Great Red Spot (Click on the image for a larger view)
features of broadly different sizes appear to move with
uniform velocities. That suggests that mass motion (movement
of material) and not wave motion (movement of energy through
a relatively stationary mass) was being observed.
brightening of features in the atmosphere was followed by
spreading of cloud material. That is probably the result
of disturbances that trigger convective (upwelling and downwelling)
pattern of east-to-west winds extends as far poleward as
60 degrees north and south, roughly similar to the pattern
seen in more temperate areas where belts and zones are visible.
Previous investigations led scientists to believe the near-polar
regions (above 45 degrees latitude) are dominated by convective
upwelling and downwelling. Voyager showed they apparently
are not, at least up to 60 degrees latitude, and probably
associated with the Great Red Spot, Jupiter's most prominent
atmospheric feature, moves in a counter-clockwise (anticyclonic)
direction. At the outer edge, material appears to rotate
in four to six days; near the center, motions are small
and nearly random in direction.
spots appear to interact with the Great Red Spot and with
instruments observed auroral emissions, similar to Earth's
northern lights, in the polar regions, in ultraviolet and
visible light. Pioneer 10 and 11 didn't see the ultraviolet
emissions during their encounters. The auroral emissions
appear to be related to material from Io that spirals along
magnetic field lines to fall into Jupiter's atmosphere.
also saw cloud-top lightning bolts, similar to superbolts
in Earth's high atmosphere.
temperature at 5 to 10 millibars (1/200th to 1/100th Earth's
surface atmospheric pressure) is about 160 Kelvins (-170
degrees Fahrenheit). An inversion layer -- a warmregion
above a cold layer, similar to the phenomenon that traps
smog in the Los Angeles Basin -- exists near the 150-millibar
level. (Pressure at Earth's surface is about 1,000 millibars.)
Voyagers observed ionospheric temperatures that changed
with altitude, reaching about 1,100 Kelvins (1,500 degrees
Fahrenheit). That was also not observed by Pioneers 10 and
11, and Voyager scientists believe they are witnessing large
temporal or spatial changes in the ionosphere of Jupiter.
Voyagers measured helium in the upper atmosphere; its percentage
compared to hydrogen is important to understand composition
and history of the atmosphere -- and the primordial cloud
of which the Sun and planets formed. Relative abundance
of helium to hydrogen is about 11 percent by volume.