Friday, April 1, 2016

Weather systems on Jupiter

The vivid colours seen in Jupiter's clouds are the result of subtle chemical reactions of the trace elements in its atmosphere. The colours correlate with the cloud's altitude: blue lowest, followed by browns and whites, with reds highest (including the GRS). The coloured zones are regions of upward moving convective currents triggered by Jupiter's hot interior. On the other hand, the darker belts are made of downward sinking material. Because of such fluid dynamics, these two are always found next to each other.

Interesting features can be observed on the above coloured image, including the blue barges and plumes in the Equatorial Zone (EZ). The South Equatorial Band (SEB) is very active with a prominent wakefield next to the GRS. It looks as if  the flow is breaking up into individual elements, known as eddies. Unfortunately, the average seeing during this observation was poor and zooming in on such detail is not possible.

The zones and belts are zonal jet streams with velocities up to 650 km/hr and where wind direction alternates between them. One expects therefore strong wind shear visible only under excellent observation conditions as distinctive brown-coloured features next to bands, especially the SEB and North Equatorial Band (NEB).

Upward moving gases in Jupiter's atmosphere bring white clouds of ammonia and water/ice from beneath. Downward moving gases are darker as they sink down.

Jupiter's atmosphere is filled with methane, a gas which is a strong absorber of sunlight at 890 nm and therefore its presence appears as dark bands as in the right image below. The bright clusters in this image consist of high-rising energetic plumes high up in the atmosphere, able to reflect sunlight before it enters the planet's methane-dark interior. Each of these bright areas consists of massive convection cells rising very high that are low in methane, equivalent to the orange-hue areas highlighted in the coloured image below to the left. The dark streaks in both the EZ and SEB are made up of a higher concentration of methane gas (as shown by the right image below) which is sinking down to deeper layers and therefore seen as dark filaments in the coloured image.

If we were to create an illusion of depth on the basis of methane-deficient, high level clouds, the resulting image would be something similar to the one shown on the left. Especially prominent are the equatorial zone (EZ) and the great red spot (GRS). The GRS is an exceptionally energetic weather process, twice the size of planet earth, which rises high up in the atmosphere of Jupiter.

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