Courses in Astrophotography

A Guide to Jovian Activity & Nomenclature

By Damian Peach

Introduction

As many observers are well aware, the descriptions used by observers in describing Jovian activity is often confusing, and many often get there SEB's and NTBs in a muddle!. Here i present a guide to the Jovian atmosphere, and the correct descriptions and nomenclature (as outlined by the BAA Jupiter Section.) All examples our outlined with appropriate imagery when possible.

Jovian Atmospheric Basic Information

Standard nomenclature for the belts, zones, and currents of Jupiter's atmosphere (redrawn from: Rogers JH, 'The Giant Planet Jupiter', Cambridge University Press, 1995). South is up.

The Jovian atmosphere presents a defined structure of belts and zones, which are all defined by a multitude of jetstreams encircling the globe. Above is a link showing all the correct descriptions, locations and abbreviations for almost all of the belts, zones and jetstreams. Below, you will find sections commenting on the most relevant belts, zones and Jetstreams with there "usual" observed activity commented on:

South Polar Region (SPR)

This dark area covers the southern pole of Jupiter and is usually pretty featureless visually. Occasionally, small dark and bright spots can be followed in High resolution CCD images, but for the most part, the area is quiet.

A typical image of the SPR showing little detail, other than dark streaks. D. Peach - Dec 2002.

South South South Temperate Belt & Zone (SSSTB or S3TB and SSSTZ or S3TZ)

Here is where small storms start to become noticeable. They usually take the form of small brighter anti-cyclonic storms, and some can become quite prominent. The S3TB isn't usually definable as a separate belt, though the S3TZ often is well defined, especially in recent years.

An image of this area showing a bright anticyclone on the edge of the SPR. Also note the S3TB can be seen as a darker belt section just north. Many smaller dark spots are seen within the S3TZ, as is a small bright storm on its northern edge. D. Peach - Feb 2003.

South South Temperate Belt and Zone (SSTB and SSTZ.)

This belt often presents a great amount of interesting detail, the most well know of which are the frequent bright anti-cyclonic storms which propagate within the belt (usually between 5 and 8 storms are present at one time.) These can be well seen visually in high quality telescopes as small as 5" aperture. They are actually not small by our earthly standards, ranging between ~1500 - 3000km across, their brightness due to the high ammonia ice clouds marking the tops. In 2002, for the first time, amateur astronomers followed the collision of two of these storms, which merged into one larger storm. These storms can last several years.

Other interesting detail is visible within the belt such as more irregular cyclonic circulations, and occasionally dark spots. The SSTZ however is usually very quiet, with occasional interesting details, such as small dark spots.

The SSTB showing its familar SSTB anti-cyclonic ovals (5 are visible in this image.) Also note two larger, and more irregular cyclonic storms between the ovals. This image shows a pretty normal level of activity for the belt. D. Peach - Jan 2003.

South Temperate Belt and Zone (STB and STZ.) South Temperate Belt North Jetstream (STBn)

The STB has historically been an area of notable activity, as for over 60 years it was the site of what are called the three great white ovals. These formed from a type of disturbance (which i will mention in more detail later) called a South Tropical Disturbance that occurred during the 1930s. They were named BC, DE and FA. These huge storms persisted until the late 1990s, when after all the formed a close grouping during the 1997 apparition after passing the GRS, BC and DE collided during Solar conjunction in 1998. This new larger oval (named BE) was formed, and remained prominent throughout the 1999-2000 apparition. However, amazingly, again after BE and FA passed the GRS in late 1999, these two storms collided in March 2000. This time though the amateur and professional communities were able to follow (for the first time) the collision of two huge anti-cyclones, which formed one final storm which still persists today - Oval BA.

The STB itself usually consists of streaks of dark material scattered around the Planet, but in recent years the belt has all but disappeared.

