OH Emission Research Articles

Multi-instrument investigation of troposphere-ionosphere coupling and the role of gravity waves in the formation of equatorial plasma bubble

Present study investigates the role of gravity waves in the generation of equatorial plasma bubbles (EPBs) during geomagnetic quiet conditions using co-located observations from Gadanki (13.5oN, 79.2° E) an all sky airglow imager, Gadanki Ionospheric Radar Interferometer (GIRI) and Ionosonde observations from Tirunelveli (8.7° N, 77.8° E). To avoid any changes occurring in the background ionosphere, four consecutive nights of observation during 03–06 February 2014 is used. Out of these four nights, three nights (i.e., 03, 05 and 06 February 2014) exhibit occurrence of EPBs in the OI 630 nm airglow emission and radar plumes and there is no bubble occurrence during one night, though the ionospheric peak altitude (h′F) value is more than 350 km in all these nights. During these four nights the structures observed in the E-region drifts and gravity waves noted in the mesospheric OH emissions are analyzed. It is found that there are common periodic oscillations in the OH peak emission altitude and E-region in three nights (03, 04 and 05 February 2014). The mesospheric gravity wave structures are ray traced to their potential sources in the lower atmosphere and also for the possibility of their propagation to the E-region. Our results suggest that apart from horizontal wavelength and amplitudes, the propagation angle of gravity wave may also be important for seeding of the Rayleigh-Taylor (R-T) instability. Thus, it gives an insight about the role of lower – middle and upper atmospheric coupling on the occurrence of the noted EPBs.

Surface Activation of Poly(Methyl Methacrylate) with Atmospheric Pressure Ar + H2O Plasma

The atmospheric pressure of Ar + H 2 O plasma jet has been analyzed and its effects on the poly(methyl methacrylate) (PMMA) surface has been investigated. The PMMA surface treatment was performed at a fixed gas flow-rate discharge voltage, while varying the plasma treatment time. The Ar + H 2 O plasma was studied with optical emission spectroscopy (OES). Optimum plasma conditions for PMMA surface treatment were determined from relative intensities of Argon, hydroxyl radical (OH), oxygen (O) I emission spectra. The rotational temperature T rot of Ar + H 2 O plasma was determined from OH emission band. The PMMA surfaces before and after plasma treatment were characterized by contact angle and surface free energy measurements, X-ray photoelectrons spectroscopy (XPS), atomic force microscope (AFM) and UV-spectroscopy. The contact angle decreased and surface free energy increased with plasma treatment time. XPS results revealed the oxygen to carbon ratio (O/C) on plasma-treated PMMA surfaces remarkably increased for short treatment time ≤60 s, beyond which it has weakly dependent on treatment time. The carbon C1s peak deconvoluted into four components: C–C, C–C=O, C–O–C and O–C=O bonds and their percentage ratio vary in accordance with plasma treatment time. AFM showed the PMMA surface roughness increases with plasma treatment time. UV-visible measurements revealed that plasma treatment has no considerable effect on the transparency of PMMA samples.

OH as an Alternate Tracer for Molecular Gas: Quantity and Structure of Molecular Gas in W5

Abstract We report column densities of molecular gas in the W5 star-forming region as traced with OH 18 cm emission in a grid survey using the Green Bank Telescope. OH appears to trace a greater column density than does CO in 8 out of 15 cases containing OH emission detections; the two molecules trace the same column densities for the other 7 cases. OH and CO trace a similar morphology of molecular gas with a nearly one-to-one correspondence. The mass of molecular gas traced by OH in the portion of the survey containing OH emission is 1.7 (+0.6 or −0.2) × 104 M ⊙, whereas the corresponding CO detections trace 9.9 (±0.7) × 103 M ⊙. We find that for lines observed in absorption, calculations assuming uniform gas and continuum distributions underestimate column density values by one to two orders of magnitude, making them unreliable for our purposes. Modeling of this behavior in terms of OH cloud structure on a scale smaller than telescopic resolution leads us to estimate that the filling factor of OH gas is a few to 10 percent. The total molecular gas content of W5 may be approximately two to three times what we report from direct measurement, because we excluded absorption line detections from the mass estimate.

