Hydroxyl Emission Research Articles

Long-term temperature trend in the mesopause region according to observations of hydroxyl airglow in Zvenigorod

An analysis of the long-term change of the average annual OH* temperature, the values of which were obtained from nighttime spectral observations of the hydroxyl emission bands at the Zvenigorod scientific station (56° N, 37° E) from 1957 to 2022, is presented. This series of OH* temperatures, reflecting the thermal state of the mesopause region, is the longest among all known observations. On its basis, estimates of the linear trend and response of temperature to changes in solar activity was made both in general over the entire set of data and for different time intervals. In the first case, the trend was −0.23 ± 0.04 K/yr. In the second case, the analysis showed strong cooling (−0.53 ± 0.34 K/yr) until the 1970s and its slowdown to −0.14 ± 0.03 K/yr thereafter. A comparison of the results of the analysis with other measurements and model calculations shows that the latter have lower trend values. It is assumed that the reasons for the temperature trend, in addition to the growth of greenhouse gases, the main of which is CO2, may be long-term changes in the dynamics of the upper atmosphere.

Analytical Approximations of the Characteristics of Nighttime Hydroxyl on Mars and Intra-Annual Variations

Observations of vibrationally excited hydroxyl (OH*) emissions are widely used to obtain information about the dynamics and composition of the atmosphere. We present some analytical approximations for the characteristics of the hydroxyl layer in the Martian atmosphere such as OH* concentration at the maximum and height of the maximum, as well as relations for estimating the influence of various factors on the OH* layer in night conditions. These characteristics depend on the temperature of the environment, concentration of atomic oxygen, and their vertical gradients. The relations are applied to the results of numerical modeling using the global atmospheric circulation model for prediction of seasonal behavior of the hydroxyl layer on Mars. Annual and intra-annual variations in the concentration of excited hydroxyl and layer height from the modeling data have both some similarities with those of the Earth and significant differences. The concentration and height maximum in the equatorial, northern and southern midlatitudes vary depending on the season; the maximum concentration and the minimum height fall on the first half of the year. Model calculations confirmed the presence of the peak OH* concentration at polar latitudes in winter at an altitude of approximately 50 km with the volume emission densities of 2.1, 1.4, and 0.6 × 104 photons cm–3 s–1 for vibrational level transitions 1–0, 2–1, and 2–0, respectively. The relations obtained may be used for the analysis of measurements and interpretation of their variations.

Simplified Relations for the Martian Night-Time OH* Suitable for the Interpretation of Observations

Observations of excited hydroxyl (OH*) emissions are broadly used for inferring information about atmospheric dynamics and composition. We present several analytical approximations for characterizing the excited hydroxyl layer in the Martian atmosphere. They include the OH* number density at the maximum and the height of the peak, along with the relations for assessing different impacts on the OH* layer under night-time conditions. These characteristics are determined by the ambient temperature, atomic oxygen concentration, and their vertical gradients. The derived relations can be used for the analysis of airglow measurements and the interpretation of their variations.

Exploring Altitudinal Resolution of Twilight Airglow Red Lines Using Twilight Photometer

AbstractTwilight Photometer observations were carried out at low latitude station Kolhapur (16039’42.2”N, 74014’20.8”E) India, during the period 1 January 2009 to 31 December 2011 to yield a reasonable qualitative picture of the day‐to‐day variability of the vertical distribution of the atmospheric aerosols from about 6 km to a maximum of 350 km. In this study, one attempt was made to observe twilight airglow red lines having wavelengths in between 6100 Å and 7100 Å using the vertical profiles of aerosols. The rate of change of red light due to the twilight airglow shows narrow peaks with ∼600%–1000% rise in intensity than due to aerosol twilight glow. Our observations provides information about ionized Nitrogen (N2) emissions at 6482.05 Å, 6610.56 Å and 6482.70 Å, oxygen red emission lines of 6300 Å and 6364 Å, emission caused by formation of a molecule of nitric oxide (NO), metallic emissions of sodium four red lines between 6500 and 6700 Angstroms and lithium near 6708 Å, hydroxyl (OH) emission at 6329 Å and red sprites emissions (at altitudes 50–90 km). The principal aspiration of this study is to highlight the conspicuous capability of Semiautomatic twilight photometer to study the twilight airglow emission lines. This is the first attempt in India to obtain the twilight airglow data using Twilight photometer. Twilight Photometer, although currently seldom used, is still a very effective and the most appropriate ground based passive remote sensing tool for long‐term monitoring of different atmospheric components in a wide range of altitude for day‐to‐day basis. It is an efficient system having a simple and inexpensive underlying principle of operations, yet exhibits extremely accurate and precise usage and can be operated by even a person of average skill. However, it can be seen that the resultant data was consistent with nearest peer technologies, such as LIDARs, Balloon‐Borne instruments, rocket measurements, satellite observations etc.

