GEM 2013 Summer Workshop

GEM 2013 Summer WorkshopStudent Tutorial __ _ Sunday 16 June 2013

The Outer Magnetosphere

David A. MacklerPhD CandidateThe University of Texas at San AntonioSouthwest Research [email protected]

Outer Magnetospheric StructuresStudent Tutorial __ _ Sunday 16 June 2013

• Bow Shock• Magnetosheath• Magnetopause• Magnetospheric

Boundary Layers– Low-Latitude Boundary

Layer (LLBL)– High-Latitude Boundary

Layer (Plasma Mantle)– Exterior Cusp

• Magnetotail

Bow ShockStudent Tutorial __ _ Sunday 16 June 2013

Solar wind is supersonic; standing shock front forms when the solar wind impinges on our magnetosphere and diverts plasmaPlasma in this region is largely collisionless; no viscosity for energy dissipation, wave modes are Alfvénic rather than sonicStands ~15-20 Re upstream. The shape is roughly parabolic

https://ase.tufts.edu/cosmos/view_picture.asp?id=112

Fast mode shock: Shock front travels faster than the MHD fast mode wave

Slow Mode Fast Mode

Bow ShockStudent Tutorial __ _ Sunday 16 June 2013

Bow shock slows and heats the solar wind plasma, strongest gradient near the sub-solar pointBow shock includes perpendicular [dusk] and parallel [dawn] components. Perpendicular shocks increase both density and field strengthPerpendicular shocks above Critical Alfvén Mach number ~2.7: Super-Critical. Earth’s bow shock is typically super-critical

Sckopke et al., [1983]

Spreiter et al., [1966]

MagnetosheathStudent Tutorial __ _ Sunday 16 June 2013

Turbulent region of space between the bow shock and the magnetopause. Parameters fluctuate due to changes in the solar windMagnetic reconnection: When IMF Bz is south field lines carry magnetosheath particles into high latitude regions

− Profound coupling to the ionosphereParticles are the shocked solar wind with contributions from the ionosphere [O+] when IMF Bz is NORTH and magnetosphere (higher eV) when IMF Bz is SOUTH

MagnetosheathStudent Tutorial __ _ Sunday 16 June 2013

SW Vs. MS: Bt ↑, un ↓, T ↑, ρ ↑

• SW ~1.5 – 10 keV ~10 cm-3 ~400-750 km/s ~5-10 nT• MS ~0.1 - 1 keV ~20 cm-3 ~200-300 km/s ~20-40 nT

Magnetosheath particles entering the dayside cusps contribute to the dayside auroral precipitation (E < 0.5 keV ‘soft electrons’ mostly 6300 Å)

B field is weaker than the magnetosphere

Wang et al. [2003]Hu et al. [2009]

MPBS

IMF draping across and interacting with the magnetopause – Plasma Depletion Layer

MagnetopauseStudent Tutorial __ _ Sunday 16 June 2013

Abrupt magnetic boundary between the Earth’s magnetosphere and the surrounding plasma

─ Controls the transport of mass/momentum/energy

Stand off distance can be approximated by pressure balance ~10 Re

IMF Bz North:− Closed field lines− No mass transport− Momentum and energy transported by

waves

IMF Bz South:− Open field lines− Mass, momentum, and energy

transport− ReconnectionBn = 0:− Tangential Discontinuity, no mass

transferBn ≠ 0:

− Rotational Discontinuity, transfer across MP

~800 km

10’s km/s

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swswrBv

242

Magnetospheric Boundary LayersStudent Tutorial __ _ Sunday 16 June 2013

Low Latitude Boundary Layer (LLBL)− Low latitude dayside, extending into

dawn/dusk − Partially thermalized with MS− Sharp inner boundary

Not actual ‘Boundaries’− Regions near Earth influenced by magnetosheath

plasma− Connected by magnetopause reconnection− Map to high latitude regions near the cusp

Hasegawa, 2012

− Flow can be seen in all directions, generally tailward(~100 km up to MS)

− less dense than MS (~0.5 - 10 cm3)− Energy similar to MS (~0.1 – 1 keV)

