Nightglow Emission Research Articles

Plasma irregularities in the tropical F‐region detected by OI 7774 Å and 6300 Å nightglow measurements

Simultaneous measurements of the permitted OI 7774 Å and the forbidden OI 6300 Å nightglow emissions were carried out at Cachoeira Paulista (geographic 22.7°S, 45.0°W), Brazil, during the period of April 1978 to March 1979. Both the emissions were observed with tilting filter‐type photometers. During spread‐F conditions, on several nights, both the emissions showed simultaneous short‐time large intensity depletions, indicating the presence of large‐scale irregularities in the F‐region. Data for the period September‐October 1978 are presented and discussed. The depletions observed are possibly associated with the passage of F‐region holes or bubbles drifting across the sky.

Observations of the optical spectrum of the dayside magnetospheric cleft aurora

Optical spectra of the cleft aurora in the region 5000–8500 Å were measured in December, 1977 at Cape Parry, N.W.T. A Michelson interferometer was used at a resolution of 10 cm −1. The auroral features observed were OI (5577, 6300-64, 7774, 8446 Å), OII (7319-30 Å), NI (5200 Å), Hα, O 2 atm (1,1), some weak N 21P bands and possibly some Meinel bands of N 2 +. In addition, nightglow emissions of Na and OH were observed. Theoretical predictions of the OI and NI emission rates using the model of Link et al. (1980) fit the observed rates reasonably well if a 40 eV Maxwellian incident electron spectrum is assumed. The predicted rates for OII exceed the observed value by a factor of 4. It is suggested that the ionization cross-section may be over-estimated.

Seasonal variations of the correlation among nightglow radiations and emission mechanism of OH nightglow emission

Seasonal variations of correlations are studied, between the intensity changes of the OH(6-2) and (8-3) bands, of the OH(6-2) band and the O 2(0-l) atmospheric band, of the O 2(0-l) band and the NaD lines, of the OH(6-2) band and the NaD lines, of the 5577 A line and the O 2(0-l) band, of the 5577 A line and the NaD lines and of the 5577 A line and the OH(6-2) band, based on the data which are taken nearly simultaneously on the same nights from March 1978 to February 1979. It is found that the strength of intensity correlations between these radiations indicates a clear seasonal variation, except for the intensity correlations between the OH(6-2) and (8-3) bands and between the OH(6-2) band and the O 2(0-l) band. The emission mechanism of OH bands is investigated, based on the frequency distribution of the experimental π value [= ( ΔI I )/( ΔT T ) ] and on the intensity correlation between the OH(6-2) band and the O 2(0-l) band. It is found that the emission mechanism of OH bands favors the ozone mechanism in place of the O 2 ∗ mechanism.

Oscillations of intensity and temperature of nightglow emissions: [01] 557.7 nm and 630.0 nm lines, and OH(6-2) band

Clear oscillations of intensity of the oxygen green and red lines and those of intensity and temperature of the OH(6-2) band, which were obtained during two total lunar eclipse nights, are presented. The wave periods found range mainly from 25 to 40 min. In connection with these clear oscillations of intensity and temperature, we have examined intensity variations of these airglow emissions on other nights and found two nights during which only the green line indicates clear oscillations in the post-midnight hour. Our results favor the suggestion of Peterson (1979).

Association between plasma bubble irregularities and airglow disturbances over Brazilian low latitudes

Meridional profiles of OI 6300 Å nightglow emission measured using a scanning photometer over Cachoeira Paulista, a low latitude station, often show propagating patches of airglow disturbances with north to south and west to east velocity components, occurring mostly in the premidnight period. 132 measurements carried out during a period of 26 months since January 1978, show significant seasonal dependence in the occurrence of these disturbances, with most of the events occurring in the spring‐summer months and with very rare occurrence during the winter solstice. The north to south propagation velocities lie in the range of 150 to 350 m/s. A case by case comparison of the occurrences of these airglow disturbances with simultaneous ionograms over Cachoeira Paulista show that almost the totality of these disturbances are accompanied by strong range type echoes in the ionograms and vice versa. These results therefore support our earlier contention that these types of airglow disturbances might be manifestations of the equatorial plasma bubbles.

Influence of gravity wave activity on lower thermospheric photochemistry and composition

The wind and temperature oscillations of internal gravity waves can cause horizontal variations of a factor of two in minor gas number densities in the lower thermosphere over length scales of several hundred kilometers. The variations are due both to vertical transport of constituents whose lifetimes are long compared to the wave period and to chemical activity driven by temperature dependent reaction rate coefficients. The nightglow emission of the hydroxyl radical provides a remote sensor of wave activity between 80 and 90 km. Theoretical calculations show that the horizontal variations in the atomic hydrogen distribution are the largest single contributor to wave structure in the nightglow followed by the effects of temperature fluctuations on the rate coefficient of the reaction H + O 3 → O 2 + OH v′ > 0).

