Baddeley et al.
Progress in Earth and Planetary Science(2023) 10:53
https://doi.org/10.1186/s40645-023-00585-9

Progress in Earth andPlanetary Science

Open Access

REVIEW

Space and atmospheric physics on Svalbard:a case for continued incoherent scatter radarmeasurements under the cusp and in the polar
cap boundary region
Lisa Baddeley1,3* , Dag Lorentzen1,3, Stein Haaland1,3, Erkka Heino2, Ingrid Mann2, Wojciech Miloch4,
Kjellmar Oksavik1,3, Noora Partamies1,3, Andres Spicher2 and Juha Vierinen2

Abstract
Incoherent scatter radars (ISRs) represent the only instrument (both ground and space based) capable of making
high temporal and spatial resolution measurements of multiple atmospheric parameters—such as densities, temperatures, particle velocities, mass flux—over an altitude range covering the entire mesosphere/lower thermosphere/
ionosphere (MLTI) system on a quasi-continuous basis. The EISCAT Svalbard incoherent scatter radar (ESR), located justoutside Longyearbyen (78.15◦N) on Svalbard, is the only currently operating facility capable of making such measurements inside the polar cusp—an area of significant energy input into the atmosphere and characterized by heating
instabilities and turbulence. The ESR was built in the mid-1990s and has provided valuable data for the international
experimental and modelling communities. New radar technologies are now available, in the form of phased arraysystems, which offer new data products and operational flexibility. This paper outlines the achievements and current
research focus of the ESR and provides scientific arguments, compiled from inputs across the international scientificcommunity, for a new phased array ISR facility on Svalbard. In addition to the fundamental scientific arguments,
the paper discusses additional benefits of continued ISR observations on Svalbard, building on the key findingsof the ESR. Svalbard has a large network of complementary instrumentation both focused on the MLTI system (e.g.
the Kjell Henriksen auroral Observatory, the Svalbard SuperDARN radar and the Svalrak sounding rocket launch facility) with synergies to other research fields, such as meteorology and oceanography. As a further holistic system science view of the Earth becomes more important, a new ISR on Svalbard will be important also in this respect with its
ability to provide datasets with a wide range of scientific applications. Increased activity in space has highlighted
problematic issues such as space debris. A changing Arctic has also seen increased human activity via the opening
up of new shipping routes, which are reliant on GNSS technology that is effected by severe turbulence in the MLTI
system. As such, societal applications of a future ISR are also presented. The accessibility and logistical support
for such a facility is also briefly discussed.
Keywords Ionosphere, Atmospheric science, Space weather, Cusp, Polar cap, Plasma turbulence, Space debris,
Incoherent scatter radar, Atmospheric escape*Correspondence:
Lisa Baddeley
lisab@unis.no
Full list of author information is available at the end of the article© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
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1 IntroductionThe
mesosphere/lower
thermosphere/Ionosphere(MLTI) system extends from 60 to 600 km altitude andconsists of a mixture of ionized and neutral gas components, the ratio between, chemical make-up and temperature of the two components varying as a functionof altitude and latitude. Figure 1 shows a typical altitude
profile of the ionized and neutral components of theatmosphere derived using the IRI-16 (Bilitza et al. 2017)
and the NRL-MSIS 2.0 (Emmert et al. 2021) models. The
ionized component (the density profile shown in Fig. 1,
left hand panel) is directly controlled by electromagnetic
forces, driven from above by interactions with the solar
wind (the continuous stream of charged particles emanating from the Sun) and the Earth’s magnetosphere (theregion in the vicinity of Earth, where the ionized particle
dynamics are controlled, in addition, by the geomagnetic
field). The neutral component (the density profile of themain constituents is shown in Fig. 1, right hand panel), incomparison, is driven by the gas dynamics of the Earth’s

atmosphere from below. However, the tight coupling
between the neutral and ionized component, can also
result in both the forcing of the neutral atmosphere, due
to the magnetospheric drivers, or the generation of ionospheric currents via neutral wind-driven processes. The
partial ionization of the atmosphere at these altitudes
also results in a separation of temperature profiles forthe ionized and neutral components. These are shown in
Fig. 1, middle panel. The above processes lead to a highly
complex, dynamic system with energy and momentum
deposition from both above and below causing atmospheric heating and chemical changes. The coupled natureof the atmospheric system resulting in these effects canalso propagate deeper into the lower atmosphere. An
additional source of energy is also present due to a continuous flux of cosmic dust and meteoroids which fall
into the Earth’s atmosphere. The ablation of meteors
entering into the atmosphere leads to the formation ofsmall solid particles, the meteoric smoke particles, whichlead to changes in atmospheric chemistry.

Fig. 1 Typical MLTI profiles over Svalbard in December. Left hand panel: Electron density profile at 1200UT (red) and 0000UT (black) using the IRI-16
model. Middle panel: Neutral (Tn), Ion (T) and Electron (Te) temperature profiles at 1200UT. Right hand panel: Neutral density profiles of various
components, atomic oxygen (O), molecular oxygen (O2), molecular nitrogen (N2), atomic hydrogen (H) using the NRL-MSIS 2.0 modelBaddeley et al. Progress in Earth and Planetary Science(2023) 10:53

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The auroral zone, in the shape of an oval, is centredaround ∼ 65◦ geomagnetic latitude at local midnightand ∼ 75◦ geomagnetic latitude at local noon. Poleward of this auroral zone is the polar cap region. Figure 2 shows these two regions schematically on a polar
projection, MLT (Magnteic Local Time) plot with magnetic noon (12 MLT) at the top of the plot, dawn (06MLT) to the right, dusk to the left (18 MLT) and midnight (00 MLT) at the bottom. This co-ordinate system
is fixed with respect to the Sun, with the Earth rotating
beneath it. In the figure, the fields of view of the proposed new Svalbard ISR and the EISCAT_3D system(discussed later in the document) are shown, together
with some typical phenomena that are observed, anddiscussed later, in the polar ionosphere. Inside thepolar cap and auroral zone, there are additional energy
sources and coupling mechanisms to consider as the
Earth’s geomagnetic field is directly connected to thatof the Sun (the Interplanetary Magnetic Field, IMF)
which is embedded within the solar wind. The solar

wind–magnetosphere–ionosphere connection results
in a multitude of effects such as:• Variation in the location and latitudinal extent of theauroral zone, and consequently the size of the polarcap.
• Driving of the ionized component of the Earth’s
atmosphere above ∼200 km into a global circulation
pattern (shown as cyan contour lines in Fig. 2). The
pattern’s magnitude, direction and structure is associated with the strength and direction of the IMF.
Momentum transfer between the ionized and theneutral atmospheric components then results in frictional heating and motion of the neutral atmosphere.
• Energetic particle precipitation into the MLTI system. The particles deposit their energy through ionization and dissociation of the atmospheric gasses
generating a variety of auroral forms and localized
heating effects. The penetration depth of the particles is determined by their initial energy resulting in

Fig. 2 Magnetic Local Time (MLT) plot showing the location of both the Svalbard ISR and new EISCAT_3D fields of view (at 300 km) (see Fig. 3) at 4
different MLT periods in relation to the main auroral oval and dayside cusp region. Other phenomena (such as polar cap patches) are also marked
on for context

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momentum transfer across the entire MLTI altitude
range.
• Joule heating of the neutral atmosphere through horizontal current systems, set up as a result of current
closure of field aligned (Birkeland) currents flowing
along geomagnetic field lines.
• Loss of atmospheric mass via ion and neutral outflow, where material is transported upward along
magnetic field lines from the ionosphere and into themagnetosphere.
• Creation of waves, instabilities and turbulence in the
MLTI system. The resulting structuring of the plasma
can span a wide range of temporal and spatial scales,from sub-second to hours and from hundreds of kilometres to scale-sizes of the order of the ion gyroradius (e.g. Tsunoda 1988).

be above the horizon, ideal for precise measurements oforbital parameters. This is the same reason why Svalbard
is one of the main ground station hubs for numerous satellite missions.
Over the last 5 years there have been several review
papers (e.g. Sarris 2019; Palmroth et al. 2021; Heelis andMaute 2020) which have summarized the current understanding of the Earth’s MLTI system. The papers havealso highlighted the various knowledge gaps, instrumental and modelling challenges faced by the scientific community. An underlying theme is the need for (quasi-)
continuous observations over the MLTI altitude range
of key parameters like temperatures of the neutral andionized constituents, conductivities, electric fields, neutral wind velocities and mass input that are necessary toquantify the energy input into the Earth’s atmosphere.
Such observations should be obtained over a multitudeof spatial scales from kilometres to meters, and temporalscales from hours to sub-second. In this respect, there is
only one instrument capable of stepping up to the challenge—a phased array incoherent scatter radar (ISR).