Influence of sudden stratospheric warming on the mesosphere/lower thermosphere from the hydroxyl emission observations and numerical simulations

We present the results of studying the behavior of temperature and of the atomic oxygen concentration in the mesopause region during the 2013 January major Sudden Stratospheric Warming (SSW). The data on the hydroxyl molecule OH(6-2), 834.0 nm emission intensity and rotational temperature were analyzed. These data were obtained through spectrometric measurements at the Geophysical Observatory of the Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (51.8°N, 103.1°E, Tory), and at the Zvenigorod Station at the Obukhov Institute of Atmospheric Physics of the Russian Academy of Sciences (55.7°N, 36.8 E°). We calculated the concentration of atomic oxygen and its variations by using the data of the OH emission measurements. We revealed, that the response of the mesopause characteristics for two longitudinally spaced mid-latitude regions essentially differs. Thus, from the Tory Station data, the maximal increase in the OH emission intensity (by a factor of ∼2) and in the concentration [O] (by a factor of ∼3) occurred during the sudden stratospheric warming (SSW) evolution, whereas, from the Zvenigorod Station data, the OH emission intensity increase (by a factor of ∼3) and the concentration [O] increase (by a factor of ∼3.5) was observed at the SSW recovery phase. As a result of numerical modeling using the Middle and Upper Atmosphere Model (MUAM), it was shown, that the cause for the revealed effect may probably be longitudinal differences in the diurnal variation in the vertical wind at the mesopause heights over the indicated stations during the SSW. One may elucidate these differences through the generation of non-migrating tides due to a non-linear interaction between the intensified stationary planetary wave 1 (SPW1) and migrating tides and forcing a set of high-frequency PWs at the stratospheric heights. All these waves are capably of propagating into the MLT region and produce observed changes in behavior of the OH emission intensity, temperature and atomic oxygen concentration over Tory and Zvenigorod.

The semidiurnal tide for individual nights derived consistently from O2 and OH intensities and temperatures

The semidiurnal tide is studied with 159 special cases from the large airglow database acquired at El Leoncito (31.8ºS, 69.3ºW). These cases correspond to nights which exhibit similar periods in the temperature and intensity variations of the OH(6-2) and O2b(0–1) emissions. We find that all the periods (except one) are between 9 and 15.5 h. The phase distributions of these cases are narrow enough to ensure the identification as the semidiurnal tide, and their progression with altitude is consistent with downward phase propagation. The mean temperature amplitudes are large for both emissions. We obtain new values for Krassovsky's ratio including its phase. The vertical wavelength is determined independently for each emission using the relation suggested by the Hines and Tarasick theory. Mean vertical wavelengths derived for O2 are longer than those for OH. The longest monthly mean wavelengths are observed from May to August. The mean ratio of temperature amplitudes between the two emissions corresponds to moderate wave attenuation during the upward propagation of the tide.

Measurements of the High Temperature Ignition Delay Times and Kinetic Modeling Study on Oxidation of Nitromethane

ABSTRACTIgnition delay times of the nitromethane (NM)/O2/Ar mixtures were measured behind reflected shock waves in the temperature range of 1200–2000 K, pressures of 2.0 and 10.0 atm, equivalence ratios of 0.5, 1.0, and 2.0, and fuel concentrations of 0.5%, 1.0%, and 2.0%. OH emission intensity and pressure evolution were used for the ignition delay time determination. Two-stage ignition behavior was observed in the experiments. The ignition delay time decreases sharply with pressure increasing and equivalence ratio decreasing. In addition, a sub-model including 24 updated reactions for nitromethane oxidation was proposed based on ab initio calculation with CCSD(T)/CBS//B3LYP/6–311 + G(3DF, 3P) level. The present model and the Mathieu’s model (Mathieu et al. Fuel 182(2016): 597) were then validated against present measured ignition delay times, as well as some laminar flame speed data and ignition data in the literature. The present model shows better or comparable predictions with the experimental data. The main species concentration evolution and reaction analysis were presented, based on which the experimentally observed two-stage ignition behavior was interpreted.

