Methane Absorption Research Articles

On the possibility of separation of aerosol and methane absorption in the long-wavelength spectral range for giant planets

To determine the aerosol absorption component of the effective optical depth τeffκ, a special method has been developed. It is based on the implausible effect of the decrease of the aerosol scattering component τeffa in dependence on the atmospheric pressure P, if τeffκ = 0. It is the elimination of this effect by selecting the values of τeffκ that allows the latter to be determined. This method was tested with the data of observations of the North Equatorial Belt (NEB) of Jupiter’s disk in the methane absorption bands at λ = 619 and 727 nm. This allowed us to determine the values of τeffκ and the imaginary part of the refractive index of aerosol particles (ni = 0.00063, 0.00065, 0.0007, and 0.00069 at λ = 605.5, 631.3, 714.7, and 741.4 nm, respectively) and to correctly specify the characteristic of the vertical structure of clouds of the planet.

The influence of nitrogen fertiliser rate and crop rotation on soil methane flux in rain-fed potato fields in Wuchuan County, China

As one of the important greenhouse gases, the characteristics and principles of methane exchange characteristics in cultivated lands have become hot topics in current climate change research. This study examines the influences of nitrogen fertilisation, temperature and soil water content on methane exchange characteristic and methane exchange functional gene-pmoA gene abundance based on experimental observations of methane exchange fluxes using the static chamber–gas chromatographic method and measurements of methanotroph gene copy numbers in three growing periods by real-time PCR in rain-fed potato fields. The results indicate that the rain-fed potato fields were a CH4 sink with an average annual methane absorption (negative emission) of 940.8±103.2gCH4-C/ha/year. The cumulative methane absorption first exhibited flat and subsequently increasing trend with the increase of nitrogen fertilisation from 0~135kgN·ha−1. Methane cumulative absorption significantly increased with the increase of temperature when temperatures were below 19.6°C. Methane oxidation capacity (methanotroph pmoA gene copy numbers) showed an increasing and subsequently decreasing trend with the increase of soil moisture. Crop rotation was observed to increase the methane absorption in rain-fed potato fields and nearly one time higher than that under continuous cropping. A mechanism concept model of the methane exchange in rain-fed potato fields was advanced in this paper.

FAINT LUMINESCENT RING OVER SATURN’S POLAR HEXAGON

Springtime insolation is presently advancing across Saturn's north polar region. Early solar radiation scattered through the gaseous giant's atmosphere gives a unique opportunity to sound the atmospheric structure at its upper troposphere/lower stratosphere at high latitudes. Here, we report the detection of a tenuous bright structure in Saturn's northern polar cap corresponding to the hexagon equatorward boundary, observed by Cassini Visual and Infrared Mapping Spectrometer on 2013 June. The structure is spectrally characterized by an anomalously enhanced intensity in the 3610–3730 nm wavelength range and near 2500 nm, pertaining to relatively low opacity windows between strong methane absorption bands. Our first results suggest that a strong forward scattering by tropospheric clouds, higher in respect to the surrounding cloud deck, can be responsible for the enhanced intensity of the feature. This can be consistent with the atmospheric dynamics associated with the jet stream embedded in the polar hexagon. Further investigations at higher spectral resolution are needed to better assess the vertical distribution and microphysics of the clouds in this interesting region.

Variations of the volume scattering coefficient of aerosol in the Jovian atmosphere from observations of the planetary disk

Data on variations of the volume scattering coefficient σ a (P) with depth in the atmosphere of Jupiter are presented. They were obtained from the analysis of the spectrophotometric observations of Jupiter in 1993 and 1995 in the methane absorption bands of λ = 887, 864, 842, 727, and 619 nm and reduced to the wavelength λ = 887 nm. In the σ a (P) dependences obtained from the data of 1993, aerosol layers of a finite optical thickness are undoubtedly distinguished: four layers in the upper part of the atmosphere and one deeper layer. The maxima of σ a (P) in these layers are at the altitude levels approximately corresponding to the pressure values of 1.1 and 16 bar, respectively. In 1995, the value of σa(P) in the upper part of the atmosphere and in the deeper layer increased relative to the values of 1993 by less than 5% and up to 60%, respectively. At the deeper atmospheric levels, the spectral dependence of σ a (P) was revealed, which probably points to the change of the size of aerosol particles.

