Dawn-Dusk Oscillation of the Io Plasma Torus and the Vasyliunas E-V Theorem A. J. Dessler Dept. of Atmospheric Science Texas A&M University College Station, Texas and B. R. Sandel Lunar and Planetary Laboratory University of Arizona Tucson, Arizona Boston MOP Meeting 15 July 2011

IO TORUS DAWN-DUSK OFFSET Approaching Ansa Dawn Ansa Dusk Ansa Receding Ansa Viewed from Voyager Viewed from Earth Torus w/ Ribbon on inner (i.e., Jupiter) side

OSCILLATION OF IO TORUS A Voyager Earth A is Magnetic Anomaly at λ III ~110° Approaching Dawn A Approaching Dawn Dusk Ansa Receding Ansa Dusk Ansa Receding Ansa

Magnetic Anomaly – Announced (John Clarke et al Birmingham DPS meeting). Quantitatively defined (Denis Grodent et al JGR and Hess et al JGR). Weak B

Dessler & Sandel, 1979 data from Voyager Schneider & Trauger, 1991 data from Earth 12 years apart

Areas A and B are equal Anomaly magnetic field maps to equator Anomaly magnetic field maps to equator

No Anomaly change in B-field at Equator Flux tube Big-Foot resistant to interchange Flux tube Big-Foot resistant to interchange

EFFECT OF MAGNETIC ANOMALY A Dusk Magnetic-Anomaly flux tubes map to equator to form impoundment region Limited Outflow Limited Outflow Dawn A

Central Meridian Longitude (System III) CML provides snapshots of Ribbon Distances Dawn minus Dusk Distance

Anomaly between Dawn and Noon Maximum outflow – Max Offset Anomaly between Dusk and Midnight Minimum outflow – Minimum Offset Dawn minus Dusk Ribbon Distance Outflow from torus toward tail causes Torus Offset

Maximum Outflow from torus toward Tail Max Offset DawnDusk Noon

Local-Time range of Anomaly at given CML viewed from Earth Anomaly out of the way. Maximum Outflow – Max Offset Noon to Dawn Anomaly ~110° Dawn minus Dusk Ribbon Distance

Minimum Outflow from torus toward Tail Dawn Dusk Noon Midnight

Midnight to Dusk Local-Time positions of Anomaly at given CML viewed from Earth Anomaly Impedes Outflow Anomaly out of the way. Maximum Outflow Noon to Dawn Dawn minus Dusk Ribbon Distance

C ONCLUDING T HOUGHTS The Improved Magnetic-Anomaly Model explains the torus oscillation. Other Jovian spin-periodic phenomena can be explained by this Magnetic-Anomaly Model. The Vasyliunas E-V Theorem is important. E is a result of V, E cannot cause V. Please contact me for more information, wild ideas, or discussion.

Extra slides follow

TIME-VARYING ELECTRIC-FIELD HYPOTHESIS This idea suffers two flaws: (a) Where is the E-field created so it knows Jupiter’s rotational phase? Problem: As plasma flows down tail, a varying V X B field is created at different distances — all longitude phases are mapped back to torus. Therefore, E-field will not work. (b) Inconsistent with the Vasyliunas E-V Theorem. GRL Problem: V X B can create E, but E cannot cause magnetospheric plasma to move. No E-field will work.

CONCLUSIONS 1. The Magnetic Anomaly vital to the Magnetic-Anomaly Model has been discovered, and the Vasyliunas E-V Theorem provided needed guidance. 2. The torus oscillation is explained by an improved Magnetic-Anomaly Model. The Magnetic-Anomaly Model is open for exploitation. Examples of Jovian spin-periodic phenomena that could be explained by the Magnetic-Anomaly Model: a. How Active Sector works. It contains many Jovian spin-periodic phenomena. See Sect in "PJM". b. The 10-hour Plasmoid "bubbles" travelling down the Jovian tail reported by McComas et al. Science c. The Simpson Clock – highest energy and flux of relativistic electrons released from Jupiter when Magnetic Anomaly faces sunward. d. The Lyman-alpha bulge. e. Extension to Saturn spin-periodic phenomena?

Longitudinal Extent of Anomaly Longitudinal Extent of Anomaly AA

A Noon A Dawn A Midnite A Dusk A Midnite A Dusk A Noon A Dawn Position of Anomaly for given CML Observed from Earth