J. K. Burchill

Swarm in situ observations of F region polar cap patches created by cusp precipitation

High-resolution in situ measurements from the three Swarm spacecraft, in a string-of-pearls configuration, provide new insights about the combined role of flow channel events and particle impact ionization in creating F region electron density structures in the northern Scandinavian dayside cusp. We present a case of polar cap patch formation where a reconnection-driven low-density relative westward flow channel is eroding the dayside solar-ionized plasma but where particle impact ionization in the cusp dominates the initial plasma structuring. In the cusp, density features are observed which are twice as dense as the solar-ionized background. These features then follow the polar cap convection and become less structured and lower in amplitude. These are the first in situ observations tracking polar cap patch evolution from creation by plasma transport and enhancement by cusp precipitation, through entrainment in the polar cap flow and relaxation into smooth patches as they approach the nightside auroral oval.

Anisotropic core ion temperatures associated with strong zonal flows and upflows

The Swarm satellites observe strongly anisotropic ion temperatures at 500 km altitude. The ion temperature anisotropy ratios going up to 5 for the strongest electric fields presented in this paper. The largest observed anisotropy ratios exceed the values predicted by theories of collisional heating in strong flows by a factor of 2, indicating that collisional cross sections should perhaps be revised for O+ ion colliding with O. Temperature anisotropy is also found not to be a simple function of electric field strength. This could be understood in terms a time delay needed to advect hot anisotropic ion velocity distributions from strongly collisional regions below 400 km to weakly collisional regions at 500 km and above. The mirror force associated with these events is insufficient to account for the observed upward flows (>500 m/s). For gyroresonant heating to be consistent with our observations, an additional mechanism for field-aligned acceleration is required.

Thermal ion imagers and Langmuir probes in the Swarm electric field instruments

The European Space Agencys three Swarm satellites were launched on November 22, 2013 into nearly-polar, circular orbits, eventually reaching altitudes of 460 km (Swarm A and C) and 510 km (Swarm B). Swarms multi-year mission is to make precision, multi-point measurements of low-frequency magnetic and electric fields in Earths ionosphere for the purpose of characterizing magnetic fields generated both inside and external to the Earth, along with the electric fields and other plasma parameters associated with electric current systems in the ionosphere and magnetosphere. Electric fields perpendicular to the magnetic field B→ are determined through ion drift velocity v→i and magnetic field measurements via the relation E→⊥=−v→i×B→. Ion drift is derived from two-dimensional images of low-energy ion distribution functions provided by two Thermal Ion Imager (TII) sensors viewing in the horizontal and vertical planes; v→i is corrected for spacecraft potential as determined by two Langmuir probes (LPs) which also measure plasma density ne and electron temperature Te. The TII sensors use a microchannel-plate-intensified phosphor screen imaged by a charge-coupled device to generate high-resolution distribution images ( 66x40 pixels) at a rate of 16 s−1. Images are partially processed on board and further on the ground to generate calibrated data products at a rate of 2 s−1; these include v→i, E→⊥, and ion temperature Ti in addition to electron temperature Te and plasma density ne from the LPs.

Interplanetary magnetic field and solar cycle dependence of Northern Hemisphere F region joule heating

Joule heating in the ionosphere takes place through collisions between ions and neutrals. Statistical maps of F region Joule heating in the Northern Hemisphere polar ionosphere are derived from satellite measurements of thermospheric wind and radar measurements of ionospheric ion convection. Persistent mesoscale heating is observed near postnoon and postmidnight magnetic local time and centered around 70° magnetic latitude in regions of strong relative ion and neutral drift. The magnitude of the Joule heating is found to be largest during solar maximum and for a southeast oriented interplanetary magnetic field. These conditions are consistent with stronger ion convection producing a larger relative flow between ions and neutrals. The global-scale Joule heating maps quantify persistent (in location) regions of heating that may be used to provide a broader context compared to small-scale studies of the coupling between the thermosphere and ionosphere.

Ionospheric Conductances and Currents of a Morning-Sector Auroral Arc From Swarm-A Electric and Magnetic Field Measurements†

We show the first ionospheric Hall and Pedersen conductances derived from Swarm magnetic and electric field measurements during a crossing of a morning sector auroral arc. Only Swarm-A was used, with assumptions of negligible azimuthal gradients and vanishing eastward electric field. We find upward field-aligned current, enhanced Hall and Pedersen conductances, and relatively weak electric field coincident with the arc. Poleward of the arc the field-aligned current was downward, conductances lower, and the electric field enhanced. The arc was embedded in a westward electrojet, immediately equatorward of the peak current density. The equatorward portion of the electrojet could thus be considered conductance dominant and the poleward portion electric field dominant. Although the electric field measured by Swarm was intense, resulting in conductances lower than those typically reported, comparable electric fields have been observed earlier. These results demonstrate how Swarm data can significantly contribute to our understanding of the ionospheric electrodynamics.

Alfvén waves in the auroral region, their Poynting flux, and reflection coefficient as estimated from Swarm observations: ALFVÉN WAVE REFLECTION

The European Space Agency’s Swarm constellation can measure electric field, magnetic field, and plasma density on board multiple satellites at altitudes of about 500 km. Based on the data set at high latitudes, we estimate Poynting flux and ionospheric reflection coefficients of Alfvén waves with scale sizes of about 10–100 km. The reflection coefficients are generally higher surrounding the cusp and auroral regions than in the polar cap and higher in the summer than in the winter hemisphere. In the summer (winter) hemisphere the reflection coefficients generally peak on the dayside (nightside). Distributions of the reflection coefficients are not controlled by those of in situ plasma density. Poynting flux of the Alfvén waves maximizes surrounding the cusp and near-midnight auroral region with magnitudes approaching 1 mW/m2, which are consistent with previous magnetospheric observations. The observed Poynting flux is downward on average for both hemispheres, and the magnitudes do not exhibit clear hemispheric asymmetry.

Ionospheric electron heating associated with pulsating auroras: A Swarm survey and model simulation

In this paper we report a study on the plasma signatures (electron temperature, plasma density and field-aligned current) of patchy pulsating auroras in the upper F-region ionosphere using Swarm satellite data. Via a survey of 38 patch crossing events, we repeatedly identify a strong electron temperature enhancement associated with the pulsating aurora. On average, the electron temperature at Swarm satellite altitudes (~460 km) increases from ~2200 K at sub-auroral latitudes to a peak of ~3000 K within the pulsating auroral patch. This indicates that pulsating auroras may act as an important heating source for the nightside ionosphere. On the other hand, no well-defined trend of plasma density variations associated with pulsating auroras is identified at Swarm altitudes. The field-aligned currents within the pulsating aurora patch are mostly upward, with mean magnitudes on order of ~1 μA/m2. We then perform a numerical simulation to explore the potential mechanisms underlying the strong electron heating associated with the pulsating aurora. Via simulations we find that, to account for the realistic electron temperature observation in a major portion of our events, pulsating auroras are likely accompanied by substantial magnetospheric heat fluxes around the order of ~1010 eV/cm2. We propose that such magnetospheric heat fluxes may be pertinent to one long-hypothesized feature of pulsating auroras, namely the co-existence of an enhanced low-energy plasma population in magnetic flux tubes threading the pulsating aurora, in addition to the energetic electron precipitation.

MULTISCALE GEOSPACE PHYSICS IN CANADA

Abstract 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 Canadas 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 Canadas leadership position in ground-based geospace science, centered on the Canadian Geospace Monitoring program; a description of Canadas 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 Canadas 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.