Optimal designs for the methane flux in troposphere

The understanding of methane emission and methane absorption plays a central role both in the atmosphere and on the surface of the Earth. Several important ecological processes, e.g., ebullition of methane and its natural microergodicity request better designs for observations in order to decrease variability in parameter estimation. Thus, a crucial fact, before the measurements are taken, is to give an optimal design of the sites where observations should be collected in order to stabilize the variability of estimators. In this paper we introduce a realistic parametric model of covariance and provide theoretical and numerical results on optimal designs. For parameter estimation D-optimality, while for prediction integrated mean square error and entropy criteria are used. We illustrate applicability of obtained benchmark designs for increasing/measuring the efficiency of the engineering designs for estimation of methane rate in various temperature ranges and under different correlation parameters. We show that in most situations these benchmark designs have higher efficiency.

Miniaturized Photoacoustic Trace Gas Sensing Using a Raman Fiber Amplifier

This paper presents the development of a Raman fiber amplifier optical source with a maximum output power of 1.1 W centered around 1651 nm, and its application in miniaturized 3D printed photoacoustic spectroscopy (PAS) trace gas sensing of methane. The Raman amplifier has been constructed using 4.5 km of dispersion shifted fiber, a 1651 nm DFB seed laser and a commercial 4W EDFA pump. The suppression of stimulated Brillouin scattering (SBS) using a high frequency modulation of the seed laser is investigated for a range of frequencies, leading to an increase in optical output power of the amplifier and reduction of its noise content. The amplifier output was used as the source for a miniature PAS sensor by applying a second modulation to the seed laser at the resonant frequency of 15.2 kHz of the miniature 3D printed gas cell. For the targeted methane absorption line at 6057 cm-1 the sensor system performance and influence of the SBS suppression is characterized, leading to a detection limit (1σ) of 17 ppb methane for a signal acquisition time of 130 s, with a normalized noise equivalent absorption coefficient of 4.1•10-9 cm-1 W Hz-1/2 for the system.

WASP-80b has a dayside within the T-dwarf range

WASP-80b is a missing link in the study of exo-atmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterisation, thanks to its host star's properties. We observed the planet through transit and during occultation with Warm Spitzer. Combining our mid-infrared transits with optical time series, we find that the planet presents a transmission spectrum indistinguishable from a horizontal line. In emission, WASP-80b is the intrinsically faintest planet whose dayside flux has been detected in both the 3.6 and 4.5 $\mu$m Spitzer channels. The depths of the occultations reveal that WASP-80b is as bright and as red as a T4 dwarf, but that its temperature is cooler. If planets go through the equivalent of an L-T transition, our results would imply this happens at cooler temperatures than for brown dwarfs. Placing WASP-80b's dayside into a colour-magnitude diagram, it falls exactly at the junction between a blackbody model and the T-dwarf sequence; we cannot discern which of those two interpretations is the more likely. Flux measurements on other planets with similar equilibrium temperatures are required to establish whether irradiated gas giants, like brown dwarfs, transition between two spectral classes. An eventual detection of methane absorption in transmission would also help lift that degeneracy. We obtained a second series of high-resolution spectra during transit, using HARPS. We reanalyse the Rossiter-McLaughlin effect. The data now favour an aligned orbital solution and a stellar rotation nearly three times slower than stellar line broadening implies. A contribution to stellar line broadening, maybe macroturbulence, is likely to have been underestimated for cool stars, whose rotations have therefore been systematically overestimated. [abridged]

Influence of solar activity on seasonal variations of methane absorption in the atmosphere of Saturn

