1. THEMIS The THEMIS mission approach to addressing the substorm question
TIME HISTORY OF EVENTS AND MACROSCALE INTERACTIONS DURING SUBSTORMS
RESOLVING THE MYSTERY OF WHERE, WHEN AND HOW AURORAL ERUPTIONS START
The THEMIS mission
approach to addressing the substorm question
Fall AGU,
Dec 5, 2005

2. TIME HISTORY OF EVENTS AND MACROSCALE INTERACTIONS DURING SUBSTORMS (THEMIS)
SCIENCE GOALS:
Primary:
“How do substorms operate?”
One of the oldest and most important questions in Geophysics
A turning point in our understanding of the dynamic magnetosphere
First bonus science:
“What accelerates storm-time ‘killer’ electrons?”
A significant contribution to space weather science
Second bonus science:
“What controls efficiency of solar wind – magnetosphere coupling?”
Provides global context of Solar Wind – Magnetosphere interaction
PROGRAMMATIC:
Selected in March 2002 for Phase A studies
Selected in April 2003 to proceed to Phase B: MIDEX#5
Confirmed in May 2004 to full mission development
Critical design review, June 2004
Launch no later than March 2007 on a D2925
Current launch date: October 19, 2006
2YR mission; prime seasons: February 2007; February 2008.
RESOLVING THE PHYSICS OF ONSET AND EVOLUTION OF SUBSTORMS
Principal Investigator
Vassilis Angelopoulos, UCB
Project Manager
Peter Harvey, UCB
Industrial Partner
SWALES Aerospace
EPO Lead
Nahide Craig, UCB

3. FGM ESA/IDPU EFI/SPB SCM ASI SST Science Team
THEMIS is an international program
Science Team
FGM
ESA/IDPU
EFI/SPB
SCM
ASI
SST

4. Mission elements
Probe conjunctions along Sun-Earth line recur once per 4 days over North America.
Ground based observatories completely cover North American sector; determine auroral breakup within 1-3s …
… while THEMIS’s space-based probes determine onset of Current Disruption and Reconnection each within <10s.
: Ground Based Observatory

5. Current Disruption Model
Substorm phenomena THEMIS will address ?
Current Disruption Model
time
Event
0 sec
Current Disruption
30 sec
Auroral Eruption
60 sec
Reconnection
Reconnection Model
time
Event
0 sec
Reconnection
90 sec
Current Disruption
120 sec
Auroral Eruption
Rarefaction wave ? ?
GBO P3 P4 P5 P1 P2
Flows
Timing between current disruption, reconnection and ground onset withing 30s time resolution
Macroscale Interactions (causal relationship)
Capture outward motion (1600km/s) of rarefaction wave and inward motion of flows and boundary layer poynting flux
Ionospheric coupling
Cross-tail current reduction (P5u/P4) vs flows
Field aligned current generation by Rx flow vorticity, pressure gradients (dP/dz, dP/dx).
Cross-scale coupling to local modes
Field line resonances (10Re, 5min)
Ballooning modes, KH waves (1Re, 1min)
Weibel, CCI, kinetic Alfven waves (0.1Re, 6Hz)

6. THEMIS CCE CD detection
CD triangulation and onset determination as on AMPTE/CCE [Lui et al, 1988].
To Tail
THEMIS
CCE
Spin axis
To Earth
To Sun
Method exploits finite ion gyroradius to remotely sense approaching ion boundary and
measure boundary speed (V⊥)

7. Remote Sensing by Ion Sounding
Proton Energy
Gyroradius for B = 10 nT
10 keV
~ 0.22 Re
50 keV
~ 0.59 Re
100 keV
~ 0.83 Re
200 keV
~ 1.17 Re
Separation of 1 hr MLT on the ground corresponds roughly to ~ 2.6 Re at a geocentric distance of ~ 10 Re.
A ~1 hr MLT worst-case separation between ground onset and projected spacecraft location (mapping uncertainty) can be mitigated by using ~200 keV ion sounding.
Triangulation of the expansion velocity measured at two nearby locations assuming a nearby source (V=1.5Re/min = constant over ~2min => need ~3Re proximity).

8. The 3D nature of the CD process
Lopez & Lui [1990]
GOES 6 detected dB at ~08:30 UT, GOES 5 at ~08:33 UT, and CCE (R ~ 8.0 Re) at ~08:35 UT

9. The 3D nature of the Rx process
0204UT
JGR [Angelopoulos et al, 1995]
Substorm Onset: ~0202UT
Ygsm
Xgsm
0215UT
Ygsm

10. Remote sensing of Rx onset
Based on techniques derived to determine location and onset time of plasmoid release from ISEE3 energetic particle data (X=-220Re) [Richardson and Cowley, JGR 1985]
Resolved paradox of earlier findings by Scholer et al 1984 that energetic particle acceleration was derived (assuming temporal interpretation) to be at distances inconsistent with plasmoid release.
Needed to invoke electric field pushing particles away from boundary
Needed to invoke spatial interpretation of dispersion

