Cloud Encounters Research Articles

Monte Carlo Predictions of Aero-Engine Performance Degradation Due to Particle Ingestion

Aero-engines, which encounter clouds of airborne particulate, experience reduced performance due to the deposition of particles on their high-pressure turbine nozzle guide vanes. The rate of this degradation depends on particle properties, engine operating state and the duration of exposure to the particle cloud, variables that are often unknown or poorly constrained, leading to uncertainty in model predictions. A novel method coupling one-dimensional gas turbine performance analysis with generalised predictions of particle deposition is developed and applied through the use of Monte Carlo simulations to better predict high-pressure turbine degradation. This enables a statistical analysis of deterioration from which mean performance losses and confidence intervals can be defined, allowing reductions in engine life and increased operational risk to be quantified. The method is demonstrated by replicating two particle cloud encounter events for the Rolls-Royce RB211-524C engine and is used to predict empirical particle properties by correlating measured engine performance data with Monte Carlo model inputs. Potential improvements in the confidence of these predictions due to more tightly constrained input and validation data are also demonstrated. Finally, the potential combination of the Monte Carlo coupled degradation model with in-service engine performance data and particle properties determined through remote or in situ sensing is outlined and its role in a digital twin to enable a predictive approach to operational capability is discussed.

Discovery of Magellanic Stellar Debris in the H3 Survey

Abstract We report the discovery of 15 stars in the H3 survey that lie, in projection, near the tip of the trailing gaseous Magellanic Stream (MS). The stars have Galactocentric velocities <−155 km s−1, Galactocentric distances of ≈40 to 80 kpc (increasing along the MS), and [Fe/H] consistent with that of stars in the Small Magellanic Cloud. These 15 stars comprise 94% (15 of 16) of the H3 observed stars to date that have R GAL > 37.5 kpc, −350 km s−1 < V GSR < −155 km s−1, and are not associated with the Sagittarius Stream. They represent a unique portion of the Milky Way’s outer halo phase space distribution function and confirm that unrelaxed structure is detectable even at radii where H3 includes only a few hundred stars. Due to their statistical excess, their close association with the MS and HI compact clouds in the same region, both in position and velocity space, and their plausible correspondence with tidal debris in a published simulation, we identify these stars as debris of past Magellanic Cloud encounters. These stars are evidence for a stellar component of the tidal debris field far from the Clouds themselves and provide unique constraints on the interaction.

Cross‐Scale Quantification of Storm‐Time Dayside Magnetospheric Magnetic Flux Content

AbstractA clear understanding of storm‐time magnetospheric dynamics is essential for a reliable storm forecasting capability. The dayside magnetospheric response to an interplanetary coronal mass ejection (ICME; dynamic pressure Pdyn > 20 nPa and storm‐time index SYM‐H < −150 nT) is investigated using in situ OMNI, Geotail, Cluster, MMS, GOES, Van Allen Probes, and THEMIS measurements. The dayside magnetic flux content is directly quantified from in situ magnetic field measurements at different radial distances. The arrival of the ICME, consisting of shock and sheath regions preceding a magnetic cloud, initiated a storm sudden commencement (SSC) phase (SYM‐H ~ +50 nT). At SSC, the magnetopause standoff distance was compressed earthward at ICME shock encounter at an average rate ~−10.8 Earth radii per hour for ~10 min, resulting in a rapid 40% reduction in the magnetospheric volume. The “closed” magnetic flux content remained constant at 170 ± 30 kWb inside the compressed dayside magnetosphere, even in the presence of dayside reconnection, as evident by an outsized flux transfer event containing 160 MWb. During the storm main and recovery phases, the magnetosphere expanded. The dayside magnetic flux did not remain constant within the expanding magnetosphere (110 ± 30 kWb), resulting in a 35% reduction in pre‐storm flux content during the magnetic cloud encounter. At that stage, the magnetospheric magnetic flux was eroded resulting in a weakened dayside magnetospheric field strength at radial distances R ≥ 5 RE. It is concluded that the inadequate replenishment of the eroded dayside magnetospheric flux during the magnetosphere expansion phase is due to a time lag in storm‐time Dungey cycle.

