May 20, 1997

Continued input on the STrZ Oval/Red Spot Interaction

From Glenn Orton


What is the time scale for this interaction (based on the smaller Voyager precedent) to involve the entire GRS? Is there any reason to re-point the GRS observations planned for C9 in June (which were prejudiced toward the trailing turbulent "wake") anywhere else, such as toward the leading edge of the GRS?



The images from Don Parker on May 15 indicate that the STrZ disturbance has shifted northward and begun to "circumnavigate" the Red Spot. Based on early measurements by Elmer Reese and Voyager measurements, the time interval before it would pollute the Red Spot is about 6-7 days. Therefore if we are to see fading of the red aspect of the GRS it should be within this week.

Whether this merits retargeting is up to the AWG. We do have very high resolution of BC in Voyager for comparison.

The following messages provide further insight into the dynamics of the problem. Smaller "Voyager eddies" follow the same path. We can measure accelerations that these features experienced for comparisons with data obtained during this interaction.

From: agustin sanchez

The White Tropical Oval and the Great Red Spot

We would like to add some data on the "White Tropical Oval" (WTO) that interacted with the GRS on mid May 1997, which can be of interest for enthusiastic jovian observers.

This Oval formed probably around 1983 when the southern edge of the South Equatorial Belt was very active in smaller anticyclonic, visually dark, spots. We followed it photographically from 1983 to 1987, and since then continuously through CCD imaging mainly with the 1-m telescope at Pic-du-Midi (J. Lecacheux, P. Laques and F. Colas) and by D. Parker, I. Miyazaki and the GEA group in Spain with their 0.4 m telescopes. A first report by our team was presented at the 26th DPS meeting (A. Sanchez-Lavega et al., Bull. Amer. Astron. Soc., Vol. 26, 1102, 1994).

The main interest of this feature resides in its latitude location (very close to the GRS), relatively large size, long lifetime, and in the resemblances and differences with the GRS. It was rare, since no other similar vortex has been previously reported in the STrZ (aside of the GRS), according to historical records (Peek, Rogers). In addition, its current interaction with the GRS can give information on the nature of the jovian vortices.

Up to now we have performed about 350 measurements (1983-present) of its position, motions and interactions with other jovian tropical features, as well as photometric measurements in the 400 to 1000 nm spectral range during different epochs. Here are the main preliminary parameters for this vortex based on the above observations:

We expect to report these observations and data in length, as well as the interaction between the WTO and the GRS, in the forthcoming DPS meeting.

Agustin Sanchez-Lavega

From: Amy Simon

Measurements of HST/WFPC2 data

Using the April '97 and Oct. '96 HST/WFPC2 data, I was able to obtain a drift rate of the White South Tropical oval (STrZ oval) of 0.39 deg/day W and of 0.28 deg/day W for the GRS. Also see the figure caption.

As a check, extrapolating this drift rate backwards gives a reasonable location for the oval in the Oct. '95 data.

Here are the relevant numbers (all coordinates graphic):

Using the GRS east edge, the spots would be expected to interact on June 24 (112 days after the April 4, '97 data) (note: this assumes continued laminar flow -- which would only be the case if the systems did not interact and the Red Spot and the STrZ Oval DID NOT modify the zonal flow.)

From Glenn Orton

(excerpted from a message)

We have arranged with Mt. Stromlo /Siding Spring Observatory to take over the IRTF-type Galileo support monitoring program while the IRTF is down (!) for shutter refurbishment. Their images will have pixel pixel sizes about twice as big as the IRTF images. The observations will be made nightly.

Walter Wild has also agreed to make observations routinely from Yerkes.

COMMENT: Welcome aboard -----Keep us informed on your progress!!!