This sequence of images shows how the STB ovals merged to leave one larger oval today. These oval mergers remain some of the most dramatic events to have occurred on the Planet in modern times. Images courtesy Don Parker, FL, USA

This image from 1998 shows more interesting activity. A small very dark spot is present on the STB (which at its peak appeared almost as dark as a transit shadow!.) Also of note is many tiny STBn jetstream spots. These small dark spots, rapidly prograde along the STB, and are usually destroyed when they encounter the rim of the Great Red Spot. Image courtesy Don Parker, FL, USA. Oct 1998.

South Tropical Zone (STrZ or STropZ)

This area of Jupiter is the narrow, usually bright zone present between the STB and SEB south edge. It is best know as the location of the Great Red Spot. But other activity is also very much of note. This area has also been the place where South Tropical Disturbances (STropD) arise. The great South Tropical Disturbance (which was responsible for the formation of the STB Great White Ovals) lasted over 35 years, between 1901 and 1939. This disturbance takes the form of a closed circulation in the STrZ with a defined, curved preceding and following ends. This circulation slowly drifts around the STrZ, passing the GRS on its way. This particular form of disturbance has not been seen for many years now.

Click for full size image.

A diagram showing the typical appearance of a South Tropical Disturbance.

Other features occasionally appear in the STrZ such as small anti-cyclonic ovals. Several such storms have been followed during the last several years, many of which seem to occur in the area p. the GRS. Indeed some have actually been drawn into the GRS, and destroyed. Also, periodically a South Tropical Band will develop in the zone, from the p. edge of the GRS.

An image showing a small Anti-cyclonic oval in the STrZ, and broken up South Tropical Band. D. Peach - Feb 2002.

The Great Red Spot (GRS) and Red Spot Hollow (RSH.)

Surely the most famous and certainly the largest storm in the Solar System, the Great Red Spot has captivated astronomers since the first observations of it were made back in 1821. Since the storm storm has shown variations in colour, size and drift rate. The storm is slowly shrinking, and is now around 1/3 smaller in length than it was back in the 1890s, though even today, it could still swallow the Earth easily.

The spot shows almost yearly changes in colour, but in the past decades, the colour has varied from "brick red" during the 1960s, to "pale pink" in later years. During the last few years the colour has remained "light orange", though had darkened slightly during 2002-03. Its drift rate tends to remain constant, and has slowly been increasing in longitude during the last several years.

During turbulent events called SEB revivals (discussed below) the GRS shows distinct changes, with the spot darkening as the SEB fades away, then fading away after the SEB revives.

Two images showing two very different views of the GRS. A photograph from the 1.5m telescope at the Catalina Observatory taken in the 1960s, and a current image taken in Feb 2003 by Damian Peach. The dramatic difference in colour is very apparent. Left: Courtesy Catalina Observatory. Right: D. Peach - Feb 2003.

South Equatorial Belt south jetstream (SEBs.)

This jetstream marks the southern edge of the SEB. It fairly frequently shows periods of heightened activity, when small jetstream spots develop, and quickly retrograde along the belt, almost always being destroyed when they enter the GRS hollow. These spots have a distinctive appearance as the example images show, and during outbreaks of them, usually several are present along the length of the SEBs at one time.

A solitary SEBs jetstream spot is visible on the meridian of this image from Dec 2000. This is an excellent example of the classic appearance of these spots. Image courtesy Don Parker, FL, USA.

South Equatorial Belt south component (SEBS)

This refers to the dark southern component of the South Equatorial Belt (SEB.) Note this shouldn't be confused with the SEBs jetstream!.

South Equatorial Belt (SEB.)

This is one of the two primary belts on Jupiter, and is also probably the most active belt on the entire Planet. It is also seen of periodic disturbances, including the spectacular SEB revival.

1. SEB Fade/Revival: The most spectacular of all Jovian atmospheric events . Over the course of several months, the SEB will fade away, leaving usually just a faint SEBN component. Also during these times, the GRS darkens. This state can persist for over 18months, then suddenly, without warning a brilliant white spot/dark spot pair will erupt on the SEBN around ~5- degrees p. the GRS. From this "source" dark material violently erupts spreading out in one direction on the SEBn jetstream, and on the other along the SEBs jetstream. As this new dark material errupts, and spreads the whole SEB is eventually restored again. The GRS then usually fades in colour as the belt again darkens.

