Rick:

I have looked at my data for the three cases you plotted. My conclusion
is that we may be able to do something with the event spanning Dec. 5
and 6, focussing on the period from 23:40 to 24:00 on Dec. 5. This event
will require very careful photometric reduction from me, since I see it
very near the SW limit of my field of view (FOV). It's a good thing the
moonshade is gone, or I'd not have seen it at all. For the other two
events the arc you see is too close to the edge of my FOV to be useful,
and in any event, the geometry of the event around 10 UT on Dec. 6th is
wrong for tomography.

I have plotted my images in negative format in PostScript plots, and
have uploaded the plots to the usual place (pub/leger). The file names
are given below in my comments on the three events. The images have been
dark-subtracted, flat-fielded, and approximately converted to Rayleighs.
The full-scale brightness in each plot is 150 R of 630.0 nm.

I have interpreted your remarks about the orientation of your imager to
mean that if I invert the plot, with the title at the bottom of the
page, then the top of each image is roughly N, and the 9 o'clock
position is roughly E. All the comments below are based on this
assumption.

Dec. 5, 00:28 - 01:40 UT: (96120520.ps, 3 pages)
From 00:29 through 00:57 I see no aurora within my field of view. After
00:59 I see a faint enhancement at the extreme SW limit of my FOV, which
may correspond to the arc running approximately through your zenith
between 01:01 and 01:37. However, I cannot resolve the arc well enough
to do anything with it. After about 01:20 an arc moves into my FOV from
the NE.

Dec. 5, 23:27 - Dec. 6, 00:36 UT: (96120521.ps, 1 page; 96120620.ps, 1 page)
At 23:34 I see a faint, structured glow around the southern 1/3 of my
horizon. After 23:45 the glow moves toward my zenith, especially from
the SW, until at about 23:52 it stops and begins to fade. The
similarities between this glow and the arc running SE->NW through your
zenith at 23:48 lead me to conclude tentatively that we are observing
the same arc during this period. Subsequently, after 00:06 UT on Dec. 6,
I see active, structured aurora moving from the SW into my zenith. Your
plot does not appear to show anything corresponding to this, but flat-
fielding may bring out something.

Dec. 6, 09:51 - 10:43 UT: (96120621.ps, 2 pages)
From 09:51 until about 10:23 I see very faint SW-NE trending emission
features that are no longer discernible after 10:25. From 09:51 on I
also see a glow on my SE horizon, which varies in brightness but
appears to move steadily toward my zenith throughout the period shown.
It is possible that this may relate to the arc running through your
zenith from 10:24 through 10:54. However, since we cannot view a common
volume in the arc along sight lines approximately transverse to the arc,
I don't see how we can do tomography with it. If my vision here is too
limited, please show me what I'm missing.

I need to determine the exact orientation of my imager, since it was
reinstalled again this fall. I also need to reduce my field calibration
data and review the flat-fielding. However, I trust that what you have
in the PostScript plots will suffice for the CIT conference. If you need
anything more, please let me know ASAP.

It occurs to me that your PAIM Tool could help us make more sense of
these events. If you concur, I'll try to finish off a utility routine I
started writing to linearize the zenith distance in my images.

Best regards,

Dave