Statistical Correction of Mesoscale Variances of the Upper Atmospheric Temperature Based on Observations of the Night Hydroxyl Emission in Zvenigorod

Statistical Correction of Mesoscale Variances of the Upper Atmospheric Temperature Based on Observations of the Night Hydroxyl Emission in Zvenigorod

Studying a Long-Lasting Meteor Trail from Stereo Images and Radar Data

Unique observation of a long-lasting meteor trail of about half an hour duration is described. The trail resulted from a burning meteor from the Leonid storm flux in the middle latitudes over eastern Siberia. We describe three-dimensional morphological characteristics of both the meteor and the long-lasting trail using data from wide-angle CCD cameras. Additionally, we present the meteor and the trail radiolocation characteristics obtained with a meteor radar and ionosonde. The background dynamics of the upper atmosphere at the height where the long-lasting trail developed were observed using data from the meteor radar and Fabry-Perot interferometer. The obtained results allowed the conclusion that the dynamics of a long-lasting trail are conditioned by the wind. However, during the first minutes of trail development, it is possible that a high-speed component is present, resulting from explosion of the meteor body in the atmosphere. A primitive spectral analysis of the long-lasting trail’s optical emissions and earlier studies point to hydroxyl molecules as a possible source of the glow. We believe the enhanced hydroxyl emission could be related to interaction of excited O(1D) oxygen atoms with meteor body water in the Earth’s upper atmosphere.

Seeking celestial positronium with an OH-suppressed diffraction-limited spectrograph.

Celestially, positronium (Ps) has been observed only through gamma-ray emission produced by its annihilation. However, in its triplet state, a Ps atom has a mean lifetime long enough for electronic transitions to occur between quantum states. This produces a recombination spectrum observable in principle at near IR wavelengths, where angular resolution greatly exceeding that of the gamma-ray observations is possible. However, the background in the near IR is dominated by extremely bright atmospheric hydroxyl (OH) emission lines. In this paper, we present the design of a diffraction-limited spectroscopic system using novel photonic components-a photonic lantern, OH fiber Bragg grating filters, and a photonic TIGER 2D pseudo-slit-to observe the Ps Balmer alpha line at 1.3122 µm for the first time, to our knowledge.

First Detection of Hydroxyl Radical Emission from an Exoplanet Atmosphere: High-dispersion Characterization of WASP-33b Using Subaru/IRD

Abstract We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the dayside of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2 m Subaru telescope. The telluric and stellar lines are removed using a detrending algorithm, SysRem. The residuals are then cross-correlated with OH and H2O planetary spectrum templates produced using several different line lists. We check and confirm the accuracy of OH line lists by cross-correlating with the spectrum of GJ 436. As a result, we detect the emission signature of OH at K p of km s−1 and v sys of −0.3 km s−1 with a signal-to-noise ratio (S/N) of 5.4 and a significance of 5.5σ. Additionally, we marginally detect H2O emission in the H-band with an S/N of 4.0 and a significance of 5.2σ using the POKAZATEL line list. However, no significant signal is detected using the HITEMP 2010, which might be due to differences in line positions and strengths, as well as the incompleteness of the line lists. Nonetheless, this marginal detection is consistent with the prediction that H2O is mostly thermally dissociated in the upper atmosphere of the ultra-hot Jupiters. Therefore, along with CO, OH is expected to be one of the most abundant O-bearing molecules in the dayside atmosphere of ultra-hot Jupiters and should be considered when studying their atmospheres.

