Airglow Measurements Research Articles

The O2 Herzberg I bands in the equatorial nightglow

Abstract Simultaneous measurements of the nightglow profiles of the O 2 Herzberg I bands, the O 2 Atmospheric (0-0) band and the atomic oxygen green line, carried out at Alcântara (2.3 °S; 44.4 °W), are presented and discussed. This is the first measurement of the vertical profile of the Herzberg I band to be carried out at equatorial latitudes. The atomic oxygen concentration derived from the O 2 Atmospheric (0-0) band emission profile is used to test a photochemical scheme to explain the measured O 2 ( A 3 Σ u + − X 3 Σ g − ) nightglow emission based on atomic oxygen recombination. The kinetic analysis is carried out assuming the emission ratio Herzberg I: Herzberg II = 5:1, 10:1 and the extreme case where Herzberg II brightness = 0. For all three cases studied, the quenching rates required to explain the measurements are higher than the values derived from previous airglow measurements.

Airglow measurements of possible changes in the ionosphere and middle atmosphere

A brief review of mechanisms for oxygen airglow excitation is presented in the light of predicted mesosphere and lower thermosphere changes for increased carbon dioxide and methane. From this it is concluded that airglow is extremely sensitive to global change. Possible airglow measurements are reviewed, and an assessment given of the potential for the detection of change. The primary problem in the determination of trends is shown to be the natural variability of airglow, for which the two main factors are solar variability, and dynamics. Examples of solar and dynamical influences are shown. Independent monitoring of the solar flux can in principle allow the separation of the solar influence, but the dynamical one is more difficult. One solution proposed is to make ground-based measurements around a zonal ring of fixed latitude, with longitude separations that are as equally spaced as possible. Such an observing system has now been initiated as a SCOSTEP project, with the name PSMOS, the Planetary Scale Mesopause Observing System. It is expected that PSMOS will make a significant contribution towards the determination of such trends.

Atomic hydrogen and ozone concentrations derived from simultaneous lidar and rocket airglow measurements in the equatorial region

Nighttime atomic hydrogen and ozone concentrations are derived from simultaneous measurements of the vertical profiles of upper mesospheric airglow emissions and atmospheric sodium. The airglow profiles were obtained in a sounding rocket experiment launched from Alcântara (2.5°S, 44.2°W) on May 31, 1992. A lidar operating at the launch site was used to measure sodium at the time of the rocket experiment. A total of 10 airglow photometers, 6 forward looking and 4 side looking, observed the OI 557.7 nm, O2 Herzberg and O2 atmospheric (0,0) bands, sodium D lines, OI 630 nm, OH(8,3) band, and the airglow continuum. The simultaneous ground‐based sodium lidar and onboard sodium airglow measurements made it possible to derive the ozone concentration at heights between 85 and 100 km. The hydrogen concentrations were then calculated from the O2 atmospheric (0,0), OH(8,3) and the ozone profiles. The results suggest that the hydrogen concentration varied from 1 × 109 cm−3 at 85 km to 1 × 108 cm−3 at 100 km, values much higher than those suggested by recent model atmospheres and by some rocket observations at middle and high latitudes. Although the method of obtaining the concentrations of the minor constituents in the upper atmosphere is an indirect optical technique, this is the first time that these concentrations have been measured by rocket in the equatorial region.

Reference model of mesospheric atomic hydrogen

Atomic hydrogen for this model has been inferred from the hydroxyl airglow measurements on Solar Mesosphere Explorer (SME) spacecraft between 10 and 1.3 μbar (80–93 km). During the day Meinel band emission of OH is proportional to the product of ozone and hydrogen. Since daytime ozone has been inferred from the O 2( 1Δ g) emission, daytime hydrogen can be inferred. Very large annual and semiannual changes are found in this region. At 40°N the summer-to-spring ratio of atomic hydrogen exceeds a factor of 4 at 10 μbar (80 km).