An area of intense study by the research community is
the magnetospheric cusps. These are two funnel shaped
regions in the Northern and Southern Hemispheres
where energetic particles from the solar wind have directaccess to the Earth’s magnetosphere and MLTI system.
They are influenced by magnetic reconnection between
the IMF and the geomagnetic field at the magnetopause;the dayside boundary of Earth’s magnetosphere.
Once they enter into the MLTI system, the precipitating particles cause localized heating, turbulence andoptical phenomena like the dayside aurora. The aforementioned global circulation pattern is initiated as aresult of this reconnection process. The cusp also has relevance for low altitude polar-orbiting satellite missions
as they experience a highly variable atmospheric drageffect as they pass through this region (Lühr et al. 2004).
Although the reconnecting area at the magnetopause
can be a few thousands km2 wide, the resulting footprintin the MLTI system is relatively small (from less than
50 km in latitude to greater than 100 km in longitude,
Fasel 1995; Moen et al. 1999; Newell and Meng 1992;
Hosokawa et al. 2012), meaning there are only a few landbased locations, such as Svalbard and the remote interiorof the Antarctic continent, where these phenomena canbe observed through a combination of radar and optical instrumentation. At these high latitudes, there is nocontamination from solar EUV due to the 24 h darkness conditions of the polar night (November–Februaryin Svalbard) allowing processes in and around the cusp
region to be studied unambiguously.
Another research area of increasing importance, especially in a societal context, is that of space debris. The
polar regions are extremely well suited for observationsof space objects, due to the frequent revisit period of
objects with highly inclined polar orbits. At Svalbard,
nearly every orbit of a polar orbiting space object will

1.1 Incoherent scatter radars (ISRs)

ISRs have provided vital input to the exploration andunderstanding of Earth’s middle and upper atmosphere since the technique was first proposed by Gordon(1958). Their importance and future role within scientific research was recently highlighted by a White Paper(Varney 2022) written in response to the National Academy of Sciences, Engineering and Medicine (US NASEM
2022) Decadal Survey 2023–2032. An excellent, more in
depth review of the scientific contribution provided bythese systems, in addition to a general science case for
their continued use, is given by McCrea et al. (2015).
In recent (<10) years there have only been eleven such
systems providing measurements of the MLTI system
in routine operation (Sondrestrom, Aricebo, PFISR,
RISR-N, RISR-C, Millstone Hill, ESR, EISCAT mainland,
PANSY, MU and Jicamarca). Details of the radars can befound in Table 1. Aricebo was irreparably damaged andshut down in 2020 and Sondrestrom was shut down in
2018. Due to operational constraints, the PANSY radar
only routinely provides data up to 90 km altitude (Satoet al. 2014). A new ISR system in China has just come(as of 2022) into operation at Sanya (Yue et al. 2022).
Of these systems, there are five in the polar cap/auroralzone regions capable of making measurements acrossthe full MLTI altitude range and only one in the vital
cusp region—the EISCAT (European Incoherent Scatter)
Svalbard Radar (ESR) (Wannberg et al. 1997). It forms
part of the larger EISCAT network which also includes a
UHF and VHF system in Tromsø, Norway as well as two
remote receive sites in Kiruna, Sweden and Sodankylä,Baddeley et al. Progress in Earth and Planetary Science(2023) 10:53

Table 1 Incoherent scatter radar parameters
Name

Location (geographic
latitude, longitude)

Operatingfrequency(MHz)

EISCAT Svalbard Radar

78◦9 N 16◦1 E

500

RISR (Resolute Bay) N/C

74 43 N 94 54 W

442

EISCAT Tromsø UHF/VHF

69◦35 N 19◦13 E

928/224PFISR (Poker Flat)

65◦6 N 147◦28 W

449

MU

34◦51’ N 136◦6 E

47
440

◦

◦

Millstone Hill

42 36 N 71 30 W

Jicamarca

11◦57 S 76◦52 W

50

PANSY

69◦ S, 39◦36 E

47

Sondrestrom (shutdown in 2018)66◦59 N 50◦57 W

1290

Aricebo (shutdown in 2020)

18 26 N 66 38 W

430

EISCAT_3D Transmitter site (oper- 69 20 N 20 18 E
ational from 2023 onwards)

223

◦

◦
◦

◦

◦
◦

Finland. The current EISCAT systems all rely on dishantennas (either a cassegrain or parabolic cylinder
design) which can be tilted into position using a series ofmotors.
The more modern high latitude ISRs use a phased array
design called AMISR (Advanced Modular ISR) (Valentic
et al. 2013). These systems (which consist of thousandsof smaller, dipole shaped antenna elements arranged in agrid formation) offer significant improvements in termsof both data coverage and operation. The arrays can beelectronically steered into any pointing direction nearly
instantaneously and are not reliant on one or severaltransmitters. The two polar cap AMISRs located in Resolute Bay, Canada (RISR 2022), and auroral region AMISR
located at Poker Flat, Alaska (PFISR 2022), are all monostatic (meaning the transmitter is co-located with thereceiver system) phased arrays.
The next generation of phased array ISR will be the
EISCAT_3D system (EISCAT 2022), located in Northern
Scandinavia, which is due to become operational in 2023.
The system will replace the current EISCAT (Tromsø,
Kiruna, Sodankylä) configuration in mainland Northern Scandinavia and will represent the first tri-static(one main transmitter/receiver site accompanied by two
remote receiver sites) phased array radar in the world.
The radar parameters are shown in Table 1. Mono-static
systems, though highly effective, must make assumptions (for example, in regard to the mapping of electricfields along a magnetic field line) to derive some of the
MLTI parameters. The tri-static capability will add a
new dimension to the datasets as full 3D-vector quantities of the needed parameters will be obtained across awide range of altitudes, latitudes and longitudes centredaround the main auroral region (∼65◦ ). The field of view

Page 5 of 24(fov), however, will not extend up to the latitudes of cusp
region of the MLTI system (as can be seen from Figs. 2
and 3).
The ESR has made many significant contributions
to the understanding of the Earth’s atmospheric system, with a particular focus on the cusp region, since its
inception nearly 30 years ago. One of the ongoing issues(in addition to wear and tear) is that, due to its growing
age, replacement parts (such as transmitter klystrons) arealmost impossible to obtain. It is thus envisaged that theradar is coming towards its end-of-life within the next 10
years.
In this paper we put forward a science case for a newphased array ISR facility on Svalbard. We consider incoherent scatter studies at high latitudes highlighting theessential part that the current ESR has played. We identify outstanding research questions for which high latitude and cusp ISR observations are essential. We discuss
the benefit from having comparative observations at
different latitudes and altitudes (including from otherground-based and space-based systems). We show how
such a radar would be invaluable and also critical for
future satellite missions by complementing their in situ
measurements. There is a brief discussion regarding thedesign and location of a possible new ISR facility. We
finally discuss the additional benefits (including logistical and collaborational) of maintaining such a facility on
Svalbard, with its long history of ground-based researchfacilities across several different scientific disciplines.

2 Current understanding and knowledge gaps
in the polar MLTI system
In the following sections, distinct research areas havebeen identified and discussed. It should be noted, however, that due to the highly coupled nature of the MLTI
system many of the observed phenomena are intrinsically linked, i.e. polar cap patches (Sect. 2.2) travel withthe background convection velocity and are often associated with auroral phenomena (Sect. 2.1) and plasma turbulence; ion outflow (Sect. 2.3) can be directly related toauroral features (Sect. 2.1). The different phenomena areshown schematically in Figs. 2 and 4.
2.1 Reconnection—convection, the polar cusp and auroral
phenomena

The dayside cusp aurora is the product of the interaction
between the solar wind and the Earth’s magnetospherethrough magnetic reconnection between the IMF and thegeomagnetic field at the dayside magnetopause. A prerequisite for reconnection to occur is that a significant component of the two merging magnetic fields is anti-parallel
to each other, creating a magnetic shear across the magnetopause. The evolution of the ionospheric footprint

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of newly reconnected field lines manifests itself by theconvective motion of the ionospheric plasma and in thedayside cusp aurora. At the magnetopause, this evolution
is controlled by the dayside reconnection rate, giving riseto the magnetic tension forces and magnetosheath flows,
whilst in the ionosphere, it is controlled by the conductive load at the end of the field line. The MTLI systemin the auroral and polar cap regions are thus subject tothis additional energy input in comparison to lower latitudes. Multi-spacecraft missions (CLUSTER, THEMIS,
and MMS) have identified a wide range of transient phenomena in the upstream solar wind, at the bowshock, inthe magnetosheath, and at the magnetopause. Hot flow
anomalies, foreshock bubbles, magnetosheath jets, flux
transfer events (FTEs), and surface waves are thought
to play a significant role in the solar wind–magnetosphere–ionosphere coupling (Zhang et al. 2022). Thesephenomena are associated with the aforementioned variations in the IMF and solar wind dynamic pressure that
deform the Earth’s magnetopause. Much is still poorly
understood regarding how magnetic reconnection plays
out across the magnetopause. There currently exists noglobal dataset that describes the full 3D electrodynamics across the dayside magnetopause. However, the large
areas of the magnetopause magnetically map to relatively
smaller areas in the ionosphere (Newell and Meng 1992),
and the phenomena manifest themselves through a variety of ionospheric signatures such as auroral precipitation and ionospheric convection, which can be measured
by ground-based instruments, such as coherent scatterradars (CSRs) (e.g. The Super Dual Auroral Radar Network, SuperDARN, (Chisham et al. 2007; Nishitani et al.
2019) and ISRs. On a large scale (>500 km), plasma convection is recognized as having a general twin cell configuration with the plasma moving from the dayside cusp
region, across the polar cap and into the nightside oval
before flowing back to the dayside at lower latitudes (asshown schematically by the cyan lines in Fig. 2). This
circulation is, to a high extent, determined by the IMF
north/south orientation. For southwards directed IMF,
magnetopause reconnection opens previously closed
field lines convecting over the polar cap. This leads toan anti-sunward convection in the polar cap. For northwards directed IMF, lobe reconnection (on already open
lobe field lines) sets up a sunward convection in the dayside polar cap. The large SuperDARN network provides
observations of this large scale flow on a routine basisand has built up a database spanning over 25 years (e.g.
Lockwood and McWilliams 2021). The large-scale auroral morphology is determined by the configuration ofelectrical currents that flow along magnetic field-lines,
both into and out of the ionosphere. Dayside aurora
is a result of such currents, where upward currents arecarried by downward precipitation electrons. The dayside cusp aurora is typically produced by a high flux(∼ 2–5 mW m−2 of low-energy (< 0.5 keV) electrons colliding with atomic oxygen at high altitudes (200–400 km),which in turn produces high intensity (∼ 2–30 kR) oxygen optical emissions at 630.0 nm. The optical emissions are accompanied by thermal heating of the plasma
and turbulence. The latitudinal/longitudinal extent of
the cusp (e.g. Moen et al. 1999; Newell and Meng 1992)
can provide vital information regarding reconnection processes at the dayside magnetopause. On scales
smaller than this however, the flows can be turbulent anddynamic in nature and not fully understood (Lyons et al.
2016). The relative drift or velocity shears between theionized and neutral components of the MLTI system also
result in significant localized heating effects, although the
dynamics and interactions between the two components
is not fully understood. Studies using the ESR, in combination with other Svalbard instrumentation, have shownthat the response time of the neutral component can varysignificantly, depending on the auroral activity at a given
time ( e.g. Billett et al. 2020; Kosch et al. 2011). Statistical studies with the ESR have also shown an unexplained
afternoon ’hot spot’ which occurs at around 15 MLT (e.g.
Cai et al. 2016). Whilst the magnitude of heating which
occurs is statistically related to the polarity of the IMF,
the smaller scale dynamics, including local auroral precipitation (and the field aligned current systems), are also
thought to play a part (e.g. Aikio et al. 2002). Early radarobservations using both CSRs and ISRs (Van Eyken et al.
1984; Goertz et al. 1985) reported flow signatures thatwere interpreted as ionospheric footprints of flux transfer events. Later, several types of poleward moving transients have been found, including flow channel events(Pinnock et al. 1993), pulsed ionospheric flows (Provan
et al. 1998), poleward-moving radar auroral forms (Milanet al. 2000) and fast flow channels (Herlingshaw et al.
2020). A particular phenomena of reversed flow events,
RFEs (Rinne et al. 2007; Oksavik et al. 2011) was discovered using the ESR indicating that the meso-scale ionospheric convection is often quite complex in the cusp andpolar cap. ESR studies have shown multiple anti-parallel
flow channels less than 50 km wide (e.g. Oksavik et al.
2004, 2005) embedded in the large-scale convection andof just a few minutes duration. Sounding rocket observations have also identified structured flows at 4–6 km
scale (e.g. Oksavik et al. 2012).
In addition to the dynamic flows in and across thepolar cap regions, there are a multitude of auroral structures and features. The different structures are indicative of different interactive processes and cover a hugevariety of spatial (from 100 s km to 10 s m) and temporal (from hours to sub-second) scales. They can include

