Proposal lead: Prof Steve Milan, University of Leicester () - Ravens Auroral and magnetospheric imaging mission
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Proposal lead: Prof Steve Milan, University of Leicester (steve.milan@le.ac.uk)
Ravens • Auroral and magnetospheric imaging mission • 1 1
Ravens
Proposing team
Steve Milan, Nigel Bannister
University of Leicester, UK
Eric Donovan, Emma Spanswick
University of Calgary, Canada
Nikolai Østgaard, Kjellmar Oksavik
University of Bergen, Norway
Kirsti Kauristie, Minna Palmroth
Finnish Meteorological Institute, Finland
Benoit Hubert
University of Liége, Belgium
Hermann Opgenoorth, Stas Barabash,
Hans Nilsson
Swedish Institute of Space Physics (IRF), Sweden
Andrew Fazakerley
University College London, UK
Malcolm Dunlop
Proposal lead and contact Rutherford Appleton Laboratory, UK
Steve Milan Pontus Brandt, Joseph Westlake
Radio and Space Plasma Physics Group The Johns Hopkins University Applied Physics
Department of Physics and Astronomy Laboratory, USA
University of Leicester
James Wild
Leicester LE1 7RH, UK
University of Lancaster, UK
steve.milan@le.ac.uk
Tel: +44 116 223 1896 Iannis Dandouras, Benoit Lavraud
IRAP, France
Mission website: www.ion.le.ac.uk/ravens.html Mervyn Freeman
British Antarctic Survey, UK
Susan McKenna-Lawlor
National University of Ireland (Maynooth),
Space Technology Ireland, Ltd., Ireland.
The Norse god Odin on his horse Sleipnier with his
Ravens, Huginn (thought) and Muninn (memory), at
his side. The ravens were Odin’s eyes and ears, con-
tinuously circling the world to gather news for their
master. Woodcut by Gerhard Munthe (1849-1929).
Ravens • Auroral and magnetospheric imaging mission • 2 2
Ravens – A proposal to the ESA M-Class mission opportunity call 2015
ESA Cosmic Visions 2015-2025
Contents
Title page 1 4. Proposed Mission Configuration 32
Proposing team 2 5. Management Scheme 38
0. Executive Summary 3 Annex A. Bibliography 43
1. Science Objectives 5 Lead proposer contact details 46
2. Science Requirements 16
3. Proposed Science Instruments 21
0. Executive Summary
Science objectives. The Ravens magnetospheric and auroral imaging mission will determine the in-
teraction of the magnetosphere with the solar wind, and the transport of plasma and the dissipation
of energy within it. Ravens will provide for the first time global, continuous, 3D, and conjugate ob-
servations of key magnetospheric regions: the plasma sheet, plasmasphere, ring current, and iono-
sphere, measurements that are critical to understanding the globally-coupled magnetosphere.
These Ravens observations are required not only to understand solar wind-magnetosphere coupling,
but also the control of all processes within the magnetosphere, such as magnetic field perturbations,
radiation belt variability, large-scale current flow, and ionospheric disturbances. Ravens is the first
mission that recognizes that the Earth is coupled to space through two polar regions, which do not
respond similarly to solar wind forcing, and both regions have to be measured simultaneously to ob-
tain information about the complete system. In addition, Ravens observations will supply a continu-
ous stream of data optimized for Space Weather now- and forecasting, and the validation and de-
velopment of European global physics-based magnetospheric models, which are key to providing a
full understanding the geospace environment and its impact on society.
The Earth’s magnetosphere is not a passive recipient of solar wind input, but displays emergent
structures and behaviours that reveal its nature as a highly non-linear system driven far from equi-
librium by a continuous but variable energy source. Moreover, energy is not channelled smoothly
from the outer boundary of the magnetosphere to the inner boundary of the atmosphere, but com-
plex positive and negative feedback processes between intersecting and interacting hot and cold
plasma regions – the plasma sheet, the plasmasphere, the ring current, the ionosphere, the atmos-
phere – modulate the energy flow within and the coupling with the solar wind on the outside. In this
regard, the magnetosphere is a microcosm of processes active in astrophysical systems throughout
the Universe, processes responsible for creating diversity, structure, and complex behaviour wher-
ever plasmas of different origins and characters interact.
The Ravens mission will provide a step-change in our understanding of our immediate space envi-
ronment and answer fundamental problems in magnetospheric science, relevant also to other mag-
netospheric systems, including the following key questions, which are directly aligned with interna-
tional research priorities as laid out by the Committee on Space Research (COSPAR Roadmap “Un-
derstanding Space Weather to Shield Society” [Schrijver et al., 2015]):
• How does a magnetosphere assemble and organize itself?
• What are the feed-back loops in solar wind-magnetosphere coupling?
• What creates geomagnetic storms?
• Why are the northern and southern auroras asymmetric?
Ravens • Auroral and magnetospheric imaging mission • 3 3
Mission Strategy. The Ravens mission will monitor the global response of the magnetosphere to
incoming solar wind disturbances using a suite of remote-sensing instrumentation including Far Ul-
traviolet (FUV) and X-ray auroral imagers, Extreme Ultraviolet (EUV) plasmasphere imagers, and en-
ergetic neutral atom (ENA) cameras. Ravens will provide for the first time (a) continuous measure-
ments of the auroras, (b) frequent and systematic measurements of the auroras from both hemi-
spheres (true “global auroral imaging”), and (c) continuous and stereoscopic remote-sensing of the
plasmasphere and ring current.
Ravens will comprise two identically-instrumented spacecraft, payload mass ~130 kg, in highly-
elliptical polar orbits, with apogee close to 8 RE over each pole. The orbits of the two spacecraft will
be phased such that one spacecraft is at perigee while the other is at apogee. Hence, one of the
spacecraft will always be in a position to monitor auroral activity, and for long periods the two
spacecraft will be ideally located to view both northern and southern hemisphere auroras simulta-
neously. From multi-wavelength imaging the entire energy range of the incident electrons im-
portant for ionospheric electrodynamics will be derived. One spacecraft will always be in a position
to monitor the plasmasphere and ring current, and for long periods stereoscopic views will enable
reconstruction of 3D plasma structures. Ravens will be supported by a suite of ground-based ob-
servatories, both north and south, and computational physics-based modelling of the magneto-
sphere, providing a systems level approach to magnetospheric sensing and understanding.
Programmatics and Costs. Ravens is built on existing technology, much of which has flown on pre-
vious missions. Little technology needs to be developed, making a launch in the 2025 time-frame a
certainty. Hence, Ravens represents a low-risk investment for high science return. The overall mis-
sion cost to ESA is estimated to be 359 M€, which is lower than the cost envelope of an M-class mis-
sion.
