High latitude airglow observations of correlated short-term fluctuations in the hydroxyl meinel 8-3 band intensity and rotational temperature

An application of a tilting filter photometer for the ground-based measurement of the atmospheric temperature at the mesopause altitude (~85km) is described. The technique uses selected rotational emission lines of the OH Meinel night airglow to determine a rotational temperature. A sampling rate of approximately one per minute with a precision of ±5K can be achieved with a field of view (4-km transverse at the mesopause height) sufficient to detect fine structure variations in the temperature and intensity. The systematic error of these measurements is comparable with those of rocket in situ measurements by falling spheres or parachute-borne thermistors. Results obtained March 1974, at Ester Dome, Alaska, indicate the presence of systematic fluctuations in the rotational temperature and the 8-3 band intensity of period 16 min and amplitude 2–4 per cent.     

On the rotational temperature of airglow hydroxyl emissions

It is argued that available observational information does not support the contention (recently advanced by Suzuki and Tohmatsu, 1976) that the rotational temperature derived from an airglow hydroxyl emission band depends systematically on the quantum number (ν′) of the vibrational state from which the band originates. In particular, it is shown that bands originating from ν′ = 6, 7 and 8, measured simultaneously, exhibit rotational temperatures which (within the experimental errors) are equal.     

Nightglow OH (8, 3) band intensities and rotational temperature at 23°S

The OH (8, 3) band airglow emission has been observed over 1 year at a latitude of 23°S. The average band intensity observed was 385 Rayleighs with a nocturnal range typically less than 100 R. The nocturnal variation in rotational temperature was usually less than 10°K, and the mean temperature was 179°K. The nocturnal variation of intensity is usually uncorrelated with that of the rotational temperature. Time average values of these parameters do, however, show some correlation. On some occasions large post-twilight and pre-dawn intensity enhancements are observed.     

An interpretation of the rotational temperature of the airglow hydroxyl emissions

The rotational temperature of the airglow hydroxyl emissions arising from various schemes of vibrational transitions was obtained by using spectroscopic data from six observational sources. The rotational temperature was found to depend systematically on the quantum number (ν') of the upper vibrational level from which the relevant band originates. It has a doubly degrading characteristic with respect to ν' taking maximal values at ν' = 6 and 9, which exceed considerably the atmospheric temperature. It drops off quickly as ν' decreases from 9 to 7, and then from 6 to 3 after making an abrupt rise at ν' = 6. This ν'-dependence of the rotational temperature is in favor of the hypothesis that there are two routes of excitation of the hydroxyl airglow: O₃ + H = OH(ν ? 9) + O₂, and HO₂ + O = OH(ν ? 6) + O₂. The present result implies also that the relaxation time of rotation of OH in the upper mesosphere is as long as 0.1 sec; a value an order of magnitude larger than that inferred in earlier laboratory experiments.     

Determination of the effective height of fluctuations of hydroxyl emission

The results of triangulation measurements of the height of hydroxyl emission from the fluctuations in rotational temperature are described. The height of maximum fluctuations of the temperature varies from night to night and even during one night from 80 to 100 km.     

Distributions of the Venus 1.27-μm O2 airglow and rotational temperature

Imaging spectroscopic observations of the Venus 1.27-μm O₂ airglow were carried out with ground-based telescopes from 2002 to 2007. Spectral image cubes were taken with the Okayama Astrophysical Observatory/infrared imaging spectrometer (superOASIS), the Gunma Astronomical Observatory/near-infrared camera and NASA's Infrared Telescope Facility/cryogenic echelle spectrograph (CSHELL). The rotational temperature shows weak positive correlation with the airglow intensity. However, there are some regions that have almost same intensities but different temperatures. The intensities tend to decrease from the anti-solar point to the terminator besides local features. These results indicate that there are local strong downward flows superimposed on the subsolar-to-antisolar circulation.     

On the detection and utilization of gravity waves in airglow studies

We develop here theoretical relations between fluctuations of airglow brightness, fluctuations of temperature as revealed by airglow, and the atmospheric gravity waves that are believed to cause these fluctuations. We note and account for differences between our relations and those obtained by Krassovsky (1972, Ann. Geophys. 28, 739) and Weinstock (1978, J. geophys. Res. 83, 5175), correcting both of the latter in the process. We explicitly repudiate the need for a nonlinear treatment of O₂(¹Σ_g) emissions as it was asserted by Weinstock, one aspect of the nonlinear treatment he gave, and the conclusions he drew from that treatment, including, inter alia, the conclusion that temperature fluctuations carry more meaning as a diagnostic than do brightness fluctuations. Instead, we note the dependence of both types of fluctuation on variable gravity-wave parameters, which dependence can be applied to the study of gravity waves via airglow or of airglow via gravity waves. As a first step, we note the ability of the present analysis to account for certain observations of OH and O₂(¹Σ_g) emissions that have been, until now, inadequately or incorrectly explained, and we stress the importance of the proper measurement of parameters such as wave frequency and propagation speed if our own tentative explanations are to be put to the test and further progress is to be made.     

