#  AuroraMag: Twin Explorer of Asymmetry in Aurora and Solar Wind-
Magnetosphere Coupling

Ankush Bhaskar<EMAIL_ADDRESS>Jayadev  Pradeep Shyama
Narendranath Dibyendu  Nandy Bhargav  Vaidya Priyadarshan  Hari Smitha V.
Thampi Vipin K.  Yadav Geeta  Vichare Anil  Raghav Dibyendu  Chakrabarty R.
Satheesh  Thampi  Tarun Kumar Pant

###### Abstract

In the present-day context, small satellites and their constellations
consisting of varying sizes (nano, micro, pico satellites) are being favored
for remote sensing and in situ probing of the heliosphere and terrestrial
magnetosphere-ionosphere system. We introduce a mission concept aimed at
concurrently observing Earth’s northern and southern auroral ovals while
conducting in situ measurements of particles, fields, and temperature. The
mission concept consists of two small satellites, each having an identical
auroral X-ray imager, an in situ particle detector, a magnetometer pair, and
an electron temperature analyzer onboard in an elliptical polar orbit
(400X1000 km ). This mission would assist the space weather community in
primarily answering important questions about the formation, morphology, and
hemispherical asymmetries that we observe in the X-ray aurora, the fluxes of
precipitating particles, Solar Energetic Particles, currents, and cusp
dynamics. Once realized, this would be the first dedicated twin spacecraft
mission of such kind to simultaneously study hemispheric asymmetries of solar-
wind magnetosphere coupling. This study reveals the intricacies of the mission
concept, encompassing orbital details, potential payloads, and its underlying
scientific objectives. By leveraging the capabilities of small satellites,
this mission concept is poised to make significant contributions to space
weather monitoring and research.

###### keywords:

Aurora, solar wind-magnetosphere coupling, smallsat mission , X-ray ,
asymmetry

††journal: Advances in Space Research

[1]organization=Space Physics Laboratory, Vikram Sarabhai Space Centre, ISRO ,
city=Trivandrum, postcode=, country=India

[2]organization= U. R. Rao Satellite Centre, ISRO , city=Bengaluru, postcode=,
country=India

[3]organization= Indian Institute of Geomagnetism , city=Mumbai, country=India

[4]organization= Indian Institute Technology- Indore , city=Indore,
country=India

[5]organization=Center of Excellence in Space Sciences India, Indian Institute
of Science Education and Research Kolkata , city=Kolkata, country=India
[6]organization=Depratment of Physiscs, University of Mumbai , city=Mumbai,
country=India

[7]organization= Indian Institute of Space Science and Technology ,
city=Trivandrum, country=India

[8]organization= Physical Research Laboratory , city=Ahamdabad, postcode=,
country=India

##  1 Introduction

Understanding and predicting space weather has become of paramount importance
in the current space era as the number of satellites will continue to increase
along with the usage of space (Virgili et al., 2016). The continuous stream of
particles originating from the Sun, known as Solar wind, compresses the
Earth’s magnetic cavity, forming a comet-like structure. Figure 1 shows the
Magnetohydrodynamic simulation of the solar wind-forced space environment of
the Earth and reveals the typical global-scale configuration of the steady
state magnetosphere (Das et al., 2019). The supersonic solar wind carrying
solar magnetic fields impacts the Earth’s magnetosphere from the day side
(left of image), forming a bow shock structure around the magnetopause which
plays a crucial role in shielding the inner atmosphere from the solar wind. On
the night side, magnetic reconnection and dynamics induced by the solar wind
lead to the formation of an extended magnetotail and a current sheet.

The solar wind magnetosphere coupling is the key to understanding and
forecasting the influence of solar wind on the Earth’s space environment. The
colorful displays in the northern and southern high latitude region, known as
Aurorae are an excellent manifestation of this coupling. Humans have observed
auroras since the Stone Age, but scientific study has only developed in recent
centuries(for example Eather (1980); Hayakawa et al. (2015); Bhaskar et al.
(2020)).

Fig. 1: The global shape of the magnetosphere is very well depicted by the
Magnetohydrodynamic simulation. Also, it clearly shows local time asymmetries
in the shape and configuration of the magnetosphere. Magnetic fields are
depicted by curved lines, with deep red, yellow, and green depicting solar
wind, magnetosphere, and reconnected field lines, respectively.

Aurorae have been observed on several planets besides Earth, including Jupiter
and Saturn (Bhardwaj & Gladstone, 2000; Tao et al., 2011). Ever since the dawn
of the space era, aurora has been observed routinely by space-based imagers
like imagers onboard NOAA and DMSP satellites, along with ground-based
networks in high latitude region(Frank & Craven, 1988; Lühr et al., 1998;
Chisham et al., 2007; Burch, 2000). After decades of research using space and
ground-based platforms, there remain several unresolved questions that require
investigation to better understand solar wind-magnetosphere-ionosphere
coupling. One of the key features of aurora is its hemispherical asymmetry.
Studying the asymmetry of auroras in the Northern and Southern Hemispheres is
important in the field of space weather and planetary science. There are only
a handful of reports (Laundal & Østgaard, 2009; Liou & Mitchell, 2019)
containing investigation on the auroral asymmetry.

There are some constraints to using ground-based simultaneous observations of
both hemispheres have a narrow field of view and do not capture full auroral
shape. In the past, The Imager for Magnetopause-to-Aurora Global
Explorer(IMAGE)-like missions had some sporadic coverage of simultaneous
observations of the aurora (Laundal & Østgaard, 2009; Liou & Mitchell, 2019).
Defense Meteorological Satellite Program (DMSP), has been observing aurora in
UV along with in situ measurements of precipitatining electrons and ions and
significantly enhanced our understanding of auroral dynamics (Gussenhoven et
al., 1981; Shiokawa et al., 1997; Zhou et al., 2003). Not only auroral
development and particle precipitation but hemispherical asymmetry has also
not been studied in the context of global effects of penetration electric
fields during storms and substorms. This is important as the interplay of
field-aligned currents plays a crucial role in determining the global effects
of penetration electric fields. It is known that the field-aligned currents
close through the ionospheric currents in the polar region and through
currents (e.g. tail current) in the magnetotail. However, there is no
dedicated mission at present to address the hemispherical asymmetry and
disproportionate global effects (e.g. Hui et al. (2017) of storms and
substorms in a comprehensive manner.

There are several upcoming small satellite missions to probe the geospace
environment (Miyashita et al., 2023). Here we discuss a few of them to give
some idea of the current scenario of geospace probing using smallsats.
Geostationary Transfer Orbit Satellite(GTOsat) is a 6U CubeSat mission from
the USA (Blum et al., 2020). The orbit of GTOsat is about 185 km $\times$ 5.5
$R_{E}$ in altitude with a low inclination of $<25^{o}$. GTOSat’s main
targeted science is radiation belt dynamics. Another upcoming 12U Cubesat
mission from Japan is going to capture global images of the magnetopause and
cusps through soft X-ray emission, GEOspace X-Ray Imager (GEO-X) with an
apogee of $\sim$ 40 $R_{E}$ (Ezoe et al., 2020). Magnetospheric Constellation
(MagCon) from the USA, aims to study the energy storage and release processes
in the magnetotail during substorms (Kepko, 2018). In this constellation,
there are 12 proposed spacecraft planned for distribution between 6-8 and 25
$R_{E}$ with a low inclination orbit. Each spacecraft will measure particles
and DC magnetic fields. Self-Adaptive Magnetic Reconnection Explorer (AME)
from China is intended to study magnetic reconnection at magnetopause and
magnetotail by using one mother spacecraft and 12 CubeSats (Dai et al., 2020).
Ionospheric Neutron Spectrometer and Polar Explorer (INSPIRE) satellite is a
microsat intended to probe ionospheric dynamics(Chandran et al., 2021;
Evonosky et al., 2018). The number of proposed small satellite missions is
steadily increasing, indicating a growing trend in such endeavors.

Following this brief overview, it is clear that there is presently no specific
mission dedicated to exploring the hemispherical asymmetry of the aurora.
Moreover, simultaneous imaging of aurora and particle measurements over the
northern and southern hemispheres are currently not available from space-based
platforms. Such measurements are very crucial to understanding the asymmetries
in auroral formations and magnetospheric energy depositions in the southern
and northern hemispheres. The present mission concept, featuring twin
spacecraft for the study of the aurora, builds upon the foundation laid in
Bhaskar et al. (2023). In the upcoming section, we delve into the pivotal
scientific themes that guide the development of the proposed mission concept.

##  2  Driving Science of Hemispheric Asymmetries

###  2.1 Dynamics of X-ray Aurora and Asymmetry

Fig. 2: The figure shows modeled auroral energy deposits in the (left)
northern and (right) southern hemispheres using OVATION Prime model (Newell et
al., 2009)

Aurorae are ubiquitous phenomena with radiation emitted in a broad
electromagnetic band. Magnetospheric electrons precipitate along the poleward
field lines experiencing an acceleration in parallel electric fields and
impacting the ionosphere leading to auroras. The visible aurora results from
the excitation of atmospheric molecules such as N and O. X-rays are generated
by the bremsstrahlung of the keV electrons as they precipitate towards the
poles. The precipitating accelerated electrons can be described by a
Maxwellian distribution and by a power law at lower energies representing the
pre-acceleration electrons. The X-ray spectrum generated by bremsstrahlung
would depend on the initial energy distribution of the electrons and loss
rates as they travel through the atmosphere. The X-ray image and spectra
during aurora can be inverted to map the spatial distribution of the
precipitating electrons and their spectra. Most of what is known about X-ray
auroral emissions is from observations from the PIXIE instrument (Østgaard et
al., 2001) on the POLAR satellite that was in operation from 1996 to 2003.
Published results from these measurements are in the energy range of 3 keV to
22 keV. The only image of X-rays $<3$ keV of the aurora is from a single
observation of Earth by Chandra X-ray Observatory (Elsner et al., 2005). Here
again, there are no spectroscopic measurements in this band. These X-ray
measurements have shown variability at the time scale of minutes. The X-ray
emission has a narrow structure within the arc with additional discrete
emissions. The periodic space-based X-ray observation of the aurora will
provide valuable data on the uncharted territory of X-ray emissions of the
aurora.