Comparison of ALOHA‐93, ANLC‐93 and ALOHA‐90 observations of the hydroxyl rotational temperature and gravity wave activity

Hydroxyl airglow measurements during the ALOHA‐93, ALOHA‐90 and ANLC‐93 campaigns are used to evaluate features of the temperature variation of the mesopause region. Each campaign shows a persistent pattern in the averaged local time variation of temperature with peak‐to‐peak amplitudes of 5 K to 15 K, suggestive of the presence of tidal modulation. The nightly temperature variance, after detrending to remove low frequency variations due to tides, is shown to be significantly less during the Hawaiian campaigns than during the ANLC‐93 and other campaigns at sites where significant orographic excitation of waves might be expected.

Analysis of Lyman α and He I 584‐Å airglow measurements using a spherical radiative transfer model

We report on the scattering and excitation mechanisms of the terrestrial exospheric H I 1216‐Å and He I 584‐Å airglow emissions by comparing simulations from a radiative transfer model with spectroscopic measurements from an Earth‐orbiting satellite. The purpose of these comparisons are twofold: to assess the sensitivity of the input parameters to the model results and to test the applicability of the model to airglow analysis. The model incorporates a spherically oriented atmosphere to account for the extended scale heights of the exospheric scatterers as well as to properly mimic scattering across the terminator region from the dayside to the nightside hemispheres. Spectroscopic Lyman α and He I 584‐Å data were obtained by the STP78‐1 satellite that circumnavigated the Earth in a noon/midnight orbit at an altitude of 600 km. The “best fit” analysis of the Lyman α data acquired on March 25, 1979, requires scaling the hydrogen density distribution obtained from the MSIS‐90 (Hedin, 1991) atmospheric model by 45–50%, the exospheric temperature by 90–100%, and the Lyman α solar flux predicted by EUV91 model (Tobiska, 1991) by 1.9–2.0. Similar analysis of the He I 584‐Å data acquired on March 5, 1979, requires scaling the helium density distribution obtained from the MSIS‐90 (Hedin, 1991) atmospheric model by 60–80% and the exospheric temperature by 105–115% while using a line center 584‐Å solar flux of 1.44×1010 photons cm−2 s−1 Å−1.

E Region neutral winds in the postmidnight diffuse aurora during the atmospheric response in Aurora 1 Rocket Campaign

Measured E region neutral winds from the Atmospheric Response in Aurora (ARIA 1) rocket campaign are compared with winds predicted by a high‐resolution nonhydrostatic dynamical thermosphere model. The ARIA 1 rockets were launched into the postmidnight diffuse aurora during the recovery phase of a substorm. Simulations have shown that electrodynamical coupling between the auroral ionosphere and the thermosphere was expected to be strong during active diffuse auroral conditions (Walterscheid and Lyons, 1989). This is the first time that simulations using the time history of detailed specifications of the magnitude and latitudinal variation of the auroral forcing based on measurements have been compared to simultaneous wind measurements. Model inputs included electron densities derived from ground‐based airglow measurements, precipitating electron fluxes measured by the rocket, electron densities measured on the rocket, electric fields derived from magnetometer and satellite ion drift measurements, and large‐scale background winds from a thermospheric general circulation model. Our model predicted a strong jet of eastward winds at E region heights. A comparison between model predicted and observed winds showed modest agreement. Above 135 km the model predicted zonal winds with the correct sense, the correct profile shape, and the correct altitude of the peak wind. However, it overpredicted the magnitude of the eastward winds by more than a factor or 2. For the meridional winds the model predicted the general sense of the winds but was unable to predict the structure or strength of the winds seen in the observations. Uncertainties in the magnitude and latitudinal structure of the electric field and in the magnitude of the background winds are the most likely sources of error contributing to the differences between model and observed winds. Between 110 and 135 km the agreement between the model and observations was poor because of a large unmodeled jetlike feature in the observed winds (140 m s−1). Agreement between the present simulation and the earlier simulations of Walterscheid and Lyons (1989) is favorable, although the winds in the present simulation are considerably weaker for particle precipitation of similar characteristic energy and flux. The reasons for the difference were the smaller latitudinal extent of the model diffuse aurora and the weaker electric fields in our simulation. We have shown that the enhanced electron densities and electric fields associated with the postmidnight diffuse aurora provide the potential for a rapid acceleration of the zonal winds as shown by Walterscheid and Lyons (1989). However, the modeled response to the large‐scale electric field is too great. This suggests that the assimilated mapping of ionospheric electrodynamics (AMIE) electric field is also too large. The actual electric field is most likely reduced locally in regions of enhanced ionization and conductivity within the diffuse aurora. In addition, we have shown that the “exotic” jetlike wind feature between 110 and 135 km is not aurorally forced. However, it may be the result of an enhancement of the Hall drag relative to the Coriolis force that modifies the geostrophic balance with the large‐scale pressure gradient.

