[1] We investigate the two-dimensional structure of auroral poleward boundary intensifications (PBIs). PBIs are a nightside auroral intensification that has been studied primarily with ground-based meridian scanning photometers (MSPs). They have a signature that in the MSP data, appears as an increase in intensity at or near the magnetic separatrix and is often seen to extend equatorward. They are also associated with fast flows in the tail and are thus important to the dynamics of the plasma sheet. MSP data provide information about the temporal evolution of the aurora in one spatial dimension, in this case roughly along a magnetic meridian. This paper is motivated by a desire to determine the physics of PBIs that is revealed by their two-dimensional structure. To do this, we have identified a number of PBI events in the CANOPUS Rankin Inlet and Gillam MSPs that occurred at times when high-resolution, two-dimensional images of the aurora over the same region were also available. The two-dimensional images used in this study were obtained by the Freja UV imager, from October 1992 to January 1993, and by the CANOPUS Gillam all-sky imager during the winter viewing season of 1996-1997. We find that PBIs, as observed by the MSPs, are either equatorward extending or nonequatorward extending. Equatorward extending PBIs are either north-south aligned structures or east-west arcs propagating mostly equatorward, but we were not able to determine without doubt which type is the most prevalent. We suggest that equatorward extending PBIs may be the auroral footprint of two major modes of energy transfer in the plasma sheet: multiple, narrow, earthward fast-flow channels in the plasma sheet and sequences of azimuthally broad and primarily earthward propagating phase fronts initiating near the separatrix. Nonequatorward extending PBIs are found to mostly be a series of multiple bead-like intensifications along the poleward boundary of the aurora zone. Such PBIs may be evidence for shear instabilities at the separatrix boundary on the flanks of the magnetotail.INDEX TERMS: 2764 Magnetospheric Physics: Plasma sheet; 2704 Magnetospheric Physics: Auroral phenomena (2407); 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions; KEYWORDS: poleward boundary intensifications, north-south auroral structures, auroral streamers, plasma sheet bursty flows, bursty bulk flows Citation: Zesta, E., E. Donovan, L. Lyons, G. Enno, J. S. Murphree, and L. Cogger, Two-dimensional structure of auroral poleward boundary intensifications,

Low-energy plasmas having temperatures of order 1 eV or less are found commonly in the ionospheres and space environments of Earth and other planets. Measuring the density, temperature, drift velocities, phase-space anisotropies, and other properties of these plasmas presents numerous challenges. Examples are distortions of particle trajectories due to spacecraft wakes, spacecraft charging, and particle gyromotion in magnetized plasmas. Furthermore, these plasmas are known to organize into structures as small as tens of meters across, traversed by spacecraft in tens of milliseconds or less. The Suprathermal Plasma Imager (SPI) was developed to address these challenges. The SPI is optimized for measurements of particles with ∼1 eV energies, and of the suprathermal extension of those populations up to several hundred eV. The SPI is sensitive to particle flux intensities of order 6×105 cm−2 s−1 sr−1 eV−1 and greater. It produces 3024-pixel images corresponding to two-dimensional (angle/energy) cuts through plasma velocity distribution functions, with an image frame rate of up to 100 s−1. The SPI has a cylindrical sensor head measuring 37.5 mm in diameter and 14 cm long, with a mass of 350 g. The relatively small size and mass of the sensor allow it to be deployed easily on a boom, outside of the spacecraft’s electrical sheath and in a region where wake perturbations are reduced. The SPI sensor head contains no electronic circuitry, but instead creates a visible image of the particle distribution with a system of dc-biased grids, microchannel plates, and a phosphor screen. The phosphor image is transferred via an imaging fiber-optic cable to an instrument box in the main spacecraft body, where it is sampled with a charge-coupled device and support electronics. Inside the sensor, angle/energy images of incident particle distributions are formed by a pair of concentric hemispherical grids. The incident energies Ei accessible to the analyzer lie in the range 0⩽Ei⩽Emax where Emax≈qΔV/3, ΔV being the potential difference between the hemispheres. For an ideal analyzer, energy resolution ΔE/E is ⩽22% over most of the imaged energy range, degrading at energies below Emax/10. Angular resolution varies from 2° to 8° full width at half maximum between Emax and Emax/10. Energy and angular resolutions are degraded in the presence of a potential difference between the sensor and surrounding plasma. A 37.5-mm-diam version of the analyzer with a 0.86-mm-wide aperture has an ideal energy-dependent geometry factor of ≈5×10−4 eV sr cm2 for a square detector pixel of width 0.28 mm. Laboratory testing shows degraded energy resolution compared to ideal values, due in part to particle scattering within the analyzer. The SPI was tested successfully in flight on the GEODESIC auroral sounding rocket on 26 February 2000.

