-2026, https://doi.org/10.5194/essd-18-2397-2026, 2026
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We provide observations of the geostationary Meteosat satellite with contrails labeled by three people complemented with detailed cloud information. Contrails influence climate but are hard to identify in satellite imagery. With this study, we support contrail detection development and evaluation, stress the subjectivity of human labeling and reveal which meteorological conditions highlight or hide contrails. This dataset contributes to a better understanding of aviation’s climate impact.
Josef Zink and Simon Unterstrasser
Atmos. Chem. Phys., 26, 3145–3165, https://doi.org/10.5194/acp-26-3145-2026, https://doi.org/10.5194/acp-26-3145-2026, 2026
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The climate impact of aviation-induced contrail cirrus clouds is strongly influenced by the number of ice crystals that form in the wake of an aircraft under certain conditions. In this study, we investigate how engine-related aspects influence the number of ice crystals formed for hydrogen combustion. We derive suitable (scaling) relations that can be integrated into large-scale models used to estimate the climate impact of contrail cirrus clouds.
Josef Zink, Simon Unterstrasser, and Ulrike Burkhardt
Atmos. Chem. Phys., 26, 3125–3143, https://doi.org/10.5194/acp-26-3125-2026, https://doi.org/10.5194/acp-26-3125-2026, 2026
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The climate impact of aviation-induced contrail cirrus is strongly influenced by the number of ice crystals that form in an aircraft's exhaust plume. In this study, we systematically investigate the key microphysical processes of contrail formation for hydrogen combustion. A large simulation data set provides the basis for a data-driven parameterization of ice crystal number that can be integrated into large-scale models.
Gregor Neumann, Andreas Marsing, Theresa Harlass, Daniel Sauer, Simon Braun, Magdalena Pühl, Christopher Heckl, Paul Stock, Elena De La Torre Castro, Valerian Hahn, Anke Roiger, Christiane Voigt, Simon Unterstraßer, Jean Cammas, Charles Renard, Roberta Vasenden, Arnold Vasenden, and Tina Jurkat-Witschas
Atmos. Meas. Tech., 18, 6795–6816, https://doi.org/10.5194/amt-18-6795-2025, https://doi.org/10.5194/amt-18-6795-2025, 2025
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This study presents the first successful in-flight emission characterization of a turboprop engine using a fully autonomous airborne measurement platform, offering new insights into the atmospheric impacts of regional aviation. By equipping the high-altitude Grob G 520 Egrett with a suite of custom and modified commercial instruments, we demonstrate precise, high-resolution measurements of aerosol particles, trace gases, and contrail ice in the engine exhaust plume at cruise altitudes.
Annemarie Lottermoser and Simon Unterstrasser
Atmos. Chem. Phys., 25, 7903–7924, https://doi.org/10.5194/acp-25-7903-2025, https://doi.org/10.5194/acp-25-7903-2025, 2025
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Contrail cirrus significantly contributes to aviation's overall climate impact. As hydrogen combustion and fuel cell use are emerging technologies for aircraft propulsion, we simulated individual contrails from hydrogen propulsion during the first 6 min after exhaust emission, termed the vortex phase. The ice crystal loss during that stage is crucial, as the number of ice crystals has a large impact on the further evolution of contrails into contrail cirrus and their radiative forcing.
Andreas Bier, Simon Unterstrasser, Josef Zink, Dennis Hillenbrand, Tina Jurkat-Witschas, and Annemarie Lottermoser
Atmos. Chem. Phys., 24, 2319–2344, https://doi.org/10.5194/acp-24-2319-2024, https://doi.org/10.5194/acp-24-2319-2024, 2024
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Using hydrogen as aviation fuel affects contrails' climate impact. We study contrail formation behind aircraft with H2 combustion. Due to the absence of soot emissions, contrail ice crystals are assumed to form only on ambient particles mixed into the plume. The ice crystal number, which strongly varies with temperature and aerosol number density, is decreased by more than 80 %–90 % compared to kerosene contrails. However H2 contrails can form at lower altitudes due to higher H2O emissions.
