OH Airglow Emission Research Articles

Simulations and observations of plasma depletion, ion composition, and airglow emissions in two auroral ionospheric depletion experiments

In an ionospheric depletion experiment where chemically reactive vapors such as H2O and CO2 are injected into the O+ dominant F region to accelerate the plasma recombination rate and to reduce the plasma density, the ion composition in the depleted region is modified, and photometric emissions are produced. We compare in situ ion composition, density, and photometric measurements from two ionospheric depletion experiments with predictions from chemical modeling. The two injections, Waterhole I and III, were part of an auroral perturbation experiment and occurred in different ambient conditions. In both injections a core region of greater than fivefold plasma depletion was observed over ≈5‐km diameter within seconds of the injection, surrounded by an outer region of less drastic and slower depletion. In Waterhole I the plasma density was depleted tenfold over a 30‐km diameter region after 2 min. The ambient O+ density was drastically reduced, and the molecular O2+ abundance was enhanced fivefold in the depletion region. OH airglow emission associated with the depletion was observed with a peak emission intensity of ≈1 kR. In Waterhole III the ambient density was a decade lower, and the plasma depletion was less drastic, being twofold over 30 km after 2 min. The airglow emissions were also much less intense and below measurement sensitivity (30 R for the OH 306.4‐nm emission; 50 R for the 630.0‐nm emission). In the chemical model the major ion chemical production and loss processes in the injection are considered, and the continuity equations for major ion and airglow‐producing species are solved numerically to simulate the temporal‐spatial profiles of plasma depletion, ion composition, and airglow emissions. The simulations indicate that the overall depletion rates in different parts of the depletion region are governed by different parameters.

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.

Photographic Parallax Heights of Infrared Airflow Structures

WE recently presented infrared photographs of the night sky which show moving, changing structures1 and argued that these were due to OH airglow emission. A stringent test of the validity of our assertion is the determination of the height of discrete emission patches using parallax photographs from two widely separated sites. Observations were made during the night of May 2–3, 1973, from Capilla Peak Observatory (elevation 2,855 m) and from a station 20 km west of Albuquerque (1,760 m). The sites are separated by 64.8 km, and the Albuquerque site is located 42.3° west of north from Capilla Peak. Consecutive exposures of 5 min centred about 15° east of north were taken simultaneously at each site with f/1.2 cameras from the end of twilight till the beginning of dawn.

A Balloon Study of the OH Airglow Emission From Evening Twilight to Sunrise

A balloon-borne interference filter photometer designed to measure the OH band emission at 2 μm was flown from Fort Churchill, Canada, during the night of August 1–2, 1968. Observations of the intensity of the Q branch of the 8–6 band are presented and compared with results obtained with a 1.66 μm OH photometer carried in the same gondola. The morning and evening twilight variations observed are in agreement with those predicted by models based on mesospheric ozone photochemistry. The observed nighttime increase in the OH emission is not predicted by the theoretical models.

Photochemical heating of the mesosphere and lower thermosphere

A diurnally varying photochemical-diffusive model of a neutral oxygen-hydrogen mesosphere and lower thermosphere has been used to calculate the heating rates resulting from the absorption of solar ultraviolet radiation. The model extended from 60 to 160 km and permitted a coherent study to be made of this region, unlike previous investigations. In the thermosphere, where most of the absorption is by O 2 , only about 35 % of the solar energy input appeared as local heating. The remainder of the input was primarily removed as chemical energy in the form of a downward flux of atomic oxygen into the mesosphere. This chemical energy was converted into heating by reactions occurring near the mesopause. In the mesosphere, where absorption by O 3 becomes important, a significant amount of the heating is realized indirectly by chemical reactions. An important consequence of this indirect heating is that it continues at night between about 80 and 100 km, unlike the situation in the thermosphere where there is almost no nocturnal heating in the model. Airglow emissions, primarily by electronically excited O 2 in the thermosphere and especially by vibrationally excited OH in the mesosphere, represent important cooling mechanisms in the model. In particular it is estimated that at 88 km. the OH airglow emission could remove about 30 % of the local energy input averaged over 24 hours. DOI: 10.1111/j.2153-3490.1972.tb01532.x

A diffusive-photochemical study of the mesosphere and lower thermosphere and the associated conservation mechanisms