Vertical neutral wind in the equatorial F-region deduced from electric field and ion density measurements

DC electric field and ion density measurements near density depletion regions (that is, equatorial plasma bubbles) are used to estimate the vertical neutral wind speed. The measured zonal electric field in a series of density depletions crossed by the San Marco D satellite at 01.47-01.52 UT on 25 October 1988, can be explained if a downward neutral wind of 15–30 m s −1 exists. Simultaneously, the F-region plasma was moving downward at a speed of 30–50 m s −1 These events appear in the local time sector of 23.002̄23.15 in which strong downward neutral winds may occur. Indeed, airglow measurements suggest that downward neutral velocities of 25–50 m s −1 are possible at times near midnight in the equatorial F-region.

Vertical neutral wind in the equatorial F-region deduced from electric field and ion density measurements

DC electric field and ion density measurements near density depletion regions (that is, equatorial plasma bubbles) are used to estimate the vertical neutral wind speed. The measured zonal electric field in a series of density depletions crossed by the San Marco D satellite at 01.47-01.52 UT on 25 October 1988, can be explained if a downward neutral wind of 15–30 m s−1 exists. Simultaneously, the F-region plasma was moving downward at a speed of 30–50 m s−1 These events appear in the local time sector of 23.002̄23.15 in which strong downward neutral winds may occur. Indeed, airglow measurements suggest that downward neutral velocities of 25–50 m s−1 are possible at times near midnight in the equatorial F-region.

Six-hour zonally symmetric tidal oscillations of the winter mesopause over the South Pole Station

Four complete cycles of a 6-h quasi-mono-chromatic variation in OH Meinel (3,1) and (4,2) band airglow brightness ( I) and rotational distribution temperature ( T) were observed with a near infrared (1.0–1.7 μ) Michelson Interferometer operating at the South Pole Station in Antarctica. The simultaneous occurrence of a quasi-periodic variation in I and T suggests the presence of a coherent wave phenomenon in the mesopause region. A power spectral density analysis of a continuous 24-h recording of I and T on 24 May 1992, indicates a 6 ± 1-h period oscillation (Sivjee et al., EOS 74 (Suppl.), 48,5A 11A-10 1993a). The propagation of 6-h wave-like disturbances in the high latitude winter mesopause is substantiated by more recent extended-period airglow measurements at ∼81.6°N latitude around Eureka, Canada (Sivjee et al, EOS 74 (Suppl.), 43, 5A 21A-4, 1993b; Sivjee et al, Planet. Space Sci. 42, in press, 1994). The period and coherency of the oscillation point to a tidal origin, while its occurrence at a geographic pole suggests a zonally symmetric tide. Unlike the globally dominant migrating tides, and other zonally propagating tides, for which the quantities that generate airglow fluctuations vanish at the pole, the 6-h zonally symmetric standing tide has its maximum amplitude in these quantities at the poles. To examine whether the observed airglow variations were consistent with a zonally symmetric non-migrating tide, comparisons with airglow theory were made in terms of Krassovsky's ratio ( Ann. Geophys. 28, 739, 1972) (the ratio of the fractional change in brightness to the fractional change in temperature). The observed value was 9 ± 3 for amplitude and 30° ± 15° for phase, with I leading T. The agreement with the predicted amplitudes is good for the modes which are sharply peaked near the pole. The predicted phase of I relative to T is not as large as the observed value, but is in the right sense and a mixture of modes could readily account for the larger observed phase. The latter is consistent with the predicted phase at the 95% confidence level. The magnitude of the predicted Krassovsky's ratio for a 6-h period gravity wave is reasonably close to the observed value. However, we rule out a gravity wave source because the predicted phase indicates that the temperature fluctuation leads the brightness fluctuation, opposite to what is observed, and the absolute difference between the observed and predicted phase is quite large. We conclude that considerations based on tidal theory and a model of wave driven fluctuations in OH airglow strongly favor an interpretation in terms of a zonally symmetric tide over zonally propagating tides and gravity waves.

