THEMIS Dayside

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


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:


- 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


- 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


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


• 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)

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


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


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


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

THEMIS Dayside

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