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Guest post: Marco Vedovato, “Jupiter: a little analysis about the GRS-LRS encounter” February 15, 2009

Posted by dorigo in astronomy, news, physics, science.
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Marco Vedovato, in his daily life, is a structural engineer. As an amateur astronomer, when his children allow him to do this, his main interest is the atmosphere of Jupiter, the giant planet of the Solar System, and he partecipates, as a measurer, to the Jupos Project, an international investigation about Jupiter. He is also the vice-manager of the Jupiter Program for the Italian Amateur Astronomic Union. When I saw his extremely interesting analysis of the Jovian atmosphere I begged him to write about it for this site. You can find the resulting piece below.

Last year I amused myself to analyze one aspect of the encounter between two Jupiter spots. For this aim, I used WinJupos, a software for measuring the Jupiter images (see here). In the following picture, a map composed by using some very good images, the reader will be able to meet the protagonists of this tale (click on the picture to get the full image!):

The first one is the famous Great Red Spot (GRS), a long-lived anticyclonic circulation, centered around -22,5ø South latitude, existing at least since the second half of 18th century. The second one is a smaller reddish spot (LRS, Little Red Spot), probably born around the end of 2007 and the beginning of 2008, a residue of a previous “Tropical Disturbance”, observed during the 2007.

It is well-known that the GRS has a 90-days oscillation around its mean motion in the Jupiter outer atmosphere; having a look to the map above, GRS is moving very slowly in longitude (with the same latitude) from left to right, forward to the increasing longitudes (retrograde motion). This lazy motion is not constant but presents an oscillation around the main drift. In the following graph the red points are the GRS center, the ones on the left (blue) and right (green) side are the ends of GRS; it is easy to note a period close to 90 days.

Instead the LRS moved in the opposite direction (prograde motion) than the GRS (and with higher speed), so an encounter was inevitable. In the the picture below, a graph I obtained before the encounter, using few points but from very good images (i.e. those of C. Go, F. Carvalho, A. Wesley, G. Grassman and others). I noted, also in the LRS case, an oscillation around the interpolating line.

After the encounter the LRS was quickly destroyed. The following graph documents the collision.

I was interested to see if this LRS oscillation were similar to the GRS one, with the same period and if in phase or not. So I matched “in parallel” the relative motions (by using a modified reference system for the LRS, artificially changing its speed, to have more or less the same slope for both the drifts); a light correlation between the two oscillations seems noticeable. I do not know whether the effect is casual or if it is real. In this last case, are the two oscillations determined by a same cause, hidden in atmospheric currents embedded in deeper layers?

John Rogers, Jupiter director of the British Astronomical Association, wrote me this comment: “Very interesting. Perhaps the oscillation of the GRS has an effect on the nearby LRS? Or perhaps the synchrony is a coincidence — it is difficult to say!

I’ll have to prepare further analysis when there will be similar opportunities.

(Marco Vedovato)


1. Amara - February 17, 2009

Nice work, Marco! If I were you, I would try to publish the analysis, but with an idea of why the correlation between the two oscillations. I’m not an atmospheric scientist, but I think
the work by M. Roos-Serote could help give insight to that question.

I hope that you continue!

2. Marco - February 17, 2009

Thanks for the lovely comment and for your encouragement, Amara.You’re very nice.
I am not a good scientist as you or Tommaso; I’m only a “poor” amateur. Of course I’d like to find a way to produce a model of this phenomenon and this model will have to be different from the oscillating eddy in my sink! My wife probably would say I am crazy to think to Jupiter while observing a sink… but she doesn’t know this little secret of mine! For this purpose I will have to ask help from a physicist; meanwhile I hope to find further confirmations. I think that this kind of observations could give interesting indications about the Jupiter deep atmospheric currents. Thanks for the bibliography that seems very interesting and useful.

3. msantander - February 18, 2009

Ciao Marco,

I really enjoyed your post, I was thinking if the translational speed (or its modulation) of these giant hurricanes in the jovian atmosphere could be used as a way to map lower layers of the planet. I was thinking about how tornados change velocity when they hit the ground here on Earth (which means, when the conditions in the bottom of the vortex suddenly change, even when there would be no “ground” in Jupiter’s case) and if the same could apply to Jupiter, I don’t know.
I’m just thinking out loud here and I don’t have the slightest idea about how these things work, probably you could hear something better from an specialist in Computational Fluid Dynamics. I think I had too much coffee today! 🙂
Keep up the good work!


4. Marco - February 18, 2009

Hi Marcos and thanks for your feedback.
As far as the specialist in Fluid Dynamics you’re right.
Of course we cannot match our tornados and the Jupiter ones, where there is no ground.

The dynamic of the outer atmosphere is modulated from a pattern of currents, blowing parallel to lines of latitude. Slow currents coexist with faster currents (“jetstrems”); i.e. GRS floats in the South Tropical current [1]. It is interesting to note that GRS is a long-lived feature but its life is destined to finish sooner or later. Ancient GRS observations probably describe others GRSs. So also GRS is only a temporary feature that, as an Arab Phoenix revives from its own ashes, in this case when in the South Tropical latitudes a “Disturbance” appears, creating a very large Circulating Current that -step by step- shrinks into a smaller size. If a Disturbance appears when a GRS already exists, the circulating current is destroyed after few months; also in this case, is there a resonance between the speeds of the winds and the rotation period that prevents the existence of two GRS? What is the deep source that allows the arising of the Circulating Current? It would be interesting to study Jupiter also from this point of view. A good example of resonance on Jupiter outer atmosphere probably is the spacing between the equatorial projections (Festons) whose mutual angular distance is close to 30°, a submultiple of 360°.

By the way, here you can find an animated GIF I prepared two years ago, showing the effect of the Circulating Current! (see image on the bottom and click on to start the animation).

Jupiter is really an amazing planet, a very complex laboratory for studying fluidodynamic!

[1] The Giant Planet Jupiter (chapt. 4), John H. Rogers; Cambridge Un. Press

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