[2] Circulation of the GRS observed even more closely (2014, Dec 2nd.)


GRS circulation observed even more closely

The Great Red Spot, now at L2 = 220, is still strongly reddish and exceptionally small, only 14.2 deg long and 9.1 deg wide (+/-0.4 deg) (2014 Oct-Nov.), although it now has complex dark streaks around it. 
Earlier this year we measured the internal circulation of the GRS from amateur images, and found exceptionally short rotation periods of 3.6 days in 2014 Jan. (our report no.7) and 3.6—3.8 days in 2014 Feb. (M. Jacquesson, unpublished).  A similar analysis of images in 2014 Nov. by M. Jacquesson confirms a rotation period of 3.8 days.  Moreover, the motions within the GRS can be seen within less than an hour in images on Nov.1.
The internal rotation was revealed by a dark spot near the edge of the GRS as shown in the attached image file. All images were map-projected and then stretched to make the GRS approximately circular for measuring the position angle, as usual.  A single dark spot was clearly tracked from Nov.2-13, with P = 3.78 (+/-0.3) days.  A similar dark spot was also present on the same track on Nov.18-19, but it was absent on Nov.15, so we cannot be sure if it was temporarily obscured or replaced by a new feature.
The attached animation shows something even more special: the internal rotation of the GRS tracked during a single passage across the disk in 3 images by Isao Miyazaki on Nov.1.  This has never before been achieved from ground-based images.  The circulation is clearly visible over the first, 47-minute interval, and to a lesser degree over the second, 15-minute interval!   Moreover, the sinuous blue-grey streak in the p. ansa appears to be twisting tighter over this timescale, as the dark patch at its centre (marked O in the first frame) remains more-or-less stationary.  Ten hours later, this feature had become the dark spot which we then tracked.
The detection of these phenomena on Nov.1 was due not only to the excellence of Miyazaki’s images, but also to the fortunate occurrence of dynamic, high-contrast features in the GRS at that time.  Those of you who can obtain v-hi-res images may likewise be able to capture the rotation of the GRS during a single passage across the disk – and perhaps even more dynamic phenomena.  
John Rogers & Michel Jacquesson
2014 Dec.2


John H. Rogers, Ph.D.
Jupiter Section Director,
British Astronomical Association

John H. Rogers, Ph.D. Jupiter Section Director,
British Astronomical Association