The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a collaborative science mission between ESA and the Chinese Academy of Sciences (CAS). SMILE is a novel self-standing mission to observe the coupling of the solar wind and Earth's magnetosphere via X-Ray imaging of the solar wind -magnetosphere interaction zones, UV imaging of global auroral distributions and simultaneous in-situ solar wind, magnetosheath plasma and magnetic field measurements. The SMILE mission proposal was submitted by a consortium of European, Chinese and Canadian scientists following a joint call for mission by ESA and CAS. It was formally selected by ESA's Science Programme Committee (SPC) as an element of the ESA Science Program in November 2015, with the goal of a launch at the end of 2021.In order to achieve its scientific objectives, the SMILE payload will comprise four instruments: the Soft X-ray Imager (SXI), which will spectrally map the Earth's magnetopause, magnetosheath and magnetospheric cusps; the UltraViolet Imager (UVI), dedicated to imaging the auroral regions; the Light Ion Analyser (LIA) and the MAGnetometer (MAG), which will establish the solar wind properties simultaneously with the imaging instruments. We report on the status of the mission and payload developments and the findings of a design study carried out in parallel at the concurrent design facilities (CDF) of ESA and CAS in October/November 2015.

The imaging and rapid-scanning ion mass spectrometer (IRM) is part of the Enhanced Polar Outflow Probe (e-POP) instrument suite on the Canadian CASSIOPE small satellite. Designed to measure the composition and detailed velocity distributions of ions in the ∼ 1-100 eV/q range on a non-spinning spacecraft, the IRM sensor consists of a planar entrance aperture, a pair of electrostatic deflectors, a time-of-flight (TOF) gate, a hemispherical electrostatic analyzer, and a micro-channel plate (MCP) detector. The TOF gate measures the transit time of each detected ion inside the sensor. The hemispherical analyzer disperses incident ions by their energy-per-charge and azimuth in the aperture plane onto the detector. The two electrostatic deflectors may be optionally programmed to step through a sequence of deflector voltages, to deflect ions of different incident elevation out of the aperture plane and energy-per-charge into the sensor aperture for sampling. The position and time of arrival of each detected ion at the detector are measured, to produce an image of 2-dimensional (2D), mass-resolved ion velocity distribution up to 100 times per second, or to construct a composite 3D velocity distribution by combining successive images in a deflector voltage sequence. The measured distributions are then used to investigate ion composition, density, drift velocity and temperature in polar ion outflows and related acceleration and transport processes in the topside ionosphere.

The Suprathermal Electron Imager (SEI) on the Enhanced Polar Outflow Probe (e-POP) experiment uses a microchannel-plate-intensified charge-coupled device (CCD) detector to record two-dimensional, energy-angle images of electron distributions for energies up to 350 eV. Alternatively, the SEI can be biased to measure positive ions at energies that include the ambient ionospheric population (< 1 eV) and extending to 350 eV. At the highest measurement resolution, distribution images are 64 pixels in diameter and are read out at a rate of 100 images per second. The SEI's field of view is 360• × ±4• , and includes viewing of the nadir and ram directions, nominally. At high latitude the nominal orientation allows coverage of most pitch angles. The SEI is included on e-POP to address the mission's principal scientific objectives, the first being to characterize polar ion outflow and its drivers including ambipolar electric fields generated by suprathermal electron populations, and direct energization of ions by plasma waves or through frictional heating. In addition, the SEI's focus on low energies and high time resolution allows a unique view of suprathermal particle populations and their role in wave-particle interactions, in support of e-POP's second scientific objective: to study plasma waves and wave propagation in the high-latitude ionosphere. Observations taken within geophysically quiet regions indicate that the instrument can track bulk ion flow velocity with a resolution of order 25 m/s or better.