Mitigating X2‐AP interface cost using quantum teleportation

Many problems in cellular communications cannot be solved classically. Due to its robustness, quantum computing can enrich the classical with other dimensions, security and cryptic-natured. However, the awareness about how to fully bridge the classical and quantum communications is not fully realised. In other words, the quantum phenomena are not totally utilised within the classical dimension. This work rather discusses directions and evaluations for future quantum solutions to traditional cloud mobile networks. Particularly, using quantum correlation phenomena to enhance the performance of X2 application protocol (X2-AP) by reducing the signalling overhead regarding the delay and power consumption that classical cloud encounter. Through modelling the latency of both paradigms using ‘MATLAB’, this work promises a delay reduction when adapting quantum method into the cloud. This study also models the power consumption and energy efficiency of traditional and quantum-based cloud networks. This work also shows, via modelling the power consumption, that installing a quantum-based paradigm is not a power costly method; rather, it shows identical power and energy efficiency figures with a possibility of improvement.

Cloud Encounter Impact on Operational and Economical Effectiveness of Hybrid-Laminar-Flow-Control Aircraft

Hybrid laminar flow control (HLFC) on transport aircraft is one of many promising fuel reduction technologies. However, due to high sensitivities of HLFC toward operational boundary conditions, estimations of its overall benefit are usually afflicted with large uncertainties. Among the critical environmental factors is the degradation of laminarity when flying through clouds at high altitudes. This paper provides an assessment on operational and economical effectiveness of HLFC aircraft with a detailed inclusion of the cloud encounter effect in three steps. First the expected time in cloud (TIC) in a real route network with cloud data given by the European Centre for Medium-Range Weather Forecast is analyzed, yielding an average TIC of 10%. Subsequently, HLFC fuel efficiency with and without considering the cloud effect on mid- to long-range aircraft is dealt with. Results show an average drop of fuel benefit from 12.8 to 12.0% due to clouds. The effectiveness of lateral route optimization to reduce the impact of clouds is investigated in the last analysis. Outcomes show that these mitigation strategies are economically beneficial for few cases only. The overall picture confirms that cloud encounter must not be neglected when assessing aircraft with HLFC.

The Long-term Evolution of Star Clusters Formed with a Centrally Peaked Star Formation Efficiency Profile

Abstract We have studied the long-term evolution of star clusters of the solar neighborhood, starting from their birth in gaseous clumps until their complete dissolution in the Galactic tidal field. We have combined the “local-density-driven cluster formation model” of Parmentier & Pfalzner with direct N-body simulations of clusters following instantaneous gas expulsion. We have studied the relation between cluster dissolution time, t dis, and cluster “initial” mass, M init, defined as the cluster mass at the end of the dynamical response to gas expulsion (i.e., violent relaxation), when the cluster age is 20–30 Myr. We consider the “initial” mass to be consistent with other works that neglect violent relaxation. The model clusters formed with a high star formation efficiency (SFE, i.e., gas mass fraction converted into stars) follow a tight mass-dependent relation, in agreement with previous theoretical studies. However, the low-SFE models present a large scatter in both the “initial” mass and the dissolution time, a shallower mass-dependent relation than high-SFE clusters, and most dissolve within 1 Gyr (cluster teenage mortality). Both groups differ in their structural properties on average. Combining two populations of clusters, high- and low-SFE ones, with domination of the latter, yields a cluster dissolution time for the solar neighborhood in agreement with that inferred from observations, without any additional destructive processes such as giant molecular cloud encounters. An apparent mass-independent relation may emerge for our low-SFE clusters when we neglect low-mass clusters (as expected for extragalactic observations), although more simulations are needed to investigate this aspect.

