Inside Clouds Research Articles

Realistic representation of mixed-phase clouds increases projected climate warming

Clouds are the main source of uncertainties when projecting climate change. Mixed-phase clouds that contain ice and supercooled-liquid particles are especially hard to constrain, and climate models neither agree on their phase nor their spatial extent. This is problematic, as models that underestimate contemporary supercooled-liquid in mixed-phase clouds will underestimate future warming. Furthermore, it has recently been shown that supercooled-liquid water in mixed-phase clouds is not homogeneously-mixed, neither vertically nor horizontally. However, while there have been attempts at observationally constraining mixed-phase clouds to constrain uncertainties in future warming, all studies only use the phase of the interior of mixed-phase clouds. Here we show, using novel satellite observations that distinguish between cloud-top and interior phase in mixed-phase clouds, that mixed-phase clouds are more liquid at the cloud top globally. We use these observations to constrain the cloud top phase in addition to the interior in a global climate model, leading to +1 °C more 21st century warming in NorESM2 SSP5-8.5 climate projections. We anticipate that the difference between cloud top and interior phase in mixed-phase clouds is an important new target metric for future climate model development, because similar mixed-phase clouds related biases in future warming are likely present in many climate models.

Inertial particles in a turbulent/turbulent interface

Turbulent interfaces are ubiquitous in the nature and in many important canonical flows (wakes, jets, mixing layers, boundary layers). In nature, the sharp edges of atmospheric clouds are defined by a turbulent/non-turbulent interface, where the droplet-laden turbulent cloud interior mixes with the unladen outer air. This study presents statistics of sub-Kolmogorov-scale inertial particles, in a parameter range representative of cloud droplets, in a sheared turbulent–turbulent interface. The study focuses on the effect of the inhomogeneous turbulent field on the particles’ clustering properties and settling velocity modification. Wind tunnel experiments were carried out in a well-characterised facility where a grid containing 81 independent gas/liquid injectors generates both high intensity turbulence and a field of small inertial droplets. These atomisers, located at the entrance of the test section, contribute significantly to the carrier phase turbulence and are used to create the sheared turbulent/turbulent interface. Selecting which atomisers are on or off enables us to control the mean velocity profile and the gradient of turbulent intensity through the tunnel cross-section. The resulting carrier flow is characterised by a gradient of mean velocity, turbulent velocity rms, and a sharp interface separating two regions with different turbulent scales. Particles’ velocities and diameters were measured with a Phase Doppler Particle Analyser, at closely-spaced positions across the turbulent interface. In agreement with previous experimental studies on the topic, particles are shown to be transported from the turbulent side, with higher turbulence intensity, to the low-intensity side by large-scale-energetic eddies. Newly observed in our results is an enhancement of particle preferential concentration and settling velocity in the sheared interface region, caused by the interaction between particle trajectories and turbulent structures of different sizes.

Revolutionizing cosmology: the small bang model and its implications on universe genesis