Conclusions. Ravens will be ESA’s first magnetospheric imaging mission. Ravens is a cost-effective,
next-generation mission delivering science that will transform our understanding of magnetospheric
dynamics and, by extension, plasma physics throughout the cosmos. It builds upon principles devel-
oped for previous imaging missions, but with an innovative two-spacecraft mission design that will
provide the observations necessary to answer fundamental questions regarding the behaviour of the
coupled solar wind-magnetosphere system.
Ravens • Auroral and magnetospheric imaging mission • 4 4
1. Science Objectives
1.1. Introduction
The magnetosphere represents the outer boundary of our immediate environment, shielding the
Earth and its atmosphere from the solar wind. Although the magnetosphere is central to our surviv-
al as a species, we still have a poor understanding of how it forms, how it is coupled to the solar en-
vironment on the outside, how it is coupled to the atmosphere on the inside, and how it responds to
extreme solar disturbances. Ravens will for the first time give a System Level understanding of mag-
netospheric structure, magnetospheric dynamics, and geomagnetic storms. Ravens will determine
the interaction of the magnetosphere with the solar wind, and the transport of plasma and the dis-
sipation of energy within it. This is key to understanding external influences on the Earth, the radia-
tion environment in near-Earth space, and the fundamental physical processes occurring in magnet-
ized plasmas, such as magnetic reconnection and charged particle acceleration.
Figure 1.1. (Left) A schematic showing the main features of the magnetic topology and plasma regions of the
magnetosphere, including the plasma sheet (orange), ring current (red), plasmasphere (dark blue), and magne-
totail lobes (light blue). The magnetospheric regions are interconnected with the polar atmosphere and iono-
sphere along magnetic field lines; precipitation of charged particles from these regions produces auroral fea-
tures that track the evolution and interconnection of these regions. (Right) A sequence of auroral images (Po-
lar-UVI) from 28 August 1998, preceding and during the impact of an interplanetary shock on the magneto-
pause, showing features associated with specific processes in the overlying magnetosphere.
Astrophysical systems comprise plasma, usually a mixture of plasmas from a variety of sources and
of different character. The Earth’s magnetosphere is an example of the emergent structures and
phenomena which arise from the non-equilibrium dynamics driven by the interaction of mixtures of
hot and cold magnetized plasmas of different origins, in the Earth’s case the solar wind and the
planetary ionosphere. Structure arises as a consequence of the interaction, leading to the formation
of different plasma regions – the hot plasma sheet, the cold ionosphere and plasmasphere, the ring
current region, the radiation belts, and the evacuated magnetotail lobes – with complex overlaps,
interactions, and feedbacks in the energy exchanges between them, the solar wind, and the Earth’s
atmosphere (Fig. 1.1). The interest in Ravens arises from the recognition that geospace must be un-
derstood as a complex coupled system, in which fundamental plasma processes, magnetospheric
morphology, and global dynamics interact. For instance, the magnetosphere breaths with a natural
rhythm, the substorm cycle, that produces vivid auroral displays every few hours. The solar wind is
gusty, but this does not explain the inherent characteristic quasi-periodicity of magnetospheric dy-
namics; even in the event of constant solar wind driving, time-dependent behaviour arises. Rather,
this is symptomatic of a non-linear storage-and-release system that accumulates energy tapped
from the solar wind before explosively dissipating it in the atmosphere in intense, short-duration
bursts. This non-linear behaviour arises because of the structure that emerges from the magnetic
flux and plasma transport processes that are driven by the solar wind interaction itself (Fig. 1.2).
Ravens • Auroral and magnetospheric imaging mission • 5 5
Figure 1.2. Ravens will explore the cou-
pling that produces magnetospheric struc-
ture and time-dependent dynamics.
Ravens will study the magnetospheric engine that drives dynamics, it will study the magneto-
spheric structure that emerges as a consequence of the dynamics, and it will study the feedback
mechanisms which cause time-dependent behaviour to arise. The NASA Time History of Events and
Macroscale Interactions during Substorms (THEMIS) multi-satellite mission was predicated on the
dichotomy of the inside-out vs. outside-in scenario of substorm triggering. Ravens will answer the
question: why does spontaneous time-dependent behaviour (substorms and geomagnetic storms)
occur at all?
The Earth’s magnetosphere acts as a laboratory for exploring the large-scale dynamics of the envi-
ronments of other magnetized astrophysical systems. In particular, the magnetosphere presents an
unparalleled opportunity to study the emergent structures and behaviours that arise when a non-
linear plasma system is driven into a non-equilibrium state through the continuous and variable ex-
ternal forcing of a stellar wind (Fig. 1.3).
Figure 1.3. The interaction between many astrophysical bodies and
their environments is thought to be mediated by magnetic fields.
The red giant Mira (above) reveals in UV a bow shock and long tail
with structure similar to that of a magnetosphere [Wareing, 2008].
Comet Encke (right) had its magnetotail docked by the impact of a coronal mass ejection and the resulting so-
lar wind-magnetosphere coupling [Jia et al., 2009]. In this sequence of images, the Sun is to the left and the
sheath and magnetic cloud of the CME can be seen as the labelled light and dark regions labelled “Sheath” and
“Flux rope”.
The Earth’s magnetosphere is small in comparison with most other astrophysical systems, and is cer-
tainly more accessible, and yet its sheer volume presents a formidable challenge to characterizing its
structure and dynamics in either an average sense or instantaneously through in situ observations.
However, remote-sensing, and in particular imaging, of the plasma and magnetic environment of the
Earth is a tractable approach to studying the systems level structure and behaviour of the magneto-
sphere. The NASA Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite mission
made great strides towards true systems-level science (see the review “Magnetospheric Imaging:
Promise to Reality” by Burch [2005]), providing global images of the auroras, the plasmasphere, and
the ring current. However, the images of the different regions of the magnetosphere provided by
IMAGE were not continuous, and they were not necessarily contemporaneous. In contrast, the most
significant disturbances of the magnetospheric system, geomagnetic storms, evolve rapidly, on time-
scales less than an hour, but last from 10s of hours to days and involve all regions of the magneto-
sphere. Lack of suitable, continuous, high temporal resolution global observations has been the ma-
jor stumbling block to understanding how of the coupled Sun-Earth system works.
Ravens • Auroral and magnetospheric imaging mission • 6 6
The Ravens magnetospheric imaging mission will study this highly-interacting system, directly ad-
dressing the ESA Cosmic Vision themes 2.1. From the Sun to the edge of the Solar System and 1.3.