The interhemispheric asymmetry in aurora is very crucial to understanding the
energy budget of the magnetosphere. Past observations from DMSP satellites in
the UV band has helped to model the energy deposited in the magnetosphere.
Also, the hemispheric asymmetry of aurora has been investigated using long-
term ground-based observations from the Arctic and Antarctica (Hu et al.,
2014). Figure 2 shows the model output of OVATION Prime model (Newell et al.,
2009) during the main phase of the geomagnetic storm on February 27, 2023. The
auroral oval pattern is almost similar, but there is an asymmetry in deposited
energy. Thus observing aurora in x-rays and simultaneously over both the
auroral oval will provide first-of-its-kind measurements.

###  2.2 Dynamics of Radiation Belts and Asymmetry in particle precipitation

Along with, remote sensing of the aurora, many space-based in situ
observations of trapped and precipitating electrons have been continuously
carried out, which has assisted in fathoming the energetics of the auroral
particles. (Baker et al., 2012; Reeves et al., 2003; Roederer, 2012; Schiller
et al., 2016). The radiation belt harbors high-energy electrons and protons
which are accelerated by various magnetospheric processes (Fok et al., 2008;
Tsurutani et al., 1981; Miyoshi et al., 2010). Specifically, the outer
radiation belt is highly dynamic and varies from minute to solar cycle time
scales. Figure 3 shows the variability of relativistic electrons of 1.8 MeV
for different L-shells as measured by the Van Allen Probe A. The variability
of particle fluxes is the net effect of injection, energization, transport,
and loss. Transient events like geomagnetic storms, interplanetary shocks,
solar wind dynamic pressure changes, and bursts of wave activity cause sudden
energization or losses of the particles within the magnetosphere (Shprits et
al., 2008; Thorne, 2010; Baker et al., 2012; Kanekal et al., 2016; Bhaskar et
al., 2021; Chakraborty et al., 2022). The observatory class missions like
NASA’s Van Allen Probes (Spence et al., 2013) and Exploration of energization
and JAXA’s Radiation in Geospace (ERG) (Miyoshi et al., 2018) have immensely
improved our understanding about the radiation belt source and sink processes.

The past or current missions were not specifically dedicated to measuring
simultaneously particle fluxes precipitating in the southern and northern
hemispheres. The asymmetry in particle deposition in the auroral regions is
not well explored. Thus there is a need to have simultaneous in situ
measurements of the precipitating particle fluxes along with imaging aurora
which will give a better understanding of the sink and acceleration processes
of the magnetospheric particles.

Fig. 3: Radition belt variability as observed in MeV electrons measured by
REPT onboard Van Allen Probe A.

###  2.3 Dynamics of Magnetospheric currents and Asymmetry

The dynamic and complex magnetospheric current systems include magnetopause
current, magnetotail current, ring current in the outer radiation belt,
substorm current wedge, field-aligned currents (FACs) connecting magnetosphere
and ionosphere, DP2 current cells, etc. The eastward and westward electrojets
flowing in the auroral zone are primarily the Hall currents and are confined
to the auroral oval because of the enhanced ionization due to precipitating
particles (Treumann & Baumjohann, 1997). The eastward electrojet flows from
afternoon to midnight through dusk and terminates at Harang discontinuity. The
westward electrojet on the other hand flows through morning and midnight
extending till the evening sector. Due to the tilt of the Earth’s magnetic
axis, differences in solar radiation introduce differences in the day-night
conductivities in the polar region, which results in hemispheric differences
in auroral intensities (Laundal & Østgaard, 2009). The increased radiation
around the poles enhances the thermospheric response to external disturbances.
In addition to seasons, solar wind impact angle, angle of inclination, IMF By
orientation, etc. give rise to the hemispheric asymmetries in the
magnetospheric current systems. The potential patterns, high-latitude plasma
convection, thermospheric density, and wind profiles are not symmetric in both
hemispheres due to the IMF-By component (Cowley, 1981; Förster et al., 2008;
Østgaard et al., 2011; Reistad et al., 2016; Tanaka, 2001; Yamazaki et al.,
2015; Förster & Haaland, 2015). The effects of IMF By on the penetration
electric field (e.g. Chakrabarty et al. (2017)) and ring current (e.g. (Kumar
et al., 2020)) have also been brought out. These are important indications
that IMF By can play an important role in generating the global asymmetry of
the effects of space weather events.

The compression of the magnetospheric cavity due to impinging solar wind with
an angle twist, distorts the magnetic field geometry, displacing the
footpoints of the magnetic field lines in both hemispheres. One such clue can
be obtained from the dependence of the effects of the penetration of electric
fields on the solar wind azimuthal angle as shown by Rout et al. (2017). These
could result in the latitudinal differences in the occurrence of the aurora,
Region 1, and Region 2 currents, and their MLT patterns.

Fig. 4: Simulated magnetosphere currents for the impact of ICME (Roy & Nandy,
2023). The left panel shows a view from the Sun-side to a plane parallel to
the Earth’s dipole axis. The top-right panel shows a view from the west (dusk)
of a plane normal to the equatorial plane. The bottom-right panel portrays a
view from the north pole to the equatorial plane. The day and night
hemispheres of the Earth are colored with white and black, respectively.

The impulses of solar wind pressure, ICMEs, substorms, and FACs introduce the
asymmetries in the ring current. The partial ring current that couples the
high and low latitude currents can also cause the hemispheric differences.
Chapman-Ferraro current flows in the magnetopause region. The tail current is
primarily described as an equatorial nightside westward current outside 6.6 RE
that flows in the vicinity of stretched magnetic field lines, closes on the
magnetopause, and is carried by particles with energy less than 20 keV. The
neutral sheet current separates the north and south lobes in the magnetic
tail. The magnetotail gets shifted due to solar wind and also can make the
north and south lobes asymmetric, changing the dynamics in both hemispheres.
The global (3D) view of the induced current density distribution in the
magnetosphere following the impact of a coronal mass ejection as simulated by
the CESSI-STORM module(Roy & Nandy, 2023). Figure 4 demonstrates the current
enhancement in the various regions of the magnetosphere like the magnetopause
region (dayside), polar cap regions, and the neutral sheet region in the
magnetotail. This simulation represents an overall understanding of the
anisotropic and asymmetric impact of the coronal mass ejection on the Earth’s
magnetospheric currents.

The observations to date and simulation studies indicate there is a need to
have simultaneous magnetic field measurements from both hemispheres, which
will help to investigate these asymmetries in magnetospheric currents in a
more comprehensive manner.

###  2.4 High Energetic Particle’s Access to Earth and Asymmetry

####  2.4.1 Solar Energetic Particles

Fig. 5: Solar Energetic Particle event of September 10, 2017, as observed by
(top two panels) Advanced Composition Explorer (ACE) at L1 and (bottom panel)
observed by Van Allen Probe -B inside the magnetosphere.

The high-energy protons, electrons, and heavy ions of Solar Energetic
Particles (SEPs) are accelerated to relativistic speeds by solar transient
events including solar flares, ICMEs, and interplanetary shocks(Reames, 2013;
Klein & Dalla, 2017). These particles are capable of penetrating deep inside
the magnetosphere and affect satellites and even astronauts. The fraction of
the penetrated population gets quasi-trapped and contributes to the inner
irradiation belt (Hudson et al., 1995; Richard et al., 2009; O’Brien et al.,
2018; Filwett et al., 2020; Pandya & Bhaskara, 2021). The East-west anisotropy
within the magnetosphere has been well studied using in situ measurements by
various spacecraft such as Van Allen Probes (O’Brien et al., 2018). Figure 5
shows one of the strongest SEP events observed within the magnetopshere by The
Relativistic Proton Spectrometer (RPS) instrument onboard Van Allen Probe-B.
The sharp increase observed in electron and ion fluxes shown on top panels
indicates the arrival of SEP at the L1 point also observed by the ACE
spacecraft. After some time lag, we do see an increase in Proton differential
Isotropic Flux (FPDI). Due to asymmetry in the geomagnetic field, there is
expected interhemispheric asymmetry in the penetration of these particles. To
investigate this asymmetry, trapping, and the propagation of SEPs within the
magnetosphere simultaneous in situ measurements at both hemispheres will be of
extraordinary importance.

####  2.4.2 Origin of Ground Level Enhancements

The sudden and short-lived sporadic increases in neutron detection have been
occasionally observed by instruments placed to measure cosmic rays. These
incidents were first documented by Forbush in 1942 and were subsequently
termed ”Ground Level Enhancements” (GLEs)(Forbush et al., 1950). Researchers
have proposed that GLEs might be associated with solar energetic particles
(SEPs). To date, there have been a total of 71 GLEs recorded since 1942,
including 16 during Solar Cycle 23 (Cliver, 2006; Gopalswamy et al., 2012). In
general, it is assumed that extreme SEP events leading to GLEs are linked to
solar flares and shocks caused by coronal mass ejections (CMEs). However, the
origin of these GLEs remains a subject of debate (Aschwanden, 2012; Firoz et
al., 2014; Klein et al., 2014; Nitta et al., 2012). GLEs are a subset of SEP
events that are observable on the Earth’s surface, but many more energetic SEP
events do not result in GLEs. Consequently, distinguishing between GLE events
and SEP events can be somewhat ambiguous (Nitta et al., 2012).

Researchers have thought that high-energy SEP particles interact with upper
atmospheric nuclei and undergo spallation reactions, which produce numerous
protons and neutron particles. While charged particles like protons interact
electromagnetically with their surroundings along their path, neutrons, being
charge-neutral, travel to the ground with minimal interaction. This leads to
an observed increase in neutron flux at high-latitude neutron monitoring
observatories. The observation of high-energy particles from ground and space-
based platforms is critical in shedding light on the physical mechanisms
underlying the formation of GLEs and the interconnections between SEP and GLE
events.