System analysis of aircraft with natural laminar flow and forward swept wings

The objective of this paper is an enhanced analysis and assessment of a short-to-medium range aircraft configuration with natural laminar flow (NLF) and forward swept wings (FSW) designed by DLR. It is intended to show how the proposed aircraft concept could contribute to a more economic and ecologic operation. By implementing a multidisciplinary simulation and assessment framework, the net-benefit on air transportation system level is evaluated from airline perspective under consideration of realistic airline network conditions. Therefore operational aspects (e.g. stage length) and environmental factors (e.g. insect contamination, cloud encounter) which affect the aircraft effectiveness are included into the assessment. Apart from modeling the technology intended effect of fuel saving on airline economics, the study also aims to determine unintentional repercussions (e.g. change in maintenance effort, emissions, noise) which arise due to the design and the operation of the FSW–NLF concept. The overall goal of the paper is to provide aircraft operators with a better understanding of the behavior of NLF aircraft under realistic operational boundary conditions as well as to demonstrate resulting trade-offs between economical and ecological effectiveness.

End-cretaceous cooling and mass extinction driven by a dark cloud encounter

We have identified iridium in an ~5m-thick section of pelagic sediment cored in the deep sea floor at Site 886C, in addition to a distinct spike in iridium at the K–Pg boundary related to the Chicxulub asteroid impact. We distinguish the contribution of the extraterrestrial matter in the sediments from those of the terrestrial matter through a Co–Ir diagram, calling it the “extraterrestrial index” fEX. This new index reveals a broad iridium anomaly around the Chicxulub spike. Any mixtures of materials on the surface of the Earth cannot explain the broad iridium component. On the other hand, we find that an encounter of the solar system with a giant molecular cloud can aptly explain the component, especially if the molecular cloud has a size of ~100pc and the central density of over 2000protons/cm3. Kataoka et al. (2013, 2014) pointed that an encounter with a dark cloud would drive an environmental catastrophe leading to mass extinction. Solid particles from the hypothesized dark cloud would combine with the global environment of Earth, remaining in the stratosphere for at least several months or years. With a sunshield effect estimated to be as large as −9.3Wm−2, the dark cloud would have caused global climate cooling in the last 8Myr of the Cretaceous period, consistent with the variations of stable isotope ratios in oxygen (Barrera and Huber, 1990; Li and Keller, 1998; Barrera and Savin, 1999; Li and Keller, 1999) and strontium (Barrera and Huber, 1990; Ingram, 1995; Sugarman et al., 1995). The resulting growth of the continental ice sheet also resulted in a regression of the sea level. The global cooling, which appears to be associated with a decrease in the diversity of fossils, eventually led to the mass extinction at the K–Pg boundary.

The Nebula Winter: The united view of the snowball Earth, mass extinctions, and explosive evolution in the late Neoproterozoic and Cambrian periods

Encounters with nebulae, such as supernova remnants and dark clouds in the galaxy, can lead to an environmental catastrophe on the Earth through the negative climate forcings and destruction of the ozone layer by enhanced fluxes of cosmic rays and cosmic dust particles. A resultant reduction in primary productivity leads to mass extinctions through depletion of oxygen and food starvations as well as anoxia in the ocean. The model shows three levels of hierarchical time variations caused by supernova encounters (1–10kyrs), dark cloud encounters (0.1–10Myrs), and starbursts (~100Myrs), respectively. This “Nebula Winter” model can explain the catastrophic phenomena such as snowball Earth events, repeated mass extinctions, and Cambrian explosion of biodiversities which took place in the late Proterozoic era through the Cambrian period. The Late Neoproterozoic snowball Earth event covers a time range of ca. 200Myrs long spanning from 770Ma to the end of Cambrian period (488Ma) with two snowball states called Sturtian and Marinoan events. Mass extinctions occurred at least eight times in this period, synchronized with large fluctuations in δ13C of carbonates in the sediment. Each event is likely to correspond to each nebula encounter. In other words, the late Neoproterozoic snowball Earth and Cambrian explosion are possibly driven by a starburst, which took place around 0.6Ga in the Milky Way Galaxy. The evidences for a Nebula Winter can be obtained from geological records in sediment in the deep oceans at those times.

