281 research outputs found
In situ observation of atmospheric oxygen and carbon dioxide in the North Pacific using a cargo ship
Atmospheric oxygen (O2) and carbon dioxide (CO2) variations in the
North Pacific were measured aboard a cargo ship, the New Century 2
(NC2), while it cruised between Japan and the United States between
December 2015 and November 2016. A fuel cell analyzer and a nondispersive
infrared analyzer were used for the measurement of O2 and
CO2, respectively. To achieve parts-per-million precision for the
O2 measurements, we precisely controlled the flow rates of the
sample and reference air introduced into the analyzers and the outlet
pressure. A relatively low airflow rate (10âŻcm3âŻminâ1) was
adopted to reduce the consumption rate of the reference gases. In the
laboratory, the system achieved measurement precisions of 3.8 per meg for
ÎŽ(O2âŻââŻN2), which is commonly used to express
atmospheric O2 variation, and 0.1âŻppm for the CO2 mole
fraction. After the in situ observation started aboard NC2, we found that
the ship's motion caused false wavy variations in the O2 signal
with an amplitude of more than several tens of ppm and a period of about
20âŻs. Although we have not resolved the problem at this stage, hourly
averaging considerably suppressed the variation associated with ship motion.
Comparison between the in situ observation and flask sampling of air
samples aboard NC2 showed that the averaged differences (in situâflask)
and the standard deviations (±1Ï) are â2.8âŻÂ±âŻ9.4 per meg
for ÎŽ(O2âŻââŻN2) and â0.02âŻÂ±âŻ0.33âŻppm
for the CO2 mole fraction. We compared 1Â year of in situ data for
atmospheric potential oxygen (APO; O2 +1.1âĂâCO2)
obtained from the broad middle-latitude region
(140°âŻEâ130°âŻW, 29°âŻNâ45°âŻN) with
previous flask sampling data from the North Pacific. This comparison showed
that longitudinal differences in the seasonal amplitude of APO, ranging from
51 to 73 per meg, were smaller than the latitudinal differences.</p
Distorted wave impulse approximation analysis for spin observables in nucleon quasi-elastic scattering and enhancement of the spin-longitudinal response
We present a formalism of distorted wave impulse approximation (DWIA) for
analyzing spin observables in nucleon inelastic and charge exchange reactions
leading to the continuum. It utilizes response functions calculated by the
continuum random phase approximation (RPA), which include the effective mass,
the spreading widths and the \Delta degrees of freedom. The Fermi motion is
treated by the optimal factorization, and the non-locality of the
nucleon-nucleon t-matrix by an averaged reaction plane approximation. By using
the formalism we calculated the spin-longitudinal and the spin-transverse cross
sections, ID_q and ID_p, of 12C, 40Ca (\vec{p},\vec{n}) at 494 and 346 MeV. The
calculation reasonably reproduced the observed ID_q, which is consistent with
the predicted enhancement of the spin-longitudinal response function R_L.
