Cloud Formation Processes Research Articles

Molecular cloud matching in CO and dust in M33. II. Physical properties of giant molecular clouds

Understanding the physical properties such as mass, size, and surface mass density of giant molecular clouds or associations (GMCs/GMAs) in galaxies is crucial for gaining deeper insights into the molecular cloud and star formation (SF) processes. We determine these quantities for the Local Group flocculent spiral galaxy M33 using Herschel dust and archival $^ CO(2-1) $ data from the IRAM 30m telescope, and compare them to GMC/GMA properties of the Milky Way derived from CO literature data. For M33, we apply the Dendrogram algorithm on a novel 2D dust-derived Nhtwo map at an angular resolution of $18.2''$ and on the $^ CO(2-1) $ data and employ an factor map instead of a constant value. Dust and CO-derived values are similar, with mean radii of $ for the dust and $ for CO respectively. However, the largest GMAs have a radius of around $150\,$pc, similar to what was found in the Milky Way and other galaxies, suggesting a physical process that limits the size of GMAs. The less massive and smaller M33 galaxy also hosts less massive and lower-density GMCs compared to the Milky Way by an order of magnitude. Notably, the most massive ($>$ a few $10^6\ M_ odot $) GMC population observed in the Milky Way is mainly missing in M33. The mean surface mass density of M33 is significantly smaller than that of the Milky Way and this is attributed to higher column densities of the largest GMCs in the Milky Way, despite similar GMC areas. We find no systematic gradients in physical properties with the galactocentric radius in M33. However, surface mass densities and masses are higher near the center, implying increased SF activity. In both galaxies, the central region contains $ of the total molecular mass. The index of the power-law spectrum of the GMC masses across the entire disk of M33 is $ and $ for dust- and CO-derived data, respectively. We conclude that GMC properties in M33 and the Milky Way are largely similar, though M33 lacks high-mass GMCs, for which there is no straightforward explanation. Additionally, GMC properties are only weakly dependent on the galactic environment, with stellar feedback playing a role that needs further investigation.

Hysteresis in Water Content of Ultrafine Glassy Organic Aerosol Particles

AbstractWater content of aerosol particles is atmospherically important. Water content of organic aerosol (OA) particles has been estimated by assuming thermodynamic equilibrium. Here, we discovered that the hysteresis phenomenon occurred to water content of glassy ultrafine OA particles, demonstrating that thermodynamically non‐equilibrium states need to be considered. Hygroscopic growth for monodisperse ultrafine particles (sucrose and glucose) was investigated for the temperature range from 252 to 296 K. Hysteresis was not observable at 296 K, consistent with literature data. However, hysteresis in water content was observed at sub‐273 K. The lowest relative humidity (RH), at which hygroscopic growth of particles did not depend on exposure history to water vapor, was defined as threshold RH. Threshold RH for 100 nm particles was approximately the same as the glass transition points when hysteresis clearly happened, demonstrating that water diffusion in a highly viscous matrix of organic aerosols was the key to the phenomenon. Employment of a kinetic multi‐layer model quantitatively predicted threshold RH as a function of temperature, exposure time, and the particle size. Considering the temperature and RH range of Earth's atmosphere, we hypothesize that hysteresis in water content for organic aerosols ubiquitously occurs in the upper troposphere, impacting chemical aging and cloud formation processes.

Toward an Understanding of Uric Acid Particle Dissolution: Surface and Bulk-Driven Water Activity.

Uric acid particles contribute to kidney stones, and natural processes for the elimination of stones depend on solute-solvent interactions. The process of uric acid dissolution has previously been understood via the lens of solubility; however, for pure and mixed salt solutions, these approaches do not provide a comprehensive picture of nanoscale particle solution thermodynamics. Unlike solubility measurements, water activity measurements provide us with information about the chemical potential responsible for the migration of water molecules driving the dissolution of particles. In this work, we used in situ experimental tools to estimate water activity values for pure uric acid aqueous droplets at different stages of droplet growth. The process of cloud formation, i.e., water condensation on a solute particle resulting in aqueous droplet formation, was leveraged to compare the water affinity for nanosized uric acid particles with a well-studied inorganic salt, sodium chloride. Specifically, we investigated microscopic uric acid particles (nanoparticles <300 nm, amorphous and super micron particles >5 μm, crystalline) and the mechanism of water uptake. The growth of droplet volume (Growth Factor, GF) for uric acid particles is experimentally observed for supermicrometer crystalline particles (>1 μm) at subsaturated humidity conditions (<100% RH). In addition, the water activity of submicrometer-size uric acid particles is estimated under subsaturated and supersaturated humidity conditions. These measurements provide us with information about the volume growth of droplets as water condenses in particles exposed to different humidity conditions. Our observations under subsaturated humidity conditions show that the uric acid particles have limited volume growth (<1% change per volume and <10% change per volume for crystalline and amorphous measurement, respectively). From the experimental data, the affinity of uric acid solute with water as a solvent is quantified in terms of water activity.