Michael A. Olesik, Jakub Banaśkiewicz, Piotr Bartman, Manuel Baumgartner, Simon Unterstrasser, and Sylwester Arabas
Geosci. Model Dev., 15, 3879–3899, https://doi.org/10.5194/gmd-15-3879-2022, https://doi.org/10.5194/gmd-15-3879-2022, 2022
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In systems such as atmospheric clouds, droplets undergo growth through condensation of vapor. The broadness of the resultant size spectrum of droplets influences precipitation likelihood and the radiative properties of clouds. One of the inherent limitations of simulations of the problem is the so-called numerical diffusion causing overestimation of the spectrum width, hence the term numerical broadening. In the paper, we take a closer look at one of the algorithms used in this context: MPDATA.
Andreas Bier, Simon Unterstrasser, and Xavier Vancassel
Atmos. Chem. Phys., 22, 823–845, https://doi.org/10.5194/acp-22-823-2022, https://doi.org/10.5194/acp-22-823-2022, 2022
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We investigate contrail formation in an aircraft plume with a particle-based multi-trajectory 0D model. Due to the high plume heterogeneity, contrail ice crystals form first near the plume edge and then in the plume centre. The number of ice crystals varies strongly with ambient conditions and soot properties near the contrail formation threshold. Our results imply that the multi-trajectory approach does not necessarily lead to improved scientific results compared to a single mean trajectory.
Dennis Hillenbrand and Simon Unterstrasser
J. Env. Com. Air Transp. Sys. Discuss., https://doi.org/10.5194/jecats-2026-16, https://doi.org/10.5194/jecats-2026-16, 2026
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We study contrail formation behind future fuel cell-based aircraft fueled by hydrogen. Simulations show that, under certain conditions, small droplets can form via a process not occurring in current plumes. This can increase ice crystal numbers in contrails, boosting their climate impact. The effect is strongest in cold air and for high plume mixing rates with air. We suggest to decrease the mixing rate and exhaust humidity by technical design to reduce the climate impact of such aircraft.
Benjamin Ascher and Fabian Hoffmann
Atmos. Chem. Phys., 26, 11747–11770, https://doi.org/10.5194/acp-26-11747-2026, https://doi.org/10.5194/acp-26-11747-2026, 2026
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Arctic clouds with liquid and ice have important effects on climate. To investigate how ice crystals and liquid droplets grow in shallow Arctic clouds, we conducted high-resolution simulations. We find that drier air above the cloud leads to a greater sublimation rate of ice beneath the cloud and recycling of particles necessary for ice formation within the cloud. We also find that the amount of sublimation and recycling is affected by the rate of temperature change with height above the cloud.
Simon Braun, Magdalena Pühl, Andreas Marsing, Daniel Sauer, Gregor Neumann, Elena de la Torre Castro, Valerian Hahn, Michael Lichtenstern, Paul Stock, Christopher Heckl, Dennis Hillenbrand, Anke Roiger, Christiane Voigt, Simon Unterstraßer, Arne Vasenden, Roberta Vasenden, Jean Cammas, Florian Thorey, Catherine Mackay, Charles Renard, and Tina Jurkat-Witschas
EGUsphere, https://doi.org/10.5194/egusphere-2026-2887, https://doi.org/10.5194/egusphere-2026-2887, 2026
This preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).
Short summary
Short summary
In this work, we share the results of first in-flight emission and contrail measurements behind a fuel cell exhaust emulator, with the goal of quantifying the contrail properties for this new aviation propulsion concept. An artificial dilution tracer system was used to assess plume dilution and derive emission indices. At ambient temperatures close to the homogeneous freezing threshold, a strong temperature-dependence of the number of contrail ice crystals, due to droplet freezing, was observed.
Johannes Kainz, Daniel P. Harrison, and Fabian Hoffmann
Atmos. Chem. Phys., 26, 9443–9451, https://doi.org/10.5194/acp-26-9443-2026, https://doi.org/10.5194/acp-26-9443-2026, 2026
Short summary
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Marine Cloud Brightening (MCB) aims to counter global warming. It suggests to increase cloud reflectance by spraying aerosols from which additional cloud droplets can form. We demonstrate that MCB can be applied to cumulus clouds. The impact of aerosol particles released by a single aerosol sprayer using simulations is analyzed. The study draws conclusions on the optimal placement height of the sprayer to optimize aerosol transport, the ability to form new cloud droplets, and the area affected.