Life and habitability in the Solar System. To achieve this, Ravens must continuously measure the
time-dependent rate of magnetic flux transport within the magnetosphere and it must measure the
evolving morphology of geospace, the reservoirs of magnetic and hot and cold plasmas in the tail
and inner magnetosphere. Ravens will for the first time provide this vital continuous coverage by
utilizing two spacecraft. It will also allow observations of the auroras in the northern and southern
hemispheres simultaneously, which will provide information on the magnetic mapping between
magnetospheric regions and the ground in a way that has only very rarely been possible previously
(see Fig. 1.8) and never with identical cameras. These two innovations will provide a tremendous
advance in our understanding of magnetospheric dynamics.
In addition, a focus on coordinated ground-based observations and modelling will greatly enhance
the science return of the mission. For instance, large collaborative ground-based observatories such
as SuperDARN and SuperMAG, and large networks of all-sky imagers will be important complements
for Ravens (see Sect. 2.5). Ravens will harness existing and developing ground-based observatories
to provide measurements supportive of the science goals that cannot be obtained from spacecraft,
including detailed measurements of ionospheric parameters such as conductances and horizontal
plasma motions. It will also incorporate state-of-the-art physics-based modelling to provide a 3D,
time-dependent framework within which to assimilate and synthesise the space- and ground-based
observations.
In summary, the Ravens Science Questions are:
• How does a magnetosphere assemble and organize itself?
• What are the feed-back loops in solar wind-magnetosphere coupling?
• What creates geomagnetic storms?
• Why are the northern and southern auroras asymmetric?
To address these questions, Ravens will investigate the Magnetospheric Engine, Magnetospheric
Structure, and Magnetospheric Feedback.
1.2. The Magnetospheric Engine
1.2.1. Magnetic reconnection and magnetic flux transport. The dynamics of the magnetosphere
are driven by the fundamental plasma process of magnetic reconnection occurring at the magneto-
pause and in the magnetotail, the Dungey cycle [Dungey, 1961]. To first order, magnetized plasmas
of different origins cannot mix, leading to cellular regions of space demarcated by thin current
sheets. The boundary between interplanetary space, dominated by the solar wind and it’s embed-
ded solar or interplanetary magnetic field (IMF), and the magnetosphere is such a current sheet, the
magnetopause. Magnetic reconnection occurs at such boundaries to create a topological intercon-
nection of the magnetic fields, allowing ingress and egress of plasma and imparting tangential stress
between regions (Fig. 1.4). The rates and time-dependence at which reconnection occur at the
magnetopause and in the magnetotail are central to creating the dynamics and structure of the
magnetosphere. The factors which control magnetic reconnection, and hence magnetospheric dy-
namics and energy deposition in the atmosphere, are not understood. Ravens will for the first
time make continuous global observations of the auroras and the polar caps, allowing unbroken
determination of the rates of magnetic reconnection and the factors that influence these. The au-
roral oval maps to the plasma sheet, the region of closed magnetic flux sandwiched between the
open lobes. The dim polar cap inside the northern and southern auroral ovals map to the lobes and
the size of these indicates the proportion of flux that is open [e.g. Laundal and Østgaard, 2010]. The
rate at which the polar caps expand and contract is a measure of the reconnection rates (Figs. 1.5
and 1.6): as magnetic reconnection occurs at the magnetopause the polar caps expand; when re-
connection occurs in the magnetotail the polar caps contract, accompanied by an explosive en-
Ravens • Auroral and magnetospheric imaging mission • 7 7
hancement of precipitation into the ionosphere, causing increased electrical conductance and ener-
gy deposition [Cowley and Lockwood, 1992; Milan et al., 2003]. The expansions and contractions of
the polar caps are linked to ionospheric motions which in turn lead to frictional heating of the at-
mosphere. The rates of energy deposition in the atmosphere by precipitation and Joule heating
are not well known; Ravens will address this and determine the factors that influence it. By imag-
ing both polar hemispheres in the entire energy range important for ionospheric electrodynamics,
Ravens will provide an unprecedented picture of how the Earth is coupled to space.
Auroral images and combined ionospheric plasma flow measurements can provide localised meas-
urements of reconnection rates along the open/closed boundary [Hubert et al., 2006, 2008; Chisham
et al., 2008], identifying meso-scale structure within reconnection regions. This is important for
probing reconnection spatial and temporal sub-structure within the magnetotail and at the magne-
topause, either reconnection transients within substorms (e.g. poleward boundary intensifications,
Lyons et al. [1999]), quiet-time magnetotail reconnection [e.g. Grocott et al., 2005], subsolar recon-
nection (flux transfer events or FTEs, e.g. Milan et al. [2000a]), or high latitude cusp reconnection
[Chisham et al., 2004; Milan et al., 2000b; Imber et al., 2006].
Figure 1.4. The magnetic topology of the
magnetosphere. Magnetic reconnection oc-
curring at the dayside magnetopause at a rate
ΦD has interconnected with closed magnetic
field lines (red) to create open magnetic field
lines (blue). Tangential stress stretches the
open field lines to produce an extended mag-
netotail in which magnetic energy accumu-
lates. Reconnection occurs sporadically in the
nightside magnetosphere to reclose magnetic
flux at a rate ΦN. The open magnetic flux con-
tent of the magnetosphere, FPC, dictates the
size of the polar caps, the dim regions encir-
cled by the auroral ovals. The combined ac-
tion of dayside and nightside reconnection
creates a time-dependent transport of mag-
netic flux across the polar caps, at a rate ΦPC,
which also leads to antisunwards drift of the
ionosphere across the poles.
Although there is still great debate about the factors that control the dayside reconnection rate [e.g.
Borovksy, 2014], there has been some success in relating this to upstream solar wind conditions [e.g.
Newell et al., 2007; Milan et al., 2007, 2012]: the magnetosphere seems to accumulate open flux at
the rate that magnetic flux is transported towards it in the solar wind, that is linear driving. Howev-
er, the magnetospheric response to solar wind driving is varied. As first speculated by Lockwood and
Cowley [1992] and later confirmed [e.g. Milan et al., 2003, 2007] the episodic disconnection of open
flux is related to the occurrence of substorms; that is, substorms represent the closure of the Dun-
gey cycle and are a fundamental aspect of the solar wind’s interaction with the magnetosphere.
Sometimes the response is inherently time-dependent, releasing magnetic flux and depositing ener-
gy in discrete bursts: substorms. At other times, the magnetotail reconnection rate adjusts itself to
the dayside rate, the magnetosphere does not accumulate energy and substorms do not occur: the
result is a laminar convection state known as steady magnetospheric convection (SMC) events. The
proportions of time that the magnetosphere displays SMC or substorm behaviours, the factors
that govern the response, and the ramifications for energy deposition in the atmosphere are not
known. Previous imaging has been discontinuous, prohibiting measurements over all phases of all
behaviours. Ravens will provide for the first time continuous observations of the coupling to ad-
dress these issues. Over a three-year mission, assuming 3 substorms a day, Ravens will observe
3500 substorms, with continuous monitoring of changes in open flux.