Aerosol‐Cloud Interactions From Aviation Soot Emissions

AbstractCurrent models estimate global aviation contributes approximately 5% to the total anthropogenic climate forcing, with aerosol‐cloud interactions having the greatest effect. However, radiative forcing estimates from aviation aerosol‐cloud interactions remain undetermined. There is an expected significant increase in aircraft emissions with aviation demand expected to rise by over 4% per year. Soot may play an important role in the ice nucleation of aircraft‐induced cirrus formation due to a high emission rate, but the ice nucleating properties are poorly constrained. Understanding the microphysical processes leading to atmospheric ice crystal formation is crucial for the reliable parameterization of aerosol‐cloud interactions in climate models due to their impact on precipitation and cloud radiative properties. Ice nucleation of aircraft‐emitted soot is potentially affected by particle morphology with condensation of supercooled water occurring in pores followed by ice nucleation. However, soot has heterogeneous properties and undergoes atmospheric aging and oxidation that could change surface properties and contribute to complex ice nucleation processes. This review synthesizes current knowledge of ice nucleation catalyzed by aviation in the cirrus regime and its effects on global radiative forcing. Further research is required to determine the ice nucleation and microphysical processes of cirrus cloud formation from aviation emissions in both controlled laboratory and field investigations to inform models for more accurate climate predictions and to provide efficient mitigation strategies.

Cloud micro- and macrophysical properties from ground-based remote sensing during the MOSAiC drift experiment.

In the framework of the Multidisciplinary drifting Observatory for the Study of Arctic Climate Polarstern expedition, the Leibniz Institute for Tropospheric Research, Leipzig, Germany, operated the shipborne OCEANET-Atmosphere facility for cloud and aerosol observations throughout the whole year. OCEANET-Atmosphere comprises, amongst others, a multiwavelength Raman lidar, a microwave radiometer, and an optical disdrometer. A cloud radar was operated aboard Polarstern by the US Atmospheric Radiation Measurement program. These measurements were processed by applying the so-called Cloudnet methodology to derive cloud properties. To gain a comprehensive view of the clouds, lidar and cloud radar capabilities for low- and high-altitude observations were combined. Cloudnet offers a variety of products with a spatiotemporal resolution of 30 s and 30 m, such as the target classification, and liquid and ice microphysical properties. Additionally, a lidar-based low-level stratus retrieval was applied for cloud detection below the lowest range gate of the cloud radar. Based on the presented dataset, e.g., studies on cloud formation processes and their radiative impact, and model evaluation studies can be conducted.

Impact of Planetary Parameters on Water Clouds Microphysics

Potentially habitable exoplanets are targets of great interest for the James Webb Space Telescope and upcoming mission concepts such as the Habitable Worlds Observatory. Clouds strongly affect climate and habitability, but predicting their properties is difficult. In Global Climate Models (GCMs), especially those aiming at simulating Earth, cloud microphysics is often crudely approximated by assuming that all cloud particles have a single, constant size or a prescribed size distribution and that all clouds in a grid cell are identical. For exoplanets that range over a large phase space of planetary properties, this method could result in large errors. In this work, our goal is to determine how cloud microphysics on terrestrial exoplanets, whose condensable is mainly water vapor, depend on aerosol properties and planetary parameters such as surface pressure, surface gravity, and incident stellar radiation. We use the Community Aerosol and Radiation Model for Atmospheres as a 1D microphysical model to simulate the formation and evolution of clouds including the processes of nucleation, condensation, evaporation, coagulation, and vertical transfer. In these 1D idealized experiments, we find that the parameters that determine the macrophysical thermal structure of the atmospheres, including surface pressure and stellar flux, impact cloud radiative effect (CRE) most significantly. Parameters such as gravity and number density of aerosols working as cloud condensation nuclei affect the microphysical processes of cloud formation, including activation and vertical transfer. They also have a significant, though weaker effect on CRE. This work motivates the development of more accurate GCM cloud schemes and should aid in the interpretation of future observations.