Netta Yeheskel, Matthew W. Christensen, Fabian Hoffmann, Graham Feingold, and Guy Dagan
Atmos. Chem. Phys., 26, 8765–8781, https://doi.org/10.5194/acp-26-8765-2026, https://doi.org/10.5194/acp-26-8765-2026, 2026
Short summary
Short summary
Aerosols influence cloud formation, structure, and radiative effects. As air masses move from the subtropics to the tropics, clouds transition from shallow to deeper systems. Using five years of satellite observations and numerical simulations, we find a robust aerosol impact on this Lagrangian cloud evolution: higher aerosol levels produce thicker, more reflective clouds, enhancing cooling and modifying energy and moisture transport toward the tropics.
Anna Weber, Fabian Hoffmann, and Bernhard Mayer
Atmos. Chem. Phys., 26, 8001–8020, https://doi.org/10.5194/acp-26-8001-2026, https://doi.org/10.5194/acp-26-8001-2026, 2026
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The vertical evolution of microphysical cloud properties in low-level mixed-phase clouds during a marine cold air outbreak in the Arctic is analyzed based on measurements collected during the HALO–(𝒜𝒞)3 campaign. In particular, pseudo-vertical profiles of cloud thermodynamic phase and the cloud droplet size are constructed. The measured vertical profiles are compared to predictions from an entraining parcel model to investigate the influence of ice processes on supercooled liquid water droplets.
Hannes Bruder, Robin N. Thor, Malte Niklaß, Katrin Dahlmann, Roland Eichinger, Florian Linke, Volker Grewe, Sigrun Matthes, and Simon Unterstrasser
Geosci. Model Dev., 19, 3551–3567, https://doi.org/10.5194/gmd-19-3551-2026, https://doi.org/10.5194/gmd-19-3551-2026, 2026
Short summary
Short summary
We develop an easy-to-use tool to estimate the per-flight climate effect of CO2 and non-CO2 emissions, based only on aircraft size as well as origin and destination airports. The implemented model results from a comparison of Multiple and Symbolic Regression approaches and exhibits a mean relative error of 21 % with respect to climate response model results. The simplified method is designed for climate footprint assessment and covers jet-powered passenger aircraft with over 20 seats.
Jung-Sub Lim and Fabian Hoffmann
Atmos. Chem. Phys., 26, 5427–5446, https://doi.org/10.5194/acp-26-5427-2026, https://doi.org/10.5194/acp-26-5427-2026, 2026
Short summary
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We used high-resolution simulations to track individual cloud droplets within marine clouds. We discovered that while droplets grow similarly, they evaporate differently depending on their specific history of exposure to dry air. This helps resolve ambiguities in interpreting field observations, where droplet history is often unknown. We also propose a simple formula to capture this variability, offering a more accurate tool for representing cloud evolution in models.
Prasanth Prabhakaran, Timothy A. Myers, Fabian Hoffmann, and Graham Feingold
Atmos. Chem. Phys., 26, 5151–5167, https://doi.org/10.5194/acp-26-5151-2026, https://doi.org/10.5194/acp-26-5151-2026, 2026
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Short summary
We explore how climate change and aerosol affect the evolution of marine low-clouds. Using high-resolution simulations, we find that warming has a stronger impact on these clouds, but aerosol becomes more important after the clouds form precipitation. Our results suggest that attempts to brighten these clouds using aerosol may become less effective in a warmer future due to the decrease in cloud cover.
Josef Zink, Cornelius Weiß-Rehm, Simon Unterstrasser, and Ulrike Burkhardt
EGUsphere, https://doi.org/10.5194/egusphere-2026-1088, https://doi.org/10.5194/egusphere-2026-1088, 2026
Short summary
Short summary
The study introduces a novel parameterization for the number of contrail ice crystals formed on ambient aerosols entrained into the exhaust plume behind aircraft burning hydrogen. This parameterization can be integrated into large-scale models to assess the radiative impacts of contrails originating from a fleet of aircraft with hydrogen combustion.
Vanessa Santos Gabriel, Luca Bugliaro, Mara Montag, Sabrina Ries, Ziming Wang, Kai Widmaier, Matteo Arico, Simon Unterstrasser, Johanna Mayer, Deniz Menekay, Andreas Marsing, Elena de la Torre Castro, Liam Megill, Monika Scheibe, and Christiane Voigt
Earth Syst. Sci. Data, 18, 2397–2412, https://doi.org/10.5194/essd-18-2397-2026, https://doi.org/10.5194/essd-18-2397-2026, 2026
Short summary
Short summary
We provide observations of the geostationary Meteosat satellite with contrails labeled by three people complemented with detailed cloud information. Contrails influence climate but are hard to identify in satellite imagery. With this study, we support contrail detection development and evaluation, stress the subjectivity of human labeling and reveal which meteorological conditions highlight or hide contrails. This dataset contributes to a better understanding of aviation’s climate impact.
