Jupiter in 2000/2001 Part II: Infrared and ultraviolet wavelengths

A review of multispectral imaging of the jovian atmosphere

John H. Rogers, Tomio Akutsu, & Glenn S. Orton



In 2000/2001, Jupiter was imaged at more wavelengths more intensively than ever before.  This article reviews the data sets available, and reports on the major features detected in them, especially a novel pattern of largescale waves over the the North Equatorial Belt (NEB).

The images came from amateur contributors, and from the NASA Infrared Telescope Facility,  and from the Cassini and Galileo spacecraft. Images were taken not only in visible wavelengths, but also in the ultraviolet and in the near-infrared methane absorption bands (all these wavelengths being sensitive to levels above the main cloud layers); in near-infrared continuum bands (penetrating within the main cloud layers); and in the mid-infrared thermal band (revealing emission from below the cloud layers).

Polar hoods and anticyclonic ovals were, as usual, among the most prominent bright features in the methane-band images. These images also revealed major disturbances affecting the South and North Equatorial regions.  The South Equatorial Disturbance, a solitary wave in the visible clouds, showed massive disruption of the upper haze layers in the infrared (see Paper III of this report).

The NEB waves were a series of large diffuse methane-dark patches, representing variations in the thickness of high-altitude haze over the belt, with a 'wavelength' of 20-25 deg. longitude.  The most conspicuous of the patches were aligned with visible features, particularly the p. sides of visible barges, where there was anticyclonic eddying. Longitude measurements show that the waves moved at the same speeds as the underlying visible features, i.e. in the range between System II and System III, and anomalies in their motion were related to visible cloud events. There was no sign of any phase speed that was different from the speed of the underlying visible features. Therefore the waves were controlled by the lower-lying tropospheric circulations.

These NEB waves in 2000/2001 may have been a consequence of the ongoing NEB broadening event, and they became indistinct just as the NEB broadening became complete. They had many similarities to 'slow-moving thermal waves' reported by previous mid-infrared observers, which were also most conspicuous when barges were present. We propose that these waves are induced by the curving and eddying of the tropospheric NEBn jetstream, and that they propagate upwards as warm waves which cause thinning of the high-altitude haze as well as enhanced mid-infrared emission.




Jupiter has never been studied with higher resolution and frequency than it was in 2000/2001, not only in the visible waveband [ref.1], but also in other wavebands from the infrared to the ultraviolet. Multispectral imaging was carried out by amateur observers, by spacecraft, and by professional observatories. This great effort was partly due to the unprecedented dual flyby by the Cassini and Galileo spacecraft [ref.2], and partly due to the recent improvements in both amateur and professional ground-based detectors.  These multispectral observations provide three-dimensional views of Jupiter's clouds, giving new insight into the dynamics of the atmosphere. 

In a previous report [ref. 3], we reviewed the imaging of Jupiter in the near-infrared methane absorption band at 0.89 mm, which is now being carried out by several amateur observers as well as by spacecraft.  In this report, we consider the imaging in all near-infrared (IR) and ultraviolet (UV) wavebands during 2000/2001, reviewing the data sets available, and describing the major features detected in them.  Feature numbers are taken from our report on observations in visible light [ref.1, hereafter Paper I].  As the planet was in a largely typical state, this will serve as a review of multispectral probing of the jovian atmosphere.  Table 1 summarises the wavebands which have been accessed by different observatories.   Fig.1 shows how they penetrate to different levels in the atmosphere, relative to the various cloud layers presently believed to exist....

Data sets

General appearance of the planet in multispectral images, 2000/2001

            including discussions of SEBn/NEBs; NEB; and NPR

The wave pattern over the North Equatorial Belt


Thus, thermal waves over the NEB are always present, but are most prominent when barges exist. The spacing and motion of the warm waves is similar to that of the barges. They may be centred over the barges or up to 20 deg. p. them; but sometimes there is no clear relationship. Broadly, then, these properties are the same as those of the methane-dark waves in 2000/2001, and we predict that the methane-dark waves will be shown to coincide with warm waves at the 250-mbar level. A possible model is that meanders in the NEBn jetstream, particularly where it curves around barges, give rise to thermal fluctuations which propagate upwards and prograde, so they may be centred 5-20 deg. p. the barge at the 250-mbar level, and 20-40 deg. further p. at the 10-20 mbar level.  The variability in the spatial relationships could be because of the variable spacing of the barges; possibly this constrains the angle at which the waves can propagate upwards.  However it may also reflect the meteorological state of the NEB; thus in 2000/2001, as the NEB broadening event became compete, the average length and periodicity of the methane-dark waves underwent a rapid lengthening.  In conclusion, we believe that the 2000/2001 methane images do show the thermal waves, and for the first time it has been possible to see their structure clearly and track their motion precisely....


Note added in proof  [2004 March 5]:

The Cassini Composite Infrared Spectrometer maps, showing global atmospheric temperatures on dates in 2001 January, have now been published [F.M. Flasar et al., Nature 427, 132-135 (2004)].  In the map at a level of ~243 mbar, the most striking features are 9 warm patches at ~15 deg.N, and 7 of them correspond to the methane-dark patches reported here. The two largest warm areas coincide with the two largest methane-dark
patches (p. barges B1 and B5), and 5 other warm spots all map 3-4 deg. p. the longitudes of other methane-dark patches 
One interesting exception is a warm spot at L3 = 185 which coincides with white spot Z, suggesting that a methane-dark patch either did not form here or was less visible because of the underlying bright oval.  In the Cassini map at a level of ~1 mbar, the only persistent features at this latitude are two large, very warm areas centred ~20 deg. p. the two largest methane-dark patches (p. barges B1 and B5).  Each of these has a warm 'tail' extending Nf. and there are indications of warm spots or waves spreading Nf. along these tails at ~1-2 deg/day.  Thus the Cassini maps not only suggest a ~20 deg. offset due to vertical propagation of the waves (agreeing with that observed by the IRTF in 1988), but also suggest complex dynamics in the stratosphere.



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