A. Vallance Jones

Canopus — A ground-based instrument array for remote sensing the high latitude ionosphere during the ISTP/GGS program

Proper interpretation ofin situ satellite data requires a knowledge of the global state of the magnetosphere-ionosphere system. CANOPUS is a large-scale array of remote sensing equipment monitoring the high latitude ionosphere from the north-central to the north-west portion of North America. The array comprises thirteen magnetometers and riometers four meridian scanning photometers, a digital allsky imager and an auroral radar linked by geostationary satellite to a central receiving node in Ottawa, where the data are archived and made available in near real time to participating scientists. This paper provides a technical description of the various instruments in the CANOPUS array, and contains a summary of the key parameters which will be provided to the Central Data Handling Facility (CDHF) located at NASA/Goddard Space Flight Center, for use by the ISTP/GGS community.

An oxygen-hydrogen atmospheric model and its application to the OH emission problem

Abstract An improved time-dependent mesospheric model has been constructed in an attempt to explain more quantitatively the main features of the OH emission. Vertical transport processes are taken into account by means of a height-dependent vertical eddy diffusion coefficient. The oxygen-hydrogen photochemical scheme employed is described in detail. The photochemistry is extended to take account of the different excited vibrational levels of OH which is assumed to be produced preferentially in the upper levels by the hydrogen-ozone reaction. On this basis, important characteristics of the observed emission are correctly predicted, including the rapid intensity decrease before sunrise, the midday maximum (comparable to the nighttime value) and the evening minimum following sunset. As with other published models, the predicted OH nightglow intensity decreases steadily throughout the night in disagreement with the generally erratic intensity variations observed at mid-latitudes. It is shown that changes in dynamic conditions, simulated by temporal variations of K by a factor of 10, produce variations in emission intensity by a factor as high as 1.8 and consequently it is concluded that changes in the dynamic structure of the emission region may be responsible for the longer term nighttime deviations from the simple model. The predicted height profiles of OH† concentration for high and low vibrational levels are quite different by day, with the former extending downward as low as 50–60 km, while the latter cut-off sharply below 80 km as do the nighttime profiles for all vibrational levels. Since these daytime distributions are sensitive to the modes of vibrational quenching, it is suggested that observations of the profiles would be of value in deciding between alternative quenching schemes.

The height, spectrum and mechanism of type-B red aurora and its bearing on the excitation of O(1S) in aurora☆

Abstract The height of the lower red border of type-B aurora has been determined by triangulation using TV cameras at two ground stations. A mean height of 91.4 ± 1.1 km was determined from a set of 12 measurements made under ideal conditions. A TV spectrograph was used simultaneously to seek possible spectral changes between 6400 and 6900 A which would be indicative of changes in the vibrational distribution in the N 2 First Positive bands. No significant difference was found in this distribution between the spectra from 93 and 122 km. The height distribution of contributions to the OI 5577 A emission relative to the N + 2 First Negative emission was modelled from 80 to 160 km. Contributions from electron impact on atomic O, O + 2 dissociative recombination and N 2 (A)ue5f8O energy transfer were included. Account was taken of recent laboratory data on O( 1 S) quenching. It was concluded that these processes could explain the excitation of O( 1 S) in normal aurora and the height distribution of OI 5577 A in type-B red aurora. It was confirmed that the lifetime ofO( 1 S) in type-B red auroral rapid time variations is about 0.5 s and it was found from the model that the observed time variation can be reproduced by the mechanisms considered, provided the concentration of NO in the auroral atmosphere is about 1 × 10 9 at 95 km. Before reasonable certainty can be attained in the correctness of the interpretation it will however be necessary to have reliable simultaneous observations of neutral atmospheric composition particularly for O and NO as well as unchallengeable measurements of the yields of O( 1 S) for the processes considered and for several other processes which have been suggested recently.

