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/C 100’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 B C D E A Sibeck et al. [GRL, 2008] 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/C 100’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 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 2008-08-08 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 DZ=1000-3000km, DR=1000km Science Objectives: MHD scale FTE: Structure and evolution Electron energization Reconnection: North-south structure Role of cold magnetospheric plasma Z R Diffusion region

Extended Phase – 4th Dayside (Oct 2011 - Feb 2011) Apogee= 12 RE for all (should we go higher?) 24-hour orbital period DZ=200-1000km, DR=200km Science Objectives: Kinetic scale FTE: Structure and evolution Electron energization Reconnection: North-south structure Z R Diffusion region

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

Dayside Science Phase: 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)

Dayside Science Phase: 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 FTE Jiang Liu et al. [GRL,2008] While arrows: Flows Black arrows: B perturbations Color Background: Pressure

Two-spacecraft direct measurements of LLBL thickness magnetopause Oieroset et al. [2008, GRL] TH-E ion energy LLBL TH-A ion energy TH-A TH-E LLBL LLBL Inner edge of LLBL TH-E and TH-A bordered the LLBL at 16:32 UT: -> 0.9 RE (50 ion skin depths) thick at 13.5 MLT !

Northward IMF: Evidence for Single and Dual-Lobe Reconnection Song and Russell [1992] 12.5 MLT THEMIS E BGSM (nT) M’sphere MP Ions (eV) electrons 0o electrons 180o - Uni-directional heated electrons -> single lobe reconnection - Bi-directional heated electrons -> dual lobe reconnection McFadden et al. [GRL, 2008] [Onsager et al., 2001; Lavraud et al., 2006]

Multispacecraft Observations of single and dual lobe reconnection TH-B B C E TH-C TH-E 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

- Nearly stagnant (different from standard flowing LLBL) Evidence for deep solar wind entry across the dayside magnetopause during northward IMF with strong By Oieroset et al. [2008, GRL] 13.5 MLT 16 UT 17 Mixed magnetosheath-magnetospheric ion region earthward of magnetopause - On closed field lines - Density ~ 6 cm-3 - Nearly stagnant (different from standard flowing LLBL)

- Leads to substantial solar wind entry across the dayside MP TH-A TH-E LLBL - Dual-lobe reconnection occurs even with a significant IMF By (> Bz) - Leads to substantial solar wind entry across the dayside MP

Sibeck et al. [GRL, 2008] A |B| B E C |B| D E A D |B| C |B| B |B|

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 THEMIS D Ions electrons VN VLMN BLMN

The bulk flow is perpendicular to the magnetic field Vperp Vpara (km/s)

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

5 THD V ACE B THB B Density V_x V_y V_z Temp. Ppla+ Pmag Ppla+ Pmag+ Pram 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 on the 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 Wave bursts: - 4 KHz E and B THEMIS C BGSM (nT) Ions (eV) magnetosheath M’sphere Density (cm-3) Particle Bursts: 3D ion and electron distributions every 3s 128 DC magnetic field vectors/s 256 DC electric field vectors/s

36 Full 3D Ion and Electron Distributions Sampled in the Reconnection Layer! BGSM (nT) Ions (eV) VGSM (km/s) Reconnection jet VExB VExB V|| Triple counterstreaming ion beams!

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 magnetopause A E C D THEMIS-E ion energy B THEMIS-A ion energy Inner edge of CDPS 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