Ravens • Auroral and magnetospheric imaging mission • 8 8
When the magnetosphere undergoes substorm cycles, it is thought that the accumulation of open
flux causes the magnetosphere to inflate and the tail magnetopause flares outwards. This increases
the cross-sectional area that the magnetosphere presents to the solar wind and leads to the build-up
of pressure in the tail. This in turn increases the chance of the onset of magnetotail reconnection in
the central tail. It is not known what controls the open flux threshold for substorm onset, nor in-
deed what causes the delay in onset of magnetotail reconnection to give substorm behaviour.
Continuous observations of open flux content using high-cadence imaging will allow this to be ex-
plored.
Figure 1.5. (Left) observations of the expand-
ing/contracting polar cap (a and b) over a period of
11 days (c) from IMAGE-SI. Large enhancements in
dayside reconnection (e) occur during solar wind
disturbances. These produce large enhancements
in polar cap size, which in turn drive enhanced
magnetotail reconnection, injecting plasma from
the plasma sheet into the inner magnetosphere,
enhancing the ring current, here sensed by the
magnetic perturbation it produces, measured as
depressions in the Sym-H index. Enhanced polar
cap sizes and ring current intensity are thought to
be linked, though the link is not understood.
Figure 1.6. (Right) Observations of the auroras on
timescales of a few hours show the characteristric
“breathing” of the magnetosphere, known as the sub-
storm cycle, the open flux of the polar cap (FPC) increas-
ing and decreasing as the polar cap expands and con-
tracts (a). Expansions occur during periods of magne-
topause reconnection associated southwards-directed
IMF, BZ < 0 (d). Contractions are associated with mag-
netotail reconnection, that is the occurrence of sub-
storms (two minor, two major in this example), leading
to enhanced auroral emissions (b) and activations of the
auroral electrojets (c). The observations of FPC allow the
dayside and nightside reconnection rates (e) and the
magnetic flux transport in the Dungey cycle (f) to be
quantified. Ravens will provide such observations con-
tinuously for the duration of the mission; previously this
was only possible for periods of 10 hours (IMAGE).
1.2.2. Temporal and spatial variability. While expansions and contractions of the polar caps reveal
the cycles of the magnetospheric engine, specific features within the auroras reveal the working
parts of that engine, allowing the spatial and temporal variability of reconnection to be investigated.
Ravens • Auroral and magnetospheric imaging mission • 9 9
Reconnection at the magnetopause and in the magnetotail is episodic due to the natural variability
of the solar wind, but also by an apparent inherent variability within the reconnection process itself.
At the magnetopause during southward IMF this manifests itself as quasi-periodic bursts of recon-
nection, known as flux transfer events (FTEs), with repetition periods thought to range from 10s of
seconds to several minutes [e.g. Lockwood and Wild, 1993]. FTEs can have characteristic auroral
signatures which were first identified in global auroral images by Milan et al. [2000a]. When the IMF
is directed northwards, “lobe” magnetic reconnection occurs at high latitudes, tailwards of the open-
ings of the cusps. Under sufficiently dense solar wind conditions, the footprint of the reconnection
site can be visible as an auroral “cusp spot” within the noon-sector polar cap (see Fig. 1.7), its loca-
tion in local time being controlled by the east-west orientation of the IMF [Milan et al., 2000b; Frey
et al., 2002]. Unlike southward-IMF reconnection, lobe reconnection is not constrained to occur
equally in the northern and southern hemispheres, and indeed the interrelation of lobe reconnec-
tion in the two hemispheres is unknown. A special case occurs when the IMF is oriented directly
northwards: in this situation lobe reconnection can occur in both hemispheres on the same IMF field
line, known as “dual-lobe reconnection”, closing previously open flux [Imber et al., 2006]. This pro-
cess has profound implications for magnetospheric dynamics as it is postulated to be the most effi-
cient magnetospheric mass-loading process known (see also Sect. 1.3.5). The cadence of previous
imagers has not been sufficient to properly analyse the dynamics of flux transfer events nor cusp
spots. More importantly, the conjugate nature of these cusp and substorm features is entirely
unknown as interhemispheric observations are not available. Ravens will provide high cadence,
interhemispheric observations, with identical instruments, of dayside and nightside reconnection
signatures.
Figure 1.7. IMAGE-WIC images of the global FUV auroral dis-
tribution during a particularly active period. Note the unusual-
ly large cusp features in the first three images.
Figure 1.8. Simultaneous views of the auroras in the northern and
southern hemispheres by the Polar and IMAGE spacecraft show
that while some features are symmetrical, many are not, challeng-
ing current understanding of the mapping of the magnetic field
between hemispheres and the fundamental plasma-physical pro-
cesses that result in auroral emission. Observations of this nature
are exceedingly rare due to the lack of coordination between pre-
vious missions.
This study was selected for the cover
of Nature (v. 460, no. 7254, 2009),
reflecting the importance attached
to the acquisition of conjugate auro-
ral images for improving our under-
standing of magnetospheric struc-
ture and dynamics. Taken from
Laundal and Østgaard [2009].
Ravens • Auroral and magnetospheric imaging mission • 10 10Based on simultaneous imaging by IMAGE and Polar it is now well established that the substorm on-
set locations in the conjugate hemispheres are usually asymmetric, controlled by the orientation of
the IMF [Østgaard et al., 2004; Wang et al., 2007], though the reasons for this asymmetry are poorly
understood. Laundal and Østgaard [2009] reported that the auroras can be completely asymmetric
(see Fig. 1.8), which may be the first clear observations of interhemispheric currents due to seasonal
differences [Richmond and Roble, 1987; Benkevich et al., 2000]. Simultaneous interhemispheric
imaging provided by Ravens will for the first time allow study of this important but poorly-
understood asymmetric interaction between solar wind, magnetosphere and ionosphere.
1.3. Magnetospheric Structure and Feedback
1.3.1. Relationship between dynamics and structure. The observed structure of the magneto-
sphere is created by the dynamics associated with solar wind-magnetosphere coupling (Fig. 1.1).
