In the nomenclatura of jovian belts and zones, the "tropics" are occupied by zones, and not belts, in both hemispheres. Each of these two zones separate the two great equatorial belts from the temperate regions. We need to note first that this only a question of nomenclatura, because the real tropics on Jupiter are situated directly in what is called the "Equatorial zone" (at 3° south and north), due to the limited 3° axial tilt of the planet. The "tropical zones" are thus situated much more higher in latitude.

None the less, the tropical zones somtimes show a dark belt within. In the north tropical zone (NTrZ) can be seen a very subtle belt, the north tropical belt (NTrB), but only when the north equatorial belt is in its narrow phase. When the NEB is in its broad phase, it reaches the latitude of the NTrB so this delicate belt cannot be detected. But, the phenomenon that we call south tropical belt (STrB) is different : this is a normally limited belt (in lenght), but darker and somewhat broader than its northern counterpart, and that is created by the activity of the Great red spot (GRS). As a matter of fact, the STrB appears when dark material from the south component of the SEB, which goes from east to west, is trapped around the GRS, which has a counterclockwise movement. Then that material now runs from west to east, in a prograding direction, into the STrZ (see figure below).

This belt appear from time to time, whithout any apparent reason. The three last apparitions were in 2001, 1998, and 1991. It is at the very end of october 2001 that began the last developpement of a STrB. The montage below shows the evolution :

11 november 2001 : the dark material from the SEB has already turned around the GRS. The blue arrow points at the STrB almost at the very begining of its developpement. The two orange arrows point at two little anticyclonic structures that must be associated with the activity produced by the presence of the GRS. They were to disappear in the following weeks. Circled by dark clouds, the GRS, visually quite pale, has a very esthetical eye-shape aspect.

21 november and 7 december 2001 : the STrB is now well visible, although still short. One of the two cyclonic structure has already disappear.

10 and 17 december 2001 : we see here the BTrS at its height, very long, and giving to the SEB a typical "triple" aspect. In reality, as good CCD and webcam documents from that period show it, the BTrS is much more longer than in those drawings, although very finer and subtler.

15 january 2002 : the gap between the GRS and the STrB proves that at that period, the flux of dark material from the SEBs has ceased. The little belt will soon disappear.

By clicking here you will access another similar montage made by Hideo Einaga, from the Japan ALPO, with a digital camera and a 10" newtonian telescope. IMPORTANT : to have the page opened, you will have to click on "OK" to the right side of the URL window. The two montages are quite close to one another...

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