Seasonal variations of methane absorption distribution over the disk of Saturn at the levels of visible clouds and an overcloud haze have been found from the results of observations in the period from 1965 to 2011. The meridional behavior of the methane absorption at the equinox moments in 1966 and 1995 is opposite in phase to the analogous data obtained at the equinox in 1980. During the equinox in 2009, no difference in the methane absorption (expected to be analogous to that in 1980) between the southern and northern hemispheres at the mid latitudes of Saturn were observed, though all of the physical and orbital characteristics of Saturn at the equinox moments in 1966 and 1980, as well as in 1995 and 2009, are practically the same. Several years before the equinoxes in 1966, 1980, and 1995, the solar activity was rather high, while the Sun was in its minimum activity before the 2009 equinox. As has been shown, the dynamic time scale in the mid troposphere of Saturn may be of several dozens of hours if the condensation and convection are accounted for. In this case, large changes of the insolation in the UV spectral range may yield substantial short-term dynamical changes. At the equinox in 2009, convection in the atmosphere of Saturn was as low as possible; because of this, the deep cloud layers in the winter northern hemisphere remained “frozen” after the emersion from the rings’ shadow, while there were practically no active processes on the Sun. Due to this, the low-active cloud layer that had been shadowed before by the rings remained at the same level below the tropopause. This allowed a thick overcloud layer of gaseous methane and ammonia to be easily detected. Because of this, in the low-active hemisphere, where there had been winter before, the methane absorption remained practically the same and equal to the absorption in the hemisphere, where there had been summer before.

Zonal differences in the vertical structure of the cloud cover of Jupiter from the measurements of the methane absorption bands at 727 and 619 nm

Data on the contours of absorption bands of methane at λ = 619 and 727 nm obtained for the latitude belts of Jupiter in 2013 have been analyzed. From the spectral values of reflectivity, the changes in the aerosol and gas components of the effective optical depth in dependence on the depth in the atmosphere were found. Zonal differences in the vertical structure of the cloud cover of Jupiter were revealed; they were quantitatively estimated, and the levels where the linear size or the nature of aerosol particles probably changed were determined. The signs indicating the presence of the aerosol layer deep in the atmosphere were found.

Absorption coefficients of the methane–nitrogen binary ice system: Implications for Pluto

The methane–nitrogen phase diagram of Prokhvatilov and Yantsevich (1983. Sov. J. Low Temp. Phys. 9, 94–98) indicates that at temperatures relevant to the surfaces of icy dwarf planets like Pluto, two phases contribute to the methane absorptions: nitrogen saturated with methane N2‾:CH4 and methane saturated with nitrogen CH4‾:N2. No optical constants are available so far for the latter component limiting construction of a proper model, in compliance with thermodynamic equilibrium considerations. New optical constants for solid solutions of methane diluted in nitrogen (N2:CH4) and nitrogen diluted in methane (CH4:N2) are presented at temperatures between 40 and 90K, in the wavelength range 1.1–2.7μm at different mixing ratios. These optical constants are derived from transmission measurements of crystals grown from the liquid phase in closed cells. A systematic study of the changes of methane and nitrogen solid mixtures spectral behavior with mixing ratio and temperature is presented.

Novel hyperbranched polysiloxanes containing acetoacetyl groups synthesized through transesterification reaction.

Development of an innovative strategy to prepare hyperbranched polysiloxanes (HBPS) is highly desirable due to the significant shortcomings of conventional fabrication approaches: the precursors need pre-synthesis, the hydrosilylation reaction is conducted using costly catalysts, and hydrolysis of organosiloxanes easily results in gelation. Here, novel HBPS containing acetoacetyl groups (HBPS-Ac) are synthesized through a cost-efficient and easily controllable transesterification reaction. It is shown by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), (1) H NMR, and gas chromatography (GC) measurements that the polymerization process is a straightforward technique to prepare new HBPS. The polymers are capable to remove formaldehyde due to the highly efficient reaction of the active methylene in the acetoacetyl group with formaldehyde at room temperature. Notably, coatings incorporating 4 wt% of the polymers allow for formaldehyde absorption, while integrated performances are kept almost unaffected. Therefore, HBPS-Ac are promising as scavengers for formaldehyde.

