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Heavy (O+) ion energization and field-aligned motion in and near the ionosphere are still not well understood. Based on observations from the CASSIOPE Enhanced Polar Outflow Probe (e-POP) at altitudes between 325 km and 730 km over one year, we present a statistical study (24 events) of ion heating and its relation to field-aligned ion bulk flow velocity, low-frequency waves and field-aligned currents (FACs). The ion temperature and field-aligned bulk flow velocity are derived from 2-D ion velocity distribution functions measured by the suprathermal electron imager (SEI) instrument. Consistent ion heating and flow velocity characteristics are observed from both the SEI and the rapid-scanning ion mass spectrometer (IRM) instruments. We find that transverse O+ ion heating in the ionosphere can be intense (up to 4.5 eV), confined to very narrow regions (∼ 2 km across B), is more likely to occur in the downward current region, and is associated with broadband extremely low frequency (BBELF) waves. These waves are interpreted as linearly polarized perpendicular to the magnetic field. The amount of ion heating cannot be explained by frictional heating, and the correlation of ion heating with BBELF waves suggest that significant wave-ion heating is occurring and even dominating at altitudes as low as 350 km, a boundary that is lower than previously reported. Surprisingly, the majority of these heating events (17 out 24) are associated with core ion downflows rather than upflows. This may be explained by a downward-pointing electric field in the low-altitude return current region.

The CASSIOPE Enhanced Polar Outflow Probe (e-POP) is a Canadian small-satellite mission dedicated to the study of polar ion outflows and related magnetosphere-ionosphere coupling processes in the topside ionosphere. Scheduled for launch in 2009, it will carry eight scientific instruments, including imaging plasma and neutral particle sensors, magnetometers, dual-frequency GPS receivers, CCD cameras, a radio wave receiver and a beacon transmitter, for in-situ particle, field, and current measurements and auroral imaging and radio measurements. We present an overview of the e-POP mission, its current status and plan of observations and data distribution during the operation phase of the mission.

The overarching objective of the ILWS Geospace program is to facilitate system level science. This demands synoptic observations such as global auroral imaging. At present, there is no funded mission during ILWS that incorporates a global auroral imager. The imaging community needs to move now to address this important gap. While doing so, it is interesting to take stock of global auroral observations that have not been achieved, or that have been achieved only to a limited extent. These include simultaneous imaging across all relevant scales, spectral resolution of sufficient quality to allow for global maps of characteristic energy and energy flux of precipitating electrons, continuous global auroral imaging for time periods spanning long-duration geomagnetic events, systematic interhemispheric conjugate observations, auroral observations magnetically conjugate to in situ measurements, and automatic classification of auroral images. These observations can be achieved within the next decade. If they are, then they will facilitate exciting new science.

Over the past four decades, Canadian scientists and their industrial partners have made major contributions to both the technology of auroral imaging and to the advancement of knowledge through the...

A joint ground-spacecraft study of the polar cap from January to March, 1997 shows that the dawn and dusk boundaries identified on the meridian scanning photometer scans from Eureka, in the central polar cap, agree well with the boundaries seen by the Interball-2 UVAI images for northward interplanetary magnetic field (IMF) B z conditions. These boundaries are displaced duskward when B y is positive and dawnward when B y is negative. There are observable discrete emissions (above airglow) from the polar cap during much of the time. From four periods of extended observations, two contrasting types of polar caps emerge. For northward IMF B z the polar cap is constricted in the dawn–dusk direction. Sun-aligned arcs emerge from the auroral oval (from the dawn flank with B y positive and the dusk flank with B y negative) and drift across the polar cap. In some cases, but not all, they appear following transients in the IMF B y or B z . For southward IMF B z the central polar cap frequently has F-region plasma patches extending across much of the polar cap and drifting antisunward. Two auroral substorms occur, the first one (10 February 1997) showing a poleward auroral expansion along much of the oval and followed by a series of elongated, periodic F-layer patches. The second substorm (02 March 1997) has a poleward expansion confined to the midnight sector and the F-layer patches which subsequently appear are quite different (fainter and less extended), perhaps reflecting differing stability of ion flow patterns across the polar cap. While the extended views of the polar cap from the ground reveal much of the dynamics of polar arcs and patches in response to solar wind IMF changes, there are still unanswered questions as to the triggering mechanisms for both. And the onset and progress of auroral substorms in relation to F-layer patch formation and motion requires further investigation. One polar arc on January 22 recorded by the UVAI and the Eureka photometer permitted a determination of the UVAI sensitivity, indicating 1 CCD count corresponded to 1.5 R of 630 nm emission. This calibration value is specific to this type of aurora (low energy with a I630/I558 ratio of >1). The UVAI images showed that the arc was a theta aurora, indicating that such auroras can be excited by either energetic electrons or soft electrons.