The Small Bang Model (SBM) introduces a revolutionary framework for the genesis of the universe, challenging conventional cosmological theories. By sug-gesting the universe originated from a zero-mass state, facilitated by antimatter black holes, the SBM provides fresh insights into galaxy formation and the dis-tribution of matter and antimatter. This paper outlines the SBM’s foundational principles, contrasts it with the Big Bang theory, and highlights its potential to resolve longstanding cosmological puzzles. Notably, it presents empirical valida-tions demonstrating distinct mass relationships between supermassive black holes and their host galaxies, supporting a novel classification into matter and anti-matter galaxies. The Small Bang model is founded on two pivotal concepts: the theory of Cosmic Inflation and the principle of ’Shunyata Universe’s Genesis’ (or’Emptiness Universe’s Genesis’), a framework envisioning the universe’s incep-tion as small, empty, and cold, entirely devoid of matter or energy. Within this Shunyata beginning, the cosmos as we witness today, abundant in matter and energy, was forged during the 2µs duration of cosmic inflation. Throughout this period, the substantial energy of the Inflaton field was harnessed either through the mediation of micro black holes or directly by the Inflaton’s influence on the spacetime fabric itself. This era was marked by the continuous creation of matter and antimatter particle pairs (such as proton-antiproton and electron-positron, including the creation of photon-antiphoton pairs), permeating the entire expand-ing universe. The SBM predicts that the massive annihilation of antiparticles, induced by the inflaton field throughout the entire universe in the final 15 ns of cosmic inflation, generated two tomographic scans: Cosmic Antiproton Tomogra-phy (CAT) radiation and Cosmic Positron Tomography (CPT) radiation. These two tomographies serve as evidence of the inflaton field’s existence, allowing us to calculate its principal parameters and also to create images of the interiors of hydrogen clouds that formed the first galaxies at the end of cosmic inflation. This phenomenon has not yet been fully understood by physicists because the photons from CAT radiation have shifted into the microwave range, generating the Cos-mic Microwave Background (CMB), and the CPT radiation has transitioned into the FM range, producing the Cosmic FM Background (CFMB), which is 1013 times weaker than the CMB. This weaker signal can be confused with noise gen-erated by FM equipment, thus remaining undetected. These SBM findings offer a groundbreaking perspective on the early universe’s dynamics and the distribu-tion of cosmic matter, and dark matter origin, deepening our understanding of cosmic inflation. Consequently, we invite physicists to study, comprehend, and assess the new cosmological Shunyata beginning, proposed by the Small Bang Model.

Cosmic-ray induced ionization rates and non-thermal emissions from nuclei of starburst galaxies

ABSTRACT Cosmic rays are the only agent capable of ionizing the interior of dense molecular clouds and, thus, they are believed to play an essential role in determining the physical and chemical evolution of star-forming regions. In this work, we aim to study cosmic-ray induced ionization rates in starburst environments using non-thermal emissions of cosmic rays from starburst nuclei. To this end, we first revisit cosmic-ray models, which could explain data of non-thermal emissions from radio to X-ray and gamma-ray from nuclei of three prototypical starburst galaxies NGC 253, M82, and Arp 220. These models are then applied to predict ionization rates in starburst environments, which gives values around 10−14 s−1. Such a high value of the ionization rate, which is 2 to 3 orders of magnitude higher than the typical values found in the Milky Way, is probably due to relatively high rates of supernova explosions occurring within the nuclei of these starburst galaxies. We also discuss in more detail the case of NGC 253, where our predicted ionization rate is found to be, in most cases, a few times smaller than the values inferred from molecular line observations of clouds in the starburst nucleus. The general framework provided in this work illustrates how the use of non-thermal emission data could help to provide more insights into ionization rates or, more generally, cosmic-ray impact in starburst environments.

Organic Chemistry in the H2-bearing, CO-rich Interstellar Ice Layer at Temperatures Relevant to Dense Cloud Interiors

Ice chemistry in the dense, cold interstellar medium (ISM) is probably responsible for the formation of interstellar complex organic molecules (COMs). Recent laboratory experiments performed at T ∼ 4 K have shown that irradiation of CO:N2 ice samples analog to the CO-rich interstellar ice layer can contribute to the formation of COMs when H2 molecules are present. We have tested this organic chemistry under a broader range of conditions relevant to the interior of dense clouds by irradiating CO:15N2:H2 ice samples with 2 keV electrons in the 4–15 K temperature range. The H2 ice abundance depended on both, the ice formation temperature and the thermal evolution of the samples. Formation of H-bearing organics such as formaldehyde (H2CO), ketene (C2H2O), and isocyanic acid (H15NCO) was observed upon irradiation of ice samples formed at temperatures up to 10 K, and also in ices formed at 6 K and subsequently warmed up and irradiated at temperatures up to 15 K. These results suggest that a fraction of the H2 molecules in dense cloud interiors might be entrapped in the CO-rich layer of interstellar ice mantles, and that energetic processing of this layer could entail an additional contribution to the formation of COMs in the coldest regions of the ISM.

