Dayglow Spectrum Research Articles

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.

N2(A) in the Terrestrial Thermosphere

AbstractRecent work has indicated the presence of a nitric oxide (NO) product channel in the reaction between the higher vibrational levels of the first electronically excited state of molecular nitrogen, N2(A ), and atomic oxygen. A steady‐state model for the N2(A) vibrational distribution in the terrestrial thermosphere is here described and validated by comparison with N2 A‐X, Vegard‐Kaplan dayglow spectra from the Ionospheric Spectroscopy and Atmospheric Chemistry spectrograph. A computationally cheaper method is needed for implementation of the N2(A) chemistry into time‐dependent thermospheric models. It is shown that by scaling the photoelectron impact production of ionized N2 by a Gaussian centered near 100 km, the level‐specific N2(A) production rates between 100 and 200 km can be reproduced to within an average of 5%. This scaling, and thus the N2 electron impact ionization/excitation ratio, is nearly independent of existing uncertainties in the 2–20 nm solar soft X‐ray irradiance. To investigate this independence, the N2 electron‐impact excitation cross sections in the GLOW photoelectron model are replaced with the results of Johnson et al. (2005, https://doi.org/10.1029/2005JA011295) and the multipart work of Malone et al. (2009 https://doi.org/10.1103/PhysRevA.79.032704) (Malone, Johnson, Young, et al., 2009, https://doi.org/10.1088/0953-4075/42/22/225202; Malone, Johnson, Kanik, et al., 2009, https://doi.org/10.1103/PhysRevA.79.032705; Malone et al., 2009, https://doi.org/10.1103/PhysRevA.79.032704), together denoted J05M09. Upon updating these cross sections it is found that (1) the total N2 triplet excitation rate remains nearly constant; (2) the steady state N2(A) vibrational distribution is shifted to higher levels; (3) the total N2 singlet excitation rate responsible for the Lyman‐Birge‐Hopfield emission is reduced by 33%. It is argued that adopting the J05M09 cross sections supports (1) the larger X‐ray fluxes measured by the Student Nitric Oxide Explorer (SNOE) and (2) a temperature‐independent N2(A)+O reaction rate coefficient.

Cassini-UVIS observation of dayglow FUV emissions of carbon in the thermosphere of Venus

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37nm resolution by the UVIS instrument during the Cassini flyby of Venus. The intensities of the ultraviolet multiplets of carbon at 126.1, 156.1 and 165.7nm are determined using a least squares fit technique applied to all dayglow spectra recorded by UVIS along the Cassini track. These intensities are compared with the results of a full radiative transfer model of these emissions, that includes the known photochemical sources of photons and resonant scattering of sunlight. The carbon density profile of the Venus thermosphere has never been directly measured and is taken from a model. We find a serious disagreement between these observations and modeling that can be accounted for by applying a scaling factor to the carbon column. This needed scaling factor is found to increase monotonically with solar zenith angle, suggesting a possible photochemical origin to the disagreement, possibly involving the photochemistry of molecular oxygen to which the carbon density is highly sensitive.