Tidal and solar cycle effects on the OI 5577 Å, NaD and OH(8,3) airglow emissions observed at 23°S

The upper mesosphere airglow emissions OI 5577, NaD and OH have been observed at Cachoeira Paulista (22.7°S; 45.0°W) Brazil. Nocturnal variations and their seasonal dependencies in amplitude and phase, and the annual variations of these emissions are presented, analysing the data obtained from 1977 to 1982 during the ascending phase of the last solar cycle. The nocturnal variations of the OI 5577 emission and the OH rotational temperature showed a significant semidiurnal oscillation, with the phase of maximum moving from midnight in January to early morning in June. Semiannual variation of the OI 5577 and NaD emissions with the maximum intensities in April/May and October/November were observed. The OH rotational temperature, however, showed an annual variation, maximum in summer and minimum in winter, while no significant seasonal variation was found in the OH emission intensities. Long-term intensity variations are also presented with the solar sunspot numbers and the 10.7 cm flux.     

OH and O2 airglow emissions during the 1998 leonid outburst and the 2002 leonid storm

In order to enhance our understanding of the possible influence of meteor ablation on the enrichment in OH and O₂ of the lower thermosphere we studied intense Leonid meteor activity by using the SATI (Spectral Airglow Temperature Imager) interferometer of the Instituto de Astrofísica de Andalucía. We measured the emission rate and rotational temperature of OH and O₂ airglow emission layers during two observation periods of high meteoric activity: the 1998 Leonid outburst and the 2002 Leonid storm. The results show that there is not a clear relation of O₂ and OH airglow emission and rotational temperature with meteoric activity.     

Springtime effects in the mesosphere and ionosphere observed at northern midlatitudes

Nighttime volume emission rates and rotational temperatures, obtained from simultaneous observations of molecular oxygen and hydroxyl airglow at Almaty (43.25°N, 76.92°E) and Sierra-Nevada (37.2°N, 356.7°E), along with ionospheric density derived from foF2 in the vertical sounding ionograms over Almaty are analysed to study the variability and coupling of parameters observed in the upper mesosphere and ionosphere during the period of February - April, 2000.Ionospheric critical frequency measurements and airglow observations by the Mesopause Rotational Temperature Imager (MORTI) at Almaty and the Spectral Airglow Temperature Imager (SATI) at Sierra-Nevada Observatories show an increase in long-period planetary wave (PW) activity from the end of February until the middle of March, 2000.Very good agreement was found in the temporal variations of emission rates and rotational temperatures from March 1-15, 2000 measured at the Almaty and Sierra-Nevada sites. Similar perturbations could also be seen in the ionospheric critical frequency (ΔfoF2) obtained as a difference between current foF2 values and an ionospheric background level.The perturbations observed have been interpreted employing the Met office stratospheric model results. Latitudinal structure of a quasi 5-day wave was identified, for which the first-symmetric-mode amplitude and symmetric behaviour of phase are in good agreement with theoretical prediction. The analysis of the Met office stratospheric data indicate the presence of westward-propagating PW with periods of ∼5 and 10 days during the period of interest. The temporal correlation between planetary scale oscillations observed in the datasets examined (ionospheric, optical and meteorological) suggest dynamical coupling with the stratosphere. A negative disturbance in ΔfoF2 of ∼25% observed 1 day before a sharp increase in the MORTI mesospheric rotational temperature registered on March 10 at Almaty, is also discussed in the context of the possible stratosphere/mesosphere/ionosphere coupling.     

Temperature variation at mesopause levels during winter solstice at 78°N

Atmospheric temperatures from the polar mesopause are deduced from spectrophotometric measurements of hydroxyl bands and lines in the night airglow made at 78°N during December and January 1980/81 and 1982/83. An overall mean temperature of 220 K is found with a range from 172 to 257 K in the daily mean values. Several warm periods lasting 3–6 days may be due to heat dissipated by gravity waves. One week of consistently low temperatures was apparently connected to a stratospheric warming. Both datasets show a warmer mean temperature later in January than for early and mid-December. The polar OH airglow seems to peak at or just above the mesopause. The data also indicate that the mesopause is situated at approx. 90 km with an upper temperature gradient of 1 K km^?1 indicating a very shallow mesopause. A superposed epoch analysis of 19 consecutive 24-h periods reveals a semidiurnal variation in the temperature around winter solstice with an amplitude of 5 K. No diurnal variation of amplitude greater than 1 K is apparent. Average wind velocity deduced from the amplitude of the semidiurnal temperature variation is 9 m s^?1.     

Inhomogeneities and wavelike variations of the rotational temperature of atmospheric hydroxyl

Quiet and disturbed variations of the rotational temperature of the hydroxyl emissions of the night sky in band 4-1 are described. Examples are given of wavelike propagation of the disturbances of rotational temperature.     