11. …Remote sensing of Rx onset
Rx detection via time-of-flight of energetic particles. dt versus 1/V. Spatial or temporal?
Temporal is easy: LTEMPORAL = slope (dt versus 1/V)
Spatial: LACTUAL=LTEMPORAL*(VE/VB)
Assuming local E-field maps to reconnection E-field
VE=average convection speed, VB=boundary speed from finite gyroradius
VE ,VB not constant (measured) unless distance to Rx is small (~5-10RE)
Richardson and Cowley had VB but not VE
Computed V assuming L was consistent with Near-Earth source
Showed it is consistent with E-fields observed in Near-Earth tail
Determination of Rx location requires a-priori assurances of source proximity
Need to bracket Rx site with 2 spacecraft
This measured VE/VB will be average value from source to observation

12. example from Geotail data
…Remote sensing:
example from Geotail data
Determination of L
E.g., Sarris et al., JGG 1996
Determination of VB
To be done by THEMIS SST
Mounting very similar to GT ICS/EPIC

13. Mission designer predicts compliance with requirements
Substorm recurrence = 3.75 hrs
Encounter probability = 1/5
Residence needed = 19hrs/substorm
Over North America
Probes <±2RE of each other
In plasma sheet (inc<9o)
Limit shadows < 3hrs .
Courtesy: R. Nemzek
THEMIS’s minimum requirement is to study >5 substorms with 4-probes
Need 94 hrs total; have >200hrs / year for 2 year mission
THEMIS’s baseline requirement is to study > 10 substorms with 4-probes while using 5th probe in a variety of dX, dY, dZ configurations
Need 188 hrs / year; have >200hrs / year

14. …. regardless of launch day
4-probes
Tail Season #1
5-probes

15. Conjunctions and their quality look good
(pre-midnight ones are best)…….
Tail Season #1
Tail Season #2

16. Story may be more complex: Energy dissipation via Alfvén waves. [e. g
Story may be more complex: Energy dissipation via Alfvén waves? [e.g., Nakamura et al., 2005]
THEMIS’s 3D electric field measurements may be able to answer this question as well

17. First bonus: What produces storm-time “killer” MeV electrons?
Affect satellites and humans in space
ANIK telecommunication satellites lost for days to weeks during space storm
Source:
Radially inward diffusion?
Wave acceleration at radiation belt?
THEMIS:
Tracks radial motion of electrons
Measures source and diffusion
Frequent crossings
Measures E, B waves locally
Prelude to RBSP?
SST can do crude O+ detection, with proper calibration

18. Important for solar wind energy transfer in Geospace
Second bonus: What controls efficiency of solar wind – magnetosphere coupling?
Important for solar wind energy transfer in Geospace
Need to determine how:
Localized pristine solar wind features…
…interact with magnetosphere
THEMIS:
Alignments track evolution of solar wind
Inner probes determine entry type/size

19. …additional potential for dawn/dusk sector conjunctions over 2-5RE scales
See Sabine Frey poster
Wednesday Morning
Wednesday Morning 1
0800
SM31A-0398
MCC Level 1
THEMIS Orbit Design and Its Science Potential; *S Frey, et al. POSTER   [Abstract]

20. … as well as potential conjunctions w/ Cluster
THEMIS will launch in 2006 with 1st tail season in February 2007.
Potential for Cluster correlative studies:
2007-Jan-28
2007-Feb-28
2007-Mar-23
THEMIS can benefit from Cluster’s Solar Wind and ionospheric monitoring; Cluster can benefit from THEMIS’s upstream, sheath and m-pause monitoring.

21. Mission overview: Constellation and instrument redundancy
SST
ESA
EFIa
EFIs
FGM
SCM
Tspin=3s
BGS
CCAS
Operations
UCB
Release
Encapsulation
& launch
Mission I&T
UCB
Probe instruments:
ESA: Thermal plasma SST: Super-thermal plasma FGM: Low frequency magnetic field SCM: High frequency magnetic field
EFI: Electric field
Instrument I&T
UCB
Ground

22. Ground observatory progress
10/20 UCB&UCLA built GBOs deployed, providing data & experience
All (10) UCLA-provided EPO stations deployed in the US
Tuesday Morning 1
0800
SM21A-0362
MCC Level 1
THEMIS Ground Based Observatories *B Jackel, E Donovan, M Greffen, V Angelopoulos, S Mende, S Harris, W Rachelson, C Russell, D Pierce, D Dearborne POSTER   [Abstract]

23. Probe flight hardware progress
First bus pre-integrated at Swales Aerospace, delivered to UCB, 11/30.
F1-3 instrument suites assembled, suite TV tested, delivered to MI&T
F4-5 instrument suites assembled, in TV testing, expect delivery 12/16
Known issues: electron ESA m-channel plates a bit noisier than FAST
- Have time/replacement plates to address as MI&T is progressing

24. Probe Carrier progress nominal

25. Achievements and Potential
All instruments meet requirements and have been delivered
Spacecraft design meets requirements (mass, power and telemetry)
Spacecraft is magnetically and electrostatically clean
SST science bonus:
Low energy <30keV, good overlap w/ ESA 40keV max)
SST may be able to discriminate keV O+
In summary: THEMIS has state of the art, comprehensive instrumentation, that is fully capable of answering its science objectives and of becoming a very powerful observation platform when combined with other missions.
Looking forward to engaging the entire community in an exciting science program ahead of us!