White paper on collaborative observations
between ERG and EISCAT
written byERG - EISCAT joint project team(Contributors: Y. Ogawa, Y. Miyoshi, K. Shiokawa, I. Shinohara,
K. Hosokawa, S. Tam, and Y. Miyashita)

Updated on November 27, 2016

History of this manuscript:
2016-09-12: Y. Ogawa prepared the first draft of the white paper after discussion with Y.
Miyoshi and I. Shinohara.
2016-09-12: Y. Miyoshi modified the draft of the white paper.
2016-09-13: K. Shiokawa commented on the draft, and Y. Ogawa modified it.
2016-09-14: K. Hosokawa prepared an updated figure for the draft.
2016-09-14: Plans of the ERG-EISCAT collaborative observations was discussed at the EISCATScience oversight committee (SOC) meeting at Tromsoe, Norway, based on thedraft.
2016-09-20: Y. Ogawa distributed the draft to ERG mailing list members and Y. Miyoshi to PIsof ERG instruments, and asked them comments and inputs on it.
2016-10-03: S. Tam commented on the draft.
2016-10-19: Y. Miyashita gave an input and comments on the draft.
2016-10-19: Y. Ogawa updated the draft based on all the comments and inputs.
2016-10-21: T. Ulich (chair of the SOC) received the latest draft, to discuss the ERG-EISCAT
collaborative observations at the council meeting in UK (November 2-3).

Executive Summary
This document outlines potential collaborative observations and scientific studies involving theERG satellite and EISCAT radars during the mission commissioning phase of the ERG in 2017 and2018. It describes background of the missions, science targets by mission phase, and possible data
usage during the coordinated ERG and EISCAT observations.

1. Introduction
The European Incoherent Scatter (EISCAT) scientific association was founded in 1975, and has
conducted observations of the polar upper atmosphere over northern Scandinavia since 1981 andover Svalbard since 1996. The EISCAT radars enable us to measure ionospheric parameters(electron density, electron and ion temperatures, and ion velocity) from the D-region ionosphere(above about 60 km) to the topside ionosphere (up to about 1500 km). Combination of the EISCAT
systems in northern Scandinavia and Svalbard allows extended investigations of the polar
ionosphere in the polar cap, auroral zone, and sub-auroral region. Previous and present researches
have been focused on solar influences of Earth's environment in conjunction with many spacecrafts(e.g., Cluster II since 2000, and SWARM since 2014). Coordinated EISCAT observations with thesatellites have been conducted as Common Program (CP), special program (SP) including the third
party program, and/or special programs of all EISCAT associations (AA).
One of important opportunities as next coordinated observations with satellites is collaborative
magnetospheric and ionospheric researches with JAXA's Exploration of energization and Radiationin Geospace (ERG) mission (see Figure 1), which is scheduled to launch late in the Japanese Fiscal
Year 2016 (April 2016-March 2017). A main science target of the ERG satellite mission is tounderstand the generation and loss of relativistic electrons through cross-energy and cross-regional
coupling processes involving different plasma populations and regions [Miyoshi et al., 2012]. The
satellite will provide in situ data of ion and electron distribution functions with wide energy range(10 eV to 20 MeV for electrons, 10 eV/q to 180 keV/q for ions with mass discriminations), electricand magnetic fields, and plasma waves in the inner magnetosphere and auroral region (Maximum
dipole L-value is expected to be about 9.5). The coordinated ERG and EISCAT observations are
beneficial for many scientists studying upper atmospheric and magnetospheric physics and will be
widely used to understand various geophysical and plasma-physical phenomena occurring between
ionosphere and magnetosphere.
The joint missions with the ERG satellite and EISCAT radars will take place for about two yearsafter the launch of ERG satellite. Here we address outline of scientific targets for the coordinated
ERG and EISCAT observations, and also possible data usage of the coordinated observations.

Figure 1: Schematic illustration of the ERG satellite (M-class mission of ISAS/JAXA)

