Brian James Jackel

Ground‐based optical determination of the b2i boundary: A basis for an optical MT‐index

[1] The equatorward boundary of the proton aurora corresponds to a transition from strong pitch angle scattering to bounce trapped particles. This transition has been identified as the b2i boundary in Defense Meteorological Satellite Program (DMSP) ion data [Newell et al., 1996]. We use ion data from 29 DMSP overflights of the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) Meridian Scanning Photometer (MSP) located at Gillam, Canada, to develop a simple algorithm to identify the b2i boundary in latitude profiles of proton auroral (486 nm) brightness. Applying this algorithm to a ten year set of Gillam MSP data, we obtain ∼250,000 identifications of the optical b2i, the magnetic latitude of which we refer to as b2i Λ . We intercompare ∼1600 near-simultaneous optical and in situ b2i Λ , concluding that the optical b2i Λ is a reasonable basis for an optical equivalent to the MT-index put forward by Sergeev and Gvozdevsky [1995]. Using ∼17,000 simultaneous measurements, we demonstrate a strong correlation between the optical b2i Λ and the inclination of the magnetic field as measured at GOES 8. We develop an empirical model for predicting the GOES 8 inclination, given theuniversal time, dipole tilt, and the optical b2i Λ , as determined at Gillam. We also show that in terms of information content, the b2i boundary is an optimal boundary upon which to base such an empirical model.

Width and structure of mesoscale optical auroral arcs

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.

Rotation Measures of Compact Sources in the Canadian Galactic Plane Survey

The Canadian Galactic Plane Survey is providing new rotation measures (RMs) for compact extragalactic sources in the Galactic plane at a solid-angle density of roughly 1 source per square degree. To date, we have derived reliable RM values for 380 sources along lines of sight through the disk of the Galaxy in the first and second quadrants. The purpose is to provide a data set useful for studies of the magneto-ionic component of the Galactic interstellar medium (ISM). We present the method used to obtain the measurements and the resulting RMs.

Large-scale vortex dynamics in the evening and midnight auroral zone : Observations and simulations

We use Canadian Auroral Network for the OPEN Program Unified Study All-Sky Imager (ASI) and Meridional Scanning Photometer (MSP) data as the basis for a study of the dynamics of large-scale (hundreds of kilometers) auroral vortices. We consider 28 events corresponding to a range of auroral activity levels. Three of these are presented in detail, one corresponding to growth phase, one to pseudo-breakup and one to expansive phase onset. We show that vortex formation starts from a discrete arc with half thickness δ of the order of 20 km. This arc intensifies near the poleward boundary of enhanced proton aurora, as seen in the Hydrogen β (Hβ) MSP data and becomes azimuthally structured. This structuring is in the form of vortices with wavelength of the order of ∼ 2πδ. The vortices intensify and extend radially, leading to broadening of the initial arc. While the sizes and growth rates of the vortices vary, the overall scenario of vortex evolution is similar for all of the events. Structures that develop during the growth phase saturate at latitudes matching the poleward boundary of Hβ emissions and pseudo-breakup structures saturate further poleward. Expansive phase onset vortices expand poleward in a similar fashion, but we do not observe any saturation stage, presumably due to limitations imposed by the ASI field of view. We present results of shear flow ballooning vortex modeling in which we used initial conditions and parameters consistent with our observations. On the basis of our model results, we speculate that all of these experimentally observed vortices are the result of shear flow ballooning instability in the hot proton region in the near-Earth plasma sheet.

Global observations of substorm injection region evolution: 27 August 2001

We present riometer and in situ observations of a substorm electron injection on 27 August 2001. The event is seen at more than 20 separate locations (including ground stations and 6 satellites: Cluster, Polar, Chandra, and 3 Los Alamos National Laboratory (LANL) spacecraft). The injection is observed to be dispersionless at 12 of these locations. Combining these observations with information from the GOES-8 geosynchronous satellite we argue that the injection initiated near geosynchronous orbit and expanded poleward (tailward) and equatorward (earthward) afterward. Further, the injection began several minutes after the reconnection identified in the Cluster data, thus providing concrete evidence that, in at least some events, near-Earth reconnection has little if any ionospheric signature.

