more probably fairly close to the belt near one of its ends. If a projection has been by-passed by one of the curving wisps, the enclosed light area will not, of course, be elliptical but will assume a shape resembling that of a kidney bean ."
While these bluish-gray features, or festoons, are almost always present, the shape and characteristic of each individual feature can be subject to change over short periods of time. This morphology is of great interest. Peek observed in 1941 a projection that grew enormously in just 2 days . Shapes and sizes of the features are so prone to change that it can be difficult to keep track of them reliably. Certainly, from one week to the next, these projections can change in shape to the point that an observer who does not carefully track them will have trouble reliably identifying the same feature the next week. From 1959 to 1964, the Association of Lunar and Planetary Observers (A.L.P.O.) made a special effort to follow these features close to solar conjunction. Thus, during that time it was possible to track and recover individual features from one apparition into the next, proving that they could exist for long periods of time. However, in recent history these projections and festoons have not been so reliably followed.
The probe from the Galileo spacecraft actually descended through one of these bluish-gray features and detected a lower than expected level of water vapor . But, to the visual observer, they appear as dark features, trailing back into the Equatorial Zone (EZ). Often, bright ovals are seen immediately following these festoons, seemingly imbedded in the hook of the festoons themselves. The vertical structure of these bluish-gray features is quite fascinating and will be further discussed in Chap. 4.
To the untrained observer, the equatorial zone (EZ) can appear quite uneventful. Yet, there is actually much to watch for here. During 1999, the EZ was very active with projections and festoons from the NEBs intruding prominently into the zone. On November 25, 1999 I noticed that the EZ was actually darker than the north polar region (NPR) and almost as dark as the south polar region (SPR). On August 05, 2000 it was noted by many observers, and confirmed on cCd images, that the EZ was greatly disturbed, giving the EZ an overall dusky appearance, such that the south tropical zone (STrZ) was actually the brightest zone on the planet (Fig. 3.16). These disturbances can be seen from time to time.
Visually, the EZ most often appears as the brightest feature on the planet, cream or alabaster in color. This was the case during the apparitions of 2000-2001, 2001-2002, 2002-2003, and 2003-2004. However, there are exceptions. Closer examination usually reveals there is more going on here. During Jupiter's history, the EZ has occasionally taken on a darker, yellow-ochre to brownish color, or sometimes a dusky appearance as the EZ undergoes a coloration event. Sometimes this effect can be subtle.
During the 1999-2000 apparition the EZ was bright and the festoons coming off the NEBs were very intense and prominent. Several of these festoons could be seen at various locations around the planet. The space between these festoons was generally bright and alabaster in color. However, by September 2001 the festoons were no longer so intense and the color of the EZ had begun to change. During 2000-2001 the EZ underwent a coloration event that would last beyond 2004.
By September 2001, the EZ coloration event gave a curious appearance to the planet. Compared to 1999, the decline of the projections and festoons gave a somewhat "clean" appearance to the EZ. These normally prominent features were conspicuous by their lack of intensity! The EZ had taken on a yellowish to yellow-ochre coloration for fully three-quarters of the distance from the NEBs to the SEBn.
CM1=110.4 CM2=232.1 CM3=171.4
Fig. 3.16. Jupiter with a very disturbed EZ. The NTB is prominent with a couple of small projections on the southern edge. The northern edge of the NEB is withdrawn and undulating, and the SEB is split into two components. One of the Galilean moons is casting a shadow on Jupiter's globe. August 5, 2000. South is up. (Credit: Donald C. Parker).
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