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auroral arcs, proton aurora, cusp (dayside) aurora, poleward moving auroral forms (PMAFs), polar cap aurora
and transpolar arcs, to name but a few. The polar cusp
is identified as the ‘source region’ of several other phenomena such as ion upflow and neutral upwelling (seeSect. 2.3 of this manuscript). The link between upflow
and the cusp has been investigated using the ESR in conjunction with both optical instruments (e.g. Moen et al.
2004; Lorentzen et al. 2007) and rockets (e.g. Burchill
et al. 2010; Lund et al. 2012; Lessard et al. 2020; Moser
et al. 2020). PMAFs are discrete auroral structures (Fasel
1995) which move polewards out of the cusp region at
speeds that may exceed 500 m/s (Milan et al. 1999; Oksavik et al. 2005). They range in spatial extent from lessthan 50 km in latitude to greater than 100 km in longitude, occasionally, with time between successive PMAFsof less than 5 min (Fasel 1995; Hosokawa et al. 2012).
PMAFs are related to changes in the solar wind but areoften seen to occur spontaneously (Frey et al. 2019). They
are associated with convection flow enhancements andturbulent small scale flow channels. ESR observations
have revealed some of the complex nature of the energy
deposition into the MLTI system by PMAFs (e.g. Skjæveland et al. 2011) as well as showing how they are related
to other phenomena, such as polar cap patches (which
are discussed later in Sect. 2.2 of this paper). The studies of dayside aurora and convection are thus vital forthe understanding of the solar wind–magnetosphere–
ionosphere interaction. There are several unansweredquestions that are important in order to improve ourunderstanding of this interaction:of the phenomena combined with the size of the interaction region (∼ 1010 km2). It would require hundreds(if not thousands) of spacecraft to make simultaneous
multi-point observations of the magnetopause reconnection region. However, large areas of the magnetopause map magnetically to relatively small areas in theionosphere (e.g. Moen et al. 1999; Newell and Meng
1992), and the phenomena manifest themselves througha variety of ionospheric signatures (such as auroral precipitation and convection), which can be measured byground-based instruments, including ISRs.
Whilst the current ESR has made significant contributions to the research field, the observations are severely
limited by temporal and spatial constraints due to existing observational data sets, e.g. one single radar beam
direction, multiple discrete radar beams with poor angular and/or range resolution, or the maximum slew rateof a single radar dish. Consequently, it is difficult to fully
characterize and quantify the full MLTI dynamics since
assumptions must be made as to whether the phenomena
under observation are undergoing temporal or spatialchanges (i.e. is it multiple structures moving through theradar field of view or is it a static structure with temporalvariations?). A new phased array radar in Svalbard would
offer ground-breaking information to these fundamental
questions through its ability to electronically point multiple beams. The new ISR will build on previous work
looking at large scale flow bursts and FTEs (e.g. Nishitani et al. 1999; Fear et al. 2017) over an extended area
along the dayside polar cap boundary. The combinationof instrumentation allows the smaller spatial scale observations of densities, temperatures and velocities madeby the ISR to be placed within the larger scale (>500 km)
flow dynamics of the ionospheric system (measured by
CSRs). The radar will be a pathfinder to pinpoint both theboundary itself, and the plasma motion across it (Lockwood et al. 2005). The new radar will give unprecedented
measurements from the ground of how the instantaneousreconnection rate varies across an extended region of thedayside magnetopause. From its vantage point under thepolar cusp, the new radar will provide trailblazing instantaneous monitoring of the footprints of multiple magnetic field lines along an area that potentially covers mostof the dayside magnetopause, and from just one single
radar site.
The proposed radar will also provide critical information on how plasma moves across the polar cap boundary. Outstanding questions to be addressed include:• Is magnetic reconnection continuous in time or sporadic and over what time scales does it occur?
• Does reconnection take place in a single, large regionof the magnetopause or rather in many smaller areas
simultaneously?
• Are there ionospheric footprints that can reveal
this—e.g. can PMAFs be used to infer the extent of
the reconnection X-line?
• Why do PMAFs also occur during IMF northward
conditions?
• How are dayside auroral forms affected by the magnitude and orientation of the IMF?
• What is the response time for dayside auroral phenomena in relation to the arrival of solar wind structures at the magnetopause?
• What role do the small scale plasma flows and auroral precipitation play in the formation of the afternoon hot spot?
In situ observations of such reconnection phenomena
with spacecraft is challenging given the transient nature• Is the momentum transfer spontaneous at the polar
cap boundary, or does it vary with MLT in responseto changes in IMF By?

Baddeley et al. Progress in Earth and Planetary Science(2023) 10:53

Page 8 of 24• How long does momentum transfer continue into
the polar cap, as the magnetic tension force pulls themagnetic field lines towards the nightside?
• What is the rotation rate of magnetic flux tubes,
when there are strong shears in the convection due toa strong IMF By component?

features of polar cap patches, which are localized areas ofenhanced plasma density that are being transported withthe large-scale convection pattern (e.g. Jin et al. 2019b;
Oksavik et al. 2006; Moen et al. 2007). In fact, Carlson(2012) mentions that “Not until an incoherent scatterradar (ISR) measurements capability was created (...), wasit possible to put the various mechanisms proposed for
creating patches to a definitive test.” The authors usedmechanical scan modes to map the basic plasma parameters over a wide spatial area with temporal resolutionsof just a few minutes (Carlson et al. 2002, 2004; Carlson2012).
Polar cap patches (or more precisely gradients associated with them) are considered as one of the most important sources of small-scale irregularities in the polar cap
at F-region altitudes (Tsunoda 1988). Patches are believed
to be subject to the gradient drift instability (GDI) (Linson and Workman 1970; Simon 1963), which can cause
density irregularities to grow and reach sizes of the orderof the ion gyroradius (Tsunoda 1988) and kinetic scales(Gary and Cole 1983). Consequently, polar cap patches
become increasingly more fine-structured as they travel
across the polar cap (Weber et al. 1984; Gondarenko andGuzdar 2004), and may increasingly impact the transionospheric propagation of radio waves. Additionally,in situ observations, using rockets, of a patch with kmscale gradients present already near its origin close to thecusp regions (Spicher et al. 2015) reinforced the view that
other mechanisms, such as flow shears (Carlson et al.
2007) or particle precipitation (Kelley et al. 1982; Oksavik
et al. 2012), may initially structure the patches, leading tomulti-step processes.
Improving our understanding of polar cap patches, i.e.
their creation, transport, and exit into the auroral oval,
as well as the mechanisms responsible for their structuring is thus a crucial aspect for space weather mitigation(see Sect. 2.5) and to better understand development of
turbulence in plasmas. Additional capabilities to monitor patches came with the phased array radars allowing
to follow their formation and the associated cusp dynamics (Nishimura et al. 2021) and the structuring in 3D (e.g.
Dahlgren et al. 2012; Forsythe and Makarevich 2018;
Lamarche and Makarevich 2017; Lamarche et al. 2020).
With Svalbard being ideally located just below the “patch
entry” region (between 9 and 15 MLT) every morning, aphased-array system would provide invaluable information about patch creation and initial structuring, helping
addressing questions that could not be resolved with asystem providing observations in only one direction.
Polar cap patches are just one of the many dynamic
phenomena that is believed to be important in the context of plasma structuring at high latitudes (Keskinen
and Ossakow 1983; Kintner and Seyler 1985). Particle