Left: An image of the last SEB revival to occur, underway in April 1993. Note the very turbulent nature of the belt in this image. Courtesy 2.5m NOT, La Palma. Right: A diagram of how an SEB revival spreads and restores the SEB.

2. Mid-SEB Outbreak: Another type of periodic activity seen to occur in the SEB, are outbreaks of white spots roughly 100+ degrees following the GRS location. These white spots erupt from a source in the centre of the SEB (around 100 deg f. the GRS), and these spots slowly prograde toward the GRS. These outbreaks also give the SEB a very turbulent appearance, though are not as spectacular as SEB revivals. Note these outbreaks should not be confused with the Post GRS turbulent region mentioned below.

This image from Aug 1998 shows the last Mid-SEB outbreak underway. Note the turbulent rifted appearance of the SEB. Image Courtesy Don Parker, FL, USA.

3. Post GRS turbulent region: This type of activity (which is almost always present) occurs in the area of SEB immediately following the GRS. This turbulence occurs by bright spots erupting in the SEB, around 50 deg f. the GRS, which slowly prograde toward it. New spots can be seen to periodically erupt in this region, and the level of activity can sometimes be high. Note the describing this type of activity as an "SEB disturbance" is not appropriate, since it is always present to some degree.

An image showing a new bright rift erupting in the Post GRS region. Note that many white rifts can be seen across this region. Image D. Peach - Dec 2002.

South Equatorial Belt north component (SEBN.)

This refers to the Northern component of the South Equatorial Belt. It is often dark with many tiny rifts and spots along it. Occasionally large storms have developed in this area, encircling the whole SEBN and neighbouring EZS. This last occurred during the 1999 apparition, and persisted into 2001. It was termed the South Equatorial Disturbance. More is covered on this event below.

Equatorial Zone South region (EZS.)

This area tends to be bright, and many bright spots and small rifts occur here. As mentioned above, during 1999 a brilliant white storm erupted in this region, spreading dark and bright material around the entire EZS. This disturbance remained active into 2001

An image showing the South Equatorial Disturbance in Dec 1999. Note the brilliant rift cutting through the SEBN, which marked the source of the disturbance. Image Courtesy Don Parker, FL, USA.

The Equatorial Zone (EZ.)

Well known among observers as the most dynamical and rapidly changing region on the whole Planet. Dark material is usually present across the zone, and in some years spectacular arrays of "Festoons" persist, emanating from the southern edge of the North Equatorial Belt (NEB.)

The Jovian EZ in 1999, displaying a spectacular array of dark festoons. The activity across the zone is usually somewhat more chaotic than this most years. Image D. Peach - Oct 1999.

The Jovian EZ in 2003, displaying a "typical" level of rather chaotic activity. Image Courtesy Eric Ng, Hong Kong, Jan 2003.

North Equatorial Belt (NEB.)

The darkest and most prominent belt on the entire Planet, and is easily seen even in a 50mm telescope. It always shows a multitude of activity the most relevant and interesting of which is covered below.

1. NEB expansion event: This term refers to periods when the NEBN edge expands northward to give the belt a much "thicker" appearance. This usually begins with dark material across the NEBn edge, amassing and eventually forming a more Northern boundary to the belt. These expansion events usually occur every 3 years, and persist for around an apparition.

The NEB showing how it appears when expanded (1997), and in a more normal state (1998.) Images Courtesy Don Parker, FL, USA.

2. NEBs projections (Festoons.): These blue features on the NEBs mark the bases of the Festoons that project across the EZ, and can be seen almost all the time.

3. NEBs/EZN white plumes: These bright areas are usually situated alongside the NEBs projections, and in smaller telescopes can sometimes look like "huge ovals".

These above mentioned features can all be seen in the EZ example images clearly.