Searching for T dwarfs in the ρ Oph dark cloud L 1688

We present a list of T dwarf candidates in the dark cloud L 1688 in the ρ Oph star-forming region. These candidates are selected with infrared colours sensitive to T dwarf characteristics of methane absorptions and of cool atmospheres. The 1.6-μm methane feature is diagnosed by on–off imaging using an H-band and an intermediate-band methane filter, calibrated to a set of known brown dwarfs of M, L, and T types in the field. Another methane feature at 3.3 μm is traced with the Spitzer/Infrared Array Camera (IRAC) [3.6] − [4.5] colour. For cool atmospheres, the H − [4.5] and K − [4.5] colours are utilized. With an additional criterion of mid-infrared brightness to eliminate extragalactic interlopers, a total of 28 T dwarf candidates have been identified. A comprehensive assessment was conducted to estimate the level of contamination of our sample by young stellar variability, by extragalactic sources sharing the same colour behaviour, or by foreground T dwarfs. Though extragalactic sources may contribute up to about half of the false positives, our candidates show close spatial association with the dark cloud, rather than randomly distributed as a background population would have been. Furthermore, even though our candidates are not selected a priori by a colour–magnitude relation, they mostly follow the 1 Myr isochrones, ascertaining their youth. Our selection methodology provides guidance to search for T dwarfs in other star-forming regions. Our candidate list, when comparing with those in the literature, which often rely on a single criterion on cool temperature or methane, is more conservative but should be more secure for follow-up spectroscopic confirmation of a T dwarf sample at the early evolutionary stage.

DIRECT SPECTRUM OF THE BENCHMARK T DWARF HD 19467 B

HD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R~30 observations obtained simultaneously across the $JH$ bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5+/-1 dwarf with effective temperature Teff=$978^{+20}_{-43}$ K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits.

Densitometry and Thermometry of Starburst Galaxies

With a goal toward deriving the physical conditions in external galaxies, we have conducted a survey and subsequent high spatial resolution imaging of formaldehyde (H2CO) and ammonia (NH3) emission and absorption in a sample of starburst galaxies. In this article we present the results from a subset of this survey which focuses on high spatial resolution measurements of volume density-and kinetic temperature-sensitive transitions of the H2CO molecule. The volume density structure toward the nuclear region of NGC 253 has been derived from ? ≠4 arcsec NRAO Very Large Array (VLA) measurements of the 110-111 and 211-212 K-doublet transitions of H2CO. The kinetic temperature structure toward NGC 253 and NGC 4945 has been derived from ? ≠0.5-1.0 arcsec measurements of the H2CO 3K-1K+1-2K-1K+1 (near 218 GHz) and 5K-1K+1-4K-1K+1 (near 365 GHz) transitions acquired using the Atacama Large Millimeter/submillimeter Array (ALMA). These measurements have allowed us to characterize the dense gas and kinetic temperature structure within these star forming galaxies, which is a first step toward associating dense star-forming gas and the heating processes at work within galaxies.

Seasons on Saturn. II. Influence of solar activity on variation of methane absorption

Seasons on Saturn. II. Influence of solar activity on variation of methane absorption

Seasons on Saturn. I. Changes in reflecting characteristics of the atmosphere at 1964–2012

Due to considerable tilting of the equator to the orbital plane, presence of rings and elongation of the orbit around the Sun, Saturn is strongly affected by seasonal changes in the solar radiation influx. Such change of the mode of irradiation of Saturn's atmosphere should affect physical properties and optical characteristics of the cloud cover and/or haze above the clouds of the planet, as well as on the vertical structure of the atmosphere at different latitudes. Once in 14,7 terrestrial years we have the equality of conditions of insolation for both hemispheres, when the planet's rings are visible edge-on to a terrestrial observer. Therefore, these moments are interest for comparative study of possible differences in atmospheric characteristics of the northern and southern hemispheres. In recent years, possibilities for such observations were in 1966, 1980, 1995 and 2009. Using the observational data on the distribution of reflective characteristics of the atmosphere on the visible planetary disk, we have compared the results of calculations in the framework of a two-layer model of Saturn's atmosphere for above moments of equinoxes. It was found that in moments of equinox in 1966, 1980 and 1995 for spring hemisphere, which had just emerged from the rings shadow, the planetary latitudinal belts differ significantly from the other zones by the values of scattering component of the optical thickness τ_c of gas layer above the clouds, the volume concentration of aerosol cloud n, and imaginary part of refractive index n_i of cloud particles. But at the time of the equinox in 2009, in the spring hemisphere the expected changes of reflective and absorptive characteristics – did not happen. There methane absorption remained at the same high level and does not form any high-altitude haze and/or rarefied cloud layer. Because they have the photochemical nature, we can assume an insufficient amount of incoming energy into the atmosphere for the possibility of the formation a photochemical aerosol layer in the lower stratosphere and/or upper troposphere of Saturn.

