AuroralAcceleration–WhattoExpectatJupiter
R. E. Ergun and F. Bagenal
University of Colorado Boulder, CO 80303
Juno.May,2015
1
Point of this Talk
•  The driving forces of Jupiter’s aurora (Io and strong rotation) are quite distinct
from those at Earth.
•  None-the-less, auroral acceleration processes at Jupiter should be similar to
those at Earth. But we expect surprises!
•  We observe three types of acceleration processes at Earth: upward current
region, downward current region, and Alfvenic acceleration.
•  Jupiter’s three types of aurora is expected to have a mixture of these
acceleration processes, but may have unique characteristics.
•  One needs to carefully scale the Earth and Juno observations to make
comparisons. Juno orbits at higher speeds than do Earth satellites and Jupiter’s
magnetic field is significantly stronger than Earth’s. These differences result in
different observational time scales.
•  Studying acceleration processes with Juno observations will be very, very
interesting. Universal processes can be identified.
Juno.May,2015
2
Acceleration Processes at Earth
Alfven
Aurora
Upward Current
Downward Current
Alfven Aurora
Juno.May,2015
3
Jupiter’s Aurora
Downward Current?
Upward Current
Alfven Aurora
λi: O(100’s km) same
as at Earth.
ρi: O(1 km)
λe: O(10’s km) same
as at Earth.
Juno.May,2015
4
Jupiter’s Aurora
Polar Aurora
Juno.May,2015
5
Acceleration Processes and Jupiter’s Aurora
Polar Aurora
Upward Current Region: Main Oval; Io Wake Region: Most
Polar Aurora
Alfven Aurora: Io Spot; Polar Aurora Boundaries; Dark Region?
Downward Current Region: Dark Region?
Juno.May,2015
6
Jupiter’s Main Oval: An Upward Current Region
Juno.May,2015
7
Jupiter’s Main Oval: Angular Momentum Transfer
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8
Jupiter’s Main Oval: Angular Momentum Transfer
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9
Jupiter’s Main Oval: Angular Momentum Transfer
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10
Jupiter’s Main Oval: Angular Momentum Transfer
Juno.May,2015
11
Jupiter’s Main Oval: Angular Momentum Transfer
Ray et al.
alters
conductance
with energy
fluxes.
Hill et al. in
Black
Ray et al. in
red.
Juno.May,2015
12
Jupiter’s Main Oval: Angular Momentum Transfer
Juno.May,2015
13
Jupiter’s Main Oval: Upward Current Region
(1)  Parallel electric fields (double layers).
(2)  Perpendicular electrostatic shocks.
(3)  Accelerated electrons.
(4)  Anti-Earthward ion beam.
(5)  Strong wave activity.
(6)  Deep density cavity.
Juno.May,2015
14
Upward Current Region
Juno.May,2015
15
Upward Current Region: Magnetic Fields
350
300
(nT)
Electrons
Energy (eV)
E ALONG ΔB
V
(mV/m)
DC Bz
East-West
FAST ORBIT 1843a
About the same ΔB (East-West).
250
200
600
300
500 km; 10 s
0
-300
-600
104
103
102
Magnetic field deflections are
expected to be the same as at
Earth. The time scale will be
faster.
9
101
6
15
Flux
m 2)
10
Juno.May,2015
5
16
Upward Current Region: Electric Fields
FAST ORBIT 1858
500
250
0
-250
-500
1000
500
0
-500
-1000
-1500
102
101
101
100
10-1
:06:35 :06:40 :06:45 :06:50 :06:55 :07:00
3953.1 3950.3 3947.4 3944.5 3941.6 3938.6
70.8
71.0
71.1
71.2
71.3
71.4
21.2
21.2
21.2
21.2
21.2
21.2
Minutes from 1997-02-09/06:06:35
6
7
4
-4
-12
-250
-500
1000
500
0
-500
-1000
-1500
Electrons (eV) Density (cm )
104
103
0
-3
102
101
9
Log eV/
cm2-s-sr-eV
0
4
10
103
Log eV/
cm2-s-sr-eV
5
(mV/m)
10
Log (V/m)2/Hz
Ions (eV)
Freq. (kHz)
UT
ALT
ILAT
MLT
(mV/m)
500
250
Electrons (eV) Density (cm-3)
(mV/m)
(mV/m)
FAST ORBIT 1858
10
5 to 50 V/m
500 km; 10 s
5
Electric
field amplitudes should
be 0considerably larger and,
depending
on boundary layer
104
thickness,
much faster time scale.