EUV spectroscopy of the Venus dayglow with UVIS on Cassini

We analyze EUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus on 24 June 1999, a period of high solar activity level. Emissions from OI, OII, NI, CI and CII and CO have been identified and their disc average intensity has been determined. They are generally somewhat brighter than those determined from the observations made with the HUT spectrograph at a lower activity level, We present the brightness distribution along the foot track of the UVIS slit of the OII 83.4 nm, OI 98.9 nm, Lyman-ß + OI 102.5 nm and NI 120.0 nm multiplets, and the CO C–X and B–X Hopfield–Birge bands. We make a detailed comparison of the intensities of the 834 nm, 989 nm, 120.0 nm multiplets and CO B–X band measured along the slit foot track on the disc with those predicted by an airglow model previously used to analyze Venus and Mars ultraviolet spectra. This model includes the treatment of multiple scattering for the optically thick OI, OII and NI multiplets. It is found that the observed intensity of the OII emission at 83.4 nm is higher than predicted by the model. An increase of the O + ion density relative to the densities usually measured by Pioneer Venus brings the observations and the modeled values into better agreement. The calculated intensity variation of the CO B–X emission along the track of the UVIS slit is in fair agreement with the observations. The intensity of the OI 98.9 nm emission is well predicted by the model if resonance scattering of solar radiation by O atoms is included as a source. The calculated brightness of the NI 120 nm multiplet is larger than observed by a factor of ∼2–3 if photons from all sources encounter multiple scattering. The discrepancy reduces to 30–80% if the photon electron impact and photodissociation of N 2 sources of N( 4S) atoms are considered as optically thin. Overall, we find that the O, N 2 and CO densities from the empirical VTS3 model provide satisfactory agreement between the calculated and the observed EUV airglow emissions.

UVIS observations of the FUV OI and CO 4P Venus dayglow during the Cassini flyby

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. We use a least-squares fit method to determine the brightness of the OI emissions at 130.4 and OI 135.6 nm, and of the bands of the CO fourth positive system which are dominated by fluorescence scattering. We compare the brightness observed along the UVIS foot track of the two OI multiplets with that deduced from a model of the excitation of these emissions by photoelectron impact on O atoms and resonance scattering of the solar 130.4 nm emission. The large optical thickness 130.4 nm emission is accounted for using a radiative transfer model. The airglow intensities are calculated along the foot track and found to agree with the observed 130.4 nm brightness within ∼10%. The modeled OI 135.6 nm brightness is also well reproduced by the model. The oxygen density profile of the VTS3 model is found to be consistent with the observations. We find that self-absorption of the (0, v″) bands of the fourth positive emission of CO is important and we derive a CO vertical column of about 6.4 × 10 15 cm −2 in close agreement with the value provided by the VTS3 empirical atmospheric model.

Analysis of the Astro‐1/Hopkins Ultraviolet Telescope EUV–FUV dayside nadir spectral radiance measurements

The Hopkins Ultraviolet Telescope (HUT) was one of three ultraviolet Astro‐1 observatory instruments on space shuttle Columbia in December 1990 (STS‐35), covering the 830–1850 Å wavelength interval (first order) at ∼3.3 Å spectral resolution. Satellite altitude was 360 km. Dayside nadir measurements were performed during a single orbit on 7 December 1990 under solar maximum (F10.7 = 222), geomagnetically quiet (Ap = 4) conditions, covering late morning local times (solar zenith angle < 48°). These data constitute a reference dayglow radiance spectrum comprising a number of thermospheric emission features, including several weak features neighboring bright optically thick emissions, that have not yet received adequate explanations, in part owing to questions regarding spectral intensity calibration, dynamic range, etc., associated with older data sets. In this paper, the HUT extreme ultraviolet (EUV)–far ultraviolet (FUV) nadir dayglow spectrum is presented along with the results of a modeling analysis using a development version of the Atmospheric Ultraviolet Radiance Integrated Code (AURIC). The analysis relies on currently available laboratory data and first‐principles excitation and transport modeling codes and utilizes constraints drawn from the FUV spectral region data to study several EUV emissions of interest for which past airglow data are sparse. The focus is on the airglow in the 980–1200 Å region, which is particularly rich in emission features affected by thermospheric conditions. Emissions investigated in detail include (1) the optically thick OI 989 Å multiplet and associated 1172 Å fluorescence, (2) the OI 1026 Å sextuplet blended with atomic hydrogen Lyman β, (3) the atomic nitrogen multiplets at 1134 and 1200 Å consisting of optically thick components excited by e− + N and optically thin components excited by e− + N2 and hν + N2, (4) a number of other NI and N+ features (e.g., N+ 1085 Å) excited by N2 dissociative ionization, (5) the Birge‐Hopfield I (N2 BH‐1) system, and (6) the resonance lines of argon (Ar 1048 and 1067 Å).

