Bill Kurth's Email on Bow Shocks
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 Jupiter....
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:
  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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 other.
  7. 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...
  8. 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.
  9. 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.