Characterization of auroral radar power spectra and autocorrelation functions

Radar backscatter is a commonly used tool for studying plasma instabilities in the auroral E region. Analysis of the received signals typically involves moments of the scattered power spectrum such as total power, mean Doppler shift, and spectral width; in some cases the spectral asymmetry may also be of interest. This paper presents the steps required to estimate spectral moments directly from the autocorrelation function, and some advantages and limitations of working in the lag domain are discussed. Recent measurements of auroral spectra at UHF (440 and 933 MHz) are used to motivate the discussion and as test cases. The utility of parametric models is also studied with an emphasis on determining whether spectra are more nearly Gaussian or Lorentzian. A model autocorrelation function is introduced, with spectral characteristics similar to a Voigt distribution but a more convenient functional form.

Substorm development as observed by Interball UV imager and 2-D magnetic array

Abstract 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.

Substorm associated spikes in high energy particle precipitation

Using data from the 13 instrument CANOPUS riometer array in north-central Canada, we have examined a large number of substorm events. Here, we focus on a substorm associated transient spike of significant absorption. We present a statistical analysis of temporal structure, propagation characteristics, and relative occurrence of absorption spikes seen with the CANOPUS array. We also present examples of both isolated transient spike events and a single propagating event. Seen from any one station, the spike lasts several minutes. More globally, it typically takes tens of minutes to propagate across the CANOPUS array. The propagation is in general a combination of azimuthal (ie., East or West) and poleward motion. Spikes are associated with the vast majority of substorms and at least some pseudobreakups. Simultaneous X-ray images confirm that the spike is a spatially localized region of high-energy precipitation and not, for example, a boundary. We discuss possible magnetospheric sources of this precipitation.

On the 630 nm red-line pulsating aurora: Red-line Emission Geospace Observatory observations and model simulations†

Abstract. In this study, we present observations of red-line (630 nm) pulsating auroras using the camera system of Red-line Emission Geospace Observatory (REGO), during a geomagnetic storm interval. We also develop a time-dependent model to simulate the 630 nm auroral pulsations in response to modulated precipitation inputs, and compare the model outputs with REGO observations. Key results are as follows. (1) Notwithstanding the long radiative timescale of the 630 nm emission, red-line auroras can still be modulated by pulsating electron precipitations and feature noticeable oscillations, which constitute the red-line pulsating auroral phenomena. (2) In a majority of cases, the oscillation magnitude of red-line pulsating auroras is substantially smaller than that of the concurrent pulsating auroras seen on THEMIS whitelight images (generally dominated by 557.7 nm green-line emissions). Under certain circumstances, e.g., when the characteristic energy of the precipitation is very high, some of the pulsating auroras may not show discernible imprints on red-line. (3) The altitude range contributing most to the red-line pulsating aurora is systematically lower than that of the steady-state red-line aurora, since the slower O(1D) loss rate at higher altitudes tends to suppress the oscillation range of the 630 nm emission rate. (4) We find that some pulsating auroral patches are characterized by enhanced red-to-green color ratio during their on-time, hinting that the percentage increase of the red-line auroral component exceeds that of the green-line auroral component for those patches. We suggest that those special patches might possibly be associated with lower energy (<1 keV) electron precipitations.

Low-cost multi-band ground-based imaging of the aurora

Modern auroral research uses a variety of optical instruments ranging from photometers to spectral imagers. We report our results in developing an inexpensive auroral imager, which captures true-colour images using four wide-band channels. While not replacing dedicated highly sensitive cameras with filter wheels and narrow bandpass filters, the advantages of capturing the colour should not be underestimated. The colour not only provides more information about the physical processes in the ionosphere but also enhances both manual and automated image processing due to the discriminating power of colour information. We have operated our auroral imager RAINBOW in Athabasca, Alberta, Canada for over a year. RAINBOW can acquire images every ten seconds and operate even in moonlit conditions. A clever design using inexpensive optical components provides a field-of-view of approximately 150 degrees, and an external shutter provides protection from direct sunlight. We discuss the issues related to imager hardware and colour calibration. Future applications are also highlighted.