Atmospheric Band Emission Research Articles

Satellite observations of gravity wave momentum flux in the mesosphere and lower thermosphere (MLT): feasibility and requirements

Abstract. In the recent decade it became evident that we need to revise our picture of how gravity waves (GWs) reach the mesosphere and lower thermosphere (MLT). This has consequences for our understanding not just of the properties of the GWs themselves, but in particular of the global circulation in the MLT. Information on spectral distribution, direction, and zonal mean GW momentum flux is required to test the theoretical and modeling findings. In this study, we propose a constellation of two CubeSats for observing mesoscale GWs in the MLT region by means of temperature limb sounding in order to derive such constraints. Each CubeSat deploys a highly miniaturized spatial heterodyne interferometer (SHI) for the measurement of global oxygen atmospheric band emissions. From these emissions, the 3-D temperature structure can be inferred. We propose obtaining four independent observation tracks by splitting the interferograms in the center and thus gaining two observation tracks for each satellite. We present a feasibility study of this concept based on self-consistent, high-resolution global model data. This yields a full chain of end-to-end (E2E) simulations incorporating (1) orbit simulation, (2) airglow forward modeling, (3) tomographic temperature retrieval, (4) 3-D wave analysis, and (5) GW momentum flux (GWMF) calculation. The simulation performance is evaluated by comparing the retrieved zonal mean GWMF with that computed directly from the model wind data. A major question to be considered in our assessment is the minimum number of tracks required for the derivation of 3-D GW parameters. The main result from our simulations is that the GW polarization relations are still valid in the MLT region and can thus be employed for inferring GWMF from the 3-D temperature distributions. Based on the E2E simulations for gaining zonal mean climatologies of GW momentum flux, we demonstrate that our approach is robust and stable, given a four-track observation geometry and the expected instrument noise under nominal operation conditions. Using phase speed and direction spectra we show also that the properties of individual wave events are recovered when employing four tracks. Finally, we discuss the potential of the proposed observations to address current topics in the GW research. We outline for which investigations ancillary data are required to answer science questions.

Combined multi-band infrared camouflage and thermal management via a simple multilayer structure design.

Infrared camouflage is crucial for high-temperature objects to avoid detection, and spontaneous infrared radiation is also an important way for high-temperature objects to dissipate heat. Therefore, selective infrared emission has become significant for the coating design of surfaces such as aircraft, which require low emission in the atmospheric window band (3-5 µm and 8-14 µm) and high emission outside it (5-8 µm). This Letter employs a simple multilayer film structure to achieve selective regulation of the material emission spectrum. Combining the transfer matrix method and genetic algorithm, a multilayer film structure containing 12 layers of three high-temperature-resistant materials (SiO2, TiO2 and Ge) has been designed. It shows fairly low emissivity in two main bands of infrared detection (ε3∼5µm=0.14, ε8∼14µm=0.21) and high emissivity outside them (ε5∼8µm=0.86), and this infrared selectivity can be well maintained with the incident angle rising from 0 to 60 deg. The Poynting vector distribution in the material at different incident wavelengths is analyzed to further explore the interference mechanism to achieve spectral selective emission. The significance of this work lies in the construction of a relatively simple coating design while ensuring efficient infrared camouflage and thermal management performance.

Nighttime O(1D) and corresponding Atmospheric Band emission (762 nm) derived from rocket-borne experiment

Based on common volume rocket-borne measurements of temperature, densities of atomic oxygen and neutral air, we derived O(1D) nighttime concentrations and corresponding Atmospheric band emission (762 nm). This is one of the first retrievals of the nighttime O(1D) concentration. Recently, Kalogerakis, Sharma and co-workers have suggested a new production path of O(1D) based on the reaction of vibrationally excited OH and O. We calculate Atmospheric band volume emission related to the population of O2(b1Σg+) from O(1D) and compare with total Atmospheric band emissions observed during the same rocket launch. This allows an estimation of the relative contribution of the new Kalogerakis-Sharma mechanism (KSM) to the total Atmospheric band emission. The concentration of O(1D) due to KSM amounts to several tens cm−3 with a peak around 95 km. The KSM gives an essential contribution to the total Atmospheric band volume emission (762 nm). Additionally, we illustrate analytically that the expressions for volume emission by the new KSM and the traditional two-step mechanism have similar functional dependences on the atmospheric concentrations of O and O2. This causes an ambiguity, when interpreting Atmospheric band observations in terms of the one mechanism or the other.