Newell and Meng, 1992


IMF Bz North (closed field lines):− High lat. reconnection, transports to LLBL− Low velocity flow, KH instability grows (non-

linear)− LLBL is thick (many Re)

IMF Bz South (open field lines):− Low lat. Reconnection− Higher velocity flow, KH instability might not

grow− LLBL is thin (< 1 Re) or disappears

Earth's Magnetic Field in the Magnetosphere

Solar Wind Magnetic Field

Solar Wind Earth's Magnetic Field in the Magnetosphere


Southward IMF

Solar Wind

Northward IMF

Earth's Magnetic Field in the Magnetosphere


Solar Wind Earth's Magnetic Field in the Magnetosphere


Southward IMF

Solar Wind

Northward IMF


High Latitude Boundary Layer (Plasma Mantle)− High latitude magnetosphere, tailward of the

cusp− De-energized MS particles− Often has no sharp inner boundary− Tailward flow(~100 – 200 km/s)− Low density (~0.01 - 1 cm3)− Energy similar to MS (~0.1 – 1 keV)− Open field lines− Gradual transition from sheath to lobe

Geotail satelliteFar downtail (-170, 28, 20) Re [GSM]4 distinct MS – PM – Lobe crossings

Shodhan et al., 1996

MS

Lobe

Mantle


IMF Bz South:− Mantle becomes thicker− O+, He+, from ionosphere (polar wind)− Velocity filter effect

Flow speed, density, and temperature all decrease away from the magnetopause subsolar point

− Faster particles can make it to lower L shells− Less energetic particles are convected more

Trattner et al., 2001


Exterior Cusp (High-altitude Cusp)− Dayside boundary of the polar cap− ~8-15 Re− Centered at noon LT, extends ~3 h each

side− ~2 Re wide− Coupled to but distinct from low-altitude

cusp− Plasma is characteristic of magnetosheath− Open field lines, both IMF Bz North and

South− Low speed, disordered, possibly turbulent

flowsCurrent exterior cusp research is diverse − High-frequency waves− Shock region/Rotational discontinuity− Stagnant Exterior Cusp (SEC) – higher density− Cusp Diamagnetic Cavity (CDC) – B ≈ 0− MeV ions and electrons

Cusp ion precipitationNorthward IMF


Cluster observations of a Lobe – Exterior Cusp pass

Lobe Cusp

Lavraud et al., 2004

MagnetotailStudent Tutorial __ _ Sunday 16 June 2013Nightside outer magnetosphere that is stretched out by the solar wind. Open field lines are ‘horizontal’

Site of nightside reconnection that leads to dipolarization, substorms, geomagnetic storms, plasmoids

Dungey [1965] estimated the magnetotail:− SW plasma flows over the polar cap in ~3

hours− LMT ~600 Re

MagnetotailStudent Tutorial __ _ Sunday 16 June 2013

FINAL NOTE:MT is highly dynamic, i.e. depending on the solar wind and IMF there is twisting, flapping, and flaring (diameter increases)

Lobe Diameter:− Assume conservation of magnetic flux from

cap to tail− DMT ~20 Re

Lobes− Open, anti-parallel B field− Strong field, low density (~0.01 cm-3)

Plasma Sheet Boundary Layer (PSBL)− Intermediate energy and density− Sunward ‘counter streaming’ ions

Central Plasma Sheet− Hot [Te ~0.1-1 keV, Ti ~0.5-5 keV]− higher density (~0.1-1 cm-3)

Eastman et al., 1984

tailtailopse

lobepc

BRBR 22

21sin2

Enjoy GEM and Snowmass Village!

Extra Slides

Earth’s MagnetosphereStructure and Dynamics

• Solar wind impinging on the magnetosphere: compresses dayside, stretches nightside

• Rotating Earth (Dynamo Theory)– Magnetic field induced by liquid iron (conducting) in the

outer core: coriolis force– Creates vertical convection: Taylor columns

• Dayside / nightside reconnection– Dungey Cycle– Open / closed field lines

• Convection ‘pumps’ energetic particles to the inner magnetosphere - aurora

Student Tutorial __ _ Sunday 16 June 2013

Kivelson, M., and Russell, C. Introduction to Space Physics

Documents

GEM 2013 Summer Workshop