Gravity waves in the upper mesosphere over Antarctica: Lidar observations at the South Pole and Syowa

Lidar observations of the mesospheric Na layer were made at the south pole(90°S) and Syowa (69°S) during the winters of 1990 and 1985, respectively. These observations are used to characterize the gravity wave activity in the upper mesosphere at both sites. Strong wave activity is observed throughout the winter at both the south pole and Syowa and shows remarkable similarity with observations from several midlatitude and low‐latitude sites. The quasi‐monochromatic gravity waves exhibit the same general relationships between their wavelengths, observed periods, and amplitudes as observed at lower latitudes. The average growth length of these waves is approximately 26 km, indicating that the wave field at both Antarctic sites is strongly influenced by dissipation and saturation processes. The spectra and variances of the density perturbations associated with quasi‐random wave field at the south pole are reported. The vertical wavenumber and temporal frequency spectra follow power‐law shapes. The mean index of the vertical wavenumber spectrum is −2.4, and the mean characteristic wavelength is 14 km. The mean index of the temporal frequency spectrum is −1.7. The mean density variance at the south pole is (5.7%)2 and is similar in magnitude to that observed at a variety of lower‐latitude sites. With no tropospheric convection during the polar night and little orographic forcing over the relatively featureless Antarctic plateau, these observations suggest that nonlinear processes, rather than the source characteristics, primarily determine the characteristics of the gravity wave field in the upper mesosphere. These observations show two other distinct features. The mean Na layer over Antarctica is significantly lower and broader (centroid height ≈ 90 km and rms width ≈ 4.8 km) than at lower latitudes, reflecting the stronger downwelling and warmer winter temperatures in the mesopause region at high latitudes. Strong coherent oscillations were observed in the bottomside density contours of the Na layer with periods close to the inertial period. These oscillations were also observed in OH airglow measurements and appear to be associate with planetary scale waves.

Image plane detector spectrophotometer: construction and nightglow observations

Following the theoretical simulation of an image plane detector spectrophotometer (IPDS) presented in a previous paper, a ground-based IPDS for airglow measurements is constructed. This low resolution spectrometer can measure a molecular band spectrum at 12 wavelength positions simultaneously without mechanical scan. The band brightness and rotational temperature of the emitter can be obtained from the measurements. We describe the optical design and calibration of the instrument and present some results of mesospheric nightglow observations. The evaluation and analysis on the performances of the new instrument are also given. The result shows that, although the constructed instrument does not represent the optimized IPDS, the instrument performed reasonably well, and with some improvements the IPDS has great potential of being used to study small-scale oscillations in airglow layers.