2.2 Plasma instabilities, turbulence and ionosphericphenomena

The high-latitude ionosphere is known to be highly
inhomogeneous, with the presence of “irregular” structures (‘irregularities’) and instabilities. These instabilities, which may lead to turbulence, generally occur
when energy that has been stored unstably is redistributed (Baumjohann and Treumann 1997). The associatedplasma structuring occurs over scales covering several
orders of magnitudes from hundreds of kilometres toscale sizes shorter than the oxygen ion gyroradius (e.g.
Kintner and Seyler 1985; Kelley 2009; Nishimura et al.
2022; Spicher et al. 2022). Assuming it can be describedusing fluid-like turbulence models (to what extend this isapplicable remains an open question), it cascades fromthe energy source to the dissipation scales (Kintner andSeyler 1985). Characterizing high-latitude ionosphereshould thus both address the sources of energy, i.e. theprocesses leading to turbulence, as well as the natureof the irregularities, i.e. the characteristics of the fluctuations and energy redistribution. Inhomogeneities inplasma density and electric fields are predominant near
the cusp regions and around the auroral oval (e.g. Heppner et al. 1993; Jin et al. 2015, 2019), and fluctuations in
density can impact the propagation of trans-ionosphericradio waves (e.g. Basu et al. 1988a; Bland et al. 2018) as
well as signals from Global Navigation Satellite Systems(GNSS) (e.g. Carlson 2012; Jacobsen and Dähnn 2014).
The study of such structures has thus significant importance for our technology infrastructure (e.g. Moen et al.
2013) and is discussed further in Sect. 2.5 Studies using
current radar infrastructures, such as AMISRs, havehelped advance our understanding of irregularity growthand decay as well as effects on scintillations, especiallyin the polar cap and auroral regions (e.g. Dahlgren et al.
(2012); Forsythe and Makarevich (2018); Lamarche and
Makarevich (2017); Lamarche et al. (2020); Makarevich et al. (2021); Lamarche et al. (2022); Semeter et al.
(2017)).
ESR has contributed to better understanding of thehigh-latitude ionospheric plasma structuring at various scales (Kersley et al. 1988; Rinne et al. 2007; Carlson2012). Thanks to its fortunate location under the cusp,
where plasma enters the polar cap, it has been a pathfinder to shed light onto the formation and dynamic

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precipitation and inhomogeneous flows (such as RFEs,
detailed in Sect. 2.1) are fundamental features related
to auroral forms (Oksavik et al. 2004; Moen et al. 2008)
and commonly coincide with density irregularities (e.g.
Basu et al. 1988b; Dyson and Winningham 1974; Kelley et al. 1982; Oksavik et al. 2011; Spicher et al. 2016,2020). At macro-scales, F-region plasma structures may
result directly from low-energetic particle precipitation(Moen et al. 2002; Kelley et al. 1982; Millward et al. 1999)
or from instability processes in connection with fieldaligned currents (Kintner and Seyler 1985; Ossakow and
Chaturvedi 1979; Keskinen and Ossakow 1983). Inhomogeneous flows can, for instance, lead to shear instabilities
such as the Kelvin–Helmholtz instability (KHI) (Keskinen
et al. 1988) and to “stirring” (Kelley 2009; Burston et al.
2016) at large scales, and generate small-scale instabilities(Ganguli et al. 1994). Generally, the relative importanceof the different mechanisms responsible for the formation and evolution of plasma irregularities (and whether
the mechanisms actually occur) is not fully assessed.
This is partially due to observational limitations, as current research infrastructures do not provide volumetricmeasurements of densities and fields covering all thescales involved, making it impossible to fully monitor
both the sources and the irregularities ( e.g. Nishimura
et al. 2022). For instance, ESR “scans” combined within situ data were recently used as representative inputs
to numerical simulations of KHI (Spicher et al. 2020).
It could be shown that KHI could structure the plasma
quickly, however, the simulations could not be fully constrained because of “incomplete” observations, largely
due to restricted resolution. Consequently, contributions(or lack of contributions) from other mechanisms such
as GDI or precipitation could not be assessed. A new
system providing volumetric and higher-resolution data
would be necessary to evaluate the importance of the different mechanisms causing irregularities.
Testing turbulence theories also requires averaging
over 3D volumes (Kintner and Seyler 1985). Currently,
in situ studies of spectral characteristics associated withturbulence (e.g. Kintner and Seyler 1985; Ivarsen et al.
2019; Spicher et al. 2014, and references therein) provide merely information along the rocket or satellite
trajectories. Having a system providing high-resolution
multi-point measurement would help characterizing thenature of the structuring and the cascading of the energy
across the scales, using for instance aspects from techniques such as those applied to meteor radars (Vierinen
et al. 2019) or LOw-Frequency Radio interferometer
ARray (LOFAR) (Mevius et al. 2016). For GNSS disturbances, scale-sizes of the order of a few hundred meters
are crucial (e.g. Kintner et al. 2007). Furthermore, it
has been shown that several of the relevant instabilities

could possibly have fast growth rates (within minutes)(e.g. Makarevich 2016; Burston et al. 2016; Oksavik et al.
2012), with structuring evolving rapidly with time (e.g.
Deshpande and Zettergren 2019; Spicher et al. 2022).
Having a system encompassing the outer scales with resolution better than hundreds of meters (for GNSS related
studies) and smaller with sub-second temporal resolution
would thus be optimal.
A new phased array system on Svalbard would help
address outstanding questions including (e.g. Nishimura
et al. 2022):• Which mechanisms are important for triggering
plasma instabilities and forming ionospheric irregularities and when do they occur?
• How is energy distributed across different scales in
the ionosphere? Which scales are dominant for given
geomagnetic conditions?
• How does the energy cascade towards dissipation
scales and which processes contribute most to heating of the MLTI system?
• How does the coupling within the MLTI systemaffect irregularity creation and decay?
Further significant advances are expected in the auroral
regions using EISCAT​_ 3D (McCrea et al. 2015). However, as highlighted in this manuscript, the cusp is aunique region in the MLTI systems where irregularities
are also observed to peak (Jin et al. 2015, 2019a; Spogli
et al. 2009). A new phased array system on Svalbard,
working in tandem with the polar cap AMISRs (RISRN and RISR-C) would increase the combined ISR spatial coverage and allow greater tracking of turbulence
and irregularities as they move from their source region
across the polar cap region.
A new radar, with an unprecedented spatial resolution
across multiple latitudes and longitudes should also beable identify wave structures, which have their energy
source both internal (through e.g. drifting particle populations, (e.g. Baddeley et al. 2005; Mager and Klimushkin 2008) and external (through e.g. Kelvin-Helmholtz
wave signatures that propagate along the magnetopause(e.g. Rae et al. 2007; Samson 1991) to the Earth’s magnetosphere. Observations using optical instrumentation
have shown that the waves can structure auroral arcs (e.g.
Rankin et al. 2021 and references therein) and produce
multiple transpolar arcs (Zhang et al. 2020). ESR observations have also allowed the ionospheric heating andsmall scale field aligned current system associated withwave generated arcs inside the oval to be observed (e.g.
Baddeley et al. 2017; Pitout et al. 2003). Modelling work
investigating the structuring of the waves, along with theionospheric response, such as energy dissipation rates

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require high time resolution, altitude profile measurements of ionospheric conductivities and electric fields(e.g. Pilipenko et al. 2008; Fenrich et al. 2019). A new ISR,
with a 3D volumetric imaging capability will be able toprovide these.

The ESR has provided valuable information on local
ionization, which can be inferred from height profiles ofelectron and ion densities (e.g. Vickers et al. 2014; Bjoland et al. 2021). Upward acceleration due to the mirror forces depends strongly on the plasma temperature,
which has also been derived from ESR measurements
over a wide range of altitudes (e.g. Maeda et al. 2005).
ESR measurements of the vertical ion velocity (e.g.
Oyama et al. 2005; Yamazaki et al. 2017) have provided
information about the initial upflow process set up byelectrostatic fields. ESR observations also indicate thatcomposition of the outflow can be assessed (e.g. Vickers
et al. 2013). Likewise, recent studies using PFISR (Zouet al. 2017) have provided detailed observations of short
lived, but highly dynamic ion outflow resulting from asudden compression of the magnetosphere by the solar
wind. Comparison with a global MHD model provided
additional observational confirmation as to the validity ofthe model itself.
Due to their high orbital speed, low-altitude spacecraftin polar orbits can only provide snapshots of ionosphericparameters and processes of importance for ionosphericoutflow. Observations of cold plasma above the exobase
and in large regions of the magnetosphere are notoriously
difficult due to spacecraft charging effects (e.g. Moore
et al. 2016; André et al. 2021). Ground-based incoherent scatter radars do not suffer from these deficiencies.
An ISR radar can thus provide crucial information toenhance our knowledge about ion and neutral outflow inpolar regions. Outstanding questions include:

2.3 Ion outflow and neutral upwelling

As an important supplier of plasma, the ionosphere possesses a significant influence on magnetospheric properties and processes. In the polar cap, due to the fact thatthe magnetic field lines are open to the solar wind, nohydrostatic equilibrium exists. Consequently, ions canbe transported along magnetic field lines from the ionosphere to the magnetosphere (e.g. Chandler et al. 1991;
Yau and Andre 1997). Ions of ionospheric origin, primarily H+ and O+, are characterized by low thermal energy
of typically a few eV. The escape process is therefore
often referred to as cold ion outflow, which can have a
profound and direct effect on magnetospheric dynamics
since a mixture of cold plasma and/or heavier ions likeoxygen significantly alter fundamental plasma properties
and instability thresholds in various regions of the magnetosphere (e.g. Yamauchi 2019; Toledo-Redondo et al.
2021).
Ion outflow is a consequence of ionization of the upper
atmosphere combined with upward and outward transport, and thus depends strongly on local ionosphericconditions. Ionization is primarily driven by solar illumination and thus possesses a pronounced seasonal anddiurnal variation (e.g. Maes et al. 2015; David et al. 2018).
Upward motion of ions is initially driven by an ambipolar electric field set up by the difference in scale height
between electrons and ions. Additional acceleration
mechanisms such as the mirror force and the centrifugal
force (e.g. Comfort 1988; Cladis et al. 2000) provide further energization. Near the cusp and auroral zone, additional ionization and energization mechanisms, including
particle precipitation, Joule heating, quasi-static electricfields, and wave-particle interactions also operate (e.g.
Dandouras 2021).
Enhancements in neutral density have also been
observed at high altitudes (i.e. at 400 km and above) by
a variety of spacecraft (e.g. CHAMP at ∼ 400 km and
GRACE at ∼ 500 km (Kervalishvili and Lühr 2018). In thecusp region the neutral density is consistently enhanced
at these altitudes by ∼ 35% (Kervalishvili and Lühr 2013)and has been likened to ’speed bumps’ causing a deceleration in satellites passing thorough the region (Lühr et al.
2004). The enhancements have been linked to upwellingof neutral particles from the MLTI system. Suggested
energization mechanisms are similar to those proposed
for ion upwelling and outflow and the two are often seen
to occur in parallel (e.g. Kervalishvili and Lühr 2013).