###  2.5 Dynamics of Cusp and Asymmetry

The Earth’s cusp is a region where the solar wind particles interact directly
with our planet. The Earth’s cusp region has garnerated significant attention
in space physics research due to its unique and dynamic nature. This
transitional zone serves as a crucial entry point for solar wind particles and
energy into the magnetosphere, playing a pivotal role in magnetospheric
dynamics (Smith & Lockwood, 1996). Recent studies utilizing satellite
observations, ground-based measurements, and advanced modeling techniques have
provided unprecedented insights into the complex plasma processes like
magnetic reconnection, and particle acceleration occurring within the cusp
(Fuselier et al., 2000; Chen et al., 1998). Furthermore, the cusp’s
variability and hemispheric asymmetric response to varying solar wind
conditions have been explored to understand its impact on geomagnetic
activity, auroral dynamics, and radiation belt dynamics (Kistler et al., 2010;
Weygand et al., 2023; Zhou et al., 2006).

####  2.5.1 Characterising FTE and Cusp interaction events

The Dungey convection cycle represents a fundamental phenomenon in space
physics, wherein there is a transfer of energy and momentum from the solar
wind to the magnetosphere, leading to circulation within the interconnected
magnetosphere-ionosphere system. This cycle is observable through the movement
of ionospheric plasma, which flows in an antisunward direction across the
polar cap and then returns in a sunward direction just outside the polar cap
within the auroral ovals, as described by Dungey (1961). One of the primary
processes that initiates this convection cycle is the development of an open
magnetic field line due to magnetic reconnection via the solar wind southward
$B_{z}$ component. The plasmoids generated during this process are typically
referred to as Flux transfer events (FTEs) as they transfer the flux from the
magnetosphere via the cusp interaction to the ionosphere. The FTEs and cusp
interaction is primarily mediated by inter-change reconnection as shown in
several MHD and hybrid-Vlasov simulations (see panel B figure 6) (e.g., Ala-
Lahti et al., 2022; Paul et al., 2023). Such interactions in the dayside are
crucial to understand as they channel both the Poynting flux and hydrodynamic
energy flux from the Magnetosphere to the Ionosphere. Simultaneous
measurements using the Cluster spacecraft and the SWARM satellites have
reported such an event and the schematic diagram is shown in panel A of figure
6 (Dong et al., 2023). The inversion profile in the Filed-aligned Currnets
(FACs )measured by SWARM (about 500 km orbit) is shown in panel C of the
figure after a time delay of reconnection activity at the cusp detected by
Cluster. Such a profile in FAC has also been reproduced by simulations as
shown in panel D of the figure.

The small satellites would be essential to provide additional evidences of
such energy transfer events using simultaneous multi-point observations with
existing magnetospheric missions like Magnetospheric Multiscale (MMS) and the
upcoming Solar Wind Magnetosphere Ionosphere Link Explorer (SMILE). In
addition, the effect of FTEs on inducing hemispheric asymmetry in the FAC
would also be an important scientific aspect to target which will need twin
smallsats simultaneously observing both hemispheres. Moreover, the in situ
measurements of high-energy particles and ionospheric temperature are
essential to link the high-energy protons injection due to acceleration via
the interchange reconnections of FTEs with the cusp.

Fig. 6: Panel (A) shows the cartoon of simultaneous observation of field-
aligned currents (FACs) structure by Cluster and Swarm in the polar cusp
region (adopted from Dong et al. (2023)). The difference of FACs from MHD
simulations using MagPIE Paul et al. (2023) is shown in panel (B). The black
dotted line in the panel (C) corresponds to an FAC observation by Dong et al.
(2023). The black circles on the dotted curve represent the points where the
data has been resampled. The solid red dots in panel (C) represent the
temporal difference of FAC $J_{\parallel DIFF}$ obtained from the resampled
observational data and the red solid line represents a spline fit to the
scatter points. Panel (D) corresponds to the $J_{\parallel DIFF}$ obtained for
simulated FTE Cusp interaction (see Paul et al. (2023)

####  2.5.2 Cusp heating

It is known that the electron temperature (Te) in the F region of the
ionosphere is determined by the competition between various heating, cooling,
and energy flow processes (Schunk & Nagy, 1978). The heat gained by the
ambient electron gas from the photoelectrons and from collisions with the
neutrals increase the Te above the ion and neutral temperatures. The hot
ambient electrons then lose energy in Coulomb collisions with the ambient ions
and in collisions with the neutral thermosphere. Therefore, the Te depends on
the relative importance of the various heating, cooling, and energy flow
processes, and this in turn is dependent upon altitude, latitude, local time,
season, solar activity, and space weather conditions. The electron energy
balance is especially complicated at high latitudes owing primarily to the
presence of additional heat sources (Schunk & Nagy, 1978), and actually, the
Te morphology is indicative of cusp-like precipitation (Pallamraju et al.,
2004). In the dayside cusp and the nocturnal auroral oval, precipitating
energetic electrons are an important heat source for the ambient electron gas.
Throughout the polar cap, convection electric fields having their source in
the magnetosphere are responsible for a significant amount of Joule
dissipation. In addition, field-aligned electron currents which are present at
high latitudes cause further complications in electron energy balance
considerations because of the need to consider thermoelectric energy
transport. The hemispherical asymmetry in cusp temperature due to the particle
precipitation has been studied using DMSP observations (Newell & Meng, 1988).

This hemispheric asymmetry has profound implications for magnetospheric
dynamics, plasma transport processes, and the overall response of the
magnetosphere to solar wind variations. Understanding the cusp hemispheric
asymmetry is crucial for deciphering the intricacies of magnetospheric
interactions and their influence on space weather phenomena in different
hemispheres. Therefore, continuous in situ measurements of temperature could
assist in investigating various heating processes and quantifying them.

###  2.6 Space Weather Impact Monitoring

As mentioned earlier, the high-latitude ionosphere gets incident by
precipitating particles and joule heating via magnetospheric-ionospheric
currents. During intense or severe geomagnetic storms the energy entering into
the magnetosphere-ionosphere system increases by orders of magnitude. The
particle precipitation and joule heating in high latitudes cause changes in
lower ionosphere conductivities, increasing radio wave absorption, and changes
in atmospheric composition. The transient space weather events do affect
existing space-based objects like communication and navigation satellites,
space debris, space stations, and even airplanes. Humans in high altitudes
near-polar regions and astronauts in space can easily get affected by sudden
increases in the radiation dose. The Indian Space Research Organization (ISRO)
has recently launched its first solar mission to the L1 point. The mission
reached L1 on January 6, 2024, and has begun scientific observations of solar
wind and the Sun, alongside NASA’s ACE and WIND missions. In light of this,
currently, there is continuous monitoring of solar wind and the Sun. There is
a need to have a magnetospheric mission that will observe both hemispheres of
the Earth simultaneously and quantify solar wind energy entering the
magnetosphere-ionosphere system. The twin smallsat mission to study solar
wind-magnetosphere coupling is timely as space weather forecasting has become
a crucial aspect of the current space era. Moreover, the missions to monitor
the upstream solar wind, including ACE, WIND, and Aditya-L1 will provide the
required critical inputs on solar and solar wind conditions to evaluate the
geoeffectiveness of solar transients.

Given science motivation and space weather monitoring aspects, there is an
urgent need to have small satellite missions to study the magnetospheric
variability and space weather impact. Smallsat missions have a quick
turnaround time which will help to realize missions promptly. Currently, there
is no dedicated ongoing space mission to explore asymmetry using simultaneous
observations from both hemispheres, which demands a dedicated twin smallsat
mission to observe and quantify hemispherical asymmetry in Auroral and solar
wind-magnetosphere coupling. Here we propose a twin small satellite
magnetospheric mission, ”AuroraMag” to address the posed science problems and
improve space weather forecasting. The observations from this will assist the
global community in resolving multiple science questions in the auroral
dynamics, radiation belt physics, SEPs-GLEs, Cusp-solar wind interaction, and
solar wind-magnetosphere coupling processes. The following sections present
details on the mission concept, payloads, and mission requirements.

##  3 Mission Concept and Primary Science objectives

We propose two identical smallsats separated by optimal angular distance and
having $\sim 1000$km Sun-Synchronous circular polar orbit. Figure 7 shows the
cartoon of the twin smallsats observing both hemispheres simultaneously. The
orbital parameters are optimized to get maximum auroral oval in the field-of-
view (FOV) and longer simultaneous observation of it from both hemispheres.
The orbital characteristic is discussed in more detail in the next section.

Fig. 7:  Schematic of the AruroraMag Twin smallsat mission concept (not to
scale). AruroraMag-N will see a full northern auroral oval whereas
AruroraMag-S will see a full southern auroral oval. A Black dashed circular
orbit is shown for an alternative sun-synchronous orbit around 1000 km.

The following are the primary science objectives of the proposed mission
concept.

  * 1.

Investigate the hemispheric asymmetry of solar wind magnetosphere coupling in
the southern and northern hemispheres during quiet and disturbed
magnetospheric conditions by simultaneous

    * 1..1

imaging of aurora in X-ray.

    * 1..2

in situ measurements of particle precipitation

    * 1..3

measurements of magnetospheric/ionospheric currents

    * 1..4

in situ measurement of ionospheric electron density and temperature

  * 2.

Estimate energy budget of the magnetosphere: Joule heating and Particle
precipitation and their hemispherical asymmetric response.

  * 3.

Probe the high-latitude heating of the ionosphere and Cusp dynamics and, FTEs.

  * 4.

Determine the role of Magnetospheric waves in particle precipitation by
combining observations from the spacecraft and ground-based observations

The science objectives, required instruments, and desired measurement
specifications are summarized in Table 1. To address the identified science
problems, we need an X-ray imager, particle detectors, electron temperature
analyzers, and magnetometers onboard two spacecraft.