Effect of OH emission on the temperature and wind measurements derived from limb-viewing observations of the 1.27 µm O2 dayglow

Abstract. The O2(a1Δg) emission near 1.27 µm is well-suited for remote sensing of global wind and temperature in near-space by limb-viewing observations to its bright signal and extended altitude coverage. However, vibrational–rotational emission lines of the OH dayglow produced by the hydrogen–ozone reaction (H+O3→OH•+O2) overlap the infrared atmospheric band emission (a1Δg→X3Σg) of O2. The main goal of this paper is to discuss the effect of OH emission on the wind and temperature measurements derived from the 1.27 µm O2 dayglow limb-viewing observations. The O2 dayglow and OH dayglow spectrum over the spectral region and altitude range of interest is calculated by using the line-by-line radiative transfer model and the most recent photochemical model. The method of four-point sampling of the interferogram and sample results of measurement simulations are provided for both O2 dayglow and OH dayglow. It is apparent from the simulations that the presence of OH dayglow as an interfering species decreases the wind and temperature accuracy at all altitudes, but this effect can be reduced considerably by improving OH dayglow knowledge.

A previously unrecognized source of the O2 Atmospheric band emission in Earth's nightglow.

Earth's night sky continuously produces a faint chemiluminescence known as nightglow. Two prominent nighttime emissions around 90 km are the O2 Atmospheric and the OH Meinel band systems. Despite a plethora of studies since their identification seven decades ago, substantial gaps persist in our understanding of the mechanisms that control them. This report shows that oxygen atoms connect these two emissions: Fast, multiquantum, vibrational-to-electronic relaxation of OH(v) by O atoms activates a pathway that generates O2 Atmospheric band emission. This newly discovered source exhibits a strong altitude dependence and can contribute a majority of the observed O2 Atmospheric band emission when the peaks of the OH and O-atom layers overlap. The new findings call for a reinterpretation of Earth's nightglow emissions and a revision of relevant atmospheric models.

Atmospheric band fitting coefficients derived from a self-consistent rocket-borne experiment

Abstract. Based on self-consistent rocket-borne measurements of temperature, the densities of atomic oxygen and neutral air, and the volume emission of the atmospheric band (762 nm), we examined the one-step and two-step excitation mechanism of O2b1Σg+ for nighttime conditions. Following McDade et al. (1986), we derived the empirical fitting coefficients, which parameterize the atmospheric band emission O2b1Σg+-X3Σg-0,0. This allows us to derive the atomic oxygen concentration from nighttime observations of atmospheric band emission O2b1Σg+-X3Σg-0,0. The derived empirical parameters can also be utilized for atmospheric band modeling. Additionally, we derived the fit function and corresponding coefficients for the combined (one- and two-step) mechanism. The simultaneous common volume measurements of all the parameters involved in the theoretical calculation of the observed O2b1Σg+-X3Σg-0,0 emission, i.e., temperature and density of the background air, atomic oxygen density, and volume emission rate, is the novelty and the advantage of this work.

Empirical values of branching ratios in the three-body recombination reaction for O(1S) and O2(0,0) airglow chemistry

The branching ratios ε and α in the three-body recombination reaction for O(1S) greenline and O2(0,0) atmospheric band airglow chemistry represent the fraction of O2 that branch into the b1∑g+ and c1∑u- electronic states, respectively. In the present work, the empirical values of these branching ratios have been deduced using a numerical optimization approach. They were obtained using the optimization scheme known as the Covariance Matrix Adaptation Evolution Strategy (CMA-ES) with our MACD-00 model and simultaneous volume emission rate (VER) measurements of the O(1S) greenline and O2(0,0) atmospheric band emissions. The CMA-ES was employed as the optimization algorithm that would match the O(1S) and O2(0,0) VER profiles simulated by the MACD-00 model to observations made by OXYGEN/S35, S310.10, NASA Flight 4.339, ETON flights P229H and P230H, OASIS, SOAP/WINE, MULTIFOT, and WINDII. We found that most of the values deduced for ε were in the [0.1, 0.3] range, while most of the values of α were in the [0.01, 0.03] range. Excluding the outliers, the average branching ratio values involving the production of O2(b1∑g+) and O2(c1∑u-) were determined to be ε = 0.15 ± 0.02 and α = 0.018 ± 0.004, respectively. Overall, the simulations showed good agreement with the observations albeit with some discrepancies in the peak altitudes and shape of the profiles, possibly due to small perturbations in the observed VER profiles that are not considered in our simulations.

