A. G. McNamara

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.

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.

Relationships between radio aurora, visual aurora and ionospheric currents during a sequence of magnetospheric substorms

Abstract In an earlier paper the latitudinal and longitudinal structure of ionospheric current flow during a sequence of magnetospheric substorms was presented (McDiarmid and Harris, 1976). In the present paper the relationships between the electrojets, the radio aurora observed at 48 MHz and the all-sky camera-recorded visual aurora are presented for the same substorm sequence. The previously described morphology of radio aurora during substorms is confirmed and the observed relationships can be explained.

Comparative study of Langmuir probe characteristics in different ionospheric conditions

Abstract This paper examines the role played by the high energy tail of the electron distribution function on Langmuir probe characteristics. A model is developed to derive the mean energy and the density of the hyperthermal electrons from probe characteristics for two ionospheric rocket flights involving different plasma conditions. The hyperthermal electrons are shown to influence the electron temperature measurement even if they constitute only a small fraction of the total electron concentration. The influence of the geomagnetic field, the collisions and the velocity of the vehicle on the probe data are also examined.

The relationship of auroral absorption to the electron energy distribution of the plasma

Abstract An auroral absorption event in the D-region of the atmosphere has been studied by simultaneous measurements of electron temperature, electron density and hyperthermal electrons with a Langmuir probe, and of radio absorption coefficient by 30 MHz riometers. The absorption of the radio waves cannot be explained only by the enhancement of the electron density but requires that the electron collision frequency v be increased above its normal value by the presence of a high energy tail in the electron distribution function. A model is used to determine the characteristics of the hyperthermal electrons in order to evaluate their contribution to the collision frequency and to the absorption coefficient. Good agreement is found between theoretical and experimental values.

Observations of type 4 VHF radar Doppler spectra during a Ps6 pulsation event

Abstract It has been suggested (Fejer et al. , 1986, J. geophys. Res . 91 , 13583) that type 4 auroral Doppler spectra are caused by a true two-stream instability in regions of enhanced electron temperature and intense electric fields. In such regions, type 4 spectra are expected to be observed when the Hall current direction becomes approximately parallel to the radar wave vector so that the latter is inside the two-stream unstable cone. The validity of this assumption is tested by the use of 50 and 60 MHz CW Doppler radar data during a Ps6 pulsation event. The CW radar data are supported with BARS (Bistatic Auroral Radar System) and MARIA (Magnetometer and Riometer Array) data, both instruments being parts of the CANOPUS program. It is demonstrated that type 4 irregularities are highly directional; most likely along the Hall current direction. The simultaneous observations of type 4 spectra by both CW radars favor the scaling of the Doppler shift according to transmitter frequency, although the observed type 4 Doppler velocity is found to be about 5% higher on 50 MHz than it is on 60 MHz.