Changes in the characteristics of the upper layers of the Jovian atmosphere from the data on the integral observations of the planetary disk

From the spectral values of the geometric albedo of Jupiter in the methane absorption bands of 887, 864, 842, 727, and 619 nm measured in 1993 and 1995, the changes in the aerosol and gaseous components of the effective optical depth in dependence on the depth in the atmosphere have been found. In 1995, the aerosol scattering component of the optical depth was 0–5% (depending on the depth of the atmospheric level) higher than that in 1993. The results of the data processing for 1993 unambiguously indicate the presence of three aerosol layers separated by gaps at the atmospheric pressure levels of approximately 0.38 and 0.52 bar. In the data for 1995, the signs of the formation of a new aerosol layer at the atmospheric pressure level of 15–18 bar were found.

Spectroscopic follow-up of L- and T-type proper-motion member candidates in the Pleiades

(Abridged) We report on the near-infrared low-resolution spectroscopy and red optical (Z-band) photometry of seven proper-motion, very low-mass substellar member candidates of the Pleiades cluster with magnitudes in the interval J=17.5-20.8 and K=16.1-18.5 mag. Spectra were acquired for six objects with the LIRIS and NIRSPEC instruments mounted on the 4.2-m WHT and the 10-m Keck II telescopes. Z-band images of two of the faintest candidates were collected with ACAM/WHT. The new data confirm the low temperatures of all seven Pleiades candidates. From the imaging observations, we find extremely red Z-J and Z-K colors that suggest that the faintest target, Calar Pleiades 25, has a Galactic rather than extragalactic nature. We tentatively classify the spectroscopic targets from early-L to ~T0 and suggest that the L/T transition, which accounts for the onset of methane absorption at 2.1 micron, may take place at J,K ~ 20.3, 17.8 mag in the Pleiades (absolute values of M_J ~ 14.7 and M_K ~ 12.2 mag). We find evidence of likely low-gravity atmospheres based on the presence of triangular-shape H-band fluxes and the high flux ratio K/H (compatible with red H-K colors) of Calar Pleiades 20, 21, and 22, which is a feature also seen in field low-gravity dwarfs. Weak KI absorption lines at around 1.25 micron are probably seen in two targets. These observations add support to the cluster membership of all seven objects in the Pleiades. The trend delineated by the spectroscopic sequence of Pleiades late-M and L dwarfs resembles that of the field. With masses estimated at 0.012-0.015 Msol (solar metallicity and 120 Myr), Calar Pleiades 20 (L6 +/- 1), 21 (L7 +/- 1), and 22 (L/T) may become the coolest and least massive Pleiades members that are corroborated with photometry, astrometry, and spectroscopy. Calar Pleiades 25 (<0.012 Msol) is a firm free-floating planetary-mass candidate in the Pleiades.

Study on the Formaldehyde Adsorption Kinetics of Dry Waters

Dry waters with an average diameter of 82 μm were prepared by a high speed mixed route. The formaldehyde absorption kinetics of dry waters was investigated by simulating indoor formaldehyde pollution in glass chamber. The results showed that pseudo-second order model could be used to simulate the adsorption process; the adsorption rate was highest in the initial 60 minutes; when the adsorption lasted for 180 minutes, the adsorption reached equilibrium.

Spatial variations of methane absorption on Jupiter according to the results of quasicontinuous CCD spectrophotometry

Spectrophotometry observations of Jupiter were carried out during four nights in November–December 1999. Three hundred and eighty eight CCD-spectrograms of the central meridian of the planet were obtained and processed with doubly overlapped longitudes with a step of 1.8°. Latitudinal variations in central depths of methane absorption bands were studied corresponding to the wavelengths of 619, 725, 798, and 887 nm. It has been shown that these variations are mainly present at all longitudes, but for different absorption bands the positions of maxima and minima do not coincide. Zonal differences do not correlate with positions of dark and bright cloud belts in absorption, with one exception for the band 887 nm, which for a long time shows a well-expressed minimum in the equatorial zone of Jupiter. The 798 nm band reveals great dispersion of the depths at low latitudes as compared to other bands, which can be related with the presence of the ammonium absorption band. Comparison of the latitudinal absorption band variability at wave-lengths 619 and 725 nm shows a “loop-like” form of the relation between the depths of these bands in the low-latitude zone of Jupiter. Indicative estimates of the effective optical depth formation and absorption and their difference in the framework of simple two-layer model indicate the existence of vertical heterogeneity of the cloud cover varying with latitude.