Dark Dragon Breaks Magnetic Chain: Dynamical Substructures of IRDC G28.34 Form in Supported Environments

We have comprehensively studied the multiscale physical properties of the massive infrared dark cloud G28.34 (the Dragon cloud) with dust polarization and molecular line data from Planck, FCRAO-14 m, James Clerk Maxwell Telescope, and Atacama Large Millimeter/submillimeter Array. We find that the averaged magnetic fields of clumps tend to be either parallel with or perpendicular to the cloud-scale magnetic fields, while the cores in clump MM4 tend to have magnetic fields aligned with the clump fields. Implementing the relative orientation analysis (for magnetic fields, column density gradients, and local gravity), velocity gradient technique, and modified Davis–Chandrasekhar–Fermi analysis, we find that G28.34 is located in a trans-to-sub-Alfvénic environment; the magnetic field is effectively resisting gravitational collapse in large-scale diffuse gas, but is distorted by gravity within the cloud and affected by star formation activities in high-density regions, and the normalized mass-to-flux ratio tends to increase with increasing density and decreasing radius. Considering the thermal, magnetic, and turbulent supports, we find that the environmental gas of G28.34 is in a supervirial (supported) state, the infrared dark clumps may be in a near-equilibrium state, and core MM4-core4 is in a subvirial (gravity-dominant) state. In summary, we suggest that magnetic fields dominate gravity and turbulence in the cloud environment at large scales, resulting in relatively slow cloud formation and evolution processes. Within the cloud, gravity could overwhelm both magnetic fields and turbulence, allowing local dynamical star formation to happen.

Exploring the excess of cloud condensation nuclei and rain suppression using a minimal three-dimensional Boussinesq model with bulk cloud microphysics

Over the years, there have been discussions about the possibility of air pollution affecting the process of rain formation. In this study, we have developed a simplified model that represents the atmospheric dynamics and cloud microphysics to explore the impact of pollution on rain formation. We used an existing three-dimensional minimal model consisting of five equations, for which we added a simple bulk parametrization that represents the role of cloud condensation nuclei (CCN) in cloud formation processes. We conducted numerical tests using two CCN profiles, with either one or two accumulation layers and modified their abundance to explore the effects of different CCN concentrations and distributions. We conducted four numerical tests corresponding to the two aforementioned profiles with polluted and low-polluted scenarios. The numerical simulations suggested that a layer with high CCN concentration close to the surface tends to suppress precipitation, while the same concentration distributed over two layers tends to enhance the efficiency of rain formation. The simulations also showed that CCN particles far from the surface produced higher cloud tops and longer events, consistent with previous research. Although the model includes a stable representation of precipitating turbulent convection with bulk cloud microphysics, we expect its simplicity and conservation properties to allow for deeper theoretical analyses that can help us better understand the physical processes involved in the studied phenomenon. We hope this model will serve as a tool to explore different aerosol-related scenarios within the context of minimal models.

Fully time-dependent cloud formation from a non-equilibrium gas-phase in exoplanetary atmospheres

Context. Recent observations suggest the presence of clouds in exoplanet atmospheres, but they have also shown that certain chemical species in the upper atmosphere might not be in chemical equilibrium. Present and future interpretation of data from, for example, CHEOPS, JWST, PLATO, and Ariel require a combined understanding of the gas-phase and the cloud chemistry. Aims. The goal of this work is to calculate the two main cloud formation processes, nucleation, and bulk growth consistently from a non-equilibrium gas phase. The aim is also to explore the interaction between a kinetic gas-phase and cloud microphysics. Methods. The cloud formation is modelled using the moment method and kinetic nucleation, which are coupled to a gas-phase kinetic rate network. Specifically, the formation of cloud condensation nuclei is derived from cluster rates that include the thermochemical data of (TiO2)N from N = 1 to 15. The surface growth of nine bulk Al, Fe, Mg, O, Si, S, and Ti binding materials considers the respective gas-phase species through condensation and surface reactions as derived from kinetic disequilibrium. The effect of the completeness of rate networks and the time evolution of the cloud particle formation is studied for an example exoplanet, HD 209458 b. Results. A consistent, fully time-dependent cloud formation model in chemical disequilibrium with respect to nucleation, bulk growth, and the gas-phase is presented and first test cases are studied. This model shows that cloud formation in exoplanet atmospheres is a fast process. This confirms previous findings that the formation of cloud particles is a local process. Tests on selected locations within the atmosphere of the gas-giant HD 209458 b show that the cloud particle number density and volume reach constant values within 1 s. The complex kinetic polymer nucleation of TiO2 confirms results from classical nucleation models. The surface reactions of SiO[s] and SiO2[s] can create a catalytic cycle that dissociates H2 to 2 H, resulting in a reduction of the CH4 number densities.