However, the observed ID_p is much larger than the calculated one, which was
consistent with neither the predicted quenching nor the spin-transverse
response function R_T obtained by the (e,e') scattering. The Landau-Migdal
parameter g'_N\Delta for the N\Delta transition interaction and the effective
mass at the nuclear center m^*(r=0) are treated as adjustable parameters. The
present analysis indicates that the smaller g'_{N\Delta}(\approx 0.3) and
m^*(0) \approx 0.7 m are preferable. We also investigate the validity of the
plane wave impulse approximation (PWIA) with the effective nucleon number
approximation for the absorption, by means of which R_L and R_T have
conventionally been extracted.Comment: RevTex 3, 29 pages, 2 tables, 8 figure
Multiwavelength temporal and spectral variability of the blazar OJ 287 during and after the 2015 December flare: A major accretion disc contribution
© 2018 The Author(s). We present a multiwavelength spectral and temporal analysis of the blazar OJ 287 during its recent activity between 2015 December and 2016 May, showing strong variability in the nearinfrared (NIR) to X-ray energies with detection at Îł -ray energies as well. Most of the optical flux variations exhibit strong changes in polarization angle and degree. All the interband time lags are consistent with simultaneous emissions. Interestingly, on days with excellent data coverage in the NIR-UV bands, the spectral energy distributions (SEDs) show signatures of bumps in the visible-UV bands, never seen before in this source. The optical bump can be explained as accretion-disc emission associated with the primary black hole of mass ~1.8 Ă 1010Mâ while the little bump feature in the optical-UV appears consistent with line emission. Further, the broad-band SEDs extracted during the first flare and during a quiescent period during this span show very different Îł -ray spectra compared to previously observed flare or quiescent spectra. The probable thermal bump in the visible seems to have been clearly present since 2013 May, as found by examining all available NIR-optical observations, and favours the binary supermassive black hole model. The simultaneous multiwavelength variability and relatively weak Îł -ray emission that shows a shift in the SED peak is consistent with Îł -ray emission originating from inverse Compton scattering of photons from the line emission that apparently contributes to the little blue bump
Estimation of fire-induced carbon emissions from Equatorial Asia in 2015 using in situ aircraft and ship observations
Inverse analysis was used to estimate fire carbon
emissions in Equatorial Asia induced by the big El Niño event in 2015.
This inverse analysis is unique because it extensively used high-precision
atmospheric mole fraction data of carbon dioxide (CO2) from the
commercial aircraft observation project CONTRAIL. Through comparisons with
independent shipboard observations, especially carbon monoxide (CO) data,
the validity of the estimated fire-induced carbon emissions was demonstrated.
The best estimate, which used both aircraft and shipboard CO2
observations, indicated 273âTgâC for fire emissions from
SeptemberâOctober 2015. This 2-month period accounts for 75â% of the annual total fire emissions and 45â% of the annual total net carbon flux within the region, indicating that fire emissions are a dominant driving force of interannual variations of carbon fluxes in Equatorial Asia.
Several sensitivity experiments demonstrated that aircraft observations
could measure fire signals, though they showed a certain degree of
sensitivity to prior fire-emission data. The inversions coherently estimated
smaller fire emissions than the prior data, partially because of the small
contribution of peatland fires indicated by enhancement ratios of CO and
CO2 observed by the ship. In future warmer climate conditions,
Equatorial Asia may experience more severe droughts, which risks releasing a
large amount of carbon into the atmosphere. Therefore, the continuation of
aircraft and shipboard observations is fruitful for reliable monitoring of
carbon fluxes in Equatorial Asia.</p
Kilonova from post-merger ejecta as an optical and near-Infrared counterpart of GW170817
Recent detection of gravitational waves from a neutron star (NS) merger event GW170817 and identification of an electromagnetic counterpart provide a unique opportunity to study the physical processes in NS mergers. To derive properties of ejected material from the NS merger, we perform radiative transfer simulations of kilonova, optical and near-infrared emissions powered by radioactive decays of r-process nuclei synthesized in the merger. We find that the observed near-infrared emission lasting for >10âd is explained by 0.03âMâ of ejecta containing lanthanide elements. However, the blue optical component observed at the initial phases requires an ejecta component with a relatively high electron fraction (Ye). We show that both optical and near-infrared emissions are simultaneously reproduced by the ejecta with a medium Ye of âŒ0.25. We suggest that a dominant component powering the emission is post-merger ejecta, which exhibits that the mass ejection after the first dynamical ejection is quite efficient. Our results indicate that NS mergers synthesize a wide range of r-process elements and strengthen the hypothesis that NS mergers are the origin of r-process elements in the Universe