An investigation of long-distance propagation of gravity waves under CAWSES India Phase II Programme

Abstract. Coordinated measurements of airglow features from the mesosphere–lower thermosphere (MLT) region were performed at Allahabad (25.5° N, 81.9° E) and Gadanki (13.5° N, 79.2° E), India to study the propagation of gravity waves in 13–27° N latitude range during the period June 2009 to May 2010 under CAWSES (Climate And Weather of Sun Earth System) India Phase II Programme. At Allahabad, imaging observations of OH broadband emissions and OI 557.7 nm emission were made using an all-sky imager, while at Gadanki photometric measurements of OH (6, 2) Meinel band and O2 (0, 1) Atmospheric band emissions were carried out. On many occasions, the nightly observations reveal the presence of similar waves at both locations. Typically, the period of observed similar waves lay in the 2.2–4.5 h range, had large phase speeds (~ 77–331 m s−1) and large wavelengths (~ 1194–2746 km). The images of outgoing long-wave radiation activity of the National Oceanic and Atmospheric Administration (NOAA) and the high-resolution infrared images of KALPANA-1 satellite suggest that such waves possibly originated from some nearby convective sources. An analysis of their propagation characteristics in conjunction with SABER/TIMED temperature profiles and Horizontal Wind Model (HWM 2007) wind estimates suggest that the waves propagated over long distances (~ 1200–2000 km) in atmospheric ducts.

O2(b(1)Σ(+)(g), υ = 0, 1) relative yields in O((1)D) + O2 energy transfer.

Energy transfer from O((1)D) to O2 is the main source of O2(b(1)Σ(+)(g) in vibrational levels υ = 0 and 1 in the Earth's thermosphere. Knowledge of the relative yields for O2(b(1)Σ(+)(g) production in υ = 0 and 1 is essential for a reliable interpretation and modeling of the O2 atmospheric band emissions (b(1)Σ(+)(g) - X (3)Σ(-)(g) from these two vibrational levels. We report laboratory measurements of the relative yields at room temperature. In the experiments, O2(b(1)Σ(+)(g), υ = 0, 1) is generated by O((1)D) + O2 collisions following partial photodissociation of O2 at 157.6 nm. O2(b(1)Σ(+)(g), υ = 0, 1) emission detection is used to monitor the temporal evolution of the vibrational level populations. The measured fractional yield for υ = 1 is 0.8 ± 0.1, in contrast with the results of previous studies that indicated dominant O2(b(1)Σ(+)(g), υ = 0) production. A revision is warranted of the values used for these relative yields in atmospheric models.

Modeled O2 airglow distributions in the Martian atmosphere

We use a three‐dimensional atmospheric model to study the airglow emissions from molecular oxygen in the Martian atmosphere. We estimate the O2 Herzberg I & II, the Chamberlain, and the Infrared Atmospheric band emissions from different sets of kinetic parameters available in the literature. As expected, the enhanced production of atomic oxygen during daytime leads to stronger emissions at 12 hour local time than at 00 hour local time. Nevertheless, at night, the strongest emissions are found in the subtropics and around the terminator where the photochemistry of atomic oxygen is more active. Among the simulated emissions, we find that the Infrared Atmospheric emission is the most intense, as expected, and has maximum intensity reaching a few megarayleighs over the poles during the equinoctial seasons, and an average intensity over the equatorial latitudes of 50 kilorayleighs. We investigate the impact of different levels of water and dust content on airglow and we observe that the airglow structure is modulated by variations in the background atmospheric conditions. Moreover, comparisons of the emission with observations from instruments on board Mars orbiters and with ground‐based measurements from Earth allow us to validate the consistency of our airglow model. Finally, we observe that the emission profiles from all band systems show structures; a double‐layer profile is very frequent, and is representative of the vertical distribution of the current measurements of O2 nightglow. This paper emphasizes the advantage of using three‐dimensional global circulation models for the diagnostic of O2 photochemistry in CO2‐dominated atmospheres.