Middle ultraviolet emission from ionized iron

We present middle ultraviolet spectra between 2300 and 2700 Å showing emissions due to singly ionized iron and magnesium. The spectra were observed by the Ionospheric Spectroscopy and Atmospheric Chemistry (ISAAC) instrument on the United States Air Force's Advanced Research and Global Observing Satellite (ARGOS). The emission from ionized magnesium has been previously observed and studied; however, the ionized iron lines near 2400 and 2600 Å are newly identified in the Earth's middle ultraviolet dayglow spectrum. Newly calculated fluorescence efficiencies for excitation of the optical emissions are also presented.

한반도 상공 고층대기의 중간 자외선 대기광 모델

For the planned experiments of Korea Sounding Rocket-III (KSR-III), we have constructed a model of MUV dayglow in the mid-latitude. The model computes relative intensities of individual emission lines in the Vegard-Kaplan and 2PG band systems of in the wavelength range of 2500-3500. In addition to the emission lines, solar scattered continuum was computed by an extended LOWTRAN7 code, in which we have included solar scattering in altitudes higher than 100 km by using MSIS90 thermosphere model. Ratios among vibrational bands of VK and 2PG system, were computed from the observed MUV dayglow spectra of Cleary et al. (1995). The model provides MUV dayglow intensitiy profiles with a wavelength resolution of 3.13 as a function of altitude. The computed intensity profiles have been utilized in designing the KSR-III airglow photometers.

The N2 + O+ charge‐exchange reaction and the dayglow N2+ emission

Dayglow spectra were recorded by the Arizona Airglow Experiment from the payload bay of the shuttle, STS‐74. These spectra are used to reexamine the role of the prominent N2+ first negative emission from the dayglow thermosphere. Many reports of the N2+ emissions identify problems in validating the intensity of the emission. Also, an extended vibrational and rotational structure of the bands remains unexplained in the historical analysis. These anomalies appear to be due to the charge‐exchange reaction, N2+O+(2D,2P)→N2++O, which is the dominant source of N2+ ions in the sunlit atmosphere at high altitudes. In the present work the N2+ emission was considered to originate from two separate ion sources. First are those emissions originating from ions produced by photoionizaton and electron bombardment; these emissions can be modeled. Second are the emissions originating from ions produced by the charge‐exchange reaction; these emissions cannot be modeled. Synthetic emission profiles due to the first ion source were modeled and subtracted from the observed spectrum, leaving emission profiles resulting from the charge‐exchange ion source. These residual vibrational and rotational profiles were analyzed to retrieve resonance scattering rates for these ions. These scattering rates can be used to estimate the N2+ first negative emission rate expected from the thermosphere with a model of the atmosphere. It is suggested that measurements of the N2+ emission rate can be used to determine the daytime concentration of the oxygen ion, O+(2D,2P). Although the present work appears to resolve the question of the extended vibrational and rotational band structure, it does not help the excess intensity problem significantly. It does point out that O+ must play an important role in intensity problems.