A merged data set from Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) and Magnetometers-Ionospheric Radars-All-Sky Cameras Large Experiment (MIRACLE) magnetometer stations is used to study variations observed at widely separated locations. Three years of 10-s data are analyzed using canonical correlation techniques to determine the temporal offset of similar fluctuations observed at pairs of sites. Nearly simultaneous ( 10-min delay). Correlated episodes occur more often (roughly 10% of the time) when sites are in the dawn/dusk sectors and less often (∼5%) for noon/midnight configurations.

Results of the study of two substorms from Interball auroral UV measurements and two-dimensional patterns of equivalent ionospheric currents derived from the MACCS/CANOPUS and Greenland magnetometer arrays are presented. Substorm development in 2-D equivalent ionospheric current patterns may be described in terms of the formation of two vortices in the equivalent currents: a morning vortex related to downward field-aligned current and an evening vortex related to upward field-aligned current. Poleward propagation of the magnetic disturbances during substorm expansive phase was found to be associated mainly with a poleward displacement of the morning vortex, whereas the evening vortex remained approximately at the same position. As a result, the initial quasi-azimuthal separation of the vortices was replaced by their quasi-meridional separation at substorm maximum. Interball UV images during this period showed the formation of a bright auroral border at the poleward edge of substorm auroral bulge. The auroral UV images showed also that the auroral distribution in the region between the polar border and the main auroral oval tends to have a form of bubbles or petals growing from a bright protuberant region on the equatorward boundary of the auroral oval. However, the resolution of the UV imager was not sufficient for the reliable separation of such the structures, therefore, this result should be considered as preliminary. Overlapping of the auroral UV images onto equivalent current patterns shows that the bright substorm surge was well collocated with the evening vortex whereas the poleward auroral border did not coincide with any evident feature in equivalent ionospheric currents and was located several degrees equatorward of the morning current vortex center related to downward field-aligned current. The ground-based magnetic array allowing us to obtain instantaneous patterns of equivalent ionospheric currents gives a possibility to propose a new index for substorm activity such as the magnitude of the total current between the centers of the morning and evening vortices. Such integral index would not depend on where the substorm is located and be unaffected by the migration of substorm activity poleward or equatorward.

Arc widths were calculated for 3126 stable auroral arcs observed by an all-sky camera located in Gillam, Manitoba. The camera is filtered to accept 5577-A emissions and has a single-pixel spatial resolution of 1.7 km at zenith. The measured mean width of stable mesoscale arcs located within ±5° of magnetic zenith is 18 km with a standard deviation of 9 km. The width distribution exhibits a steep cutoff below 8 km; when combined with studies of small-scale auroral structure this cutoff suggests a gap in the occurrence of arcs with widths of order 1 km. This feature of the arc width spectrum argues against the notion of a turbulent cascade of energy from larger to small scales. Residuals from the Gaussian fits are only about 3% of the arc amplitude on average, indicating little sub-structure within arcs at scales down to the measurement resolution.

High spatial and temporal resolution observations of auroral forms made by the University of Calgary Portable Auroral Imager are reviewed. Observations include auroral forms with apparent widths of on the order of tens to hundreds of meters and lifetimes of less than a second to several tens of seconds. Included here is a class of multiple auroral arc systems exhibiting a strikingly asymmetric internal topology. It is shown that such systems of multiple linear arcs may be explained by mode conversion of field-line resonance shear Alfven waves to inertial Alfven waves. A survey of small-scale, short-lived auroral vortices (curls) occurring on thin auroral forms within the active aurora has also been performed, with some results being reviewed here. The Kelvin-Helmholtz instability as a responsible mechanism is discussed in light of the observationally acquired statistical data. Observations of small-scale “black” auroral arcs and vortices are briefly reviewed as well.

Direct imaging of the magnetosphere by the IMAGE spacecraft will be supplemented by observation of the global aurora, the footprint of magnetospheric regions. To assure the simultaneity of these observations and the measurement of the magnetospheric background neutral gas density, the IMAGE satellite instrument complement includes three Far Ultraviolet (FUV) instruments. In the wavelength region 120-190 nm, a downward-viewing auroral imager is only minimally contaminated by sunlight, scattered from clouds and ground, and radiance of the aurora observed in a nadir viewing geometry can be observed in the presence of the high-latitude dayglow. The Wideband Imaging Camera (WIC) will provide broad band ultraviolet images of the aurora for maximum spatial and temporal resolution by imaging the LBH N2 bands of the aurora. The Spectrographic Imager (SI), a monochromatic imager, will image different types of aurora, filtered by wavelength. By measuring the Doppler-shifted Ly-α, the proton-induced component of the aurora will be imaged separately. Finally, the GEO instrument will observe the distribution of the geocoronal emission, which is a measure of the neutral background density source for charge exchange in the magnetosphere. The FUV instrument complement looks radially outward from the rotating IMAGE satellite and, therefore, it spends only a short time observing the aurora and the Earth during each spin. Detailed descriptions of the WIC, SI, GEO, and their individual performance validations are discussed in companion papers. This paper summarizes the system requirements and system design approach taken to satisfy the science requirements. One primary requirement is to maximize photon collection efficiency and use efficiently the short time available for exposures. The FUV auroral imagers WIC and SI both have wide fields of view and take data continuously as the auroral region proceeds through the field of view. To minimize data volume, multiple images are taken and electronically co-added by suitably shifting each image to compensate for the spacecraft rotation. In order to minimize resolution loss, the images have to be distortion-corrected in real time for both WIC and SI prior to co-adding. The distortion correction is accomplished using high speed look up tables that are pre-generated by least square fitting to polynomial functions by the on-orbit processor. The instruments were calibrated individually while on stationery platforms, mostly in vacuum chambers as described in the companion papers. Extensive ground-based testing was performed with visible and near UV simulators mounted on a rotating platform to estimate their on-orbit performance. The predicted instrument system performance is summarized and some of the preliminary data formats are shown.

