611 research outputs found
Hot methane line lists for exoplanet and brown dwarf atmospheres
We present comprehensive experimental line lists of methane (CH4) at high
temperatures obtained by recording Fourier transform infrared emission spectra.
Calibrated line lists are presented for the temperatures 300 - 1400 degC at
twelve 100 degC intervals spanning the 960 - 5000 cm-1 (2.0 - 10.4 microns)
region of the infrared. This range encompasses the dyad, pentad and octad
regions, i.e., all fundamental vibrational modes along with a number of
combination, overtone and hot bands. Using our CH4 spectra, we have estimated
empirical lower state energies (Elow in cm-1) and our values have been
incorporated into the line lists along with line positions (cm-1) and
calibrated line intensities (S' in cm molecule-1). We expect our hot CH4 line
lists to find direct application in the modeling of planetary atmospheres and
brown dwarfs.Comment: Supplementary material is provided via the Astrophysical Journal
referenc
Spectroscopic Constants, Abundances, and Opacities of the TiH Molecule
Using previous measurements and quantum chemical calculations to derive the
molecular properties of the TiH molecule, we obtain new values for its
ro-vibrational constants, thermochemical data, spectral line lists, line
strengths, and absorption opacities. Furthermore, we calculate the abundance of
TiH in M and L dwarf atmospheres and conclude that it is much higher than
previously thought. We find that the TiH/TiO ratio increases strongly with
decreasing metallicity, and at high temperatures can exceed unity. We suggest
that, particularly for subdwarf L and M dwarfs, spectral features of TiH near
0.52 \mic, 0.94 \mic, and in the band may be more easily measureable
than heretofore thought. The recent possible identification in the L subdwarf
2MASS J0532 of the 0.94 \mic feature of TiH is in keeping with this
expectation. We speculate that looking for TiH in other dwarfs and subdwarfs
will shed light on the distinctive titanium chemistry of the atmospheres of
substellar-mass objects and the dimmest stars.Comment: 37 pages, including 4 figures and 13 tables, accepted to the
Astrophysical Journa
First space-borne measurements of methanol inside aged southern tropical to mid-latitude biomass burning plumes using the ACE-FTS instrument
International audienceFirst measurements from space of upper tropospheric and lower stratospheric methanol profiles within aged fire plumes are reported. Elevated levels of methanol at 0–45° S from 30 September to 3 November 2004 have been measured by the high resolution infrared spectrometer ACE-FTS onboard the SCISAT satellite. Methanol volume mixing ratios higher than 4000 pptv are detected and are strongly correlated with other fire products such as CO, C2H6, and HCN. A sensitivity study of the methanol retrieval, accounting for random and systematic contributions, shows that the retrieved methanol profile for a single occultation exceeds 100% error above 16.5 km, with an accuracy of about 20% for measurements inside polluted air masses. The upper tropospheric enhancement ratio of methanol with respect to CO is estimated from the correlation plot between methanol and CO for aged tropical biomass burning plumes. This ratio is in good agreement with the ratio measured in the free troposphere (up to 12 km) by recent aircraft studies and does not suggest any secondary production of methanol by oxidation in aged biomass burning plumes
Upper Tropospheric Water Vapour Variability at High Latitudes- Part 1: Influence of the Annular Modes
Seasonal and monthly zonal medians of water vapour in the upper troposphere and lower stratosphere (UTLS) are calculated for both Atmospheric Chemistry Experiment (ACE) instruments for the northern and southern high-latitude regions (60-90° N and 60-90°S). Chosen for the purpose of observing high-latitude processes, the ACE orbit provides sampling of both regions in 8 of 12 months of the year, with coverage in all seasons. The ACE water vapour sensors, namely MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) and the Fourier Transform Spectrometer (ACE-FTS) are currently the only satellite instruments that can probe from the lower stratosphere down to the mid-troposphere to study the vertical profile of the response of UTLS water vapour to the annular modes. The Arctic oscillation (AO), also known as the northern annular mode (NAM), explains 64 % (r = -0.80) of the monthly variability in water vapour at northern high latitudes observed by ACE-MAESTRO between 5 and 7 km using only winter months (January to March, 2004-2013). Using a seasonal time step and all seasons, 45% of the variability is explained by the AO at 6.5 ± -0.5 km, similar to the 46 % value obtained for southern high latitudes at 7.5 ± 0.5 km explained by the Antarctic oscillation or southern annular mode (SAM). A large negative AO event in March 2013 produced the largest relative water vapour anomaly at 5.5-km (+70 %) over the ACE record. A similarly large event in the 2010 boreal winter, which was the largest negative AO event in the record (1950-2015), led to \u3e 50 % increases in water vapour observed by MAESTRO and ACE-FTS at 7.5 km
Balloon-borne radiometer measurement of Northern Hemisphere mid-latitude stratospheric HNO3 profiles spanning 12 years