Variability of the mesopause temperature and concentrations of reactive components of the mid-latitude atmosphere during sudden stratospheric warmings

We investigated the variations in the temperature regime, atomic oxygen, and ozone concentrations during the 2013 January major sudden stratospheric warming (SSW) and the 2017 February minor SSW. Data from the spectrometric observations of the hydroxyl emission at the longitudinally spaced mid-latitude sites Tory (51.8° N, 103.1° E) and Zvenigorod (55.7º N, 36.8º E), SABER TIMED satellite measurements and MERRA reanalysis were analysed. Concentrations of the atomic oxygen and ozone at the OH emission layer were calculated by using experimental data on the emission intensity and rotational temperature of the OH molecule, photochemical model of OH radiation, and MSISE-E-90 model. Significant changes in the OH temperature and emission intensity, as well as in the concentrations of atomic oxygen and ozone during the SSWs were revealed. These effects may be caused by variations in the height of the hydroxyl emission layer due to the enhancement of vertical motion in the atmosphere during the SSW. We found an increase in the day-to-day variability of the mesopause temperature up to 3 times in comparison with the mean seasonal values. This may indicate the SSW-associated intensification of the manifestation of the traveling planetary waves activity in the upper atmosphere.

Temperature determination in a shock tube using hydroxyl radical A-X band emission

Temperature determination in a shock tube is one of the most important factors to understand the relevant flow physics inside. In the present study, the reservoir temperature determination in a shock tube using the ultraviolet emission spectra of hydroxyl radical (OH) A-X band was carried out. A radiation model for the OH A-X transition was developed, and it was validated using the benchmark data. Curve fit parameters, such as a peak-to-peak ratio and the absolute peak intensity of the P-branch, are proposed to evaluate the rotational temperature and the OH number density from the measured emission spectra. In the shock tube experiments, humid air from the atmosphere was employed as a test gas, and a small amount of the ultraviolet OH emission was measured behind the reflected shock wave. The measured spectrum was converted to the rotational temperature and the number density using the present model of the OH A-X emission. Then, the evaluated rotational temperature was compared with the calculated values of the reservoir condition behind the reflected shock wave. A good agreement was detected between the measured and the calculated temperatures, which are 4020 ± 290 K and 4110 ± 220 K, respectively. It was recognized that the reservoir temperature behind the reflected shock wave is well described by the present model of the OH A-X ultraviolet emission.

Water and OH Emission from the Inner Disk of a Herbig Ae/Be Star

Abstract We report the detection of hot H2O and OH emission from the Herbig Ae/Be star HD 101412 using the Cryogenic Infrared Echelle Spectrograph on the Very Large Telescope. Previous studies of Herbig Ae/Be stars have shown the presence of OH around some of these sources, but H2O has proven more elusive. While marginal water emission has been reported in the mid-infrared, and a few Herbig Ae/Be stars show water emission in the far-infrared, water emission near 2.9 μm has not been previously detected. We apply slab models to the rovibrational OH, H2O, and CO spectra of this source and show that the molecules are consistent with being cospatial. We discuss the possibility that the detection of the CO overtone bandhead emission, detection of water emission, and the large line to continuum contrast of the OH lines may be connected to its high inclination and the λ Boö nature of this star. If the low abundance of refractories results from the selective accretion of gas relative to dust, the inner disk of HD 101412 should be strongly dust-depleted, allowing us to probe deeper columns of molecular gas in the disk, enhancing its molecular emission. Our detection of C- and O-bearing molecules from the inner disk of HD 101412 is consistent with the expected presence, in this scenario, of abundant volatiles in the accreting gas.

Near-UV and optical spectroscopy of comets using the ISIS spectrograph on theWHT

We present an analysis of long-slit cometary spectroscopy using the dual-arm ISIS spectrograph on the 4.2 m WHT. Eleven comets were observed over two nights in 2016 March and we detected the OH (0-0) emission band at 3085 {\AA} in the spectra of five of these comets. Emission bands of the species NH, CN, C$_{3}$, C$_{2}$, NH$_{2}$ and [OI] were also detected. We used Haser modelling to determine molecular production rates and abundance ratios for the observed species. We found that our average abundances relative to OH and CN were generally consistent with those measured in previous studies.

