Post on 17-Jan-2016
description
THEMIS Dayside
- Lessons learned from the coast phase and the 1st dayside season
- Current plans for the 2nd dayside season and the extended phases
Orbit for Coast Phase
Coast Phase: May-September 2007
Apogee: ~15 RE
Spacecraft Separation: 1-3 RE between leading and trailing S/C100’s km between inner three S/C
Ideal for studying the structure and dynamics of the magnetopause and boundary layer:
Unique THEMIS contributions:
- Transmission of Hot Flow Anomalies through the bow shock [Eastwood et al., 2008]
- FTE structure and remote sensing {Sibeck et al.; Lui et al.; Liu et al., 2008]
- Thick subsolar LLBL during northward IMF and implications for dual-lobe reconnection [McFadden et al., 2008; Oieroset et al., 2008; Li et al., 2008]
Structures of Flux Transfer Events
Sibeck et al. [GRL, 2008]
BC
DE
A
Lui et al. [2008; JGR}
Orbit for Coast Phase
Coast Phase: May-September 2007
Apogee: ~15 RE
Spacecraft Separation: 1-3 RE between leading and trailing S/C100’s km between inner three S/C
Ideal for studying the structure and dynamics of the magnetopause and boundary layer:
Unique THEMIS contributions:
- Transmission of Hot Flow Anomalies through the bow shock [Eastwood et al., 2008]
- FTE structure and remote sensing {Sibeck et al.; Lui et al.; Liu et al., 2008]
- Thick subsolar LLBL during northward IMF and implications for dual-lobe reconnection [McFadden et al., 2008; Oieroset et al., 2008; Li et al., 2008]
what we wished we had during the coast phase
• Burst data at the magnetopause and bow shock– 3s full 3-D electron distributions for the determination of field line
topology at the magnetopause and in FTE
• 24/7 onboard plasma moments
• EFI on all spacecraft
1st Dayside Season
2008-08-08
Dayside Science Phase: May-September 2008
1 S/C at 30 RE: pristine solar wind 1 S/C at 18 RE: solar wind/foreshock 3 S/C at 11-12 RE: magnetopause/magnetosheath
ideal for studying the response of magnetopause processes to various solar wind conditions
Unique THEMIS contributions:
- MP-Bow Shock crossings 5-min apart due to arrival of solar wind discontinuities [Hui Zhang, GSFC].
- Extreme MP motion (800 km/s) due to a Hot Flow Anomaly [Jacobsen, Oslo].
The deformation and expansion of the MP
from 4-spacecraft measurements
MP moved outward by 4.8 RE in 71s
Bulge moved tailward along the MP at 350 km/s
what we wished we had during the dayside phase
• More magnetopause crossings by the 3 inner spacecraft– Some passes have zero crossings even for THD (12 Re
apogee)– THA (Apogee= 11 Re) had much fewer MP crossings
• 24/7 onboard plasma moments
what we wished we had during the dayside phase
• More magnetopause crossings by the 3 inner spacecraft– Some passes have zero crossings even for THD (12 Re
apogee)– THA (Apogee= 11 Re) had much fewer MP crossings
• 24/7 onboard plasma moments
• More time to look at the data [Sibeck]
2nd Dayside Season (July-Oct 2009)
• Apogees=12.9, 11.6, 11.6, 19.5, 30.4 RE
• Spacecraft alignment every 8 days
Science Objectives:
• SW coupling
Extended Phase – 3rd Dayside (Sept-Nov 2010)
• Apogee= 12 RE for all (should we go higher?)• 24-hour orbital period Z=1000-3000km, R=1000km
Science Objectives: MHD scale• FTE:
– Structure and evolution– Electron energization
• Reconnection: – North-south structure– Role of cold magnetospheric plasma
Diff
usio
n re
gion
R
Z
Extended Phase – 4th Dayside (Oct 2011 - Feb 2011)
• Apogee= 12 RE for all (should we go higher?)• 24-hour orbital period Z=200-1000km, R=200km
Science Objectives: Kinetic scale• FTE:
– Structure and evolution– Electron energization
• Reconnection: – North-south structure
Diff
usio
n re
gion
R
Z
Extended Phase – Dawn-Dusk (between dayside and nightside phases)
– 3-probes "string-of-pearls":– ~100 km – 1 RE separations along-track
Science:– Strong E- field, wave effects– on particle source/losses
• Coast Phase:– FTE structure and remote sensing– Thick LLBL during northward IMF and
implications for dual-lobe reconnection
• Dayside Science Phase:– Extreme magnetopause motion caused by a
Hot Flow Anomaly (HFA)
• Coast Phase:– FTE structure and remote sensing– Thick LLBL during northward IMF and
implications for dual-lobe reconnection
• Dayside Science Phase:– Extreme magnetopause motion caused by a
Hot Flow Anomaly (HFA)
Remote Signatures of a FTEJiang Liu et al. [GRL,2008]
While arrows: Flows
Black arrows: B perturbations
Color Background: Pressure
Two-spacecraft direct measurements of LLBL thickness
TH-E and TH-A bordered the LLBL at 16:32 UT: -> 0.9 RE (50 ion skin depths) thick at 13.5 MLT !