Satellite detection of hazardous volcanic clouds and the risk to global air traffic

Remote sensing instruments have been used to identify, track and in some cases quantify atmospheric constituents from space-borne platforms for nearly 30 years. These data have proven to be extremely useful for detecting hazardous ash and gas (principally SO2) clouds emitted by volcanoes and which have the potential to intersect global air routes. The remoteness of volcanoes, the sporadic timings of eruptions and the ability of the upper atmosphere winds to quickly spread ash and gas, make satellite remote sensing a key tool for developing hazard warning systems. It is easily recognized how powerful these tools are for hazard detection and yet there has not been a single instrument designed specifically for this use. Instead, researchers have had to make use of instruments and data designed for other purposes. In this article the satellite instruments, algorithms and techniques used for ash and gas detection are described from a historical perspective with a view to elucidating their value and shortcomings. Volcanic clouds residing in the mid- to upper-troposphere (heights above 5 km) have the greatest potential of intersecting air routes and can be dispersed over many 1,000s of kilometres by the prevailing winds. Global air traffic vulnerability to the threat posed by volcanic clouds is then considered from the perspectives of satellite remote sensing, the upper troposphere mean wind circulation, and current and forecast air traffic density based on an up-to-date aircraft emissions inventory. It is concluded that aviation in the Asia Pacific region will be increasingly vulnerable to volcanic cloud encounters because of the large number of active volcanoes in the region and the increasing growth rate of air traffic in that region. It is also noted that should high-speed civil transport (HSCT) aircraft become operational, there will be an increased risk to volcanic debris that is far from its source location. This vulnerability is highlighted using air traffic density maps based on NOx emissions and satellite SO2 observations of the spread of volcanic clouds.

Tracking volcanic sulfur dioxide clouds for aviation hazard mitigation

Satellite measurements of volcanic sulfur dioxide (SO2) emissions can provide critical information for aviation hazard mitigation, particularly when ash detection techniques fail. Recent developments in space-based SO2 monitoring are discussed, focusing on daily, global ultraviolet (UV) measurements by the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite. OMI’s high sensitivity to SO2 permits long-range tracking of volcanic clouds in the upper troposphere and lower stratosphere (UTLS) and accurate mapping of their perimeters to facilitate avoidance. Examples from 2006 to 2007 include eruptions of Soufriere Hills (Montserrat), Rabaul (Papua New Guinea), Nyamuragira (DR Congo), and Jebel at Tair (Yemen). A tendency for some volcanic clouds to occupy the jet stream suggests an increased threat to aircraft that exploit this phenomenon. Synergy between NASA A-Train sensors such as OMI and the Atmospheric Infrared Sounder (AIRS) on the Aqua satellite can provide critical information on volcanic cloud altitude. OMI and AIRS SO2 data products are being produced in near real-time for distribution to Volcanic Ash Advisory Centers (VAACs) via a NOAA website. Operational issues arising from these improved SO2 measurements include the reliability of SO2 as proxy for co-erupted ash, the duration of VAAC advisories for long-lived volcanic clouds, and the potential effects of elevated concentrations of SO2 and sulfate aerosol in ash-poor clouds on aircraft and avionics (including cumulative effects after multiple inadvertent transits through dilute clouds). Further research is required in these areas. Aviation community assistance is sought through continued reporting of sulfurous odors or other indications of diffuse volcanic cloud encounters, in order to validate the satellite retrievals.