103
Juno.May,2015
102
101
9
17
6
104
103
Ions (eV)
Upward Current Region: Waves
0
10
102
101
104
103
102
101
101
100
10-1
:06:35 :06:40 :06:45 :06:50 :06:55 :07:00
3953.1 3950.3 3947.4 3944.5 3941.6 3938.6
70.8
71.0
71.1
71.2
71.3
71.4
21.2
21.2
21.2
21.2
21.2
21.2
Minutes from 1997-02-09/06:06:35
6
7
Log eV/
cm2-s-sr-eV
0
4
10
103
UT
ALT
ILAT
9
MLT
Log eV/
cm2-s-sr-eV
5
4
-4
Log (V/m)2/Hz
Ions (eV)
Freq. (kHz)
UT
ALT
ILAT
MLT
Freq. (kHz)
-250
-500
1000
500
0
-500
-1000
-1500
Electrons (eV) Density (cm-3)
(mV/m)
(mV/m)
FAST ORBIT 1858
500
250
-12
102
101
c
6
7
Log eV/
cm2-s-sr-eV
101
4
-4
101
100
10-1
:06:35 :06:40 :06:45 :06:50 :06:55 :07:00
500 km;3944.5
10 s 3941.6 3938.6
3953.1 3950.3 3947.4
70.8
71.0
71.1
71.2
71.3
71.4
21.2
21.2
21.2
21.2
21.2
21.2
Minutes from 1997-02-09/06:06:35
x 10
-12
x 10 to 100
Ion-cyclotron waves should have
higher frequencies and
amplitudes may be much more
intense.
Juno.May,2015
Log (V/m)2/Hz
Ele
10
18
4
345
Upward Current Region: Waves
-4
Source region. Will Juno find it?
-10
-7
Log (V/m)2/Hz
HF E OMNI
(kHz)
340
335
600
400
200
0
Fri Jan 22 11:01:04 1999
LF Eperp
(kHz)
-14
-4
Long Duration
10.0
UT
Log (V/m)2/Hz
2
0
355
350
Radio frequency emissions have considerably
1.0
higher frequencies
0.1
Juno.May,2015
:28:28
:28:30
:28:32
:28:34
Log (V/m)2/Hz
Densit
(cm-3)
PWT
(kHz)
6
-14
19
Electrons (eV) Density (cm-3)
-1500
10
102
101
101
4
-4
101
100
10-1
:06:35 :06:40 :06:45 :06:50 :06:55 :07:00
3953.1 3950.3 3947.4 3944.5 3941.6 3938.6
70.8
71.0
71.1
71.2
71.3
71.4
21.2
21.2
21.2
21.2
21.2
21.2
Minutes from 1997-02-09/06:06:35
104
103
102
101
Freq. (kHz)
Log eV/
6
7
104
103
-12
UT
ALT
ILAT
MLT
6
7
500 km; 10 s
x 5 to 10
100Electrons
4
About the same
-4
should have higher
energies.