Multispacecraft observations are analyzed to examine the dynamics of thin current sheet evolution during the early phases of a substorm during the period 0630–0800 UT on December 10, 1996. The ground signatures showed two activations, one latitudinally localized at 0731 UT and another, larger expansion around 0800 UT. A local model consisting of two current sheets (a thin current sheet and a thicker plasma sheet) was developed utilizing two-spacecraft magnetic field measurements within the magnetotail. Extension of the thin current sheet model to the inner magnetotail shows that during most of the growth phase, the thin current sheet intensified simultaneously and at the same rate in the mid-magnetotail (∼30 RE) and near geosynchronous orbit. These results show that a thin current sheet extended from the near-geostationary region to the midtail, and that the entire current sheet responded to the driving in a coherent way. Furthermore, timings suggest that the onset-associated disturbances were observable in the midtail before the ground or geosynchronous signatures.

Ionospheric convection inferred from Super Dual Auroral Radar Network (SuperDARN) HF radar measurements is compared with an equivalent ionospheric convection derived from ground magnetometer data in the dayside winter high-latitude ionosphere. Although there was general agreement between observed convection patterns produced by radars and magnetometers, there were significant differences in details. The orientation of equivalent convection vectors inferred from magnetic data was often opposite to the convection vectors determined by the SuperDARN radars in the poleward part of the convection vortex structure, though the agreement was reasonable in its equatorward part. The magnitudes of convection vectors determined from radar data and those inferred from magnetometer data were often different. The observed differences are attributed to strong horizontal inhomogeneity in the ionospheric conductivity distribution for winter conditions. It is possible that magnetic disturbances in the dark high-latitude ionosphere are strongly affected by field-aligned currents at the terminator that separates regions of the sunlit highly conducting ionosphere and dark poorly conducting ionosphere.

Enhancements of the O(¹D) 630 nm and O(¹S) 558 nm volume emission rates were detected by WINDII, the Wind Imaging Interferometer on board the Upper Atmosphere Research Satellite, UARS, as its limb-locked fields of view crossed the South Atlantic magnetic anomaly zone during periods of high geomagnetic activity. The enhancement attributed to electron precipitation is 20 R for the 630 nm red line and 3 R for the 558 nm green line, less than the natural variability of these nightglow emissions as seen from below. Nevertheless, statistical tests indicate with 95% confidence that the enhancements are significantly distinguishable from the natural variability. The red enhancement lies west of the green because eastward drifting trapped electrons move toward lower mirror altitudes in this region. These enhancements are energetically consistent with earlier measurements of electron fluxes in this region; we estimate the total precipitation energy deposition rate at a few megawatts.

The time-dependent phase structure of Alfven waves on open and closed field lines is studied. In accord with previous observations we find that Alfven waves on near-Earth closed field lines exhibit a poleward phase motion unless they are close to the plasmapause, in which case the motion may be equatorward. Alfven waves generated on tail-like closed or open field lines threading the plasma sheet boundary layer have received much less attention but may be shown to have an equatorward phase motion [Liu et al., 1995]. Phase mixing in the magnetotail proves to have a much richer behavior than that on near-Earth (dipole-like) closed field lines as not only the Alfven frequency varies across the background field lines but the field-aligned wavenumber varies too. The two contributions tend to cancel each other partially for typical tail equilibria. Observations are given of a double oval configuration showing long-period pulsations on the poleward portion of this oval. Equatorward phase motion is observed and supports the theory presented here. These observations illustrate that Pc5 pulsation activity can be much richer than previously thought and can occur at locations not in the dipole-like region, as is usually supposed. The concepts presented in this paper provide a powerful framework with which to interpret observations related to auroral arcs, substorms, and magnetospheric equilibria.

A simple model for the generation of poleward moving multiple auroral structures in the nightside ionosphere is described. The model is based upon the premise that field line resonance oscillations are responsible for auroral arc generation. The auroral structures are considered to be a result of interference between Alfven field line resonance oscillations on different L shells. Because of the dependence of the Alfven resonance frequency on L shell, any two neighboring L shells which oscillated initially with the same phase, after some time appear to be in opposite phase. That results in the appearance of counter-directed electric fields at these L shells and a large field-aligned current between them, which can produce the electron acceleration along the magnetic field and be responsible for auroral arc generation. The out of phasing between the oscillating L shells begins first at low latitudes and then propagates poleward producing poleward moving auroral arcs. The model requires that oscillations be maintained for many cycles of the waves and the source for energy is ultimately derived from magnetospheric convection in the plasma sheet. The field line resonance interference model explains periodic behavior in such auroral activity having frequencies in the Pc5 range. It is significant that the period of oscillation may be greater than that for the Alfven resonant oscillations, which implies that two separate frequencies may appear on the same field line. The poleward propagation of the auroral arcs in this model is a result of the poleward propagation of interference maxima rather than any real plasma or wave propagation.