Simultaneous observations of sodium density and the NaD, OH (8, 3), and OI 5577‐Å, nightglow emissions

Simultaneous observations of the vertical distribution of sodium density and the intensities of the OI 5577‐Å, NaD, and OH (8, 3) airglow emissions show that the nocturnal variations of the emissions are well correlated with those of the sodium at 91, 87, and 84 km, respectively. In the case of NaD and OH (8, 3) these heights correspond closely to expected heights of peak airglow emission, although in the case of OI 5577 Å, maximum emission would be expected from about 4 km higher. The correlated variations appear to be caused by atmospheric waves having vertical wavelengths between 10 and 15 km whose phases propagate downward with velocities between 1 and 2 km hr−1. The amplitude of the correlated nocturnal variations in sodium density on the bottom side of the layer is normally too large to be explained as the direct result of atmospheric density changes. These large variations could be the result of vertical motions of the layer or might be caused by changes in the equilibrium between sodium and its oxide. On a number of occasions, large nocturnal changes in sodium density were seen to be closely correlated with changes in OH rotational temperature, suggesting a temperature effect on the chemical equilibrium. Enhanced sodium density, observed on days of exceptionally high OH (8, 3) band rotational temperature, could either be the result of increased sublimation from sodium‐bearing aerosols or again might be caused by a temperature dependence of the sodium photochemistry.

Nightglow emissions of OH(X²π): Comparison of theory and measurements in the (9‐3) band

The visible airglow experiments on the Atmosphere Explorer C and E satellites have viewed the (9‐3) band nightglow emission of the excited hydroxyl radical in the lower thermosphere at tropical latitudes. The surface brightnesses observed at similar local times vary by approximately a factor of 2. Comparison of the measurements with time‐dependent photochemical calculations shows reasonable agreement and indicates that temporal changes in atmospheric transport processes are the most likely explanation of the nightglow variations.

Effect of internal gravity waves upon night airglow temperatures

Large quasi‐periodic fluctuations are observed simultaneously in the rotational temperature of the nightglow emission from both O 2 (¹Σ g ) and OH. The fluctuation amplitude usually is several times larger in the former and the O 2 (¹Σ g ) fluctuations often lead those of OH in phase. This behavior is consistent with that expected for internal gravity waves propagating upward over the ˜ 10 km vertical separation between the two emission layers. The most prominent periods are 1‐2 hours and the full range of oscillation in temperature at 95 km sometimes approaches 100° K.

Airglow variations and dynamics in the lower thermosphere and upper mesosphere—III. Variations during stratospheric warming events

The 5577 Å, Na and OH nightglow emissions observed at Haute Provence were examined for possible changes during the stratospheric warming events. It has been found that during the midwinter major warmings the emission intensities exhibit marked increases of the order of 100%, persisting for about a week. In addition, it has been shown by an analysis of the superposed epoch type that the sudden enhancement in the emission intensities occurs almost simultaneously with the splitting of the stratospheric polar vortex. The results may confirm that the influence of the circulation changes associated with the stratospheric warming extends up to at least the lower thermosphere, causing redistributions of photochemical minor constituents by the effect of transport processes and the change of aeronomic properties.

Gas phase chemical kinetics of sodium in the upper atmosphere

THE existence of a layer of atomic sodium in the upper atmosphere near 90 km has been clearly demonstrated by analyses of daytime and twilight airglow emissions of D-line radiation at 5,890 and 5,896 A (refs 1 and 2) as well as by direct laser backscatter measurements (see, for example ref. 3). Following Chapman4 chemical reactions involving atomic sodium and atmospheric oxygen species have been invoked to explain the chemical dynamics of the sodium layer and the nightglow emission of D-line radiation. In addition, Chapman has also proposed that similar reactions involving newly ablated sodium are responsible for the occurrence of long enduring visible meteor trails5. Unfortunately, previous quantitative attempts to model sodium-induced upper atmospheric chemiluminescence have suffered from rather poor estimates of the appropriate reaction rate constants. Here we provide more reasonable estimates of rate constants and show how these new kinetics parameters can dramatically alter calculations of chemiluminescent efficiency.

Polar enhancements of nightglow emissions near 6230A

Night airglow emissions near 6230A, as observed from the Ogo 4 spacecraft in 1967‐8, show enhancements at polar latitudes by more than a factor of ten over mid and low latitude values. The enhancements are generally not symmetrical with either the north pole or the auroral oval. They are attributed in part to increases in the Meinel band emissions of OH, particularly as associated with a stratospheric warming event, and in part to increases in nitric oxide densities in the lower thermosphere.