10-1
:06:35 :06:40 :06:45 :06:50 :06:55 :07:00
3953.1 3950.3 3947.4 3944.5 3941.6 3938.6
70.8
71.0
71.1
71.2
71.3
71.4
21.2
21.2
21.2
21.2
21.2
21.2
Minutes from 1997-02-09/06:06:35
Juno.May,2015
Log (V/m) /Hz
101
Ions (eV)
9
103
102
101
Log eV/
cm2-s-sr-eV
0
4
10
103
102
cm2-s-sr-eV
5
Log (V/m)2/Hz
Ions (eV)
Freq. (kHz)
UT
ALT
ILAT
MLT
10
9
Log eV/
cm2-s-sr-eV
-250
-500
1000
500
0
-500
-1000
-1500
0
104
2
0
Electrons (eV) Density (cm-3)
(mV/m)
(mV/m)
FAST ORBIT 1858
500
250
Log eV/
cm2-s-sr-eV
Upward Current
Region: Electrons
5
-12
20
Upward Current Region: Electrons
Juno.May,2015
21
Upward Current Region: Ions
102
101
101
0
4
10
9
103
102
101
104
103
102
101
101
UT
ALT
ILAT
MLT
100
10-1
:06:35 :06:40 :06:45 :06:50 :06:55 :07:00
3953.1 3950.3 3947.4 3944.5 3941.6 3938.6
70.8
71.0
71.1
71.2
71.3
71.4
21.2
21.2
21.2
21.2
21.2
21.2
Minutes from 1997-02-09/06:06:35
6
7
100
500 km; 10 s
Log eV/
cm2-s-sr-eV
5
About the same
x 5 to 10
10-1
-12
:06:35 :06:40 :06:45 :06:50 :06:55 :07:00
3953.1 3950.3
3947.4 3944.5
3941.6 should
3938.6
Anti-Jovian
ion
beams
70.8
71.0
71.1
71.2
71.3
71.4
21.2
21.2
21.2
21.2
21.2
have higher energies. 21.2
Minutes from 1997-02-09/06:06:35
Log eV/
cm2-s-sr-eV
Freq. (kHz)
10
4
-4
4
-4
Log (V/m)2/Hz
Ions (eV)
Freq. (kHz)
UT
ALT
ILAT
MLT
104
103
Ions (eV)
0
-250
-500
1000
500
0
-500
-1000
-1500
6
7
2
500
250
Electrons (eV) Density (cm-3)
(mV/m)
(mV/m)
FAST ORBIT 1858
101
Log (V/m) /Hz
103
102
Log eV/
cm2-s-sr-eV
9
Log eV/
cm2-s-sr-eV
Electrons (eV)
0
104
-12
Juno.May,2015
22
Integrated Electric Field and Ion Beam
•  DC Electric Fields
Juno.May,2015
23
(mV/m)
Upward
1000
500
0
-500
Current
-1000
-1500
Region: Density
Electrons (eV) Density (cm )
-250
-500
1000
500
0
-500
-1000
-1500
10
104
103
102
101
101
100
10-1
:06:35 :06:40 :06:45 :06:50 :06:55 :07:00
3953.1 3950.3 3947.4 3944.5 3941.6 3938.6
70.8
71.0
71.1
71.2
71.3
71.4
21.2
21.2
21.2
21.2
21.2
21.2
Minutes from 1997-02-09/06:06:35
6
7
4
-4
Ions (eV)
101
Log eV/
cm2-s-sr-eV
9
103
102
Log (V/m)2/Hz
0
4
10
Log eV/
cm2-s-sr-eV
5
-12
. (kHz)
Ions (eV)
Freq. (kHz)
UT
ALT
ILAT
MLT
-3
0
Electrons (eV) Density (cm-3)
(mV/m)
(mV/m)
FAST ORBIT 1858
500
250
10
5
0
104
9
500 km; 10 s
103
102 /5 to /10
101
104
103
102
Density cavity may not be as
deep – the densities at ~2 RJ are
low to begin with.
