A Diagnostic Study of the Global Distribution of Contrails, Part II: Future Air Traffic Scenarios

The global distribution of the contrail coverage is computed for several scenarios of aviation in the years 2015 and 2050 and compared to 1992 using meteorological analysis data representative of present temperature and humidity conditions and assuming 0.5% cover in a reference region 30° W–30° E, 35° N–75° N covering parts of western Europe and the North Atlantic. The mean contrail coverage of the Earth is computed to increase by a factor of about three compared to 1992 and to reach 0.25% in 2015. For three different scenarios of aviation and for constant climatic conditions, the global mean contrail coverage reaches values between 0.26% and 0.75% for 2050. Contrail coverage increases more strongly than total fuel burn mainly because of more traffic in the upper troposphere and because of more efficient engines with cooler exhaust. The overall efficiency of propulsion is expected to grow from about 0.3 in the fleet average of 1992, to 0.4 in 2015, and to 0.5 in 2050. The expansion of air traffic makes Canada, Alaska, the North Pacific route from North America to Japan and most of the Asian continent new regions where contrails are expected to cover more than 0.5% on average

Millimeter Interferometric HCN(1-0) and HCO+(1-0) Observations of Luminous Infrared Galaxies

We present the results on millimeter interferometric observations of four luminous infrared galaxies (LIRGs), Arp 220, Mrk 231, IRAS 08572+3915, and VV 114, and one Wolf-Rayet galaxy, He 2-10, using the Nobeyama Millimeter Array (NMA). Both the HCN(1-0) and HCO+(1-0) molecular lines were observed simultaneously and their brightness-temperature ratios were derived. High-quality infrared L-band (2.8-4.1 micron) spectra were also obtained for the four LIRGs to better constrain their energy sources deeply buried in dust and molecular gas. When combined with other LIRGs we have previously observed with NMA, the final sample comprised nine LIRGs (12 LIRGs' nuclei) with available interferometric HCN(1-0) and HCO+(1-0) data-sufficient to investigate the overall trend in comparison with known AGNs and starburst galaxies. We found that LIRGs with luminous buried AGN signatures at other wavelengths tend to show high HCN(1-0)/HCO+(1-0) brightness-temperature ratios as seen in AGN-dominated galaxies, while the Wolf-Rayet galaxy He 2-10 displays a small ratio. An enhanced HCN abundance in the interstellar gas surrounding a strongly X-ray-emitting AGN, as predicted by some chemical calculations, is a natural explanation of our results.Comment: 43 pages, 11 figures, accepted for publication in Astronomical Journal. Higher resolution version is available at http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN2/HCN2.pd

Understanding the History of Two Complex Ice Crystal Habits Deduced From a Holographic Imager

The sizes and shapes of ice crystals influence the radiative properties of clouds, as well as precipitation initiation and aerosol scavenging. However, ice crystal growth mechanisms remain only partially characterized. We present the growth processes of two complex ice crystal habits observed in Arctic mixed-phase clouds during the Ny-Ålesund AeroSol Cloud ExperimeNT campaign. First, are capped-columns with multiple columns growing out of the plates' corners that we define as columns on capped-columns. These ice crystals originated from cycling through the columnar and plate temperature growth regimes, during their vertical transport by in-cloud circulation. Second, is aged rime on the surface of ice crystals having grown into faceted columns or plates depending on the environmental conditions. Despite their complexity, the shapes of these ice crystals allow to infer their growth history and provide information about the in-cloud conditions. Additionally, these ice crystals exhibit complex shapes and could enhance aggregation and secondary ice production

Massive Quiescent Cores in Orion. I. Temperature Structure

We have mapped four massive cores in Orion using the \ammonia (J,K) = (1,1) and (J,K) = (2,2) inversion transitions, as part of our effort to study the pre--protostellar phase of massive star formation. These cores were selected to be quiescent, i.e. they contain no apparent IR sources and are not associated with any molecular outflows. These cores are one order of magnitude more massive than dark cloud cores and have about twice the line width. This paper focuses on their temperature structure. We find a statistically significant correlation between the gas kinetic temperature and the gas column density. The general trend is for the gas to be colder where the column density is higher, which we interpret to mean that the interiors of these cores are colder than the regions surrounding them. This is in contrast with dark cloud cores, which exhibit relatively flat temperature profiles. The temperature gradient within the massive quiescent Orion cores is consistent with an external radiation source heating the dust, and dust--gas collisions providing relatively close coupling between dust and gas temperatures. From linewidth and temperature, we also obtained the spatial distribution of the turbulence. An anticorrelation is found between the intensity of emission and the degree of turbulence. Thus, we suggest that the initial stage of massive pre--protostellar cloud cores is relatively quiescent condensations which are cooler than their surroundings.Comment: 32 pages, 10 figures, accepted by Ap