Sr. |  Science objective/Questions |  Required Instrument |  Measurement specification
---|---|---|---
1 |  Interhemispheric Asymmetry in Auroral X-ray emissions and energy deposition |  X-ray Imager |  Energy: 0.3 to 3 keV , FOV:$45^{\circ}$
2 |  Radiation belt dynamics and particle precipitation |  X-ray Imager, MERiT, and Magnetometer |  Precipitating electron fluxes, Electrons (5 keV to 10 MeV)
3 |  Cusp plasma and interaction with solar wind |  ETA |  Electron Temperature (${}^{\circ}K$)
4 |  Solar Energetic Particles entry into to Magnetosphere |  MERiT |  Protons (200 keV to 100 MeV)
5 |  Magnetospheric currents and interhemispheric asymmetry |  Magnetometer |  Vector magnetic field variations (accuracy $<1$ nT)
Table 1: Science Requirements Matrix

##  4 Orbital Geometry

One of the critical aspects of designing a twin smallsat mission concept for
simultaneous observations of Earth’s northern and southern auroral ovals is
the optimization of an orbital geometry that is conducive to meeting the
specific science objectives of the mission. An ideal orbital configuration for
the twin satellites should enable both the onboard X-ray imagers and in situ
instruments to have concurrent coverage over the auroral latitudes (typically
poleward of 45° in terms of geographic latitudes) in both hemispheres,
ensuring maximum favorable observational time in each orbit.

The orbital geometry for the AuroraMag mission concept was optimized with the
help of 3D orbital simulations implemented using the poliastro astrodynamics
package (Rodríguez et al., 2016) of python for spacecraft orbital propagation,
along with the astropy (Robitaille et al., 2013) and matplotlib (Pajankar &
Pajankar, 2022) libraries for vector algebra computations and 3D
visualizations. A similar implementation of python-based 3D simulations of
spacecraft-borne observational geometries has been extensively detailed by
Pradeep & Sunilkumar (2023), which was appropriately modified and adapted for
the present work. Note that for simplicity, the simulations carried out in
this work assume the Earth to be a perfect sphere having a radius equal to
Earth’s mean volumetric radius of 6371 km, and the due to this assumption is
expected to be negligible for the purpose of this analysis. The rendered 3D
simulations helped arrive at two optimized orbital configurations for
AuroraMag: a primary elliptical configuration (400 km $\times$ 10000 km
orbits), and an alternative circular configuration (1000 km orbit).

###  4.1 Elliptical Configuration: 400 km $\times$ 10000 km Orbits

Primarily, a twin elliptical orbital configuration is envisaged for AuroraMag,
in which the two smallsats (hereafter referred to as AuroraMag-N and
AuroraMag-S) are placed into two separate polar elliptical orbits. The two
orbits are identical in size and shape, but antipodal in terms of the location
of their respective periapses. The rationale behind going for an elliptical
orbit is to obtain coverage of a significant range of altitudes for in situ
profiling (using ETA, MERiT, and Magnetometer), while positioning the orbital
apogee over the targeted auroral oval to maximize observation/imaging of the
auroral latitudes.

The orbits are optimized to a perigee altitude of 400 km and apogee altitude
of 10000 km, which corresponds to a semimajor axis of 11571 km and
eccentricity of 0.41483018. This comfortably enables comprehensive in situ
profiling of magnetospheric parameters over the 400$-$10000 km altitude range
over each orbit. It was decided not to lower the perigee below 400 km as the
effect of atmospheric drag at lower altitudes can lower the apoapsis over
time, necessitating intermittent orbit corrections and diminishing the mission
lifetime. The 10000 km apogee enables comfortable viewing of the full auroral
ovals by the X-ray Imagers with a field-of-view of $\sim$45.8° ($\pm$22.9°),
which corresponds to a latitudinal imaging extent of over 130° from the
apogee. An even larger apoapsis is not preferred, considering possibly coarse
spatial resolution for the imagers and increased launch costs.

The two polar elliptical orbits are oriented antipodally so that the apoapses
are over the respective target aurorae. Thus AuroraMag-N, which is designated
to observe the northern auroral oval, is placed in an orbit with perigee over
the South Pole (i.e., an argument of perigee of 270°). On the other hand, the
orbit of AuroraMag-S has its perigee over the North Pole (i.e., argument of
perigee of 90°) so that it covers the southern auroral oval on approaching
apogee. The smallsats are intended to travel in opposite directions in their
orbits, but synchronised to reach their respective apoapses and periapses at
the same time, facilitating similar solar illumination conditions for the two
spacecraft throughout. It is to be noted that since this proposed
configuration of AuroraMag involves two orbits with diametrically opposite
periapses and opposite-moving satellites, it may not be possible to achieve
the mission through a single launch; two separate launches may be required to
inject the twin smallsats into the indented orbits and achieve the stated
objectives.

An inclination of 90° is adopted for both orbits to achieve coverage of the
northern and southern auroral latitudes ($>$45° in either hemisphere). Given
the direct correlation between the auroral ovals and the Earth-sun vector,
both the satellites would be injected in an orbital plane perpendicular to the
day-night terminator (i.e., noon-to-midnight orbits) for best coverage of
auroral latitudes & longitudes. It would have been ideal for the two smallsats
to be in Sun-Synchronous Orbits (SSOs) in which case they would have
maintained their orbital planes, but the significant ellipticity and large
apoapsis of 10000 km implicate that it may not be feasible to achieve sun-
synchronicity (Boain, 2004; Liu et al., 2019). Thus, the two orbits in this
configuration may undergo gravitational perturbations and gradually drift over
time, and appropriate orbital correction maneuvers may be required to
compensate for this. Nevertheless, these drifts may not significantly affect
our observations given the large spatial coverage of the imager FOVs from the
apoapses. Since we are not opting for SSOs, there are no additional
constraints on the inclination and perfectly polar orbits (90° inclination)
are adopted.

Incorporating the above considerations, 3D simulations were rendered to
optimize the elliptical orbital configuration for AuroraMag. Table 2
summarises the optimized orbital parameters for the same. Figure 8 presents 3D
visualizations of the simulated twin elliptical orbital configuration of
AurorMag around Earth, with the red and blue cones representing the FOVs of
AuroraMag-N and AuroraMag-S respectively, along with representative auroral
data from the NOAA Ovation Model (Newell et al., 2014) for a visual reference
of our observational target.

Sl. No | Parameter | Optimized Value
---|---|---
1. | Semimajor Axis | 11571 km
2. | Inclination | 90°
3. | Eccentricity | 0.41483018
4 | Orbital Period |  $\sim$206.45 minutes
5. | Argument of Periapsis | 270° (AuroraMag-N) & 90°(AuroraMag-S)
6. | FOV of X-ray Imagers | 45.8° ($\pm$22.9°)
Table 2: Optimized parameters for the twin elliptical orbital configuration of
AuroraMag smallsat mission concept. Fig. 8: (a) 3D visualization of the
optimized twin elliptical orbit configuration for AuroraMag mission concept,
simulated around Earth ($blue$ sphere) as per the optimized parameters listed
in Table 2. The dark-shaded spherical region represents the night-side
hemisphere of Earth under equinox conditions. The $red$ orbit corresponds to
AuroraMag-N satellite and the $blue$ orbit corresponds to AuroraMag-S. The 3D
$red$ and $blue$ 3D cones represent the 45.8° FOV of X-ray imagers onboard
AuroraMag-N and AuroraMag-S, respectively. The auroral ovals are visualised in
$green$ colour using data from NOAA’s OVATION Model (for the date 30 March
2023); (b) Simulated representation of northern auroral oval observation by
AuroraMag-N; (c) Simulated representation of southern auroral oval observation
by AuroraMag-S. The axes in each 3D plot correspond to Cartesian coordinates
($x$, $y$, and $z$), representing distance in kilometers (km).

The python-based 3D simulations were invoked to determine the achievable
duration of simultaneous observations of the auroral latitudes in each orbital
period. For this, the two smallsats were simultaneously propagated over time
along their respective simulated orbits using the in-built functions of
poliastro. At each time step of the simulation, the fields of view of imagers
onboard the two satellites (adopted as 45.8°) were visualized as 3-dimensional
cones, and the intersection of these cones with the spherical surface of the
planet (assumed to be a perfect sphere) was used to determine the spatial
coverage of the observations over the Earth. It is to be noted that since we
are employing X-ray Imagers rather than UV or visible wavelength detectors,
our observations are not likely to be affected by scattered solar radiation on
the sunlit hemisphere, enabling unhindered characterisation of the day-side
aurora in addition to the night-side (Imhof et al., 1995). The results of this
simulation analysis are presented in Figure 9. It is seen that for this
configuration, we can achieve as long as around 132 minutes ($\sim$2.2 hours)
of simultaneous observations of the auroral latitudes ($>$45° geographical
latitude) over the two hemispheres, during every single orbital period (which
is about 206.45 minutes or 3.44 hours for either orbit).

Fig. 9: Results of 3D orbital simulations: time evolution of the FOV
latitudinal coverage of AuroraMag X-ray imagers, simulated for the twin
elliptical orbital configuration as per optimized parameters listed in 2. The
$y$-axis corresponds to Earth’s geographical latitudes, while the $x$-axis
denotes observation times, starting from an arbitrary point. The $red$ shaded
region indicates the latitudinal coverage of the AuroraMag-N imager and the
$blue$ shaded region indicates that of the AuroraMag-S imager. The thin $red$
curve corresponds to the latitudinal ground trace of AuroraMag-N, and the thin
$blue$ curve corresponds to that of AuroraMag-S. The horizontal $green$-shaded
regions indicate typical auroral latitudes in either hemisphere ($>$45∘
geographical latitude), and the vertical $gray$ lines indicate the time bounds
within which simultaneous observation of northern and southern auroral
latitudes is achievable.

