Here are two images showing that great changes take place on Jupiter's surface over time.
The first was taken about 2 years ago, in June 2007. As can be seen, the SEB had practically disappeared and the Equatorial Zone was awash with diagonal bands.
The second was taken this morning. Notice how the two main belts are now very distinct, with the white Equatorial Zone now very plain as compared with 2 years ago. However, the NEB now has large brown swirls (seen near the centre line of Jupiter in the image).