Dust effects on mixed-phase clouds and precipitation during a super dust storm over northern China

Dust aerosols have been generally regarded as efficient ice nuclei (IN), but their influences on mixed-phase clouds and precipitation are poorly quantified. In this study, combining satellite observations, reanalysis data and the Weather Research and Forecasting (WRF) model, we investigate the impacts of dust aerosols on mixed-phase clouds and precipitation during a super dust storm over northern China. The Suomi National Polar-Orbiting Partnership (S-NPP) satellite observed a super dust storm from March 15–19, 2021 in northern China, followed by heavy precipitation between March 17 and 19. The results showed that the occurrence of super dust storms may play an important role in cloud formation and precipitation processes. Furthermore, numerical modeling revealed that dust aerosols can increase the ice crystal number concentration (QNi) and decrease the cloud droplet number concentration (QNc) in mixed-phase clouds through the Wegener–Bergeron–Findeisen (WBF) process, in which the maximum increase in QNi can reach 21%. Simultaneously, the mass mixing ratios of rain, graupel and snow increased due to dust aerosols. Consequently, precipitation could increase by up to 9.8% in northern China. This study could provide evidence for understanding the mechanisms of dust effects on mixed-phase clouds over northern China.

Modeling dust mineralogical composition: sensitivity to soil mineralogy atlases and their expected climate impacts

Abstract. Soil dust aerosols are a key component of the climate system, as they interact with short- and long-wave radiation, alter cloud formation processes, affect atmospheric chemistry and play a role in biogeochemical cycles by providing nutrient inputs such as iron and phosphorus. The influence of dust on these processes depends on its physicochemical properties, which, far from being homogeneous, are shaped by its regionally varying mineral composition. The relative amount of minerals in dust depends on the source region and shows a large geographical variability. However, many state-of-the-art Earth system models (ESMs), upon which climate analyses and projections rely, still consider dust mineralogy to be invariant. The explicit representation of minerals in ESMs is more hindered by our limited knowledge of the global soil composition along with the resulting size-resolved airborne mineralogy than by computational constraints. In this work we introduce an explicit mineralogy representation within the state-of-the-art Multiscale Online Nonhydrostatic AtmospheRe CHemistry (MONARCH) model. We review and compare two existing soil mineralogy datasets, which remain a source of uncertainty for dust mineralogy modeling and provide an evaluation of multiannual simulations against available mineralogy observations. Soil mineralogy datasets are based on measurements performed after wet sieving, which breaks the aggregates found in the parent soil. Our model predicts the emitted particle size distribution (PSD) in terms of its constituent minerals based on brittle fragmentation theory (BFT), which reconstructs the emitted mineral aggregates destroyed by wet sieving. Our simulations broadly reproduce the most abundant mineral fractions independently of the soil composition data used. Feldspars and calcite are highly sensitive to the soil mineralogy map, mainly due to the different assumptions made in each soil dataset to extrapolate a handful of soil measurements to arid and semi-arid regions worldwide. For the least abundant or more difficult-to-determine minerals, such as iron oxides, uncertainties in soil mineralogy yield differences in annual mean aerosol mass fractions of up to ∼ 100 %. Although BFT restores coarse aggregates including phyllosilicates that usually break during soil analysis, we still identify an overestimation of coarse quartz mass fractions (above 2 µm in diameter). In a dedicated experiment, we estimate the fraction of dust with undetermined composition as given by a soil map, which makes up ∼ 10 % of the emitted dust mass at the global scale and can be regionally larger. Changes in the underlying soil mineralogy impact our estimates of climate-relevant variables, particularly affecting the regional variability of the single-scattering albedo at solar wavelengths or the total iron deposited over oceans. All in all, this assessment represents a baseline for future model experiments including new mineralogical maps constrained by high-quality spaceborne hyperspectral measurements, such as those arising from the NASA Earth Surface Mineral Dust Source Investigation (EMIT) mission.