Condensed‐phase nitric acid in a tropical subvisible cirrus cloud

In situ observations in a tropical subvisible cirrus cloud during the Costa Rica Aura Validation Experiment on 2 February 2006 show the presence of condensed‐phase nitric acid. The cloud was observed near the tropopause at altitudes of 16.3–17.7 km in an extremely cold (183–191 K) and dry (<5 ppm H2O) air mass. Relative humidities with respect to ice ranged from 150–250% throughout most of the cloud. Optical particle measurements indicate the presence of ice crystals as large as 90 μm in diameter. Condensed HNO3/H2O molar ratios observed in the cloud particles were 1–2 orders of magnitude greater than ratios observed previously in cirrus clouds at similar HNO3 partial pressures. Nitric acid trihydrate saturation ratios were 10 or greater during much of the cloud encounter, indicating that HNO3 may be present in the cloud particles as a stable condensate and not simply physically adsorbed on or trapped in the particles.

In-situ aircraft observations of the 2000 Mt. Hekla volcanic cloud: Composition and chemical evolution in the Arctic lower stratosphere

An instrumented NASA aircraft made comprehensive, in-situ measurements of trace gas concentrations and aerosol properties while flying through the eruptive cloud from Mt. Hekla in February and March, 2000. The data reveal novel aspects of the properties and evolution of the volcanic cloud in the lower arctic stratosphere. Thirty-five hours after the initial, sub-Plinian explosion on February 26, 2000, the aircraft intersected the cloud at an altitude of 11.3 km. SO 2 concentrations in the cloud exceeded 1 ppmv, but no H 2S was observed. Large HF concentrations of ∼50 ppbv were nearly equal to the HCl concentration, the same ratio of halogen species adsorbed on fallen ash. Although reactive nitrogen species are rarely detected in volcanic clouds, significant HNO 3 concentrations of 3 ppbv above background were measured. A bimodal aerosol size distribution with total number densities exceeding 8000 particles/cm 3 and total aerosol volume of 65 μm 3/cm 3 was observed. Approximately 1/3 of the fine aerosol particles were non-volatile (volcanic ash) and the remaining 2/3 were volatile (sulfate aerosol and ice). The volcanic cloud was highly structured with clearly delineated boundaries. In the 18-day period following the initial eruption, increases in SO 2, sulfate aerosol, HCl, and HF volume mixing ratios were again detected. Analysis of the partitioning of sulfur between the gas and aerosol phases in these later cloud encounters shows that the rate of SO 2 oxidation to sulfuric acid was broadly consistent with changing OH concentrations at the time of the vernal equinox.

The molecular clouds in the environs of the supernova remnants G349.7+0.2 and G18.8+0.3

We present the results of a new high-resolution study of the molecular gas associated with the supernova remnants (SNRs) G349.7+0.2 and G18.8+0.3. The observations were performed with the SEST telescope in the 12 CO J = 1-0, 2-1 and 3-2 lines (beams of 45, 23 and 15, respectively). The present observations have provided, for the two SNRs, new evidence in support of the existence of physical interaction between the SN shocks and the adjoining molecular clouds. In the case of G349.7+0.2, the new observations revealed for the first time the internal structure of the shocked cloud, as well as the kinematical consequences of the impact of the SNR shock on the molecular cloud. From these observations we were able to constrain the conditions of the pre-shocked gas. The molecular cloud associated with G349.7+0.2, centered near ν LSR = +16.2 km s -1 , has a linear size of about 7 pc, a mass of ∼10 4 M ○. and a volume density of ∼10 3 cm -3 . The high line ratios derived are indicative of the existence of shocks in the cloud. From the asymmetries observed in the line shapes we propose that the SN shock cloud is running into the denser part of the cloud and has probably begun to disrupt it, pushing the eastern component clumps away from us, and the western fragments toward us. After comparing our estimates of the column density of the intervening gas with similar calculations based on ASCA X-rays spectral fitting we conclude that the best way to make these results compatible is by assuming that the associated cloud is placed behind G349.7+0.2 along the line of sight, and the SNR/molecular cloud encounter is taking place on the far side of the SNR. This model also provides a natural explanation for the lack of strong X-ray absorption in the central region of G349.7+0.2. Evaporation of part of the associated cloud must be responsible for the central X-ray emission. The comparison with IRAS infrared data provides additional support for the hypothesis of SNR/cloud physical interaction. From the study of the molecular gas in the neighborhood of the five OH (1720 MHz) masers detected in G349.7+0.2 we find that in three cases the maser peak velocity coincides with the local CO peak velocity, while in the remaining two cases the maser peak velocity agrees with a secondary, blended CO component. We conclude that the masers are excited at the sites where a non-dissociative C-type shock, locally transverse to the line of sight (or forming a large angle with it), hits a denser molecular clump. For the SNR G18.8+0.3, the new higher resolution observations have revealed excellent morphological agreement between one of the cloud components and the SNR shock front towards the eastern limb. The associated molecular mass is estimated to be ∼4.4 x 10 4 M ○. and the cloud volume density ∼1200 cm -3 . The analysis of the line ratios in this case revealed a maximum of R 2-1/1-0 = 1.25 at a position that exactly matches an indentation in the radio continuum emission in the remnant's shell, providing additional evidence of SNR/molecular cloud interaction.