Mars mesosphere and thermosphere coupling: Semidiurnal tides

The National Center for Atmospheric Research thermosphere ionosphere general circulation model for Earth has been modified to examine the three‐dimensional structure and circulation of the upper atmosphere of Mars (MTGCM) (Bougher et al., 1988b, 1990). Recent examination of Mariner 9 UVS airglow measurements taken during a global dust storm provide evidence of large temperature variations and atomic oxygen distributions uncorrelated with solar activity and the corresponding MTGCM in situ driven winds. We suspect significant forcing of the thermosphere from below as a result of upward propagating gravity waves or tides generated by solar heating of airborne dust (Stewart et al., 1992). The effects of upward propagating tides are introduced into the MTGCM by appropriately specifying its lower boundary condition according to classical tidal theory. We initially adapt the terrestrial scheme used by Fesen et al. (1986) to a Mars model appropriate to Mariner 9 near‐solar‐minimum conditions. Estimates of the amplitude and phase of the likely dominant semidiurnal (2,2) mode at the mesopause (∼100 km) are specified for a range of possible lower atmosphere dust conditions. MTGCM simulations contrasting tidally driven fields with solar‐only forced ones show a dramatic change in the horizontal and vertical wind patterns, whereby the global temperature and oxygen distributions are also modified significantly. This semidiurnal component predominates below 135 km, while the in situ solar‐driven diurnal component is largely dominant above. Constructive interference serves to enhance midafternoon exospheric temperatures toward Mariner 9 observed values. The thermospheric response and the altitude of penetration of these semidiurnal tides is found to be much greater during solar minimum periods when dissipation due to viscosity and thermal conductivity is diminished from that at solar maximum. Finally, the Martian response during dusty periods is predicted to be much larger than that typically observed for Earth. Martian dust‐driven tides, especially during solar minimum time periods, cannot be ignored when addressing the Mars thermospheric structure and dynamics.

Reference model of mesospheric atomic hydrogen

Atomic hydrogen for this model has been inferred from the hydroxyl airglow measurements on Solar Mesosphere Explorer (SME) spacecraft between 10 and 1.3 μbar (80–93 km). During the day Meinel band emission of OH is proportional to the product of ozone and hydrogen. Since daytime ozone has been inferred from the O 2( 1Δ g) emission, daytime hydrogen can be inferred. Very large annual and semiannual changes are found in this region. At 40°N the summer-to-spring ratio of atomic hydrogen exceeds a factor of 4 at 10 μbar (80 km).

Atomic oxygen concentrations from airglow measurements of atomic and molecular oxygen emissions in the nightglow

Simultaneous measurements of oxygen emissions can be used to derive the concentration of atomic oxygen in the atmosphere. The atomic oxygen profiles obtained from different emissions measured in the same campaign are used to test the photochemical mechanisms chosen to explain the different emissions in the scenario of atomic oxygen recombination. In this paper we derive and compare atomic oxygen profiles from nightglow observations of O 2( a 1 Δ g − X 3 ∑ g −), O 2( b 1∑ g +− X 3∑ g −), O 2( A 3∑ u +− X 3∑ g −), O 2( A′ 3 Δ u − a 1 Δ g ), O 2( c 1∑ u −− X 3∑ g −) and O( 1 S− 1 D) emissions, taken by different authors in different atmospheric conditions.

Effects of vibrationally excited molecular nitrogen on ionospheric-thermospheric coupling for different levels of solar activity

An analysis has been made of the interaction between neutral and ionized thermospheric components and processes of the generation, transfer and dissipation of vibrationally excited nitrogen molecules. Analytical expressions for these interactions with the topside thermosphere have been developed. It has been shown that the collision frequency ν ei is a direct measure of the excited components N 2,ν Naturally, a complete analysis of N 2,ν and its effects is possible only when it is rationally combined with airglow measurements. As an example, the saturation effects of N 2,ν have been considered for different levels of solar activity, in particular the considerable increase of [NO +] [O 2 +] during a very active Sun and its role in restricting electron density growth rates.