2. ERG satellite orbits and instruments
The ERG satellite will have an orbit with apogee geocentric distance of 6.2 RE, perigee altitude of300 km, inclination angle of 31°, and orbital period of about 9 hours. Initial apogee local time of theERG is 09 LT. The L-shell of the apogee altitude depends on season, and the expected
Maximum dipole L-value is about 9.5, where the EISCAT mainland radars are located. Figure 2shows an example of footprint of the ERG satellite over Scandinavia. When footprint of the ERG
approaches the EISCAT radar site, the ERG is able to measure continuously magnetosphericplasma , and fields and waves for about 4-6 hours within the field of view of several groundobservations.. Figure 3 shows time variations of conjunctions near Tromsø (Geographic latitude of
69.6 deg, Geographic longitude of 19.2 deg). The footprints of the ERG at apogee will come to theEISCAT location every season. Coordinated observations will be realized in the morning sector(00-05 MLT) about three months after the launch, in the evening sector (15-20 MLT) ten –elevenmonths after the launch, and in the nightside (20-02 MLT) five – seven months after the launch andalso ten-eleven months after the launch.
The International Geomagnetic Reference Field (IGRF-12) will be used to calculate the magnetic
footprints of the ERG observations. However, it may not be easy to find one-to-one correspondencebetween the ERG and EISCAT, because the field line tracing depends on the magnetic field model.
We think that meso/large scale phenomena such as diffuse/pulsating aurora would be good subjects
for comparison between ERG and EISCAT data, because we may observe wide-spread aurora
phenomena within FOV.
The instrumentation for the ERG mission is summarized in Figures 4 and 5. The ERG measureselectrons with wide energy range (from 17 eV to 20 MeV), ions with mass discriminations (H+, He+,
He++, O+. etc) from 10 eV/q to 180 keV/q, and electric and magnetic fields with wide frequencyrange. The ERG has burst mode capabilities of field experiments to identify the wave form. The
ERG has burst mode capabilities of fields experiments. More information on the experiments on
ERG can be found in Miyoshi et al. [2012].

Figure 2: A predicted footprint of the ERG satellite over Scandinavia. A dotted line indicates theERG footprint. Field-of-view of all-sky cameras at Tromsø, Sodankyla, and Tjautjas issuperimposed.

Figure 3: Time variations of predicted footprints of the ERG near Tromsø, Norway.

Figure 4: Particle measurements of the ERG satellite. The ERG measures ions with mass
discriminations (H+, He+, He++, O+. etc)

Figure 5: Electric and magnetic field measurements of the ERG satellite. Data from burst
measurements are labeled in red.

3. Science targets by mission phase
We prioritize science objectives of the two-year joint observations with the ERG satellite andEISCAT radars according to the location of the spacecraft. The observation period is divided into
three phases. Science targets for joint observation are identified for each phase. Figure 6 shows thelocation of various wave modes in the inner magnetosphere and plasma sheet. These wave modes
are regarded as the primary processes for controlling the flux of energetic electrons in the outerzone radiation belt. As well as the ERG and EISCAT coordinated observations, several joint studies
with ERG satellite have been planned (e.g., ERG and Van Allen Probes by Takahashi et al. [2014];
ERG and SuperDARN by Hori et al. [2016]), and thus collaborations with other satellites andground-based projects are also important for comprehensive understanding of coupling system ofthe magnetosphere and ionosphere.

Figure 6: Schematic illustration of wave modes in the inner magnetosphere and plasma sheet andmajor processes in the outer zone radiation belt [Thorne, 2010].

3.1 Phase 1: Morning sector (00-05 MLT)
After commissioning operation of the ERG satellite, the normal mission by all scientificinstruments will start three months after the satellite launch. The spacecraft will be ideally locatedfor studying characteristics and generation mechanisms of chorus waves and pulsating aurora in themorning sector. Figure 7 shows ERG orbits during the phase 1. The ERG measures internallygenerated dawnside chorus waves and resultant pitch angle scattering of energetic electrons.,
whereas EISCAT radars simultaneously observe electron density modulations due to pulsating
aurora and estimate precipitating electron energy spectrum and fluxes. From the previousobservations, wide energy electron precipitations from keV to a few hundred keV are expectedassociated with the pulsating aurora [Miyoshi et al.,, 2015]. During the ERG-EISCAT observations,burst mode observations of the ERG wave instruments and fine channel observations of a few keVelectrons will be used for identification of chorus wave modulation and its relation to pulsating
aurora.

Figure 7: ERG orbits during the phase 1.

3.2 Phase 2: Nightside sector (20-02 MLT)
Magnetic storm and auroral substorms frequently occur during equinox. Significant contributionof hot O+ ions (> keV) to inner magnetospheric plasma pressure during the magnetic storm has been
discussed in the previous study. However, response of mass transfer between ionosphere andmagnetosphere to solar wind variations is not fully understood. ERG will simultaneously measurecold (< 100 eV) and hot O+ ions (> keV) in the inner magnetosphere, whereas EISCAT measures
time and height variations of ionosperic O+ upflow. Ion instruments with time resolution of 8-sec
are desirable during the magnetic storm.
Energetic particle injection is important for understanding seeds for the radiation belt. Injection iscaused by substorm dipolarization in the near-Earth magnetotail. Energetic particles then drift in theinner magnetosphere around the Earth and precipitate into the ionosphere and even into the upperatmosphere. The ERG satellite will observe not only dispersed drift echoes away from the particle
acceleration region but also dispersionless injection in the acceleration region or in a region
magnetically connected to the acceleration region. On the other hand, the EISCAT radars canmonitor injection by observing energetic particle precipitation associated with injection. Combining

ERG and EISCAT observations will deepen our understanding of how and to what energy particles
are accelerated.
3.3 Phase 3: Evening sector (15-20 MLT)
During a magnetic storm, EMIC waves are often excited in the evening sector near theplasmapause. However, contribution of the EMIC waves to loss of electrons in the radiation belts
and its relation to proton precipitation into the ionosphere are not clear yet. In this phase 3, weinvestigate excitation of the EMIC waves in the dusk sectors with ERG wave and ion measurements,
whereas ground-based optical instrument can simultaneously identify proton aurora at the samesectors. High-speed meridional scans of the EISCAT UHF radar is effective for investigation of thealtitude profile of electron density in the sub-auroral region (see Figure 9). Burst mode of ion andwave instruments are desirable during the coordinated observations.