TH-Eion energy
TH-Aion energy
magnetopause
Inner edge of LLBL
TH-A
TH-E LLBLLLBL
LLBL
Oieroset et al. [2008, GRL]
Northward IMF: Evidence for Single and Dual-Lobe Reconnection
McFadden et al. [GRL, 2008]
THEMIS E
- Uni-directional heated electrons-> single lobe reconnection
- Bi-directional heated electrons -> dual lobe reconnection
BGSM
(nT)
Ions(eV)
electrons 0o
electrons 180o
MP
12.5 MLT
M’sphere
[Onsager et al., 2001; Lavraud et al., 2006]
Song and Russell [1992]
TH
-ET
H-C
TH
-B
BCE
Multispacecraft Observations of single and dual lobe reconnection
All spacecraft detected unidirectional heated magnetosheath electrons further upstream of the magnetopause and bi-directional electrons closer to the magnetopause
-> the ordering of uni-directional and bi-directional electrons is spatial
Evidence for deep solar wind entry across the dayside magnetopause during northward IMF with strong By
Mixed magnetosheath-magnetospheric ion region earthward of magnetopause - On closed field lines - Density ~ 6 cm-3
- Nearly stagnant (different from standard flowing LLBL)
16 17UT
13.5 MLTOieroset et al. [2008, GRL]
- Dual-lobe reconnection occurs even with a significant IMF By (> Bz)
- Leads to substantial solar wind entry across the dayside MP
TH-A
TH-E LLBL
A
D
E
B
C
B
DA
C
E
|B|
|B|
|B|
|B|
|B|
Sibeck et al. [GRL, 2008]
THEMIS Orbits on the Dayside
Coast Phase: May-September 2007
All probes in the same orbit
Prime Science Phase: After September 2007
1 S/C at 30 RE 1 S/C at 18 RE 3 S/C at 10-12 RE
ideal for studying the response of magnetopause processes to various solar wind conditions
Magnetopause moving at extreme velocity (vN~ 800 km/s)
Caused by a Hot Flow Anomaly
Knut Jacobsen, University of Oslo
Magnetopause expanding outward at a speed of 800 km/s
VN
VL
MN
BL
MN
Ion
sel
ectr
on
s
THEMIS D
The bulk flow is perpendicular to the magnetic field
Vpara (km/s)
Vperp
What caused the extremely fast outward expansion of the magnetopause?
• Nothing in the pristine solar wind pressure (measured by ACE and Geotail) could account for this motion
• THEMIS B, located just upstream of the bow shock, observed a hot flow anomaly and associated drop in the dynamic pressure
V_x
V_y
V_z
ACE B
THB B
Density
Ppla+
Pmag
Temp.
THD V
Ppla+
Pmag+
Pram
5
Hot Flow Anomaly
Interpretation:
The dramatic drop of the upstream pressure associated with a hot flow anomaly causes the outward expansion of the magnetopause
Conclusion:
Kinetic effects (not present in MHD) can have global consequences onthe magnetosphere
2008-08-08
Dayside Science Phase: May-September 2008
1 S/C at 30 RE: pristine solar wind 1 S/C at 18 RE: solar wind/foreshock 3 S/C at 10-12 RE: magnetopause/magnetosheath
ideal for studying the response of magnetopause processes to various solar wind conditions
Burst Mode (High Resolution) Data at the Magnetopause and Bow Shock
THEMIS C
Ions(eV)
Density (cm-3)
Particle Bursts:- 3D ion and electron distributions every 3s- 128 DC magnetic field vectors/s- 256 DC electric field vectors/s
magnetosheathM’sphere
Wave bursts:- 4 KHz E and B
BGSM
(nT)
Reconnection jet
36 Full 3D Ion and Electron Distributions Sampled in the Reconnection Layer!
VGSM
(km/s)
BGSM
(nT)
Ions(eV)
Triple counterstreaming ion beams!
VE
xB
V||
VE
xB
Summary
• The 5-spacecraft THEMIS mission is great for magnetopause investigations
• The complete THEMIS data and software is open to the world at:
themis.ssl.berkeley.edu
- Cold-dense plasma sheet on closed field lines
- Presence of mixed magnetosheath-magnetospheric electrons in the layer
Thickness of CDPS: THEMIS-E and THEMIS-A
THEMIS-E and THEMIS-A borders cold dense plasma sheet at 16:32 UT→ thickness can be measured
Cold dense plasma sheet was 0.9 RE thick at 16:30 UT, 0.65 Re 30 minutes earlier
A
BD
EC
THEMIS-Eion energy
THEMIS-Aion energy
magnetopause
Inner edge of CDPS