###  4.2 Circular Configuration: 1000 km Orbit

In addition to the primary elliptical orbital configuration, we also present
the simulation results for an alternative circular orbit configuration for
AuroraMag: a 1000 km noon-to-midnight sun-synchronous orbit for the twin
smallsats. In this mission design, both AuroraMag-N and AuroraMag-S are placed
into the same 1000 km near-polar orbit (semimajor axis or orbital radius of
7371 km), propagating in the same direction, and separated by an angle of 180°
along the orbital plane. Given the circular orbit (eccentricity of 0) with
1000 km altitude, sun-synchronocity can be achieved in this case by adopting
an orbital inclination of about 99.45∘ (Boain, 2004), making the orbit near-
polar and slightly retrograde to the Earth’s rotation.

This circular configuration provides a few advantages: (i) being a single-
orbit twin satellite configuration, the two smallsats can be injected into
orbit in a single launch, reducing the overall mission cost; (ii) the sun-
synchronous orbit maintains orbital plane as required with minimal orbit
corrections; (iii) both satellites can be used to study both Northern and
Southern auroral ovals, giving significant favourable observational durations
(around 84 minutes in every $\sim$104-minute orbit). However, this
configuration also suffers from a couple of major drawbacks: (i) the circular
orbit only offers a constant altitude (i.e., 1000 km) for in situ
measurements, making it impossible to obtain vertical profiles of
magnetospheric parameters, unlike the previous elliptical configuration which
facilitated profiling of the magnetosphere from 400 km to 10000 km; (ii) the
lower orbital altitude also limits the spatial coverage of the imagers; for
1000 km altitude, a FOV 119.6° is feasible, which gives a latitudinal coverage
just over 50°, which may not necessarily cover the entire auroral oval, giving
only a partial picture. Owing to these drawbacks, we strongly recommend the
twin elliptical orbital configuration for the AuroraMag mission concept,
although the circular configuration can be considered a cost-effective
alternative albeit with significantly diminished science returns.

The 3D orbital simulations enabled an interesting exploration of possible
observational geometries for the AuroraMag twin smallsat mission concept. It
should be noted that this exercise assumed a perfect sphericity for the Earth,
ignoring the flattening of about 0.003353, but this is not expected to make
any significant change in the results obtained. Atmospheric refraction effects
and the actual altitude of occurrence of auroral emissions (around 300 to 400
km) have not been incorporated in the observational geometry computations
carried out, but these are not likely to have a significant impact on the
present analysis. The auroral data visualized in Figures 8 should only be
treated as a representative picture, as the data has been taken from the NOAA
Ovation Model forecast for a single date (30 March 2023).

##  5 Payloads

###  5.1 Aurora X-ray Imager

A wide coverage of the auroral region with high cadence, imaging, and
spectroscopy would be the most ideal scenario. The X-ray imager aims to map
the electrons precipitating into the ionosphere by measuring their
bremsstrahlung emission in X-rays. Though the emission extends to hundreds of
keV under high geomagnetic activity, we focus on the soft X-ray region where
the studies are limited to isolated short observations from balloons and
Astronomy satellites. This is a niche wavelength region that is also a link to
the Vis-UV auroras and their high-energy counterparts. Additionally, a
component of the solar wind charge exchange emission (SWCX) that plays an
important role in the loss of atoms from the exosphere is primarily in the
soft X-ray band. With the SMILE mission operational in $\sim 2025$, global
views of the SWCX emission would be possible and a closer view by the X-ray
imager would provide a complementary view. X-ray imager would specifically
attempt to address the following

  * 1.

Is the X-ray aurora driven by the the same population of electrons causing
aurora in the VIS/UV?

  * 2.

What component of the X-ray emission in the Polar Regions comes from charge
exchange emission?

  * 3.

What is the correlation between variability in the solar wind and the
spectral, morphological, and temporal variations in X-ray aurora?

  * 4.

Is there a diffuse X-ray emission from non-accelerated precipitating electrons
in the absence of geomagnetic disturbances?

The instrument is an X-ray Pinhole camera which will image the auroral arc and
also measure the spectrum. Auroral ovals are typically between 60∘ to 80∘
latitudes and expand to lower latitudes during storms and substorms. X-ray
imager has a FOV of 130∘ to cover a 20∘latitude at any instant as the
satellite moves across the poles using two image plane detectors with
individual pinholes and appropriate mounting on the satellite. In addition to
images, the X-ray camera will also provide the soft X-ray spectrum in the
$\approx$ 0.3 to 3 keV range having a resolution of $\sim$ 100 eV at 1 keV.
The imager will help map the auroral oval’s boundaries and fine structures
during storms/substorms. Two sets of identical imagers could be mounted on
AuroraMag to capture the aurora. The X-ray imager will be developed as a
heritage of the Auroral X-ray Imaging Spectrometer payload of the Disturbed
and Quiet Time Ionosphere-Thermosphere System at High Altitudes (DISHA)
mission.

###  5.2 Electron and Proton particle sensor

The high latitude of the Earth is bombarded by energetic particle
precipitation. To measure this particle detectors need to be deployed on the
spacecraft platform. Recently, the Miniaturized Electron pRoton Telescope
(MERiT) was flown on the 3U CubeSat, Compact Radiation belt Explorer,
(CeREs)(Kanekal et al., 2019; Kanekal & Miyoshi, 2021). It is a low-mass, low-
power, compact instrument. MERiT consists of front-end Avalanche Photodiodes
(APDs) followed by a sequence of Solid-State Detectors (SSDs) enclosed within
shielding made of Tungsten (W) and Aluminum (Al). The Avalanche Photodiodes
measure low-energy electrons (5-200 keV), while Solid-State Detectors measure
higher-energy electrons (1 MeV) with $30\%$ energy resolution. We proposed to
utilize this detector to measure precipitating electrons and protons in the
auroral region.

The X-ray imaging will provide information on the energetic electrons that
will produce X-rays. We need to depend on particle detectors (electron and
proton) to get the complete details of precipitating electron energies.
Therefore, by combining the in situ particle measurements with the X-ray
measurements, one can also derive important information about the energy
dependence of the generation and evolution of X-ray aurora and further
identify the physical processes in underlying auroral features in greater
detail. The detectors will be mounted facing the zenith.

###  5.3 Magnetometer

Magnetic field measurements with high accuracy are essential onboard AuroraMag
to achieve identified science objectives. The in situ magnetic field
measurements are crucial to study the magnetospheric and ionospheric current
systems and deriving the pitch angle distribution of measured particles by
MERit payload. Two identical fluxgate magnetometers (FGM) are proposed onboard
each AurorMag spacecraft. They could be mounted on two opposite sides of the
spacecraft body by using a deployable boom. The broad primary specifications
of the FGM required for achieving the intended science objectives are listed
in Table 3.

Parameter | Specs
---|---
Range, Resolution, Accuracy |  $\pm$ 60,000 nT, 1 nT, 2 nT
(2 ranges) |  $\pm$ 20,000 nT, 0.5 nT, 1 nT
Sampling rate | 8 vectors/s for FGM sensors, 16 bit/sample
Operating Temperature | Sensors and Electronics: - 20 deg C to + 55 deg C
Non-linearity | ¡ 10 ppm
Total FGM Mass | 3 kg [Sensors: 0.5 kg; Electronics: 2.25 kg; Harness/Thermal: 0.25 kg]
Raw Power | 15.0 W
Size (Triaxial sensor) | 85 mm $\times$ 65 mm $\times$ 55 mm
Table 3: Specifications of the proposed FGM

The FGM sensors could be developed as a heritage of the magnetometer on ISRO’s
Adity-L1 spacecraft. Additional information on the magnetometer can be
obtained by referring to Yadav et al. (2018).

###  5.4 Electron Temperature Analyser (ETA)

The Electron Temperature probe (ET probe) was initially designed by Hirao &
Miyazaki (1965) which was later improved by Hirao & Oyama (1970) in Japan.
This ET probe was used in several rocket experiments in Japan ($\sim$50
flights) and also in India (Jain et al., 1981). The probe was also used in
HINOTORI (Oyama, 1991), OHZORA (Oyama & Abe, 1987), and Exos-D (Abe et al.,
1990).
This probe is one of the modifications of the resonance probe, in which the
i-v characteristic curve is modified by superposing the RF voltage on the d-c
biased probe. However, this instrument was not designed to have Ne measurement
capability. In this context, Oyama et al. (2015) proposed a modification to
the basic ETA to enable the measurement of both Neand Ne. This instrument is
compact, with low power consumption, and low data rate Oyama et al. (2015),
and is suitable for smallsat missions. For the AurorMag mission, we propose to
have this Electron Temperature & density Analyser (ETA), with the programmable
capability to work in either Ne and Te mode or only in Tee. mode depending on
the altitude.

As mentioned earlier, the Te is obtained by measuring the shift in the
floating potential because of the applied RF signal, and Ne measurement is
done by considering the impedance effect on the probe, similar to the
impedance probe principle, by detecting the upper hybrid resonance frequency.
The details can be found in Oyama et al. (2015).

The proposed ETA sensor consists of two semicircular copper electrodes of
$\sim$150 mm in diameter and thickness of $\sim$2 mm with $\sim$10 mm gap
between the two disks. In the Te mode, these two disks are electrically
separated. When a sinusoidal voltage ($\sim$200 kHz) is added to the sweeping
voltage of one disk, while the other is fed only with the DC sweeping voltage.
By Subtracting these two signals using a differential amplifier, we can
eliminate noise from the ambient plasma, including a variation of the floating
potential of the satellite, and purely detect floating potential shift, which
can be related to Te. For the Ne measurements, we need to have the frequency
sweep mode to obtain the Electron Density (Ne). Currently, the minimum
frequency is 200 kHz, which means the lowest detection limit is $\sim$1000
electrons/cc. In an orbital altitude of $\sim$800-1000 km, we may expect the
diurnal minimum of electron density could be as low as $\sim$200 electrons/cc.
In these cases also, the Te mode will be able to provide temperature
measurement. For example, the more recent Tatiana-2 mission was an
experimental scientific education microsatellite in a circular near-polar,
quasi-Sun-synchronous circular orbit at $\sim$830 km altitude which provided
measurements of Te (Liu et al., 2015). Depending on the mission period and the
selected altitude, we will decide whether ETA will have both Ne and Te modes
or only in Tee mode. The payload mass is expected to be $\sim$1-1.5 kg, and
the power requirement will be within $\sim$5W.