Low-resolution atmospheric thermal emission spectra collected by balloon-borne radiometers over the time span of 1990–2002 are used to retrieve vertical profiles of HNO3, CFC-11 and CFC-12 volume mixing ratios between approximately 10 and 35 km altitude. All of the data analyzed have been collected from launches from a Northern Hemisphere mid-latitude site, during late summer, when stratospheric dynamic variability is at a minimum. The retrieval technique incorporates detailed forward modeling of the instrument and the radiative properties of the atmosphere, and obtains a best fit between modeled and measured spectra through a combination of onion-peeling and global optimization steps. The retrieved HNO3 profiles are consistent over the 12-year period, and are consistent with recent measurements by the Atmospheric Chemistry Experiment-Fourier transform spectrometer satellite instrument. This suggests that, to within the errors of the 1990 measurements, there has been no significant change in the HNO3 summer mid-latitude profile
First space-borne measurements of methanol inside aged tropical biomass burning plumes using the ACE-FTS instrument
International audienceFirst measurements from space of upper tropospheric and lower stratospheric methanol profiles within aged fire plumes are reported. Elevated levels of methanol at 0–45° S from 30 September to 3 November 2004 have been measured by the high resolution infrared spectrometer ACE-FTS onboard the SCISAT satellite. Methanol volume mixing ratios higher than 4000 pptv are detected and are strongly correlated with other fire products such as CO, C2H6, and HCN. A sensitivity study of the methanol retrieval, accounting for random and systematic contributions, shows that the retrieved methanol profile is reliable from 8.5 to 16.5 km, with an accuracy of about 20% for measurements inside polluted air masses. The upper tropospheric enhancement ratio of methanol with respect to CO is estimated from the correlation plot between methanol and CO for aged tropical biomass burning plumes. This ratio is in good agreement with the ratio measured in the free troposphere (up to 12 km) by recent aircraft studies and does not suggest any secondary production of methanol by oxidation in aged biomass burning plumes
Line Intensities and Molecular Opacities of the FeH Transition
We calculate new line lists and opacities for the
transition of FeH. The 0-0 band of this transition is responsible for the
Wing-Ford band seen in M-type stars, sunspots and brown dwarfs. The new
Einstein A values for each line are based on a high level ab initio calculation
of the electronic transition dipole moment. The necessary rotational line
strength factors (H\"onl-London factors) are derived for both the Hund's case
(a) and (b) coupling limits. A new set of spectroscopic constants were derived
from the existing FeH term values for v=0, 1 and 2 levels of the and
states. Using these constants extrapolated term values were generated for v=3
and 4 and for values up to 50.5. The line lists (including Einstein A
values) for the 25 vibrational bands with v4 were generated using a
merged list of experimental and extrapolated term values. The FeH line lists
were use to compute the molecular opacities for a range of temperatures and
pressures encountered in L and M dwarf atmospheres. Good agreement was found
between the computed and observed spectral energy distribution of the L5 dwarf
2MASS-1507.Comment: 52 pages, 3 figures, many tables, accepted for publication in the
Astrophysical Journal Supplement
Derivation of tropospheric methane from TCCON CHâ‚„ and HF total column observations
The Total Carbon Column Observing Network (TCCON) is a global ground-based network of Fourier transform spectrometers that produce precise measurements of column-averaged dry-air mole fractions of atmospheric methane (CHâ‚„). Temporal variability in the total column of CHâ‚„ due to stratospheric dynamics obscures fluctuations and trends driven by tropospheric transport and local surface fluxes that are critical for understanding CHâ‚„ sources and sinks. We reduce the contribution of stratospheric variability from the total column average by subtracting an estimate of the stratospheric CHâ‚„ derived from simultaneous measurements of hydrogen fluoride (HF). HF provides a proxy for stratospheric CHâ‚„ because it is strongly correlated to CHâ‚„ in the stratosphere, has an accurately known tropospheric abundance (of zero), and is measured at most TCCON stations. The stratospheric partial column of CHâ‚„ is calculated as a function of the zonal and annual trends in the relationship between CHâ‚„ and HF in the stratosphere, which we determine from ACE-FTS satellite data. We also explicitly take into account the CHâ‚„ column averaging kernel to estimate the contribution of stratospheric CHâ‚„ to the total column. The resulting tropospheric CHâ‚„ columns are consistent with in situ aircraft measurements and augment existing observations in the troposphere
Repumping and spectroscopy of laser-cooled Sr atoms using the (5s5p)3P2 - (5s4d)3D2 transition
We describe repumping and spectroscopy of laser-cooled strontium (Sr) atoms
using the (5s5p)3P2 - (5s4d)3D2 transition. Atom number in a magneto-optical
trap is enhanced by driving this transition because Sr atoms that have decayed
into the (5s5p)3P2 dark state are repumped back into the (5s2)1S0 ground state.
Spectroscopy of 84Sr, 86Sr, 87Sr, and 88Sr improves the value of the (5s5p)3P2
- (5s4d)3D2 transition frequency for 88Sr and determines the isotope shifts for
the transition.Comment: 4 pages, 5 figure
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