Observations of molecular oxygen Atmospheric band emission in the thermosphere using the near infrared spectrometer on the ISS/RAIDS experiment

Observations of airglow emission using the RAIDS (Remote Atmospheric and Ionospheric Detection System) instruments on the International Space Station Kibo module are reported and compared to a photochemical model of the emission process. Launched in Sept. 2009, RAIDS performed routine observations of the O2(b1Σ → X3Σ) Atmospheric band (O2 A‐band) transition during solar minimum conditions from October 2009 to December 2010. Limb brightness of the (0,0), (0,1) and (1,1) vibration band emissions were measured in the altitude range 80 to 180 km with the Near Infrared Spectrometer (NIRS) instrument, one of eight limb viewing instruments in the RAIDS experiment. Comparison of observed brightness profiles with the model shows very good agreement for the (0,0) and (0,1) bands. The model underestimates the (1,1) brightness profiles throughout the region, especially near the peak. Reasonable variations of composition and selected rate constants do not account for the underestimation of (1,1) band brightness. A contributing factor could be in the assumption of detailed balance and the accepted energy transfer pathways that redistribute energy between the v = 0 and v = 1 states.

A seasonal study of mesospheric temperatures and emission intensities at Adelaide and Alice Springs

Aerospace imagers operating at Alice Springs (23°42′S, 133°53′E) and Adelaide (34°55′S, 138°36′E) have collected more than 4‐year of OH and O2 atmospheric emission data. Images taken over the course of each moonless night at 5‐min intervals were used to determine OH Meinel (6, 2) and O2 Atmospheric (0, 1) band emission intensities and temperatures, as well as atmospheric gravity wave parameters. The NCAR general circulation model TIME‐GCM was run for years 2002–2005 for comparison with these data. The data presented here show the interannual variability of OH and O2A emissions at two sites, Alice Springs and Adelaide, over a 4‐a period. It was found that the TIME‐GCM successfully reproduces many observed features of the data, including equinoctial maxima associated with the diurnal tide, a 6‐h phase shift between OH temperature and intensity maxima, and springtime OH intensity enhancements at Alice Springs. However, the model tends to underestimate the depth of the summertime temperature minimum at both sites, possibly due to inadequate specification of the seasonal variation of gravity waves in the model. The model does, however, successfully describe many of the mesospheric changes observed during the 2002 stratospheric warming event.

O(1S), OH, and O2(b) airglow layer perturbations due to AGWs and their implied effects on the atmosphere

The O(1S) (green line) night airglow emission in response to atmospheric gravity wave (AGW) perturbations was simulated with a linear, one‐dimensional model. The results were combined with previously modeled O2(b, 0–1) atmospheric band and OH Meinel band emission response (Liu and Swenson, 2003) to derive amplitude and phase relations among multiple airglow layers in response to gravity waves with various intrinsic parameters and damping rates (β). The simulations show that the vertical profile of the standard deviation of the perturbed green line volume emission rate (VER) has a centroid altitude that is 3 km lower and a full‐width‐half‐maximum 2.1 km smaller than the unperturbed VER profile, similar to findings for the OH and O2(b) band layers. Relative phase differences and amplitudes of vertically propagating waves can be deduced from zenith observations of the layers. Airglow weighted responses to waves are related through a cancellation factor (CF) for both layer intensity and temperature. The vertical wavelength can be deduced from relative phase information of three airglow layers separated in altitude. The vertical flux of horizontal momentum associated with gravity waves is deduced from intrinsic wave parameters. Wave damping versus altitude is used to deduce the flux divergence and local accelerations resulting from dissipative waves. The simulations are useful in calculating wave information and wave effects on the atmosphere from multiwavelength, zenith airglow observations.