101
101
Juno.May,2015
100
24
6
7
4
-4
Alfven Aurora
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25
Alfven Aurora
Juno.May,2015
26
Alfven Aurora
Juno.May,2015
27
Alfven Aurora
TheionosphericresonatoratJupiterhasafrequencyofroughly
Figure 1. Fragment of the Io-A S-burst storm of 14 March 2005. (a) Dynamic spectra for complex
S-bursts and (b) comparatively simple linearly drifting S-burst patterns recorded about 22 min earlier. The
20Hz(Earthis<1Hz).TheDopplershiCcouldberoughlythe
spectrograms were calculated by applying a windowed Fourier transform to observational data sampled at
sameorder.
!66 MHz. Owing to high pass filtering applied for enhancing the contrast of S-burst patterns, the L-burst
storm below 23.5 MHz that accompanies the S-bursts seen in the spectrogram (Figure 1b) is not clearly
28
Juno.May,2015
visible.
Acceleration Processes and Jupiter’s Aurora
Polar Aurora
Upward Current Region: Main Oval; Io Wake Region: Most
Polar Aurora
Alfven Aurora: Io Spot; Polar Aurora Boundaries; Dark Region?
Downward Current Region: Dark Region?
Juno.May,2015
29
Downward Current Region: Where is it?
Juno.May,2015
30
Downward Current Region: What to Look For
(1) Anti-Jovian accelerated
electrons: field-aligned and
broader energy.
(2)  Strong wave activity
(3)  Parallel electric fields
(double layers).
(4)  Perpendicular electrostatic
shocks (diverging).
(5)  Ion conics.
Juno.May,2015
31
Downward Current Region: Magnetic Field
East –West DB indicates
downward current. Amplitudes
should be similar.
Magnetic field deflections are
expected to be the same as at
Earth. The time scale will be
significantly faster.
Juno.May,2015
32
Eperp(
0
-250
-500
150
100
50
0
-50
-100
-150
(eV) 180o
-500
-1000
250
102
101
0
Ions (eV)
-500
10
102
101
cm -s-sr-eV
VLF Eperp
Log eV/
(kHz)
2
Ions (eV)
102
101
6
7
104
103
102
101
4
-5
15
10
5
0
-11
:16:16
:16:18
:16:20
:16:22
:16:24
Time (UT) Minutes from 1998-02-21/08:16:16
???
About the
4
-5
same
10
5
0
0
10
10-2
2
15
LF Eperp
(kHz)
~50 km; 1 s
Log eV/
cm2-s-sr-eV
103
Log (V/m) /Hz
(eV) 180o
104
6
7
104
103
-250
(V/m)2
E|| (mV/m)
500
10
104
103
0
10-4
10-6
10-8
Anti-Jovian, field-aligned
electron beams. Broad
energy.
:24:10
:24:12
Juno.May,2015
Log eV/
cm2-s-sr-eV
500
Log eV/
cm2-s-sr-eV
Eperp (mV/m)
1000
Log (V/m)2/Hz
FAST ORBIT 5938
E||(mV/m)
Downward Current Region: Electrons
-11
33
:24:14
:24:16
:24:18
:24:20
Time (UT) Minutes from 1997-08-22/05:24:10
Ions (eV)
104
103
Downward Current
Region: Waves
2
10
101
FAST ORBIT 5938
VLF Eperp
(kHz)
-1000
0
-250
-500
102
FAST ORBIT 1747
103
102
101
4
-5
Log (V/m)2/Hz
15
10
5
0
-11
:16:16
:16:18
:16:20
:16:22
:16:24
Time (UT) Minutes from 1998-02-21/08:16:16
15
10
(kHz)
Log eV/
cm2-s-sr-eV
104
c
x10
-6
:24:10
:24:12
:24:14
:24:16
:24:18
:24:20
Time (UT) Minutes from 1997-08-22/05:24:10
6
7
LF E OMNI
(eV) 180o
>100 km; >2 s
10-6
10-8
103
101
Ions (eV)
-11
10
104
LF Eperp
(kHz)
5
0
0
x1010-2
10
10-4
250
(V/m)2
E|| (mV/m)
500
10
Log (V/m)2/Hz
0
-500
15
5
Wed Nov 8 11:32:45 2000
500
4
-5
Log eV/
cm2-s-sr-eV
Eperp (mV/m)
1000
Log eV/
cm2-s-sr-eV
6
7
Log (V/m)2/Hz
(
101
0
-12
:03:00 :03:10 :03:20 :03:30 :03:40 :03:50 :04:00
Time (UT) Minutes from 1997-01-30/00:03:00
Juno.May,2015
34
10
Downward Current
Region: Ions
2
101
FAST ORBIT 5938
0
-500
-1000
500
102
101
250
x10 15
0
VLF Eperp
Log eV/ (kHz)
-250
-500
10
(eV) 180o
104
103
102
101
(V/m)2
Ions (eV)
103
102
101
-11
Log (V/m) /Hz
Ion conics?
