Well, I've not done this for a long time, primarily because I'm
personally quite confused about the region Cassini has been
traversing since the PSG meeting. I'm also concerned
about complications in the interpretation of our data based on Ed
Smith's comment at the MAPS meeting that some of the shocks we
are seeing may be IP shocks and have nothing at all to do with
Anyway, I've had some people ask about what we're seeing and
I've asked some other's what they are seeing; evidently I'm
not the only one scratching my head.
So, to get things rolling, again, hopefully in preparation for
the May workshop, I've decided to write down some times when
Cassini RPWS sees what look like shocks and send them out
to you for comments. It would be nice for you to tell me if
you concur or not with times I've mentioned, add your own times,
and add any information you might want to suggest about whether
we're in the s/w, m'sheath, or otherwise... Tomato throwing
is frowned upon, however.
I should outline what I've done:
Attached is an Excel spreadsheet
which has entries for each
possible boundary we've reported and which now contains a number
of new ones based on a quick survey of our data.
The spreadsheet has columns for RPWS, CAPS, MIMI, and MAG. If
I've heard of any comments from the other teams either confirming
a boundary we've reported or mentioning a new one, there is a
time listed based on the information from the other team. I
hope Ed Smith doesn't mind that I included some times he have
me on a hand-written list at the PSG meeting. If there is
a time under MAG, but not RPWS, for example, it means MAG has
identified this event.
If there is a blank line in the sheet, it's because I'm not
at all confident that we've caught all possible shocks during
the time interval between the preceding and succeeding rows.
I have NOT taken the time to nail times down to anything
closer than about 15 minutes, especially in the entries after
about day 15. I'll try to go back and do a better job at doing
this, but if you have a better time, please let us know.
For the interval after about day 15, RPWS sees frequent
occurrences of what I would call ion-acoustic waves which
are normally upstream phenomena but which seem to be found
both before and after many of these shock-like features.
I've tried to use the existence of Langmuir waves to indicate
the "upstream" region. In most cases, it appears that these
waves truly are only seen on one side of the shock, and not the
I've also interpreted all shocks as bow shocks in that I
have tried to decide (based on Langmuir waves) whether we were
upstream or downstream. Of course, any of these could be IP
shocks and the in/outbound indication is irrelevant...
There are long (hours or days) when we see continuum
radiation with a sharp low-frequency cutoff. None of these
reach the few-hundred Hz frequencies we saw inside the magnetosphere
on days 9 and 10, hence, I don't believe any of the later
observations of continuum radiation would consititute entry
into the lobe. However, this statement would not rule out
entry into a LLBL. I leave it up to the rest of you to
suggest other evidence of such regions. Absent any such
evidence, one might conclude that we're seeing continuum
radiation "spilling" out of the magnetosphere over the magnetosheath
plasma frequency in a region where the m'sheath density is
low compared to that on the dayside. We could be in either
the sheath or the s/w.
The ??? you see for all of the most recent entries means that
I really am not sure about whether these are IP or bow shocks or
whether they are inbound or outbound. This spreadsheet should be
considered a "working" document. Only after discussions with
you and your diverse data sets would I feel comfortable about
any of these identifications.
If any of you feel so inclined, you could return copies of this
spreadsheet with your own boundaries/times/comments and I'll
try to collate and redistribute them.