Lunar Tides in the Mesopause Region Obtained from Summer Temperature of the Hydroxyl Emission Layer

Lunar Tides in the Mesopause Region Obtained from Summer Temperature of the Hydroxyl Emission Layer

Semi-annual variation of excited hydroxyl emission at mid-latitudes

Abstract. Ground-based observations show a phase shift in semi-annual variation of excited hydroxyl (OH∗) emissions at mid-latitudes (43∘ N) compared to those at low latitudes. This differs from the annual cycle at high latitudes. We examine this behaviour by utilising an OH∗ airglow model which was incorporated into a 3D chemistry–transport model (CTM). Through this modelling, we study the morphology of the excited hydroxyl emission layer at mid-latitudes (30–50∘ N), and we assess the impact of the main drivers of its semi-annual variation: temperature, atomic oxygen, and air density. We found that this shift in the semi-annual cycle is determined mainly by the superposition of annual variations of temperature and atomic oxygen concentration. Hence, the winter peak for emission is determined exclusively by atomic oxygen concentration, whereas the summer peak is the superposition of all impacts, with temperature taking a leading role.

Femtosecond inscription of semi-aperiodic multi-notch fiber Bragg gratings using a phase mask.

We present an innovative concept of a semi-aperiodic phase mask design that enables the realization of multi-notch fiber Bragg gratings (FBG). This design utilizes the overlap and interference of near-infrared ultrashort laser pulses diffracted by short sequenced phase mask sections, which not only allows for a highly stable and reproducible inscription of a large number of wavelength filters but also paves the way towards full aperiodic phase masks. The semi-aperiodic FBG inscribed by this phase mask enables versatile notch filters showing multiple non-equidistant resonances. Those filters target applications, for instance in ground-based telescopes, where a large number of hydroxyl emission lines emitted in the upper atmosphere at near-infrared wavelengths restrict the observation of faint extraterrestrial objects.

Thermally induced emission from hydroxyl groups in fused silica optical fibers

Abstract Hydroxyl is one of the most common impurities in fused silica optical fibers. For an optical fiber based sensor operating at lower temperatures, hydroxyl presence in the fiber core causes absorption in the near infrared region. When the sensor is exposed to a high temperature environment, emission from hydroxyl can be strong enough to affect accuracy of the sensor. To better understand the hydroxyl emission phenomenon in silica optical fibers at high temperatures, the emission intensity of step index, pure silica core, multimode fibers was measured at temperatures from 600 °C to 1200 °C, and was used to evaluate the activation energy of the thermally induced emission. The removal of hydroxyls by annealing the silica fiber in a nitrogen environment was also conducted at selected temperatures to determine the time dependence of the process. The measurements and calculations show that the hydroxyl emission intensity increases exponentially with temperature, and that the hydroxyl removal process also follows an Arrhenius relationship. The results give insight into appropriate optical fiber sensor designs to minimize signal degradation caused by hydroxyl emission intensity change.

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.

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.

Realization of aperiodic fiber Bragg gratings with ultrashort laser pulses and the line-by-line technique

We demonstrate the fabrication of aperiodic fiber Bragg gratings (AFBGs) for their application as filter elements. Direct inscription was performed by focusing ultrashort laser pulses with an oil-immersion objective into the fiber core and utilizing the line-by-line technique for flexible period adaptation. The AFBGs inscribed allow for the suppression of 10 lines in a single grating and are in excellent agreement with simulations based on the specific design. Applications in astronomy for the suppression of hydroxyl emission lines are discussed.

Comparison between seasonal variations in tidal and internal gravity wave activity as derived from observations at Maimaga and Tiksi

Since 2015, simultaneous observations of temperature of the high-latitude mesopause (87 km) have been made at Maimaga (63.04° N, 129.51° E) and Tiksi (71.58° N, 128.77° E) stations. These stations record spectra with Shamrock (Andor) photosensitive infrared spectrographs detecting the OH (3, 1) band in the near-infrared region (about 1.5 μm). We analyze temperature data obtained in observation seasons from 2015 to 2017. Standard deviations of temperature σ from its mean values are taken as characteristics of wave activity at night. We have obtained standard temperature deviations corresponding to internal gravity waves (IGW) (σgw) and tidal waves (σtd). Mean night rotational temperatures of hydroxyl emission almost coincide, and seasonal variations of gravity and tidal waves have a similar form during two seasons of simultaneous observations at Tiksi and Maimaga.

Сравнение сезонных вариаций активности приливных и внутренних гравитационных волн по наблюдениям на станциях Маймага и Тикси

Since 2015, simultaneous observations of temperature of the high-latitude mesopause (87 km) have been made at Maimaga (63.04° N, 129.51° E) and Tiksi (71.58° N, 128.77° E) stations. These stations record spectra with Shamrock (Andor) photosensitive infrared spectrographs detecting the OH (3, 1) band in the near-infrared region (about 1.5 μm). We analyze temperature data obtained in observation seasons from 2015 to 2017. Standard deviations of temperature σ from its mean values are taken as characteristics of wave activity at night. We have obtained standard temperature deviations corresponding to internal gravity waves (IGW) (σgw) and tidal waves (σtd). Mean night rotational temperatures of hydroxyl emission almost coincide, and seasonal variations of gravity and tidal waves have a similar form during two seasons of simultaneous observations at Tiksi and Maimaga.

