Circumpolar Cyclones (CPC)
This thread is dedicated to the observation of circum polar cyclones.
Two major classes of observations are accessible for Juno, especially for JunoCam.
Those are short-term observations performed within one perijove pass, and long-term observations over the lifetime of Juno's exploration of Jupiter.
Within a short-term observation period, one of the major goals is an analysis of wind fields within and between the vortices around Jupiter's poles.
Morphological considerations as well as time-lapse animations are a first step of describing the short-term dynamics of the vortex patterns.
Animations can be used as a basis for more advanced data reduction methods. Example reduction goals are wind fields approximated by maps of vectors describing cloud feature motion.
Further reduced are vorticity maps, or maps about the position, size and type of vortices or jets.
Long-term observations include the evolution of the overall pattern of the circumpolar cyclones.
Since Juno's first observation of Jupiter's polar region, in JunoCam images, we see a south polar cyclone slightly displaced from the south pole.
This south polar cyclone is surrounded by five circumpolar cyclones. This pentagonal pattern oscillated a bit, but in the longer run it turned out to be astonishingly stable with respect to Jupiter's L3 coordinate system.
Astonishingly, since the surroundings of the CPCs appear to behave much more chaotically.
The north pole has been just behind the terminator on Jupiter's night side since the beginning of the mission. JunoCam has been able to observe eight circumpolar cyclones (CPCs) around the north pole.
JunoCam was able to identify parts of a pretty large anticyclone closer to the north pole than the CPCs during one of the perijoves. Towards a north polar cyclone JunoCam has only been able to detect vague hints.
These eight northern CPCs are forming an almost regular ditetragonal pattern. A ditetragon is like a regular octagon, except each second corner displaced radially by a common amount.
The north polar octagon turned out to be rather stable with respect to L3, too.
Objectives of long-term observations include the evolution of the morphology of the circum-polar cyclones, as well as the stability and oscillations of the polar and circumpolar vortices, especially the cyclones.
More advanced are time series describing the evolution of wind fields and vorticity maps in the long run.
Jupiter's polar vortex patters have not been anticipated.
Obvious physical questions are:
How could these polar vortex patterns form, and why are they so stable?
Why does the vortex structure differ from Saturn's, and why are even Jupiter's northern and southern CPC patterns different?
Juno's, and especially JunoCam's observations constrain future theoretical models.
Downloads
- jnc_polS_4PJs.jpg [0.96 MB]
- jnc_pj05_S_enh3.zip [5.50 MB]
- pj10_polS_anim_zoom3.zip [21.84 MB]
15 Comments
Here is some more evidence of a north polar CPC with an anticyclonic eye. It has been observed during PJ28.
PJ24 north polar CPC animation derived from 4 images. The gif is animated forward and backword, kind of an extended blink. Note the slow rotation near the core of the CPCs, like solid body rotation, or even slower.
The maps are rotated clockwise by 37 degrees relative to System III with 0 to the right.
Link to the animated gif described below:
junocam.pictures/gerald/uploads/20180518/jnc_pj12_polN_HD_reproj_hiTDI_3frames_076_077_079_reg_blended.gif
This animated gif is derived from the three PJ-12 images #076, #077, and #079. It shows how far we have been able to acquire data of the northern CPCs within Jupiter's twilight zone using more than two TDI steps A context-sensitive hipass filter has been applied to adjust for local contrast and brightness variability.
The three images have been blended in order to obtain a smoother result, after reprojecting them to a common vantage point, and cropping them to full HD format.
For an account of the CPCs at PJ12, please see Part I of the report I've posted on the PJ12 thread.
--John Rogers.
And here is a zipped file containing a montage featuring additional versions of the north polar mosaic from my previous comment:
Upper left: An approximately true color/contrast mosaic of Jupiter's north polar region (same is in the previous comment except).
Upper right: A mosaic of Jupiter's north polar region with enhanced colors and contrast.
Lower left: The approximately true color/contrast version with a latitude/longitude grid. Latitudes are planetographic.
Lower right: A diagram showing the areas covered by the different source images/data. Unless otherwise noted the data is from JunoCam.
Here is a mosaic of JunoCam images from perijoves 1, 3, 4 and 5. The effects of the varying global illumination have been removed. The mosaic shows Jupiter's north polar region in orthographic projection from directly above. Because the north pole is in winter darkness, an inverted, heavily processed and colorized JIRAM mosaic was used to fill the gap at the north pole. This represents an attempt to guess what this area might look like in visible light. Small scale details in the cloud morphology should be fairly accurate/realistic but the overall contrast, brightness and color are more uncertain. They are based partially on a visual comparison of the JunoCam and JIRAM data farther from the pole where useful data from both instruments is available. It is difficult to guess how accurate this is but it is definitely far better than leaving this area blank. Unfortunately we will not be seeing all of this area clearly in visible light any time soon unless Juno lasts well into the 2020s (JUICE will also be orbiting Jupiter during northern hemisphere winter).
The JIRAM data appears a bit different from the JunoCam data in the mosaic. This is partially because the JIRAM data suggests that the area very near the pole really is a bit different from areas farther from the pole. Another factor is that the JIRAM data is of somewhat higher resolution than the JunoCam data and that unlike JunoCam, JIRAM it is not affected by the difficult illumination conditions in the far north.
Figure 7. This composite south polar view of the planet, released by NASA on 2017 May 25, was a compilation of views from 3 different perijoves, as indicated here. As the pentagon of cyclones is not centred on the pole, it was not coherently shown. Original image credit: NASA/JPL-Caltech/SwRI/ MSSS/Betsy Asher Hall/Gervasio Robles.
Figure 6: Examples of ‘vortex crystals’ formed in magnetized electron columns, a laboratory model of non-viscous fluid turbulence, as shown in [ref.5]. (Colour represents vorticity, all in the same sense, ranging from low (light green) to high (red).)
Figure 5. Angular velocities and wind speeds within the CPCs at PJ3, measured by JHR from JunoCam images projected by GE. In the lower panel, individual CPCs are colour-coded and connected by lines. (Similar results were obtained from images at PJ1 and PJ4, not shown here.)
Figure 4. North polar projection maps of the CPCs composited from pairs of perijoves (PJ1 to PJ6) and from four perijoves with the ditetragon delineated (PJ6 to PJ9).
Figure 3. South polar projection maps of the CPCs at single perijoves (PJ-1, 3, 5, & 7) and in pairs with the pentagon delineated (PJ-1&4, PJ-6&8). Red crosses mark the south pole.
Figure 2. North polar view of the planet, composited from views directly above the pole at perijoves 1, 3, 4 & 5. (Small rotations and offsets were applied but are not indicated.)
Here is the first of the illustrations from the JunoCam team's report that we have just posted.
Figure 1. South polar view of the planet, composited from views directly above the pole at perijoves 1 and 4. In Figures 1-4, the component maps were correctly aligned in System III longitude (L3), except for rotations of a few degrees, and small offsets, to optimise the register of the CPCs.
With the discovery of the polar polygons being reported by the JunoCam and JIRAM teams in Nature tomorrow, I have posted a more extensive report on the JunoCam observations on the BAA Jupiter Section web pages, with some composite illustrations. The report is at:
https://britastro.org/node/12654
animations at:
https://britastro.org/node/12655
A PDF of the report (with miniature copies of the figures) is attached here. I will upload the full-size figures to this page shortly.