Nitric acid uptake on subtropical cirrus cloud particles

The redistribution of HNO3 via uptake and sedimentation by cirrus cloud particles is considered an important term in the upper tropospheric budget of reactive nitrogen. Numerous cirrus cloud encounters by the NASA WB‐57F high‐altitude research aircraft during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers‐Florida Area Cirrus Experiment (CRYSTAL‐FACE) were accompanied by the observation of condensed‐phase HNO3 with the NOAA chemical ionization mass spectrometer. The instrument measures HNO3 with two independent channels of detection connected to separate forward and downward facing inlets that allow a determination of the amount of HNO3 condensed on ice particles. Subtropical cirrus clouds, as indicated by the presence of ice particles, were observed coincident with condensed‐phase HNO3 at temperatures of 197–224 K and pressures of 122–224 hPa. Maximum levels of condensed‐phase HNO3 approached the gas‐phase equivalent of 0.8 ppbv. Ice particle surface coverages as high as 1.4 × 1014 molecules cm−2 were observed. A dissociative Langmuir adsorption model, when using an empirically derived HNO3 adsorption enthalpy of −11.0 kcal mol−1, effectively describes the observed molecular coverages to within a factor of 5. The percentage of total HNO3 in the condensed phase ranged from near zero to 100% in the observed cirrus clouds. With volume‐weighted mean particle diameters up to 700 μm and particle fall velocities up to 10 m s−1, some observed clouds have significant potential to redistribute HNO3 in the upper troposphere.

Summary of the cloud chemistry modeling intercomparison: Photochemical box model simulation

We report results of a cloud chemistry numerical modeling intercomparison, which shows good agreement among gas‐aqueous photochemistry box models that are being used in the community. For the case studied, cloud chemistry depleted concentrations of CH2O, CH3OOH, HNO3, and O3, while H2O2 (in the absence of sulfur chemistry), NO, and NO2 increased. Because parcels of air usually flow in and out of cloud in a matter of minutes rather than remain in cloud for an hour, an optional simulation was performed in which frequent brief cloud encounters were represented. Representing a cloud intermittently rather than continuously does not alter the total concentration of many of the species. However CH2O and HCOOH concentrations are decreased and increased, respectively, because of the timing of the CH2O production during clear‐sky intervals and its destruction during cloudy intervals. Further differences between a continuous cloud simulation and an intermittent cloud simulation are expected if pH is allowed to vary during the cloud periods. Simulating an intermittent cloud brought out the importance of using a chemistry time step that is a multiple of the cloud time step because deviations of results from a simulation in which the chemistry time step did not coincide with the appearance and disappearance of cloud were quite large. To better quantify the effect of cloud on HOx photochemistry, future investigations should include nonmethane hydrocarbon and sulfur chemistry. Future cloud chemistry modeling intercomparisons should bring in cloud physical and chemical measurements so that the models can be evaluated with observations.