On the Origin of the Moon and the Continents

All astronomical bodies originate inside clouds of gas and dust, therefore there should be a common process that leads to their condensation. In a galactic cloud there is always a gradient of speeds from point to point. Thanks to it, vortices originate that rake the material of the surrounding cloud gradually forming large gaseous disks, inside which vortices of second order develop that concentrate the matter of their orbits forming smaller and much denser disks, within which third order vortices further concentrate the matter. The dense cores of these vortices finally condense in massive bodies: sun, planets and satellites. The result should be a well ordered planetary system with no “debris” around and where both planets and satellites obey to a precise rule of the distances from their central body. The solar system complies with these conditions with three main exceptions. First, in an orbit where a large planet should be there is only a huge number of scattered asteroids. Second, Earth and its moon with all evidence were not formed in the same vortex, which means that Moon originated somewhere else. Third, Neptune’s satellite system has been shattered by the intrusion of a foreign body, Triton, and its largest satellites are missing. These exceptions seem to be strictly connected to each other and all due to a unique event, that is: Triton has diverted the largest Neptune satellite towards the Sun. This satellite impacted at high speed against the missing planet, scattering myriads of fragments from its mantle and pushing it towards the sun, where it eventually fell. The planet had at least 4 satellites some of which remained in their previous orbit, but two of them were dragged towards the sun and were captured by Earth. The largest became its lonely moon while the second fell on its surface giving origin to the continents. This event happened about 3,96 billion of years ago, as it is proven by the ages of the numerous samples brought from the moon.

A Radar Reflectivity Image Prediction Method: The Spatial MIM + Pix2Pix

Radar reflectivity images have the potential to provide vital information on the development of convective cloud interiors, which can play a critical role in precipitation prediction. However, traditional prediction methods face challenges in preserving the high-frequency component, leading to blurred prediction results. To address this issue and accurately estimate radar reflectivity intensity, this paper proposes a novel reflectivity image prediction approach based on the Spatial Memory in Memory (Spatial MIM) networks and the Pix2Pix networks. Firstly, a rough radar reflectivity image prediction is made using the Spatial MIM network. Secondly, the prediction results from the Spatial MIM network are fed into the Pix2pix network, which improves the high-frequency component of the predicted image and solves the image blurring issue. Finally, the proposed approach is evaluated using data from Oklahoma in the United States during the second and third quarters of 2021. The experimental results demonstrate that the proposed approach yields more accurate radar reflectivity prediction images.

Validation and traceability of miniaturized multi-parameter cluster radiosondes used for atmospheric observations

In this work we designed and developed a cluster of light expendable radiosondes that can float passively inside warm clouds to study their micro-physical processes. This involves the tracking of both saturated and unsaturated turbulent air parcels. The aim of this new kind of observation system is to obtain Lagrangian statistics of the intense turbulence inside warm clouds and of the lower intensity turbulence that is typical of the air surrounding such clouds. Each radiosonde in a cluster includes an electronic board, which is mounted onto a small, biodegradable balloon filled with a mixture of helium and air. The cluster is able to float inside clouds for a few hours and to measure air temperature, pressure, humidity and the associated position, velocity, acceleration and magnetic field readings of each radiosonde along their trajectory.

Cold atomic gas identified by H I self-absorption

Context. Stars form in the dense interiors of molecular clouds. The dynamics and physical properties of the atomic interstellar medium (ISM) set the conditions under which molecular clouds and eventually stars form. It is, therefore, critical to investigate the relationship between the atomic and molecular gas phase to understand the global star formation process. Aims. Using the high angular resolution data from The H I/OH/Recombination (THOR) line survey of the Milky Way, we aim to constrain the kinematic and physical properties of the cold atomic hydrogen gas phase toward the inner Galactic plane. Methods. H I self-absorption (HISA) has proven to be a viable method to detect cold atomic hydrogen clouds in the Galactic plane. With the help of a newly developed self-absorption extraction routine (astroSABER), we built upon previous case studies to identify H I self-absorption toward a sample of giant molecular filaments (GMFs). Results. We find the cold atomic gas to be spatially correlated with the molecular gas on a global scale. The column densities of the cold atomic gas traced by HISA are usually on the order of 1020 cm−2 whereas those of molecular hydrogen traced by 13CO are at least an order of magnitude higher. The HISA column densities are attributed to a cold gas component that accounts for a fraction of ~5% of the total atomic gas budget within the clouds. The HISA column density distributions show pronounced log-normal shapes that are broader than those traced by H I emission. The cold atomic gas is found to be moderately supersonic with Mach numbers of approximately a few. In contrast, highly supersonic dynamics drive the molecular gas within most filaments. Conclusions. While H I self-absorption is likely to trace just a small fraction of the total cold neutral medium within a cloud, probing the cold atomic ISM by the means of self-absorption significantly improves our understanding of the dynamical and physical interaction between the atomic and molecular gas phase during cloud formation.

