Dean TalboysDept. Physics and Astronomy, University of Leicester

Saturn’s High-Latitude Field-Aligned Currents and the Aurora

CHARM Presentation, JPL, 26th January 2010

Taken from Clarke et al, 2005

Image Credit: Wayne Pryor (UVIS)

Taken from Stallard et al, 2008

Cassini VIMS in situ imaging

Cassini UVIS in situ imaging

What is the origin of Saturn’s auroral emission?

Hubble Space Telescope remote imaging

Kristian Birkeland

Magnetosphere-Ionosphere coupling current System

Solar wind interaction

Bunce et al., 2003

Image A: January 16th: 05:31 UT Image B: January 17th: 03:21 UT

Bunce et al., 2008

HST observations with high-latitude in situ Cassini observations

Ene

rgy

/ eV

Br /

nT

Bθ /

nT

Bφ

/ nT

|B| /

nT

BA

UT (DOY)Radial (Rs)Co-lat (deg)LT (dec hr)

Rev 37: In situ Cassini observations

Bunce et al., 2008

Noon-Midnight X-Z plane

Equatorial X-Y plane

Image B: January 17th: 03:21 UT

o

BI

Estimate the FAC density to be:

BA

j||I~275 nA m-2

Bunce et al., 2008

HST observations with high-latitude in situ Cassini observationsB φ

/ nT

I / M

A ra

d-1Co

-Lat

/ de

g

Solar wind interaction

Characterization of high-latitude current systems from mid-2006 to mid 2007

Rev 31Ring current boundariesSchippers’ boundary

Statistical oval

Noon-Midnight X-Z planeEquatorial X-Y plane

Dawn-Dusk Y-Z plane

C

D

C

ΔBr /

nT

ΔBθ /

nT

Bφ /

nTC

o-La

t/deg

Ene

rgy

(eV

)

Ring current boundariesSchippers’ boundaryStatistical oval

SH

Ring current boundariesSchippers’ boundaryStatistical oval

NH

SH Currents for Revs 31-35

Purple – Upward region 0

Red – Upward

region 1a

Orange – Upward

region 1b

Green – Downward region 2

NH Currents for Rev 31-34

Red – Upward region 2

Green – Downward region 3

Green – Downward region 1

Noon-Midnight X-Z plane Equatorial X-Y plane

Field-aligned current signatures during 2008

Rev 74

Examples of ‘Lagging’ Field SignaturesA B

Solar wind interaction

Examples of ‘Leading’ Field SignaturesC D

Solar wind interaction

Summary and Open Questions• The joint HST-Cassini campaign associated for the first time the high-

latitude field-aligned currents with the aurora.• Near-simultaneous in situ observations of the field-aligned currents

and imaging of the aurora are of primary value.• How does the main auroral oval (X-ray,UV,IR,Radio) at different local

times relate to the field-aligned currents?• How do the two different types of upward FAC (those generated by

sub-corotating flow shears and those from the unusual super-corotating flow shears) relate to the morphology of the aurora?

• What dynamical event is occurring to produce the super-corotating flows (with associated ‘leading’ field signatures) that are unanticipated by various models.

• How does the sub-structure in the upward FAC relate to the fine structure in the aurora?