1. Jupiter’s Polar Auroral Emisssions
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

2. Jupiter’s Aurora

3. Cowley’s Theoretical Frame

4. Dungey Cycle

5. Vasyliunas Cycle

6. Sub-corotating Hill Region

7. Cowley’s Theoretical Frame

8. Cowley’s Theoretical Frame

9. 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

10. 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

11. Auroral Emitted Power

12. 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

13. 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

14. Polar Auroral Regions

15. 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

16. 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

17. Swirl Region
Faint, patchy, and short-lived (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

18. 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

19. Active Region
Polar flares: bright transient events
Arc-like feature

20. 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

21. 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”

22. 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

23. 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