Microphysical and thermodynamic phase analyses of Arctic low-level clouds measured above the sea ice and the open ocean in spring and summer

Abstract. Airborne in situ cloud measurements were carried out over the northern Fram Strait between Greenland and Svalbard in spring 2019 and summer 2020. In total, 811 min of low-level cloud observations were performed during 20 research flights above the sea ice and the open Arctic ocean with the Polar 5 research aircraft of the Alfred Wegener Institute. Here, we combine the comprehensive in situ cloud data to investigate the distributions of particle number concentration N, effective diameter Deff, and cloud water content CWC (liquid and ice) of Arctic clouds below 500 m altitude, measured at latitudes between 76 and 83∘ N. We developed a method to quantitatively derive the occurrence probability of their thermodynamic phase from the combination of microphysical cloud probe and Polar Nephelometer data. Finally, we assess changes in cloud microphysics and cloud phase related to ambient meteorological conditions in spring and summer and address effects of the sea ice and open-ocean surface conditions. We find median N from 0.2 to 51.7 cm−3 and about 2 orders of magnitude higher N for mainly liquid clouds in summer compared to ice and mixed-phase clouds measured in spring. A southerly flow from the sea ice in cold air outbreaks dominates cloud formation processes at temperatures mostly below −10 ∘C in spring, while northerly warm air intrusions favor the formation of liquid clouds at warmer temperatures in summer. Our results show slightly higher N in clouds over the sea ice compared to the open ocean, indicating enhanced cloud formation processes over the sea ice. The median CWC is higher in summer (0.16 g m−3) than in spring (0.06 g m−3), as this is dominated by the available atmospheric water content and the temperatures at cloud formation level. We find large differences in the particle sizes in spring and summer and an impact of the surface conditions, which modifies the heat and moisture fluxes in the boundary layer. By combining microphysical cloud data with thermodynamic phase information from the Polar Nephelometer, we find mixed-phase clouds to be the dominant thermodynamic cloud phase in spring, with a frequency of occurrence of 61 % over the sea ice and 66 % over the ocean. Pure ice clouds exist almost exclusively over the open ocean in spring, and in summer the cloud particles are most likely in the liquid water state. The comprehensive low-level cloud data set will help us to better understand the role of clouds and their thermodynamic phase in the Arctic radiation budget and to assess the performance of global climate models in a region of the world with the strongest anthropogenic climate change.

ALMA-IMF

Context.Among the most central open questions regarding the initial mass function (IMF) of stars is the impact of environment on the shape of the core mass function (CMF) and thus potentially on the IMF.Aims.The ALMA-IMF Large Program aims to investigate the variations in the core distributions (CMF and mass segregation) with cloud characteristics, such as the density and kinematic of the gas, as diagnostic observables of the formation process and evolution of clouds. The present study focuses on the W43-MM2&amp;MM3 mini-starburst, whose CMF has recently been found to be top-heavy with respect to the Salpeter slope of the canonical IMF.Methods.W43-MM2&amp;MM3 is a useful test case for environmental studies because it harbors a rich cluster that contains a statistically significant number of cores (specifically, 205 cores), which was previously characterized in Paper III. We applied a multi-scale decomposition technique to the ALMA 1.3 mm and 3 mm continuum images of W43-MM2&amp;MM3 to define six subregions, each 0.5–1 pc in size. For each subregion we characterized the probability distribution function of the high column density gas,η-PDF, using the 1.3 mm images. Using the core catalog, we investigate correlations between the CMF and cloud and core properties, such as theη-PDF and the core mass segregation.Results.We classify the W43-MM2&amp;MM3 subregions into different stages of evolution, from quiescent to burst to post-burst, based on the surface number density of cores, number of outflows, and ultra-compact HII presence. The high-mass end (&gt;1M⊙) of the subregion CMFs varies from close to the Salpeter slope (quiescent) to top-heavy (burst and post-burst). Moreover, the second tail of theη-PDF varies from steep (quiescent) to flat (burst and post-burst), as observed for high-mass star-forming clouds. We find that subregions with flat secondη-PDF tails display top-heavy CMFs.Conclusions.In dynamical environments such as W43-MM2&amp;MM3, the high-mass end of the CMF appears to be rooted in the cloud structure, which is at high column density and surrounds cores. This connection stems from the fact that cores and their immediate surroundings are both determined and shaped by the cloud formation process, the current evolutionary state of the cloud, and, more broadly, the star formation history. The CMF may evolve from Salpeter to top-heavy throughout the star formation process from the quiescent to the burst phase. This scenario raises the question of if the CMF might revert again to Salpeter as the cloud approaches the end of its star formation stage, a hypothesis that remains to be tested.