The opening of magnetic field lines allows ingress of solar wind plasma into near-Earth space; the
stretching and increase in volume of these flux tubes as they form the geomagnetic tail creates two
regions of space containing a very dilute plasma, the magnetotail lobes. Magnetic reconnection in
the central plane of the tail causes the magnetic field lines of the lobes to converge, sandwiching
plasma in a plasma sheet. This dense plasma is heated by the reconnection process, creating a res-
ervoir of hot plasma. Reconnection injects this plasma into the inner magnetosphere where it be-
comes trapped; the resulting plasma pressure (dominated by ions) is to first-order in balance with
the J×B force, where J are the required electrical currents and B is the perturbed field. This electrical
current is what is referred to as the ring current, in the case of an azimuthally symmetric pressure
distribution [Parker, 1957]. Particles from the plasma sheet and ring current precipitate into the at-
mosphere enhancing the ionospheric density and modifying its conductivity. The atmosphere feeds
ionospheric plasma up into the magnetosphere creating an inner region which does not participate
in the Dungey cycle flow, but corotates with the Earth: the plasmasphere acts as a reservoir of
dense, cold plasma deep in the magnetosphere. The ionosphere is mostly produced by solar illumi-
nation and photochemistry, but is also modified by processes occurring due to transport in the Dun-
gey cycle and precipitation from the overlying plasma regions. As the polar caps expand and con-
tract, the size and relative locations of the different plasma regions change, such that they overlap
and interact (Fig. 1.9). These regions are created by the dynamics, but once formed they also
feedback on the dynamics, altering the behaviour of the system, leading to highly non-linear be-
haviour. This behaviour is not understood and it is a central aim of Ravens to investigate this be-
haviour and understand the influence of each region on the system.
Figure 1.9. FAST ion energy spectra
(left panel) for 135 hours bracketing
two geomagnetic storms (depressions
in Sym-H, top left). The data is from
successive passes of the evening sec-
tor auroral oval (see footprints bot-
tom right). During these storms, the
equatorward (inner) boundary of the
ion plasma sheet undergoes signifi-
cant movement in latitude, carrying it
deep into the inner magnetosphere,
across the outer radiation belts.
Studying the two-dimensional spatio-
temporal interaction of different
plasma regions is a primary objective
of Ravens.
1.3.2. Plasma sheet. The plasma sheet is supplied with solar wind plasma through the convective
transport associated with the Dungey cycle. This cycle keeps the plasma sheet sandwiched between
the overlying magnetotail lobes, though sometimes the nightside auroras show a double-oval con-
Ravens • Auroral and magnetospheric imaging mission • 11 11figuration, which is not currently understood. When the convection cycle slows, due to low dayside
reconnection, the magnetosphere can become topologically complex and transpolar arcs (TPAs) or
theta aurora bisect the polar cap (Fig. 1.10). There is controversy regarding whether TPAs occur as a
consequence of field-aligned currents associated with convection flow shears on open magnetic field
lines or whether they represent a protrusion of the plasma sheet to unusually high latitudes, closed
magnetic flux bisecting the open lobes [e.g. Zhu et al., 1997]. Recently proposed formation mecha-
nisms [Milan et al., 2005; Fear et al., 2014] suggest that TPAs may be magnetically conjugate, but
not symmetrically located in the two hemispheres; the conjugacy or lack thereof of TPAs is crucial to
understanding this phenomenon [Østgaard et al., 2003]. To investigate these complex magneto-
spheric topologies and connect their origins to solar wind-magnetosphere interactions and magne-
tospheric dynamics, Ravens will observe transpolar arcs and other auroral phenomena in both
hemispheres under a wide range of solar wind and IMF conditions, including events where those
conditions are changing rapidly.
During enhanced geomagnetic activity, intense particle precipitation into the atmosphere and Joule
heating lead to the upwelling and outflow of heavy ionospheric ions into the plasmasheet, impacting
subsequent magnetospheric behaviour [e.g. Gazey, 1996]. Currently, the rate of mass-loading of
the plasmasheet and its relationship to specific outflow-mechanisms is poorly understood. Ravens
will investigate ionospheric outflow rates and their relation to geomagnetic activity.
Fig. 1.10. DE1 observations of a transpolar arc or theta aurora. Interhemispheric
observations of such arcs are essential to further understanding of their compli-
cated magnetic topology.
1.3.3. Ring current. The plasma acceleration and transport processes that form ring currents are
universal phenomena that are still surrounded by mystery. Recent observations and modelling
strongly imply that “fronts” of plasma are not simply convected in and heated adiabatically [Yang et
al., 2008]. Instead, plasma instabilities seems to play a critical role in overcoming the “pressure ca-
tastrophe”, by transporting plasma in finger-like structures into the inner magnetosphere, not unlike
interchange instabilities. In-situ measurements have only been able to speculate on their nature,
and no imaging mission has been able resolve these yet in the ring current, but IMAGE-WIC images
have revealed patterns in the auroras that are consistent with modelled interchange instabilities in
the ring current [Yang et al., 2008]. Ravens will investigate interchange instabilities, charge ex-
change losses, adiabatic drift mechanisms, and ring current-plasmasphere interactions within the
inner magnetosphere.
Figure 1.10. Example of the
dynamic ring current. IM-
AGE/HENA images showing a
transition from a highly asym-
metric main phase ring current
to a symmetric recovery phase
ring current.
The acceleration of plasma sheet plasma and its transport inwards is critical for controlling dynamics
of the inner magnetosphere. The resulting plasma pressure is highly dynamic (Fig. 1.10) and severe-
ly distorts the magnetic field of the inner magnetosphere [Tsyganenko et al., 2003], which is the
governing framework for the outer electron radiation belt. Ravens will investigate the inward
transport of plasma to form the ring current and the magnetospheric behaviours, e.g. substorms,
that cause this.
Ravens • Auroral and magnetospheric imaging mission • 12 12The pressure also drives a 3D current system, which is the so-called partial ring current (PRC) during
storm main phases and the symmetric ring current during recovery phases. Its ionospheric field-
aligned current counterpart is the Region-2 FAC system, which connects the magnetosphere and
ionosphere, producing fast, localized flows known as Sub-Auroral Polarization Streams (SAPS)
[Brandt et al., 2008], modifying the convective flows driven by the Dungey cycle (Fig. 1.11). Ravens
will investigate the role of the ring current in magnetosphere-ionosphere coupling and geomag-
netic storm phenomena.
Figure 1.11. A typical plasma pressure distribution
depicted here in the equatorial plane, retrieved
from IMAGE/HENA images; simultaneous TEC and
ionospheric flow measurements from Millstone
Hill and SuperDARN provide the ionospheric re-
sponse such as SAPS that are a core part of dis-
rupting navigation systems.