Fluctuations in mid-latitude 6300 Å airglow and their relationship to F-region irregularities

Observations of fluctuations in the 6300 Å airglow emission at night have been studied using a tilting filter photometer. Spectral analysis of the fluctuations shows that at times the fluctuations are primarily due to wavelike disturbances with relatively well defined periods. At other times the spectrum of the fluctuations contains significant power only at long periods and there is a relatively sharp cut-off at the short period end. Most spectra are of these two types and are probably indicative of gravity waves. A third category is observed in which the spectra are of the form $\text{P∽?}{}^{\mathrm{?1.3}}$ Fewer spectra of this type are observed when the magnetic activity increases and the periods of spectral peaks observed changes with magnetic activity. The total power in the airglow fluctuations increases with K_p and the occurrence of spread F.     

Determination of atomic oxygen density from rocket borne measurement of hydroxyl airglow

A rocket experiment was conducted which measured the infrared bands of the excited hydroxyl radical in the night airglow. The OH emission was found in a layer centered at 87 km having a half-width of 6 km and a total emission of 1.1 MR. The atomic oxygen altitude profile, ranging from 1.3 × 10¹⁰ atoms/cm³ at 83 km to 3 × 10¹¹ atoms/cm³ at 90 km is determined from the hydroxyl airglow measurements. This derivation is based on the steady state balance between ozone formation from atomic oxygen and its destruction by hydrogen which produces the OH infrared emission.     

The interpretation of 6300 Å airglow observations of ionospheric irregularities

The variations in intensity of 6300 Å airglow throughout the ionosphere above an observor are represented by a three dimensional Fourier series. Filtering effects caused by the field of view of an observing instrument are then calculated assuming that all Fourier components move with the same velocity. The results suggest that the observations of Mullaney et al. (1972) can be interpreted as the power spectrum of horizontal structures in the airglow.     

On the equilibrium nature of the rotational temperature of hydroxyl airglow

The rotational temperature of the hydroxyl at Zvenigorod almost reflects the actual temperature of the environment.     

Nightglow (557.7 nm of OI) in the central polar cap

The 557.7 nm OI night airglow emission was measured in the central polar cap by ground-based photometric systems at Thule Air Base, Greenland during the winter seasons from 1972–1973 to 1974–1975 and at Thule-Qanaq, Greenland during the winter season of 1973–1974. The behavior of the 557.7 nm night airglow emission in the polar cap was found to be quite different from that observed at mid and low latitudes. No diurnal variation greater than ±5% exist in the data. Large amplitude variations in the 557.7 nm daily average emission intensities can change by up to a factor of approximately 8 over periods ranging from 4 to 19 days. These long-term airglow variations cover at least a 100 km horizontal range as determined by a correlation coefficient of 0.94 between daily average 557.7 nm airglow intensities observed at Thule Air Base and Thule-Qanaq. An interplanetary magnetic field sector related behavior is evident in the daily average intensities which shows an increase of intensity in a positive (+) sector and a decrease of intensity in a negative (?) sector. No significant correlation was found between the 557.7 nm daily average intensities and Zurich sunspot number R_Z, although a season to season positive trend was evident. Correlations between the 557.7 nm daily average intensities and planetary magnetic indices ΣK_p and A_p were found to be inconclusive due to sector related effects. The Barth and Chapman mechanisms are discussed as possible source mechanisms for the 557.7 nm airglow in the central polar cap, and a hypothesis is presented to explain the airglow variations.     

Studies of the motion of equatorial 630.0 nm airglow depletions

An all-sky-mapping filter photometeer has been used to study equatorial 630.0 nm nightglow intensity depletions. A generally eastward drift of the ～ 0m/sec. At times two airglow depletions moving at different velocities were observed simultaneously; in one case they merged. Simultaneous interferometric determinations of doppler shifts in the 630.0 nm line indicated that the velocity of the neutral atmosphere does not appear to be correlated with the drift of the airglow depletions. The results are compared with other observations.     

Voyager U.V. spectrometer observations of He 584 Å dayglow at Jupiter

The intensity of Jupiter's He 584 Å airglow has been measured by the Voyager U.V. spectrometers. The disc-averaged brightness is about 4 Rs and limb darkening is present. The intensity probably varies with longitude, the variation being out of phase with the H Lyman-α intensity bulge. Modelling of resonance scattering of the solar He 584 Å line by Jupiter's atmosphere has shown that the hydrogen and helium emissions can be explained about equally well by at least two self-consistent scenarios involving the structure (temperature and eddy diffusion coefficient) and excitation of the atmosphere. All our evidence points to a dramatic change of conditions in the Jovian atmosphere in the time between Pioneer and Voyager encounters.     

Time and altitude variations of vibrationally excited states of atmospheric hydroxyl

A time dependent one-dimensional theoretical model has been used to deduce averaged properties of the hydroxyl molecule airglow. Vertical profiles and time variations of the total amount of excited states have been established. The results are in close agreement with experimentally observed properties. Calculations have been made to examine the relative importance of the deactivation processes and to give limiting values to the adjustable coefficients. During the day, both collisional quenching and chemical deactivations are important, and reduce the emission by approximately the same factor while during the night collisional quenching seems to be negligible.