Comparison subpolar mesopause OH(6-2) temperature over Yakutia with the calculated data of NRLMSISE-00 model for 1999-2015

The analysis of changes in temperature of mesopause region based on fluctuation measurements of rotational temperature and intensity of molecular emission of hydroxyl OH (6-2) excited at ∼87 km altitude is presented. Observations were carried out at the Maimaga station (63°N, 129.5°E), at a distance of 120 km to the north from Yakutsk. Measurements were conducted with a digital infrared spectrograph. The temperature was determined from the distribution of the emission intensity in the different branches of the molecular hydroxyl band. Comparison OH(6-2) temperature with the calculated data of NRLMSISE-00 model was defined based on the data received from 1999 to 2015. 2320 midnight temperature values of hydroxyl OH (6-2) suitable for comparison were obtained at the Maimaga station over 16 years of measurements. The NRLMSISE-00 model describes temperature changes at the height of the mesopause region from October to April within the experimental fluctuations with a seasonal temperature variation of ∼ 35 K, deviations from the experimental values are no more than 7 ± 4 K. A correlation analysis was performed to compare the rotational temperature OH (6-2) and the NRLMSISE-00 model calculations. When the number of observations at the station Maimaga more than 180 days (about six months) correlation coefficient R> 0.7. This means that the NRLMSISE-00 model accurately describes the temperature changes of the subauroral mesopause.

Ignition and early stage combustion of H2–O2 mixture upon the photodissociation of O2 molecules by UV laser radiation: Experimental and numerical study

The ignition and combustion of H2O2 mixture upon the photodissociation of O2 molecules by the resonance laser radiation with a wavelength of 193 nm are studied both experimentally and computationally. The experimental test bench equipped with CARS and fluorescent diagnostic techniques was created and applied for the measurement of the induction time and velocity of combustion front during laser-induced ignition of the H2O2 mixture in the model chamber. The complementary experiments on measuring the temperature and recording the emission of OH(X2Π) and OH(A2Σ+) radicals indicate that it is possible to ignite the H2O2 mixture with ϕ= 1–3 and P0 = 1–3 atm at a rather low temperature ∼700 K, which is below the autoignition temperature, under the action of focused laser radiation (λ= 193 nm) with the energy in the pulse of ∼25–150 mJ. And the induction time is rather small and varies in the range of 8–50 µs depending on mixture parameters and laser pulse energy. The analysis of ignition and combustion processes in the H2O2 mixture under the action of resonance laser radiation is carried out on basis of two-dimensional numerical simulation with the use of the detailed kinetic mechanism of H2 oxidation supplemented by the set of reactions describing the formation of electronically excited radicals OH(A2Σ+). A special methodology for the calculation of the radiation absorption and determination of oxygen atoms concentration along the laser beam path was applied. The elaborated model allows us to describe the experimentally measured data for the induction time, the velocity of the combustion front, the space-time distribution of the OH radicals in the ground and excited states, and the temperature evolution in the focal region of the initiating laser radiation.

Neutral temperature and atmospheric water vapour retrieval from spectral fitting of auroral and airglow emissions

Abstract. We have developed a spectral fitting method to retrieve upper atmospheric parameters at multiple altitudes simultaneously during times of aurora, allowing us to measure neutral temperatures and column densities of water vapour. We use the method to separate airglow OH emissions from auroral O+ and N2 in observations between 725 and 740 nm using the High Throughput Imaging Echelle Spectrograph (HiTIES) located on Svalbard. In this paper, we describe our new method and show the results of Monte Carlo simulations using synthetic spectra which demonstrate the validity of the spectral fitting method and provide an indication of uncertainties on the retrieval of each atmospheric parameter. We show that the method allows for the retrieval of OH temperatures with an uncertainty of 6 % when contamination by N2 emission is small. N2 temperatures can be retrieved with uncertainties down to 3 %–5 % when N2 emission intensity is high. We can determine the intensity ratio between the O+ doublets at 732 and 733 nm (which is a function of temperature) with an uncertainty of 5 %.