Atomic and molecular emissions in the middle ultraviolet dayglow

Dayglow spectra in the middle ultraviolet, obtained during a sounding rocket flight from White Sands Missile Range in 1992, have been analyzed to determine the altitude distributions of thermospheric atomic and molecular species and to address a number of problems related to airglow excitation mechanisms. Among the atomic and molecular profiles retrieved are the N2 second positive, N2 Vegard‐Kaplan and NO gamma band systems, and the OI 297.2 nm, OII 247.0 nm, and NII 214.3 nm emissions. A self‐consistent study of the emission profiles was conducted by comparing observed intensities with one another and to forward models. Model photoelectron and photon fluxes were generated by the field line interhemispheric plasma model (FLIP) and two solar flux models. Neutral densities were obtained from mass‐spectrometer/incoherent scatter (MSIS)‐90. The results from the data analysis suggest that the major species' densities are within 40% of MSIS values. Evidence for the accuracy of the modeled densities and fluxes is seen in the close agreement between the calculated and observed intensities of the N2 second positive emission. Analysis of the OI 297.2 nm emission shows that the reaction N2(A) + O is the dominant source of O(1S) in the daytime thermosphere. The data imply that the vibrationally averaged yield of 0(1S) from the reaction is 0.43±0.12, which is smaller than the laboratory value measured for the N2(A, v′ = O) level. The cause of a disagreement between model and data for the Vegard‐Kaplan emission is unclear, but the discrepancy can be eliminated if the N2(A)+O quenching coefficient or the A state lifetime is increased by a factor between 2 and 4. The observed intensity of OII 247.0 nm is greater than expected by a factor of 2, implying possible inadequacies in the EUVAC and/or EUV91 solar models used in the analysis.

Lyα–induced Fluorescence of H2and Co inHubble Space TelescopeSpectra of a Comet Shoemaker‐Levy 9 Impact Site on Jupiter

Far-ultraviolet spectra of Jupiter obtained on 1994 July 20 in the region of the Shoemaker-Levy 9 G-fragment impact site contain features that differ markedly from the typical Jovian dayglow spectrum. These features are identified as fluorescence of H2 due to pumping by solar Lyα photons, which requires the presence of a substantial population of H2 in the second excited vibrational state; normal atmospheric temperatures preclude such an elevated H2 (v'' = 2) population in thermal equilibrium. The observed fluorescence includes approximately 600 rayleighs (R) of Lyα-induced fluorescence in addition to the 500 R of solar fluorescence estimated for typical Jovian dayglow at the time of the observations. The weaker (14, v'') transitions of the CO fourth positive band system are also excited primarily by resonant and fluorescent scattering of solar Lyα photons. As a result of their low-oscillator strengths and the large Lyα flux, these bands remain unsaturated up to column densities ≥1017 cm-2, therefore providing reliable upper limits for the CO band emission produced by the (14, 3), (14, 4), and (14, 5) transitions at 1317, 1354, and 1392 A, respectively. Comparing the derived upper limits to estimates inferred from millimeter-wave data, we demonstrate that there is no contradiction between observations in the two spectral regions.

The Ultraviolet Spectrum of the Jovian Dayglow

The ultraviolet spectra of molecular hydrogen H2 and HD due to solar fluorescence and photoelectron excitation are calculated and compared with the Jovian equatorial dayglow spectrum measured at 3 A resolution at solar maximum. The dayglow emission is accounted for in both brightness and spectral shape by the solar fluorescence and photoelectron excitation and requires no additional energy source. The emission is characterized by an atmospheric temperature of 530 K and an H2 column density of 10(exp 20) cm(exp -2). The dayglow spectrum contains a cascade contribution to the Lyman band emission from high-lying E and F states. Its relative weakness at short wavelengths is due to both self-absorption by H2 and absorption by CH4. Strong wavelength coincidences of solar emission lines and absorption lines of H2 and HD produce unique line spectra which can be identified in the dayglow spectrum. The strongest fluorescence is due to absorption of the solar Lyman-beta line at 1025.72 A by the P(1) line of the (6, 0) Lyman band of H2 at 1025.93 A. The fluorescence lines due to absorption of the solar O 6 line at 1031.91 A by vibrationally excited H2 via the Q(3) line of the (1, 1) Werner band at 1031.86 A are identified. The fluorescence lines provide a sensitive measure of the atmospheric temperature. There occurs an exact coincidence of the solar O 6 line at 1031.91 A and the R(0) line of the (6, 0) Lyman band of HD at 1031-91 A, but HD on Jupiter is difficult to detect due to the dominance of the H2 emission where the HD emission is particularly strong. Higher spectral resolution and higher sensitivity may make possible such a detection. The high resolution (0.3 A) spectra of H2 and HD are presented to stimulate search for the HD on Jupiter with the Hubble Space Telescope.