Richard Maier, Fabian Jakub, Fabian Hoffmann, and Bernhard Mayer
EGUsphere, https://doi.org/10.5194/egusphere-2026-1417, https://doi.org/10.5194/egusphere-2026-1417, 2026
Short summary
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Most atmospheric models only use 1D radiation, neglecting any 3D radiative effects. Here, we show that the dynamic TenStream solver provides a computationally efficient way to represent these effects. Like full 3D radiation, it causes daytime clouds to organize into streets, grow larger, and contain more liquid water. We show that this occurs because 3D radiation does not shade cloud updrafts and modifies the surface energy balance, resulting in an increased latent heat flux into the atmosphere.
Josef Zink and Simon Unterstrasser
Atmos. Chem. Phys., 26, 3145–3165, https://doi.org/10.5194/acp-26-3145-2026, https://doi.org/10.5194/acp-26-3145-2026, 2026
Short summary
Short summary
The climate impact of aviation-induced contrail cirrus clouds is strongly influenced by the number of ice crystals that form in the wake of an aircraft under certain conditions. In this study, we investigate how engine-related aspects influence the number of ice crystals formed for hydrogen combustion. We derive suitable (scaling) relations that can be integrated into large-scale models used to estimate the climate impact of contrail cirrus clouds.
Josef Zink, Simon Unterstrasser, and Ulrike Burkhardt
Atmos. Chem. Phys., 26, 3125–3143, https://doi.org/10.5194/acp-26-3125-2026, https://doi.org/10.5194/acp-26-3125-2026, 2026
Short summary
Short summary
The climate impact of aviation-induced contrail cirrus is strongly influenced by the number of ice crystals that form in an aircraft's exhaust plume. In this study, we systematically investigate the key microphysical processes of contrail formation for hydrogen combustion. A large simulation data set provides the basis for a data-driven parameterization of ice crystal number that can be integrated into large-scale models.
Levin Rug, Willi Schimmel, Fabian Hoffmann, and Oswald Knoth
Geosci. Model Dev., 18, 9039–9059, https://doi.org/10.5194/gmd-18-9039-2025, https://doi.org/10.5194/gmd-18-9039-2025, 2025
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We present the Chemical Mechanism Integrator (Cminor) v1.0, a tool to predict concentrations of chemical compounds undergoing arbitrary reactions. Cminor is an advanced, open-source solver to model either combustion chemistry, or atmospheric chemistry and its direct influence on condensation of cloud droplets and the subsequent processing of aerosol. It uses the superdroplet idea, making it particularly feasible for coupling with such models, which is part of future work.
Gregor Neumann, Andreas Marsing, Theresa Harlass, Daniel Sauer, Simon Braun, Magdalena Pühl, Christopher Heckl, Paul Stock, Elena De La Torre Castro, Valerian Hahn, Anke Roiger, Christiane Voigt, Simon Unterstraßer, Jean Cammas, Charles Renard, Roberta Vasenden, Arnold Vasenden, and Tina Jurkat-Witschas
Atmos. Meas. Tech., 18, 6795–6816, https://doi.org/10.5194/amt-18-6795-2025, https://doi.org/10.5194/amt-18-6795-2025, 2025
Short summary
Short summary
This study presents the first successful in-flight emission characterization of a turboprop engine using a fully autonomous airborne measurement platform, offering new insights into the atmospheric impacts of regional aviation. By equipping the high-altitude Grob G 520 Egrett with a suite of custom and modified commercial instruments, we demonstrate precise, high-resolution measurements of aerosol particles, trace gases, and contrail ice in the engine exhaust plume at cruise altitudes.
Graham Feingold, Franziska Glassmeier, Jianhao Zhang, and Fabian Hoffmann
Atmos. Chem. Phys., 25, 10869–10885, https://doi.org/10.5194/acp-25-10869-2025, https://doi.org/10.5194/acp-25-10869-2025, 2025
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Scientists usually use snapshots of atmospheric data to glean understanding of time-evolving atmospheric processes. We examine how much can be learned about processes from snapshots using examples from cloud and atmospheric physics. We couch the analysis in terms of the theory of ergodic systems, space-time-exchange, and the Deborah number – concepts that are commonly applied in other branches of physics. We discuss the reasons for the varying degrees of success.