• What is the relative contribution to ion and neutral
upwelling by Joule heating and soft particle precipitation in the cusp?
• What part does Alfvenic induced heating of the ionosphere play in enhancing the Joule heating rates?
• What is the role of local plasma conditions, such astemperature, density and vertical velocity, in ion outflow?
A challenge with the existing ESR is the limited signal-tonoise (S/N) ratio, in particular in the topside ionosphere(above the ionospheric F-layer). A higher transmitting
power, better beam control, and strongly improved S/Nratio, which would be a possibility with a new phasedarray ISR facility, will overcome this problem and allow
for a much better probing and characterization of thecritical altitude range between the F-layer and theexobase.
2.4 Energetic particle precipitation, EPP

Energetic particle precipitation (EPP), where incoming
protons and electrons have high energies of 1–1000 MeV,

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Page 11 of 24

and tens of keV to several MeV, respectively, can directly
impact the Earth’s mesosphere or upper stratosphereat altitudes as low as 30 km. The enhanced ionization
caused by the precipitating particles leads to increased
attenuation of radio waves and changes in the ion-chemistry and composition of the atmosphere. The effects on
the neutral atmosphere can propagate down to the lower
parts of the stratosphere and troposphere in the coupledatmospheric column.
ISRs are important for the studies of EPP and its effecton the coupled ionosphere-atmosphere system, as they
are the only instrument type that can provide a direct
measurement of ionization profiles during EPP. The ionization profiles are important for both ionospheric andatmospheric modelling as well as in studying the D region
ionosphere (e.g. Tesema et al. 2022; Verronen et al. 2016).
Ionization profiles or inverted spectra derived from radar
data can be used in conjunction with satellites to investigate particle precipitation sources and the phenomena
modulating the precipitating spectra (e.g. Miyoshi et al.
2015).
The enhanced ionization in the middle atmospherecaused by EPP leads to the creation of odd-hydrogen(HOx ) and odd-nitrogen (NOx ), which are both efficientat depleting ozone in catalytic reactions. In addition todestroying ozone where it has been produced, odd-nitrogen has a long lifetime in the polar night allowing it todescend inside the polar vortex down to approximately
30 km altitude where it can also deplete stratosphericozone (Jia et al. 2020). Changes in the ozone concentration of the middle atmosphere lead to variations of theradiative and chemical balance potentially affecting tropospheric climate through dynamical downward coupling.
This top-down mechanism, coupling energetic particle
precipitation and the surface climate, is a possible sourceof natural regional climate variability in the polar regions(Gray et al. 2010; Seppälä et al. 2014), which can become
more significant with climate change (Maliniemi et al.
2020).
EEP during substorms and pulsating aurora form aparticularly important part of EPP that affects the ozone
concentration (Andersson et al. 2014; Seppälä et al. 2015;
Tesema et al. 2020; Verronen et al. 2021). Observations
from incoherent scatter radars in the auroral regions havebeen used, for example, to study the source and precipitating spectra (Sivadas et al. 2017) of the electrons, EEP
effects on the neutral atmosphere (Enengl et al. 2021), thespatial extent of the precipitation (Cresswell-Moorcock
et al. 2013), and to create and validate precipitation models (Wissing et al. 2011).
Another category of EPPs is Solar Proton Events(SPEs). During SPEs the strongly increased ionization in

the middle atmosphere reaches to lower altitudes whichenables the use of ISRs to study the aeronomy of the middle atmosphere including, for example, the transition of
charge from free electrons to negative ions and the effective recombination coefficient (e.g. Collis and Rietveld
1990; Collis 1996; Hargreaves et al. 1987, 1993; Verronen
et al. 2006).
A new ISR located in the polar cap boundary region
would be beneficial to complement the existing networkof operational ISRs and EISCAT_3D at auroral latitudes.
The long periods of polar night and midnight sun in thehigh Arctic, on Svalbard, enable studies of middle atmospheric phenomena that are affected by solar illuminationin addition to EPP. An ISR in the polar cap would giveinformation on the increased ionization that produces­NOx and ­HOx within the relatively constrained atmospheric column of the stratospheric polar vortex during
winter. These observations could be correlated and contrasted with satellite-borne observations of the concentration of these chemical species.
EPP at the latitudes of the polar cap boundary region
is another important question itself. Due to fairly few
detailed or long-term observations, many assumptions
are typically made when discussing this topic. For SPEs apolar cap location could be used to study the uniformityof proton precipitation as a function of MLT and latitude(when contrasted with other observations from lower
latitudes). An ISR close to the polar cap boundary is also
perfectly positioned to study the contribution of high latitude pulsating aurora on the global EEP. These high latitude pulsating aurora events are almost only of the lessenergetic sub-type called amorphous pulsating aurora(Partamies et al. 2022). Furthermore, only by volumetric observations of electron density, will it be possible toresolve fine-scale precipitation within auroral structures,such as patchy aurora. A new ISR, on Svalbard, depending on placement and design (see Sect. 2.9 in regard to‘sea clutter’), would allow electron density profiles tobe measured deeper down into the atmosphere, which
would improve our understanding of both electron andproton effects in the high-latitude atmosphere. Some keyunanswered questions on EPP include:• What is the contribution of high-latitude EPP to theglobal energy deposition?
• How large is the electron contribution to the ionization during solar proton events?
• What is the role of spatial structuring of pulsating
aurora in the precipitation energy?
• How does the lower atmospheric composition effectthe ozone depletion during different EPP events?

Baddeley et al. Progress in Earth and Planetary Science(2023) 10:53

2.5 Space weather forecasting

Many of the phenomena described in the previous sections can impact man-made systems which modern
society is nowadays heavily reliant on. For example, signals from satellites orbiting around the Earth must passthrough the MLTI region to reach a variety of receiver
stations on the ground such as GNSS and communication devices. Structures and irregularities in the ionospheric plasma density, which are due to turbulence andinstabilities, have been shown to impact the propagationof radio waves through wave diffraction and refraction.
This leads to scintillation in the received signal, which inthe context of GNSS, can result in positioning errors, oreven loss of the satellite signal (e.g. Oksavik et al. 2015; Jinet al. 2019a; Moen et al. 2013; Prikryl et al. 2010; Semeter
et al. 2017). In addition to navigation and positioning services, GNSS satellites are also used in other critical infrastructure such as a global time management for banking
systems, financial institutions, power and communication networks. The ionospheric effects on the man-madeinfrastructure intensify during increased solar activity(which is often revealed through solar storms and coronal mass ejections (CMEs)), which can lead to geomagnetic storms. The associated strong ionospheric currents,
energetic particle precipitations, or plasma irregularities
can cause various problems such as HF blackouts (e.g.
Bland et al. 2018), failures in power grids and loss, failureor shutdown of orbiting satellites (Ferguson et al. 2015)
or previously mentioned disruption in the propagation oftrans-ionospheric radio waves. Geomagnetic storms canalso cause problems for directed drilling methods used by
the oil and gas industry (Reay et al. 2005). These effects
are all contained under the umbrella term ’Space Weather
Effects’, and many governments (e.g. USA (US Department of Homeland Security 2019), UK (UK Government,
Dept of Business Innovation and Skills 2015), Canada(Government of Canada 2021)) and the European Union(EU Department of Defence Industry and Space 2021)
have developed specific programs dedicated to the societal effects and mitigation plans in place in case of severe
space weather events. Some estimates for different typesof space weather events indicate a potential daily loss in
the Gross Domestic Product from 6.2 to 42 billion dollars
for the USA alone (Oughton et al. 2017). As such, there
is considerable ongoing effort directed towards models which will have the ability to forecast space weather
events, both in the long term but also, more importantly,
the short term (so called nowcasting). A loss of sea ice(amongst other reasons) has meant increased activity(such as shipping and tourism) in isolated areas within
the arctic regions. One aspect is related to navigation incomplicated and shallow waterways where a small disruption or error in navigation or communication systems

Page 12 of 24

can have far reaching consequences. The ability for space
weather forecasting with applications to more local, small
scale regions in specific areas of the Arctic is thus also
apparent. Studies have shown that the risk of systems
experiencing positing errors is greater at high latitudes(Jacobsen and Dähnn 2014). This is also reflected in the
global picture of ionospheric plasma irregularities andvariability (Jin et al. 2019a). A recent report looking intorisk and venerability around Svalbard (Governor of Svalbard (Sysselmesteren 2016)) specifically discusses space
weather and highlights the need for further investigation. The ability for ISRs to provide full altitude profiles ofdensities and temperatures of the MLTI system has significantly increased our understanding both in terms ofobservations of specific space weather events but also inthe context of providing data for, and developing physicsbased and semi-empirical global and local space weathermodels. A new phased array ISR on Svalbard is vital for
nowcasting and forecasting, as well as for modelling ofspace weather in the high latitude regions.
2.6 Meteoroid materials, polar mesospheric summer
echoes (PMSEs), ice and dusty plasma

