gem 2013 summer workshop
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GEM 2013 Summer Workshop. Student Tutorial __ _ Sunday 16 June 2013. The Outer Magnetosphere. David A. Mackler PhD Candidate The University of Texas at San Antonio Southwest Research Institute [email protected]. Outer Magnetospheric Structures. - PowerPoint PPT PresentationTRANSCRIPT
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
o
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
Magnetospheric Boundary LayersStudent Tutorial __ _ Sunday 16 June 2013
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
Solar Wind Magnetic Field
Southward IMF
Solar Wind
Northward IMF
Earth's Magnetic Field in the Magnetosphere
Solar Wind Magnetic Field
Solar Wind Earth's Magnetic Field in the Magnetosphere
Solar Wind Magnetic Field
Southward IMF
Solar Wind
Northward IMF
Magnetospheric Boundary LayersStudent Tutorial __ _ Sunday 16 June 2013
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
Magnetospheric Boundary LayersStudent Tutorial __ _ Sunday 16 June 2013
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
Magnetospheric Boundary LayersStudent Tutorial __ _ Sunday 16 June 2013
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
Magnetospheric Boundary LayersStudent Tutorial __ _ Sunday 16 June 2013
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