High-resolution television observations by the University of Calgary portable auroral imager of the small-scale spatially periodic distortions of auroral forms known as “curls” are presented. During winter 1995 and 1997 field trips to Rabbit Lake, Saskatchewan, Canada, a large amount of video data containing auroral curls was acquired. Analysis of this data set has led to much improved insight into the properties of these features. Observed spatial and temporal characteristics are presented, with results compared to those of earlier surveys wherever applicable. Striking parallels between the characteristics of these ∼1 km scale size curls and the characteristics of the ∼ 100 km scale size auroral “spirals” observed by the Freja UV imager are pointed out and discussed in terms of shear-driven instabilities. In addition, observations of the interesting new phenomena of “auroral kinks” and “spinning auroral patches” are briefly described.

High-resolution optical observations by the University of Calgary Portable Auroral Imager show a frequent occurrence of asymmetric multiple small-scale auroral arc structures during auroral substorms. Whereas the classical multiple arc array tends to exhibit a fairly symmetrical configuration, with parallel motions within individual discrete arcs being opposite in direction across the center of the arc array, the multiple arcs to be discussed herein are distinguished by the presence of discrete arcs strictly equatorward of the two bright counter-streaming arcs that would ordinarily define the center of the arc array. The intensity of these parallel equatorward-lying arcs were in most cases found to decrease rapidly in the equatorward direction. By considering the topology of the structures and the spacing between arcs, observations are found to be consistent with recent theories suggesting inertial Alfven waves as a possible cause of fine-scale auroral arcs.

Measurements of mesospheric winds by an imaging Fabry-Perot interferometer located near Calgary (Lat. 51 ° 10′ N, Lon. 114 ° 13′ W) have been obtained from the P 1 (3) line of the OH(6-2) rotation band for 36 nights during the period of November 1992 to March 1993. The emission layer was observed to have a dominant eastward mean wind as well as a distinct semi-diurnal tidal component signature. Harmonic analysis has been performed on both the individual nights of data as well as on the average monthly winds. The mean winds and semi-diurnal tide of the monthly average winds are found to be typical of the winter mesopause. The daily wind patterns are seen to fluctuate with the mean winds and semi-diurnal amplitude varying by up to a few tens of meters per second. However, these fluctuations are seen to be distributed about the monthly average values. Comparison of these results with previously reported mesospheric winds and model predictions shows general agreement.

Observations of the OH(8-3) band rotational temperature have been carried out from Calgary (51 °N, 114 °W), Canada, from 1988 to 1990. The measurements have been taken in orthogonal scanning mode and the data set has been analyzed to study salient features of gravity waves in the mesospheric region from this mid-latitude station. Rotational temperature data from 36 nights showed distinct gravity wave activity during this period. The gravity wave characteristics studied include the dominant period, horizontal structure speed, implied horizontal wavelength and horizontal component of direction of propagation. The preferred direction in the horizontal wave propagation at Calgary is towards the north-west. A comparison of the observed horizontal propagation directions with the permitted directions, using model wind profiles for Calgary, shows good agreement. This indicates that the upward flow of wave energy could be modified by the background wind.

In view of a recent revival of interest in the black aurora and related phenomena, and a striking lack of information on the phenomenon in the literature, we present high spatial and temporal resolution optical observations of the black aurora made by the University of Calgary portable auroral imager. A variety of black auroral phenomena, such as black vortices, arcs, and eastward drifting black auroral patches and arc segments, were observed in the evening and midnight sector diffuse auroral oval during a field trip to Rabbit Lake, Saskatchewan, from February 25 to March 7, 1995. Observed spatial and temporal characteristics are reviewed, with statistical data presented in the form of histograms.

Observations of the OH (8-3) band airglow emission, using a multichannel tilting filter type photometer, have been carried out at Calgary (51°N, 114°W), Canada, since 1981. In this paper recent measurements of the nocturnal, seasonal and solar flux variations of the mesopause temperature, obtained from the rotational temperature of the OH (8-3) band observations, are presented. The data presented span the ascending phase of the present solar cycle viz. 1987–1988 (low solar activity) and 1990 (high solar activity). Good correlations (r = 0.73) between the OH (8-3) band rotational temperature and the 10.7 cm solar flux were observed. The mean temperature for the period investigated was about 210 K. The seasonally averaged nocturnal variations show only small irregular excursions, possibly associated with solar tides and the passage of gravity waves in the mesopause region. However, the observed rotational temperatures show considerable night-to-night changes.

