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 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 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

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