Search for high-mass protostars with ALMA revealed up to kilo-parsec scales (SPARKS)

The conditions leading to the formation of the most massive O-type stars are still an enigma in modern astrophysics. To assess the physical conditions of high-mass protostars in their main accretion phase, here we present a case study of a young massive clump selected from the ATLASGAL survey, G328.2551–0.5321. The source exhibits a bolometric luminosity of 1.3 × 104L⊙, which allows us to estimate that its current protostellar mass lies between ~11 and 16M⊙. We show high angular resolution observations with ALMA that reach a physical scale of ~400 au. To reveal the structure of this high-mass protostellar envelope in detail at a ~0.17′′ resolution, we used the thermal dust continuum emission and spectroscopic information, amongst others from the CO (J= 3–2) line, which is sensitive to the high-velocity molecular outflow of the source. We also used the SiO (J= 8–7) and SO2(J= 82,6− 71,7) lines, which trace shocks along the outflow, as well as several CH3OH and HC3N lines that probe the gas of the inner envelope in the closest vicinity of the protostar. Our observations of the dust continuum emission reveal a single high-mass protostellar envelope, down to our resolution limit. We find evidence for a compact, marginally resolved continuum source that is surrounded by azimuthal elongations that could be consistent with a spiral pattern. We also report on the detection of a rotational line of CH3OH within itsvt= 1 torsionally excited state. This shows two bright emission peaks that are spatially offset from the dust continuum peak and exhibit a distinct velocity component ±4.5 km s−1offset from the systemic velocity of the source. Rotational diagram analysis and models based on local thermodynamic equilibrium assumption require high CH3OH column densities that reachN(CH3OH) = 1.2−2 × 1019cm−2, and kinetic temperatures of the order of 160–200 K at the position of these peaks. A comparison of their morphology and kinematics with those of the outflow component of the CO line and the SO2line suggests that the high-excitation CH3OH spots are associated with the innermost regions of the envelope. While the HC3Nv7= 0 (J= 37–36) line is also detected in the outflow, the HC3Nv7= 1e(J= 38–37) rotational transition within the first vibrationally excited state of the molecule shows a compact morphology. We find that the velocity shifts at the position of the observed high-excitation CH3OH spots correspond well to the expected Keplerian velocity around a central object with 15M⊙consistent with the mass estimate based on the bolometric luminosity of the source. We propose a picture where the CH3OH emission peaks trace the accretion shocks around the centrifugal barrier, pinpointing the interaction region between the collapsing envelope and an accretion disc. The physical properties of the accretion disc inferred from these observations suggest a specific angular momentum several times higher than typically observed towards low-mass protostars. This is consistent with a scenario of global collapse setting on at larger scales that could carry a more significant amount of kinetic energy compared to the core-collapse models of low-mass star formation. Furthermore, our results suggest that vibrationally excited HC3N emission could be a new tracer for compact accretion discs around high-mass protostars.

Observations of OH and H2O Maser Emission in the Star-Forming Region S128

Results of monitoring hydroxyl and water masers in the star-forming region S128 are presented. A large number of emission features in the 1665 MHz OH line have been detected in both circular polarizations. In spite of the strong variability of the flux density in the main 1665 MHz line, the radial velocities of the features remained constant. Zeeman splitting of the 1720MHz line equal to 0.86 km/s was detected, corresponding to a longitudinal magnetic field of 3.6 mG. The variability of the H2O emission has a cyclic character with a quasi-period of 4–14 yrs. The evolution of individual features confirms that the H2O sources A and B are associated with an ionization front between two colliding CO clouds, and shows that the activity was transferred from maser B to maser A in 1999–2001.