Results are presented for the photochemical composition of an oxygen-hydrogen atmosphere extending from 60 to 160 km, in which allowance was made for both molecular and eddy diffusion. Methane, CH 4, was included in the model to investigate the importance of this gas as a source of hydrogen in the upper atmosphere. The composition was calculated for photochemical equilibrium, diffusive-photochemical equilibrium and for diurnally varying diffusive-photochemical conditions. The eddy diffusion coefficient was assumed to increase with height up to 100 km, and then to remain constant with a value of 4 × 10 6 cm 2 sec −1. Numerical values are given for the mechanism by which the oxygen content of the atmosphere is conserved in the face of dissociative and diffusive losses. The downward flux of atomic oxygen from the thermosphere was found to converge below about 90 km, the recombination to molecular oxygen occurring via reaction with hydrogen compounds. A quasi-conservative mechanism was also found to exist for the hydrogen gases in the atmosphere, local production of water vapour and molecular hydrogen significantly reducing the net loss of hydrogen to space. The formation of molecular hydrogen in the mesosphere, which was partially due to photolysis of methane, produced a distinct source region which supplied both the thermosphere and stratosphere. Comparison of the calculated gas profiles with observations indicates the need for more extensive measurements of the gas distributions in the upper atmosphere in order to place better limits on photochemical calculations. Results are also given for the OH airglow emission and for the 5577 Å airglow of atomic oxygen.

A model calculation of the diurnal variation in minor neutral constituents in the mesosphere and lower thermosphere including transport effects

The nonequilibrium calculation for various neutral constituents in the mesosphere and lower thermosphere (Hunt, 1966) was extended by including the effects of molecular and eddy diffusion. Nitrogen and its oxides were added, and more recent laboratory data for chemical reaction coefficients were used. A special numerical technique has been developed to simultaneously solve time-dependent continuity equations for 14 constituents. The preliminary result indicates that vertical eddy diffusion significantly reduces the irregular variations around 80 km and tends to lower the height of these irregular variations. However, the value of the eddy diffusion coefficient acceptable from the consideration of heat balance below ∼100 km cannot entirely smooth out these irregular distributions for atomic oxygen, ozone, and oxygen-hydrogen compounds, although the smoothing effect for nitric oxide seems to be strong enough to eliminate the irregular variations above ∼70 km. The role of the transport terms for molecular and eddy diffusion in the continuity equation is illustrated explicitly and discussed for some representative cases. We show that the dynamic model fits the observational results for ozone and nitric oxide concentrations better than the static model and also offers a more adequate explanation for the observed diurnal variation in the OH airglow emission.

Statistical Model for the Vibrational Deactivation of Molecular by Atomic Oxygen

A theoretical investigation is performed of the transfer of vibrational energy from a highly excited diatomic molecule to a free atom at thermal velocities under the special condition of a deep attractive minimum in the intermolecular potential. The model utilizes a Monte Carlo statistical analysis of classical particle trajectories, with calculations performed for selected semiempirical forms of the interaction potential. Data relevant to the ozone stable configuration are applied to the O–O2 system, with primary emphasis upon the role of the latter in atmospheric reactions which produce the OH airglow emission. A deep attractive potential well is found to be the principal parameter leading to rapid vibrational deactivation of O2, with cross sections of the same order as kinetic cross sections and with the direct collision process of an importance comparable to the atom-interchange mechanism. The fundamental concept of the “intermediate complex” is favored to best describe the details of similar reaction processes which are associated with such strong attractive forces.

Seasonal variation and interpretation of the OH rotational temperature of the airglow

The cascading to lower vibrational levels, following the formation of the excited OH molecules, is accompanied by a shift of the rotational populations to higher rotational levels if there is no collisional redistribution. This effect would cause the rotational temperature for v = 5 to be significantly higher than for v = 9 for what appear to be reasonable assumptions regarding the primary excitation mechanism. Since the observations indicate that the rotational temperature is the same for all v, it appears that collisional redistribution must occur. A series of thirty-seven spectra of the OH airglow emissions were obtained in the interval December 1958-January 1960. The seasonal variation in the rotational temperatures derived from them is probably less than 30°K and is in phase with the larger variations observed at higher latitudes. The form of the seasonal variation is similar to the form of the seasonal variation of the sodium abundance but not to that of the auroral frequency.