4. Mid-NEB rifts: These features persist in the middle of the belt, and erupt usually as brilliant white clouds. The gradual drop of in wind speed from the EZN to the NEBn shears these brilliant spots into turbulent elongated rifts, which can persist for weeks.

Three prominent dark barges stand out in this Jan 2003 image of the NEB. Image D. Peach, 2003.

5. NEBn Barges: These dark cyclonic circulations persist on the NEBn edge, and can be among the darkest features on the entire Planet. Several are usually present each apparition, and sometimes these barges even collide, as was the case in 2001. They usually appear rounded and dark, but sometimes appear elongated.

Three prominent dark barges stand out in this Jan 2003 image of the NEB. Image D. Peach, 2003.

6. NEBn Bays or White Ovals: These features, like there southern counterparts, are bright anti-cyclonic storms that persist along the NEBn edge. As with barges, several are usually present each apparition, some more prominent than others. The largest and most prominent of the features in recent years is "White Spot Z" a huge storm, which has been present for several years now.

This image shows the largest of the NEBn ovals - white spot Z on the meridian, with a smaller oval p. it. Also note NEBn barges are prominent. Image D. Peach, 2003.

North Tropical Zone (NTrZ or NTropZ.)

This bright zone is usually rather featureless, aside from wispy streaks of material emanating from the NEBn into it. Sometimes a dusky band called a North Tropical Band can persist along the zone. An example of this band is well shown in the above image of White Spot Z.

North Temperate Belt and Zone (NTB and NTZ.)

The NTB is usually third in prominence only to the NEB and SEB. It also shows interesting patterns of activity which i describe below.

1. NTB south jetstream (NTBs): This is the fastest moving jetstream on the whole Planet. Features on this jet have been followed to move notably faster than even System 1 features. Four different jetstream speeds have been observed during the last 150 years designated currents A,B,C and D. The jetstream spots themselves appear a dark "bumps" on the NTBs, and movement relative to other features can be noted easily after only 1 day.

An image from Oct 2000 showing a small NTBs jestream spot on the meridian. Note is eye shaped outline, and brighter centre. Also note another spot following behind this one by ~30 degrees. Image D. Peach, 2000

2. NTB Fading: Periodically, the NTB will gradually fade away, leaving perhaps just a few dark segments behind. This fading process usually takes a few months, but unlike the SEB the belt does not revive in an "explosive" manner, but gradually returns to prominence. The NTB is currently in a faded state at the time of writing (May 2003.)

This cylindrical projection map of the entire NTB from Feb 2002, and Jan 2003 show the dramatic change of the belt from dark and prominent, to almost completely having disappeared a year later. Images D. Peach, 2002,03.

North North Temperate Belt and Zone (NNTB and NNTZ.)

This belt often appears as detached sectors of dark material, rather than a continuous belt. In recent years this belt has been rather faded, though in some years (such as 1997) has appeared more prominent. As with the NTB, it also shows a variety of acivity.

1. NNTB south jetstream (NNTBs): This jetstream shows periodic outbreaks of dark spots, which rapidly prograde. They have a distinctive appearance as small round spots, often with a slightly blue tint to them.

An image showing two NNTBs jetstream spots approaching the meridian, and only ~25 degrees apart. Image D. Peach, Dec 2002

2. NNTB and NNTZ white ovals: As with the SSTB, the NNTB also frequently shows anti-cyclonic white ovals, though in general, they are smaller, and less numerous than there southern counterparts.

This image shows a solitary classic NNTB anticyclonic oval on the meridian. Image D. Peach, 2003.

North North North Temperate Belt & North Polar regions (N3TB, N4TB, N5TB, NPR.)

This final section covers the areas North of the NNTB. Activity across these regions, generally appears a chaotic mix of dark spots, and streaks, but as with the rest of the Planet, a defined pattern of Jetstreams covers this area. Activity in these areas generally consists of dark spots, or streaks, and also anti-cyclonic white ovals.

This image shows the many dark and bright spots that covers the far northern regions of Jupiter, and also shows two small anti-cyclonic white ovals. Image D. Peach, 2003.