Derivation of vertical wavelengths of gravity waves in the MLT-region from multispectral airglow observations

We present the derivation of gravity wave vertical wavelengths from OH airglow observations of different vibrational transitions. It utilizes small phase shifts regularly observed between the OH(3-1) and OH(4-2) intensities in the spectra of the GRIPS (GRound-based Infrared P-branch Spectrometer) instruments, which record the OH airglow emissions in the wavelength range from 1.5 μm to 1.6 μm simultaneously. These phase shifts are interpreted as being due to gravity waves passing through the OH airglow layer and affecting individual vibrational transitions at slightly different times due to small differences in their emission heights.The results are compared with co-located observations of the Na-Lidar measurements acquired between 2010 and 2014 at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR, 69.28° N, 16.01° E), Norway. This comparison shows best agreement if the mean height difference of the OH(3-1) and OH(4-2) emission is assumed to be 540 m (1σ = 160 m).The results are also compared with co-located observations of the OH(6-2)- and O2b(0-1)-transitions by means of spectrometer observations (TANGOO instrument, Tilting-filter spectrometer for Atmospheric Nocturnal Ground-based Oxygen & hydrOxyl emission measurements) performed from 2013 until 2016 at Oberpfaffenhofen (48.08° N, 11.27° E), Germany. For approximately 40% of all wave events observed with GRIPS in the period range from 0.25 h to 17 h, a quantitative estimate of the phase relationship between the OH(3-1) and OH(4-2) intensities can be retrieved from the spectra allowing derivation of vertical wavelengths. The retrieval performs best for wave periods below two hours (80% success rate) and worse for periods above ten hours (successful in less than 10% of the cases). The average wavelength determined from 102 events amounts to 22.9 km (1σ: 9.0 km). The corresponding mean wavelength determined from the TANGOO observations amounts to 22.6 km ± 10.5 km, if a mean separation of 6.5 km is assumed for the height difference between the OH(6-2) and O2b(0-1)-transitions.

Variations in the amount of water ice on Ceres' surface suggest a seasonal water cycle.

The dwarf planet Ceres is known to host a considerable amount of water in its interior, and areas of water ice were detected by the Dawn spacecraft on its surface. Moreover, sporadic water and hydroxyl emissions have been observed from space telescopes. We report the detection of water ice in a mid-latitude crater and its unexpected variation with time. The Dawn spectrometer data show a change of water ice signatures over a period of 6 months, which is well modeled as ~2-km2 increase of water ice. The observed increase, coupled with Ceres' orbital parameters, points to an ongoing process that seems correlated with solar flux. The reported variation on Ceres' surface indicates that this body is chemically and physically active at the present time.

The Direct Detection and Characterization of M-dwarf Planets Using Light Echoes

Abstract Exoplanets orbiting M-dwarf stars are a prime target in the search for life in the universe. M-dwarf stars are active, with powerful flares that could adversely impact prospects for life, though there are counter-arguments. Here, we turn flaring to advantage and describe ways in which it can be used to enhance the detectability of planets, in the absence of transits or a coronagraph, significantly expanding the accessible discovery and characterization space. Flares produce brief bursts of intense luminosity, after which the star dims. Due to the light travel time between the star and planet, the planet receives the high-intensity pulse, which it re-emits through scattering (a light echo) or intrinsic emission when the star is much fainter, thereby increasing the planet’s detectability. The planet’s light-echo emission can potentially be discriminated from that of the host star by means of a time delay, Doppler shift, spatial shift, and polarization, each of which can improve the contrast of the planet to the star. Scattered light can reveal the albedo spectrum of the planet to within a size scale factor, and is likely to be polarized. Intrinsic emission mechanisms include fluorescent pumping of multiple molecular hydrogen and neutral oxygen lines by intense Lyα and Lyβ flare emission, recombination radiation of ionized and photodissociated species, and atmospheric processes such as terrestrial upper atmosphere airglow and near-infrared hydroxyl emission. We discuss the feasibility of detecting light echoes and find that light echo detection is possible under favorable circumstances.