Comparison of the simulated outcomes of aerosol–cloud interaction by a meteorological model with and without an interactive chemistry module

With the general rise of computational capacities and the continued efforts to improve computational efficiencies, more and more studies have been utilizing state-of-the-art atmospheric models that enable cloud-resolving simulations over a global domain. Microphysical processes inside clouds, however, are on a scale much smaller than that of a cloud itself, and therefore resolving clouds in a model is not equivalent to resolving cloud microphysical processes. When aerosol–cloud interaction (ACI) is studied, chemistry models enable the prognostic calculations for chemical species, including aerosols, which can perturb cloud microphysics and eventually impact clouds and climate. The large drawback of these models is the high computational cost required for tracking chemical species in space and time that may not be affordable in some studies. As a result, some studies have used non-chemistry models with prescribed cloud droplet number concentrations n_c and compared multiple simulations with different n_c to assess the impacts of varying aerosol concentrations on clouds. In this study we assess whether the same or similar ACI can be simulated when the aerosol number is increased in a chemistry model and when n_c is raised in a non-chemistry model. A case study has been conducted over the Maritime Continent in September 2015 when an extremely large number of aerosols were observed due to fires under a dry condition brought by a strong El Niño. The comparison of the simulations by the chemistry and non-chemistry models shows that the aerosol-driven enhancement of rainfall in the chemistry simulations was not present in the non-chemistry simulations, even with prescribed n_c with certain spatial variation based on the chemistry runs. Therefore, simulated ACI may largely differ depending on the manner by which an increase or decrease of aerosols is represented in a model. The result suggests the further need for powerful computational capabilities and the pursuit of a rigorous means to incorporate aerosol species in a non-chemistry model.

Dynamics of the Cloud–Environment Interface and Turbulence Effects in an LES of a Growing Cumulus Congestus

AbstractA giga-large-eddy simulation of a cumulus congestus has been performed with a 5-m resolution to examine the fine-scale dynamics and mixing on its edges. At 5-m resolution, the dynamical production of subgrid turbulence clearly dominates over the thermal production, whereas the situation is reversed for resolved turbulence, the tipping point occurring near the 250-m scale. For cloud dynamics, the toroidal circulation already obtained in previous observational and numerical studies remains, with a strong signature on the resolved turbulent fluxes, the most important feature for the exchanges between the cloud and its environment even though numerous smaller eddies are also well resolved. The environment compensates for the upward mass flux through a large-scale compensating subsidence and the so-called subsiding shell composed of cloud-edge downdrafts, both having a significant contribution. A partition is used to characterize the dynamics, buoyancy, and turbulence of the inner and outer edges of the cloud, the cloud interior, and the far environment. On the edges of the cloud, downdrafts caused by the eddies and by evaporative cooling effects coexist with a buoyancy reversal while the cloud interior is mostly rising and positively buoyant. An alternative simulation in which evaporative cooling is suppressed indicates that this process reinforces the downdrafts near the edges of the cloud and causes a general decrease of the convective circulation. Evaporative cooling also has an impact on the buoyancy reversal and on the fate of the engulfed air inside the cloud.

The Planck Submillimeter Properties of Galactic High-mass Star-forming Regions: Dust Temperatures, Luminosities, Masses, and Star Formation Efficiency

Abstract Massive star formation occurs in the interior of giant molecular clouds and proceeds through many stages. In this work, we focus on massive young stellar objects (MYSOs) and ultracompact H ii regions (UCH ii), where the former are enshrouded in dense envelopes of dust and gas, the latter of which has begun dispersing. By selecting a complete sample of MYSOs and UCH ii from the Red MSX Source (RMS) survey database, we combine Planck and IRAS data and build their spectral energy distributions. With these, we estimate the physical properties (dust temperatures, mass, luminosity) of the sample. Because the RMS database provides unique solar distances, it also allows the instantaneous star formation efficiency (SFE) to be investigated as a function of Galactocentric radius. We find that the SFE increases between 2 and 4.5 kpc, where it reaches a peak, likely in correspondence with the accumulation of molecular material at the end of the Galactic bar. It then stays approximately constant up to 9 kpc, after which it linearly declines, in agreement with predictions from extragalactic studies. This behavior suggests the presence of a significant amount of undetected molecular gas at R G > 8 kpc. Finally, we present diagnostic colors that can be used to identify sites of massive star formation.