Optical images of [O I] 630.0-nm emission from drifting F region polar patches acquired with a sensitive all-sky imager have been analyzed to infer the ionospheric convection velocity over a period of 9 hours on December 8, 1993. The drift vectors agree well in both direction and magnitude with simultaneous measurements from a nearby digital ionosonde. The delay between interplanetary magnetic field By changes measured at IMP 8 and changes in the convection direction at the pole is estimated. A montage of the optical emission from the patches observed over the period is presented to illustrate the range of optical patch shapes, sizes, and spacings observed.

The departure of the aurora from quiet levels in a dynamic manner constitutes some type of auroral “breakup” event. Research into the auroral breakup predates the International Geophysical Year (1957/1958). This feature of the aurora, and the later, more global concept of the auroral substorm, has become a focus for much of the auroral research that occurs today. New instrumentation and global collaborations continue to refine our knowledge of the substorm process and how it proceeds in the ionosphere. In particular, global auroral imaging has advanced our understanding of the dynamics of the process and has given us the ability to put localized observations into a global perspective. Fundamentally new cycles of auroral activity are now understood to exist, and this has provided a means by which auroral activity can answer questions about magnetospheric substorm dynamics. Along with this wealth of observations has come a wide range of theories purporting to explain the mechanism of the onset of this phenomenon. There is, however, no single theory which stands out as clearly explaining the wide range of active auroral phenomena. A synthesis which combines these theories and allows them to each explain individual aspects of the problem appears to be required. This has led to a new way of understanding the active aurora as a set of processes or modules which occur either coupled together or independent of one another to form a particular event. This view represents a fundamental departure from the view of the substorm as a single unchanging entity. Auroral activity can rather be thought of as the earthward end of a diverse set of ionospheric and magnetospheric processes which couple together to form different cyclical patterns. A symbolic representation of this modularization is presented to simplify future schematics of large-scale auroral dynamics.

Optical images of the auroral bulge as seen by the Viking UV imager were compared in several cases with the substorm current wedge (SCW) upward and downward field-aligned currents (FAC) whose positions were determined using the inversion algorithm based on the substorm-related magnetic variations observed at midlatitudes. With reasonable accuracy (better than 0.5 hours MLT) the estimated longitudes of the upward FAC generally pointed to the surge or to the brightest luminousity region in the western half of the bulge. The latter feature may imply a more complicated structure of the net FACs than can be described by the simple substorm current wedge scheme. Similarly, the estimated positions of the downward FAC pointed close to the eastern termination of the bulge. The associated optical signatures of this current system ranged from the well-defined emission depletion regions to new auroral intensifications. The downward current appears to correspond in some cases at least with the division between the morning sector portion of the double oval and the nightside portion connected more directly to the substorm bulge. The results in general confirm the expected association between the auroral bulge and the SCW, as well as showing a reasonably good results from the inversion algorithm based on midlatitude magnetic observations. Our results, however, also indicate that one must be careful in interpreting the apparent motion of SCW-related field-aligned currents inferred from midlatitude observations in terms of a true westward or eastward expansion of the SCW or of the auroral bulge. The observed changes may instead sometimes be related to the redistribution of the net FACs within than a shift or expansion of the simple current system.

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.

Freja UV imager measurements of distortions of discrete arcs within the auroral distribution reveal a number of examples of periodic intensifications. Analysis of these features reveals a clear peak at 152 km separation between the intensifications with a less well defined peak at approximately twice that value. No observations at separations less than 100 km were found. Theories relating such features to shear flow regions suggest a relationship between wavelength and shear layer width. A statistical analysis indicates that the product of the wave number and the arc system width yielded a value of .7 which is consistent with theoretical predictions. The periodic features were found to occur throughout the afternoon/midnight sector with no apparent dependence on MLT. As well they appeared at a variety of locations within the auroral distribution implying the common existence of shear layers.

Statistical auroral distributions are used in combination with an empirical model of the Earth's magnetic field in an attempt to determine the large-scale magnetospheric source regions for various types of auroral luminosity. The narrow ring of structured auroral emissions during magnetically quiet intervals appears to be associated with the inner region of the nightside central plasma sheet and the dayside entry layer. Under active conditions these discrete structures expand to fill the entire central plasma sheet. The high-altitude boundary plasma sheet on the other hand is more likely to be related to diffuse auroral emissions poleward of this "oval" and to high-latitude polar auroral arcs. Under this scenario, the region of the magnetosphere bounded by the inner edge of the tail current sheet, the plasmasphere, and the dayside entry layer is the source region for the most equatorward diffuse auroral precipitation.

