Cloud pattern on Jupiter

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Cloud pattern on Jupiter

The cloud pattern on Jupiter is the visible system of colored cloud tops in the atmosphere of the planet Jupiter, remarkable for its stability. Astronomers have given names to parts of this pattern, using the word zone for the light stripes, and belt for the dark stripes, along various latitudes. The pattern and intensity of its belts and zones are famously variable, often changing markedly from opposition to opposition.

[edit] Names

There are six major belts on Jupiter:

• North and South Equatorial belts (NEB and SEB)
• North and South Temperate belts (NTB and STB)
• N. North and S. South Temperate belts (NNTB and SSTB)

There are seven major zones:

• Equatorial zone (EZ)
• North and South Tropical zone (NTropZ and STropZ)
• North and South Temperate zone (NTZ and STZ)
• N. North and S. South Temperate zone (NNTZ and SSTZ)

There are two polar regions:

• South polar region (SPR)
• North polar region (NPR)

Additionally, there are zones and belts that are more transient in nature and not always visible:

• Equatorial band (EB)
• North Equatorial belt zone (a white zone within the belt) (NEBZ)
• South Equatorial belt zone (SEBZ)
• North Tropical zone belt (an additional belt inside the white zone) (NTropZB)

When a disturbance divides a normally singular belt or zone, a N or an S is added to indicate whether the component is a northern or southern one; e.g., NEB(N) and NEB(S).^[1]

[edit] General Characteristics by Belt and Zone

Idealized illustration of Jupiter's cloud bands; they are labeled with their official abbreviations. The Great Red Spot and Oval BA are shown in the South Tropical Zone and South Temperate Belt, respectively.

After Rogers (1995), Jupiter's zonal systems--appearances and dynamics--vary substantially by latitude.

North and South Polar Regions

Extending to roughly 40-48º N/S, these bluish-gray regions are usually featureless.^[2]

North North Temperate Region

The North-North Temperate Belt (NNTB)--part of the general north-north temperate region--rarely shows more detail than the polar region(s), due to the complicating factors of limb darkening, foreshortening, and the general diffuseness of features. That said, the NNTB is the northernmost distinct belt, though it occasionally "disappears". Disturbances tend to be minor and short-lived. The North-North Temperate Zone (NNTZ) is perhaps more prominent, but also generally quiet. Other minor belts and zones in the region are only occasionally observed.^[3]

North Temperate Region

This region has a superb record, as it is part of a latitudinal regime on the planet that is easily observable from Earth. It also features the strongest prograde jet stream on the planet, a westerly current that forms the southern boundary of the North Temperate Belt (NTB). The NTB fades roughly once a decade (this was the case during the Voyager encounters), making the North Temperate Zone (NTZ) apparently merge into the North Tropical Zone (NTropZ). Other times, the NTZ is divided by a narrow belt into northern and southern components.^[4]

North Tropical Region

The NTropZ and the North Equatorial Belt (NEB) comprise this region. The NTropZ is generally stable in coloration, changing in tint only in tandem with activity on the NTB's southern jet stream. Like the NTZ, it too is sometimes divided by a narrow band, the NTropB. On rare occasions, the southern NTropZ plays host to "Little Red Spots"; as the name suggests, these are northern equivalents of the GRS. Unlike the GRS though, they tend to occur in pairs, and are always short-lived, lasting a year on average; luckily, one was present during the Pioneer 10 encounter.^[5]

The NEB is one of the most active belts on the planet. The northern NEB is characterized by anticyclonic white ovals and cyclonic "barges" (also known as "brown ovals"), with the former usually forming farther north than the latter; as in the NTropZ, most of these features are relatively short-lived. Like the South Equatorial Belt (SEB), the NEB has sometimes dramatically faded and "revived".^[6]

Equatorial Region

The Equatorial Zone (EZ) is one of the more stable regions of the planet, in latitude and in activity. The northern edge of the EZ hosts spectacular plumes that trail southwest from the NEB, which are bounded by dark, warm (in infrared) features known as festoons. Though the southern boundary of the EZ is usually quiescent, it's worth noting that observations from the late 19th into the early 20th century show that this pattern was then reversed relative to today. The EZ varies considerably in coloration, from pale to an ocher, or even coppery hue; it is also occasionally divided by an Equatorial Band (EB).^[7]

The EZ's rotation is entirely System I, which is five minutes shorter than System II (for regions north and south of the EZ); features in the EZ move roughly 390 km/hr (240 mph) relative to the other latitudes.^[8],^[9]

South Tropical Region

This region includes the SEB and the South Tropical Zone, and is by far the most active on the planet, due to the location of the strongest retrograde jet stream on the planet in this area. The SEB is usually the broadest, darkest belt on the planet; however, it is sometimes split by a zone (the SEBZ), and also can fade entirely during a SEB Revival cycle. Also characteristic of the SEB is a long train of cyclonic disturbances following the Great Red Spot.