Fabian Hoffmann, Yao-Sheng Chen, and Graham Feingold
Atmos. Chem. Phys., 25, 8657–8670, https://doi.org/10.5194/acp-25-8657-2025, https://doi.org/10.5194/acp-25-8657-2025, 2025
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Clouds reflect a substantial portion of the incoming solar radiation back into space. This capacity is determined by the number of cloud droplets, which in turn is influenced by the number of aerosol particles, forming the basis for aerosol–cloud–climate interactions. In this study, we use a simple entrainment parameterization to understand the effect of aerosol on cloud water in weakly and non-precipitating stratocumulus.
Annemarie Lottermoser and Simon Unterstrasser
Atmos. Chem. Phys., 25, 7903–7924, https://doi.org/10.5194/acp-25-7903-2025, https://doi.org/10.5194/acp-25-7903-2025, 2025
Short summary
Short summary
Contrail cirrus significantly contributes to aviation's overall climate impact. As hydrogen combustion and fuel cell use are emerging technologies for aircraft propulsion, we simulated individual contrails from hydrogen propulsion during the first 6 min after exhaust emission, termed the vortex phase. The ice crystal loss during that stage is crucial, as the number of ice crystals has a large impact on the further evolution of contrails into contrail cirrus and their radiative forcing.
Yao-Sheng Chen, Prasanth Prabhakaran, Fabian Hoffmann, Jan Kazil, Takanobu Yamaguchi, and Graham Feingold
Atmos. Chem. Phys., 25, 6141–6159, https://doi.org/10.5194/acp-25-6141-2025, https://doi.org/10.5194/acp-25-6141-2025, 2025
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Injecting sea salt aerosols into marine stratiform clouds can distribute the cloud water over more droplets in smaller sizes. This process is expected to make the clouds brighter, allowing them to reflect more sunlight back to space. However, it may also cause the clouds to lose water over time, reducing their ability to reflect sunlight. We use a computer model to show that the loss of cloud water occurs relatively quickly and does not completely offset the initial brightening.
Jung-Sub Lim, Yign Noh, Hyunho Lee, and Fabian Hoffmann
Atmos. Chem. Phys., 25, 5313–5329, https://doi.org/10.5194/acp-25-5313-2025, https://doi.org/10.5194/acp-25-5313-2025, 2025
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Rain formation in warm clouds begins when small droplets collide, but this process can be slow without larger droplets. We used simulations to explore the role of bigger droplets, known as precipitation embryos, in triggering rain. We found that they speed up rain only when their size and number exceed a critical threshold. This threshold becomes larger when collisions are naturally efficient, such as in clouds with broad droplet size distributions or strong turbulence.
Fan Yang, Hamed Fahandezh Sadi, Raymond A. Shaw, Fabian Hoffmann, Pei Hou, Aaron Wang, and Mikhail Ovchinnikov
Atmos. Chem. Phys., 25, 3785–3806, https://doi.org/10.5194/acp-25-3785-2025, https://doi.org/10.5194/acp-25-3785-2025, 2025
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Large-eddy simulations of a convection cloud chamber show two new microphysics regimes, cloud oscillation and cloud collapse, due to haze–cloud interactions. Our results suggest that haze particles and their interactions with cloud droplets should be considered especially in polluted conditions. To properly simulate haze–cloud interactions, we need to resolve droplet activation and deactivation processes, instead of using Twomey-type activation parameterization.
Fabian Hoffmann, Franziska Glassmeier, and Graham Feingold
Atmos. Chem. Phys., 24, 13403–13412, https://doi.org/10.5194/acp-24-13403-2024, https://doi.org/10.5194/acp-24-13403-2024, 2024
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Clouds constitute a major cooling influence on Earth's climate system by reflecting a large fraction of the incident solar radiation back to space. This ability is controlled by the number of cloud droplets, which is governed by the number of aerosol particles in the atmosphere, laying the foundation for so-called aerosol–cloud–climate interactions. In this study, a simple model to understand the effect of aerosol on cloud water is developed and applied.
Yao-Sheng Chen, Jianhao Zhang, Fabian Hoffmann, Takanobu Yamaguchi, Franziska Glassmeier, Xiaoli Zhou, and Graham Feingold
Atmos. Chem. Phys., 24, 12661–12685, https://doi.org/10.5194/acp-24-12661-2024, https://doi.org/10.5194/acp-24-12661-2024, 2024
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Marine stratocumulus cloud is a type of shallow cloud that covers the vast areas of Earth's surface. It plays an important role in Earth's energy balance by reflecting solar radiation back to space. We used numerical models to simulate a large number of marine stratocumuli with different characteristics. We found that how the clouds develop throughout the day is affected by the level of humidity in the air above the clouds and how closely the clouds connect to the ocean surface.