1.3.4. Plasmasphere. The plasmasphere is cold plasma of ionospheric origin that is trapped within
the corotating portion of the inner magnetosphere. The cold plasma distribution has a significant
modifying effect on a number of important particle-particle and wave-particle interactions within
the inner magnetosphere. The most important, but poorly understood, loss process for trapped
energetic electrons in the radiation belts is pitch-angle diffusion driven by self-generated whistler
mode waves. This interaction between the cold and very hot plasma regions is a key area that Ra-
vens will address.
The extent of the plasmasphere (Fig. 1.12) depends on the balance between corotation and convec-
tion, which in turn depends on the strength of the solar wind interaction and reconnection within
the magnetotail, such that the plasmasphere expands during quiet magnetospheric conditions and
contracts when the convection is strongly driven, for instance during geomagnetic storms. During
contractions the outer edges of the plasmasphere are stripped off and “drainage plumes” become
entrained within sunwards convection on the dusk-side magnetosphere [Spasojević et al., 2003] and
intersect the dayside solar wind-magnetosphere coupling region (see Sect. 1.3.5). On the other
hand, following a storm the emptied flux tubes are replenished with ionospheric plasma over a peri-
od of days. The convection process is variable on time scales ranging from minutes to days, and the
contrasting time scales of source and loss, and the variable position of the plasmapause produce a
wide variety of plasmaspheric structures, including a steady “drainage plume”, variable plasma blobs
detached from the plasmasphere, shoulders and channels. The processes by which plasmaspheric
refilling occurs and the resulting distribution of plasma along the field lines are not presently well-
understood, nor are the time-dependent processes that produce plasmaspheric loss and the
transport of cold plasma within the magnetosphere. Ravens will be able to resolve the im-
portance of these source and loss processes for plasmasphere, and study the interaction of plas-
maspheric plasma with other magnetospheric processes.
Figure 1.12. The plasmasphere as observed by the EUV instru-
ment on IMAGE. The Earth, dayside airglow, and auroras are ap-
parent in the centre of the image. The diffuse background sur-
rounding this is EUV sunlight scattered from the plasmasphere.
The outer edge of the plasmasphere represents the boundary
between corotation and convective magnetospheric flows; time-
dependent source and loss produces complex structure.
Storm-time drainage plumes can
intersect the dayside magneto-
pause where they hinder solar
wind-magnetosphere coupling.
Ravens • Auroral and magnetospheric imaging mission • 13 131.3.5. Feedback and Geomagnetic Storms. The preceding discussion indicates that solar wind-
magnetosphere-ionosphere coupling is a complicated process, involving an interplay of the plasma
regions that will be imaged by Ravens. Fig. 1.13 presents a schematic of some of the interactions
that will be studied by Ravens. It is possible that geomagnetic storms, which occur when the magne-
tosphere is subjected to extreme solar wind conditions such as a solar wind shock or greatly en-
hanced dayside coupling, represent a pathological interaction and feedback between these systems.
The following feedback paths associated with intense strong solar wind-magnetosphere coupling
have been identified, but have yet to be fully studied:
• Enhanced dayside reconnection leads to tail reconnection, injecting plasma into the inner mag-
netosphere which ultimately precipitates into the ionosphere; enhanced ionospheric conduct-
ance leads to frictional coupling between the ionosphere and atmosphere braking convection
[Grocott et al., 2009].
• Enhanced atmospheric heating associated with the auroral precipitation can lead to the outflow
of heavy ionospheric ions which mass-load the plasma sheet and modify its subsequent behav-
iour [e.g. Gazey, 1996].
• The formation of a “cold, dense plasma sheet” by solar wind capture through inward diffusion
at the magnetospheric flanks or lobe reconnection [e.g. Imber et al., 2006] can also mass-load
the plasma sheet and modify its subsequent behaviour .
• Precipitation into the inner magnetosphere enhances the ring current; outside the ring current
region this produces a magnetic perturbation that dipolarizes the magnetotail chocking
nightside reconnection. More open flux accumulates in the magnetospheric lobes, causing the
magnetotail to flare outwards until the internal pressure rises sufficiently to restart reconnec-
tion [Milan et al., 2009] (cf. relationship between open flux and ring current intensity in Fig.
1.5).
• Enhanced dayside reconnection leads to strong convection which strips the outer plasmasphere
into a drainage plume; the drainage plume mass-loads the dayside magnetopause with heavy
plasma and chokes the dayside reconnection process [Borovsky and Denton, 2006; Walsh et al.,
2014].
It is probable that the time-dependent substorm behaviour of the magnetosphere during more qui-
escent periods is also produced by similar feedback mechanisms. Another key area of uncertainty is
the influence of asymmetrical (summer/winter) ionospheric conductance on magnetospheric dy-
namics.
Figure 1.13. Flow chart of mass end energy flow between various regions in geospace.
Ravens • Auroral and magnetospheric imaging mission • 14 14The complex interplay of these processes can only be properly studied with the coordinated ob-
servations of different magnetospheric regions and processes that will be provided by Ravens. It
is essential that these observations be continuous in nature, but also of sufficiently high time reso-
lution, as storms can evolve over many 10s of hours, with many of the processes occurring at dif-
ferent stages in the storm and with different time-scales. A full understanding of storms has not
previously been achieved because of a lack of continuity in the observations. Ravens is specifically
designed to overcome this lack of continuity.
1.4. Summary of Science Objectives
Here, we summarize the Science Objectives of Ravens, which are directly aligned with international
research priorities (see Sect. 2.6). Ravens will study:
• the engine that drives magnetospheric dynamics, the magnetospheric structure that arises
as a consequence of the dynamics, and the feedback mechanisms which lead to time-
dependent behaviour;
• the factors which control magnetic reconnection at the magnetopause and in the magneto-
tail; to determine the onset thresholds for storms and substorms;
• the time-dependence and conjugacy of reconnection signatures at the magnetopause and in
the magnetotail;
• the rate of energy deposition in the atmosphere by precipitation and Joule heating and the
factors that influence it;
• the proportions of time that the magnetosphere displays steady or time-dependent behav-
iour, and the factors that govern this response;
• the conjugacy of auroral features in both hemispheres to understand complex magneto-
spheric topologies;
• mass-loading of the plasma sheet by ionospheric heavy-ion outflow, and the impact on sub-
sequent magnetospheric behaviour;
• the relationship between substorms and ring current injections, and the role of the ring cur-
rent in geomagnetic storm phenomena;
• the interaction of the ring current and plasmasphere, including interchange instabilities,
charge exchange losses, and adiabatic drift mechanisms;
• the interaction between the plasmasphere and radiation belts, including the loss processes
of trapped energetic electrons;
• plasmaspheric filling and loss mechanisms, including drainage plumes, and their interaction
with other magnetospheric processes.