The flux of cosmic dust and meteoroids which enter the
Earth’s atmosphere has been studied using radars sincethe 1940s. The cosmic dust injection also influences incoherent scatter through the formation of small solid dust
and ice particles predominantly in the lower parts of
the MLTI system (the D-region ionosphere—see Fig. 1).
These solid particles typically carry a surface charge andcontribute to the overall charge balance in the ionosphere. The presence of dust is also considered to facilitate the formation of ice particles including sizes below
the detection with optical observations. The cosmic dust
injection finally contributes to the formation of atmospheric layers, including the PMSEs observed with radars
that are also an important tracer of turbulence.
Meteor ablation is the loss of material from cosmic dust
and meteoroids at the transition between mesosphereand thermosphere (∼ 70 to 130 km). The free electrons
that are generated in the process give rise to the headechoof the meteor (Pellinen-Wannberg 2005), which travels
with the entering particles, and to the trail, which extends
along the entering trajectory for some time. High power
and large aperture radars, such as ISRs, allow observations of the headecho from high electron density region
surrounding an ablating meteor (e.g. Kero et al. 2019, andreferences therein) and at the same time the conditionsof the surrounding ionosphere (Pellinen-Wannberg et al.
2016). For a meteor radar, the advantage of a high latitude location is a better visibility of the high inclination
portion of the meteor population which provides information on the orbital and collisional evolution of small

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Page 13 of 24

solar system objects. The main feature missing from theexisting ESR system is that it suffers from sea clutter that
reduces sensitivity to meteor headechoes, because bothoriginate at a similar distance from the existing radarsite. Additionally, the system cannot interferometricallymeasure the position of the meteor headecho within theradar beam, which prevents observing a trajectory or an
unbiased radar cross section. Consequently, a future ISR
should have interferometric capabilities.
The middle atmosphere contains ice and dust particles that are influenced in their dynamics by the neutral
atmosphere and through charge interaction to the ionosphere, hence forming a dusty plasma. The ablation of
meteors entering into the atmosphere leads to the formation of small solid particles: meteoric smoke particles.
In summer the temperature near the mesopause at highand mid latitudes is so low that ice particles form, mostprobably through heterogeneous condensation onto themeteoric smoke. Satellite observations enable us to study
some of the ice particles in Polar Mesospheric Clouds(PMC) at heights from 80 to 85 km (Hervig et al. 2001).
These solid particles contribute to the overall charge balance. Through this they influence the chemistry which
is mainly ion reactions at this altitude. Dust charging
includes the attachment of electrons and ions, photoionization, photodetachment, and secondary ion emission.
The first two processes depend on the conditions of theambient ionosphere and also feedback to the ionosphere(Baumann et al. 2013). The long polar night allows investigations of the processes independent from those thatare related to the solar photon flux. Finally, the electron
precipitation couples to the charging through secondary
electron emission (Baumann et al. 2016). The charged
dust component influences the incoherent scatter observations (Rapp et al. 2013), and dust parameters are best
retrieved under conditions of high electron content andin combination with independent measurement of theneutral temperature (Gunnarsdottir and Mann 2021).
The structure and occurrence rates of PMCs are latitude dependent and satellite observations have only limited capabilities to reveal characteristics such as their
spatial structure (Gao et al. 2017), which is influenced
by dynamic processes like upward propagating waves.
The formation of PMCs and other coherent echoes isalso linked to neutral atmosphere dynamics, because
it involves its spatial structures. In addition, the mesospheric neutral temperature in the MLTI system ishighly variable and causes formation and destruction ofice particles. The dust interactions are latitude dependent
because they are influenced by ionospheric variability as
well as global atmospheric circulation and turbulence inthe neutral atmosphere.

Meteor ablation injects metallic ions into atmosphereand contributes to the formation of metal layers around80 to 110 km including sodium, which is most extensively
studied, but also iron, potassium, calcium and magnesium layers (e.g. Plane et al. 2015). The ice particles also
contribute to the formation of PMSEs. A topic of ongoing
research is to find out whether meteoric smoke particles
also contribute to the formation of coherent radar echoesthat are observed during other times of the year, i.e. Polar
Mesospheric Echoes or Polar Mesospheric Winter Echoes (Latteck and Strelnikova 2015).
The main questions of scientific interest are:• What is the influx of meteoric matter into the Earth’s
atmosphere?
• What is the distribution of orbital elements, composition, and sizes of meteoroids that cross the Earth’s
orbit?
• What are the consequences of meteoric matter to the
Earth’s atmosphere?

2.7 Space debris

Space is a valuable resource with wide-ranging societal andeconomical impacts. Earth orbiting satellites are crucial forenvironmental monitoring, navigation, and telecommunication. In the future, satellite services will be the most costeffective way of connecting half of the world’s population to
the internet. The number of man-made objects in Earth orbit
have steadily increased during the last 50+ years. The threatof a collisional cascade chain reaction unfolding in space was
identified by Kessler and Cour-Palais in 1978 (Kessler andCour-Palais 1978; Kessler et al. 2010). In 2020, there were
estimated to be approximately 106 objects over 1 cm in diameter in Earth orbit (Horstmann et al. 2021) and several orbital
regions may have already passed the critical density where
the collisional cascade chain reaction will start increasing thenumber of objects even if no new objects are launched.
The outlook for the future is challenging for humanity.
The number of objects in space will keep increasing due to
new launches and fragmentation events such as collisions
and explosions occurring in space on a fairly regular basis.
Recently, it has also been suggested that atmospheric dragexperienced by spacecraft will be reduced in the future due
to changes in radiative transfer caused by increased atmospheric CO2 content in the Earth’s troposphere, followedby subsequent cooling in the topside atmosphere. This willcause significant increases in orbital lifetimes of space debris
objects, which will further exacerbate the situation.
Continuous monitoring and development of more
tracking capacity are the primary means of mitigating therisks associated with the increased number of hazardous

Baddeley et al. Progress in Earth and Planetary Science(2023) 10:53

space objects. Observations with ground-based radars
are the most important method for characterizing the
population of space objects in Earth orbit (Klinkrad
2006). This includes calibrating statistical models ofspace debris (Flegel et al. 2009; Krisko 2014) using beampark surveys, as well as maintaining a catalogue of orbital
elements for specific objects. At the moment, the US
Space Command maintains the largest catalogue, whichcontains approximately 25,000 objects. This only covers asmall fraction of the > 1 cm diameter objects, which arethought to be potentially hazardous.
The IPY dataset obtained by ESR between 2007 and2009 was used to study the evolution of space debris asa secondary data product derived from the ionosphericradar experiment (Markkanen et al. 2009). This measurement period also coincided with the Chinese antisatellite experiment in January 2007, allowing studies of
distribution and evolution of the resulting space debris
to be made. Since then, EISCAT radar measurements
have played an important role in characterizing the spacedebris produced by several other major fragmentation
events, such as the 2009 Iridium-Cosmos satellite collision (Vierinen et al. 2009) and the 2019 Indian anti-satellite experiment. Validation of statistical space debris
models relies on regular beam-park radar observations.
An ISR is typically useful for characterizing objects
with diameters approximately larger than 0.1, (where is the radar wavelength), as smaller objects will be in
the Rayleigh scattering regime with significantly reduced
radar cross sections. The 60 cm wavelength of the existing ESR system is already relatively well suited for tracking even smaller size debris, but the smallest diameter ofpotentially hazardous objects will still be outside of reachdue to a too small radar cross section.
The primary physical parameters that a radar system
would need for observing space debris is an unbiased
observation of the radar-cross section, as well as the ability to make observations of the trajectories of objects.
None of the existing EISCAT systems have these capabilities at the moment. There are two ways to technicallyachieve these goals: 1) using a tri-static measurement
geometry like EISCAT_3D (Vierinen et al. 2017), or 2)
using interferometric angle of arrival determination. The
second option has the advantage that it can be accomplished with just one radar site.
One possible synergy with a space object tracking capable radar in Svalbard is that it can be used for diagnostics
and launch support for future spacecraft launches from
Andøya Space Port.
2.8 Supporting infrastructure

Svalbard provides a unique location, with the long polarnight (nearly three months of 24 h of darkness), ideal forPage 14 of 24

Fig. 3 Modelled fields-of-view (fovs) for both the new EISCAT_3D
system (located in Mainland Northern Norway) and a new ISR system
on Svalbard. A 30◦ elevation cut off and a vertical boresite is used
for both fovs. The colour codes indicate the fov at the different
altitudes, as indicated in the legend

the ionospheric cusp to be easily identified by groundbased radars and optics. The darkness allows for its
effects to be easily separated from those due to solar EUV
radiation, something that is logistically, extremely challenging to do with multiple ground-based instrumentation anywhere else on the globe. Consequently, Svalbard
has a long history of ground-based MLTI measurements, starting with the first international polar year in
1882–1883.
A permanent optical station has been in place in Longyearbyen since 1978; first in the Adventdalen valley,
and since 2008 on the Breinosa mountain as the Kjell
Henriksen Observatory (KHO 2022), the largest optical observatory for auroral studies in the world. Optical
instrumentation now exists at all four main settlementsof Svalbard (Longyearbyen, Ny-Ålesund, Barentsburg
and Hornsund). In addition, Svalbard is hosting multiple GNSS receivers, HF transmitters, ionosondes,
dynasondes, riometers, ground magnetometers, anatmospheric MST radar (SOUSY), and an additional
upper atmospheric HF radar (SuperDARN, Chisham
et al. 2007). The ionosphere above Svalbard also benefits from being inside the field-of-view of two additional
SuperDARN radars located in Finland and Iceland. The
ESR is co-located with several of these facilities on the
Breinosa mountain. Scientists from over 15 (as of 2022)