Andreas Bier, Simon Unterstrasser, Josef Zink, Dennis Hillenbrand, Tina Jurkat-Witschas, and Annemarie Lottermoser
Atmos. Chem. Phys., 24, 2319–2344, https://doi.org/10.5194/acp-24-2319-2024, https://doi.org/10.5194/acp-24-2319-2024, 2024
Short summary
Short summary
Using hydrogen as aviation fuel affects contrails' climate impact. We study contrail formation behind aircraft with H2 combustion. Due to the absence of soot emissions, contrail ice crystals are assumed to form only on ambient particles mixed into the plume. The ice crystal number, which strongly varies with temperature and aerosol number density, is decreased by more than 80 %–90 % compared to kerosene contrails. However H2 contrails can form at lower altitudes due to higher H2O emissions.
Prasanth Prabhakaran, Fabian Hoffmann, and Graham Feingold
Atmos. Chem. Phys., 24, 1919–1937, https://doi.org/10.5194/acp-24-1919-2024, https://doi.org/10.5194/acp-24-1919-2024, 2024
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In this study, we explore the impact of deliberate aerosol perturbation in the northeast Pacific region using large-eddy simulations. Our results show that cloud reflectivity is sensitive to the aerosol sprayer arrangement in the pristine system, whereas in the polluted system it is largely proportional to the total number of aerosol particles injected. These insights would aid in assessing the efficiency of various aerosol injection strategies for climate intervention applications.
Edward Gryspeerdt, Franziska Glassmeier, Graham Feingold, Fabian Hoffmann, and Rebecca J. Murray-Watson
Atmos. Chem. Phys., 22, 11727–11738, https://doi.org/10.5194/acp-22-11727-2022, https://doi.org/10.5194/acp-22-11727-2022, 2022
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The response of clouds to changes in aerosol remains a large uncertainty in our understanding of the climate. Studies typically look at aerosol and cloud processes in snapshot images, measuring all properties at the same time. Here we use multiple images to characterise how cloud temporal development responds to aerosol. We find a reduction in liquid water path with increasing aerosol, party due to feedbacks. This suggests the aerosol impact on cloud water may be weaker than in previous studies.
Michael A. Olesik, Jakub Banaśkiewicz, Piotr Bartman, Manuel Baumgartner, Simon Unterstrasser, and Sylwester Arabas
Geosci. Model Dev., 15, 3879–3899, https://doi.org/10.5194/gmd-15-3879-2022, https://doi.org/10.5194/gmd-15-3879-2022, 2022
Short summary
Short summary
In systems such as atmospheric clouds, droplets undergo growth through condensation of vapor. The broadness of the resultant size spectrum of droplets influences precipitation likelihood and the radiative properties of clouds. One of the inherent limitations of simulations of the problem is the so-called numerical diffusion causing overestimation of the spectrum width, hence the term numerical broadening. In the paper, we take a closer look at one of the algorithms used in this context: MPDATA.
Andreas Bier, Simon Unterstrasser, and Xavier Vancassel
Atmos. Chem. Phys., 22, 823–845, https://doi.org/10.5194/acp-22-823-2022, https://doi.org/10.5194/acp-22-823-2022, 2022
Short summary
Short summary
We investigate contrail formation in an aircraft plume with a particle-based multi-trajectory 0D model. Due to the high plume heterogeneity, contrail ice crystals form first near the plume edge and then in the plume centre. The number of ice crystals varies strongly with ambient conditions and soot properties near the contrail formation threshold. Our results imply that the multi-trajectory approach does not necessarily lead to improved scientific results compared to a single mean trajectory.
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Short summary
Particle-based cloud models use simulation particles for the representation of cloud particles like droplets or ice crystals. The collision and merging of cloud particles (i.e. collisional growth a.k.a. collection in the case of cloud droplets and aggregation in the case of ice crystals) was found to be a numerically challenging process in such models. The study presents verification exercises in a 1D column model, where sedimentation and collisional growth are the only active processes.
Particle-based cloud models use simulation particles for the representation of cloud particles...
