comparative cusp processes - uclucapnac/badmancusps_nomov.pdfbranduardi-raymont et al., jgr, 2008...
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Comparative Cusp Processes
Sarah V. BadmanJAXA ISAS, Japan
Jupiter: Pallier & Prangé, GRL, 2004
AOGS ST14-A016
Saturn: Gérard et al., JGR, 2005
Earth: Milan et al., JGR, 2000Mercury: Zurbuchen et
al., Science, 2011
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Magnetospheric Cusps•Minima in magnetic field - between sunward and
anti-sunward field lines
•Magnetosheath plasma can penetrate to the planetary ionosphere or surface
• Exists for northward and southward IMF
•Dynamics are driven by reconnection
• Location and spectrum of precipitating particles depends on IMF orientation
Tsyganenko & Russell, JGR, 1999
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Terrestrial cusp spots• Proton aurora cusp spot seen when solar wind
dynamic pressure is high Fuselier et al., JGR, 2002
• Southward IMF:
•Cusp spot merges into intense noon auroral oval
•Component reconnection occurring across broad region of low-latitude magnetopause
•Northward IMF:
• Proton cusp spot poleward of noon auroral oval
•Anti-parallel reconnection occurring at high latitude (lobe)
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Ionospheric signatures of reconnection
• Poleward moving auroral forms (dayside arc bifurcations) are signatures of transient reconnection at the magnetopause [Milan et al., JGR, 2000]
ß
ß
12 LT12 LT
22 12 14 16 18 20 22 MLT
with Defense
measurements,
evidence, iono- day-
observed study
in tran-
By- de-
precipita- and
observations demon-
colocated by as
poleward-moving backsca-
to
Region of newly opened flux ,•.•-_•,_ Main auroral oval
Merging gap••.• ..• .•.••••• ..................... Closed field lines Pola ........
.... ::• i.•: ;- ':':::-:::-•:'-
a. Radar data showing poleward flow
b. Auroral image showing splitting of arc
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Cusp aurora at other planets?
•Magnetosheath plasma density and temperature are not sufficient to produce the auroral intensities observed: ~MR (J), ~10s kR (S)
• Field-aligned potential drops are required to accelerate plasma and sufficiently increase the precipitating energy flux [Bunce et al., JGR, 2004(J), 2005(S)].
•Driven by pulses of reconnection?
Pallier & Prangé, GRL, 2004Radioti et al., JGR, 2011
Gérard et al., JGR, 2005
Jupiter (HST/STIS) Saturn (HST/STIS, Cassini/UVIS)
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In situ observations and images of Saturn’s cusp
LEMMS e
ELS e θ<20°
RPWS
INCA ions θ<30°
FAC15 November 2008 (d320)
• Cassini observed remote and in situ signatures of repeated, transient reconnection events.
• Layers of currents & poleward auroral arcs.
• Some plasma-depleted field lines
• Bursts of • electrons (keV - MeV)• upward ion conics (≥300
keV H and ~600 keV O)• whistler waves (1-100 Hz)
• Both high latitude (lobe) and low latitude (flux opening) transient reconnection are possible [Bunce et al., JGR, 2005].
Badm
an et a
l., JG
R, 201
2
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Jupiter’s cusp emissions
• UV auroral flares
• 2 min periodicity in intensity, similar to FTE occurrence
• ~100 keV electron precipitation
Waite et al., Nature, 2001
Bonfond et al., GRL, 2011
•Main oval driven by corotation-enforcement currents mapping to the middle magnetosphere
•Cusp emissions are high latitude
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Jovian X-ray emissions
• Large dots: >2 keV photons
• Electron bremsstrahlung
•Co-located with main UV emission: same accelerated magnetospheric electron population (~100 keV)
Branduardi-Raymont et al., JGR, 2008• 40 min periodicity in X-ray counts
[Gladstone et al., Nature, 2002]
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Jovian X-ray emissions
•Consistent with Ulysses observations of 16 MeV electron bursts streaming away from Jupiter [McKibben et al., PSS, 1993]. These were sometimes pulsed with ~40 min periodicity
• Location, periodicity, downward current are explained by pulsed reconnection model with outer magnetosphere plasma source [Bunce et al., JGR, 2004]
Branduardi-Raymont et al., JGR, 2008
• Small dots: <2 keV photons
• Heavy ion charge exchange (highly stripped O and S) [Elsner et al., JGR, 2005]
•Outer magnetosphere source, accelerated to ~16 MeV by low-altitude field-aligned potential
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Mercury cusps• The lack of atmosphere means the solar wind plasma
impacts on the planet’s surface: source of exosphere
•Neutral exosphere is ionized by precipitating particles Zurbuchen et al., Science, 2011
•Na and O ion fluxes enhanced over northern cusp
• Ion fluxes reflect variability in solar wind conditions
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Mercury cusps•Northern cusp region is
persistently present
• Spatial extent depends on magnetospheric dynamics
•Magnetic depression is stronger for high solar wind dynamic pressure intervals and anti-sunward IMF orientation (BX<0)
• Southern cusp expected to be larger, with more sputtering & contribution to the exosphere
Winslow et al., GRL, 2012
Slavin
et a
l., Sc
ienc
e, 201
0
?
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Summary•Magnetospheric cusps funnel plasma down to the
planet’s atmosphere or surface.
• Ionization, excitation, and sputtering occur.
•Cusp auroral features can be used to diagnose the location and type of reconnection occurring.
Tsyganenko & Russell, JGR, 1999
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Summary•Magnetospheric cusps funnel plasma down to the
planet’s atmosphere or surface.
• Ionization, excitation, and sputtering occur.
•Cusp auroral features can be used to diagnose the location and type of reconnection occurring.
Tsyganenko & Russell, JGR, 1999
•Not just funneling down:
• Saturn: 600 keV O ion conics
• Jupiter: X-ray aurora & relativistic electrons
•Mercury: heavy ion exosphere