Ravens • Auroral and magnetospheric imaging mission • 15 152. Science Requirements
2.1. Overarching Science Requirements
To achieve the science objectives summarized in Sect. 1.4, Ravens is required to make
• continuous observations of the northern and/or southern auroras
• regular views of both northern and southern auroras
• continuous imaging of the plasmasphere
• regular stereoscopic views of the plasmasphere
• continuous imaging of the ring current
• regular stereoscopic views of the ring current
In addition, the Ravens mission will be much enhanced by coordination with ground-based observa-
tories, to provide ionospheric convection measurements and magnetic perturbations associated
with the ring current and ionospheric electrojets. Data exploitation will be further enhanced by co-
ordinated physics-based modelling of the magnetosphere.
The observing requirements and instruments proposed to satisfy them (see Sect. 3) are summarized
in Table 2.1. Instrument performances are well-understood in terms of previous imaging missions,
and indeed many of the instruments proposed are heritage designs from Polar, IMAGE, or other pre-
vious imaging missions.
Table 2.1. Ravens science requirements (including cadence and spatial resolution where appropriate), related
observables, the instruments that will provide the required measurements
Requirement Observable(s) Instrument(s)
Electron auroras, energy discrimina- LBH-l and LBH-s emissions
Ravens spacecraft / instruments
UVAMC-0, -1
tion, continuous observation, 10 s, 50 from N2, bremsstrahlung X-
XIR
km (500 km for X-rays) rays
Proton auroras, continuous observa- Doppler shifted Lyman-α
Ravens-SI
tion, 10 s, 50 km from charge-exchanging H
Plasmasphere density,
30.4 nm sunlight scattered by
continuous observation, 3D recon- + EPI
He
struction, 30 min
+ +
Ring current H and O ion density in Energetic Neutral Atoms from
the 10-200/nuc keV range, continu- charge-exchanging ring cur-
NAIR-Hi, -Lo
ous observation,3D reconstruction, rent ions and outflowing
heavy ion outfloware similar to previous missions (e.g. Polar and IMAGE); new science arises from the requirement
that there are two spacecraft, allowing continuous and conjugate imaging, and that the spacecraft
are three-axis stabilized, allowing continuous pointing and hence high cadence imaging and/or long
exposure times to suppress dayglow contamination.
2.2.1. Spatial resolution and field-of-view. The spatial resolution of imaging of electron and proton
auroras needs to be of order 50 km, similar to the spatial resolution of previous imaging missions
and of the spatial resolution of ionospheric radars such as SuperDARN. To provide continuous imag-
ing from the proposed orbits (see Sect. 4), targeting latitudes poleward of 50° geomagnetic latitude,
the angular (edge-to-edge) field-of-view of the cameras is required to be 20°.
2.2.2. Electron auroras. Most auroral emission is produced by impact-excitation of atmospheric
constituents by high energy precipitating electrons. These electrons carry upward field-aligned cur-
rents and so are a key signature of magnetosphere-ionosphere coupling. High energy electrons
penetrate deeper into the atmosphere and produce ionization at lower altitudes. Deposition in the
E region (below 150 km) increases the conductance of the ionosphere, and quantifying the conduct-
ance is a key science requirement of Ravens. The energy spectrum of the precipitation can be de-
duced by simultaneously imaging at a range of wavelengths that respond differently to different
electron energies.
It is proposed to measure electron auroral emissions in four wavelength bands: the long- and short-
wavelength bands of the FUV Lyman-Birge-Hopfield emissions of N2 (LBH-l and LBH-s), OI-3s 5S0 - 2p4
3
P emission at 135.6 nm, and X-ray emissions. LBH-l emissions are proportional to the energy flux of
electrons above 1 keV. LBH-s emissions are absorbed by O, so emissions from deep in the atmos-
phere are attenuated at a spacecraft at high altitude. Hence, the ratio of intensities of LBH-l to LBH-s
are indicative of electron energies between 1 and 20 keV [Germany et al., 1994]. X-ray emission is
produced by Bremsstrahlung of electrons with energies in excess of 30 keV, and quantify the high-
energy tail (up to 150 keV) of the precipitating spectrum. OI-135.6 nm emission is proportional to
total electron flux. Cameras capable of imaging LHB-s, LBH-l and X-rays were flown on Polar (UVI
and PIXIE, respectively). Imaging at 135.6 nm was achieved with the Spectrographic Imager flown on
IMAGE (IMAGE-SI).
2.2.3. Proton auroras. Proton auroras are seen at the footprint of the magnetospheric cusp, where
they are injected from the magnetosheath by lobe reconnection [Frey et al., 2002; Phan et al.,
2003], though their relationship to similar electron auroras [Milan et al., 2000b] is still unknown.
They also precipitate on the nightside due to pitch angle-scattering in the non-dipolar field geome-
try, providing a tracer of the magnetotail magnetic topology [Donovan et al., 2003]. Due to their
much larger mass, protons are not so much affected by electric fields as the electrons are and their
interaction with waves and scattering processes are more dominant.
Proton precipitation produces Lyman-α emission as protons charge-exchange with atmospheric con-
stituents to produce excited H atoms. To distinguish emission by precipitating (down-going) protons
from the background Lyman-α emission of the atmosphere, the red-shifted wing of the Lyman-α line
is imaged. This requires a system that efficiently rejects both the geocoronal Lyman-α emitted near
the 121.6 nm rest wavelength and the NI multiplet a 120 nm. IMAGE-SI was capable of imaging pro-
ton auroral emission.
2.2.4. Dayglow suppression. The ability to suppress non-auroral emissions is vital for Ravens sci-
ence. This is necessary for conjugate imaging because the dayside aurora will be sunlit in at least
one of the hemispheres most of the time. It matters for global dynamics, because quantifying for
example the amount of open flux requires being able to identify the polar cap boundary at all local
times. Proton auroral imaging spectrographs suffer less dayglow than do electron auroral imagers
because suppression of non-Doppler shifted Lyman-α emissions does not reduce the in-band signal.
For the electron auroral imagers, filters will be used to suppress out-of-band contamination due to
dayglow, but this does decrease the in-band signal. For the electron auroral observation the re-
quirement to suppress the effects of dayglow place limits on cadence, resolution, and sensitivity.
Ravens • Auroral and magnetospheric imaging mission • 17 172.2.5. Cadence. Ravens requires auroral imaging at cadences of order 10 s to image wave processes
and rapid substorm and dayside auroral phenomena.
2.2.6. Conjugacy. Ravens requires imaging of both northern and southern auroras to study the
magnetic topology of the magnetosphere, the mapping of dayside and nightside auroral phenome-
na, and differing auroral acceleration between hemispheres.
