1. GLOBAL IMAGING OF
PROTON AND ELECTRON
AURORA IN THE FAR
ULTRAVIOLET.

2. S. B. MENDE, H. U. FREY, T. J. IMMEL
Space Sciences Laboratory, University of California Berkeley, Berkeley, CA 94720
J.-C. GERARD, B. HUBERT
University of Liege, Liege, Belgium B-4000
S. A. FUSELIER,
Lockheed-Martin Advanced Technology Center, Palo Alto, CA, 94304

3. Outline
IMAGE FUV instrument provides for the first time a global view of electron and proton precipitation.
Imaging proton auroras on the dayside permitted the discovery of proton auroral spots caused by direct entry of protons at the high latitude lobe merging site during (IMF Bz >0) [Frey et al., 2002, Fuselier et al.,
2002] and of detached dayside proton arcs [Immel et al., 2002, Burch et al., 2002].

4. Outline cont.
2. The role of protons in substorms.
Introduction to a statistical analysis of a limited set of substorms.
Data reduction to perform a “superimposed epoch analysis” of
the substorm set.
The mean properties of proton precipitation in substorms
regarding latitudinal and magnetic local time (zonal)
expansion and drift.

5. Particle energy in the magnetosphere is carried mainly by ions
(mostly protons).
Most intense auroras are generated by electrons however they
are energized “on the way down”
Electron precipitated energy is not representative of the
energy of the plasma sheet or the ring current trapped plasma.
Nightside protons generally have energies of >25 keV and
are less affected by the auroral electric fields.
Protons have significant role in substorm models. The cross
tail current is carried by ions.
The pre onset distorted magnetic field at the equator is thought
to randomize the proton pitch angle thereby causing proton
precipitation observed prior to the onset of the substorm.
Thus if we intend to explain substorms then we must understand
the behavior of protons during substorms.

6. In spite of the many years of satellite based in
situ exploration of protons, relatively very little is known
about the dynamics of proton precipitation.
Most proton measurements were made by ground
based meridian scanning photometers measuring the H
Balmer lines. From such measurements it is known that:
1. Pre-substorm protons are on the equatorward
boundary of the oval.
2. Substorm onset and the break-up arc occur in the
region of the proton precipitation. (Closed field lines)
3. During break up and after the proton aurora expands
poleward. Note: that in the presence of bright break-up aurora
the reliability of the visible light, ground based, proton auroral
observations are always controversial.

7. From a single case study using the IMAGE data we
have corroborated the ground based studies (Mende
et al., 2001). In this report we are describing a study
involving many substorms.
Although the purpose of the study is to investigate
proton auroras we will make comparisons
to simultaneous electron auroras.

8. A superimposed epoch analysis of substorms observed
in 2000 and early 2001 was performed by :
1. Re-plotting substorms in Magnetic-latitude/Magnetic-
Local-Time coordinates.
2. The substorms were re-positioned in (MLT) so that the
onset location was repositioned to MLT = 0.
3. A gaussian of the form:
y = a0 e -((x - a1)/ a2)2 + a3 + a4 x + a5 x2
where x is the magnetic latitude and y is the intensity.

9. A set of 38 substorms
were chosen for the
statistical analysis.
Criteria of choice:
1.Significant intensity
Enhancement in WIC
(electrons) at onset.
3. Discernable poleward propagation after onset.
2. No prior major substorm for at least 1 hour.
The onset location (Mag. Lat. and MLT)
of the electron precipitation was determined
from WIC data.

10. 2000/ :59:13

11. L A T
MLT
2000/1939:59:13

12. Input data in Keogram form (left)and equivalent Gaussian fit (right)
Input data in Keogram form (left)and equivalent Gaussian fit (right). Note good
correspondence in general but we lose the “double auroras” on the right.

13. Example of output data:
Amplitude (a0) of Gaussian
for WIC taken at relative
MLT=0 (I.e at the onset MLT).
Note:
Large WIC intensity increase
at onset.
The pre-event in WIC is unusual.

14. Example of output data:
Amplitude (a0) of Gaussian
for SI-12 taken at relative
MLT=0 (I.e at the onset MLT).
Note:
Moderate enhancement SI-12.
Strong pre-cursor activity
with SI-12 (often observed)

15. The magnetic latitude of the peak
of the Gaussian (a1) at the onset
MLT (top).
Poleward expansion is minimal
and the SI-12 (protons) and WIC
(electrons + protons) track each
other well.

16. The magnetic latitude width of
the peak of the Gaussian (a2) at
the onset MLT (bottom). Large
increase at onset with WIC
wider than SI-12.