The increased probability of observing polar arcs during periods of northward IMF has tended to obscure their significance in terms of magnetospheric topology because of the presumed ‘inactive’ state of the magnetosphere. However, satellite imaging has shown that these high latitude features are quite dynamic both in their intensity and spatial variations. The overall morphology of the high latitude aurora has been described by a variety of imaginative terms, but its primary optical characteristic is of a polar arc(s) extending between the dayside and nightside auroral distribution on one or both of the dawn/dusk sides of the high latitude region. This large scale morphology is controlled by the azimuth angle of the IMF and the predominant configuration is one wherein the region between the polar arc and the normal auroral distribution is filled with low intensity diffuse emission. Simultaneous particle and electric field measurements show this region exhibits a closed field line character with predominantly sunward flowing plasma. These large scale polar arcs are connected (in either a diffuse or discrete fashion) to the nightside auroral distribution with essentially equal probabilities, but exhibit a clear peak near 12 MLT. This dayside connection is commonly associated with isolated high latitude features poleward of the normal auroral distribution which probably represent processes occurring on the front surface of the magnetotail poleward of the cusp. The existence of polar arcs is not always controlled by substorm activity: polar arcs can maintain their form and position well past expansion phase suggesting that they represent a fundamental boundary in the magnetosphere which is not modified by even large substorms.

An attempt is made to reconcile two competing views as to where the auroral distribution maps from in the magnetosphere. The structure of the aurora is shown to have two distinctive parts which vary according to the magnetic activity. The low latitude portion of the structured distribution may be a near-Earth central plasma sheet phenomenon while the high latitude portion is linked more closely to boundary layer processes. During quiet times, the polar arcs may be the ionospheric signature of a source region in the deep tail low latitude boundary layer/cool plasma sheet. The structured portion of the ‘oval’ has a dominantly near-Earth nightside source and corresponds to an overlap region between isotropic 1–10 keV electrons and 0.1–1 keV structured electrons. The ionospheric local time sector between 13 and 18 MLT is the meeting point between the dayside boundary layer source region and this near-Earth nightside source. Late in the substorm expansion phase and/or start of the substorm recovery phase, the nightside magnetospheric boundaries (both the low latitude and Plasma Sheet Boundary Layers) begin to play an increasingly important role, resulting in an auroral distribution specific to the substorm recovery phase. These auroral observations provide a means of inferring important information concerning magnetospheric topology.

The ionospheric location of substorm onset is generally found to be at the most equatorward arc in the poleward portion of the diffuse aurora. The observation that most activity occurs in this region provides a reference from which the source region in the magnetotail may be assessed. This reference can be examined in two ways. First, magnetic field mappings of these onset locations to the equatorial plane suggest that the onset is associated with processes quite near the Earth. For example, for 14 cases the average GSM X value was found to be ≈ −7.8 R E . However, this identification is based on a static magnetic field model and while these results are consistent with some earlier findings there is not sufficient confidence in this technique to discriminate between topological regions in the magnetotail. A second way to examine the ionospheric onset location is in relation to the open/closed field line boundary. It is evident from Viking satellite images that optical substorm expansions can occur well equatorward of the poleward extent of emissions, both during quiet and active periods. There is no reason to suspect that this poleward region of emissions is not on closed field lines and that the onset location is therefore unrelated to the open/closed field line boundary, a result consistent with some (but not all) near-Earth mechanisms but only under some conditions with the distant tail boundary layer theory.

The authors report data taken by the Viking satellite at mid-altitudes (11,000-13,000 km) during northern hemispheric crossings of the cusp/cleft region. Particle signatures were used to divide the region into different categories. Data was looked at from the ultraviolet imager and particle diagnostics, when available. The authors discuss in detail two cases of crossing the cusp/cleft region, in order to look at the dynamics of a specific event, as opposed to other data analyses which have used large data sets to acquire good statistics, but which can thereby obscure dynamics of the actual events. Particle data were taken by the electron spectrometer ESP 1 and the ion spectrometer PISP 1/2. They looked at the spectral range 0.01 to 40 keV. The UV imager recorded 1 sec exposures of the auroral distribution once per minute. The data shows instantaneous observations of emissions, and does so for a narrow path swept by the satellite. Data indicate that the entire region is not a homogeneous region, but rather a very dynamic object. Conclusions include that the emissions observed are located at the footprint of the cleft region. The cusp region is located poleward of the region with continuous emission. The emission is observedmore » to remain at a constant magnetic latitude during the period with IMF data, though B[sub z] swung 8nT during a 30 minute period.« less

Viking images of the auroral distribution have been used to investigate the relevance of various ionospheric coordinate systems. An important aspect of the large-scale auroral shape is its dependence on the asymmetries of the Earth's internal field. Model predictions of where the aurora occurs, using the equatorial plane's volume current density, agree with observations and imply that the internal field plays a more important role that generally believed. Historically, the belief that the internal field has only small effects seems to stem from the widespread use of the corrected geomagnetic and invariant coordinate systems. These systems involve the mapping of field lines and have advantages in statistical studies and comparisons; less sophisticated systems such as the eccentric dipole coordinate system should be used in individual studies and in studies involving differentiation or integration of some observational parameters. Observations of the auraoral distribution are give to illustrate the universal time, tilt angle, and Kp variability in different coordinate systems and demonstrate that the dominant variability of the aurora is due to internal field asymmetries. A new set of coordinate systems are briefly developed as examples of how to incorporate external field models into studies of auraoral images. It is proposed thatmore » the one of these coordinate systems can be used as a test of how well an external field model can match observed auroral distributions. 19 refs., 1 tab.« less