The temperature gradient between 100 and 120 km

Oxygen density profiles inferred from Ogo 6 green nightglow emission vary too sharply between 100 and 120 km to be consistent with temperature gradients in standard model atmospheres, and the eddy diffusion coefficient K determined from these observations reaches its maximum below 115 km. For three atomic oxygen profiles obtained at geographic latitudes of -27.69, +48.89, and +59.10 the temperature profiles required to create a downward flux that varies with altitude as the integrated photolytic production rate above that altitude are calculated, assuming K to be invariant with altitude and latitude. The oxygen distribution can be reconciled with a constant eddy coefficient above 100 km if the temperature gradient reaches a value between 10 and 20 deg K/km for low values of the eddy coefficient (about 500,000 sq cm/sec) or between 30 and 50 deg K/km for a higher eddy coefficient (about 1.6 million sq cm/sec). The maximum gradient for the Jacchia (1971) model is about 10 deg K/km. These temperature profiles predict Ar/N ratios consistent with those measured by sounding rockets. The low K profiles are large enough to remove a large part of the solar energy deposited below 120 km by thermal conduction.

An observation of O+ 834 Å nightglow emission

A 40 Å resolution spectrometer was employed to measure the extreme ultraviolet nightglow emissions. The spectrometer was flown on a Black Brant V‐C rocket, which was launched at 21:08 MST on February 9, 1973, from White Sands Missile Range, New Mexico. The O+ 834 Å emission can be identified in the spectrum and has a brightness of 15±5 R. This emission is probably excited by the conjugate electrons. The data also indicate the presence of some nightglow emission in 950 to 1050 Å region that is still unidentified.

Simultaneous measurements of the OH ∗ nightglow in the (9-4), (8-3) and (5-1) bands and effects of quenching

Simultaneous measurements of the OH ∗ nightglow emission in the (9-4), (8-3) and (5-1) bands have been carried out with two coupled tilting interference filter photometers in the period from May to December 1971. The nocturnal variation of the relative intensities is interpreted, with the help of existing mesospheric models, to ascertain the importance of the quenching processes. It appears that both quenching by the molecular gas and by atomic oxygen have to be considered.

Ultra-violet nightglow spectrum from 1900 � to 3400 �

Two spectra of the ultra-violet nightglow from 1900 A to 3400 A have been recorded by a fast wide-field spectrograph during balloon flights from Aire sur Adour, France on 15 September, 1969 and on 5 October, 1970. These two spectra are composed of theOi line at 2972 A, of the molecular oxygen Herzberg band systemA3 ∑u+ →X3 ∑g− and of a molecular band system that seems to belong to the NO δ SystemX2 τ⇄C2X+, situated at 1991 A±4 A, 2060 A±4 A and 2136 A±4 A. Around 2540 A, there is absorption by ozone at the altitudes at which the spectra were recorded (35 km and 40 km). We present our calculated value of ozone absorption at 35 km, and the zenith-horizon variation of the nightglow emission.

Altitude Distribution of Hydroxyl Bands of the Δν = 2 Sequence in the Nightglow

Rocket borne measurements of the altitude distribution of the hydroxyl nightglow emission in the Δν = 2 sequence have been made. Bands originating from the upper vibrational levels (5, 6, and 7) were measured with a band-pass filter in the 1.8 μ. spectral region and bands from the lower levels (3, 4, and 5) were measured in the 1.6 μ. region. The observed emission was distributed in a layer 10 km thick with a maximum at 87 km. In the altitude region below 90 km, the distribution of O2 (1Δ) measured on the same flight was similar to the hydroxyl profiles. These observed distributions extend over a narrower range of altitude than most previous observations, but agree well with the distributions predicted by model atmosphere calculations.

Chemical factors regulating free alkali metal atoms in the upper atmosphere

In contrast to dayglow and twilight emissions, which result from resonant scattering by free alkali metal atoms, the nightglow emission is probably due to chemical reaction of alkali metal compounds. It is proposed that recombination of atomic nitrogen on a metal salt particle in a dust layer is a possible mechanism leading to emission by alkali metal atoms. Weak emission from the first negative band system of N2+ may be observed concurrently. Studies on bulk meteoritic material suggest that, because of the, high recombination coefficients observed, a layer of meteoritic dust at about 90 km would greatly perturb the atomic-particle density near this altitude.

Observations of a magnetic conjugate effect in the OI 6300 Å airglow at Saskatoon

A variation in the IO 6300 Å nightglow emission intensity at Saskatoon (60.5°N magnetic latitude) has been found to follow the changes in the solar depression angle at the magnetic conjugate region. Observations made with a multichannel Fabry-Perot spectrometer during January–March, 1967 are described and discussed. An enhancement of about 100 Rayleighs (R) was observed, corresponding to a conjugate solar depression angle change of 12°. This enhancement is at least as large as that observed at lower latitudes, implying that electron energy losses along the longer field lines are not significant.

Far infrared nightglow emission from atomic oxygen

We have observed nightglow emission in a spectral band from 50 μ to 125 μ by using a rocket-borne liquid helium-cooled telescope. The observed zenith intensity as a function of altitude is consistent with the assumption that the emission is due to the ³P1 - ³P2 fine structure transition of O I at 63 μ. At 120 km, the zenith intensity is 1.7 megarayleighs or 5.5 × 10−2 erg sec−1 cm−2 (column), and the derived value for the atomic oxygen density is 4 × 1010 cm−3.