Loading noise induced by cavitating flow and its simplified model prediction

This study employs a computational fluid dynamics approach in combination with acoustic analogy to investigate the loading noise characteristics induced by cavitating flow around a NACA66 (MOD) hydrofoil. The Large Eddy Simulation coupled with the Schnerr-Sauer cavitation model is used to capture the transient motion behaviour of the cavitating flow, which agrees well with experimental observations. The study covers three typical states of cavitation: sheet cavitation (σ = 1.44), sheet/cloud transition cavitation (σ = 1.29), and cloud cavitation (σ = 0.83). The study demonstrates that the energy of the loading noise source is concentrated in the middle-frequency band for sheet cavitation, while it is concentrated in the low-frequency band for cloud cavitation. The cavitation instability promotes loading noise to generate drastic fluctuation and even several extreme impulses, which are directly related to the processes of cloud formation and cavitation multistage shedding. Finally, a simplified model for calculating the loading noise is proposed, and its errors and equivalence are evaluated. The model can effectively predict the loading noise induced by cavitating flow and enable decoupling of data from the flow field to the sound field, which may facilitate the separation of the dipole component from the total noise in experimental measurements.

Современные особенности температурно-влажностного режима тропосферы в Сибирском секторе в различные циркуляционные периоды

The paper studies the long-term dynamics of air temperature and relative humidity anomaly indices in the surface layer and at different levels of the troposphere in Siberia and neighboring regions (European and Far Eastern sectors). As the main cause of the observed variations in climatic parameters we considered circulation factors, which were taken into account using the typification of macrocirculation processes proposed by B.L. Dzerdzeevsky. Seasonal differences were revealed in the distribution of anomaly indices and the area occupied by anomalies of different signs of annual and monthly mean temperature and relative air humidity, which are most pronounced during circulation periods of increased duration of meridional northern processes in the Siberian sector and in the Northern Hemisphere as a whole. The highest rates of change in the temperature regime in the Siberian sector over recent decades have been observed at the level of the isobaric surface AT–700 hPa (3 km), which affects the advective-dynamic factors of surface cyclo- and frontogenesis, as well as the processes of cloud formation and precipitation. In general, an increase in the heat content of the lower and middle troposphere and a decrease in the relative moisture content near the tropopause can be accompanied by an increase in the amount of the potential energy and convective instability energy reserves and can lead to an increase in climate risks in the Siberian sector.

Современные особенности температурно-влажностного режима тропосферы в Сибирском секторе в различные циркуляционные периоды

The paper studies the long-term dynamics of air temperature and relative humidity anomaly indices in the surface layer and at different levels of the troposphere in Siberia and neighboring regions (European and Far Eastern sectors). As the main cause of the observed variations in climatic parameters we considered circulation factors, which were taken into account using the typification of macrocirculation processes proposed by B.L. Dzerdzeevsky. Seasonal differences were revealed in the distribution of anomaly indices and the area occupied by anomalies of different signs of annual and monthly mean temperature and relative air humidity, which are most pronounced during circulation periods of increased duration of meridional northern processes in the Siberian sector and in the Northern Hemisphere as a whole. The highest rates of change in the temperature regime in the Siberian sector over recent decades have been observed at the level of the isobaric surface AT–700 hPa (3 km), which affects the advective-dynamic factors of surface cyclo- and frontogenesis, as well as the processes of cloud formation and precipitation. In general, an increase in the heat content of the lower and middle troposphere and a decrease in the relative moisture content near the tropopause can be accompanied by an increase in the amount of the potential energy and convective instability energy reserves and can lead to an increase in climate risks in the Siberian sector.