2
LF Eperp
(kHz)
Same
5
10-6
10-8
:24:10
:24:12
:24:14
:24:16
:24:18
:24:20
Time (UT) Minutes from 1997-08-22/05:24:10
4
-5
15
>100 km; >2 s
0
100
10-2
10-4
6
7
104
4
-5
10
cm2-s-sr-eV
E|| (mV/m)
104
103
Ions (eV)
500
Log eV/
cm2-s-sr-eV
Eperp (mV/m)
1000
6
7
10
5
0
Log eV/
cm2-s-sr-eV
10
Log (V/m)2/Hz
(eV) 180o
104
103
Log eV/
cm2-s-sr-eV
-100
-150
-11
:16:16
:16:18
:16:20
:16:22
:16:24
Time (UT) Minutes from 1998-02-21/08:16:16
Juno.May,2015
35
Downward Current Region: Electric Fields
FAST ORBIT 3956
FAST ORBIT 5938
500
250
Eperp(mV/m)
500
0
-500
-1000
0
-250
-500
150
100
50
0
-50
-100
-150
-500
10
Log eV/
cm2-s-sr-eV
(eV) 180o
104
103
102
101
6
7
Log eV/
cm2-s-sr-eV
Ions (eV)
104
103
102
101
4
-5
Log (V/m)2/Hz
LF Eperp
(kHz)
15
10
5
0
-11
(eV) 180o
-250
104
103
10
~50 km; ~1 s
102
101
Electric field amplitudes should
be considerably larger and,
104
depending
on boundary layer
3
10
thickness,
much faster time scale.
2
Ions (eV)
0
E||(mV/m)
250
:16:16
:16:18
:16:20
:16:22
:16:24
Time (UT) Minutes from 1998-02-21/08:16:16
10
101
15
Juno.May,2015
LF Eperp
(kHz)
E|| (mV/m)
500
10
5
36
6
7
Log eV/
Eperp (mV/m)
1000
4
-5
Conclusions
Main Oval/Io Tail: Upward Current Region
(1)  East-West Magnetic Field
(2)  Electrostatic Shocks (Converging)
(3)  Accelerated Electrons. Nearly mono-energetic with broad
pitch angles.
(4)  Anti-Jovian Ion Beams
(5)  Density Cavity?
(6)  Strong Wave Activity.
(7)  Parallel Electric Fields.
Ion Spot (if we are so lucky): Alfven Aurora
(1)  Strong Magnetic Field Fluctuations
(2)  Strong, Spiky Electric Fields
(3)  Bi-Directional Field-Aligned Electrons (Broad Energy)
Juno.May,2015
37
Conclusions
Somewhere: Downward Current Region
(1)  East-West Magnetic Field
(2)  Anti-Jovian Accelerated Electrons. Field-aligned with broad
energy.
(3)  Strong Wave Activity. VLF saucers.
(4)  Ion Conics
(5)  Electrostatic Shocks (Diverging)
(6)  Parallel Electric Fields.
Polar Cap: Alfven/Upward/Downward
(1) All of the Above.
Juno.May,2015
38