Recent studies have found strong evidence that ionospheric refraction can explain some of the large aspect angle VHF radio aurora observations. The spatial relationship between such observations made with the Bistatic Auroral Radar System (BARS) and simultaneous 557.7-nm emissions detected by an All-Sky Imager (ASI) has been found consistent with the above idea (Hall et al., 1990). In this paper, further results of a cross-correlation analysis of the BARS and ASI intensities are presented. Two-dimensional as well as one-dimensional (along radar beam direction) cross-correlation functions are computed for a large statistical sample of 4 months of data. It is found that for all levels of ASI intensity and/or BARS power, stronger radar echoes predominantly occur on the remote side of the optical aurorae. The results are in agreement with the model calculation of refraction by Watermann (1990). In the premidnight sector, some of the brightest aurorae are found coincident with the strongest radar echoes, and a significant fraction of weaker radar echoes occur equatorward of fainter auroral forms.

Optical observations with DE 1 and Viking demonstrate conclusively that transpolar arcs can be present simultaneously at polar latitudes in both hemispheres. The arcs observed here are aligned parallel to one another on opposite sides of the magnetic pole, and relative to the noon-midnight meridian are rotated slightly in the counterclockwise direction when viewed from above the North Pole.

Observations from the IMP-8 satellite of the interplanetary magnetic field (IMF) are compared with areas of the polar region bounded by the aurora as observed by the Viking spacecraft during quiet-time conditions (IMF Bz northward). A variety of energy-coupling functions are investigated and it is determined that the auroral distribution can be best described by the inclusion of azimuthal terms in addition to standard energy-coupling functions. The auroral distributions for Bz northward support antiparallel merging as a mechanism whereby energy is transferred to the magnetosphere from the solar wind. As well, however, when the polar angle is small the region bounded by the auroras expands and may be controlled more by wave interaction at the magnetopause. Observations by the Viking spacecraft indicate a dominance of dusk sector polar arcs in the spring time and dawn sector arcs in the fall (post equinox). Two alternative mechanisms can explain the observations. One involves the ordering of the IMF in a solar equatorial coordinate system while the other involves the Sun's polarity and the traversal of the Earth's orbit through different heliographic latitudes. A test is proposed whereby the two hypotheses can be investigated during the next solar cycle.

Observations of the 5577 Å (1 Å = 10−10 m) emission detected with an all-sky imager are superimposed onto maps of auroral E-region coherent backscatter at 50 MHz made by the bistatic auroral radar system (BARS) to obtain the spatial and temporal relationships of stable visual arcs to auroral electrojets and the Harang discontinuity. At large aspect angles, characteristic of BARS, many eastward electron-drift velocities appear poleward of the visual arcs, in agreement with a recent proposed explanation that is based on refraction through auroral ionization structures in the E region. For some observations, the radar echoes are essentially co-located with the visual aurora. When the Harang discontinuity is present, the discrete arc separates the counterstreaming electron flow. Under these circumstances, the electric field in the E region associated with the stable arc agrees with the theoretical electric-field simulation, in which the electric field with a maximum magnitude of 40 mV m−1, reverses direction across the discrete auroral arc. It is also evident from the observations that there is often no obvious spatial correspondence between the visible aurora and the velocity vectors of the electron flow. In some cases there exists electron flow with a large southward component across the stable arc.

The ultraviolet imager on board the Swedish Viking satellite was designed to provide real-time monitoring of the auroral distribution from space. This objective was achieved over the nominal lifetime of the satellite, March–December, 1986 during which period approximately 45 000 auroral images were acquired. A number of technical and operational innovations have resulted in a rich data base for studies of auroral and magnetospheric processes. Some of the significant scientific advances that have resulted from the investigation of the temporal and spatial development of the auroral distribution include observations of rapid changes of dayside aurora, the effects of this distribution due to the interplanetary magnetic field, and more detailed knowledge of the substorm process. The utilization of models of the Earth's magnetic field to map auroral signatures to the corresponding magnetospheric regions has led to an increased understanding of the mechanisms associated with the large-scale auroral distribution.