Similar to the NTropZ, the STropZ is one of the most prominent zones on the planet; not only does it contain the GRS, but it is occasionally rent by a South Tropical Disturbance (STropD), a division of the zone that can be very long-lived; the most famous one lasted from 1901 to 1939.^[10]

South Temperate Region

The South Temperate Belt (STB) is yet another dark, prominent belt, more so than the NTB; until recently, its most famous features were the long-lived white ovals BC, DE, and FA, which have since merged to form Oval BA ("Red Jr."). The STB has occasionally faded, apparently due to complex interactions between the white ovals and the GRS. The appearance of the South Temperate Zone (STZ)--the zone in which the white ovals originated--is highly variable.^[11]

South South Temperate Region

This region is difficult to observe from Earth, even more so than the NNTR; detail is subtle, and can only be studied well by large instruments, and best with spacecraft observations.^[12]

[edit] Causes

The colored bands in Jupiter's clouds are caused as different-colored layers of clouds become visible.

[edit] Layers

Jupiter's clouds are made up of three different layers, growing colder as they increase in altitude^[13]

• a top layer of ammonia; this layer is white
• below that, a layer of ammonium hydrosulfide; this layer is red or brown
• lowest of all, a layer of water, which is not normally visible

Note: Though the layer of ammonium hydrosulfide should appear white, it is possible that impurities cause the reddish-brown color.

[edit] Circulation Cells

Jupiter, like most planets with atmospheres in the solar system, has multiple circulation cells, caused by the Coriolis Effect, which occurs when a planet with a thick atmosphere spins rapidly. This causes warm air moving away from the equator of the planet and cold air moving away from the poles to become divided into east-west air currents. Jupiter has a particularly strong Coriolis Effect, due to its dense atmosphere and fast rotation. The Galileo probe recorded wind speeds of up to 220 m/s (nearly 800 km/h), increasing lower down^[14][1]. This also results in a greater number of circulation cells, compared to Earth's three.

[edit] Rising Gases

Jupiter's core is much hotter than the outer parts of its atmosphere. This causes the gases in its atmosphere to rise, cooling as they go. As they reach the altitude at which they can condense, they do so, while gases that condense at lower temperatures continue to rise. Eventually, the ammonia in the highest level of the clouds crystallizes, like snowflakes, causing the white clouds to disappear, allowing the darker ones below to become visible. Since each circulation cell is a different temperature, the different colors are arranged into bands.

[edit] Storms

The Great Red Spot is a storm feature on the border to the South Equatorial belt and has been observed for at least 300 years.

A feature in the South Temperate Belt, Oval BA, was first seen in 2000 after the collision of three small white storms, and has since appeared to have intensified. It is now approximately half the size of the Great Red Spot, and is starting to turn red. As a result, some scientists have begun calling it "Red Jr." [2]

There are always many smaller storms: brown, low pressure storms, and white, high pressure storms.

[edit] Disturbances

The normal pattern of bands and zones are sometimes disrupted for a period of time, and Astronomers call these events "Disturbances". For example, the longest lived disturbance in recorded history was a "Southern Tropical Disturbance" (STropD) from 1901 until 1939, discovered by Percy B. Molesworth on February 28, 1901. It created a darkened feature over some longitude area in the normally bright Southern Tropical zone.

Various patterns of motion are apparent all across Jupiter at the cloudtop level seen here. The Great Red Spot shows its counterclockwise rotation, and the uneven distribution of its high haze is obvious. To the east (right) of the Red Spot, oval storms, like ball bearings, roll over and pass each other. Horizontal bands adjacent to each other move at different rates. Strings of small storms rotate around northern-hemisphere ovals. The large grayish-blue "hot spots" at the northern edge of the white Equatorial Zone change over the course of time as they march eastward across the planet. Ovals in the north rotate counter to those in the south. Small, very bright features appear quickly and randomly in turbulent regions, candidates for lightning storms.

Scale: The smallest visible features at the equator are about 600 kilometers (about 370 miles) across.
Duration: The 14-frame animation spans 24 Jovian days, or about 10 Earth days. Motion occurs at about 600,000 times actual speed.

[edit] External link:

• Damian Peach. "A Guide to Jovian Activity."

[edit] References

1. ^ Ian Ridpath, Norton's Star Atlas and Reference Handbook, 19th ed., (Harlow: Addison Wesley Longman Ltd., 1998), p. 107.
2. ^ John Rogers, The Giant Planet Jupiter, (Cambridge: Press Syndicate of the University of Cambridge, 1995), p. 81.
3. ^ Rogers, pp. 85, 91-4.
4. ^ Rogers, pp. 101-5.
5. ^ Rogers, pp. 113-7.
6. ^ Rogers, pp. 125-30.
7. ^ Rogers, pp. 133, 145-7.
8. ^ Rogers, p. 133.
9. ^ Reta Beebe, Jupiter: The Giant Planet (Smithsonian Institution 1997), p. 24.
10. ^ Rogers, pp. 159-60
11. ^ Rogers, pp. 219-21, 223, 228-9.
12. ^ Rogers, p. 235.
13. ^ Bennett, Jeffrey; Donahue, Megan; Schneider, Nicholas; & Voit, Mark (2004). The Solar System: The Cosmic Perspective, (3rd ed.). San Francisco: Pearson Education, Inc. ISBN 0-8053-8930-X
14. ^ Folkner et al. "Earth-Based Radio Tracking of the Galileo Probe for Jupiter Wind Estimation." Science 31 January 1997: Vol. 275. no. 5300, pp. 644 - 646