JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. A10, 1366, 2003
Jupiter’s Polar Auroral Emisssions
D. Grodent, J.T. Clarke, J.H. Waite Jr.,
S. W.H. Cowley, J.-C. Gerard, and J. Kim
Reviewed By Hao Cao
Journal Club 03-31-2010
Jupiter’s Aurora
Cowley’s Theoretical Frame
Dungey Cycle
Vasyliunas Cycle
Sub-corotating Hill Region
Cowley’s Theoretical Frame
Cowley’s Theoretical Frame
About this Paper
• An imaging study of Jupiter’s FUV polar
aurora
• The first detailed description of the polar
auroral emissions
• Relate the polar emissions to the
theoretical frame described by Cowley et
al. [2003], and Infrared (IR) picture of the
auroral morphology
Observations
• STIS camera onboard Hubble Space
Telescope (HST)
• Winter of 2000 – 2001
• 200 far-untraviolet (FUV) images
• Sensitive to H2 Lyman and Werner bands
& H Lyman-a line
• Major improvement over previous
observations: locations, continuously
Auroral Emitted Power
Auroral Emitted Power
• Polar emissions are far more variable than
the main oval emission
• Polar emissions contribute to the total
emitted power ~30%
• Main oval emission is decoupled from the
polar emissions, indicating that they stem
from different flow dynamics
Polar Auroral Regions
• Map out in the magnetosphere at radial
distance greater than 30 Rj
Comparison with the Earth: poleward of the main auroral
oval generally on open field lines
• Specific magnetospheric source regions
associated are hard to determine
Polar Auroral Regions
Dark Region
• Dawnside crescent-shaped region
• Almost devoid of auroral emission
• Main oval on the equatorward and swirl and
active regions on the polarward
• Plasma within it flow sunward at subcorotational
speeds
• Connected with the partially emptied flux tubes
in the sunward return flows associated with the
Dungey and Vasyliunas cycles
Why Dark and Questions Raised
• Field-aligned currents downward directed
(upward moving electrons)
• Corresponds to precipitation of electrons with
energy flux of 0 to 1 mW/m^2
• H3+ emission from 0 to 0.1 mW/m^2, one order
of magnitude smaller than IR observation
• Where does the excess IR emission come from
Swirl Region
• Faint, patchy, and shortlived (10s) emission
features characterized by
turbulent motions that
occasionally form
localized clockwise swirls
• Located around the
center of the polar region
• Hard to determine to what
extent it is corotating
(or not) with the bulk of
the aurora emission
Interpretation and Problem
• Open magnetic flux
mapping to the tail lobes
• Solar wind-driven Dungey
cycle
• Open flux region should
be aurorally “dark”
• Why electrons
accelerated up to
threshold energy
• Origins of the
precipitation remains
underdetermined
Active Region
• Polar flares: bright
transient events
• Arc-like feature
Polar Flares
• Flares occurred at similar locations, the same
magnetic local time region
• Triggered by local time processes occurring near
the noon sector of the magnetosphere
• An explosive reconnection with the IMF at the
dayside magnetopause
• Flux transfer event (FTE) structures with time
scale less than 1 min and about 4 min has been
observed by Voyager and Pioneer 10 and 11
Arc-Like Features
• Distinct from flares
morphologically
• Related, if not the same,
magnetospheric
processes
• Reconnection line which
may take the form of an
arc extending poleward of
the main oval (the
Dungey cycle
magnetopause X-line)
• “Equatorward surge”
Statistical Analysis of the Active Region
• 55% of the observing
time, the emission is
between 0 and 0.5 x
10^11 W
• 7% of the time, it exceeds
1.5 x 10^11 W
• Electron energies during
brightening range from 40
to 120 keV
• Mechanism: ehance the
number flux of the
precipitated electrons
rather than their energy
Summary
• 1. The polar emissions contribute 30%, bursts ~ 100s
• 2. Three regions fixed in MLT
• 3. Dark region: return flows, Dungey and Vasyliunas
cycles, plasmoid released downtail
• 4. Swirl region: open flux, solar wind-driven Dungey
cycle
• 5. Active region: Dungey cycle magnetopause X-line,
dayside reconnection
• 6. Polar flares: bursty reconnection, FTEs
• 7. Probability: <10%
• 8. Arc-like Features: Dungey cycle magnetopause X-line