Numerical and experimental study of aerosol dispersion in the Do728 aircraft cabin

The dispersion of aerosols originating from one source, the ‘index’ passenger, within the cabin of the aircraft Do728 is studied experimentally using an aerosol-exhaling thermal manikin and in Reynolds-averaged Navier–Stokes simulations (RANS). The overall aim of the present study is the experimental determination of the aerosol spreading for the state-of-the-art mixing ventilation (MV) and to evaluate the potential of alternative ventilation concepts for controlling the aerosol spreading in RANS. For MV, the experiments showed that the ratio of inhaled to exhaled aerosol particles drops below 0.06% (volume ratio) for distances larger than two seat rows from the source. However, within a single row, the observed ratio is higher. Further, the dispersion is much weaker for a standing than for a seated index passenger. High air exchange rates and a well-guided flow prevent a dispersion of the aerosols in high concentrations over larger distances. Additionally, the positive effect of a mask and an increased air flow rate, and especially their combination are shown. In the complementary conducted RANS, the advantages of floor-based cabin displacement ventilation (CDV) which is alternative ventilation concept to MV, regarding spreading lengths and the dwell time of the aerosols in the cabin were determined. The obtained results also underline the importance of the flow field for the aerosol dispersion. Further, additional unsteady RANS (URANS) simulations of the short-term process of the initial aerosol cloud formation highlighted that the momentum decay of the breathing and the evaporation processes take place within a few seconds only.

Hygroscopic Growth Factors of Sub-micrometer Atmospheric Aerosols at Four Selected Sites in Thailand

Hygroscopic growth factor (Gf) of aerosols is related to water loading on particles in sub-saturated conditions. It is an essential parameter for assessing the role of atmospheric particles in the radiative transfer and cloud formation process. Therefore, the temporal variation in Gf of size-selected atmospheric particles from the Aitken mode (Dp £ 100 nm) and accumulation mode (Dp > 100 nm) was measured using a humidified tandem differential mobility analyser (H-TDMA) and the relationship between particle size and Gf for various locations and meteorological conditions was determined. The origin of ambient particles primarily defines their properties and governs their participation in atmospheric processes. Thus, the measurements were performed in locations with different land-use types: urban, rural, coastal-industrial, and landlocked industrial areas. The data showed site-dependent patterns of temporal and spatial changes in Gf. The results indicated that the number-weighted Gf averaged over the investigated particle size range (30–250 nm) was highest in rural areas (Gf = 1.27), followed by coastal-industrial (Gf = 1.19), urban (Gf = 1.11), and landlocked industrial areas (Gf = 1.06). Particles in the urban and landlocked industrial areas had relatively low Gf values, suggesting that they originated mainly from fossil fuel combustion, in contrast to particles at other sites which can be attributed to coastal proximity.

Transverse thermal instability of partially ionized radiative plasma with impact of neutral collisions and finite electron inertia effect in ISM

The impact of neutral friction, finite electron inertia and radiative heat-loss function on the thermal instability of viscous, partially-ionized plasma has been explored integrating the impacts of finite electrical resistivity and thermal conductivity. Normal mode analysis scheme is used to derive universal dispersion relation by means of the related linearized perturbation equations of the difficulty and a tailored thermal situation of instability is explored. It is finding that the thermal condition of instability is modified owing the occurrence of radiative heat-loss function, thermal conductivity, finite electron inertia and neutral particle. For transverse mode of propagation, we discover that the condition of thermal instability depends on the finite electron inertia, magnetic field strength, radiative heat-loss function, thermal conductivity, neutral particle and finite electrical resistivity, but independent viscosity of two-components. From the graphs, we explored that the temperature dependent heat-loss function, thermal conductivity, neutral collision frequency and viscosity of two-components demonstrates stabilizing effect, while finite electron inertia and finite electrical resistivity demonstrates destabilizing effect. Our results help’s to understand the process of molecular cloud formation in ISM.

The ability of children aged 6 and 9 years, respectively, to detect errors in a narrative based on incorrect information about evaporation in the water cycle

Children begin to fully understand evaporation at the age of 11 years, but they already have some idea of this phenomenon in preschool age. The paper presents the results of a research exploring the understanding of evaporation by 6- and 9-year-old children. The research used the method of a narrative based on incorrect information in order to verify whether and how well children would discover the errors in that narrative and how they could explain the process of evaporation. The incorrect narrative method is inspired by the science fiction film genre, which uses false assumptions to prove something that is not true. According to the research, half of the children knew that evaporation accompanies the process of cloud formation, but only half of the children who knew that (one-fourth of the respondents) could detect an error in the narrative. The reason for that is believed to be children’s lack of critical thinking and limited structured knowledge of evaporation in the water cycle in nature.