Design and modeling of a compact imaging spectrometer

A novel low-<i>f</i>-number, wide-field-of-view imaging spectrometer has been designed for measuring the day-glow spectrum over the wavelength range of 260 to 870 nm with spectral resolutions of 0.5 and 0.03 nm. The zero-obscuration all-reflective design is an <i>f</i>/2.0 imaging spectrograph using commercial gratings. The field of view along the spatial direction is 6 deg, with a spatial resolution of 0.1 mrad. The spectrometer is designed to work with a commercially available 1037 x 1340 CCD detector with 6.8 x 6.8-μm pixel size. The imaging spectrometer optics consists of an aspheric toroidal telescope, a slit, an aspheric toroidal collimator, a planar reflective grating, and three off-axis higher-order aspheric imaging mirrors. Significant improvements in the performance have been achieved by introducing aspheric toroidal elements in the design. The weight and size have been reduced by a factor of 20 as compared to previous similar instruments. A virtual prototype of the instrument has also been modeled by using integrated optical and mechanical design software.

High-resolution spectra of Jupiter's northern auroral ultraviolet emission with the Hubble Space Telescope

The first spectroscopic observations of planetary aurora with the Hubble Space Telescope (HST) are reported. These include spectral regions centered on the H2 Lyman and Werner bands of a region of Jupiter's northern aurora. The observations were made with the Goddard High Resolution Spectrograph (GHRS) using the Large Science Aperture as part of a campaign to study Jupiter at the time of the Ulysses flyby. The individual rotational-vibrational bands are resolved and the observed emissions are essentially all from H2. A rotational-vibrational temperature for H2 of 530 +/- 100 K is derived, a value significantly less than the 850-1100 K reported for Jovian H3(+) in the near-infrared but consistent with the temperature reported for fundamental-band quadrupole H2 emission. Comparison with the Faint Object Camera (FOC) images shows that the observed region was not one of the hot spots of the aurora. The results are interpreted in trms of electron impact excitation of H2 from secondary particles generated by primaries precipitating into Jupiter's atmsophere from the magnetosphere. In the region of the aurora observed, the homopause level is found to be significantly hotter but not necessarily higher than observed at nonauroral latitudes. The equatorial H2 dayglow spectrum was also detected; its intensity was 3.2 kR or 13% of the strength of the observed auroral emission.

Collisional excitation and radiative properties of N II - The strong intercombination (1D - 3P0) transition at 748 A

Laboratory measurements of EUV emission from electron-excited N2 have been obtained at medium resolution, providing N II EUV emission cross section measurements and allowing the confirmation of recent calculations by Fawcett (1987) indicating the presence of a strong intercombination line in N II at 748.37 A. The most recently available data are used to predict the basic collisional and radiative properties of N II, the plasma diagnostic properties are briefly explored, and radiative cooling coefficients are given. Some basic properties of electron-excited N II and N2 are examined in the EUV in order to diagnose emission spectra of the earth and Titan. The N II emissions in the earth dayglow, particularly at 916 A, are much brighter than current estimates of source rates. The N II 1085 A line in the dayglow contains a significant component from dissociative photoionization excitation. The N II 1085 A, 916 A, and 670 A lines in the Titan dayglow spectrum appear to be compatible with direct electron excitation of N2.