17. SI-12 (protons) drift primarily dawnward electrons
expand in both directions

18. WIC auroral intensity plot (left) and ratio of intensity to
pre-substorm value (right) for each substorm. The
mean curve is the solid line. The average intensity
enhancement is about a factor of 5.

19. SI-12 auroral intensity plot (left) and ratio of intensity to pre-substorm value
(right) for each substorm. The mean curve is the solid line.
Note: 1. The intensity enhancement is only of about a factor of two. This could
be interpreted to signify that substantial proton precipitation is present prior
to onset.
2. Pre-substorm average is < 1 erg but after onset several ergs are observed.
(For an average nightside aurora 25 counts =1 erg cm-2 sec-1.)

20. Plot of Gaussian parameter a1 (latitude of the peak) left and
a2(width of the peak) for the Substorm set. Blue =WIC,
red=SI-12. Solid line WIC mean and broken line SI-12.
Note: Latitude of protons is lower prior to onset. After onset they
track. Width of electrons becomes narrow at onset and
protons lead the widening for the first 15 minutes.

21. Statistics of the intensity just prior and at peak of intensity at
Relative MLT = 0.
Largest substorms occur at lower latitudes (WIC and SI-12).
SI-12 has significant pre-substorm intensity which increases
towards lower latitudes.

22. Ratio of peak to pre-existing aurora is relatively
constant with latitude for SI-12. It increases with latitude
for WIC.

23. Intensity pre onset and peak as a function of the actual
Magnetic Local Time of the initiation point.

24. Ratio of intensity peak and pre-onset as a function of the actual
Magnetic Local Time of the initiation point.

25. Examples of Relative MLT drift path for SI-12
And for WIC. Following an injection the auroras
Expand in MLT longitude. More often than not
they drift preferentially in one direction instead
of just expanding.
Electron auroras are caused by inverted V or
Alfven Wave processes between the equator and
the low altitude atmosphere. Protons are relatively
immune from being perturbed by those fields and
proton auroras may represent the Magnetospheric
particle distributions and dynamics.

26. Distinct duskward trace in WIC (electrons).

27. Dawnward moving proton injection and dawn-dusk expansion in WIC

28. Complex example of multilple injections
Complex example of multilple injections. Note pre-existing aurora at other MLT.

29. Strong pre-cursor proton precipitation and dawn-ward propagation.

30. Pre-cursor proton precipitation and dusk-ward propagation after injection.

31. Very intense proton injection

32. Summary of 38 cases examined :
AVERAGE SI-12 MOTION IS 3.09 MLT/UT DAWNWARD
AVERAGE WIC MOTION IS (SLIGHTLY DUSKWARD)
This is contrary to expectations based on gradient and curvature
drift in the presence of a dawn/dusk electric field. What parameters
does the direction of motion depend on?

33. SMALL SAMPLE DATA SET WAS PLOTTED AGAINST IMF.
There is some trend of SI-12 with By but more data needs to
be looked at to arrive at a definitive result.

34. No obvious trend with Bz but more data needs to
be looked at.

35. Does the intensity of the substorm depend on the distortion
of the pre-substorm magnetic field?
If the pre-onset proton intensity were related to the
distortion of the magnetic field then the substorm intensity
would be proportional to it.

36. Summary.
1. Pre-substorm protons are on the equatorward boundary of the oval.
2. Substorm onset and the break-up arc occur in the
region of the proton precipitation. (Closed field lines)
3. During break up and after the proton aurora expands Poleward. This
expansion is very similar in both components.
4. Surprise. There is no evidence for saying that either electrons or
protons lead the poleward expansion (Mende et al., 2001).
5. The average intensity enhancement in WIC is about a factor of 5.
6. The intensity enhancement of SI-12 is only of about a factor of two. This could
be interpreted to signify that substantial proton precipitation is present prior
to onset.

37. Summary continued.
8. Pre-substorm average intensity of protons is just under 1 erg but after
onset they can be several ergs (sometimes ~5). This is much
higher than the averages observed by in situ particle detectors.
9. Latitude width of electrons becomes narrow at onset and
protons lead the widening for the first 15 minutes.
10. Largest substorms occur at lower latitudes (both WIC and SI-12).
11. SI-12 pre-substorm intensity also tends to be higher at
low latitudes.
12. (Surprise) average SI-12 motioon is 3.09 MLT/UT DAWNWARD
13. Average WIC motion is insignificant.
14. There is some trend that SI-12 drift direction correlates with By but more
data needs to be looked at to arrive at a definitive result.