Herschel spectral-line mapping of the HH211 protostellar system

Context. Mid- and far-infrared observations of the environment around embedded protostars reveal a plethora of high-excitation molecular and atomic emission lines. A number of different mechanisms for the origin of these lines have been proposed, including shocks induced by protostellar jets and radiation by the embedded protostar interacting with its immediate surroundings. Aims. We employ extended spectral-line maps that spatially resolve regions where diverse excitation processes appear to dominate. Studying the morphology and excitation of the most important molecular and atomic coolants, we aim to constrain the physical conditions around the embedded protostellar system HH 211-mm. Methods. Spectro-imaging observations with Herschel/PACS provide emission from major molecular (CO, H2O and OH) and atomic coolants (e.g. [O I]). Emission line maps reveal the morphology of the observed emissions and allow associations between the different species. Comparisons are also made with mid-infrared line maps from Spitzer and sub-mm interferometers. The excitation conditions of the detected molecular species along with the ortho-to-para ratio of water are assessed through Boltzmann diagrams. Further investigations focus on constraining the CO/H2 ratio in shocks and the mass flux of the atomic jet as traced by [O I]. Results. Molecular lines are exited mainly at the terminal bowshocks of the outflow and around the position of the protostar. All lines show maxima at the SE bowshock with the exception of water emission that peaks around the central source. Excitation analysis in all positions shows that CO and H2O are mainly thermally excited at Tex ~ 350 and 90 K respectively, with the CO showing a second temperature component at 750 K towards the SE peak. Excitation analysis breaks down in the case of OH at the blue-shifted bowshock, indicating that the molecule is non-thermally excited. Comparisons between the CO and H2 column densities suggest that the X[CO] value in shocks can be up to an order of magnitude lower than the canonical value of 10−4. The water ortho-to-para ratio around the protostar is only 0.65, indicating low-temperature water ice formation followed by non-distructive photodesorption from the dust grains. The two-sided total atomic mass flux estimated from the [O I] jet sums to 1.65 × 10−6 M⊙ yr−1, a value that is very close to the mass flux previously estimated for the SiO jet and the H2Outflow. Conclusions. The bulk of the cooling from CO, OH and [O I] is associated with gas excited in outflow shocks, with the blue-shifted (SE) outflow showing evidence of a shock-induced UV field responsible for the OH emission. Water lines around the protostar reveal a very low ortho-to-para ratio that can be interpreted in terms of formation from a primordial gas reservoir in the envelope. Finally comparison of the [O I] jet mass flux with the mass fluxes derived for SiO and H2 renders HH 211 the first embedded system where an atomic jet is demonstrably shown to possess enough momentum to drive the observed molecular jets and large-scale outflows.

GAS PRODUCTS OF ARGON PLASMA INTERACTION WITH POLYARAMID AND POLY(ETHYLENE TEREPHTHALATE)

Non-equilibrium plasma is widely used for surface modification of polymer materials. Reactions of plasma active species with polymers lead not only to the surface modification, but to the formation of gaseous products, which change the plasma composition and internal plasma parameters. It results in the dependence of surface etching and modification kinetics on the quantity of material been treated (on sample sizes in a reactor). These phenomena are known as so called “loading effect” and have been studied for the treatment of polypropylene and polyimide films, poly(ethylene terephthalate) films and fabrics in oxygen and air plasma. It can be expected that gas products of noble gas plasma action on polymers will change strongly plasma parameters and modification results. In this paper, experimental data are represented on composition of gas products and their evolution rates at the treatment of polyaramid films, fibers and poly(ethylene terephthalate) fabric in low-pressure argon plasma. Poly(ethylene terephthalate) textile fabric (PET) made of monofilament yarns (SAATI, S.p.A., Italy) and polyaramide (PA) films and complex yarns “Rusar®” (Termotex, Russia) were used in experiments. Direct current discharge was excited in a flow of argon (technical grade) in a glass tube reactor with 3 cm inner diameter. Fabric samples were placed as cylinders on the reactor wall in the discharge positive column. Square of PET samples was varied from 18 to 111 cm2. The PA yarns with the total length of 550 or 1020 cm were placed in the reactor on special holder with the length of 20 cm. Total gas pressure in reactor was varied from 30 to 300 Pa at discharge current of 20 – 110 mA. Gas flow rate in the reactor was kept constant and equal to 30 cm´s-1. Gas phase analysis was carried out by the methods of plasma emission spectroscopy and mass-spectrometry. Plasma emission spectra and mass-spectra show evolution of H2, CO and H2O molecules at the treatment of PA and PET in argon plasma. Evolution rates for different gas products and their mole fractions have been obtained as functions of total gas pressure. Increase in polymer sample square has been shown to result in changing the ratios between evolution rates for different gas products. Sum of CO, H2 and H2O mole fractions increases with polymer sample square and decreases with gas pressure. Dissociation of molecular gas products results in the changing plasma active species. Oxygen and hydrogen atom lines and OH emission bands are observed in plasma emission spectra. Alteration of intensity ratio for О(3p3P ® 3s3S0) and Ar (4p3D3 ® 4s3P2) lines (IO/IAr) versus time after discharge starting shows the possible participation of oxygen atoms in heterogeneous reactions with polymers. Evolution of molecular gas products of heterogeneous reactions influences plasma properties and rates of plasma chemical reactions. The data obtained will be used for the further analysis of mechanisms of heterogeneous reactions of plasma active species with polymers.