##  6 Spacecraft Bus requirements and challenges

The payload specification, viewed from the perspective of science
requirements, has been condensed into Table 1. Key payload requirements from
the satellite bus are outlined in Table 4.

Payload |  Power |  Mass |  Dimension |  Pointing |  Data rate |  Duty Cycle |  Total Data
---|---|---|---|---|---|---|---
|  in W |  in kg |  in mm |  in deg |  in Bytes/s |  in seconds /orbit |  in KB
Mag. fluxgate sensors |  15 |  0.5 |  85x65x55 |  NA |  16 |  full orbit |  0.5 Gb
Mag. Electronics |  |  2.5 |  170x125x115 |  |  |  |
ETA |  5 |  1.5 |  15 cm diameter disc |  Forward Hemisphere |  TBD |  ¡1000km in orbit |  TBD
X-Ray Imager |  20 |  3 Kg |  TBD |  ¡ 1 |  1.4e5 |  in orbit $\pm$60 degree and above |  TBD
MERiT |  0.5 |  1.2 |  40X40X15 |  ¡1 |  TBD |  full orbit |  TBD
Table 4: Satellite Subsystems

Based on the table, it can be deduced that the overall payload mass is
approximately 9 Kg. The spacecraft is anticipated to have dimensions of 50cm x
50cm x 50cm and a mass ranging between 30-35 KG.

Achieving payload pointing requirements of $<1$ degrees involves using
actuators such as reaction wheels and magneto-torquers for momentum dumping
and initial stumbling. Sensors utilized for pointing estimation include the
Sun sensor, Earth Sensor, and star sensor. For control purposes, a MEMS-based
IMU is also employed. The inclusion of a GNSS sensor provides location
information in orbit for the magnetometer.

Assuming a total data budget requirement of approximately 2 GB per orbit for
payloads and telemetry health parameters, with the proposed orbital
inclination of $45^{\circ}$ and altitude of 400X10000 km, the orbital period
is 3.44 hr. This leads to around 7 orbits per day, resulting in approximately
14 GB of data to be downloaded daily. Two ground stations, one at the Indian
Institute of Space Science and Technology (IIST), Thiruvananthapuram, and
another at ISRO Tracking and Ranging Centre (ISTRAC), are designated for
telemetry/telecommand and data downloading requirements. An elliptical orbit
offers larger ground visibility at farther distances compared to a circular
orbit.

The Electrical Power System(EPS) in a small satellite comprises LiIon
batteries and solar panels mounted on the PCBs. The total peak power
requirement when all payloads are simultaneously active is around 50 W, but in
practice, payloads are expected to be activated only when necessary. The
spacecraft bus is expected to consume about 30W of power, and the payloads
would consume a peak power of 50W when all are active. However, after duty
cycling the payloads, power consumption will be around 25-30W per orbit. For
the 400 x 10000 km orbit, with a period of around 3.44 hours and an average
eclipse period of barely 13 minutes, the spacecraft is expected to perform
better in terms of power generation compared to a 1000 km circular orbit.

##  7 Summary

The solar wind interaction with the Earth’s magnetosphere generates global
response in currents, fields, and particles. The magnetosphere response is not
always symmetric. There are various asymmetries in solar wind interaction with
the Earth’s magnetosphere like dawn-dusk, noon-midnight, hemispheric, etc.
Understanding the asymmetries in solar wind-magnetosphere coupling is critical
for space weather forecasting. The hemispherical asymmetric is one of the
less-explored aspects of it. Investigating it using remote sensing and in
situ, observations of both hemispheres simultaneously will provide invaluable
data which was not available so far. The proposed mission concept aims to
study this asymmetric response of the magnetosphere with twin smallsats
observing southern and northern auroral ovals in x-rays along with in situ
particle, magnetic field, and temperature measurements. The science objectives
of the mission are well served by the optimized elliptical orbit with
dimensions of 400 X 10,000 km.

Simultaneous data of imaging and in situ particle and magnetic field
measurement will shed light on the degree of auroral and particle
precipitation asymmetry and causes. Electron density and temperature
measurements will probe the high-latitude heating of the ionosphere, cusp,
FTEs, and its coupling to low-latitude. Examining magnetospheric currents,
such as field-aligned currents (FACs), and intensified ionospheric currents
during space weather events is crucial for assessing the impact of space
weather on the magnetosphere-ionosphere system. Additionally, conducting
simultaneous observations in both hemispheres will aid in quantifying the
asymmetry in solar energetic particle (SEP) propagation and understanding
their connection to ground-level enhancements (GLEs). Further, collaborative
observations involving operational space missions such as ERG, THEMIS,
Cluster, and MMS, along with ground-based data from magnetometer and auroral
imager networks, will contribute significantly to unraveling the complexities
of wave-particle interaction and its role in aurora formation.

## Acknowledgments

The utilized data in this analysis is taken from the OMNI database. The data
are publicly available at Coordinated Data Analysis Web (CDAWeb)
https://cdaweb.gsfc.nasa.gov/ pub/data/wind/. We also thank the Van Allen
Probe mission team for making data available in the public domain.

