scholarly journals Assessing How Aerosols Impact Cloud Formation

2022 ◽  
Author(s):  
Timothy Logan
Keyword(s):  
Cloud Formation

Part Eight

2017 ◽  
Author(s):  
Robert J. Fogelin
Keyword(s):  
Cloud Formation ◽  
Striking Similarity ◽  
Common Life ◽  
Natural Religion ◽  
Sextus Empiricus ◽  
Argument From Design

Philo expands on the nature of his objections to the natural religion of Cleanthes: far-fetched comparisons are dismissed in matters of common life, but are appropriate objections when we rise to the level of abstruse and remote reasoning. He offers a counterargument to the design-designer hypothesis, citing Epicurus. Constancy and change are discussed; cloud formation is one example. Philo’s critique of Cleanthes’ argument from design moves through stages, with striking similarity to Agrippa’s suspension of belief as presented by Sextus Empiricus.

scholarly journals Giant Molecular Cloud Formation at the Interface of Colliding Supershells in the Large Magellanic Cloud

2021 ◽  
Author(s):  
Kosuke Fujii ◽  
Norikazu Mizuno ◽  
J R Dawson ◽  
Tsuyoshi Inoue ◽  
Kazufumi Torii ◽  
...  
Keyword(s):  
Large Magellanic Cloud ◽  
Cloud Formation ◽  
Beam Size ◽  
Star Forming ◽  
Star Forming Regions ◽  
Long Baseline ◽  
Gravitational Instabilities ◽  
Atomic Medium ◽  
High Column ◽  
Compact Array

Abstract We investigate the H i envelope of the young, massive GMCs in the star-forming regions N48 and N49, which are located within the high column density H i ridge between two kpc-scale supergiant shells, LMC 4 and LMC 5. New long-baseline H i 21 cm line observations with the Australia Telescope Compact Array (ATCA) were combined with archival shorter baseline data and single dish data from the Parkes telescope, for a final synthesized beam size of 24.75″ by 20.48″, which corresponds to a spatial resolution of ∼ 6 pc in the LMC. It is newly revealed that the H i gas is highly filamentary, and that the molecular clumps are distributed along filamentary H i features. In total 39 filamentary features are identified and their typical width is ∼ 21 (8–49) [pc]. We propose a scenario in which the GMCs were formed via gravitational instabilities in atomic gas which was initially accumulated by the two shells and then further compressed by their collision. This suggests that GMC formation involves the filamentary nature of the atomic medium.

scholarly journals Molecular Cloud Formation in Shock‐compressed Layers

2000 ◽  
Vol 532 (2) ◽  
pp. 980-993 ◽  
Author(s):  
Hiroshi Koyama ◽  
Shu‐Ichiro Inutsuka
Keyword(s):  
Molecular Cloud ◽  
Cloud Formation

scholarly journals Bacteria in the global atmosphere – Part 2: Modeling of emissions and transport between different ecosystems

2009 ◽  
Vol 9 (23) ◽  
pp. 9281-9297 ◽  
Author(s):  
S. M. Burrows ◽  
T. Butler ◽  
P. Jöckel ◽  
H. Tost ◽  
A. Kerkweg ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Residence Time ◽  
General Circulation ◽  
Bacterial Species ◽  
Circulation Model ◽  
Cloud Condensation Nucleus ◽  
Cloud Formation ◽  
Emission Region ◽  
Culturable Bacteria ◽  
Bacterial Cells

Abstract. Bacteria are constantly being transported through the atmosphere, which may have implications for human health, agriculture, cloud formation, and the dispersal of bacterial species. We simulate the global transport of bacteria, represented as 1 μm and 3 μm diameter spherical solid particle tracers in a general circulation model. We investigate factors influencing residence time and distribution of the particles, including emission region, cloud condensation nucleus activity and removal by ice-phase precipitation. The global distribution depends strongly on the assumptions made about uptake into cloud droplets and ice. The transport is also affected, to a lesser extent, by the emission region, particulate diameter, and season. We find that the seasonal variation in atmospheric residence time is insufficient to explain by itself the observed seasonal variation in concentrations of particulate airborne culturable bacteria, indicating that this variability is mainly driven by seasonal variations in culturability and/or emission strength. We examine the potential for exchange of bacteria between ecosystems and obtain rough estimates of the flux from each ecosystem by using a maximum likelihood estimation technique, together with a new compilation of available observations described in a companion paper. Globally, we estimate the total emissions of bacteria-containing particles to the atmosphere to be 7.6×1023–3.5×1024 a−1, originating mainly from grasslands, shrubs and crops. We estimate the mass of emitted bacteria- to be 40–1800 Gg a−1, depending on the mass fraction of bacterial cells in the particles. In order to improve understanding of this topic, more measurements of the bacterial content of the air and of the rate of surface-atmosphere exchange of bacteria will be necessary. Future observations in wetlands, hot deserts, tundra, remote glacial and coastal regions and over oceans will be of particular interest.

scholarly journals Condensed-phase biogenic–anthropogenic interactions with implications for cold cloud formation

2017 ◽  
Vol 200 ◽  
pp. 165-194 ◽  
Author(s):  
Joseph C. Charnawskas ◽  
Peter A. Alpert ◽  
Andrew T. Lambe ◽  
Thomas Berkemeier ◽  
Rachel E. O’Brien ◽  
...  
Keyword(s):  
Freezing Temperature ◽  
Organic Aerosol ◽  
Ice Nucleation ◽  
Mixed Phase ◽  
Cloud Formation ◽  
Fossil Fuel Combustion ◽  
Soot Particles ◽  
Ice Nuclei ◽  
Deliquescence Relative Humidity ◽  
Homogeneous Freezing

Anthropogenic and biogenic gas emissions contribute to the formation of secondary organic aerosol (SOA). When present, soot particles from fossil fuel combustion can acquire a coating of SOA. We investigate SOA–soot biogenic–anthropogenic interactions and their impact on ice nucleation in relation to the particles’ organic phase state. SOA particles were generated from the OH oxidation of naphthalene, α-pinene, longifolene, or isoprene, with or without the presence of sulfate or soot particles. Corresponding particle glass transition (Tg) and full deliquescence relative humidity (FDRH) were estimated using a numerical diffusion model. Longifolene SOA particles are solid-like and all biogenic SOA sulfate mixtures exhibit a core–shell configuration (i.e.a sulfate-rich core coated with SOA). Biogenic SOA with or without sulfate formed ice at conditions expected for homogeneous ice nucleation, in agreement with respectiveTgand FDRH. α-pinene SOA coated soot particles nucleated ice above the homogeneous freezing temperature with soot acting as ice nuclei (IN). At lower temperatures the α-pinene SOA coating can be semisolid, inducing ice nucleation. Naphthalene SOA coated soot particles acted as ice nuclei above and below the homogeneous freezing limit, which can be explained by the presence of a highly viscous SOA phase. Our results suggest that biogenic SOA does not play a significant role in mixed-phase cloud formation and the presence of sulfate renders this even less likely. However, anthropogenic SOA may have an enhancing effect on cloud glaciation under mixed-phase and cirrus cloud conditions compared to biogenic SOA that dominate during pre-industrial times or in pristine areas.

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