In this paper we present the results of a comparison of Viking UV images of the dayglow with model calculations of the dayglow in order to assess the uncertainties in the calibration of the cameras. The procedure that was adopted was to calculate the dayglow emissions using proven photoelectron and radiative transfer codes, and convolve these results with the prelaunch camera transfer functions to estimate the emission strength for the two cameras (1304 Å (1 Å = 10−10 m) and Lyman–Birge–Hopfield (LBH)). We found quite good agreement between the model and measured intensities for the 1304 Å camera. However, the results for the LBH camera suggest that there is substantial leakage of far UV (FUV) light at 2000 Å and "white" light around 3400 Å: only about 20–30% of the emission comes from the LBH dayglow. To evaluate the contamination from the longer wavelengths, we assumed that it was due to Rayleigh scattering off air molecules and reflection off surfaces. A multilayer multiple-scattering radiative transfer code allowing for Rayleigh scattering and absorption by O2 and O3 was used. The model intensities were then convolved with "known" and extrapolated camera filter response characteristics in the region from 1800 to 7500 Å to obtain model camera signal values due to long-wavelength light leakage. A preliminary estimate of the scattering contribution to the observed intensities using the first-order guess of the camera response function (CRF) beyond 2000 Å resulted in a substantial overestimation of the LBH camera intensities. To obtain a better estimate of the CRF we used an LBH image where clouds were known to be present. This allowed us to distinguish between the 2000 and 3400 Å contributions in order to obtain a modified CRF that reproduces the data for the LBH camera. The fact that both the 1304 Å dayglow camera intensities and the model results are comparable and the LBH intensities may be modelled allowing for Rayleigh scattering suggest that the calibration of the cameras in the FUV are defined to better than about 30% and so should reproduce nighttime auroral intensities at 1304 Å and for the LBH system with comparable accuracy.

The Tsyganenko long magnetospheric model (1987) has been used in conjunction with ultra-violet images taken by the Viking spacecraft to investigate the relationship of the auroral distribution to different magnetospheric regions. The model describes the large-scale structure of the magnetosphere reasonably well for dipole tilt angles near zero, but it appears to break down at higher tilt angles. Even so, a wide variety of auroral configurations can be accurately described by the model. It appears that the open-closed field line boundary is a poor indicator of auroral arc systems with the possible exception of high-latitude polar arcs. The auroral distribution typically called the oval maps to a region in the equatorial plane quite close to the Earth and can be approximately located by mapping the model current density maximum from the equatorial plane into the ionosphere. Although the model may break down along the flanks of the magnetotail, the large-scale auroral distribution generally reflects variations in the near-Earth region and can be modeled quite effectively.

The UV Imager on the Swedish Viking satellite obtained near-instantaneous (1 second exposure) spatial distributions of the entire Northern Hemisphere aurora. The short exposure time coupled with a repetition rate as rapid as three images per minute permitted scientists to observe rapid variations of the aurora in space and time. Numerous examples of impulsive changes were recorded during the 1986 emission, and many of these were of a sufficient scale that they can be expected to affect the high latitude thermosphere. Such events are not uncommon and thus present a difficult challenge for global thermospheric modelers who desire realistic auroral input parameters for their models. One important aspect is the contribution of auroral energy input not only on the nightside due to substorm effects, but impulsive events on the dayside as well. The purpose of this paper is to acquaint scientists with the dramatic variations observed by presenting selected examples of the image data.

Geospace physics research is entering a new era in Canada. Although this development has been a poorly kept secret among the informed observers, there has not been, to date, an attempt to summarize these changes in a single source and convey to the scientific world the vision and potential of the new “Northern perspective”. In this paper we make a first attempt to fill this gap, without, however, claiming authoritativeness or completeness – such a claim would be defeated by the fast-paced development in Canada on many fronts. The new Canadian perspective is based on a keen awareness of the multiscale character of geospace, and on a realistic yet innovative outlook which integrates Canada's strengths into national efforts emphasizing the use of multi-instrument techniques to attack multiscale complexities in problems. We organize our discussion in four major sections: a description of the plan to enhance Canada's leadership position in ground-based geospace science, centered on the Canadian Geospace Monitoring program; a description of Canada's latest effort to achieve major breakthroughs in our understanding of geospace transition region dynamics, centered on the Canadian small satellite experiment ePOP; a description of Canada's participations in three major international geospace missions (THEMIS, SWARM, and AMISR); and, finally, a description of two potential new Canadian-led geospace missions, Ravens and Orbitals. We will integrate key scientific goals and strategies in our narrative about these missions, and use examples to illustrate the considerable potential of these Canadian efforts.

[1] Polar patch drift speed and direction have been investigated using oxygen 630 nm images recorded by an all-sky imager at Eureka (89° CGM), Canada over an extended period, January and December 1998. Statistical studies showed that (1) the interplanetary magnetic field (IMF, from the WIND satellite) Bz component linearly controls the patch speed when Bz is between −7.5 nT and 0 nT. The speed tends to saturate when Bz is less than −7.5nT due to nonlinear coupling between the solar wind and the magnetosphere. The average patch speed of 600 m/s is in agreement with results from earlier studies; (2) The IMF By or the IMF clock angle has a clear control of the patch drift direction as determined by the drift azimuth angle. When ∣By∣ is less than 7.5nT, the drift azimuth angle is linearly and positively correlated with By. For a large ∣By∣ (>7.5 nT), the positive correlation is replaced by a negative correlated linear relation and the azimuth angle tends to turn towards 180 degrees; that is, the patches drift in an antisunward direction. These IMF By effects can be qualitatively explained by the northern winter polar ionospheric convection models developed by Weimer [1995] and Hairston and Heelis [1990]. Results from our quantitative study on the IMF control of polar patch speed and drift direction provide constraints for the development of future polar ionospheric convection models.