## References

  * Abe et al. (1990) Abe, T., OYAMA, K.-i., AMEMIYA, H. et al. (1990).  Measurements of temperature and velocity distribution of thermal electrons by the akebono (exos-d) satellite experimental setup and preliminary results.  Journal of geomagnetism and geoelectricity, 42(4), 537–554.
  * Ala-Lahti et al. (2022) Ala-Lahti, M., Pulkkinen, T. I., Pfau-Kempf, Y. et al. (2022).  Energy flux through the magnetopause during flux transfer events in hybrid-vlasov 2d simulations.  Geophysical Research Letters, 49(19), e2022GL100079. URL: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2022GL100079. doi:https://doi.org/10.1029/2022GL100079. arXiv:https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2022GL100079.  E2022GL100079 2022GL100079.
  * Aschwanden (2012) Aschwanden, M. J. (2012).  Gev particle acceleration in solar flares and ground level enhancement (gle) events.  Space science reviews, 171(1-4), 3--21.
  * Baker et al. (2012) Baker, D., Kanekal, S., Hoxie, V. et al. (2012).  The relativistic electron-proton telescope (rept) instrument on board the radiation belt storm probes (rbsp) spacecraft: Characterization of earth’s radiation belt high-energy particle populations.  In The Van Allen Probes Mission (pp. 337--381).  Springer.
  * Bhardwaj & Gladstone (2000) Bhardwaj, A., & Gladstone, G. R. (2000).  Auroral emissions of the giant planets.  Reviews of Geophysics, 38(3), 295--353.
  * Bhaskar et al. (2020) Bhaskar, A., Hayakawa, H., Oliveira, D. M. et al. (2020).  An analysis of trouvelot’s auroral drawing on 1/2 march 1872: plausible evidence for recurrent geomagnetic storms.  Journal of Geophysical Research: Space Physics, 125(10), e2020JA028227.
  * Bhaskar et al. (2023) Bhaskar, A., Pant, T., Thampi, S. et al. (2023).  Twin cubesat mission concept to study aurora and particle precipitation in northern and southern auroral ovals.  In 5th COSPAR Symposium.  Panel on Space Weather, COSPAR.
  * Bhaskar et al. (2021) Bhaskar, A., Sibeck, D., Kanekal, S. G. et al. (2021).  Radiation belt response to fast reverse shock at geosynchronous orbit.  The Astrophysical Journal, 910(2), 154.
  * Blum et al. (2020) Blum, L., Kepko, L., Turner, D. et al. (2020).  The gtosat cubesat: scientific objectives and instrumentation.  In Micro-and Nanotechnology Sensors, Systems, and Applications XII (pp. 62--71).  SPIE volume 11389.
  * Boain (2004) Boain, R. J. (2004).  Ab-cs of sun-synchronous orbit mission design, .
  * Burch (2000) Burch, J. (2000).  Image mission overview.  Space Science Reviews, 91(1-2), 1--14.
  * Chakrabarty et al. (2017) Chakrabarty, D., Hui, D., Rout, D. et al. (2017).  Role of imf by in the prompt electric field disturbances over equatorial ionosphere during a space weather event.  Journal of Geophysical Research: Space Physics, 122(2), 2574--2588.
  * Chakraborty et al. (2022) Chakraborty, S., Chakrabarty, D., Reeves, G. D. et al. (2022).  Statistical investigation on equatorial pitch angle distribution of energetic electrons in earth’s outer radiation belt during cme-and cir-driven storms.  Frontiers in Astronomy and Space Sciences, 9, 986061.
  * Chandran et al. (2021) Chandran, A., Fang, T.-W., Chang, L. et al. (2021).  The inspiresat-1: Mission, science, and engineering.  Advances in Space Research, 68(6), 2616--2630.
  * Chen et al. (1998) Chen, J., Fritz, T. A., Sheldon, R. B. et al. (1998).  Cusp energetic particle events: Implications for a major acceleration region of the magnetosphere.  Journal of Geophysical Research: Space Physics, 103(A1), 69--78.
  * Chisham et al. (2007) Chisham, G., Lester, M., Milan, S. et al. (2007).  A decade of the super dual auroral radar network (superdarn): Scientific achievements, new techniques and future directions.  Surveys in geophysics, 28, 33--109.
  * Cliver (2006) Cliver, E. (2006).  The unusual relativistic solar proton events of 1979 august 21 and 1981 may 10.  The Astrophysical Journal, 639(2), 1206.
  * Cowley (1981) Cowley, S. (1981).  Magnetospheric asymmetries associated with the y-component of the imf.  Planetary and Space Science, 29(1), 79--96.
  * Dai et al. (2020) Dai, L., Wang, C., Cai, Z. et al. (2020).  Ame: A cross-scale constellation of cubesats to explore magnetic reconnection in the solar--terrestrial relation.  Frontiers in Physics, 8, 89.
  * Das et al. (2019) Das, S. B., Basak, A., Nandy, D. et al. (2019).  Modeling star--planet interactions in far-out planetary and exoplanetary systems.  The Astrophysical Journal, 877(2), 80.
  * Dong et al. (2023) Dong, X.-C., Dunlop, M. W., Xiao, C. et al. (2023).  Simultaneous mesoscale polar cusp field-aligned currents measured on mid- and low-altitude satellites.  Geophysical Research Letters, 50(1), e2022GL102460. URL: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2022GL102460. doi:https://doi.org/10.1029/2022GL102460. arXiv:https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2022GL102460.  E2022GL102460 2022GL102460.
  * Dungey (1961) Dungey, J. W. (1961).  Interplanetary magnetic field and the auroral zones.  Phys. Rev. Lett., 6, 47--48. URL: https://link.aps.org/doi/10.1103/PhysRevLett.6.47. doi:10.1103/PhysRevLett.6.47.
  * Eather (1980) Eather, R. H. (1980).  Majestic lights. the aurora in science, history, and the arts.  Majestic lights: The aurora in science, .
  * Elsner et al. (2005) Elsner, R. F., Lugaz, N., Waite Jr, J. et al. (2005).  Simultaneous chandra x ray, hubble space telescope ultraviolet, and ulysses radio observations of jupiter’s aurora.  Journal of Geophysical Research: Space Physics, 110(A1).
  * Evonosky et al. (2018) Evonosky, W., Chandran, A., Boyajian, S. et al. (2018).  Inspiresat-1: an ionosphere exploring microsat, .
  * Ezoe et al. (2020) Ezoe, Y., Funase, R., Nagata, H. et al. (2020).  Geo-x (geospace x-ray imager).  In Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray (pp. 345--356).  SPIE volume 11444.
  * Filwett et al. (2020) Filwett, R. J., Jaynes, A. N., Baker, D. N. et al. (2020).  Solar energetic proton access to the near-equatorial inner magnetosphere.  Journal of Geophysical Research: Space Physics, 125(6), e2019JA027584.
  * Firoz et al. (2014) Firoz, K. A., Zhang, Q., Gan, W. et al. (2014).  An interpretation of gle71 concurrent cme-driven shock wave.  The Astrophysical Journal Supplement Series, 213(2), 24.
  * Fok et al. (2008) Fok, M.-C., Horne, R. B., Meredith, N. P. et al. (2008).  Radiation belt environment model: Application to space weather nowcasting.  Journal of Geophysical Research: Space Physics, 113(A3).
  * Forbush et al. (1950) Forbush, S. E., Stinchcomb, T. B., & Schein, M. (1950).  The extraordinary increase of cosmic-ray intensity on november 19, 1949.  Physical Review, 79(3), 501.
  * Förster & Haaland (2015) Förster, M., & Haaland, S. (2015).  Interhemispheric differences in ionospheric convection: Cluster edi observations revisited.  Journal of Geophysical Research: Space Physics, 120(7), 5805--5823.
  * Förster et al. (2008) Förster, M., Haaland, S., Paschmann, G. et al. (2008).  High-latitude plasma convection during northward imf as derived from in-situ magnetospheric cluster edi measurements.  In Annales Geophysicae (pp. 2685--2700).  Copernicus Publications Göttingen, Germany volume 26.
  * Frank & Craven (1988) Frank, L. A., & Craven, J. (1988).  Imaging results from dynamics explorer 1.  Reviews of Geophysics, 26(2), 249--283.
  * Fuselier et al. (2000) Fuselier, S., Trattner, K., & Petrinec, S. (2000).  Cusp observations of high-and low-latitude reconnection for northward interplanetary magnetic field.  Journal of Geophysical Research: Space Physics, 105(A1), 253--266.
  * Gopalswamy et al. (2012) Gopalswamy, N., Xie, H., Yashiro, S. et al. (2012).  Properties of ground level enhancement events and the associated solar eruptions during solar cycle 23.  Space science reviews, 171(1-4), 23--60.
  * Gussenhoven et al. (1981) Gussenhoven, M., Hardy, D., & Burke, W. (1981).  Dmsp/f2 electron observations of equatorward auroral boundaries and their relationship to magnetospheric electric fields.  Journal of Geophysical Research: Space Physics, 86(A2), 768--778.
  * Hayakawa et al. (2015) Hayakawa, H., Tamazawa, H., Kawamura, A. D. et al. (2015).  Records of sunspot and aurora during ce 960--1279 in the chinese chronicle of the sòng dynasty.  Earth, Planets and Space, 67, 1--14.
  * Hirao & Miyazaki (1965) Hirao, K., & Miyazaki, S. (1965).  Rocket-borne ionospheric direct-sounding instruments(rocket borne ionospheric direct sounding instruments to measure ion and electron density, electron temperature, thermal electron energy distribution and space electric potential versus rocket potential).  RADIO RESEARCH LABS., JOURNAL, 12, 357--380.
  * Hirao & Oyama (1970) Hirao, K., & Oyama, K.-I. (1970).  Effect of electron heating on the electron temperature probe.  Journal of geomagnetism and geoelectricity, 22(3), 341--352.
  * Hu et al. (2014) Hu, Z.-J., Ebihara, Y., Yang, H.-G. et al. (2014).  Hemispheric asymmetry of the structure of dayside auroral oval.  Geophysical Research Letters, 41(24), 8696--8703.
  * Hudson et al. (1995) Hudson, M., Kotelnikov, A., Li, X. et al. (1995).  Simulation of proton radiation belt formation during the march 24, 1991 ssc.  Geophysical research letters, 22(3), 291--294.
  * Hui et al. (2017) Hui, D., Chakrabarty, D., Sekar, R. et al. (2017).  Contribution of storm time substorms to the prompt electric field disturbances in the equatorial ionosphere.  Journal of Geophysical Research: Space Physics, 122(5), 5568--5578.
  * Imhof et al. (1995) Imhof, W., Spear, K., Hamilton, J. et al. (1995).  The polar ionospheric x-ray imaging experiment (pixie).  Space Science Reviews, 71, 385--408.
  * Jain et al. (1981) Jain, R., Nath, N., & Setty, C. (1981).  On joule heating of the equatorial electrojet e-region.  Journal of Atmospheric and Terrestrial Physics, 43(11), 1189--1197.
  * Kanekal et al. (2016) Kanekal, S., Baker, D., Fennell, J. et al. (2016).  Prompt acceleration of magnetospheric electrons to ultrarelativistic energies by the 17 march 2015 interplanetary shock.  Journal of Geophysical Research: Space Physics, .
  * Kanekal et al. (2019) Kanekal, S., Blum, L., Christian, E. et al. (2019).  The merit onboard the ceres: A novel instrument to study energetic particles in the earth’s radiation belts.  Journal of Geophysical Research: Space Physics, 124(7), 5734--5760.
  * Kanekal & Miyoshi (2021) Kanekal, S., & Miyoshi, Y. (2021).  Dynamics of the terrestrial radiation belts: a review of recent results during the varsiti (variability of the sun and its terrestrial impact) era, 2014--2018.  Progress in Earth and Planetary Science, 8(1), 1--22.
  * Kepko (2018) Kepko, L. (2018).  Magnetospheric constellation: Leveraging space 2.0 for big science.  In IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium (pp. 285--288).  IEEE.
  * Kistler et al. (2010) Kistler, L., Mouikis, C., Klecker, B. et al. (2010).  Cusp as a source for oxygen in the plasma sheet during geomagnetic storms.  Journal of Geophysical Research: Space Physics, 115(A3).