The Polarised Bent Jet of 3C 43

AbstractRadio observations of linear polarisation provide a useful probe of the physical conditions in the gaseous environments of compact steep spectrum (CSS) sources. Here, we present polarimetric VLBA observations at 8.4 GHz of the CSS quasar 3C 43. The jet in this source curves gently up to about 220 mas from the core, at which point it bends sharply, probably due to a jet–cloud encounter. Regions of polarised emission are detected along the jet, while the core component shows no significant polarisation.

Potential fuel savings due to hybrid laminar flow control under operational conditions

Hybrid laminar flow control (HLFC) is an active drag reduction technique that permits extended laminar flow on an aircraft surface and thus offers the potential for significant fuel savings. This is at the expense of an increase in system weight and specific fuel consumption. An overview of HLFC system failure types and consequences is presented as an introduction to this study, which investigated the impact of a potential loss of laminar flow due to flight in cirrus clouds. At typical cruising altitudes, the ice crystals are of a sufficient size and may result in sufficient particle flux to cause a temporary transition of the boundary layer. A computer performance model of a twin engine aircraft in the class of the Boeing 757 has been used to study the impact of alternative fuel planning scenarios on the fuel consumed by a HLFC aircraft, taking into account a model of probable cloud encounter. Based on the models, the study showed that if the fuel planning assumed 25% time-in-cloud (TIC) during the cruise, then in the extreme case of 55% TIC during the cruise, the contingency fuel (taken as 3% of the trip fuel), would be sufficient for the aircraft to complete the mission (including the alternate leg and hold).

Chance encounter with a stratospheric kerosene rocket plume from Russia over California

A high‐altitude aircraft flight on April 18, 1997, detected an enormous aerosol cloud at 20 km altitude near California (37°N). Not visually observed, the cloud had high concentrations of soot and sulfate aerosol, and was over 180 km in horizontal extent. The cloud was probably a large hydrocarbon‐fueled rocket vehicle, most likely burning liquid oxygen and kerosene. One of two Russian Soyuz rockets could have produced the cloud: a launch from the Baikonur Cosmodrome, Kazakhstan on April 6; or one from Plesetsk, Russia on April 9. Parcel trajectories and long‐lived trace gas concentrations suggest the Baikonur launch as the cloud source. Cloud trajectories do not trace the Soyuz plume from Asia to North America, illustrating the uncertainties of point‐to‐point trajectories. This cloud encounter is the only stratospheric measurement of a hydrocarbon‐fueled rocket.

Linear kinetic theory of instabilities of a gravitatingstellar disk

Linear kinetic theory is developed to describe collective oscillations (and their instabilities) propagating in a rapidly rotating disk of stars, representing a highly flattened galaxy. The analysis is carried out for the special case of a self-gravitating, infinitesimally thin, and spatially inhomogeneous system, taking into account the effects both of thermal movements of stars and of gravitational encounters between stars and giant molecular clouds of an interstellar medium. The star–cloud encounters are described with the use of the Landau collision integral. The dynamics of gravity perturbations with rare interparticle encounters is considered. Such a disk is treated by employing the well elaborated mathematical formalisms from plasma perturbation theory using normal-mode analysis. In particular, the method of solving the Boltzmann equation is applied by integration along paths, neglecting the influence of star–cloud encounters on the distribution of stars in the zeroth-order approximation. We are especially interested in important kinetic effects due to wave–star resonances, which we have little knowledge about. The kinetic effects are introduced via a minor drift motion of stars which is computed from the equations of stellar motion in an unperturbed central force field of a galaxy. The dispersion laws for two main branches of disk's oscillations, that is the classical Jeans branch and an additional gradient branch, are deduced. The resonant Landau-type instabilities of hydrodynamically stable Jeans and gradient gravity perturbations is considered to be a long-term generating mechanism for propagating density waves, thereby leading to spiral-like and/or ring-like patterns in the flat galaxies.