Sheath and bulk expansion induced by RF field in atmospheric pressure microwave plasma

A large axial volume expansion of microwave driven plasma at atmospheric pressure is attained with a low power radio frequency (RF) field at an axial location well isolated from the original plasma bulk. The gradual development of volume expansion visualized by high speed ICCD imaging suggests that the free electrons drifting toward the bias electrode promote the prodigious expansion of the sheath, generating a stable plasma stream channel between the microwave and the RF electrodes. Enhanced emissions of OH and N2 spectral lines are observed in the extended plume region for the case of argon microwave plasma, supporting the acceleration of electrons and subsequent generation of radical species. Ozone generation is kept low, below the regulation levels. The coupling of RF field within a range of a few MHz with microwave provides an efficient way of enlarging the microwave plasma volume and enhancing the production of radicals.

Interannual dynamics in intensity of mesoscale hydroxyl nightglow variations over Almaty

The method of digital difference filters is applied to the data analysis of SATI observations of hydroxyl nightglow intensity and rotational temperature at altitudes 85–90 km over Almaty (43°03' N, 76°58' E), Kazakhstan, in 2010–2017. We examine seasonal and interannual variations in monthly average values and standard deviations of variations with periods 0.4–5.4 hrs, which may be associated with internal gravity waves in the mesopause region. The monthly average temperature near the mesopause has a maximum in winter and a minimum in June. The monthly average intensity has an additional maximum in June. Standard deviation of mesoscale rotational temperature variations and characteristics of internal gravity waves are maximum in spring and autumn. The spring maximum of mesoscale OH emission intensity variations is shifted to June. Interannual variations and multi-year trends of OH rotational temperature and emission intensity may differ in detail. This may be connected with seasonal and long-term variations in the complex system of the photochemical processes, which produce the OH nightglow.

Межгодовые изменения интенсивности мезомасштабных вариаций ночного свечения гидроксила в Алма-Ате

The method of digital difference filters is applied to the data analysis of SATI observations of hydroxyl nightglow intensity and rotational temperature at altitudes 85–90 km over Almaty (43°03' N, 76°58' E), Kazakhstan, in 2010–2017. We examine seasonal and interannual variations in average monthly values and standard deviations of variations with periods 0.4–5.4 hrs, which may be associated with internal gravity waves in the mesopause region. The average monthly temperature near the mesopause has a maximum in winter and a minimum in June. The average monthly intensity has an additional maximum in June. Standard deviation of mesoscale rotational temperature variations and characteristics of internal gravity waves are maximum in spring and autumn. The spring maximum of mesoscale OH emission intensity variations is shifted to June. Interannual variations and multi-year trends of OH rotational temperature and emission intensity may differ in detail. This may be connected with seasonal and long-term variations in the complex system of the photochemical processes, which produce the OH nightglow.