Figure 8: ERG orbits during the phase 3.

Figure 9: Examples of electron density data with the EISCAT high-speed meridional scan.
Horizontal axis indicates distance from the EISCAT Tromsø UHF radar.
4 Data policy of the EISCAT, ERG, and their coordinated observations
4.1 EISCST data policy
The EISCAT data policy is summarized in page 39 of the EISCAT Bluebook Edition 2015(https://www.eiscat.se/eiscat2014/eiscat-bluebook-edition-2015/view). Common program (CP) data
are immediately distributed all over the world after their observations. Special program (SP) andPeer review program (PP) data are for exclusive use of the user who carried out the observation
during 1 year, and for exclusive use within the EISCAT membership for 2 following years. SP databy all association (AA) are for exclusive use of the all users in associates and affiliates for 1 year.
Rules of the road of EISCAT data are written in the following website:
https://www.eiscat.se/groups/Documentation/UserGuides/EISCATRules/rules_of_the_road.html
4.2 ERG data policy
Regarding a plan of data policy for normal ERG observations, the ERG-Science data will be
opened to the public via the ERG-Science Center website(http://ergsc.isee.nagoya-u.ac.jp/index.shtml.en) after necessary calibration. Necessary period forthe calibration differs depending on the instruments. We estimate the calibration will take about afew months - one year at the latest. CDF data format is used for data of all instruments of ERG.
Details of the ERG-Science Center are written by Hori et al. [2013, 2015]
4.3 Data policy of the coordinated ERG and EISCAT observations
A plan of data policy for ERG-EISCAT coordinated observations is currently under considerations.
As a plan in the on-going discussion, EISCAT team members of the coordinated observations canbasically use the ERG-Science data for the defined period for the coordinated observation studies as
the same policy as the ERG project team members. In any case, contact to the ERG project andPI(s) of instruments on ERG is necessary before any presentation and publication. Redistribution ofthe ERG-Science data without permission of the ERG project is strictly prohibited.
EISCAT observations for collaboration with the ERG satellite will be conducted as a combinationof the CP, SP, PP, and AA. All EISCAT data defined as the coordinated observations will beprocessed to make CDF format files, and integrated with other related data. The ERG team member
can also use the EISCAT data as collaborative studies. A web tool named "Conjunction Event
Finder (CEF)" [Miyashita et al., 2011] will be used to browse quick-look data from ERG satellite
and EISCAT coordinated observations.

References
EISCAT Bluebook EDITION 2015 (2015), EISCAT scientific association.
https://www.eiscat.se/eiscat2014/eiscat-bluebook-edition-2015/view
Miyashita et al. (2011), A powerful tool for browsing quick-look data in solar-terrestrial physics:"Conjunction Event Finder", Earth Planets Space, 63, e1–e4.
Miyoshi, Y. et al. (2012), The Energization and Radiation in Geospace (ERG) Project, in Dynamics
of the Earth’s Radiation Belts and Inner Magnetosphere, Geophysical Monograph Series, 199,
edited by D. Summers, I. R. Mann, D. N. Baker and M. Shultz, doi:10.1029/2012GM001304,AGU, 103–116.
Miyoshi, Y. et al.(2015), Energetic electron precipitation associated with pulsating aurora: EISCATand Van Allen Probe observations, J. Geophys Res., 120, doi:10.1002/2014JA020690.
Hori et al. (2015), CDF data archive and integrated data analysis platform for ERG-related grounddata developed by ERG Science Center (ERG-SC), J. Space Sci. Info. Jpn., vol. 4,
JAXA-RR-14-009 (ISSN 1349-1113), 75-89.
Hori et al. (2015), An integrated analysis platform merging SuperDARN data within the THEMIS
tool developed by ERG-Science Center (ERG-SC), Adv. Polar Sci., 24,doi:10.3724/SP.J.1085.2013.00069, (2013), 69–77.
Hori et al. (2016), Memorandum for ERG and SuperDARN collaborative studies.
Takahashi et al. (2014), Opportunities for cooperation: Van Allen Probes and ERG.
Thorne, R. M. (2010), Radiation belt dynamics: The importance of wave-particle interactions,Geophys. Res. Lett., 37, L22107.