100 research outputs found
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°âWâ30°âE, 35°âNâ75°âN 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 Investigations of the Energy Sources of Three Ultraluminous Infrared Galaxies, UGC 5101, Mrk 273, and IRAS 17208-0014, based on HCN to HCO+ Ratios
We present interferometric observations of three ultraluminous infrared
galaxies (ULIRGs; UGC 5101, Mrk 273, and IRAS 17208-0014) in the 3-mm
wavelength range, using the Nobeyama Millimeter Array. Both the HCN (J=1-0) and
HCO+ (J=1-0) molecular lines were observed simultaneously. HCN emission was
clearly detected at the nuclear positions of these ULIRGs, and HCO+ emission
was detected at the nuclear positions of UGC 5101 and IRAS 17208-0014. The HCN
to HCO+ brightness-temperature ratios toward the nuclei of the three ULIRGs
were derived and compared with those of lower luminosity galaxies known to be
dominated by active galactic nuclei (AGNs) or starbursts. In UGC 5101 and Mrk
273, where there is evidence for obscured AGNs from previous observations at
other wavelengths, we found high HCN/HCO+ ratios (>1.8) that are in the range
found for AGN-dominated galaxies. In IRAS 17208-0014, where the presence of a
powerful obscured AGN has been unclear, the ratio (1.7) is in between the
observed values for starburst- and AGN-dominated galaxies. The high HCN/HCO+
brightness-temperature ratios in UGC 5101 and Mrk 273 could be the consequence
of an HCN abundance enhancement, which is expected from chemical effects of the
central X-ray emitting AGN on the surrounding dense molecular gas. Our proposed
millimeter interferometric method based on HCN/HCO+ ratios may be an effective
tool for unveiling elusive buried AGNs at the cores of ULIRGs, especially
because of the negligible dust extinction at these wavelengths.Comment: 15 pages (emulateapj.sty), 8 figures (figures 1-5 resolution
reduced), Accepted for publication in Astronomical Journal, A PDF file with
high resolution is availble at
http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN/HCN.pd
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-Ă
lesund 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
The Density and Temperature of Molecular Clouds in M33
We have observed the CO J=2-1, J=3-2, and CO J=2-1 lines in a
sample of seven giant molecular clouds in the Local Group spiral galaxy M33.
The CO/CO J=2-1 line ratio is constant across the entire sample,
while the observed CO J=3-2/J=2-1 line ratio has a weak dependence on
the star formation environment of the cloud, with large changes in the line
ratio seen only for clouds in the immediate vicinity of an extremely luminous
HII region. A large velocity gradient analysis indicates that clouds without
HII regions have temperatures of 10-20 K, clouds with HII regions have
temperatures of 15-100 K, and the cloud in the giant HII region has a
temperature of at least 100 K. Interestingly, the giant HII region appears
capable of raising the kinetic temperature of the molecular gas only for clouds
that are quite nearby ( pc). The continuous change of physical
conditions across the observed range of star formation environments suggests
that the unusual physical conditions in the cloud in the giant HII region are
due to post-star formation changes in the molecular gas, rather than intrinsic
properties of the gas related to the formation of the giant HII region.Comment: 14 pages, aastex, 4 postscript figures; accepted for publication in
ApJ; also available at http://www.physics.mcmaster.ca/Wilson_Preprint
Influence of aviation fuel composition on the formation and lifetime of contrails â 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
Simulations of atmospheric OH, O-3 and NO3 reactivities within and above the boreal forest
Using the 1-D atmospheric chemistry transport model SOSAA, we have investigated the atmospheric reactivity of a boreal forest ecosystem during the HUMPPA-COPEC-10 campaign (summer 2010, at SMEAR II in southern Finland). For the very first time, we present vertically resolved model simulations of the NO3 and O-3 reactivity (R) together with the modelled and measured reactivity of OH. We find that OH is the most reactive oxidant (R similar to 3 s(-1)) followed by NO3 (R similar to 0.07 s(-1)) and O-3 (R similar to 2 x 10 5 s(-1)). The missing OH reactivity was found to be large in accordance with measurements (similar to 65 %) as would be expected from the chemical subset described in the model. The accounted OH radical sinks were inorganic compounds (similar to 41 %, mainly due to reaction with CO), emitted monoterpenes (similar to 14 %) and oxidised biogenic volatile organic compounds (similar to 44 %). The missing reactivity is expected to be due to unknown biogenic volatile organic compounds and their photoproducts, indicating that the true main sink of OH is not expected to be inorganic compounds. The NO3 radical was found to react mainly with primary emitted monoterpenes (similar to 60 %) and inorganic compounds (similar to 37 %, including NO2). NO2 is, however, only a temporary sink of NO3 under the conditions of the campaign (with typical temperatures of 20-25 degrees C) and does not affect the NO3 concentration. We discuss the difference between instantaneous and steady-state reactivity and present the first boreal forest steady-state lifetime of NO3 (113 s). O-3 almost exclusively reacts with inorganic compounds (similar to 91 %, mainly NO, but also NO2 during night) and less with primary emitted sesquiterpenes (similar to 6 %) and monoterpenes (similar to 3 %). When considering the concentration of the oxidants investigated, we find that OH is the oxidant that is capable of removing organic compounds at a faster rate during daytime, whereas NO3 can remove organic molecules at a faster rate during night-time. O-3 competes with OH and NO3 during a short period of time in the early morning (around 5 a.m. local time) and in the evening (around 7-8 p.m.). As part of this study, we developed a simple empirical parameterisation for conversion of measured spectral irradiance into actinic flux. Further, the meteorological conditions were evaluated using radiosonde observations and ground-based measurements. The overall vertical structure of the boundary layer is discussed, together with validation of the surface energy balance and turbulent fluxes. The sensible heat and momentum fluxes above the canopy were on average overestimated, while the latent heat flux was un-derestimated.Peer reviewe
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