The initial gas-phase sulfur abundance in the Orion Molecular Cloud from sulfur radio recombination lines

The abundances of chemical elements and their depletion factors are essential parameters for understanding the composition of the gas and dust that are ultimately incorporated into stars and planets. Sulfur is an abundant but peculiar element in the sense that, despite being less volatile than other elements (e.g., carbon), it is not a major constituent of dust grains in diffuse interstellar clouds. Here, we determine the gas-phase carbon-to-sulfur abundance ratio, [C]/[S], and the [S] in a dense star-forming cloud from new radio recombination lines (RRLs) detected with the Yebes 40m telescope – at relatively high frequencies (∼40 GHz ≃ 7 mm) and angular resolutions (down to 36″) – in the Orion Bar, a rim of the Orion Molecular Cloud (OMC). We detect nine Cnα RRLs (with n = 51–59) as well as nine narrow line features separated from the Cnα lines by δv = −8.4 ± 0.3 km s−1. Based on this velocity separation, we assign these features to sulfur RRLs, with little contribution of RRLs from the more condensable elements Mg, Si, or Fe. Sulfur RRLs lines trace the photodissociation region of the OMC. In these neutral gas layers, up to AV ≃ 4, the ions C+ and S+ lock in most of the C and S gas-phase reservoir. We determine a relative abundance of [C]Ori/[S]Ori = 10.4 ± 0.6 and, adopting the same [C]Ori measured in the translucent gas toward star θ1 Ori B, an absolute abundance of [S]Ori = (1.4 ± 0.4)⋅10−5. This value is consistent with emission models of the observed sulfur RRLs if N(S+) ≃ 7⋅1017 cm−2 (beam-averaged). The [S]Ori is the “initial” sulfur abundance in the OMC, before an undetermined fraction of the [S]Ori goes into molecules and ice mantles in the cloud interior. The inferred abundance [S]Ori matches the solar abundance, thus implying that there is little depletion of sulfur onto rocky dust grains, with D(S) = 0.0 ± 0.2 dex.

Live pine pollen in rainwater: reconstructing its long-range transport

Raindrops brim with pollen even when there is no ambient local pollen. How does this nonlocal pollen get inside rain? The likely answer is long-range transport beneath or inside clouds. To test this hypothesis, we captured rain-delivered pollen on Ocracoke Island, NC, USA over a 12-day interval before local pine pollen release then reconstructed its trajectory and its atmospheric exposure conditions. Findings were as follows: four rain episodes yielded a total of 632 pollen grains of which 6.7% germinated. To find pollen sources, we first identified pollen-releasing forested areas using a predictive heat sum equation for each rain episode. Next, we constructed the backward trajectory for air parcels carrying rain-delivered pollen from those forests using the MLDP atmospheric transport and dispersion model. Nonlocal sources were located at distances up to 300 km from Ocracoke Island and distances lessened with each successive episode. Below-cloud transport time was 8 and 17 h for Episodes A and B, respectively. Pollen grains were exposed to harsh atmospheric conditions during below-cloud transport, yet some grains still germinated. Atmospheric turbulence patterns changed for each episode, so distance from pollen source was poorly correlated with pollen transport time. Pollen germination was not closely correlated with either distances or transport time. In-cloud transport was more likely for pollen sampled during Episodes C and D. Pine pollen, although rarely allergenic, brings fresh insights into how atmospheric events can trigger human respiratory distress.