Solar EUV/UV and equatorial airglow measurements from San Marco-5

Equatorial airglow and solar radiation measurements from 20 to 700 nm have been conducted with two spectrophotometric instruments aboard the San Marco-5 satellite from March to December 1988. The in-flight performance of the experiment and its in-flight calibration aspects are described. Preliminary results of the solar flux measurements and the planned scheme of the airglow modelling are presented.

Comparison of a low-latitude ionospheric model with observations of oi 630 nm emission and ionospheric parameters

A comparative study is carried out between a semi-empirical low-latitude ionospheric model (SLIM), including calculated OI 630 nm airglow emission intensities predicted by the SLIM model, with ionospheric and OI 630 nm airglow measurements carried out at Cachoeira Paulista (22.7°S, 45.0°W; geomag. 11.9°S), Brazil. A long series of regular measurements of ionospheric F-region peak electron densities and peak heights, and regular zenith measurements of the OI 630 nm airglow emission intensities, made during the period 1975–1982, are used for comparison with corresponding parameters predicted by the SLIM model. Large discrepancies between the observed and model-predicted OI 630 nm intensities have been found for high solar activity, mainly due to an overestimate of the F-region peak heights by the SLIM model. Use of SLIM profiles normalized by actual F-region peak height and density observations essentially removed the disagreements. The reasons for the height discrepancies are discussed in terms of the longitudinal dependence of the geomagnetic control on the E × B vertical plasma drifts and the thermospheric neutral wind effects on the F-region. The effects of the magnetic declination angle on both the E × B ionospheric plasma drifts and thermospheric neutral winds at low-latitude suggest that ionospheric models need to address separately the longitudinal zones of magnetic declination either positive, negative or zero.

Atomic hydrogen and atomic oxygen density in the mesopause region: Global and seasonal variations deduced from Solar Mesosphere Explorer near‐infrared emissions

Atomic oxygen and atomic hydrogen have been inferred from the hydroxyl airglow measurements on Solar Mesosphere Explorer (SME) spacecraft between 0.01 and 0.0013 mbar (80–93 km). This constitutes the first measurements of the seasonal and latitudinal variations of these atomic species, in the mesopause region. At night, atomic oxygen is directly proportional to the Meinel band emission of OH. During the day the emission is proportional to the product of ozone and hydrogen. Since daytime ozone is inferred from the O2(1Δg) emission, daytime hydrogen can be inferred. Daytime atomic oxygen is then inferred from the measured hydrogen and ozone. At levels where atomic oxygen is found by both methods (at 0.0032–0.0013 mbar or 88–93 km) the day and night atomic oxygen display the same relative seasonal variations. Very large annual and semiannual changes are found in the atomic hydrogen density between 80 and 93 km. At 40°N the summer‐to‐spring ratio of atomic hydrogen exceeds a factor of 4 at 0.01 mbar (80 km). Between 80 and 90 km the odd oxygen family is found to be almost entirely atomic oxygen. Its behavior is characterized by annual variations at 40° north and south and semiannual changes at the equator; in both cases the changes are a doubling from minimum to maximum. At least part of the mid‐latitude semiannual variation in ozone is found to be due to the product of two annually varying functions. The atomic oxygen is annual and maximizes in the winter while the ozone‐oxygen partitioning, controlled mostly by temperature, maximizes in the summer due to temperature changes.

A procedure for the extraction of airglow features in the presence of strong background radiation

Ground‐based measurements of terrestrial airglow are useful for many applications in aeronomy. However, in the past observations have been limited to times and circumstances when the relatively weak airglow features are not overwhelmed by bright sky background emission due mainly to Rayleigh scattering of sunlight. In this paper we report a procedure which can be used to automatically extract weak airglow emissions in the presence of strong background radiation. The computer code developed for this purpose is user friendly and provides, in addition to retrieved airglow intensities, quantitative diagnostics which include estimates of error of measurement. The procedure is designed to allow rapid bulk processing of data which has not been possible previously.