  * Klein & Dalla (2017) Klein, K.-L., & Dalla, S. (2017).  Acceleration and propagation of solar energetic particles.  Space Science Reviews, 212, 1107--1136.
  * Klein et al. (2014) Klein, K.-L., Masson, S., Bouratzis, C. et al. (2014).  The relativistic solar particle event of 2005 january 20: origin of delayed particle acceleration.  Astronomy & Astrophysics, 572, A4.
  * Kumar et al. (2020) Kumar, S., Veenadhari, B., Chakrabarty, D. et al. (2020).  Effects of imf by on ring current asymmetry under southward imf bz conditions observed at ground magnetic stations: Case studies.  Journal of Geophysical Research: Space Physics, 125(10), e2019JA027493.
  * Laundal & Østgaard (2009) Laundal, K., & Østgaard, N. (2009).  Asymmetric auroral intensities in the earth’s northern and southern hemispheres.  Nature, 460(7254), 491--493.
  * Liou & Mitchell (2019) Liou, K., & Mitchell, E. (2019).  Hemispheric asymmetry of the premidnight aurora associated with the dawn-dusk component of the interplanetary magnetic field.  Journal of Geophysical Research: Space Physics, 124(3), 1625--1634.
  * Liu et al. (2019) Liu, F., Lu, S., & Sun, Y. (2019).  Guidance and control technology of spacecraft on elliptical orbit.  Springer.
  * Liu et al. (2015) Liu, J., Chang, F., Oyama, K. et al. (2015).  Topside ionospheric electron temperature and density along the weddell sea latitude.  Journal of Geophysical Research: Space Physics, 120(1), 609--614.
  * Lühr et al. (1998) Lühr, H., Aylward, A., Bucher, S. et al. (1998).  Westward moving dynamic substorm features observed with the image magnetometer network and other ground-based instruments.  In Annales Geophysicae (pp. 425--440).  Springer volume 16.
  * Miyashita et al. (2023) Miyashita, Y. et al. (2023).  A brief introduction of current and future magnetospheric missions.  Journal of Space Technology and Applications, 3(1), 1--25.
  * Miyoshi et al. (2010) Miyoshi, Y., Katoh, Y., Nishiyama, T. et al. (2010).  Time of flight analysis of pulsating aurora electrons, considering wave-particle interactions with propagating whistler mode waves.  Journal of Geophysical Research: Space Physics, 115(A10).
  * Miyoshi et al. (2018) Miyoshi, Y., Shinohara, I., Takashima, T. et al. (2018).  Geospace exploration project erg.  Earth, Planets and Space, 70, 1--13.
  * Newell et al. (2014) Newell, P., Liou, K., Zhang, Y. et al. (2014).  Ovation prime-2013: Extension of auroral precipitation model to higher disturbance levels.  Space Weather, 12(6), 368--379.
  * Newell et al. (2009) Newell, P., Sotirelis, T., & Wing, S. (2009).  Diffuse, monoenergetic, and broadband aurora: The global precipitation budget.  Journal of Geophysical Research: Space Physics, 114(A9).
  * Newell & Meng (1988) Newell, P. T., & Meng, C.-I. (1988).  Hemispherical asymmetry in cusp precipitation near solstices.  Journal of Geophysical Research: Space Physics, 93(A4), 2643--2648.
  * Nitta et al. (2012) Nitta, N., Liu, Y., DeRosa, M. et al. (2012).  What are special about ground-level events?  Space science reviews, 171(1-4), 61--83.
  * O’Brien et al. (2018) O’Brien, T. P., Mazur, J. E., & Looper, M. D. (2018).  Solar energetic proton access to the magnetosphere during the 10--14 september 2017 particle event.  Space Weather, 16(12), 2022--2037.
  * Østgaard et al. (2011) Østgaard, N., Laundal, K., Juusola, L. et al. (2011).  Interhemispherical asymmetry of substorm onset locations and the interplanetary magnetic field.  Geophysical Research Letters, 38(8).
  * Østgaard et al. (2001) Østgaard, N., Stadsnes, J., Bjordal, J. et al. (2001).  Auroral electron distributions derived from combined uv and x-ray emissions.  Journal of Geophysical Research: Space Physics, 106(A11), 26081--26089.
  * Oyama (1991) Oyama, K.-I. (1991).  Electron temperature measurements carried out by japanese scientific satellites.  Advances in Space Research, 11(10), 149--158.
  * Oyama & Abe (1987) Oyama, K.-i., & Abe, T. (1987).  Anisotropy of electron temperature in the ionosphere.  Geophysical research letters, 14(12), 1195--1198.
  * Oyama et al. (2015) Oyama, K.-I., Hsu, Y., Jiang, G. et al. (2015).  Electron temperature and density probe for small aeronomy satellites.  Review of Scientific Instruments, 86(8).
  * Pajankar & Pajankar (2022) Pajankar, A., & Pajankar, A. (2022).  Visualizing data with pandas and matplotlib.  Hands-on Matplotlib: Learn Plotting and Visualizations with Python 3, (pp. 211--241).
  * Pallamraju et al. (2004) Pallamraju, D., Chakrabarti, S., Doe, R. et al. (2004).  First ground-based oi 630 nm optical measurements of daytime cusplike and f-region auroral precipitation.  Geophysical research letters, 31(8).
  * Pandya & Bhaskara (2021) Pandya, M., & Bhaskara, V. (2021).  Quantitative assessment of protons during the solar proton events of september 2017.  Journal of Geophysical Research: Space Physics, 126(10), e2021JA029458.
  * Paul et al. (2023) Paul, A., Strugarek, A., & Vaidya, B. (2023).  Global-mhd simulations using magpie: Impact of flux transfer events on the ionosphere.  Journal of Geophysical Research: Space Physics, 128(11), e2023JA031718. URL: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2023JA031718. doi:https://doi.org/10.1029/2023JA031718. arXiv:https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2023JA031718.  E2023JA031718 2023JA031718.
  * Pradeep & Sunilkumar (2023) Pradeep, J., & Sunilkumar, S. (2023).  Solar occultation experiments (soe) in the venusian atmosphere: effect of orbital parameters on the spatiotemporal distribution of measurements.  RAS Techniques and Instruments, 2(1), 324--344.
  * Reames (2013) Reames, D. V. (2013).  The two sources of solar energetic particles.  Space Science Reviews, 175, 53--92.
  * Reeves et al. (2003) Reeves, G., McAdams, K., Friedel, R. et al. (2003).  Acceleration and loss of relativistic electrons during geomagnetic storms.  Geophysical Research Letters, 30(10).
  * Reistad et al. (2016) Reistad, J. P., Østgaard, N., Tenfjord, P. et al. (2016).  Dynamic effects of restoring footpoint symmetry on closed magnetic field lines.  Journal of Geophysical Research: Space Physics, 121(5), 3963--3977.
  * Richard et al. (2009) Richard, R., El-Alaoui, M., Ashour-Abdalla, M. et al. (2009).  Modeling the entry and trapping of solar energetic particles in the magnetosphere during the november 24--25, 2001 storm.  Journal of Geophysical Research: Space Physics, 114(A4).
  * Robitaille et al. (2013) Robitaille, T. P., Tollerud, E. J., Greenfield, P. et al. (2013).  Astropy: A community python package for astronomy.  Astronomy & Astrophysics, 558, A33.
  * Rodríguez et al. (2016) Rodríguez, J. L. C., Eichhorn, H., & McLean, F. (2016).  Poliastro: an astrodynamics library written in python with fortran performance.  In 6th International Conference on Astrodynamics Tools and Techniques.
  * Roederer (2012) Roederer, J. G. (2012).  Dynamics of geomagnetically trapped radiation volume 2.  Springer Science & Business Media.
  * Rout et al. (2017) Rout, D., Chakrabarty, D., Janardhan, P. et al. (2017).  Solar wind flow angle and geoeffectiveness of corotating interaction regions: First results.  Geophysical Research Letters, 44(10), 4532--4539.
  * Roy & Nandy (2023) Roy, S., & Nandy, D. (2023).  A time-efficient, data-driven modeling approach for predicting the geomagnetic impact of coronal mass ejections.  The Astrophysical Journal Letters, 950(2), L11.
  * Schiller et al. (2016) Schiller, Q., Kanekal, S., Jian, L. et al. (2016).  Prompt injections of highly relativistic electrons induced by interplanetary shocks: A statistical study of van allen probes observations.  Geophysical Research Letters, 43(24), 12--317.
  * Schunk & Nagy (1978) Schunk, R., & Nagy, A. F. (1978).  Electron temperatures in the f region of the ionosphere: Theory and observations.  Reviews of Geophysics, 16(3), 355--399.
  * Shiokawa et al. (1997) Shiokawa, K., Meng, C.-I., Reeves, G. et al. (1997).  A multievent study of broadband electrons observed by the dmsp satellites and their relation to red aurora observed at midlatitude stations.  Journal of Geophysical Research: Space Physics, 102(A7), 14237--14253.
  * Shprits et al. (2008) Shprits, Y. Y., Subbotin, D. A., Meredith, N. P. et al. (2008).  Review of modeling of losses and sources of relativistic electrons in the outer radiation belt ii: Local acceleration and loss.  Journal of Atmospheric and Solar-Terrestrial Physics, 70(14), 1694--1713.
  * Smith & Lockwood (1996) Smith, M., & Lockwood, M. (1996).  Earth’s magnetospheric cusps.  Reviews of Geophysics, 34(2), 233--260.
  * Spence et al. (2013) Spence, H. E., Reeves, G., Baker, D. et al. (2013).  Science goals and overview of the radiation belt storm probes (rbsp) energetic particle, composition, and thermal plasma (ect) suite on nasa’s van allen probes mission.  Space Science Reviews, 179, 311--336.
  * Tanaka (2001) Tanaka, T. (2001).  Interplanetary magnetic field b y and auroral conductance effects on high-latitude ionospheric convection patterns.  Journal of Geophysical Research: Space Physics, 106(A11), 24505--24516.
  * Tao et al. (2011) Tao, C., Badman, S. V., & Fujimoto, M. (2011).  Uv and ir auroral emission model for the outer planets: Jupiter and saturn comparison.  Icarus, 213(2), 581--592.
  * Thorne (2010) Thorne, R. M. (2010).  Radiation belt dynamics: The importance of wave-particle interactions.  Geophysical Research Letters, 37(22).
  * Treumann & Baumjohann (1997) Treumann, R. A., & Baumjohann, W. (1997).  Advanced space plasma physics volume 30.  Imperial College Press London.
  * Tsurutani et al. (1981) Tsurutani, B., Smith, E., Thorne, R. et al. (1981).  Wave-particle interactions at the magnetopause: Contributions to the dayside aurora.  Geophysical Research Letters, 8(2), 183--186.
  * Virgili et al. (2016) Virgili, B. B., Dolado, J. C., Lewis, H. G. et al. (2016).  Risk to space sustainability from large constellations of satellites.  Acta Astronautica, 126, 154--162.
  * Weygand et al. (2023) Weygand, J. M., Hartinger, M., Strangeway, R. J. et al. (2023).  Interhemispheric asymmetry due to imf by within the cusp spherical elementary currents.  Journal of Geophysical Research: Space Physics, 128(6), e2023JA031430.
  * Yadav et al. (2018) Yadav, V. K., Srivastava, N., Ghosh, S. et al. (2018).  Science objectives of the magnetic field experiment onboard aditya-l1 spacecraft.  Advances in Space Research, 61(2), 749--758.
  * Yamazaki et al. (2015) Yamazaki, Y., Kosch, M. J., & Sutton, E. K. (2015).  North-south asymmetry of the high-latitude thermospheric density: Imf by effect.  Geophysical Research Letters, 42(2), 225--232.
  * Zhou et al. (2003) Zhou, X.-Y., Strangeway, R., Anderson, P. et al. (2003).  Shock aurora: Fast and dmsp observations.  Journal of Geophysical Research: Space Physics, 108(A4).
  * Zhou et al. (2006) Zhou, X.-Z., Fritz, T., Zong, Q.-G. et al. (2006).  The cusp: a window for particle exchange between the radiation belt and the solar wind.  In Annales Geophysicae (pp. 3131--3137).  Copernicus Publications Göttingen, Germany volume 24.