The EUV dayglow at high spectral resolution

Rocket observations of the dayglow spectrum of the terrestrial atmosphere between 840 Å and 1860 Å at 2 Å resolution were obtained with a sounding rocket payload flown on January 17, 1985. Additionally, spectra were also obtained using a 0.125‐m focal length scanning Ebert‐Fastie monochromator covering the wavelength interval of 1150–1550 Å at 7 Å resolution on this flight and on a sounding rocket flight on August 29, 1983, under similar viewing geometries and solar zenith angles. Three bands of the N2 c′4 system are seen clearly resolved in the dayglow. Analysis of high‐resolution N2 Lyman‐Birge‐Hopfield data shows no anomalous vibrational distribution as has been reported from other observations. The altitude profiles of the observed O and N2 emissions demonstrate that the MSIS‐83 model O and N2 densities are appropriate for the conditions of both the 1983 and 1985 rocket flights. A reduction of a factor of 2 in the model O2 density is required for both flights to reproduce the low‐altitude atomic oxygen emission profiles. The volume excitation rates calculated using the Hinteregger et al. (1981) SC#21REFW solar reference spectrum and the photoelectron flux model of Strickland and Meier (1982) need to be scaled upward by a factor of 1.4 for both flights to match the observations.

A position sensitive detector for EUV remote sensing

The authors describe a photon-counting extreme ultraviolet (EUV) detector system used in a rocket-borne spectroscopic instrument for remote sensing of upper atmospheric composition and temperature. The detector uses a KBr coated microchannel plate (MCP) Z stack in combination with a wedge-and-strip image readout system. Three separate detector fields of view are used to sense the Earth dayglow spectrum (980 AA to 1040 AA, and 1300 AA to 1360 AA) and the solar EUV spectrum (250 AA to 1400 AA). The authors demonstrate high gain (2*10/sup 7/), tight pulse-height distribution (35% FWHM), and a spatial resolution of approximately 35 mu m FWHM (full width at half maximum), which is the highest resolution for a wedge-and-strip anode MCP detector flown to date. The background, image linearity, and flat-field performance are discussed. Raw spectra from the rocket flight are also presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The 2p-3s transitions in atomic oxygen

The 2p4-2p33s transitions in atomic oxygen were investigated by the MCHF method with Breit-Pauli corrections for relativistic effects. Particular attention was given to the spin-forbidden 2p4 1D-2p33s 3So transition recently identified in the satellite dayglow spectrum. A somewhat smaller branching ratio for the decay of the 3So state to the 1D state relative to 3P than that derived by Meier and Conway (1985) from modelling the 3P-3So transition was found.

The ¹D‐³S transition in atomic oxygen: A new method of measuring the O abundance in planetary thermospheres

The forbidden 2p4 ¹D ‐ 3s ³So transition of atomic oxygen at 1641 Å has been identified in the satellite dayglow spectrum of Huffman et al. (1980). By modelling the optically thick ³P ‐ ³S 1304 Å transition, a probability of 5.4 × 10−6 is determined for ³So atoms branching to the ¹D state rather than to the ³P ground state. The ratio of the 1641 Å to 1304 Å intensities is found to be a linear function of the atomic oxygen abundance; therefore the ratio can be used to determine the O concentration in optically thick planetary thermospheres.

The ultraviolet dayglow at solar maximum: 2. Photometer observations of N2 second positive (0, 0) band emission

The N2 second positive, C³Πu‐B³Πg, (0, 0) band dayglow emission at 3371 Å was observed during solar maximum with a rocket‐borne filter photometer, simultaneously with spectrometer observations of the far ultraviolet N2 and O dayglow spectrum. Modeling of the near ultraviolet dayglow spectrum indicates that the instrument also detected the N2 Vegard‐Kaplan, A³Σu+‐X¹Σg+, (0, 9) band. A spectral synthesis of these bands is used to derive emission intensities. The intensities are combined with the results of the analysis of the far UV observations reported by Meier et al. (this issue) to determine the topside neutral temperature and photoelectron flux. The effects of varying the reaction coefficient k0 for quenching of the υ′ = 0 level of the N2 A³Σu+ state are discussed. For k0 = 2.4×10−11 the derived g factor for C³Πu production is 4.4×10−8 s−1 at an altitude of 290 km, whereas for k0 = 2×10−10 it is 5.4×10−8 s−1. A synthetic spectrum of these two band systems in the wavelength region between 3000 and 4000 Å is presented.