Baddeley et al. Progress in Earth and Planetary Science(2023) 10:53

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countries have instrumentation in the area dedicated tostudies of the MLTI system.
Andøya Space Center (ASC 2022) operates two sounding rocket launch sites: one in Andøya (northern mainland Norway) and one in Ny-Ålesund (Svalrak). Bothsites are capable of launching scientific payloads into the
MLTI region above and around Svalbard.
The Svalbard archipelago is home to a vast research
network of monitoring stations covering diverse topics
such as biology, geology, glaciology, meteorology, oceanography, technology, and science tourism, in addition to
the instrumentation located in the 4 main settlements
mentioned above.
The University Centre in Svalbard (UNIS 2022) inLongyearbyen is the world’s northernmost higher education institution. UNIS provides research-based education for the next generation of Arctic experts in biology,
geology, geophysics and technology. The Arctic Geophysics Department owns and operates KHO, the Svalbard
SuperDARN radar, as well as other smaller instrumentation. UNIS offers courses to Bachelor/Masters/PhD students from across the world with a dedicated hands-on(or field) experience. For the MLTI courses this involves
fieldwork at the ESR and KHO. Educating the next generation of scientists and providing them with hands-on
experience and skills is of critical importance. Crossdisciplinary research is necessary to obtain a complete
understanding of the coupled Earth system. Recent work
has highlighted the effects of the solar wind and the IMF
on tropospheric pressure and temperatures (below 10 km
height) (e.g. Lam et al. 2014; Burns et al. 2007).
Support for research is also given through Svalbard
Integrated Earth Observing System (SIOS 2022) and
Svalbard Science Forum (SSF 2022). In addition, Svalbard hosts the only commercial satellite ground station in
the world that is capable of fully supporting all upload/
download telemetry needs of a polar orbiting satellite(14 out of 14 orbits per day). The satellite station is operated by Kongsberg Satellite Services (KSAT 2022), and itis the largest in the world with more than 100 telemetry
antennas. It supports several satellite missions including
the ESA Landsat and Sentinel missions and the NASANiSAR and PACE missions.
Both Longyearbyen and Ny-Ålesund (about 120 km
further north) have high-speed (Gb) internet connection via optical fibre. This allows high-speed download,
remote monitoring, and operation of scientific equipment. Longyearbyen is a thriving community with a dedicated power station and serves as an air and sea transport
hub for equipment and people to the Norwegian mainland. The combination of research infrastructure, commercial investment, and community support is uniquefor a high Arctic region (at nearly 80◦N). Historically,

coal mining was the main industry on Svalbard, but thisera is soon coming to an end. Currently, Norway has only
one single mine in operation (Mine 7 at Breinosa), whichis due to cease operations in 2025. Longyearbyen, andSvalbard as a whole, is now prioritizing further scientificresearch into renewable energy and climate change, with
science tourism and satellite upload/download capabilities as the main areas for financial development. It is thus
an ideal time to develop the next generation of ISR on
Svalbard.
2.9 Location and radar design

Whilst the specific location for such a facility is not themain subject for this report, various design possibilities
and considerations (logistical as well as scientific) will bebriefly presented here. The current ESR is located about
20 km outside Longyearbyen, on the mountain Breinosa.
It consists of two cassegrain dishes (one 42 m in diameterthat is fixed parallel to the magnetic field lines, one 32 m
in diameter that is fully steerable). The system is fed by asingle transmitter system consisting of 16 klystrons. The
site is connected to an optical network fibre and main
power, with a backup battery bank in case of power cuts
to maintain emergency heating, lighting and computerfunctions (but not to power the transmitters). There is aroad to the site, which must be cleared from snow regularly over the winter season. It is currently maintained
jointly by the local coal mining company and EISCAT. It
is currently unclear how road access to Breinosa will beafter closing of the coal mine (Mine 7) in 2025. One issue
with the current site is backscatter from the nearby fjords(sea-clutter) in the side lobes. Due to its dynamic nature,
it is not something that can be easily filtered out by the
analysis software (unlike a mountain, which is generally
less dynamic). As a consequence, it has limitations forthe ability to monitor the lower parts of the MLTI system. For a new site location closer to Longyearbyen, it
should be noted that there is an ongoing hearing (as of2022) in regard to designating the land near Longyearbyen (lower Adventdalen) as a protected environmental
area (Govenor of Svalbard (Sysselmesteren 2022). These
highlighted issues must be taken into account when thelocation for the new facility is decided.
A new system will be of a phased array design forreasons highlighted earlier; the advanced technology
allows near instantaneous monitoring of multiple directions simultaneously, with no moving parts, and notreliant on a small number of transmitter units (reducing risks of a single point of failure). This technology
has been proven very successful in high Arctic conditions (RISR-N, RISR-C, PFISR). RISR-N and RISR-C
rely on diesel generators for power, whilst PFISR has
mains power. Various ISRs use different operating

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Fig. 4 Schematic showing the different MLTI phenomena described in the paper. The large scale infrastructure on Svalbard (optics, SuperDARN
and the proposed ISR) are also shown

frequencies. The current ESR has an operating frequency of 500 MHz. PFISR operates at 449 MHz, RISR
at 442 MHz, and the new EISCAT_3D system will operate at 223 MHz. The frequency, and thus wavelength,  ,of the transmitted signal has direct implications for thedesign of the transmitters and also the scale sizes of thetargets it can observe.
An ISR is designed to maximize the received signal
power which is based on a variety of parameters (somecontrolled from a design point of view, and some controlled by the nature of the target and the distance toit). The generalized for m of the radar equation, in thecase of a homogenous beam filling target of volume Vs ,relevant for ISR (e.g. Farley 1996; Bowles et al. 1962) is:Pr =Pt Gt Ae
(4π )2 Rt2 Rr2

σr dVsVs(1)where Pr is the received power, Pt is the transmitter
power, Gt is the transmitter antenna gain, Ae is the effective area of the receiving antenna. The latter two terms(Gt and Ae ) are also dependant on radar wavelength, .
Rt is the distance from the transmitter to the target, Rr
is the distance from the target to the receiver and σr isthe radar scattering cross section of the target. From thisequation it can be seen that, unsurprisingly, by increasing the transmitted power, the received power is also
increased. However, the received power can also be
increased/decreased by varying the size of the antenna
field itself Ae , and the operating wavelength . This allows
some degree of flexibility when considering the size ofthe antenna field and the power source.
The spatial extent and shape of an ISR beam is determined by its radiation pattern. This, in turn, is determined by a number of design factors related to, amongst
other things, the size and number of the antenna elements and the relative distance between them. The
main pointing direction (or boresite) also influences
the shape of the radiation pattern. For the EISCAT_3D
system the main site will have a near vertical boresite (elevation angle ∼ 90◦ ). The AMISRs (which aremounted on a large panel system that is titled relative
to the ground), have a boresite with elevation anglesof ∼ 74◦(PFISR) and ∼55◦(RISR). The advantage of asmaller elevation angle is that the total radar field ofview (the furthest extent in azimuth and elevation thatthe radar beams can be electronically steered to) canbe tilted and extended towards a particular latitude
and longitude direction. The caveat is the limitation itBaddeley et al. Progress in Earth and Planetary Science(2023) 10:53

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introduces for the location of the radar, requiring no
substantial objects (e.g. mountains) in their immediate vicinity. A phased array design could also include
an electromagnetic fence to mitigate unwanted scatterfrom non-atmospheric objects (such as the aforementioned sea-clutter). These facts should all be consideredwhen a location for the system is decided. The flexibility of a new phased array system, in terms of number ofbeams, pointing directions and range resolution (operating modes), is one of its great benefits. Although thebeam steering is now electronic (and thus can be doneat the sub millisecond rate) there is still a trade-off tobe negotiated between the spatial and temporal coverage. The signal-to-noise ratio on any particular beam
(determined by the dwell time) must be sufficient toallow meaningful ionospheric parameters to be derived(i.e. with acceptable variances). Additionally, the range
resolution (along the beam) is determined by the pulse
length whilst the horizontal resolution is determinedby the angular beam width and the operating frequency(all factors still to be determined for the new system).
As a comparison, although the operating mode choices
can be almost endless, the AMISRs tend to focus
around some specific modes, dependent on the phenomena under observation. Gillies et al. (2016) used
an 11 beam scan at 1 min resolution, with the beams
separated such that it produced a ‘scan’ with a horizontal resolution of 0.25◦ magnetic latitude. Bahcivan et al.
(2010) used a similar scan with a long pulse experimentresulting in 72 km range resolution. Dahlgren et al.
(2012) extended the field of view using 25 beams in a 5
x 5 grid formation with a 1 min resolution. The grid had
a horizontal extent of 300 x 400 km at F-region heights(300 km). One of the highest spatial and temporal resolution modes was documented by Semeter et al. (2009).
The authors used a mode giving an 11 x 11 grid with a
14.6 s resolution. The grid had a horizontal extent of 65
x 60 km at E-region heights (100 km). The beams were
2 km wide with a 1.5 km range resolution. A new imaging technique called aperture synthesis radar imaging(ASRI) (e.g. Woodman 1997; Hysell and Chau 2012)
could be applied to improve the horizontal resolution.
This has been successfully implemented on other radarsystems such as Jicamarca where the effective angularbeam width was improved from ∼ 1 ◦(typical resolution
for standard ISR system) to ∼ 0.1◦ (Chau and Woodman 2001). Modelling work by Stamm et al. (2021)
has shown that ASRI could deliver an effective angularbeam width of ∼ 0.05◦ resulting in a horizontal resolution of ∼ 90 m at E-region altitude of 100 km using the
EISCAT_3D core transmitter site only. Such a set up
could be possible with the new Svalbard ISR. It is envisaged that the new ISR system will have similar, if notbetter, operating capabilities as the AMISRs (given theadvance in technology since the AMISRs were built).
The new ASRI technique also holds distinct promise.
As such the new radar will vastly improve the ability
to observe a variety of phenomena inside the polar cap
and cusp at a far higher spatial and temporal resolution
than is currently possible.
Whilst it is clear that the ISR must be of the phasedarray type, it is unclear whether a mono-static or bistatic configuration would be possible. The advantage
with mono-static systems is that the transmitter and thereceiver is co-located. In terms of operations this meansthat the microsecond timing required when transmitting and receiving the radar signal does not rely on afast internet connection. The disadvantage is that, whilst
full vector quantities can be obtained, they still requirea beam swinging technique with some assumptions
made about the ionosphere. A mono-static system, suchas the AMISRs, would still be a vast improvement overthe current system. Both RISR and PFISR have provided
valuable new insight into polar cap phenomena in great
detail (e.g. Dahlgren et al. 2014; Lyons et al. 2011; Gabrielse et al. 2018). In addition to the ASRI technique, a colocated interferometer array could also add additional
functionality, providing additional possibilities for datawith a sub-beam horizontal resolution (Grydeland et al.
2005). The ideal location for the transmitter would bein the vicinity of the main settlement of Longyearbyen,
with access to mains power, network, and transport
links. Since the power requirements for reception is several orders of magnitude less than that of the transmitter, then proximity to a large power supply is not crucial
for the receiver system. Consequently, a possible location
for a remote receiver system may be Ny-Ålesund, with its
high speed network capability.
An example field of view of a phased array radar
located near Longyearbyen is shown in Fig. 3. A 30 ◦ elevation cut off and a vertical boresite is used for the figure. The field of view of the new EISCAT_3D radar is also
shown for context. The three coloured contours show
the field of view of each radar at 125 km (green), 300 km(red), and 800 km (blue). As mentioned earlier, the fieldof view of the new EISCAT_3D site will not reach up to
the cusp and polar cap at ionospheric altitudes. The figure illustrates how a near continuous field of view at ionospheric altitudes would be possible when EISCAT_3D iscombined with a new Svalbard ISR. The two fields of view(at 300 km altitude) are also superimposed onto Fig. 2 (at4 different MLTs showing how the combination of thesesystems would allow tracking of MLTI features into thedayside cusp and polar cap, and then out of the nightside polar cap and into the nightside auroral oval. As
stated earlier in the paper, it is envisaged that the radar