2.3. Plasmaspheric imaging
Ravens will obtain global images of the plasmasphere by observing EUV sunlight at 30.4 nm reso-
nantly scattered from singly-ionised Helium, a minor magnetospheric constituent which allows ex-
trapolation of overall magnetospheric density [Sandel et al., 2003]. He+ 30.4 nm is the brightest ion
emission from the plasmasphere, it is spectrally isolated, and the background at that wavelength is
negligible. Measurements are easy to interpret because the plasmaspheric He+ emission is optically
thin, so its brightness is directly proportional to the He+ column abundance.
The imaging requirements of Ravens are similar to those of the EUV instrument flown on IMAGE:
~0.6° or ~0.1 RE in the equatorial plane seen from apogee, with a 90° (edge-to-edge) angular field-of-
view. A sensitivity of 0.2 count sec-1 Rayleigh-1 is sufficient to map position of the plasmapause with
a time resolution of 10 minutes or better.
With Ravens, simultaneous views of the plasmasphere emissions from differing viewpoints will allow
an unprecedented 3D reconstruction of the structure and dynamics of cold plasma in the magneto-
sphere.
2.4. Ring current, plasma sheet, and ion outflow imaging
Energetic neutral atoms (ENA) are produced when singly positively charged energetic ions undergo
charge exchange collisions with cold neutral atoms or molecules. The ions will become neutral and
propagate unaffected by electromagnetic fields. If the initial energy is much greater than the plane-
tary escape energy (0.6 eV/nucleon), then the ENAs are unaffected by gravitational fields and will
maintain their energy and momentum. In addition to carrying with it spectral and directional infor-
mation of the energetic ions, the ENA also is a direct measurement of the composition of those ions.
In the terrestrial magnetosphere the ring current will charge exchange with the geocorona at high
altitudes and emit ENAs, allowing the ring current and plasma sheet ion populations to be imaged,
including the inner magnetosphere ion pressure distribution and resulting currents [Roelof et al.,
2004]. At low altitudes, ENAs are emitted by charge-exchanging outflowing ionospheric ions, allow-
ing outflow processes to be studied.
The closest any cameras have come to imaging the plasma pressure of the magnetosphere was the
High Energy Neutral Atom (HENA) camera on board the IMAGE mission, which measured the veloci-
ty, trajectory, energy, and mass of ENAs in the 10-500 keV energy range. This camera covered about
65% of the plasma pressure of the inner magnetosphere, which is dominated by protons and O+ in
the ~10-300 keV range. The TWINS mission flies MENA-heritage cameras (lower energy range than
HENA and no clear mass resolution) on two spacecraft which allows retrieval of the spatially de-
pendent pitch-angle distributions of the ring current, and thus provides a better 3D representation.
The requirements of the Ravens ENA cameras is similar to IMAGE/HENA: sensitive to H, He, O, and
heavier atoms, with an angular (edge-to-edge) field-of-view of 120° × 90°, angular resolution of 5° ×
5°, energy range of 20-500 keV nucleon-1, energy resolution ∆E/E of 0.2, and a velocity resolution of
50 km s-1 (time-of-flight of 1 ns).
Ravens • Auroral and magnetospheric imaging mission • 18 182.5. Coordination with ground-based observatories and modelling
The Ravens mission will be augmented by two crucial additions: ground-based observations of the
ionosphere which provide information on the lower boundary of the magnetosphere and its cou-
pling with the atmosphere, and physics-based simulation of the magnetosphere which will allow the
physical coupling between the regions imaged by Ravens to be investigated.
2.5.1 Ground-based instrumentation. Systematic recordings of auroral phenomena with ground-
based (GB) instrument networks (magnetometers, auroral cameras and ionospheric radars) were
started in the northern Fennoscandia and Svalbard in the late 1950s during the International Geo-
physical Year. Some 30 years later the first comparison studies of GB data with satellite data were
made [Opgenoorth et al., 1980; Pellinen et al., 1984], and since then joint analysis of magnetically
conjugated GB and space-based observations has been fundamental to many advances in under-
standing the coupled solar wind-magnetosphere-ionosphere system. The following GB networks are
examples of the instrumentation that will support and augment Ravens science.
MIRACLE. The Magnetometers/Ionospheric Radars/All-sky Cameras Large Experiment (http://www.
ava.fmi.fi/MIRACLE/) is a meso-scale network of magnetometers and auroral cameras in the Fen-
noscandian sector, covering an area from sub-auroral to polar cap latitudes over a longitude range of
about two hours of local time. MIRACLE data are used to deduce value added data products, like
maps of equivalent currents, auroral precipitation fluxes, and Joule heating rates [Amm and Viljanen,
1999; Janhunen, 2001; Vanhamäki et al., 2009], parameters key to quantifying magnetosphere-
ionosphere coupling in conjunction with global auroral images.
SuperDARN. The Super Dual Auroral Radar
Network (http://superdarn.jhuapl.edu/) con-
tinues to develop as the pre-eminent means
of measuring the ionospheric convection pat-
tern at mid and high latitudes. A recent de-
cadal review of SuperDARN science [Chisham
et al., 2007] reveals the profound connection
between auroral and convection measure-
ments for studies of magnetospheric dynam-
ics; an example of combining auroral imagery Figure 2.1. Combined auroral imagery and SuperDARN
and convection maps is presented in Fig. 2.1. measurements of global ionospheric convection.
ALIS. Auroral Large Imaging System (http://alis.irf.se) is a network of steerable auroral imagers in
northern Scandinavia designed for 3D measurements.
EISCAT. The existing European Incoherent Scatter radar system (http://www.eiscat.se/) is planned
to be augmented by a new EISCAT3D system, with planned operations for at least for 30 years. EIS-
CAT3D will be unique in its capability to do volumetric imaging of ionospheric conditions, including
ion and electron temperatures, electron density and the ion velocity vector.
SuperMAG is a worldwide collaboration of ground based magnetometers. It currently includes data
from more than 300 stations. SuperMAG provides measurements of ground magnetic field perturba-
tions in the same coordinate system, identical time resolution and with a common baseline removal
approach.
Geospace Observatory Canada and THEMIS ground-based auroral imaging. Across Canada and Alas-
ka there are now more than 40all-sky imagers and soon a network of 10 imaging riometers. These
instruments provide contiguous imaging with high space and time resolution across multiple hours
of MLT and spanning the auroral oval in latitude. This network will provide small-scale quantitative
observations of the auroras in white-light, the Oxygen redline, and full-colour, as well as maps of
riometer absorption. These observations will be nested within the Ravens global images, providing
an exciting bridge between scales observed by Ravens and scales that matter for auroral electrody-
namics.
Ravens • Auroral and magnetospheric imaging mission • 19 19You can also read
