Hi Glenn (and Reta)--
Isao Miyazaki has sent the attached images. Hope you can view them.
His image of 1997 Dec. 28 has BC, DE, FA, all on the f. side of the disk, BC and DE being virtually in contact. They had never come this close before, so this strongly suggests that BC and DE were just about to merge.
His images of 1998 May 13 show a single prominent, methane-bright oval, at L3 ~ 20 (rough predictions for BC and DE would be L3 ~ 33 and 48 -- all these longitudes are rough as I have yet to do do precise measurements). I agree this is probably the result of merger of BC and DE. Call it BE? (There are some fainter white ovals p. it but similar ones have been seen before and are probably irrelevant.)
His image of 1998 March 31 (separate file) also shows the bright white oval near L3 ~ 30 but is low-resolution; I wonder if image-processing can bring anything further out of it?
Even though the actual merger was not seen, surely it would be well worth Galileo targetting the merged oval BE, ASAP, to compare its dynamics with those of BC and DE last year before the merger.
It's amazing that, after a century in which no large anticyclonic ovals were ever observed to merge, *two* such mergers have now occurred within a year! Did you and the SSI team get any interesting obs'ns of the GRS following its merger with the long-lived WO, by the way?
All the best,
---------- Forwarded message ----------
Date: Sat, 16 May 1998 22:17:32 +0900
From: Isao miyazaki (email@example.com)
I send you a 893nm image taken on 13 May. Only one white oval is visible in the STeB. Which oval did disappear? BC or DE? Did they merge? The images taken on 28 December 1997 show that they were approaching each other.
Last Year Image
I've now measured the longitudes from Miyazaki's images, and agree with your conclusions. Longitudes are below; (pred.) means predicted from the track in 1997 Aug-Nov. The longitudes measured on Dec.28 suggest that DE had begun to accelerate towards BC. The merged oval must have accelerated further; as you say, it is 8-18 degreees p. the former tracks of BC and DE. This is interesting because, during their half-century history, these ovals decelerated as they shrank. Perhaps a newly-enhanced oval, created by the merger of two of them, therefore has a more rapid drift? I must say it does not *look* much bigger, but with more and higher-resolution images over the next month or two, it will be interesting to measure its exact size and latitude as well as drift.
|1997 Aug.9 (opp.)||67||85||109|
|1997 Dec.28 (pred.)||54||70||91|
|1997 Dec.28 (obs.)||56||66||88|
|1998 May 13 (pred.)||28||39||60|
|1998 May 13 (obs.)||20.5||-||~57(May 16)|
The 5-micron rings presumably corresponded to the visually dark collars around the ovals. These have sometimes disappeared before (notably for oval FA in the late 1980s when it disappeared altogether for a while, even in Pic du Midi images, before the dark ring reappeared and showed it still present). But I guess the meteorological upheaval of the merger could well have spread white clouds around the ovals, temporarily.
It would be great if Galileo could study the dynamics of the merged oval!
On Mon, 18 May 1998, Glenn Orton wrote:
I managed to work out how to get these saved in binary jpg format!
I'm working on the data from the IRTF myself (in between getting proposals written...finishing up #3 out of 5).
I'd agree that we have a merger (from the looks of it, before March!) with FA being in just about the right place, and "BE" prograded by a few 10's of degrees.
I note again that in March, there are no 5-micron rings around any of the white ovals, although that might be a problem with our poor seeing (but I think not, actually).