On the use of simultaneous measurements of OH and O<sub>2</sub> emissions to investigate wave growth and dissipation

Abstract. Simultaneous measurements of mesospheric OH (6–2) Meinel and O2 (0–1) Atmospheric band emissions from a low-latitude station, Maui, Hawaii (20.8° N, 156.2° W) are utilized to study the wave characteristics and associated processes. Deduced temperatures show large variability in both OH and O2 data. The seasonal variability in the temperature shows a well-defined, semiannual type of oscillation, which are comparable to the ground-based rocket sounding data. The "Wave Growth Factor", a ratio of normalized perturbation amplitude in O2 to the OH temperature variability, is estimated for principal as well as residual smaller period components of the nocturnal variability. It is noticed that smaller period waves (less than 12 h) occasionally have large growth factors of about 3–4 during equinox transitions, an indication of wave amplitude amplification within the 87–94 km altitudes while a strong wave-dissipation occurs throughout the year.

Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes

Abstract Novel measurements of the seasonal variability in mesospheric temperature at low-latitudes have been obtained from Maui, Hawaii (20.8°N, 156.2°W) during a 25-month period from October 2001 to January 2004. Independent observations of the OH (6, 2) Meinel band (peak height ∼87 km) and the O2 (0–1) atmospheric band emission (∼94 km) were made using the CEDAR Mesospheric Temperature Mapper. The data revealed a coherent oscillation in emission intensity and rotational temperature with a well-defined periodicity of 181 ± 7 days. The amplitude of this oscillation was determined to be ∼5–6 K in temperature and ∼8–9% in intensity for both the OH and O2 data sets. In addition, a strong asymmetry in the shape of the oscillation was also observed with the spring maximum significantly larger than the fall peak. These data provide new evidence in support of a semi-annual-oscillation in mesospheric temperature (and airglow emission intensities) and help quantify its seasonal characteristics.

Dynamical processes related to the atomic oxygen equinox transition

Both ground based and satellite observations have shown a “springtime transition” in the night-time OI 557.7 nm airglow emission and O 2 atmospheric band emission characterized by a relatively persistent period of very low emission rates around spring equinox at mid and high latitudes, indicating depletion of the peak atomic oxygen between 95 and 100 km . The salient feature of this depletion is reproduced by the NCAR thermosphere–ionosphere–mesosphere-electrodynamics general circulation model simulation. Analysis of the simulation results shows that the mean circulation in the upper mesosphere/mesopause and lower thermosphere is altered significantly by changes in gravity wave filtering and gravity wave forcing around equinox. The change first starts in form of a distinctive circulation cell in the summer lower thermosphere when the westward jet in the summer stratosphere and mesosphere begins to reverse. The circulation cell then becomes deeper and expands to lower altitudes and to the other hemisphere. This circulation can span a large vertical depth and drives an exchange of mass and chemical species between the upper mesosphere and lower thermosphere. The variation of the peak atomic oxygen concentration around equinox is caused by this exchange, and the vertical transport of atomic oxygen dominates the diffusive transport in this process. Additional variability of the atomic oxygen and corresponding airglow emissions may result from the variability of gravity wave sources, planetary waves and transience of their amplitudes and phases, and circulation change due to late and final stratospheric sudden warming.

Airglow emissions and oxygen mixing ratios from the photometer experiment on the Turbulent Oxygen Mixing Experiment (TOMEX)

The Turbulent Oxygen Mixing Experiment (TOMEX) combined Na lidar measurements from Starfire Optical Range in Albuquerque, New Mexico, with a launch of a payload from White Sands Missile Range (WSMR), located a little over 100 km from Starfire. The payload included a trmethyl aluminum release to measure winds and diffusion, a 5‐channel ionization gauge to measure neutral densities, and a 3‐channel photometer experiment to measure atomic oxygen related airglow. The payload was launched at 0957 UT on 26 October 2000 and successfully obtained data from all the experiments. The photometer experiment consisted of three liquid nitrogen cooled filter photometers which measured emission from the O2 atmospheric band (0, 0) emission, the OH Meinel (9, 4) band, and the OI(557.7 nm) greenline. Measurements were made as the rocket went from 80 to 110 km on the upleg. The pointing of the photometers was within a few degrees of zenith. Differentiating these data allowed volume emission rates to be derived which can be inverted to form atomic oxygen density profiles. The interpretation of the data made use of simultaneous atmospheric temperature data from the Na lidar. The airglow data showed lower brightness values and lower peak altitudes for the O2 atmospheric (0, 0) band and OI(557.7 nm) emissions than predicted by the thermosphere/ionosphere/mesopshere/electrodynamics general circulation (TIME‐GCM) model. The peak altitude of the OH Meinel emission seemed nominal. Inverting the O2 atmospheric (0, 0) and OI(557.7 nm) data following McDade et al. [1986] produced O density profiles whose peak densities and peak altitudes are lower than the model values. The shape of the O density profile is also more constant with altitude than model predictions. The O mixing ratio shows a more altitude‐independent profile than given by the model, especially between 85 and 95 km. Significant deviations in the measured shape of the mixing ratio also occur at 90, 97, and 102 km. The interpretation of these data is that the O mixing ratio was significantly perturbed by the passage of an atmospheric gravity wave or tide and the subsequent convective or dynamical instabilities produced by that wave. Dynamically or convectively unstable layers at 90, 97, and 102 km at the time of the launch also appear to be reflected in the mixing ratio data.