Hectometric-scale simulations of a Mediterranean heavy-precipitation event during the Hydrological cycle in the Mediterranean Experiment (HyMeX) first Special Observation Period (SOP1)

Abstract. Offshore convection occurred over the Mediterranean sea on 26 October 2012 and was well documented during the first Special Observation Period (SOP1) of the Hydrological cycle in the Mediterranean Experiment (HyMeX). This paper analyses the triggering and organizing factors involved in this convection case study, and examines how they are simulated and represented at hectometric resolutions. For that purpose, a large-eddy simulation (LES) of this real case study is carried out with a 150 m horizontal resolution over a large domain encompassing the convective systems and the low-level flow feeding convection over the sea. This LES is then compared to a reference simulation performed with a 450 m grid spacing in the heart of the so-called “grey zone” of turbulence modelling. An increase in horizontal resolution from 450 down to 150 m is unable, for this case study, to reduce significantly deficiencies of the simulation; this is more related to an issue of initial and lateral boundary conditions. Indeed, some of the triggering factors, such as a converging low-level flow driven by a surface low-pressure system, are simulated quite similarly for both simulations. However, differences for other mechanisms still exist since greater surface precipitation amounts are simulated at 450 m. It is found that the entrainment process, characterized by small eddies at the cloud edges, is strongly underestimated at 450 m horizontal resolution, missing the mixing with the environmental air. Therefore, too rapid a development of deep convection is simulated at this horizontal resolution, associated with fast-track microphysical processes and enhanced dynamics. By contrast, at 150 m horizontal resolution, the updraught cores are mainly resolved, as are the subsiding shell, while subgrid eddies, produced by dynamical processes, are localized at the cloud interior edges, better representing the entrainment process. Furthermore, this first LES of a real Mediterranean precipitating case study highlights a convective organization with very fine-scale features within the converging low-level flow, features that are definitively out of range of models with kilometric horizontal resolutions.

ALMA CO Observations of the Gamma-Ray Supernova Remnant RX J1713.7–3946: Discovery of Shocked Molecular Cloudlets and Filaments at 0.01 pc Scales

Abstract RX J1713.7−3946 is a unique core-collapse supernova remnant (SNR) that emits bright TeV gamma-rays and synchrotron X-rays caused by cosmic rays, in addition to interactions with interstellar gas clouds. We report here on results of Atacama Large Millimeter/submillimeter Array 12CO(J = 1–0) observations toward the northwestern shell of the SNR. We newly found three molecular complexes consisting of dozens of shocked molecular cloudlets and filaments with typical radii of ∼0.03–0.05 pc and densities of ∼104 cm−3. These cloudlets and filaments are located not only along synchrotron X-ray filaments, but also in the vicinity of X-ray hotspots with month- or year-scale time variations. We argue that X-ray hotspots and filaments were generated by shock–cloudlet interactions through magnetic-field amplification up to mG. The interstellar medium density contrast of ∼105, coexistence of molecular cloudlets and low-density diffuse medium of ∼0.1 cm−3, is consistent with such a magnetic field amplification as well as a wind-bubble scenario. The small-scale cloud structures also affect hadronic gamma-ray spectra considering the magnetic field amplification on surface and inside clouds.

Stochastic Design and Analysis of User-Centric Wireless Cloud Caching Networks

This paper develops a stochastic geometry-based approach for the modeling, analysis, and optimization of wireless cloud caching networks comprised of multiple-antenna radio units (RUs) inside clouds with coordinated multi-point transmissions and guard zones. We consider Poisson cluster processes to model RUs and users, and the probabilistic content placement to cache files in RUs. Accordingly, we study the exact hit probability for a user of interest for two strategies; closest selection, where the user is served by the closest RU that has its requested file, and best power selection, where the serving RU having the requested file provides the maximum instantaneous received power at the user. As key steps for the analyses, the Laplace transform of out of cloud interference, the desired link distance distribution in the closest selection, and the desired link received power distribution in the best power selection are derived. Also, we approximate the derived exact hit probabilities for both the closest and the best power selections in such a way that the related objective functions for the content caching design of the network can lead to tractable concave optimization problems. Solving the optimization problems, we propose algorithms to efficiently find their optimal content placements. Finally, we investigate the impact of different parameters on the caching performance.

Extensive layer clouds in the global electric circuit: their effects on vertical charge distribution and storage.