The broad-lined Type-Ic supernova SN 2022xxf with extraordinary two-humped light curves
We report on our study of supernova (SN) 2022xxf based on observations
obtained during the first four months of its evolution. The light curves (LCs)
display two humps of similar maximum brightness separated by 75 days,
unprecedented for a broad-lined (BL) Type Ic supernova (SN IcBL). SN 2022xxf is
the most nearby SN IcBL to date (in NGC 3705, , at a distance of
about 20 Mpc). Optical and near-infrared photometry and spectroscopy are used
to identify the energy source powering the LC. Nearly 50 epochs of high
signal-to-noise-ratio spectroscopy were obtained within 130 days, comprising an
unparalleled dataset for a SN IcBL, and one of the best-sampled SN datasets to
date. The global spectral appearance and evolution of SN 2022xxf points to
typical SN Ic/IcBL, with broad features (up to km s) and a
gradual transition from the photospheric to the nebular phase. However, narrow
emission lines (corresponding to km s) are present in
the spectra from the time of the second rise, suggesting slower-moving
circumstellar material (CSM). These lines are subtle, in comparison to the
typical strong narrow lines of CSM-interacting SNe, for example, Type IIn, Ibn,
and Icn, but some are readily noticeable at late times such as in Mg I
5170 and [O I] 5577. Unusually, the near-infrared spectra
show narrow line peaks in a number of features formed by ions of O and Mg. We
infer the presence of CSM that is free of H and He. We propose that the
radiative energy from the ejecta-CSM interaction is a plausible explanation for
the second LC hump. This interaction scenario is supported by the color
evolution, which progresses to the blue as the light curve evolves along the
second hump, and the slow second rise and subsequent rapid LC drop. (Abstract
abridged)Comment: Accepted versio
Global Carbon Budget 2018
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere â the âglobal carbon budgetâ â is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFF) are based on energy statistics and cement production data, while emissions from land use and land-use change (ELUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) and terrestrial CO2 sink (SLAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1Ï. For the last decade available (2008â2017), EFF was 9.4±0.5âGtCâyrâ1, ELUC 1.5±0.7âGtCâyrâ1, GATM 4.7±0.02âGtCâyrâ1, SOCEAN 2.4±0.5âGtCâyrâ1, and SLAND 3.2±0.8âGtCâyrâ1, with a budget imbalance BIM of 0.5âGtCâyrâ1 indicating overestimated emissions and/or underestimated sinks. For the year 2017 alone, the growth in EFF was about 1.6â% and emissions increased to 9.9±0.5âGtCâyrâ1. Also for 2017, ELUC was 1.4±0.7âGtCâyrâ1, GATM was 4.6±0.2âGtCâyrâ1, SOCEAN was 2.5±0.5âGtCâyrâ1, and SLAND was 3.8±0.8âGtCâyrâ1, with a BIM of 0.3âGtC. The global atmospheric CO2 concentration reached 405.0±0.1âppm averaged over 2017. For 2018, preliminary data for the first 6â9 months indicate a renewed growth in EFF of +2.7â% (range of 1.8â% to 3.7â%) based on national emission projections for China, the US, the EU, and India and projections of gross domestic product corrected for recent changes in the carbon intensity of the economy for the rest of the world. The analysis presented here shows that the mean and trend in the five components of the global carbon budget are consistently estimated over the period of 1959â2017, but discrepancies of up to 1âGtCâyrâ1 persist for the representation of semi-decadal variability in CO2 fluxes. A detailed comparison among individual estimates and the introduction of a broad range of observations show (1) no consensus in the mean and trend in land-use change emissions, (2) a persistent low agreement among the different methods on the magnitude of the land CO2 flux in the northern extra-tropics, and (3) an apparent underestimation of the CO2 variability by ocean models, originating outside the tropics. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding the global carbon cycle compared with previous publications of this data set (Le QuĂ©rĂ© et al., 2018, 2016, 2015a, b, 2014, 2013). All results presented here can be downloaded from https://doi.org/10.18160/GCP-2018
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