Ground‐based observation of high‐altitude, high‐temperature emission in the O2 atmospheric band nightglow

O2(b1Σg+ − X3Σg−) atmospheric band emission, when viewed from the ground outside the auroral zone, is considered to originate in the 90–100 km altitude region, from O‐atom recombination. However, the v = 0,1 levels of the b1Σg+ state can also be generated through an energy transfer process, when O(1D) collides with O2. In the absence of specific altitude information, as in ground‐based measurements, the two sources can still be distinguished because of different characteristic temperatures. We have analyzed sky spectra from the Keck I and II telescopes on Mauna Kea, contrasting solar minimum and maximum conditions and variations with time of night. Utilizing the O2(b‐X) 1‐1 band, we find that in averaged solar minimum conditions, ∼75% of the emission comes from an altitude corresponding to 200 K, while ∼25% has a temperature near 700 K and therefore originates at high altitude. The fraction of high‐temperature emission is often considerably greater early in the evening. At solar maximum, the high altitude component can be dramatically enhanced in the early evening; emission in the 1‐1 band reaches intensitities of 100–150 R, with a rotational temperature near 1000 K. We also observe high‐J b‐X 0‐0 band lines penetrating the Fraunhofer A‐band region, the normal absorption becoming emission. Emission intensites deduced from such observations indicate that the ionospheric 0‐0 band is at least as intense as the 1‐1 band, as expected.

The Isotopic Oxygen Nightglow as Viewed from Mauna Kea

Optical spectra of the terrestrial nightglow in the 520- to 900-nanometer region, as measured by the W. M. Keck telescope on Mauna Kea in Hawaii and the associated high-resolution echelle spectrograph, showed many bands belonging to the important O 2 ( b-X ) Atmospheric Band emission system. Previous ground-based measurements have shown only a single band, from the lowest vibrational level of the emitting state. Of particular interest is the fact that at the 762-nanometer position of the b-X 0-0 band, where earlier studies have shown only absorption features, these results showed both absorption at the 16 O 16 O line positions and well-resolved emission at the positions of many of the 18 O 16 O and 17 O 16 O lines. These findings show that substantial advances can be made in understanding atmospheric emission phenomena by the use of astronomical tools.

Mesospheric energy loss rates by OH and O<sub>2</sub> emissions at 23<sup>°</sup>S

Abstract. The nightglow OH(9, 4) and O2 atmospheric (0,1) band emission intensities and their rotational temperatures T(OH) and T(O2), respectively, observed at Cachoeira Paulista (23°S, 45°W), Brazil, during the period from October 1989 to December 1990, have been analyzed to study the nighttime mesospheric energy loss rates through the radiations from the vibrationally excited OH* and electronically excited O2* bands. The total emission rates of the OH Meinel bands, O2 atmospheric (0,0) and O2 infrared atmospheric (1Δg) bands were calculated using reported data for the relative band intensities I(ν'',ν')/I(9,4), IO2A(0,0)/IO2A(0,1) and IO2(1Δg)/IO2A(0,1). It was found that there is a minimum in equivalent energy loss rate by the OH* Meinel bands during December/January (equivalent energy loss rate of 0.39K/day*, where day* means averaged over the night) and maximum in equivalent energy loss rate during September (equivalent energy loss rate of 0.98K/day*). Energy loss rate by the O2* radiation, on the other hand, is weaker than that by the OH* Meinel bands, showing equivalent energy loss rates of 0.12K/day* and 0.22K/day* during January and September, respectively.