August 12, 1998

Recent Communications about the White Ovals:

Table I - Oval positions (Visible Wavelengths)

a) BC/BE
4/4/97cent.109.684.50A. Simon
8/9/97cent?58.367J. Rogers
11/6/97cent.26.659.00A. Simon/B. West
12/28/97cent?9.856J. Rogers
5/13/98cent?29820.5J. Rogers
5/18/98cent?294.518J. Rogers
6/1/98avg28916.5W. Haas
6/3/98center28614.00A. Simon
6/6/98avg288.517.3W. Haas
6/6/98cent?28615J. Rogers
6/8/98avg284.513.8W. Haas
6/13/98avg280.511.2W. Haas
6/18/98avg27911.0W. Haas
6/20/98avg279.512.0W. Haas
6/30/98f edge267(?)2.2W. Haas
7/16/98center266.66.00A. Simon
b) DE
4/4/97cent126.2100.63A. Simon
8/9/97cent?76.385J. Rogers
11/6/97cent.42.675.00A. Simon/B. West
12/28/97cent?19.866J. Rogers
c) FA
8/9/97cent?100.3109J. Rogers
11/6/97cent63.295.63A. Simon/B. West
12/28/97cent?41.888J. Rogers
5/13/98cent?332.657J. Rogers
5/18/98cent?336.260J. Rogers
6/3/98cent319.547.50A. Simon
7/16/98cent45.78A. Simon

Transits and images were obtained by a large number of observers, including: I. Miyazaki, D. Parker, C. Post, W. Haas, J. Rogers, B. West, R. Beebe, G. Orton and many others. See also Table 1B for more positions.

Estimates on W. Haas data were made by averaging preceeding and following edge transits.

Table 1B: Oval Positions (Infrared Observations)

Our best measurements in late December were from the bright 5-micron ring, in late March (first detection of a missing white oval) using a narrow-band filter at 2.03 microns with the rest using the "L-prime" filter centered at 3.78 microns. Radiance at 2.03 microns is sensitive to particles near 100-200 mbar and higher in the atmosphere; at 3.78 to particles near 1-2 bar and higher in the atmosphere + some H3+ emission.

(yy mm dd)
97 Dec 8:4.782450790.784.5-91.565.0-72.053.5 60.6
97 Dec 18:4.782450800.690.0-81.571.5-62.561.5 51.5
97 Dec 28:4.782450810.578.0-87.562.0-70.050.5 59.5
(yy mm dd)
98 Mar 27:2.032450900.266.0-71.027.5-36.5
98 Apr 25:3.782450929.259.5-66.518.5-29.0
98 May 2:3.782450936.2
98 May 27:3.782450961.155.5-61.513.5-22.5
98 May 29:3.782450963.153.5-59.512.0-20.5
98 May 31:3.782450965.255.0-60.513.5-21.5
98 Jun 2:3.782450967.2
98 Jul 14:3.782451009.044.5-51.04.5-13.5
98 Jul 20:3.782451015.244.0-50.03.5-12.5
98 Jul 25:3.782451020.140.0-48.02.0- 9.5

I'd estimate that our centering uncertainties propagated lat/long assignment errors of about 1 degree at the 1-standard deviation level.

VERY roughly, I'd say that the drift rate between March and May of the new oval was about 3.0 m/s prograde, and since then it has slowed a little to about 2.5 m/s prograde.

While there is a darker area around the new white oval at 3.78, it is indistiguishable from the surrounding lighter area at 1.58 microns (cloud albedo) or the surrounding cooler area at 4.78 microns (i.e. no bright ring even yet!).

While our middle-infrared data are still being processed, we hope that the final images should verify our initial conclusions: the new white oval, in addition to being slightly larger than FA, is definitely colder overall.

credit: Brendan Fischer, Glenn Orton

Table II - GRS and SEB (Visible Wavelengths)

a) GRS
05/09/98f. end80?W. Haas
05/28/98cent55W. Haas
06/02/98cent63W. Haas
06/09/98cent53W. Haas
06/14/98avg52.5W. Haas
06/19/98cent63W. Haas
06/21/98avg62W. Haas
06/26/98cent62W. Haas
07/20/98cent63W. Haas
07/25/98cent67W. Haas
b) SEB activity
06/06/98p220D. Parker image
06/06/98p264??D. Parker image
06/30/98p207D. Parker image
07/20/98p170T. Pratt image
08/06/98p170A. Nikolai image
08/06/98p170T. Gross image
06/06/98f347J. Rogers
06/28/98f310D. Parker image
07/05/98f300D. Parker image
07/27/98f310T. Gross image
08/01/98f297J. McAnally

credit: D. Lehman, J.McAnally and the observers named above!


These images show the dark spot that was reported in the STB. The color images were taken Aug. 3 by D. Parker. Similar spots have been seen before and one such spot is shown in the blue HST image taken Feb. 17, 1995. This dark spot formed when White Oval FA, then translating much faster than the other ovals, compressed a larger dark cyclonic system between it and another smaller oval. The cyclonic system shrank and finally collapsed into an extremely dark spot. By October 1995, a haze cap had formed over it and it no longer appeared as a dark spot. Comparisons of the system before and after 'collapse' can be seen in Simon and Beebe, Icarus, vol. 121, 1996. Precursors to the current spot may have been seen in Nov. 1997 HST data.