The aries auroral modelling campaign: characterization and modelling of an evening auroral arc observed from a rocket and a ground-based line of meridian scanners☆

Abstract An auroral arc system excited by soft electrons was studied with a combination of in situ rocket measurements and optical tomographic techniques, using data from a photometer on a horizontal, spinning rocket and a line of three meridian scanning photometers. The ground-based scanner data at 4709, 5577, 8446 and 6300 A were successfully inverted to provide a set of volume emission rate distributions in the plane of the rocket trajectory, with a basic time resolution of 24 s. Volume emission rate profiles, derived from these distributions peaked at about 150 km for 5577 and 4709 A, while the 8446 A emission peaked at about 170 km with a more extended height distribution. The rocket photometer gave comparable volume emission rate distributions for the 3914 A emission as reported in a separate paper by McDade et al. (1991, Planet. Space Sci.39, 895). Instruments on the rocket measured the primary electron flux during the flight and, in particular, the flux precipitating into the auroral arc overflown at apogee (McEwen et al., 1991; in preparation). The local electron density and temperature were measured by probes on the rocket (Margot and McNamara (1991; Can. J. Phys.69, 950). The electron density measurements on the downleg were modelled using ion production rate data derived from the optical results. Model calculations of the emission height profile based on the measured electron flux agree with the observed profiles. The height distribution of the N2+ emission in the equatorward band, through which the rocket passed during the descent, was measured by both the rocket and the ground-based tomographic techniques and the results are in good agreement. Comparison of these profiles with model profiles indicates that the exciting primary spectrum may be represented by an accelerated Maxwellian or a Gaussian distribution centered at about 3 keV. This distribution is close to what would be obtained if the electron flux exciting the poleward form were accelerated by a 1–2 kV upward potential drop. The relative height profiles for the volume emission rate of the 5577 A OI emission and the 4709 A N2+ emission were almost indistinguishable from each other for both the forms measured, with ratios in the range 38–50; this is equivalent to I(5577) I(4278) ratios of 8–10. The auroral intensities and intensity ratios measured in the magnetic zenith from the ground during the period before and during the rocket flight are consistent with the primary electron fluxes and height distributions measured from the rocket. Values of I(5577) I(4278) in the range 8–10 were also measured directly by the zenith ground photometers over which the arc system passed. These values are slightly higher than those reported by Gattinger and Vallance-Jones (1972) and this may possibly indicate an enhancement of the atomic oxygen concentration at the time of the flight. Such an enhancement would be consistent with our result, that the observed values of I(5577) and I(8446) are also significantly higher than those modelled on the basis of the electron flux spectrum measured at apogee.

Observations and interpretation of spectra and rapid time variations of type-B aurora

Abstract Observations of type-B red and normal aurora were made with a high-speed multichannel photometer and a digital grating spectrometer. The ratio I ( O 2 + 1N; 2, 0 + 3, 1) I ( N 2 + 1N; 0, 3) measured in the 5200–5300 A region with the spectrometer was found to increase by about 16% from normal to type-B aurora. This small change is difficult to reconcile with a height below 90 km for the red border. In the type-B aurora, λ 5577 was weakened by a factor between 1.9 and 3.8 while the ratio I ( N 2 1P; 5, 2) I ( N 2 + 1N) was enhanced less than 20%. Rapid intensity variations in the type-B lower border were observed in the λ 5577 and other channels of the photometer. A revised time dependent auroral excitation-ion chemistry model is used in an attempt to reproduce the observations. The observed weakening of λ 5577 could be produced at heights equal to or less than 100 km while the short observed time lag of λ 5577 on the N2+ 1N emission is easier to explain at 100 km than at 80 km. It is concluded that some type-B lower borders may occur near 100 km although it is recognized that there is good evidence rare deep crimson lower borders lie at 80 km or below. The mechanism for the excitation of O(1S) is considered in the light of these results. None of the mechanisms examined is satisfactory on the basis of currently accepted atmospheric models and quenching rate coefficients.

Atmospheric quantal emissions: A review of recent results☆

Abstract Work on quantal emissions from the upper atmosphere over the last three to four years is reviewed. Aurora and airglow emissions from the X-ray to the microwave region are covered. Observations, interpretation, modelling and applications are considered.

Measurements of the optical emission height profiles of medium intensity aurora

Abstract Height profiles of auroral emissions at 3914 A, 4861 A, and 5577 A were obtained in two rocket flights through medium intensity stable aurora. The 3914 A N 2 + integral intensity data were compared with intensity variations predicted by an auroral model for a range of primary electron energy spectra. The observed profiles for the two flights were well reproduced respectively by a 5.6 keV mono-energtic flux and by a flux with an exponential spectrum cutting off around 12 to 15 keV. The data for 5577 A (available only above 120 km) bear a constant ratio to that for 3914 A. The emission profiles derived for 3914 A, peak at 115 and 107 km respectively.