Influence of aviation fuel composition on the formation and lifetime of contrails — a literature review

The question of how aviation fuel composition affects the formation and lifetime of contrails is a complex one. Although the theory regarding initial contrail formation is well-founded in thermodynamics and proven to be correct by measurements, there remain large uncertainties in terms of persistent contrails forming contrail cirrus. These originate both from processes which are not yet fully understood and from the complexity of quantifying the many factors of influence on their effect on climate. There is an extended cause-effect chain from fuel composition through its combustion and consequential emissions, to contrail formation and their spreading in the atmosphere, and microphysical and optical properties. These properties affect the lifetime and radiative effect of single contrails to the global and multi-annual average of the radiative effects of all contrails, and thus eventually to their climate impact. This problem extends over 17 orders of magnitude in space and time, from the scales of single molecules (about 0.1 nm) and their elementary interactions (say, 1 ns) to the global scales of climate (say, 10,000 km and 10-30 years). It is not possible to cover such a vast range with a single numerical model or with relatively few measurements

Interaction between Ionized and Molecular Gas in the Active Star-Forming Region W31

We have carried out 21 cm radio continuum, H76_\alpha radio recombination line, and various (CO, ^13CO, CS, & C^34S) molecular line observations of the W31 complex. Our radio continuum data show that W31 is composed of two extended HII regions, G10.2-0.3 and G10.3-0.1, each of which comprises an ultracompact HII region, two or more compact components, and diffuse envelope. The W31 cloud appears as an incomplete shell on the whole and consists of southern spherical and northern flat components, which are associated with G10.2-0.3 and G10.3-0.1, respectively. We detect two large and massive CS-emitting regions in the northern and southern cloud components. The large amount of dense gas may suggest that the W31 cloud has ability to form rich stellar clusters and that star formation has only recently begun. The extended envelopes of both G10.2-0.3 and G10.3-0.1 are likely to be results of the champagne flows, based on the distributions of ionized and molecular gas and the velocity gradient of H76_\alpha line emission. We find strong evidence of bipolar molecular outflows associated with the two ultracompact HII regions. In the vicinity of the ultracompact and compact HII regions in G10.3-0.1, the CO J=2-1/J=1-0 intensity ratio is high (1.4) and a small but prominent molecular gas hollow exists. These observations strongly indicate that the HII regions and their ionizing stars are interacting with the molecular cloud. Therefore, it is most likely that recently formed massive stars are actively disrupting their parental molecular cloud in the W31 complex.Comment: 26 pages, including 10 figures, accepted for publication in Ap

Modelling CO formation in the turbulent interstellar medium

We present results from high-resolution three-dimensional simulations of turbulent interstellar gas that self-consistently follow its coupled thermal, chemical and dynamical evolution, with a particular focus on the formation and destruction of H2 and CO. We quantify the formation timescales for H2 and CO in physical conditions corresponding to those found in nearby giant molecular clouds, and show that both species form rapidly, with chemical timescales that are comparable to the dynamical timescale of the gas. We also investigate the spatial distributions of H2 and CO, and how they relate to the underlying gas distribution. We show that H2 is a good tracer of the gas distribution, but that the relationship between CO abundance and gas density is more complex. The CO abundance is not well-correlated with either the gas number density n or the visual extinction A_V: both have a large influence on the CO abundance, but the inhomogeneous nature of the density field produced by the turbulence means that n and A_V are only poorly correlated. There is a large scatter in A_V, and hence CO abundance, for gas with any particular density, and similarly a large scatter in density and CO abundance for gas with any particular visual extinction. This will have important consequences for the interpretation of the CO emission observed from real molecular clouds. Finally, we also examine the temperature structure of the simulated gas. We show that the molecular gas is not isothermal. Most of it has a temperature in the range of 10--20 K, but there is also a significant fraction of warmer gas, located in low-extinction regions where photoelectric heating remains effective.Comment: 37 pages, 15 figures; minor revisions, matches version accepted by MNRA