Baddeley et al. Progress in Earth and Planetary Science(2023) 10:53

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is coming towards its end-of-life within the next 10 years.
A prudent timeline, for the user community to work towould thus be to look towards having initial funding inplace for a design study within the next 5 years, with theaim for a new radar system to be in place (either fully
operational or have entered the building stage) within thenext 10 years.

the lunar surface of the interaction of the solar wind
and the Earth’s magnetic field. LEXI is a NASA mission to launch in 2024.
4. The Solar wind Magnetosphere Ionosphere Link
Explorer (SMILE) (Branduardi-Raymont et al. 2018)
will obtain soft X-ray images of solar wind plasma
entry at the magnetopause and into the cusps, andUV images of the Northern Hemispheric auroral
oval. SMILE is a joint mission between ESA and theChinese Academy of Science to launch in 2025.

2.10 Importance of a cusp ISR for satellite and rocket
missions

The benefits of coordinated observations in both groundand space are well demonstrated across the researchcommunity. These have ranged from single spacecraft
missions (e.g. CHAMP, IMAGE, POLAR), via multiple
spacecraft flying in close formation (SWARM, CLUSTER, MMS), to satellite networks (e.g. DMSP, IRIDIUM,
POES). Spacecraft provide in situ observations of thedrivers or energy sources of the system through measurements of plasma and magnetic field parameters, dynamical processes, and boundary locations in the solar wind,magnetosphere, and topside ionosphere. Space-based
imagers can provide optical observations at multiple
wavelengths of various auroral features (e.g. IMAGE,
POLAR, DMSP, Reimei). Ground-based observations
reveal both the energy sink inside the Earth’s MLTI system (e.g. auroral features, turbulence, convection) andalso the drivers of processes which feed energy and mass
back into the magnetosphere (e.g. ion and neutral outflow) as is detailed in the previous sections.
Several new space missions will soon target the cusp
and polar cap ionosphere with innovative instrumentation far beyond the state-of-the-art. At least four missions have strong links to Norway, with co-investigatorsfrom multiple universities and/or strong scientific interest. Close conjunctions with the current ESR, and theadjacent facilities in Svalbard, play a key role for a newera of ground-breaking MLTI science:
1. The Electrojet Zeeman Imaging Explorer (EZIE 2022)
are three small satellites that will obtain magnetic
field measurements at 80 km altitude of the auroral electrojet via remote sensing using the Zeeman
effect. EZIE is a NASA mission to launch in 2024.
2. The Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS 2022) are
two identical satellites that will target spatial/temporal variation the Earth’s cusps with a separation of
only 10 s to 120 s. TRACERS is a NASA mission tolaunch in 2024.
3. The Lunar Environment Heliospheric X-ray Imager(LEXI 2022) will take global soft X-ray images from

In addition, the ground-based facilities at Svalbard haveplayed a prominent role in several mission concepts
like the NASA Meme-X (Moore et al. 2016) and the
ESA ESCAPE proposal (Dandouras et al. 2017).
Sounding rockets provide the only means by which’in situ’ observations of the MLTI system is possible.
The altitudes of interest are generally too high for highaltitude balloons (which are limited to below about
30 km) and not feasible to maintain with a low altitude spacecraft (due to satellite drag). As mentioned in
Sect. 2.8, Andoya Space Center, operates two sounding rocket launch sites both able to launch rockets
into the cusp region above or around Svalbard. The
recent Grand Challenge CUSP (CGI-CUSP) projectin 2018–2021 (Blix et al. 2019), involved 12 sounding
rockets funded by the space agencies of USA, Japan,
and Norway. The current ESR has provided groundsupport to many rocket missions, e.g. SERSIO (Lorentzen et al. 2007), CUSP (Burchill et al. 2010), ICI-2(e.g. Lorentzen et al. 2010; Moen et al. 2012; Oksavik
et al. 2012), ICI-3 (Spicher et al. 2015), RENU2 (Lessard
et al. 2020), SCIFER-2 (Lund et al. 2012) and CAPER2(Moser et al. 2020). For each rocket mission the ESR
is providing both real-time monitoring of the MLTI
system (crucial for launch decisions) and larger scale
context observations of the MLTI system throughout
the rocket flight. The ESR data sets are vital in allowing the detailed (very high temporal and spatial resolution) rocket observations to be understood and related
to the dynamics of the larger scale turbulence andprocesses within the MLTI system, prior to, after andduring the rocket flight time. The upcoming CGI-MLT(mesosphere lower thermosphere) project, 2022–2026)(Grand Challenge 2022) will also play an important rolein understanding the vertical coupling of atmosphericlayers in the MLTI system. This combination of available ground-, space- and rocket-based instrumentationis unique in the world and means the required crossscale, 3D approach can be taken, as highlighted by thereview papers in Sect. 1.

Baddeley et al. Progress in Earth and Planetary Science(2023) 10:53

3 Conclusions
The current ESR has provided an unprecedented datasetof parameters needed to characterize the MLTI region
over Svalbard, inside the cusp and polar cap regions. This
paper has summarized some of the main research topics
along with examples of how the data from the ESR has
proved vital in increasing our understanding on how
energy, mass and momentum is transferred and dissipated into the MLTI system. The paper has also provided examples of unanswered scientific questions within
the research field and provided a compelling argument
as to how a new phased array ISR on Svalbard would
address these questions. This paper discusses how Svalbard remains unique in the world in terms of its ability
to monitor the cusp region with multiple ground- androcket-based instruments. It has excellent support infrastructure, both in terms of logistics and educational
opportunities for the next generation of scientists andengineers. The new radar is also in a unique position in
its ability to provide data and monitoring in two relatively
new areas of societal concern—space debris and space
weather events. With its volumetric imaging across various spatial and temporal scales a new ISR would provide
the required data sets discussed and highlighted as a priority in the recent review papers (e.g. Sarris 2019; Palmroth et al. 2021; Heelis and Maute 2020). The location of
the radar and the proposed field of view will also complement the new EISCAT_3D system on the mainland,
allowing a near continuous coverage of the auroral, cusp
and polar cap regions from 65◦ to 82◦ latitude. A new
Svalbard ISR system should thus be a priority for the scientific community.
Abbreviations
EISCAT​	European Incoherent Scatter Scientific Association
PFISR	Poke flat incoherent scatter radar
RISR	Resolute bay incoherent scatter radar
IPY	International polar year
MLTI	Mesosphere/lower thermosphere/ionosphere system
ESA	European Space Agency
ESR	EISCAT Svalbard radar
EZIE	Electrojet Zeeman Imaging Explorer
LEXI	Lunar Environment Heliospheric X-ray Image
NASA	National Aeronautics and Space Administration
SMILE	Solar wind Magnetosphere Ionosphere Link Explorer
TRACERS	
Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites
Acknowledgements
LB acknowledges helpful discussions with R. Varney (UCLA) and C. Heinselman(EISCAT director) in the writing of this manuscript. We acknowledge the Community Coordinated Modeling Center (CCMC) at Goddard Space Flight Centerfor the use of the IRI-16 and NRL-MSIS 2.0 models https://​ccmc.​gsfc.​nasa.​gov/​
models/​IRI~2016/https://​ccmc.​gsfc.​nasa.​gov/​models/​NRLMS​IS~v2.0.
Author contributions
LB proposed the topic, organized the paper and assigned tasks to the coauthors. Individual co-authors took a lead on writing the different sections of
the paper. All authors read and approved the final manuscript.

Page 19 of 24

Funding
This work was funded through Norwegian Research Council Grant: 329681.
Availability of data and materials
Not applicable.

Declarations
Competing interests
The authors declare that they have no competing interest.
Author details
1
University Centre in Svalbard, Postboks 156, Longyearbyen, Svalbard 9171,
Norway. 2 UiT The Arctic University of Norway, Tromsø, Norway. 3 Departmentof Physics and Technology, Birkeland Centre for Space Science, Universityof Bergen, Allégaten 55, Bergen 5020, Norway. 4 University of Oslo, Oslo,
Norway.
Received: 2 November 2022 Accepted: 20 August 2023

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