A fair-weather electric field has been observed near the Earth's surface for over two centuries. The field is sustained by charge generation in distant disturbed weather regions, through current flow in the global electric circuit. Conventionally, the fair-weather part of the global circuit has disregarded clouds, but extensive layer clouds, important to climate, are widespread globally. Such clouds are not electrically inert, becoming charged at their upper and lower horizontal boundaries from vertical current flow, in a new electrical regime—neither fair nor disturbed weather; hence it is described here as semi-fair weather. Calculations and measurements show the upper cloud boundary charge is usually positive, the cloud interior positive and the lower cloud boundary negative, with the upper charge density larger, but of the same magnitude (∼nC m−2) as cloud base. Globally, the total positive charge stored by layer clouds is approximately 105 C, which, combined with the positive charge in the atmospheric column above the cloud up to the ionosphere, balances the total negative surface charge of the fair-weather regions. Extensive layer clouds are, therefore, an intrinsic aspect of the global circuit, and the resulting natural charging of their cloud droplets is a fundamental atmospheric feature.

Photon-induced desorption of larger species in UV-irradiated methane ice

ABSTRACT At the low temperatures found in the interior of dense clouds and circumstellar regions, along with H2O and smaller amounts of species such as CO, CO2 or CH3OH, the infrared features of CH4 have been observed on icy dust grains. Ultraviolet (UV) photons induce different processes in ice mantles, affecting the molecular abundances detected in the gas phase. This work aims to understand the processes that occur in a pure CH4 ice mantle subjected to UV irradiation. We studied photon-induced processes for the different photoproducts arising in the ice upon UV irradiation. Experiments were carried out in ISAC, an ultra-high vacuum chamber equipped with a cryostat and an F-type UV lamp reproducing the secondary UV field induced by cosmic rays in dense clouds. Infrared spectroscopy and quadrupole mass spectrometry were used to monitor the solid and gas phases, respectively, during the formation, irradiation and warming-up of the ice. Direct photodesorption of pure CH4 was not observed. UV photons form CHx· and H· radicals, leading to photoproducts such as H2, C2H2, C2H6 and C3H8. Evidence for the photodesorption of C2H2 and photochemidesorption of C2H6 and C3H8 was found; the latter species is so far the largest molecule found to photochemidesorb. 13CH4 experiments were also carried out to confirm the reliability of these results.

CHIMPS: physical properties of molecular clumps across the inner Galaxy

The latest generation of high-angular-resolution unbiased Galactic plane surveys in molecular-gas tracers are enabling the interiors of molecular clouds to be studied across a range of environments. The CO Heterodyne Inner Milky Way Plane Survey (CHIMPS) simultaneously mapped a sector of the inner Galactic plane, within 27.8° ≲ ℓ ≲ 46.2° and |b|≤ 0°.5, in 13CO (3–2) and C18O (3–2) at an angular resolution of 15 arcsec. The combination of the CHIMPS data with 12CO (3–2) data from the CO High Resolution Survey (COHRS) has enabled us to perform a voxel-by-voxel local-thermodynamic-equilibrium (LTE) analysis, determining the excitation temperature, optical depth, and column density of 13CO at each ℓ, b, v position. Distances to discrete sources identified by FELLWALKER in the 13CO (3–2) emission maps were determined, allowing the calculation of numerous physical properties of the sources, and we present the first source catalogues in this paper. We find that, in terms of size and density, the CHIMPS sources represent an intermediate population between large-scale molecular clouds identified by CO and dense clumps seen in thermal dust continuum emission, and therefore represent the bulk transition from the diffuse to the dense phase of molecular gas. We do not find any significant systematic variations in the masses, column densities, virial parameters, mean excitation temperature, or the turbulent pressure over the range of Galactocentric distance probed, but we do find a shallow increase in the mean volume density with increasing Galactocentric distance. We find that inter-arm clumps have significantly narrower linewidths, and lower virial parameters and excitation temperatures than clumps located in spiral arms. When considering the most reliable distance-limited subsamples, the largest variations occur on the clump-to-clump scale, echoing similar recent studies that suggest that the star-forming process is largely insensitive to the Galactic-scale environment, at least within the inner disc.